Rio Tuba FR Vol_I Main Report 090618

8/15/2019 Rio Tuba FR Vol_I Main Report 090618

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Coral Bay Nickel Corporation

Tailings Storage Facility No.2

Final Report

Volume I

Main Report

June 2009

Sumitomo Mitsui Construction Co., Ltd.


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Constitution of the Report

Volume I Main Report

Volume II Drawings

Volume III Specification

Volume IV Design Calculation

Volume V Quantity Calculation


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Coral Bay Nickel Corporation Tailings Storage Facility No.2 Final Report


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Table of Contents

Page

Chapter 1. Introduction.........................................................................................................1 1.1 Background...........................................................................................................1 1.2 Scope of This Document.......................................................................................2 1.3 Work Excluded .....................................................................................................3 1.4 References provided by CBNC.............................................................................4 1.5 Guidelines and Standards......................................................................................5

Chapter 2. Design Conditions ...............................................................................................6 2.1 Topographical Conditions.....................................................................................6 2.2 Geological Conditions ..........................................................................................6

2.2.1 Regional Geology........................................................................................... 6 2.2.2 Structural Geology ......................................................................................... 8 2.2.3 Site Geology................................................................................................... 9

2.3 Natural and Social Environment...........................................................................13 2.4 Precipitation and Runoff Analysis ........................................................................13 2.5 Design Philosophy of TSF No.2 ...........................................................................13 2.6 Design Seismic Coefficient...................................................................................14

Chapter 3. Design Review of Dam Embankment................................................................17 3.1 Topographical and Geological Condition .............................................................17

3.1.1 Topography and Geology of Dam Site........................................................... 18 3.1.2 Topography and Geology of Reservoir .......................................................... 20 3.1.3 Fault at Right Side of southern Dam site ....................................................... 21

3.2 Staged Construction..............................................................................................23 3.3 Dam Type..............................................................................................................24

3.3.1 Southern Dam................................................................................................. 24 3.3.2 Northern Dam.................................................................................................25

3.4 Dam Foundation ...................................................................................................26 3.4.1 Additional Boring Test ................................................................................... 26 3.4.2 Test Pit Investigation...................................................................................... 28 3.4.3 Geological Investigation Result ..................................................................... 29

3.5 Dam Axis ..............................................................................................................31 3.6 Zoning and Embankment Materials......................................................................32

3.6.1 Zoning of Rockfill Dam................................................................................. 32


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3.6.2 Possible Borrow Areas of Embankment Materials.........................................34 3.6.3 Borrow Areas of Embankment Materials....................................................... 40

3.7 Material Properties for Each Zone........................................................................52 3.7.1 Core Zone....................................................................................................... 52 3.7.2 Filter Zone...................................................................................................... 54 3.7.3 Rock Zone ...................................................................................................... 58

3.8 Instrument .............................................................................................................59 3.8.1 Objectives of Instrumentation ........................................................................ 59 3.8.2 Function and Arrangement of Instruments..................................................... 60 3.8.3 Data Collection............................................................................................... 62

Chapter 4. Design Review of Water Management...............................................................64 4.1 Hydrological Analysis...........................................................................................64

4.1.1 Precipitation ................................................................................................... 65 4.1.2

Peak Discharge............................................................................................... 69

4.1.3 Probable Maximum Flood for Dam Safety .................................................... 71 4.1.4 Precipitation and Peak discharge in Dry Season ............................................ 75

4.2 Consideration of Precipitation Data at Rio Tuba ..................................................79 4.3 Diversion Method .................................................................................................82

4.3.1 Required Function.......................................................................................... 82 4.3.2 Diversion Procedure....................................................................................... 82 4.3.3 Hydraulic Design ........................................................................................... 83

4.4 Spillways...............................................................................................................87 4.4.1 Required Function and Freeboard.................................................................. 87 4.4.2 Spillway for First Stage.................................................................................. 88 4.4.3 Spillway for Final Stage................................................................................. 90

Chapter 5. Structural Analysis..............................................................................................92 5.1 Stability Analysis of Foundation and Embankment..............................................92

5.1.1 General ........................................................................................................... 92 5.1.2 Factor of Safety.............................................................................................. 92 5.1.3 Slope Stability Analysis ................................................................................. 94

Chapter 6. RECOMMENDATIONS ....................................................................................102 6.1 General..................................................................................................................102 6.2 Necessity of Trial Embankment............................................................................102 6.3 Quality Control .....................................................................................................103

LIST OF TABLES IN REPORTPage

Table R 2.2.1 Summary of Regional Geology by HATCH........................................................... 8 Table R 2.4.1 Average Monthly Rainfall at Mangingidong .......................................................... 13 Table R 2.5.1 Storage Capacity of TSF-2...................................................................................... 14


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Table R 3.4.1 Results of Additional Boring Test at Southern Dam Foundation............................ 27 Table R 3.4.2 Unified Soil Classification System (ASTM D2487)............................................... 28 Table R 3.4.3 Falling Head Permeability Test Results at Borehole...............................................28 Table R 3.4.4 Test Pit Excavation Result at FTP-1 ....................................................................... 29 Table R 3.4.5 Test Pit Excavation Result at FTP-2 ....................................................................... 29 Table R 3.6.1 Test Pit Excavation Result at CTP-1....................................................................... 41 Table R 3.6.2 Test Pit Excavation Result at CTP-2....................................................................... 42 Table R 3.6.3 Results of Additional Boring Test at Rock Quarry ................................................. 46 Table R 3.6.4 Results of Specific Gravity Test of Additional Boring Core Samples.................... 46 Table R 3.6.5 Samples for Laboratory Test of Embankment Material .......................................... 49 Table R 3.6.6 Required Laboratory Tests for Materials in Their Natural States ........................... 50 Table R 3.6.7 Required Laboratory Tests for Blended Core Material........................................... 50 Table R 3.7.1 Gradation Limits of Core Zone ............................................................................... 52 Table R 3.7.2 Assumed Density of Core Zone .............................................................................. 53 Table R 3.7.3 Cohesion and Internal Friction Angle of Core Zone ............................................... 53 Table R 3.7.4 Filter Criteria........................................................................................................... 55 Table R 3.7.5 Gradation Limits of Fine Filter Zone...................................................................... 56 Table R 3.7.6 Assumed Density of Fine Filter Zone ..................................................................... 56 Table R 3.7.7 Cohesion and Internal Friction Angle of Fine Filter Zone ...................................... 56 Table R 3.7.8 Gradation Limits of Coarse Filter Zone .................................................................. 57 Table R 3.7.9 Assumed Density of Coarse Filter Zone ................................................................. 57 Table R 3.7.10 Cohesion and Internal Friction Angle of Coarse Filter Zone.................................. 57 Table R 3.7.11 Gradation Limits of Rock Zone .............................................................................. 58 Table R 3.7.12 Assumed Density of Rock Zone..............................................................................58 Table R 3.7.13 Cohesion and Internal Friction Angle of Rock Zone .............................................. 59 Table R 4.1.1 Parameter for Rainfall Intensity Curve for Puerto Station ...................................... 65 Table R 4.1.2 Design Precipitation and Design Duration for Rio Tuba TSF-2 ............................. 67 Table R 4.1.3 Peak Discharge for Each Return Period..................................................................70 Table R 4.1.4 Annual Maximum Daily Precipitation .................................................................... 73 Table R 4.1.5 Parameters for PMP ................................................................................................ 74 Table R 4.1.6 Peak Discharge for PMP ......................................................................................... 74 Table R 4.1.7 Mean Monthly Precipitation and Number of Rainy Days at Puerto Princesa

