FINAL REPORT GUIDE II INVENTORY SURVEY AND …open_jicareport.jica.go.jp/pdf/11856416_01.pdf ·...

JAPAN INTERNATIONAL COOPERATION AGENCY

THE DEPARTMENT OF PUBLIC WORKS AND HIGHWAYS

THE STUDY ON RISK MANAGEMENT FOR SEDIMENT-RELATED

DISASTER ON SELECTED NATIONAL HIGHWAYS IN THE REPUBLIC OF THE PHILIPPINES

FINAL REPORT

GUIDE II

INVENTORY SURVEY AND RISK ASSESSMENT

June 2007

Joint Venture of

Nippon Koei Co. Ltd. and OYO International Corporation

The Study on Risk Management for Sediment-Related Disaster on Final Repot Guide II Selected National Highways in the Republic of the Philippines Inventory Survey and Risk Assessment

NIPPON KOEI CO., LTD. June 2007

OYO INTERNATIONAL CORPORATION

i

PREFACE

The JICA study team has designed and developed a systematic method of Inventory Survey to create the database on road slopes along the national highways of the Philippines. This has been named the Road Slope Management System (RSMS).

The purpose of the Inventory Survey is to identify and record the conditions of disaster prone slopes into a database to be used in the risk management of road slopes. This Guide presents the standard procedures for the inventory survey and risk assessment of road slopes. The inventory survey covers only the national road network.

The general methodology for the inventory survey is explained in Chapter 1, while Chapters 2 and 3 detail the procedures for implementing the inventory survey.

In preparing this Guide, technical transfer to DPWH road engineers in-charge of road maintenance was carried out successfully through the conduct of the actual inventory surveys. The nationwide inventory survey will be implemented in the near future.

This technical guide will therefore be helpful in planning appropriate road slope management infrastructure.

The Study on Risk Management for Sediment-Related Disaster on Final Report Guide II Selected National Highways in the Republic of the Philippines Inventory Survey and Risk Assessment

NIPPON KOEI CO., LTD. ii June 2007


Definition of Terms for Risk Assessment of Road Slope Disasters (RSD) Terms Definitions

Road Slope Disaster : A road slope failure, which could stop traffic flow and be dangerous to road users and inhabitants along the road.

Disturbance : Deformation of the slope and road structures, and slope collapse, which have not reached the road.

Visible Disturbance : Signs of potential disaster such as collapse, open cracks, depression, upheaval, muddy spring water on the road or slope.

Road Closure Disaster [RCD]

: A disaster which causes closure of the whole or partial width of the road Deformations and collapses that do not close the road are not necessarily regarded as a RCD but just as a 'Disturbance'.

Loss

: Monetary amount of damage caused by a disaster, specifically defined as the sum of the reopening cost, human lives lost, and detour cost.

Risk : The total damage characterized by the potential frequency and magnitude of the disaster. Annual total loss is an expression of the risk. The risk is distinguished from the hazard, which could be defined, in case of this Study, as the overt danger to the road and road users.

Frequency of Road Closure Disasters per Year [FRCD]

: The number or RCD occurrences per year for a slope

Intensity of Road Closure Disasters of Road Section [IRCD]

: Average RCD occurrences per unit length per year for a road section, i.e. the total FRCD’s for the road section divided by its length

Terms for Organization

Terms Definitions

DE : District Engineer (Head of DPWH District Engineering Office)

DEO : District Engineering Office

DENR : Department of Environment and Natural Resources

DPWH : Department of Public Works and Highways

NAMRIA : National Mapping and Resource Information Authority

RO : Regional Office (DPWH)


NIPPON KOEI CO., LTD. iii June 2007


Terms for Road Management System

Terms Definitions

BMS : Bridge Management System

PMS : Pavement Management System

RBIA : Road and Bridge Information Application

RSMS : Road Slope Management System

Terms for Feasibility Indicators Terms Definitions

BCR : Benefit Cost Ratio

ENPV : Economic Net Present Value

EIRR : Economic Internal Rate of Return


NIPPON KOEI CO., LTD. iv June 2007


GUIDE TO MITIGATION AND MANAGEMENT OF ROAD SLOPE

DISASTERS

GUIDE II INVENTORY SURVEY AND RISK ASSESSMENT

Table of Contents CHAPTER 1 OUTLINE OF THE INVENTORY SURVEY.......................................1-1

1.1 Major Information Collected in the Inventory Survey..................................1-1 1.2 Outline of Inventory Survey .........................................................................1-1 1.2.1 Preliminary Inventory Survey (PIS) .............................................................1-4 1.2.2 Detailed Inventory Survey (DIS) ..................................................................1-5 1.3 Design of Sheet 2 to Assess Risk Level of Slopes........................................1-7 1.3.1 Seven Disaster Types on National Highways ...............................................1-8 1.3.2 Listing of Item Groups and Specific Items .................................................1-12 1.3.3 Setting of Frequency Score Contributing to FRCDp ..................................1-13 1.4 Methodology of Indicative Feasibility Assessment ....................................1-16

CHAPTER 2 PRELIMINARY INVENTORY SURVEY............................................2-1

2.1 Flow of the Preliminary Inventory Survey (PIS) ..........................................2-1 2.2 Preparatory Work ..........................................................................................2-2 2.2.1 Disaster Record .............................................................................................2-2 2.2.2 RBIA and Topographic Maps........................................................................2-3 2.2.3 Field Survey Instruments ............................................................................2-11 2.3 Screening of Surveyed Slope ......................................................................2-12 2.3.1 Screening Criteria for Soil Collapse and Rock Collapse ............................2-12 2.3.2 Screening Criteria for Road Slip.................................................................2-13 2.3.3 Screening Criteria for Debris Flow.............................................................2-13 2.3.4 Screening Criteria for River Erosion ..........................................................2-14 2.3.5 Screening Criteria for Coastal Erosion .......................................................2-14 2.4 Method of Field Survey and Completing of the Inventory Forms..............2-15 2.4.1 Method of Field Survey ..............................................................................2-15


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2.4.2 Filling in of the Inventory Form .................................................................2-16 2.5 Evaluation Procedure for the Selection of DIS Slopes ...............................2-48 2.5.1 Selection I (Evaluation by FRCDa) ............................................................2-49 2.5.2 Selection II (Evaluation by Disturbance)....................................................2-50 2.5.3 Selection III (Evaluation by FRCDp) .........................................................2-50

CHAPTER 3 DETAILED INVENTORY SURVEY ....................................................3-1

3.1 General Information......................................................................................3-1 3.1.1 Objective and Procedure for the DIS ............................................................3-1 3.1.2 Work Flow of the DIS ...................................................................................3-2 3.2 Method of Investigation (Sheet 3) ................................................................3-3 3.2.1 Tools for the Survey......................................................................................3-3 3.2.2 Procedure of Drawing Sketches....................................................................3-4 3.3 Countermeasure Planning (Sheet 4)............................................................3-11 3.3.1 Countermeasure Plan ..................................................................................3-11 3.3.2 Countermeasure Options.............................................................................3-12 3.3.3 Countermeasure Selection...........................................................................3-16 3.3.4 Completion of Sheet 4.................................................................................3-19 3.4 Indicative Feasibility Assessment (Sheet 5)................................................3-27 3.4.1 General ........................................................................................................3-27 3.4.2 Setting the Method for Inputting Required Values .....................................3-27

APPENDIX Appendix -1 Inventory Survey Forms Appendix -2 Classification of Slope Disaster Types Appendix -3 Countermeasure Options for Each Disaster Type Appendix -4 Countermeasure Selection Process for Each Disaster Type Appendix -5 Unit Cost Breakdown of Countermeasures Appendix -6 Evaluation of Unit Value of Human Lives Lost


NIPPON KOEI CO., LTD. vi June 2007


List of Tables

Page

Table 1.1 Inventory Format Sheet for PIS.....................................................................1-2 Table 1.2 Items for Each Disaster Type.......................................................................1-13 Table 1.3 Total Maximum Frequency Score for Each Factor Item Group ..................1-16 Table 2.1 Index of Topographical Maps for the Inventory Survey..............................2-10 Table 2.2 Required Field Survey Instruments .............................................................2-11 Table 2.3 Example of Sheet 1......................................................................................2-20 Table 2.4 Classification of Vegetation/ Surface Covering...........................................2-31 Table 2.5 Classification of Vegetation of Drainage Area ............................................2-32 Table 2.6 Classification of Materials of the Slope.......................................................2-32 Table 2.7 Classification of River Sediment Materials .................................................2-33 Table 2.9 Classification of River Bank Materials........................................................2-34 Table 2.10 Classification of River Bed Materials..........................................................2-34 Table 2.11 Classification of Coastal Bank Materials.....................................................2-35 Table 2.12 Classification of Coastal Materials..............................................................2-36 Table 2.13 Classification of Ratio of Bedrock Exposure Area......................................2-36 Table 2.14 Classification of Bedrock Materials ............................................................2-37 Table 2.15 Classification of Slope Types ......................................................................2-37 Table 2.16 Classification of Spring/Surface Water........................................................2-38 Table 2.17 Classification of Rainwater Flows on Valley Side Slope ............................2-38 Table 2.18 Classification of Rainwater Flows on Costal Side Slope ............................2-40 Table 2.19 Classification of Rainwater Flows on Valley Side Slope ............................2-44 Table 3.1 Objective and Procedure for the DIS.............................................................3-1 Table 3.2 Tools for Field Inspection for DIS.................................................................3-3 Table 3.3 Basic Information/Items to be Included in Sheet 3 .....................................3-5 Table 3.4 Method of Countermeasure Planning ..........................................................3-11 Table 3.5 Countermeasure Alternative Policy .............................................................3-11 Table 3.6 Unit Cost of Countermeasures (1) (2006 Price) ..........................................3-23 Table 3.7 Unit Cost of Countermeasures (2) (2006 Price) ..........................................3-24 Table 3.8 Reference Value for Estimating Reopening Cost........................................3-35 Table 3.9 Average Number of Deaths per RCD..........................................................3-38


NIPPON KOEI CO., LTD. vii June 2007


Table 3.10 Example of AADT and Percent Share of Each Vehicle Type (Baguio-Bontoc Rd)....................................................................................3-40