(1961 to 2000) ......................................................................................................... 75 Table R 4.1.8 Maximum Daily Precipitation in Dry Season............................................................76 Table R 4.1.9 Peak discharge in Dry Season for 25-year Return Period....................................... 77 Table R 4.2.1 Precipitation Data at Puerto Princesa (1961 to 2000) ............................................. 79 Table R 4.2.2 Precipitation Data at CBNC Rio Tuba (2004 to 2008)............................................79 Table R 4.2.3 Maximum Daily Precipitation at CBNC Rio Tuba (2004 to 2008).........................80 Table R 4.2.4 Comparative Table of Probable Daily Precipitation ............................................... 81 Table R 4.2.5 Revised Design Flood for Each Return Period ....................................................... 81 Table R 4.3.1 Flow Capacity of Existing Channel (Stage 1)......................................................... 84 Table R 4.3.2 Reservoir Water Level during Stage 1 .................................................................... 84 Table R 4.3.3 Reservoir Water Level during Stage 2 .................................................................... 85


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Table R 4.4.1 Flow Capacity of Spillway (First Stage) ................................................................. 88 Table R 4.4.2 Revised Design Flood ............................................................................................. 89 Table R 4.4.3 Reservoir Water Level of First Stage during 1000-year Probable Flood................ 89 Table R 4.4.4 Flow Capacity of Spillway (First Stage) ................................................................. 90 Table R 4.4.5 Revised Design Flood ............................................................................................. 91 Table R 4.4.6 Reservoir Water Level of Final Stage during Probable Maximum Flood............... 91 Table R 5.1.1 Minimum Required Factors of Safety for Slope Stability by Agencies.................. 93 Table R 5.1.2 Minimum Required Factors of Safety for Slope Stability in this Study.................. 93 Table R 5.1.3 Design Values of Each Zone for Slope Stability Analysis (Southern Dam) ........... 94 Table R 5.1.4 Cases of Slope Stability Analysis............................................................................95 Table R 5.1.5 Results of Slope Stability Analysis (First Stage) .................................................... 96 Table R 5.1.6 Results of Slope Stability Analysis (Final Stage) ................................................... 97 Table R 5.1.7 Design Values of Each Zone for Slope Stability Analysis for Northern Dam........ 98 Table R 5.1.8 Cases of Slope Stability Analysis for Northern Dam.............................................. 99 Table R 5.1.9 Results of Slope Stability Analysis for Northern Dam ........................................... 100 Table R 6.3.1 Items of Quality Control Test for Embankment...................................................... 104

LIST OF FIGURES IN REPORTPage

Fig. R 1.1.1 Location of Rio Tuba Mine..................................................................................... 1 Fig. R 1.1.2 Layout of TSF-2 planed by HATCH....................................................................... 2 Fig. R 2.1.1 Catchment Area of TSF-2 (1:50,000 Scale Map).................................................... 6 Fig. R 2.2.1 Regional Geology of South Palawan (1:1,000,000 Scale Map).............................. 7 Fig. R 2.6.1 Seismicity of the Philippines 1907-2000 by PHIVOLCS....................................... 16 Fig. R 3.1.1 1/50,000 Map around Rio Tuba Mine..................................................................... 17 Fig. R 3.1.2 Birds-eye View of Rio Tuba Mine.......................................................................... 17 Fig. R 3.1.3 Estimated Fault at right side of Southern Dam ....................................................... 21 Fig. R 3.2.1 Construction of a tailings embankment using Upstream Method ........................... 23 Fig. R 3.2.2 Construction of a tailings embankment using Downstream Method ...................... 23 Fig. R 3.2.3 Construction of a tailings embankment using Centerline Method .......................... 24 Fig. R 3.4.1 Location of Additional Boring Test at Southern Dam Foundation ......................... 26 Fig. R 3.4.2 Results of Additional Boring Test at Southern Dam Foundation............................ 27 Fig. R 3.4.3 Location of Test Pit Excavation at Southern Dam Foundation............................... 29 Fig. R 3.5.1 Layout of Southern and Northern Dams (from HATCH Report) ........................... 31 Fig. R 3.6.1 Typical Section of Rockfill Dam with Sloping Upstream Core.............................. 32 Fig. R 3.6.2 Location of Possible Borrow Areas of Filter Material ............................................ 36 Fig. R 3.6.3 Location of Additional Boring Test of Possible Quarry Site .................................. 37 Fig. R 3.6.4 Location of Fine Core Borrow Area and Rock Quarry Site.................................... 40 Fig. R 3.6.5 Planned Borrow Area of Fine Components of Core Material................................. 40 Fig. R 3.6.6 Planned Quarry Site of Coarse Components of Core Material ............................... 43 Fig. R 3.6.7 Location of Additional Boring Test and Planned Rock Quarry.............................. 45 Fig. R 3.7.1 Gradation Limits of Core Zone ............................................................................... 52


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Fig. R 3.7.2 Gradation of Core Material (Maximum Diameter: 4.75 mm)................................. 55 Fig. R 3.7.3 Gradation Limits of Fine Filter Zone...................................................................... 56 Fig. R 3.7.4 Gradation Limits of Coarse Filter Zone .................................................................. 57 Fig. R 4.1.1 Procedure for Hyetograph and Hydrograph Preparation......................................... 64 Fig. R 4.1.2 Location of Puerto Princesa .................................................................................... 65 Fig. R 4.1.3 Rainfall Intensity Curve for Short Duration in Puerto Station................................ 66 Fig. R 4.1.4 Rainfall Intensity Curve for Long Duration in Puerto Station ................................ 66 Fig. R 4.1.5 Flood Arrival Time and Rainfall Intensity Curve ................................................... 67 Fig. R 4.1.6 Hyetograph for 2-year Return Period...................................................................... 68 Fig. R 4.1.7 Hyetograph for 5-year Return Period...................................................................... 68 Fig. R 4.1.8 Hyetograph for 10-year Return Period.................................................................... 68 Fig. R 4.1.9 Hyetograph for 25-year Return Period.................................................................... 68 Fig. R 4.1.10 Hyetograph for 50-year Return Period.................................................................... 69 Fig. R 4.1.11 Hyetograph for 100-year Return Period.................................................................. 69 Fig. R 4.1.12 Hydrograph for 2-year Return Period ..................................................................... 70 Fig. R 4.1.13 Hydrograph for 5-year Return Period ..................................................................... 70 Fig. R 4.1.14 Hydrograph for 10-year Return Period ................................................................... 70 Fig. R 4.1.15 Hydrograph for 25-year Return Period ................................................................... 71 Fig. R 4.1.16 Hydrograph for 50-year Return Period ................................................................... 71 Fig. R 4.1.17 Hydrograph for 100-year Return Period ................................................................. 71 Fig. R 4.1.18 Calculation Procedure for PMP and PMF............................................................... 73 Fig. R 4.1.19 Hyetograph for PMP ............................................................................................... 75 Fig. R 4.1.20 Hydrograph for PMF............................................................................................... 75 Fig. R 4.1.21 Monthly Precipitation for 40 Years (1961 to 2000)................................................ 76 Fig. R 4.1.22 Probable Daily Precipitation in Dry Season............................................................ 77 Fig. R 4.1.23 Hydrograph in Dry Season for 25-year Return Period............................................ 78 Fig. R 4.1.24 Hydrograph in Dry Season for 25-year Return Period............................................ 78 Fig. R 4.2.1 Differences of Precipitation between at CBNC Rio Tuba and at Puerto Princesa .. 80 Fig. R 4.2.2 Probable Daily Precipitation at CBNC Rio Tuba.................................................... 80 Fig. R 4.3.1 Diversion Procedure (Stage 1) ................................................................................ 82 Fig. R 4.3.2 Diversion Procedure (Stage 2) ................................................................................ 83 Fig. R 4.3.3 Reservoir Water Level during Stage 1 .................................................................... 84 Fig. R 4.3.4 Reservoir Water Level during Stage 2 (All Season) ............................................... 85 Fig. R 4.3.5 Reservoir Water Level during Stage 2 (Dry Season).............................................. 85 Fig. R 4.4.1 Reservoir Water Level of First Stage during 1000-year Probable Flood................ 89 Fig. R 4.4.2 Reservoir Water Level of Final Stage during Probable Maximum Flood............... 91 Fig. R 5.1.1 Calculation Model of Southern Dam ...................................................................... 94 Fig. R 5.1.2 Calculation Model of Southern Dam ...................................................................... 98


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LIST OF PICTURES IN REPORTPage

Picture R 1.1.1 Existing TSF-1 and HPAL (high-pressure acid leaching) Plant..............................1 Picture R 3.1.1 Open Channel and Small Faults .............................................................................. 18 Picture R 3.1.2

Serpentinite exposed along Right Abutment of Southern Dam .............................. 19

Picture R 3.1.3 Boundary between Serpentinite and Mudstone (Open Channel) ............................ 19 Picture R 3.1.4 Boundary between Serpentinite and Mudstone (Northern Dam)............................ 19 Picture R 3.1.5 Magas-Magas Siltation Pond .................................................................................. 20 Picture R 3.1.6 Fault between Serpentinite and Mudstone observed at Location A........................ 21 Picture R 3.1.7 Fault between Serpentinite and Mudstone observed at Location B ........................ 22 Picture R 3.1.8 Fault between Serpentinite and Mudstone observed at Location C ........................ 22 Picture R 3.3.1 Available Embankment Material for Homogeneous Earthfill Type Dam............... 26 Picture R 3.4.1 Siltstone Boring Core (Sedimentary Structure is Broken) ...................................... 28 Picture R 3.5.1 Axis of Southern Dam............................................................................................. 31 Picture R 3.5.2 Axis of Northern Dam............................................................................................. 32 Picture R 3.6.1 Whitish Soil at Downstream of Southern Dam....................................................... 35 Picture R 3.6.2 Condition of Existing Concrete Aggregate Production Site.................................... 36 Picture R 3.6.3 Basalt exposed along Valley ................................................................................... 37 Picture R 3.6.4 Serpentinite exposed at Left Abutment of Southern Dam....................................... 38 Picture R 3.6.5 Condition of Existing Mined Area at Left Abutment of Southern Dam ................. 38 Picture R 3.6.6 Reforestation around Mined Land...........................................................................38 Picture R 3.6.7 Mined Land located at 1.5 km Northwest of TSF-2................................................39 Picture R 3.6.8 Mined Land located at Northern Part of TSF-1 ...................................................... 39 Picture R 3.6.9 Mined Land located at 1.5 km Northwest of TSF-1................................................ 39 Picture R 3.6.10 Dusky-read Silty Sand or Sandy Silt, Low Viscosity, 0.5m to 3.2m Depth............ 41 Picture R 3.6.11 Brownish Yellow Silt or Clayey Silt, High Viscosity, 3.2 to 4.0m Depth .............. 41 Picture R 3.6.12 Partially Weathered Serpentinite, 4.0 to 4.6m Depth.............................................. 41 Picture R 3.6.13 Reddish Silty Sand or Sandy Silt, Low Viscosity, 0.8 to 2.0m depth ..................... 42 Picture R 3.6.14 Brownish Yellow Silt or Clayey Silt, High Viscosity, 2.0 to 2.9m Depth .............. 42 Picture R 3.6.15 Sand and Gravel at Planned Coarse Core Borrow Area 1....................................... 44 Picture R 3.6.16 Sand and Gravel at Planned Coarse Core Borrow Area 2....................................... 44 Picture R 3.6.17 Planned Rock Quarry Viewed from the North........................................................ 47 Picture R 3.6.18 Serpentinite exposed by Mining.............................................................................. 47 Picture R 3.6.19 Highly Weathered Rocks with Siliceous Smaller Vain........................................... 48 Picture R 3.6.20 Crumbled Serpentinite at BH-1, 15.0 to 16.5m depth............................................. 48