Table 3.11 Estimated Vehicle Operating Cost (VOC) per Road Surface Type

and Condition per km (VOC/km) (pesos)...................................................3-43 Table 3.12 Estimates of BCR, ENPV and EIRR using Microsoft Excel ......................3-47 Table 3.13 Examples of Risk Reduction Ratios............................................................3-48

List of Figures

Page

Figure 1.1 Flow of Inventory Survey and Risk Assessment .......................................1-3 Figure 1.2 Process for Designing Sheet 2......................................................................1-8 Figure 1.3 Schematic Illustration of the Seven Disaster Types ...................................1-10 Figure 1.4 Block Diagram of Idealized Complex Earth Slide-Earth Flows................1-11 Figure 1.5 Illustration of Analysis Method of FRCDpoc (Prediction Value) ..............1-15 Figure 1.6 Framework for Indicative Feasibility Assessment .....................................1-17 Figure 2.1 Work Flow of Preliminary Inventory Survey...............................................2-1 Figure 2.2 Acquisition Flow of RBIA Road Maps........................................................2-4 Figure 2.3 Usage Flow for RBIA Maps.........................................................................2-5 Figure 2.4 Example of Road Map of the National Highway.........................................2-6 Figure 2.5 Example of Road Map of CAR....................................................................2-7 Figure 2.6 Example of Road Map ...............................................................................2-8 Figure 2.7 Example of Location Map for Inventory Survey (1:5,000) .........................2-9 Figure 2.8 Screening Criteria of Slopes for Soil and Rock Collapse ..........................2-12 Figure 2.9 Screening Criteria of Slopes for Road Slip ................................................2-13 Figure 2.10 Screening Criteria of Slopes for Debris Flow............................................2-13 Figure 2.11 Screening Criteria of Slopes for River Erosion..........................................2-14 Figure 2.12 Screening Criteria of Slopes for Coastal Erosion ......................................2-14 Figure 2.13 Field Survey Procedure ..............................................................................2-16 Figure 2.14 Locational Reference Point ........................................................................2-22 Figure 2.15 Schematic Illustration of Knick Line .........................................................2-23 Figure 2.16 Schematic Illustration of Valley Side Slope in Sheet 2-4 ..........................2-24 Figure 2.17 Schematic Illustration of Gradient of Slopes in Sheet 2-1,2......................2-24


NIPPON KOEI CO., LTD. viii June 2007


Figure 2.18 Schematic Illustration of Distance from Road to the Toe of the Mountain in Sheet 2-1,2..............................................................................2-25

Figure 2.19 Schematic Illustration of Distance from Road to Shoulder of Slopes in Sheet 2-4......................................................................................2-25

Figure 2.20 Schematic Illustration of Slope Shape in Sheet 2-1, 2, 3.4 ........................2-26 Figure 2.21 Schematic Plain View Illustration of Combined Type Slope

Shape in Sheet 2-1, 2. 3.4............................................................................2-26 Figure 2.22 Schematic Illustration of Slope Shape in Sheet 2-5 ...................................2-27 Figure 2.23 Schematic Illustration of Area of Drainage in Sheet 2-5 ...........................2-28 Figure 2.24 Schematic Illustration of Height from the Channel Bottom to the Road in Sheet 2-5 .............................................................................2-28 Figure 2.25 Schematic Illustration of Distance from the Low Water Level to the Road in Sheet 2-6 .............................................................................2-29 Figure 2.26 Schematic Illustration of Width of River at Low Water to the Road in Sheet 2-6 .............................................................................2-29 Figure 2.27 Schematic Illustration of Height from the High Water Level to the Road in Sheet 2-6 .............................................................................2-30 Figure 2.28 Schematic Illustration of Distance from the High Water

Coastline to the Road in Sheet 2-6..............................................................2-30 Figure 2.29 Schematic Illustration of Height from the High Water Level to the Road in Sheet 2-7 .............................................................................2-31 Figure 2.30 Observation Area to Determine River Sediment Materials in Sheet 2-5 ...2-33 Figure 2.31 Observation Area to Determine River Bank Materials in Sheet 2-6..........2-33 Figure 2.32 Observation Area to Determine River Bed Materials in Sheet 2-6............2-34 Figure 2.33 Observation Area to Determine Costal Bank Materials in Sheet 2-7.........2-35 Figure 2.34 Observation Area Determine Coast Materials in Sheet 2-7 .......................2-35 Figure 2.35 Schematic Illustration of Rain Flows to Valley Side Slope .......................2-38 Figure 2.36 Photograph of Erosion and Piping Hole ....................................................2-39 Figure 2.37 Schematic Mode of Disturbance in the Sheet 2-1, 3, 7..............................2-41 Figure 2.38 Schematic Mode of Disturbance in the Sheet 2-2......................................2-42 Figure 2.43 Schematic Mode of Disturbance in the Sheet 2-4......................................2-43 Figure 2.40 Schematic Mode of Disturbance in the Sheet 2-5......................................2-44 Figure 2.41 Schematic Mode of Disturbance in the Sheet 2-6......................................2-45 Figure 2.42 Existing Countermeasures..........................................................................2-48 Figure 2.43 Selection Criteria for the DIS Slopes .........................................................2-49


NIPPON KOEI CO., LTD. ix June 2007


Figure 3.1 Flowchart of Detailed Inventory Survey......................................................3-2 Figure 3.2 Flowchart of Procedure for Sheet 3 Sketch..................................................3-6 Figure 3.3 Procedure for Drawing the Sheet 3 Sketch ..................................................3-7 Figure 3.4 Legend for Use in Sheet 3............................................................................3-8 Figure 3.5 Example of Sheet 3 Sketch (1).....................................................................3-9 Figure 3.6 Example of Sheet 3 Sketch (2)...................................................................3-10 Figure 3.7 Appropriate Gradients for Cuts..................................................................3-13 Figure 3.8 General Flow of Countermeasure Selection ..............................................3-18 Figure 3.9 Procedure for Completion of Sheet 4.........................................................3-20 Figure 3.10 Procedure for Drawing Sheet 4 Countermeasure Plan...............................3-21 Figure 3.11 Remarks for Filling out of Sheet 4 .............................................................3-22 Figure 3.12 Example of Sheet 4 Countermeasure Plan (Lagawe- Banaue

Road: 301km + 200: Alternative-I) .......................................................3-25 Figure 3.13 Example of Sheet 4 Countermeasure Plan (Wright-Taft Road:

858 + 250: Alternative-II)......................................................................3-26 Figure 3.14 Instruction for Estimating the Dimension of Collapsible Volume .............3-28 Figure 3.15 Chart for Estimating Collapsible Volume ..................................................3-30 Figure 3.16 Chart for Estimating the ‘Ratio of Accumulated Volume to

Collapsible Volume’ ..............................................................................3-31 Figure 3.17 Chart showing the Relationship between Accumulation Volume

and Reopening Cost...............................................................................3-33 Figure 3.18 Charts for Estimating Reopening Cost per Length of Road

Closure...................................................................................................3-37 Figure 3.19 Reference Points for Measuring Lengths of Survey and Detour

Roads .....................................................................................................3-39 Figure 3.20 Frequency Distribution of Road Closure Days per RCD...........................3-41 Figure 3.21 Chart for Estimating the Number of Road Closure Days by

Length of Road Closure Alignment of various RCDs ................................3-42


NIPPON KOEI CO., LTD. 1 - 1 June 2007


CHAPTER 1

OUTLINE OF THE INVENTORY SURVEY

1.1 Major Information Collected in the Inventory Survey

The following information for the formulation of management policy for road slope disasters is collected and evaluated in the inventory survey:

• FRCDa and FRCDp: Actual Frequency of Road Closure Disasters and Potential Road Closure Disasters

• Hazard condition of the road slopes

• Estimate of the potential magnitude of disasters in the road slopes

• Countermeasure plans for critical road slopes

• Rough cost estimate for each countermeasure plan

• Risk and feasibility indicators for each countermeasure plan

The information is recorded on six sheets (templates) in the Integrated Table for Risk Management for Road Slope Disasters shown in Table 1.1 and Appendix I, and imported into the RSMS (Road Slope Management System) for the formulation of a systematic management plan on road slope disasters and actual maintenance work.

1.2 Outline of the Inventory Survey

The inventory survey is comprised of the Preliminary Inventory Survey (PIS) and the Detailed Inventory Survey (DIS) as shown in Figure 1.1 and Table 1.1.




Table 1.1 Inventory Format sheet for PIS

Sheet No Sheet Name

Content of Work Output

Sheet 1 General Information

Screening/ identification of slopes to be surveyed

- Location - Disaster type - Photographs

Prel

imin

ary

Inve

ntor

y

Sheet 2 Selection of Slopes for DIS

-Disaster frequency assessment - Selection of Slopes for DIS

- FRCDa - FRCDp - Evaluated result of DIS necessity

Sheet 3 Sketches

-Situation in hazard area, failure mechanism, risk object situation

-Engineering Front view of slope - Engineering cross section of slope

Sheet 4 Planning of Countermeasures

- Planning of countermeasure alternatives

- Layout of countermeasure alternatives - Cost for countermeasure alternatives

Det

aile

d In

vent

ory

Surv

ey

Sheet 5 Indicative Feasibility Assessment

-Evaluation of disaster magnitude - Evaluation of annual loss - Assessment of outcome and economic feasibility

- Disaster magnitude - Potential annual losses - Benefits from countermeasures - FRCDpwc - Feasibility indicators: BCR/ENPV/EIRR

Sheet 6 Disaster Record

- Record of disasters previous to the time of the Inventory Survey - Additional records of when

disasters occur after the Inventory Survey

- Disaster occurrence date - Disaster magnitude - Damage: RCD days, reopening cost, loss of life if any

Integrated Table of Risk Management for Road Slope Disasters

- The table was formed by importing sheets 1 to 6 into the RSMS database.

- List of major information collected in the Inventory Survey




Figure 1.1 Flow of Inventory Survey and Risk Assessment

Preliminary Inventory Survey (First Stage) Screening of slopes to be surveyed (Sheet 1)

Disaster Frequency Assessment (Sheet 2)

FRCDa≧0.1, or Visible Disturbance, or FRCDp≧0.1?