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CHAPTER 1. INTRODUCTION1.1 BACKGROUNDCoral Bay Nickel Corporation (CBNC), nickel mining and refinery processing project in Rio Tuba

at the southernmost tip of Palawan Philippines, plans to expand its annual output to 20,000 ton.

Tailings from existing plant are pumped to Tailings Storage Facility No.1 (TSF-1) located about

100m to the north of the plant. TSF-1 has a maximum impoundment capacity of 12 million m3.

Fig. R 1.1.1 Location of Rio Tuba Mine

Picture R 1.1.1 Existing TSF-1 and HPAL (high-pressure acid leaching) Plant

Palawan Island

Rio Tuba Mine


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In order to achieve storage of tailings to be increased, CBNC proposed to construct a large valley

impoundment (TSF-2) within a broad bowl shaped valley to the northwest of the existing Tailings

facility (TSF-1). The works include the construct of:

- A staged approx. 50 m high dam (Southern Dam) along the southern boundary of the facility,- A saddle dam (Northern Dam) along the northern perimeter of the facility, and.- Ancillary works including a new slurry pipeline, supernatant water return pipeline and return

water pond, associated road works and drainage interceptor trenches

In this project, HATCH (Australia) has been finished the basic design of TSF-2 for bidding.

(Herein referred to as “Hatch Report”).

Fig. R 1.1.2 Layout of TSF-2 planed by HATCH

1.2 SCOPE OF THIS DOCUMENTThe scope of work includes revision of work designed by HATCH compiled as the Hatch Report.

The main part of revision is on zone constitution and material characteristics based on the results

of additional geological investigation and laboratory tests executed in this study. Structural

calculation including re-bar arrangement for appurtenant structures of starter dam (southern dam,

initial stage), if necessary. Technical specification for embankment, excavation and so on are also

included in this study.

Southern Dam (Plan)

Northern Dam (Plan)

HPAL Plant

Existing TSF-1

TSF-2 (Plan)

Return Water Pond Plan)

1000m0 200 400 600 800


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1.3 WORK EXCLUDEDThe following items are excluded from the Scope of Work:

- Basic design data such as geography, hydrology, geology, earthquake, material parameters has been collected and analyzed in Hatch Report, which will be presented by SMM. The revisionaldesign work will be performed with those data. Hence, following tasks and evaluation are

excluded from the Scope of Work:

- Survey drawing and geographical plan;- Collection and analysis of hydrology data such as probable runoff and probable maximum

flood;

- Geological survey at the dam site, the analysis of the survey result (includes geological plan) and the analysis of the parameters used for the design;

- Collection of earthquake data, the analysis of the collected data and the evaluation ofdesign seismic coefficient and design seismic acceleration;

- Geological investigation of embankment material, the analysis of the test result (includesgeological plan), laboratory soil test and evaluation of material parameters such as

internal friction angle.

Above-mentioned data, the result of analyses and parameters shall be presented by CBNC and

those data are used as initial condition of the work.

- The construction of the tailings dam consists of two stages as proposed by CBNC. Theelevation of the dam crest is at RL 60 in the first stage, then at RL 80m in the final stage.

Revision of the height of the dam crest with the design storage of tailings is excluded from this

work.

- The design of the utilities such as the return water pond, decant system, underdrainage systemin the reservoir and the slurry distribution pipeline is referred in Hatch Report and excluded.

- The permission of the construction by Department of Environment and Natural Resources(DENR) may be required before TFS is constructed. The preparation of the documentation for

this process is excluded.

- According to CBNC, tailings and sediments disacidified in the facilities includes no toxicchemicals such as heavy metals. Hence, leakage prevention at the bottom and the side of TSF-2

is not necessary and not presented in this work. The quality of seepage water and its effect to

the underground water is not evaluated in this work.

- Structural details including calculation and drawings are studied for starter dam (southern dam,initial stage) only. Technical Specification stipulates the works for starter dam (southern dam,

initial stage) only.


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1.4 REFERENCES PROVIDED BY CBNCFollowing references are proposed to be presented by CBNC.

- Geographical Plan（AutoCAD file） - Slope stability analysis (Static Analysis, Dynamic Analysis in each stage of the construction)

and the results;

- Seepage analysis of the bedrock and the embankment, and the results;- Drawings of the embankment, the spillway and the related structures (AutoCAD file)- Hydrological data (e.g. precipitation, intensity of rainfall and runoff data) and the result of the

analyses (e.g. probable rainfall, probable runoff, flood hydrograph with different return

periods, probable maximum flood and probable maximum flood hydrograph)

- Geological survey data (including accumulation layer) and the result of the analyses (e.g.Location map of boring, geologic column section, photograph of boring core, geological

longitudinal and lateral profile, permeability test results and laboratory test results)

- Embankment material data and the result of the analyses (e.g. geographical and geologicaldata at the quarry and borrow pit, and laboratory soil test results)

- Hatch, Sumitomo Metal Mining, Tailings Storage Facility No.2, Design Progress Report,December 2006, H323681-RPT-AU02-10005

- Hatch, Coral Bay Nickel Corporation, Tailings Storage Facility No. 2, EmbankmentConstruction Materials, May 2007, H323681-00-C-24-0001

- Hatch, Sumitomo Metal Mining, Coral Bay Nickel Corporation, Geotechnical Investigationfor TSF-2, November 2007, H323681-00-C-24-0003

- Hatch, Sumitomo Metal Mining, Tailings Storage Facility No.2, Supernatant and Storm waterRecovery System – Options Assessment and System Recommendation, April 2007,

H323681-RPT-AU02-10006

- Hatch, Tailings Storage Facility No.2, Addenda to December 2006 Design Progress Report,January 2007, H323681-MP-AU01-100016

- ARS, Factual Report Geotechnical investigation, CBNC Existing Tailings Dam, January 2009,ARS-13689-13631-09

- Guria Consulting, Seismic Review of the Tailings Dam in Bataraza, Palawan Island, 2006- Hatch, Sumitomo Metal Mining, Coral Bay Nickel Corporation, Concept Study for New

Tailings Dam, July 2006, H322605-0000-C-24-0001

- Hatch, Sumitomo Metal Mining, Coral Bay Nickel Corporation, Final Design Report forTSF-2, 200?, H?-0000-?-000?