End

No

Yes

Detailed Slope Observation(Sheet 3)

Countermeasure Planning & Cost Estimation (Sheet 4)

Detailed Inventory Survey (First Stage)

Disaster Magnitude Evaluation (Sheet 5)

Feasibility Indicators on CountermeasureImplementation (BCR/ENPV/EIIR) (Sheet 5)

Indicator of Disaster Frequency Outcome (FRCDpwc) (Sheet 5)

Data Import into RSMS Database

FRCDa: Actual Frequency of RCDFRCDp: Potential Frequency of RCD

BCR: Benefit Cost Ratio ENPV: Economic Net Present Value EIIR: Economic Internal Rate of Return




1.2.1 Preliminary Inventory Survey (PIS)

The major objectives of the PIS are as follows:

• Screening of surveyed slopes,

• Estimation of Potential Frequency of Road Closure Disasters (FRCDp) of the slopes,

• Selection of slopes to be subjected to detailed surveys in the DIS.

(1) Screening of Surveyed Slopes The criteria for the screening of slopes to be surveyed are determined based mainly on the view points of road geometry and slopes that have or don’t have potential for RCD (Refer to Chapter 2). According to the criteria, slopes to be surveyed are determined during the initial activities of the PIS.

In this activity, the type of slope disaster is also identified and the result encoded in Sheet 1, which is prepared to record the general information on said slopes.

(2) Estimation of FRCDp of Slopes Investigations regarding Road Closure Disasters are focused on evaluating the level of instability of road slopes and FRCD (frequency of road closure disaster) has been developed as an indicator of slope vulnerability.

After screening of the slopes to be surveyed, the Actual Frequency of Road Closure Disaster (FRCDa) is recorded and the Potential Frequency of Road Closure Disaster (FRCDp) is estimated automatically by selecting the appropriate factor categories in Sheet 2, which has been designed to assess the instability level of slopes. The detailed procedure for estimating the vulnerability of slopes is described in Chapter 2.

FRCDa and FRCDp are defined as follows.

• FRCDa: Actual frequency of road closure disasters per year (nos. of RCD per year).

• FRCDp: Potential frequency of road closure disasters as estimated in the PIS (nos. of RCD per year).




(3) Selection of Slopes for DIS Slopes to be studied to reduce disaster occurrence are selected based on the following criteria:

Selection Criterion for DIS: FRCDa≧0.1 or Visible Disturbance is Present, or FRCDp≧0.1

This criterion indicates that a slope has caused a road closure disaster at least once in the past ten years or that a road closure disaster is expected at least once in every ten years. Slopes meeting these criteria should be selected for the conduct of DIS.

1.2.2 Detailed Inventory Survey (DIS)

The major objectives of the DIS are as follows:

• Evaluation of the hazard condition of slopes;

• Countermeasure planning;

• Cost estimate for the countermeasure;

• Estimate of the disaster’s magnitude; and

• Calculation of risk level and feasibility indicators.

Three types of inventory sheets are prepared in the study: Sheets 3, 4 and 5 and by filling out these sheets, the major information to manage slope disasters can be obtained.

(1) Detailed Observation The first activity in the DIS is the detailed observation of a slope, which is recorded in Sheet 3, where the hazard condition of a slope is shown from the front view and cross section. Through this activity, the information to estimate the disaster’s magnitude is measured and planning of the countermeasure is identified.

(2) Countermeasure Planning From the result of the detailed observation of the slope, three alternative countermeasures are planned and shown in Sheet 4. The three alternatives for countermeasure planning are shown below:




Sheet 4 is prepared for planning countermeasures together with the table of cost estimates.

(a) Alternative I: Permanent countermeasures (such as cast-in-place cribs and surface drainage work for road slopes)

(b) Alternative II: Mitigating disaster occurrence to some extent (such as retaining walls for soil collapse)

(c)Alternative III: Temporary measures to control disaster occurrence (such as vegetation for soil collapse)

(3) Cost Estimate for the Countermeasures The rough cost estimates for the planned countermeasures are computed in the appropriate table in Sheet 4. The unit costs for standard countermeasures are also computed in the estimation, which is described in Chapter 3.

(4) Estimation of Disaster Magnitude The estimate of the disaster’s magnitude, such as accumulation of soil/ rock volume generated by the predicted slope disasters, is carried out by filling out the cells in Sheet 5.

(5) Indicative Feasibility Assessment Indicative feasibility assessment (Sheet 5) is composed of three parts, enumerated as follows;

(a) Disaster Frequency and Magnitude

(b) Annual Losses without Countermeasures

(c) Feasibility Indicators for the Countermeasures

(a) Potential Disaster Frequency and Magnitude Disaster frequency was already assessed in sheet 2 and linked in this Sheet 5. Estimation of the disaster’s magnitude such as accumulation of soil/ rock volume on the road per RCD, and length of road closure is evaluated based on the ‘Detailed Observation of the DIS’ and filled out in Sheet 5.

(b) Potential Annual Losses Without Countermeasures Annual opening cost, annual value of human lives lost, and annual detour cost can be calculated in Sheet 5. For this estimation, coefficients, unit costs, and expressions are prepared in this Guide II by conducting an analysis of past disaster records.




(c) Feasibility Indicators for the Countermeasures The following indicators can be calculated for three (3) countermeasure alternatives in Sheet 5 by filling out the Risk Reduction Ratio (RRR).

Risk level outcome indicator:

Potential Frequency of RCD with Countermeasure (FRCDpwc)

Feasibility indicators:

• Benefit/ Cost Ratio (BCR)

• Economic Net Present Value (NPV)

• Economic Internal Rate of Return (EIRR)

1.3 Design of Sheet 2 to Assess Risk Level of Slopes

The evaluation of slope instability is undertaken using Sheet 2, which is designed for seven different disaster types considering the features of the various types of slope failure mechanisms and factors contributing to slope instability. Use of Sheet 2 is carried out using the process shown in Figure 1.2.




1.3.1 Seven Disaster Types on National Highways

It is important to classify the different failure types in evaluating the instability of slopes, since factors contributing to slope instability and the corresponding failure mechanisms are different for each failure type.

1. Classification of disaster types

4-1.Multiple regression analysis with dummy frequency scores

3. Setting tentative frequency score contributing to FRCDp

2. Listing of factors for each disaster type that influence slope failure

4-2. Evaluation of effectiveness of countermeasures

5. Decision on frequency scores

Seven disaster types

Updated version of Sheet 2(Seven types of Sheet2)

Updated version of Sheet 2

PIS of 332km

Nationwide conduct of PIS

Statistical analysis

Figure 1.2 Process for Designing Sheet 2

Four items per group

Future Works




The classification of slope disaster types is carried out to design a format to assess the level of instability of the slopes. The seven slope disaster types are defined as most frequently occurring in the national highways of the Philippines, which are listed as follows:

(1) Soil Collapse (SC),

(2) Rock Slope Collapse (RC),

(3) Landslides (LS),

(4) Road Slips (RS),

(5) Debris Flow (DF),

(6) River Erosion (RE),

(7) Coastal Erosion (CE),

The classification of the disaster types mentioned above is defined considering first the nature of the slope disasters occurring on the Philippine national highways and then comparing them to international text books and Japanese manuals on road slope disaster management.

The disaster types namely; Soil Collapse (SC), Rock Slope Collapse (RC), Landslides (LS) and Debris Flow (DF) are the common failure types occurring in the country’s natural slopes. On the other hand, Road Slips (RS), River Erosion (RE) and Coastal Erosion (CE) are failure types occurring on specific road structures that show various failure modes.

The schematic illustration for each disaster type is shown in Figure 1.3 and a brief explanation of each disaster type is described below. The detailed explanation of the seven disaster types are given in Appendix-2.

(1) Soil Collapse (SC) Rapid soil slope failure dominantly occurs in high cut or natural slopes with gradients of over 50 degrees. The material is generally residual soil produced by weathering of rocks or detritus soils hanging in steep slopes. Generally, collapse volumes are rather small, ranging from tens to several hundreds of cubic meters. Most soil collapse occurrences are triggered by heavy rainfall.

(2) Rock Slope Collapse (RC)




Rock slope collapse occurs in hard rock slopes with gradients over 50 degrees. Collapsing modes are free fall or rolling of rock masses of up to several tens of cubic meters. In hard rock slopes, large scale slope failures occur in natural slopes such as large scale planar slides, spread, wedge slides and toppling. Under this classification, large scale slope failures are included in the “Landslide Type”, since countermeasures used to treat large scale rock mass failures are similar to those for preventing big landslides.

1.Soil Slope Collapse “SC” 2.Rock Slope Collapse

“RC” 3.Landslide “LS”

4.Road Slip “RS” 5.Debris Flow “DF” 6.River Erosion “RE”

7.Coastal Erosion “CE”

Figure 1.3 Schematic Illustration of the Seven Disaster Types

(3) Landslides (LS)

The term “landslides” is often used in a general way to refer to all types of slope failures. However, under the current classification, a “Landslide” (LS) is defined as a large mass movement including large mass soil slide, rock wedge block slide, and rock slope toppling or

Road

Sliding Block Road

Rock fall

Crack

Less than 15m Rock

Soil

Road

Debris Flow

Culvert

CollapseRoad Slip

Earth or weathered rocks

Rock

River

Road

Attack part

Road

Sea




spreading.

The typical mode of landslides is shown in Figure 1.4, which is an internationally accepted concept.

Figure 1.4 Block Diagram of Idealized Complex Earth Slide – Earth Flows (Varnes 1978, Figure 2.1t)

(4) Road Slips (RS) “Road Slip” is a colloquial term commonly used by road engineers in the DPWH and refers to slope failure or deformation of road shoulders or pavement in roads passing through hilly areas.

Road slips occurring in many places along the national highways are caused by collapse of the valley side slope, scouring of slopes induced by water leakage from damaged drains and settlement of road embankments.

(5) Debris Flow (DF) Debris flow refers to the rapid flow of boulders, gravel, sand, silt clay and trees mixed with a large quantity of water that is mainly generated when a slope collapses during heavy rainfall. It flows down to the riverbed rapidly over ground with a gradient of above 20 degrees and stops and deposits in the riverbeds with gradients of below 10 degrees.