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1.5 GUIDELINES AND STANDARDSThe following guidelines and standards will be followed for the review design.

(1) Standards on TSF

- Philippines DENR Memorandum Order No. 99-32;- Guidelines on the Safe Design and Operating Standards for Tailings Storage, Department of

Minerals and Energy, Western Australia;

- ICOLD Bulletin 106-1996 A Guide to Tailings Dams and Impoundments - Design,Construction, Use and Rehabilitation;

- ANCOLD, 1999 Guidelines on Tailings Dam Design, Construction and Operation.(2) Department of Public Works and Highways (DPWH) Design Criteria and Standards

- National Building Code of the Philippines (NBCP);- Guidelines, Criteria and Standards for Public Works and Highways, Volumes I and II;- DPWH : Department Orders;- Philippine National Standards (PNS).

(3) Others

- Design of Reinforced Concrete: ACI 318-05 Code Edition, American Concrete Institute;- American Association of the State Highway and Transportation Officials (AASHTO)

Standard Specifications, 17th Edition, 2002;

- American Society for Testing Materials (ASTM);- Japanese Industrial Standards (JIS).


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CHAPTER 2. DESIGN CONDITIONSDesign conditions are recognized in the HATCH reports presented by CBNC.

2.1 TOPOGRAPHICAL CONDITIONSHATCH Report summarized topographical condition around TSF-2 as follows;

The site of the new TSF-2 is located within a broad valley approximately 2.5km north west of the

existing CBNC plant site. The base of the valley is approximately 30m above sea level. In plan the

valley is bowl shaped with a broad straddling the northern perimeter of the site. A very sharp

ridgeline with steep densely forested slopes forms the western abutment of the southern dam. The

eastern abutment is obscured by a low-grade laterite ore stockpile. The ore stock pile will be

removed and processed prior to commencement of construction.

The total catchment area upstream of the proposed dam site has been estimated to be 240ha

(2.4km2). This was estimated by HATCH from the 1:50,000 topographical map published by the

NMRIA (National Mapping and Resource Information Authority).

Fig. R 2.1.1 Catchment Area of TSF-2 (1:50,000 Scale Map)

2.2 GEOLOGICAL CONDITIONSHATCH Report summarized geological condition around TSF-2 as follows:

2.2.1 Regional GeologyBased on the 1:1,000,000 scale regional geological map of Southern Palawan

1 (Ref. Fig.

R 2.2.1) and the 1:50,000 scale site geology map (1990), the regional geology consists of:

1 Mines and Geosciences Bureau, 1989, Department of Environment and National Resources

Basin Boundary

Southern Dam Site

Northern Dam Site


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- Cobble and boulder alluvial deposits along all major river systems with finer grained clayeyalluvium to the south of the mining prospects,

- Sedimentary rocks, typically comprising quarts sandstone, mudstone and siltstone with minorcalcareous limestone beds,

- Quarts sandstone to the north and east of the mining prospects,- Urtramafic rocks including Serpentinised Periodotite, Harzburghite and Dunite,- Pillow Basalts with intruded Granodiorites (Quarts Diorite intrusion), and- Karstic Limestone to the northeast of the mining prospect.

Fig. R 2.2.1 Regional Geology of South Palawan (1:1,000,000 Scale Map)

The major geological units mapped within the RTN mining lease are summarized in Table

R 2.2.1.

Rio Tuba Mine


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Table R 2.2.1 Summary of Regional Geology by HATCH

Geological Unit Age Unit Name

Qa Holocene Alluvium

Ma MioceneSayab Formation

Quarts Sandstone

Ebu EoceneMt. Beauford Ultramafics

Sepentinised Peridotite and Dunite

KEbp EocenePanas Formation

Sandstone interbedded with Mudstone and Shale

Keb CretaceousEspina Basalt

Pillow Basalt and Basalt flow with Chert

The existing Rio Tuba Nickel mine is located on a prominent hill comprising ultramafic bedrock

units from the Mt. Beauford ultramafic units. The ultramafic hill is extensively weathered and is

the principal source of low-grade lateritic nickel ore used in the plant. The hill is typically gently

sloping and protrudes some 60m above the surrounding landscape.

The low-lying regions to the south and east of the site comprise alluvial sediments overlying

interbedded sandstone, shale and mudstone units of the Panas formation. To the west of the

existing mining areas, the Bulanjao mountain range has been thrust partially over the Panas

formation to the south and the Espina basalt to the northwest. The contact between the basalt and

sedimentary rocks has been partially obscured by the over-thrust ultramafics, although north of the

mining lease region geotechnical mapping did encounter the basalt units, which are

distinguishable by change in vegetation.

2.2.2 Structural GeologyThe ultramafic rock at the site is part of the Palawan ophiolite, which consists of a complete

ophiolite sequence that ranges from basal mantle Harzburgnite to a pillow lava-chert sequence.

The major geological structure at the site is associated with the boundary of the ultramafic unit,

which has been thrust over the underlying sedimentary and pillow-lava bedrock to form the

Guintalunan deposit and Mt. Bulanjao ranges. The contact between the ultramafic unit and

underlying rock has been mapped as alow angle thrust fault dipping to the south west. Based upon

regional history, the fault has been mapped as inactive and unlikely to reactivate in the future due

to limited seismic activity within the study region.

A number of high angle faults have been mapped as part of the initial 1:50,000 geological survey

undertaken during exploration for the existing mine. The high angle faulting in the location of the

new TSF has been inferred from aerial photography and trends NNE to SSW. These faults are

likely to be associated with stress relief during regional thrust faulting. No ground proofing of

these structures exists on the geological mapping.


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2.2.3 Site Geology1) Site Geology of Southern Dam

The results from the geotechnical investigation indicate that there are six major geotechnical

units within the footprint of the Southern Dam. These units include:

- Fill from the low grade stokpiles,- Alluvial sediments and slopewash from the surrounding highland,- Residual soils derived from weathering of the mudstone, siltstone and ultramafics rock

units,

- Highly shared mudstones and siltstones with minor interbedded indurated sandstone beds,- Predominantly intact, albeit closely fractured, ultramafic rocks comprising Peridotite,

Harzburghite and Dunite. All are slightly to moderately serpentinised with minor Talc

filled defects,

- Highly shared and broken Dunite and Peridotite. These rocks have been metamorphosedto Serpentinite, with abundant Talc and clay minerals. This unit is typically associated

with thrust faulting during from the formation of the Mt. Bulanjao ranges.

The southern dam will be constructed across a broad valley located at the site of the existing

Magas-Magas siltation pond. The valley floor is generally flat with minor stream channels,

which have been incised through the surficial soils. The valley floor comprises silty to clayey

alluvial soils derived from the transportation of weathered ultramafic rocks within the

upstream cathments. The alluvial soils are of variable thickness and are typically thickest

along the eastern side of the valley, corresponding to the alignment of an old natural stream

channel. The channel has since been obscured by the L1 low-grade ore stockpile, however

boreholes within this area confirm the approximate alignment of the original channel. The

alluvial soils overly residual soils, which are clearly evident in the sidewalls of the existing

Magas-Magas spillway channel.

The residual soils in the base of the valley are derived from the weathering of mudstone,

claystone and siltstone, and therefore comprise a high percentage of silt and clay size

particles (generally with more than 80% passing the 0.075 mm sieve). The fines are typically

of medium to high plasticity and classify as Sandy Clays to Clays (CL-CH) rather than Silts

(ML-MH). The inverse is true of the residual soils derived from weathering of the ultramafics

rocks.

The bedrock beneath the valley floor comprises siltstone and mudstone rocks with minor

indurated quarts sandstone beds. The siltstone and mudstone intersected during the

investigation was typically highly shared with distinct slickensided surfaces present


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throughout the core samples. Bedding planes could not be measured due to the fractured

nature of the rockmass. Where sandstone beds were intersected, the recovered core was

highly fractuated with very close to closely spaced jointing. The rockmass structure of the

siltstones and sandstones suggest historical large scale regional faulting within the site of the

proposed dam. The results from the field data tends to confirm the existence of a regional

thrust fault along the base of the Mt. Bulanjao ranges, which has been mapped from aerial

photography.

The valley side slopes are generally moderate to steep with minor ultramafics rock outcrop

along the eastern abutment. The northern most section of the Magas-Magas spillway has been

cut through highly shared dunite. Residual soils within the cutting consist of elastic clayey

silts and sandy silts (MH) and had an average thickness of between 1.5 to 2.0m.

The eastern abutment has been completed obscured by the existing L1 low grade ore

stockpile, which will be processed prior to construction of the dam. Rock exposures within

old mine workings upslope of the proposed crest of the southern dam comprise highly altered

peridotites and hazburghites. In places these rocks have been completely altered to

serpentinites with minor talc seams intersected during investigations. The thickness of the

overburden residual soils were difficult to determine particularly since the lateritic ore

stockpile is of identical origin to the residual soils derived from weathering of the peridotite

and harzburghite rock. However, in exposed mine workings to the north of the southern dam,

the combined thickness of the limonite and saprolite horizons were in excess of 10m.

The relative relationships between the major geological units are defined by a number of

major geological structures. These geological structures include some near vertical normal

faulting along the abutments and a low angle thrust fault within the western abutment of the

dam.

Six multi-staged Consolidated Un-drained (CU) Tri-axial tests were performed on

undisturbed 63mm diameter thin walled tube samples taken from within the foundation of the

southern embankment (BH07S, BH11S, BH12S, BH13S, BH15S and BH16S). Two of the

tests were carried out on low plasticity clay, indicative of the alluvial soils within the valley.

The remaining four tests were conducted on sandy clay derived from the weathering of the

mudstone and siltstone units.

The strength parameters for the alluvial and residual foundation soils (grouped together due

to their similar characteristics) indicated peak effective strength parameters, φ’ ranges from

23 to 33˚ and c’ from 0 to 11 kPa. Upon analyzing the results, a corrected average line of best

fit with values of φ’ = 30˚ and c’ = 0 kPa, and a corrected lower bound limit of φ’ = 26˚ and

c’ = 0 kPa were obtained.


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2) Site Geology of Northern DamThe results from the geotechnical investigation have identified five major geotechnical units

within the footprint of the Northern dam. These units are:

- Residual clayey silts associated with the Laterite and Limonite soils profiles,- Residual clayey mudstones within the central southern sections of the alignment,- Extremely weathered ultramafics rock comprising cobbles and boulders in a soil matrix

(Saprolite horizon),

- Highly shared mudstones and siltstones, and- Predominantly intact, albeit closely fractured ultrafic rocks coprising Periodite and

Harzburghite. All are slightly to moderately serpentinised and comprise minor Talc filled

defects.

The majority of the northern embankment alignment is situated on residual ultramafics

comprising ferruginised clayey silts overlying extremely weathered rock. The extremely

weathered rock comprises low to medium strength serpentinised peridotite and harzburghite

boulders in a clayey silt to sandy silt matrix. The upper residual material is commonly termed

the limonite horizon and is currently mind for low grade feed ore to the HPP facility. The

underlying saprolite horizon is higher grade ore which is dried, stockpiled and then direct

shipped to Japan for refining.

Remnant structures were observed in a number of road cuttings and the old mine workings to

the north east of the proposed alignment. These structures are generally sub-vertical and

reflect the major joint sets within the underlying bedrock and may form conduits for seepage

through the foundations.

The serpentinised peridotite and harzburghite bedrock underlying the saprolite zone is

typically highly to moderately weathered and highly altered in places. Brecciation was also

observed in the core samples recovered during the geotechnical investigations, indicating

some re-cementation of the fractured rock. Based on the site history the rock is likely to have

been shared during formation of the Mt. Bulanjao rock is generally of low strength with the

matrix materials comprising calcite, serpentinite and minor talc.