(6) River Erosion (RE) River erosion is a slope failure type occurring mainly in embankments and rarely in natural slopes along rivers. It is caused by continuous or repeated river erosion and scouring during floods.

(7) Coastal Erosion (CE) Coastal erosion is another slope failure type occurring along the coastline and is induced by tidal erosion of embankments and rarely on natural slopes along the coastal line.

1.3.2 Listing of Item Groups and Specific Items

To evaluate FRCDp, the specific items contributing to slope instability are selected. In this evaluation method, item groups and the specific items for completing Sheet 2 are listed below.

(1) Groups of Items for Analysis The following groups of items for analysis are listed in the Japanese Slope Inspection Format published in 1996 and should also be considered when analyzing slope conditions along national highways of the Philippines.

Group I: Geometry of Slope

Group II: Surface Condition of Slope

Group III: Disturbance of Slope

Group IV: Effectiveness of Existing Countermeasure

The above listed item groups are commonly used internationally, except for “Geological Condition.” This is listed as an item under Group II: Surface Condition of Slope. The geotechnical research on slope stability in the Philippines was not fully developed yet, as of the present, the listing of suitable item is difficult. Detailed judgment on geological conditions is rather difficult for the engineers of DPWH. So, geological condition is listed as an item under the “Surface Condition of Slope” group simply to make it easier for the civil engineers of DPWH to analyze it.

(2) Specific Items The specific items in each group are listed referring to the Japanese Slope Inspection Format published in 1996 and considered the failure mechanism of each disaster type as shown in Table 1.2 and Sheet 2-1 to 2-7 in Appendix 1.




Table 1.2 Items for Each Disaster Type

SC RC LS RS DF RE CE Group I: Geometry

- Survey length

- Height of mountain side slope

- Slope Gradient

- Distance from road to toe of slope

-Slope shape/form

Same as SC - Survey length

- Slope Gradient

- Slope shape

- Survey length

- Height of valley side slope

- Slope gradient

- Distance from road to head of slope

- Slope shape/form

- Width of channel

- Area of drainage basin

- Height from

channel bottom to the road

- Survey length

- Distance from low water to road

- Width of river at low water

- Height from high water to road surface

- Survey length

- Distance from water line at high tide to road

- Height from high tide to road

Group II: Surface Condition - Vegetation/ surface

covering - Surface

material - Ratio of

bedrock exposure

- Bed rock - Spring/ surface

water

- Vegetation/ surface

covering - Surface

material - Spring/ surface

water


covering - Surface

material -Spring/ surface

water -Direction

of dip (bedding, fault plane, joint plane, etc.)


covering - Slope

type(embankment/ natural)

- Surface material

-Spring/ surface

water -Water flow

from road to valley side slope

- Vegetation of drainage area

- Materials of river bed

- Materials of river bank

- Materials of river bed

- Materials of coastal bank

- Materials of coast line

Group III: Disturbance - Erosion - Deformation

/collapse

- Deformation /collapse

- Erosion - Deformation

/collapse


/collapse

- Slope failure in drainage area

- Trace of debris

-Deformation /collapse/ erosion


/collapse

Group IV Countermeasure Effectiveness - Countermeasure

1.3.3 Setting of Frequency Score Contributing to FRCDp

The road slope inventory survey can provide FRCDp as a risk level indicator as shown in Figure 1.5. FRCDp is calculated using the following formula.

FRCDp = FRCDpoc x CCE

FRCDpoc = ∑ FS




CCE = ∑ FRCDa / ∑ FRCDbc

FRCDa = Na/ Ya

FRCDbc = Nbc / Ybc

Where:

FRCDp= Potential frequency of RCD of a slope [nos. of RCD per year]

FRCDpoc= Potential FRCD of a slope without countermeasure [nos. of RCD per year]

CCE= Coefficient of countermeasure effectiveness for FRCDp of a countermeasure-type [coefficient]

FS= Frequency score for FRCDp (FS is assigned to each factor category of each factor item for FRCDp as shown in Figure 2.2 [nos. of RCD per year]

FRCDa= Actual frequency of RCD of a slope [nos. of RCD per year]

FRCDbc= Actual frequency of RCD of a slope before countermeasure is installed [nos. of RCD per year]

Na= Actual number of RCD of a slope in ‘Ya’ year [nos. of RCD]

Ya= Period of available disaster records of a slope [year]

Nbc= Actual number of RCD of a slope in ‘Nbc’ year before countermeasure is installed [nos. of RCD]

Ybc= Period of available disaster records of a slope before countermeasure is installed [year]




Figure 1.5 Illustration of Analysis Method for FRCDpoc (Prediction Value) A Frequency Score is assigned to each corresponding category of each factor item such as slope gradient, height, etc. and CCE are set by the pilot inventory survey of 251 km length (this was part of the preliminary inventory survey sections subject to FRCDp evaluation). The result of the analysis is shown in Table 1.3. When new data from the inventory survey is obtained, these scores and coefficients should be analyzed and revised as necessary to improve the accuracy of FRCDp prediction.

PIS Data

Multiple regression analysis with dummy parameter

Analysis of Frequency Score

Multiple regression analysis* with dummy parameter

- Geometry - Surface situation - Disturbance

Revision of Frequency Scoresin “Sheet 2”

*Multiple regression analysis with a dummy parameter is a method of minimizing the residual sum of squares between actual value (FRCDa) and the predicted value (FRCDpoc) using the correlativity of FRCDa and the slope disaster frequency factors.

** FRCDa, if countermeasure is installed, FRCDbc should be adopted instead of FRCDa

Sequence No. of slopes sorted by FRCDa**

FRC

D

Prediction value (FRCDpoc)

Actual value FRCDa (FRCDbc if countermeasure is present)

Minimizing Σ(FRCDpoc – FRCDa**)2




Table 1.3 Total Maximum Frequency Score for Each Item Group (Result of Multiple Regression Analysis with Dummy Parameter using data of

experimental preliminary Inventory) Disaster Type Item Group

SC RF LS RS DF RE CE

Geometry (Sg) 0.388 (19%)

0.328(30%)

0.130(26%)

0.423(47%)

0.166 (18%)

0.565 (65%)

0.176 (20%)

Surface Condition (Ss) 0.466 (23%)

0.322(30%)

0.10 (20%)

0.291(32%)

0.251 (28%)

0.094 (11%)

0.230 (26%)

Disturbance (Sd) 1.188 (58%)

0.432(40%)

0.27 (54%)

0.185(21%)

0.491 (54%)

0.213 (24%)

0.494 (55%)

1.4 Methodology of Indicative Feasibility Assessment

As mentioned in Chapter 1.2, an indicative feasibility assessment is carried out by completing Sheet 5. In this activity, the benefit/cost ratio (BCR), economic net present value (ENPV), and economic internal rate of return (EIRR) are estimated. These are the key indicators for planning reasonable preventive works for critical road slopes. The framework of the indicative feasibility assessment in Sheet 5 in the DIS is shown in Figure 1.6.




The methodology for calculating feasibility indicators and the detailed procedure for completing Sheet 5 are further described in Chapter 3.

FRCDp: Frequency of Potential Road Closure Disaster

Risk Reduction Ratio with Countermeasure

Losses induced by RCDp - Reopening Cost - Detour Cost - Human Lives Lost

Countermeasures for RCDp - Countermeasure I (Cost)

- Countermeasure II (Cost) - Countermeasure III (Cost)

Benefits: Decrease in Annual Losses due to the Countermeasure

Figure 1.6 Framework for Indicative Feasibility Assessment

Magnitude of RCDp: Magnitude of Potential Road Closure Disaster

Feasibility Indicators: (BCR, ENPV, EIRR)

FRCDpwc: FCDP with Countermeasure


NIPPON KOEI CO., LTD. 2-1 June 2007


CHAPTER 2

PRELIMINARY INVENTORY SURVEY

2.1 Flow of the Preliminary Inventory Survey (PIS)

Major objectives of PIS are as follows:

(1) Registry of locational data, actual disaster frequency, and factor categories for slope failure;

(2) Estimation of FRCDp of slopes; and

(3) Selection of slopes to be surveyed in detail in DIS.

To obtain information on road slopes to assess hazard condition of road slopes and selection of slopes to be surveyed in DIS, the activities shown in Figure 2.1 are carried out in PIS. The details of the procedures for each work are described in the following sections.

Detailed Inventory Survey (DIS)

(1) Preparatory Work

(4) Estimation of FRCDp & Selection of slopes for DIS

(3)Check on Factors Contributing to the Occurrence of Slope Disaster

(2) Screening of Slopes

Figure 2.1 Work Flow of Preliminary Inventory Survey




2.2 Preparatory Work

Prior to the start of the PIS, as much existing information as possible for the area to be inspected should be collected. It is very important to carry out an efficient Inventory Survey. Careful preparatory work shall be done prior to field works. The following items are to be prepared in the preparatory work:

(1) Disaster Records;

(2) Topographic and RBIA Maps;

(3) Field Survey Instruments;

(4) Camera and Computer;

(5) Vehicle; and

(6) Formulation of Survey Team.

2.2.1 Disaster Record

Disaster records along the subject route shall be collected using the Inventory Format Sheet 6 (See Appendix -1). The procedure for disaster record collection is as follows:

(a) Gathering of data on road slope disasters along the subject route from concerned offices/agencies; and

(b) Interview of person(s) who have knowledge on RSD occurrences along the subject road.

The following information is collected to fill out Sheet 6 and categorized by disaster type.

(a) Site of slope disaster (road name, station and side of road);

(b) Date and time of occurrence;

(c) Damage (personal, vehicle, building, public facilities, etc);

(d) Disaster type;

(e) Dimensions of disaster (road closure length, collapsed material, collapsed volume);

(f) Cause of the disaster;

(g) Rainfall data before the disaster;




(h) Method and cost of rehabilitation work undertaken (include reopening cost and methods);

(i) Existing countermeasures (types, stations);

(j) Photos/Sketches; and

(k) Other relevant information.