At the location of BH04N and BH05N, siltstone and laminated sandstone was intersected.

The rock appears to be part of the Panas formation and is continuous through the footprint of

the proposed TSF-2 impoundment. The boundary of the sedimentary rock appears to

correspond with the base of the saddle and has a plan thickness of approximately 150m to

200m.


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12

Two multi-staged Consolidated Un-drained Tri-axial Tests were performed on undisturbed

63mm diameter thin walled tube samples taken from within the foundation of the northern

embankment (BH07N). Both samples are representative of low plasticity clayey silt typical of

the residual limonitic soils developed on the ultramafics rocks at the northern embankment

site.

The strength parameters for the limonitic soils indicated peak effective strength parameters,

φ’ ranges from 40 to 50˚ and c’ from 0 to 5 kPa. Upon analyzing the results, a corrected

average line of best fit with values of φ’ = 42˚ and c’ = 0 kPa, and a corrected lower bound

limit of φ’ = 40˚ and c’ = 0 kPa were obtained.


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2.3 NATURAL AND SOCIAL ENVIRONMENTHATCH Report mentioned impact on surrounding environment and community as follows:

Since the proposed impoundment will be located over an existing sedimentation pond

(Magas-Magas). A large proportion of the site has already been sterilized and partially cleared.

The eastern perimeter has already been cleared during stockpiling and therefore requires little

additional clearing. Clearing along the western abutment will be staged to maintain at minimum

clearance above the tailings level as it gradually increases over the life of the plant. The

impoundment site is located in the center of CBNC mining lease, and no communities currently

inhabit this area.

2.4 PRECIPITATION AND RUNOFF ANALYSISHATCH Report mentioned rainfall around TSF-2 as follows:

Average monthly rainfall values, expressed as mm/month, are presented for three distinct rainfall

zones, namely Mangingidong at 90m ASL, Guintalunan at 50m ASL, and Pier Site at 5m ASL.

The totaled annual rainfall values for the three areas are 2,198mm, 906mm and 1,487mm

respectively. The highest rainfall values, recorded at 90m ASL, were used for the water balance.

Table R 2.4.1 Average Monthly Rainfall at Mangingidong

Month Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec. Total

Rainfall(mm)

84 52 58 81 162 243 246 271 276 376 208 141 2,198

In HATCH Report, detail data about annual maximum daily rainfall, average annual rainfall and

intensity is not available. Hydrological analysis and run-off analysis are not executed by HATCH.

2.5 DESIGN PHILOSOPHY OF TSF NO.2Design philosophy of TSF-2 instructed by CBNC is summarized as follows:

- TSF-2 has two dams; A approx. 50 m high dam (Southern Dam) along the southern boundaryof the facility and saddle dam (Northern Dam) along the northern perimeter of the facility,

- Ancillary works including a new slurry pipeline, supernatant water return pipeline and returnwater pond, associated road works and drainage interceptor trenches are constructed during

first stage,

- TFS-2 is constructed in two discrete stages which will occur approx. 5 years apart. The initialstage includes the construction of the larger southern dam to a crest elevation of RL 60m.

- The second stage includes a downstream lift to the southern dam to increase the crest levelfrom RL 60m to RL 80m. At the same time a saddle dam (Northern Dam) will be constructed at


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the northern perimeter to RL 80m. A final overflow spillway will be constructed during this

stage of the work.

- In this study, storage capacity of TSF-2 is estimated using the topographic map, which was prepared by CBNC. The cumulative volumes for each reservoir surface are shown in Table

R 2.5.1.

Table R 2.5.1 Storage Capacity of TSF-2

2.6 DESIGN SEISMIC COEFFICIENTThe ICOLD (International Commission on Large Dams) publications

2 cover comprehensively the

subject of selecting appropriate earthquake input for dam design. Two levels of design earthquakes

are generally considered: the operating basis earthquake (OBE) for normal operations; and the

maximum design earthquake (MDE) for extreme conditions.

Suggested procedures in common practice for seismicity assessment of major and/or important

tailings dams are mentioned in “Tailings Dams and Seismicity ICOLD Bulletin 98, 1995”.

According to this Bulletin, OBE and MDE are explained as follows:

Operating Basis Earthquake (OBE)

The OBE is usually selected using probabilistic seismic hazard evaluation procedure. The hazard

level selected for the OBE varies from project to project but often is chosen as the earthquake

which has a 10% probability of exceedance in a 50-year period, or an annual probability of

exceedance of one in 475. The tailings dam is expected to function in a normal manner after the

passage of the operating basis earthquake.

2 Seismicity and Dam Design (Bulletin 46 1983), Dam Design Criteria – The Philosophy of Their Selection

(Bulletin 61, 1988b), Selecting Seismic Parameters for Large Dams – Guidelines (Bulletin 72, 1989c)

Elevation(EL. m)

Height(m)

Area (m2) Average Area

(m2)

Volume(m

3)

AccumulativeVolume

(m3)

36 - 130,000 - 0 0

37 1 150,000 140,000 140,000 140,000

38 1 180,000 165,000 165,000 305,000

39 1 210,000 195,000 195,000 500,000

40 1 250,000 230,000 230,000 730,000

45 5 410,000 330,000 1,650,000 2,380,000 50 5 550,000 480,000 2,400,000 4,780,000

55 5 660,000 605,000 3,025,000 7,805,000

60 5 780,000 720,000 3,600,000 11,405,000

65 5 940,000 860,000 4,300,000 15,705,000

70 5 1,120,000 1,030,000 5,150,000 20,855,000

75 5 1,370,000 1,245,000 6,225,000 27,080,000

80 5 1,500,000 1,435,000 7,175,000 34,255,000


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Maximum Design Earthquake (MDE)

For the MDE, damage of the dam is acceptable as long as the integrity of the dam is maintained

and the release of the impounded tailings is prevented. For major tailings dams, the failure of

which could have severe downstream consequences, the maximum credible earthquake (MCE) is

usually used as the MDE. By definition, the MCE does not have any probabilistic connotation, and

its selection involves a deterministic assessment. However, in practice, this design level

earthquake is sometimes associated with earthquakes of very low probability of exceedance

(Corresponding to e.g., an annual probability of exceedance in the order of one in 10,000).