2.2.2 RBIA and Topographic Maps

The following maps are published by National Mapping and Resource Information Authority (NAMRIA) of the Department of Environment and Natural Resources (DENR) and the Department of Public Works and Highways (DPWH):

(1) Digital Road Maps of the national highways with a nominal scale of 1:5,000 （DPWH);

(2) Topographic Maps with a nominal scale of 1:50,000 (NAMRIA); and

(3) Topographic Maps with a nominal scale of 1:250,000 (NAMRIA).

(1) RBIA Maps Digital maps of the national highways can be obtained from the Road and Bridge Information Applications (RBIA) system of DPWH, which is useful for searching the field location of the road slope disaster sites. This map shows the kilometer stations, the bridges, and some elevation points on the route. However, the contour lines, which are significant information needed for the inventory survey, are not indicated on these maps. Acquisition flow of the RBIA Roads Maps from the District Engineers Office (DEO) is shown in Figure 2.2. Usage flow of the RBIA Roads Maps in this study is shown in Figure 2.3.




Figure 2.2 Acquisition Flow of RBIA Road Maps

The RBIA system can provide digital maps of the national highways for the whole country. The results of the PIS should be recorded on the road map by hand and the data entered into the RBIA system. Recorded items on the road map with a nominal scale of 1:50,000 for the PIS are as follows:

(a) PIS section and the starting point per km station; (b) Disaster type of PIS section; and (c) DIS section selected from PIS.

The RBIA digital maps of the national highways for the whole country and for the CAR are shown in Figures 2.4 and 2.5.

An example of a digital map with a nominal scale of 1:250,000 is shown in Figure 2.6. An example of location map of inventory survey site with a nominal scale of 1:5,000 drawn by hand is shown in Figure 2.7.

DPWHIPRSD Division

RBIA system

DEO

Regional Office

RBIA system

PrintsPrints




Identify the location of PIS section in the field

RBIA Maps

Figure 2.3 Usage Flow for RBIA Maps

Field Inspection

Desk work

PIS sectionDisaster Type in PIS section The slope selected for the DIS

Record

Future feedback information into the system




See Figure 2.5

Figure 2.4 Example of Road Map of the National Highways




See Figure 2.6

Figure 2.5 Example of Road Map of CAR




Identify the location of the PIS section in advance of the field inspection

Management Indication of Progress

See Figure 2.7

Figure 2.6 Example of Road Map




Figure 2.7 Example of Location Map for Inventory Survey (1:5,000)

SC

RS

RS

RS

RS

RS

SC SC

SC

RC

Selected for Detailed Inventory Survey

Selected for Detailed Inventory Survey

Km265+208

Km265+397

Km264+252

Km265+094

Km264+616

Km264+502

Km264+252

Recording on the Road Map 1. PIS section 2. Disaster type on the PIS section 3. Selection results for the DIS

Identify the location of PIS sections in the field




(2) Topographic Maps Examples of the index numbers of topographic maps with a nominal scale of 1:50,000 for use in the PIS route are shown in Table 2.1. Topographic maps are utilized together with RBIA digital maps.

Table 2.1 Index of Topographical Maps for the Inventory Survey

Road Index Number Remarks Kennon Rd 7175-III, 7175-IV

Baguio-Bontoc Rd (Halsema Highway) 7176-I, 7176-II, 7176-III,

7175-IV, 7177-II

Nueva Vizcaya- Ifugao- Mt Province Rd (Lagawe-Banaue)

7276-IV

Daang Maharlika (LZ) (Dalton Pass) 7275-III, 7275-IV

Cebu-Balamban Transcentral 3750-I, 3750-IV, 3751-I,

3751-II, 3851-III

The road is not shown on the map

N Bacalso Ave (Cebu South Rd) (Ginalitan-Alegria)

3648-IV, 3649-III

Wright-Taft- Borongan Rd 4055-I, 4055-II, 4055-III,

4055-IV

Daang Maharlika (LT) (Mahaplag –Sogod) 3951-II, 4050-IV, 4051-IV The road is not shown on the map




2.2.3 Field Survey Instruments

Field survey instruments required for the PIS are shown in Table 2.2.

Table 2.2 Required Field Survey Instruments

Tools Purpose Remarks Wheel Tape To measure the length of

a survey slope

Tape Measure To measure the Geometry of a slope such as distance from road to toe of mountainside slope, height from channel bottom to road, etc.

Inclinometer/ Any instrument used for measuring slope gradients.

To measure the gradient of the slope

Digital camera

Camera

Negative print

To photograph a slope unit and paste it on Sheet-1 as a digital image

Computer To fill in the inventory sheet. Software specifications;

(1) Windows OS (2) Microsoft Excel




2.3 Screening of Surveyed Slope

The slopes on both sides of the road (from the starting point to the end point) identified by kilometer station should be judged for potential to generate a RCD. Where the lanes in opposing directions are separated into divided carriage ways, the slopes of both carriage ways should be inspected and judged for screening.

All slopes that have had RCDs in the preceding ten years and where visible disturbances have been observed should be selected for the inventory survey. For slopes without previous RCD records, all slopes (cut slope, embankment, and natural slope) along the road should be inspected to be determined whether to conduct a detailed survey or not. The inventory survey will be based on the following screening criteria.

2.3.1 Screening Criteria for Soil Collapse and Rock Collapse

Cut or natural road slopes on mountainsides with a height of over 15 m and a distance from slope toe to the road of less than 15 m shall be surveyed in PIS (for SC, RC).

Figure 2.8 Screening Criteria of Slopes for Soil and Rock Collapse

Height over 15 m

The slope toe to road is less than 15 m

Slope height of over 15 m

The start and end points of the survey area

Survey Section 1 Survey Section 2

Cross section Front view




2.3.2 Screening Criteria for Road Slips

Roads with embankments or natural slopes along valley sides with a height of over 5 m and with a distance from the toe of the slope to the road less than 5 m shall be surveyed in the PIS.

Figure 2.9 Screening Criteria of Slopes for Road Slip

2.3.3 Screening Criteria for Debris Flow

A road section across a stream of over one (1) m in width (for DF: Debris Flow)

Between the banks of the stream are designated as a survey slope (including stream structures such as bank embankment, etc.)

Figure 2.10 Screening Criteria of Slopes for Debris Flow

A height of over 5 m

The slope toe to road is less than 5 m

Over 5m

The start and end points of survey area

Survey Section 1 Survey Section 2

stream of over 1m in width

Plan view

Road

Stream of over１ｍ in width

Profile

Road

Plan view Cross section




2.3.4 Screening Criteria for River Erosion

Area close to a river less than 15m from the river bank to the road

Cross section Figure 2.11 Screening Criteria of Slopes for River Erosion

2.3.5 Screening Criteria for Coastal Erosion

Area close to the shoreline and less than 5m from the road.

Cross section

Figure 2.12 Screening Criteria of Slopes for Coastal Erosion

Less than 15m from the riverbank to road

River

Less than 5m from the coast to road

Sea




2.4 Method for Field Survey and Completing of Inventory Forms

2.4.1 Method of Field Survey

The results of the PIS are recorded in the three (3) form sheets and RBIA road map with a nominal scale of 1:5000.

1. Inventory Sheet 1 on general information

2. Inventory Sheet 6 on records of past slope disasters

3. Inventory Sheet 2 on evaluation of frequency of RCD to select the DIS sections

Seven types of Sheet 2 have been prepared for each disaster type. The disaster type for the survey section is identified and the appropriate sheet filled in. The following three-step evaluation is conducted for each survey section:

• FRCDa: actual frequency of road closure disasters

• Presence of visible disturbance; and

• FRCDp: potential frequency of road closure disaster.

4. RBIA Road Map – Recording of the PIS section, disaster type on the PIS section and the slope selected for the DIS.

The procedure for the field survey is shown in Figure 2.13 and the Inventory Survey Formats are shown in Appendix 1.




2.4.2 Filling in of the Inventory Form

The results of the survey/field investigation are entered and/or recorded in the corresponding cell(s) of the Inventory Sheet(s). General information encoded on Sheet 1 is shared with all inventory sheets including Sheet 3 to Sheet 5 for the DIS. The FRCDp, which is calculated in Sheet 2, and the cost of countermeasures estimated in Sheet 4, are the required information to

Screening and Measurement of Slope

Identification of disaster type and selection of appropriate Sheet 2 for the corresponding disaster type (Sheet 2-1 to Sheet 2-7)

Figure 2.13 Field Survey Procedure

Filling out of Sheet 2 -Evaluation of FRCDp -Necessity of DIS

by FRCDa, Visible Disturbance,

FRCDp

Filling out of Sheet 1 General Information

Survey of Slope

- Input on Appropriate Sheet in the Computer

- Results drawn on the road map by hand

Filling out of Sheet 6 (Disaster Record)




fill up Sheet 5.

The results of the PIS are checked and approved as follows:

• The PIS is carried-out by the Regional and District Office Engineers;

• The results of the PIS is reviewed and checked by the District Engineer; and

• To be approved by a responsible engineer of the Regional Office.

When encoding the data into the sheets using a computer, it is important to fill in the numbers and symbols properly, and to follow the format required for the database of Road Slope Management System (RSMS).

(1) Inventory Sheet-1: General Information Definitions of the inventory items are as follows:

(a) Appropriate Regional Office Name of regional office should be inputted in symbol only, e.g., Region CAR is “CAR”, and Region XIII is “XIII”.

(b) Responsible DEO Input the name of the DEO which has responsibility for the management of the road section, e.g., Benguet 1st DEO and Leyte 3rd DEO.

(c) Road Name Input the road name consistent with the RBIA system since some roads have two (2) or more names, e.g., Baguio-Bontoc in CAR is called Halsema Highway or Baguio-Bontoc Road. The road name should be inputted as Baguio-Bontoc Road (same as the RBIA system).

(d) Road Section ID Input Road Section ID consistent with the RBIA system. It is named and recognized as follows.




Example; S00123LZ_04031_0154_L_DF

First 8 characters These are the same as the ROAD SECTION CODE used in the RBIA database. ‘S’+ 5 digits + Island Code (2 characters, LZ is the code of Luzon.)

Next 5 digits This expresses the kilometer post.

Next 4 digits This expresses distance meter from kilometer post to direction of destination

Next 1 character ‘L’ or ‘R’, which denotes the left or right side of the road.

Last 2 characters Corresponding to the disaster code.

The example, S00123LZ_04031_154_L_DF, denotes the point of 4031.154m of S00123LZ road section, the left side where the debris flow is most possible.

Refer to the attached digital file of Inventory List of Roads for the First eight (8) characters that is ROAD SECTION ID of RBIA as follows.

The above example of a ROAD SECTION ID in RBIA is S00621MN referring to Sayre Highway/Bukidnon 3rd DEO/Region X, Mindanao.

(e) Km Station Input the kilometer station from the start and end point of the slope unit surveyed in meters based on the Distance Pole along the national highway, e.g., the slope unit located at Km 305 + 200 to Km 355 + 300 should be inputted 305 and 200 in the cell for the starting point of the slope unit, and 335 and 300 on the cell for the end point.

Measure the kilometer station from the distance pole of the origin side because some distance pole is shifted from every one kilometer point, in case of this length between the pole to the next pole may not be one kilometer.

ROAD_ID ROAD NAME SECTION_LENGTH ROAD_SECTION_ID ENGINEERING DISTRICT REGION NAME CLASSIFICATIONR00066MN Sayre Highway 54395.766 S00646MN Bukidnon 2nd District Engineering Office Region X North-South BackboneR00066MN Sayre Highway 2181 S00647MN Bukidnon 2nd District Engineering Office Region X North-South BackboneR00066MN Sayre Highway 10942.234 S00648MN Bukidnon 2nd District Engineering Office Region X North-South BackboneR99984MN Dologon-Kisanday-Ginoyuran Road 8058 S00658MN Bukidnon 2nd District Engineering Office Region X Secondary National RoadR00104MN Maramag-Maradugao Rd 19579 S00663MN Bukidnon 2nd District Engineering Office Region X Secondary National RoadR00105MN Kibawe-Kadingilan-Kalilangan Rd 15213 S01355MN Bukidnon 3rd District Engineering Office Region X Secondary National RoadR00066MN Sayre Highway 37326 S00621MN Bukidnon 3rd District Engineering Office Region X North-South BackboneR01516MN Ticalaan-Iligan Rd (Mamaon-Ragongon Sect) 2400 S00614MN Bukidnon 3rd District Engineering Office Region X East-West LateralR00067MN Jct SH-Manolo Fortich-Libona-Indahag Rd 45687 S01353MN Bukidnon 3rd District Engineering Office Region X Secondary National RoadR00096MN CDO City-Dominorog-Camp Kibaritan Rd 52775 S01321MN Bukidnon 3rd District Engineering Office Region X Secondary National RoadR00097MN Jct SH-Sn Miguel-Del Monte Airport Rd 2392 S01352MN Bukidnon 3rd District Engineering Office Region X Secondary National RoadR00099MN Jct SH-Aglayan-Alanib-Ticalaan (Ticalaan-Paganan) 14585 S00042MN Bukidnon 3rd District Engineering Office Region X East-West LateralR00106MN Kalilangan-Lampanusan Rd 14560 S00672MN Bukidnon 3rd District Engineering Office Region X Secondary National RoadR00107MN Barandias-Dominorog Rd 27831 S00673MN Bukidnon 3rd District Engineering Office Region X Secondary National RoadR00108MN Jct Maradugao-Camp Kibaritan-Dominorog Rd 26085 S00676MN Bukidnon 3rd District Engineering Office Region X Secondary National RoadR00095MN Misamis Or-Bukidnon-Agusan Rd 18417 S01320MN Bukidnon 3rd District Engineering Office Region X Secondary National RoadR01516MN Ticalaan-Iligan Rd (Mamaon-Ragongon Sect) 3605 S00616MN Bukidnon 3rd District Engineering Office Region X East-West Lateral




(f) Side of Survey The valley side and the mountainside slope of the road should be separately registered. ‘Right side of road’ and ‘Left side of road’ can be selected by pull-down menu on the EXCEL spreadsheet.

‘Right side of road’ means the right hand slope toward the terminal side, ‘Left side of road’ means the left hand slope toward the terminal side, where the reference point is 0+000, located in Manila, that is, survey measurement should be reckoned in increasing kilometer stationing.

(g) Disaster Type ‘Disaster type’ should be inputted by pull-down menu on the EXCEL spreadsheet.

The guidelines to determine the classification of the disaster type are described in Appendix 2.

(h) Name of Surveyor Name of surveyor of the preliminary inventory survey is inputted in text.

(i) Photographs Photographs are taken showing the site condition. The general view should be considered. The photographs should focus on the portions of the disaster that are judged to require further investigation. Photographs taken by digital camera should be imported as digital files into the appropriate cells of Sheet 1. Photographs using non-digital camera should be pasted by hand as a printed picture on the appropriate cell of Sheet 1.

<Photographs are very important information in the Inventory Survey. Photographs shall be encoded to Sheet 1, every day after the field work.>




Table 2.3 Example of Sheet 1

Items Definition

Region Regional Office of the Road Section managed; e.g. CAR, I, VI, XII….

Office in charge DEO of the route managed; e.g. BENGUET 1st DEO

Road Name Follow the Road Name of RBIA List. e.g. BANAUE – LAGAWE Road

Nueva Vizcaya Ifugao Mt Province Road (Road Name of RBIA List)

Station Should be entered based on the distance from origin (MANILA) to destination as per the kilometer post on the national highway. e.g. from Km241+300 to Km241+550

(Station) Length e.g. 250 (in metric)

Side of Survey From starting point (MANILA) towards end point.

Disaster Type e.g. Road Slip

Checked by Section Chief of Maintenance/Planning

Approved by District Engineer (or his assistant)

Photographs General View Portion which should be paid close attention.




(2) Inventory Sheet 2: Selection of Sections for the Detailed Inventory Survey Sheet 2 comes in seven (7) variations, for the different disaster types. The engineer selects the appropriate form based on the disaster type identified during the field inspection in the preliminary inventory survey (refer to Appendix 1). These are as follows:

• Sheet 2-1 for Soil Slope Collapse;

• Sheet 2-2 for Rock Slope Collapse;

• Sheet 2-3 for Landslides;

• Sheet 2-4 for Road Slips;

• Sheet 2-5 for Debris Flow;

• Sheet 2-6 for River Erosion; and

• Sheet 2-7 for Coastal Erosion.

(a) Evaluation of Actual Road Closure Disaster Input the corresponding number of road closure disasters on the appropriate cell in Sheet 2 for the last ten (10) years for the slope unit surveyed, e.g., in case road closure disaster occurred five (5) times at the site, then input ‘5’ in the cell.

The frequency is counted without considering the closed period (day, hour), for example, if the road is closed for two weeks continuously, then the number of road closure is only one (1) as also the case when the road is closed for three hours.

The number of road closure disasters in the past ten years shall be counted based on the disaster records of the responsible DEO or according to the recollection of the inhabitants of the area.

The record of past RCD shall be arranged in Sheet 6.

(b) Evaluation of Disturbance Situation If ‘visible disturbance’ is present, input ‘1’ on the appropriate cell of Sheet 2. ‘Visible disturbance’ refers to collapse, cracks, depression, bulge, muddy spring water and other annoyance on the road body or slope which can be a warning of potential RCD.

(c) Evaluation of the Potential Frequency of Road Closure Disaster Potential Frequency of Road Closure Disaster (FRCDp) is estimated by checking the items contributing slope instability such as ‘Geometry,’ ‘Surface Situation,’ ‘Disturbance,’ and




‘Effectiveness of Existing Countermeasures’.

The FRCDp evaluated on Sheet 2 is linked to Sheet 5 for the evaluation of annual losses without countermeasures and indicative feasibility assessment of the countermeasure, which is an important indicator to establish a reasonable management plan.

The definitions for each of these items are as follows:

1) Geometry

a) Length of survey section (in connection with SC, RF, LS, RS, RE, CE; Sheet 2-1,2,3,4,6,7)

Locational Reference Points (or kilometer posts) are installed in every 1 km interval along the roadside, which is used as reference in measuring the length of the survey section.

Figure 2.14 Locational Reference Point

The length of the survey section (L) is automatically calculated in Sheet 1, where the length of the survey section (L) is the distance between the start and the end point of the survey section.

L (m)

Slope unit

Starting point of unit End point of unit Front view




b) Height of mountain-side slope (in connection with SC, RF; Sheet 2-1,2) The height of the slope is measured from the road or slope toe up to the knick line. The knick line is the abrupt changing line from the gentler upper slope to a steeper lower slope.

Figure 2.15 Schematic Illustration of Knick Line Knick: The junction where a gently inclined pediment and the adjacent mountain slope meet at a sharp angle.

Knick line: A line formed by the angle of a knick in a slope, especially in a desert region where there is an abrupt transition from a pediment surface to the mountain slope.

Knick point: Any interruption or break of slope; especially the point of abrupt change or inflection in the longitudinal profile of a stream or of its valley, resulting from rejuvenation, glacial erosion, or the outcropping of a resistant bed (Glossary of Geology, 3rd ed. (AGI).

Knick line in this Guide; A line formed by the angle of a knick, which is the junction where a gently inclined pediment and the adjacent road slope meet at a sharp or gentle angle.

Ridge Knick line

Knick line Height

Knick Line

H (m)




c) Height of valley side slope (in connection with RS; sheet 2-4) The height of the slope is measured from the slope shoulder to the toe.

Figure 2.16 Schematic Illustration of Valley Side Slope in Sheet 2-4

d) Gradient of slope (in connection with SC, RF; Sheet 2-1,2) An average gradient of a slope is measured from a road or slope toe up to the knick line or the average gradient of the slope is measured from the slope shoulder to the toe.

Figure 2.17 Schematic Illustration of Gradient of Slopes in Sheet 2-1, 2

Gradient: degree of inclination or rate of ascent or descent, of an inclined part of the Earth’s surface with respect to the horizontal; the steepness of a slope. It is expressed as a ratio (vertical to horizontal), an angle (in degrees) (Glossary of Geology 3rd ed. ,AGI).

H (m)

Road

Road

Gradient θ(°)

Knick Line Road Gradient

θ(°)




e) Distance from the road to the toe of a mountain side slope (in connection with SC, RF; Sheet 2-1, 2) The distance from the slope toe to the road is measured as shown in the illustration below.

Figure 2.18 Schematic Illustration of Distance from Road to the Toe of the Mountain in Sheet 2-1, 2

f) Distance from the road to the toe of the valley side slope (in connection with RS) The distance from the slope head to the road is measured as shown in the illustration below.

Figure 2.19 Schematic Illustration of Distance from Road to Shoulder of Slopes

in Sheet 2-4

Slope Toe

D (m)

Road Slope Head

D (m)




g) Slope shape/form (in connection with SC, RF, LS, RS; Sheet 2-1, 2, 3, 4) The slope shapes/form is classified into four (4) types.

1) Ridge type 2) Straight type 3) Valley type

Figure 2.20 Schematic Illustration of Slope Shape in Sheet 2-1, 2, 3, 4 Source: Japanese Slope Inspection Manual

1) Ridge Type: Convex Slope, 2) Straight Type: Planar slope, 3) Concave Slope

The fourth is the combined type, which is characterized by the presence of two or more types in a successive slope unit as illustrated below.

Figure 2.21 Schematic Plain View Illustration of Combined Type Slope Shape in Sheet 2-1, 2, 3, 4)

Start point of slope

End point of slope

Valley type Ridge type

top

toe

top

toe

toe

top

top

toe

top

toe

top

toe

top

toe top

toe top

toe




h) Width of a channel (in connection with DF; in Sheet 5) Distinguish the width of the channel from the width of the stream.

Figure 2.22 Schematic Illustration of Slope Shape in Sheet 2-5

Channel: (a) The bed where the natural body of surface water flows or may flow; a natural passageway or depression of perceptible extent containing continuously or periodically flowing water, or forming a connecting link between two bodies of water; a watercourse. (b) The deepest or central part of the bed of a stream, containing the main current, and occupied more or less continuously by water.

Riverbed: The channel containing or formerly containing the water of a river.

River bottom: The low-lying alluvial land along a river (Glossary of Geology, 3rd ed. AGI).

High Water Level

Bridge

Channel

W (m)




i) Area of drainage basin (in connection with DF; Sheet 2-5) The area of the drainage basin is estimated from the topographic map with a nominate scale of 1:50,000 as illustrated in the Figure 2.23. Trace the ridge, to realize the drainage basin area on the map, which is a line that rises above a surface. The drainage basin area is enclosed by a watershed, which is the ridge.

Figure 2.23 Schematic Illustration of Area of Drainage in Sheet 2-5

Drainage basin: A region or area bounded by a drainage system that gathers water originating from precipitation and contributes to a particular stream channel, or to a lake, reservoir, or other body of water (Glossary of Geology 3rd ed., AGI).

j) Height from the channel bottom to the road (in connection with DF; Sheet 2-5)

The height from the channel bottom to the road is shown in the figure below.

Cross section Figure 2.24 Schematic Illustration of Height from the Channel Bottom

to the Road in Sheet 2-5

←Drainage basin area

A (km2)

Road

Channel

H (m)

Bridge




k) Distance from the low water level to the road (in connection with RE; Sheet 2-6)

The distance from the low stream level to the road is shown in the figure below.

Figure 2.25 Schematic Illustration of Distance from the Low Water Level to the Road in Sheet 2-6

l) Width of the river at low water level discharge (in connection with RE; Sheet 2-6) The width of the river at low water level discharge is shown in the figure below.

Figure 2.26 Schematic Illustration of Width of River at Low Water to the Road in Sheet 2-6

Road

Revetment

High water level

Low water

W (m)

Road

Revetment High water level

Low water level

W(m)




m) Height from the high water level to the road surface or head of revetment (in connection with RE; Sheet 2-6) The high water level to the road surface or head of revetment is shown in the figure below.

Figure 2.27 Schematic Illustration of Height from the High Water Level

to the Road in Sheet 2-6

The high water level can be estimated using a trace of the flow, engineer’s experience and information provided by inhabitants, etc.

n) Distance from the high water coast line to the road (in connection with CE; Sheet 2-7) The distance from the high water coast line to the road is shown in the figure below.

Figure 2.28 Schematic Illustration of Distance from the High Water Coastline to the Road in Sheet 2-6

High water: Water at the maximum level reached during a tidal cycle (Glossary of Geology, 3rd ed. AGI).

Road

Revetment

High water level

Low water

H (m)

Road

Sea

D (m)

Plan view




o) Height from the high water level to the road formation or head of revetment (in connection with CE; Sheet 2-7) The height is measured from the high water level to the head of revetment, if it is higher than the road level as shown in the figure below.

Figure 2.29 Schematic Illustration of Height from the High Water Level to the Road in Sheet 2-7

2) Surface condition a) Vegetation (in connection with SC, RF, LS, RS; Sheet 2-1, 2, 3, 4)

Table 2.4 Classification of Vegetation/Surface Covering

Bare Classified as ‘Bare’ if more than 50% of the area has no vegetation. Grasses Classified as ‘Grasses’ if more than 50% of the area is mainly

grassland. Trees Classified as ‘Trees’ if more than 50% of the area are trees. Artificial protection Classified as ‘Artificial protection’ in case a disaster countermeasure

has been constructed on the slope.

b) Vegetation of drainage area (in connection with DF; Sheet 2-5) The dominant vegetation in the drainage area from the roadside of the slope unit surveyed is classified, as defined in the table below.

Road

High Water Level

Head of Revetment H (m)




Table 2.5 Classification of Vegetation of Drainage Area Bare Classified as ‘Bare’ if more than 50% of the area has no vegetation. Grasses Classified as ‘Grasses’ if more than 50% of the area is mainly

grassland. Trees Classified as ‘Trees’ if more than 50% of the area are trees. Artificial protection Classified as ‘Artificial protection’ in case a disaster countermeasure


c) Materials of the slope surface (in connection with SC, RF, LS, RS; Sheet 2-1, 2, 3, 4)

The materials on the slope surface can be classified based on the table below.

Table 2.6 Classification of Materials of the Slope

Silt, Clay 1/4096 mm-1/16 mm A soft sticky substance that can be pressed and formed into different shapes and figures.

Sand 1/16 mm-2 mm Pebbles, 2 mm-64 mm, Cobbles 64 mm-256 mm, Boulder 256 mm-4096 mm Artificial protection Classified as ‘Artificial protection’ in case a disaster countermeasure





d) River Sediment Materials (in connection with DF; Sheet 2-5) The classification of the materials of the river sediment can be determined based on the table below.

Figure 2.30 Observation Area to Determine River Sediment Material in Sheet 2-5

Table 2.7 Classification of River Sediment Materials

Cobble, Boulder 64 mm-256 mm, 256 mm-4096 mm Pebbles 2 mm-64 mm Sand Silt, Clay

1/16 mm-2 mm 1/4096 mm-1/16 mm A soft sticky substance that can be pressed and formed into different shapes and figures.

Bedrock Classified as ‘Bedrock’ in case more than 50% of area is bedrock.

e) Riverbank materials (in connection with RE; Sheet 2-6) The materials in the riverbank will be observed and classified based on the table below.

Figure 2.31 Observation Area to Determine River Bank Materials in Sheet 2-6

Road

Revetment

River water

River bank

River Sediment




Table 2.9 Classification of River Bank Materials Cobble, Boulder 64 mm-256 mm, 256 mm-4096 mm Pebbles 2 mm-64 mm Sand 1/16 mm-2 mm Silt, Clay 1/4096 mm-1/16 mm

A soft sticky substance that can be pressed and formed into different shapes and figures.

Bedrock Classified as ‘Bedrock’ if more than 50% of the area is bedrock. Artificial protection Classified as’ Artificial protection’ in case a disaster countermeasure

has been constructed on the riverbank.

f) Riverbed Materials (in connection with RE; Sheet 2-6) Similarly, the materials on the riverbed can be classified based on the table below.

Figure 2.32 Observation Area to Determine River Bed Materials in Sheet 2-6

Table 2.10 Classification of River Bed Materials Cobble, Boulder 64 mm-256 mm, 256 mm-4096 mm Pebbles 2 mm-64 mm Sand 1/16 mm-2 mm Silt, Clay 1/4096 mm-1/16 mm


Bedrock Classified as ‘Bedrock’ if more than 50% of the area is bedrock.

g) Coastal Bank Materials (in connection with CE) The same classification is used to determine the materials found in coastal banks.

Road

Revetment

River bed

River water




Figure 2.33 Observation Areas of Determine Coastal Bank Materials in Sheet 2-7

Table 2.11 Classification of Coastal Bank Materials

Cobble, Boulder 64 mm-256 mm, 256 mm-4096 mm Pebbles 2 mm-64 mm Sand 1/16 mm-2 mm Silt, Clay 1/4096 mm-1/16 mm


Bedrock Classified as’ Bedrock’ if more than 50% of the area is mostly bedrock.

Artificial protection

Classified as ‘Artificial protection’ in case a disaster countermeasure has been constructed on the riverbank.

h) Materials of Coast (in connection with CE; Sheet 2-7) The materials found in the coast is measured and classified based on the table below.

Figure 2.34 Observation Areas to Determine Coastal Materials in Sheet 2-7

Road

Revetment

Sea

Coastal bank Road

Road

Revetment Sea

Coast




Table 2.12 Classification of Coastal Materials

Cobble, Boulder

64 mm-256 mm, 256 mm-4096 mm

Pebbles 2 mm-64 mm Sand 1/16 mm-2 mm Silt, Clay 1/4096 mm-1/16 mm


Bedrock Classified as ‘Bedrock’ if more than 50% of the area is mostly bedrock.

i) Ratio of Bedrock Exposure Area (in connection with SC; Sheet 2-1) The estimate of the bedrock exposure area of the slope unit surveyed can be classified in accordance with the table below.

Table 2.13 Classification of Ratio of Bedrock Exposure Area

40%<AR More than 40% of the area is distributed with bedrock. 20%<AR<40% Equal to or less than 40% and more than 20% of the area is bedrock. 0%<AR<20% Equal to or less than 20% and more than 0% of area is bedrock. 0%=AR The area of the slope unit surveyed is not a bedrock.




j) Bedrock Materials (in connection with SC; Sheet 1)

Table 2.14 Classification of Bedrock Materials Fractured rock

Most of the rocks are with cracks, open joints or other signs of disintegration.

Weathered rock

Most of the rocks are changed color to brownish. Some of the rock fragments can be broken by hand. Less than half of the rock material is broken into pieces.

Soft fresh rock

No visible sign of rock material weathering/alteration. Rock body can be shaved off by paper cutter or can be pressed and formed into different shapes by a hammer.

Hard fresh rock

No visible sign of rock material weathering/alteration. Rocks cannot be pressed and formed into different shapes.

Unknown Cannot be observed due to the condition of the slope unit surveyed, which has dense vegetation.

Soft rock: (b) Rock that is relatively nonresistant to erosion.

Hard rock: (b) Rock that is relatively resistant to erosion (Glossary Of Geology 3rd ed. (AGI).

k) Slope Type (in connection with RS; Sheet 2-4)

Table 2.15 Classification of Slope Types

Embankment slope

100% of the area of the surveyed slope surface is embankment.

Combined or unknown

The area of the surveyed slope surface is combined of embankment and in-situ materials, or it is unknown

Natural slope 100% of the area of the surveyed slope surface is natural or in-situ materials.




l) Spring/Surface Water (in connection with SC, RC, LS, RS in Sheet 2-1, 2, 3, 4)

Table 2.16 Classification of Spring/Surface Water

Present Spring/surface water is present on the slope unit surveyed.

None Spring/surface water is not present on the slope unit surveyed.

Spring: Place where ground water flows naturally from a rock or soil onto the land surface. Its occurrence depends on the nature and position of the water table, and topography (Glossary Of Geology 3rd ed. (AGI).

m) Rainwater Flows from Road to Valley Side Slope (in connection with RS; Sheet 2-4)

Table 2.17 Classification of Rainwater Flows on Valley Side Slope

Yes Rainwater flows on the road and concentrates on the valley side slope.

No Rainwater does not flow from the road to the valley side slope.

Refer to the figure below, which considers topography such as drain.

Figure 2.35 Schematic Illustration of Rain Flows to Valley Side Slope

Spring water on a slope

Rain Fall

decline

Up hill grade

trace of water flow

(plan view) (cross section)




Drain: (a) A small and narrow natural watercourse. (b) A channel, conduit, or waterway, either natural or artificial, for draining or carrying-off excess water from an area, such as a ditch designed to lower the water table so that land may be farmed; a sewer or stream in a given direction or to an outlet (Glossary of Geology, 3rd ed. AGI).

3) Disturbance a) Erosion on the Slope (in connection with SC; Sheet 2-1) Erosion: (a) The general or group of processes whereby the materials of the Earth’s crust are loosened, dissolved, or worn away, and simultaneously moved from one place to another, by natural agencies, which include weathering, solution, corrosion, and transportation, but usually excluding mass wasting; specifically the mechanical destruction of the land and the removal of material (such as soil) by running water (including rainfall), waves and currents, moving ice, or wind.

Erosion surface: A land surface shaped and subdued by the action of erosion, especially by running water.

Piping: Erosion by percolating water in a layer of subsoil, resulting in caving and in the formation of narrow conduits, tunnels, or “pipes” through which soluble or granular soil material is removed; especially the movement of material from the permeable foundation of a dam or levee, by the flow or seepage of water along underground passages (Glossary Of Geology 3rd ed. (AGI).

Erosion Piping hole Figure 2.36 Photograph of Erosion and Piping Hole

b) Erosion in the Valley side Slope (in connection with RS 2-4) Same definition can be given as above.




c) Erosion in the Coastal side Slope (in connection with CE; Sheet 2-7) Erosion of the coastal bank is classified as described in the Table 2.18

Table 2.18 Classification of Rainwater Flows on Coastal Side Slope

Broken revetment The revetment material is removed by erosion due to runoff from the road or by wave action.

Erosion of revetment foundation The revetment foundation material is scoured by the flow of surface water from the road or by waves.

Erosion of coastal banks or revetment




d) Deformation/Collapse (in connection with SC, LS, CE; Sheet 2-1, 3, 7) Deformation/collapse in Sheet 2-1, 3, and 7 are illustrated schematically as shown in Figure 2.37.

Collapse/slump Cracks, Crevices

Fallen/Inclined trees Depression/ Upheaval Figure 2.37 Schematic Mode of Disturbance in Sheet 2-1, 3 and 7

Soil or Weathered Rock

Road

SC

Rock

Original line

Road Slip Surface

Displaced Material

Original line Depression

Bulge

Slip Surface




e) Deformation/collapse on the slope (in connection with RC; Sheet 2-2) Deformation/collapse in Sheet 2-1, 3, 7 is illustrated schematically, as shown in the Figure 2.38

Fall, Collapse Open cracks below overhang

Toppling Sliding direction of open cracks

Crossed open cracks to cause wedge-shaped slide Figure 2.38 Schematic Mode of Disturbance in the Sheet 2-2

Rock fall: (a) The free falling or precipitous movement of a newly detached segment of bedrock (usually massive, homogeneous, or jointed) of any size from a cliff or other very steep slope; it is the fastest form of mass movement and is most frequent in mountain areas and during spring time when there is repeated freezing and thawing of water in cracks in the rock. Movement may be straight downwards, or in a series of leaps and bounds down the slope; it is not guided by an underlying slip surface.

Rock Fall

Crack

Road

Open crack

Road Road




Topple: A mass movement that consists of the forward rotation of a unit or units about some pivotal point, below or under the unit, influenced by the action of gravity and forces exerted by adjacent units or by fluids in cracks. It is tilting without collapse (Varnes and 1978 and Glossary of Geology, 3rd ed., AGI).

f) Deformation/Collapse on the Slope (in connection with RS; Sheet 2-4) Deformation/collapse in Sheet 2-1, 3 and 7 are illustrated schematically, as shown in Figure 2.50.

Cracks/Crevices on the road Depression on the road

Fall Slump on valley side slope Figure 2.39 Schematic Mode of Disturbance in the Sheet 2-4




g) Slope Failure Condition in Drainage Area (in connection with DF; Sheet 2-5) Classification of slope failure condition in drainage area is classified as shown in the Table 2.19

Table 2.19 Classification of Rainwater Flows on Valley Side Slope More than 5 collapses

More than 5 collapses had occurred in the drainage area.

2-4 collapses Between 2-4 collapses had occurred in the drainage area. 1 collapse Only 1 collapse had occurred in the drainage area. Unknown The condition on the slope unit surveyed cannot be observed

due to the presence of vegetation.

h) Trace of Debris on or Beside the Road (in connection with DF; Sheet 2-5) Example of trace of debris shown in Figure 2.40

Present

None In case there is no trace, classify as ‘None’.

Figure 2.40 Schematic Mode of Disturbance in Sheet 2-5




i) Deformation/Collapse/Erosion (in connection with RE; Sheet 2-6) Deformation/collapse in the Sheet 2-1, 3 and 7 are illustrated schematically, as shown in Figure 2.41.

Fall, Slump, Erosion on river bank slope

Figure 2.41 Schematic Mode of Disturbance in Sheets 2-6

4) Existing Countermeasure

i) Guard fence ii) Concrete catch wall

Road

River

Attack part

Bridge




iii) Retaining Wall iv) Rock shed

v) Shotcrete vi) Vegetation

vii) Slope drainage/road drainage viii) Gabion




ix) Small check dam (less than 10m height) x) Sabo dam (equal to more than 10m height)

xi) Revetment for river bank xii) Groin/Spur dike

xiii) Revetment for river bank xiv) Revetment with foundation

Road Foundation




xv) Revetment without foundation xvi) Wave-absorbing works Figure 2.42 Existing Countermeasures

2.5 Evaluation Procedure for the Selection of DIS Slopes

The criteria for the selection of DIS slopes are summarized and shown in Figure 2.43. The details of each selection follow afterwards.

Road

Wave-absorbing/dissipating works




Figure 2.43 Selection Criteria for the DIS Slopes

2.5.1 Selection I (Evaluation by FRCDa)

In case of Selection I:

Road Closure Disaster (RCD):

It includes not only whole, but also partial road closure. In the survey, deformations and collapses that do not cause road closures were not considered/regarded as RCD, but merely as ‘disturbance’.

Actual Frequency of RCD (FRCDa): FRCDa =Na/Ya (no./year)

I. Sites of Occurrence of Past Disasters (FRCDa ≥ 0.1)

III. FRCD (Freq. of Road Closure Disaster) (FRCDp ≥ 0.1)

Selection I

Selection III

- Geometry - Geological/Hydrological Conditions - Surface Conditions

Evaluation of Items Causing Road Disasters

If FRCDa is equal to or greater than 0.1 (no. per year), the section should be selected for the DIS.

II. Visible Deformation (Slopes/Roads) Selection II




Where,

Na: Number of RCDs in the past (no.)

Ya: Period with Disaster Record (years)

2.5.2 Selection II (Evaluation by Disturbance) In case of Selection II:

Disturbance: Deformation of the slope and/or road structures and slope collapse, which do not affect/reach the road, is treated as a ‘disturbance’.

2.5.3 Selection III (Evaluation by FRCDp)

In case of Selection III:

Potential Frequency of RCD (FRCDp):

FRCDp is calculated as the total of the factor scores for such items as slope gradient, height, slope materials, disturbance situation, etc., where factor scores are assigned for each type of disaster.

Estimation of FRCDp:

FRCDp= (Sg+ Ss+ Sd) × Ce

- Sg: Frequency Score Attributable to Geometry

- Ss: Frequency Score Attributable to Surface Condition

- Sd: Frequency Score Attributable to Disturbance

- Ce: Coefficient of Effectiveness of Countermeasure: (0.01 to 0.9)

If a visible disturbance is present on the PIS slope unit, the section should be selected for the DIS.

If FRCDp is equal to or greater than 0.1 (no./year), the section should be selected for the DIS.

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