From these considerations, HATCH requested that Guria Consulting (Australia) carry out the

seismic review for a tailings dam at Rio Tuba using database such as Seismicity of the Philippines

(Fig. R 2.6.1), Earthquake density Map in the Philippines and so on. Concluding remarks 3

by

Guria Consulting are given as follows:

Concluding Remarks (by Guria Consulting)

1. Generally, the corresponding seismic hazard results for medium soil sites in the Philippinesdetermined by Thenhaus and others (1994) are in general agreement with those presented by the

GSHAP (*1). Unfortunately, however, the former results do not extend to Palawan Island. Hencethe GSHAP (*2) results for the site on this island become important. Using these, it is estimated

that there is a 90% chance that the PGA will not exceed 0.08-0.16 g in a 50-year period.

2. The reviewer of this report has pointed out that LP (*3) structures may experience potentiallydamaging intensities during their lifetime. This is due to the frequency of destructive earthquakesin the vicinity of the main Philippines archipelago. Although these events are typically several or

many hundreds of kilometres from the site, they are strong generators of LP strong ground

motion; their energy is transmitted more efficiently over these distances than SP (*4) motion andtheir shaking duration is significantly greater giving rise to a greater capacity for damage. Forexample, a PGA of 0.08 g (or more) at a ground period of more than 0.5 s is estimated to have

occurred in 1948.

3. It is recommended that a new seismic hazard study be commissioned for the site to include thefollowing topics:-

i) Establish the Background Seismicity in the region of Palawan Island leading to a more

accurate assessment of the seismic hazard than has hitherto been possible;

ii) Long period (LP) strong ground motion effects at the site. This is critical for structures withnatural periods of 0.5 s or more.

iii) Output for i) and ii) should enable dynamic analyses of the structure for particular design

events for specific site geology;

iv) A study on the potential for liquefaction and tsunamigenic effects;

*1: Global Seismic Hazard Assessment Program

*2: Peak Ground Acceleration

*3: Long Period

*4: Short Period

3 Report of Seismic Review of the Tailings Dam in Bataraza, Palawan Island, Guria Consulting (Australia)


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Fig. R 2.6.1 Seismicity of the Philippines 1907-2000 by PHIVOLCS

A new seismic hazard study has not yet been done following the recommendation by Guria

Consulting. In addition, HATCH Report does not mention the parameters of the OBE and the

MCE.

Without final seismic assessment, there is no way to use the following parameters in this study:

- Peak Ground Acceleration of the OBE : 0.15g- Peak Ground Acceleration of the MCE : 0.25g

The parameters mentioned-above meet the guidelines of “Philippines DENR Memorandum Order

No. 99-32” 4

.

4 Section 15 Guidelines to Design Dam Embankment of On-land Mill Tailings Storage, b. n which seismic

consideration in the design of impoundment shall not be less than 0.15 and 0.25g under Operation BaseEarthquake (OBE) and Maximum Credible Earthquake (MCE) respectively.

Rio Tuba Mine


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CHAPTER 3. DESIGN REVIEW OF DAM EMBANKMENT3.1 TOPOGRAPHICAL AND GEOLOGICAL CONDITION

TSF-2 is located at uppermost stream of Tuba River which runs between mine and Bulanjao

Mountain. TSF-2 consists of one dam located at south (southern dam) and one saddle dam located

at north (northern dam). Northern dam is placed at the uppermost stream of Tuba River to

reinforce the enclosure. Southern dam is placed at the downstream to block up the tailings.

Planned dam site is located at 5 km upstream of river mouth.

Fig. R 3.1.1 1/50,000 Map around Rio Tuba Mine

Fig. R 3.1.2 Birds-eye View of Rio Tuba Mine

Northern DamExisting TSF-1

Southern Dam (Plan)

HPAL Plant

Bulanjao Mountain

Northern Dam (Plan)

HPAL Plant

Existing TSF-1Tuba River

2.5km0 0.5 1 1.5 2

Southern Dam

Bulanjao Mountain

TSF-2 (Plan)

TSF-2 (Plan)

1,000m0 200 400 600 800


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Site survey was held on January 14, 2009 to January 17, 2009. Findings are described below.

3.1.1 Topography and Geology of Dam SiteGeography at south dam and north dam are described below:

- Dam site is located at uppermost stream of Tuba River. Peat bog exists at north of south dam,which is located at the south of TSF-2 dam reservoir.

- Elevation of bottom of valley at dam site is about RL 35m and its width is about 250m.- Angle of abutment at right bank is about 20 degree. Angle of abutment at left bank is

considered to be about 20 degree although original angle is unclear due to surface excavation.

Both of the angle at right and left bank are gentle slope.

- Abutment of right bank is covered with shrub, and rock are exposed here and there. Shape ofthe abutment is relatively thin in river flow direction. At the abutment of left bank, surface soils

have been mined as ore.

- In the following picture, north dam is planned over the forest from left to right. Although smallhill is shown in the map, original geology could not be observed due to large storage of mine.

Geography at southern dam and northern dam are described below:

- At the location of southern dam, deposition of sandstone and mudstone are found in river bed.Serpentinite are found in mountain slope of right and left bank. Fault is expected to exist at the

boundary of geological stratum.

- At the location of northern dam, mudstone deposition are found at the center of planned site.Boundary of geological stratum, or fault, runs from north to south across the northern dam, and

serpentinite are found at the west of fault. Depositions of sandstone and mudstone are

considered to form geology of valley.

- There is a 5 m-wide open channel (no surface protection, jut excavated) on the right abutmentof southern dam. Weathered serpentinite and small fault (N40E, V) are found at the surface of

this channel (Ref. Picture R 3.1.1).

Picture R 3.1.1 Open Channel and Small Faults


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- Serpentinite are exposed along the right abutment of the southern dam, which is not weatheredas sandstone (Ref. Picture R 3.1.2).

Picture R 3.1.2 Serpentinite exposed along Right Abutment of Southern Dam

- Boundary between serpentinite and mudstone are found at the downstream of excavated openchannel (Ref. Picture R 3.1.3). Direction of this boundary is N46E, 70S. Serpentinite and

mudstones are weathered, red clayey soil.

Picture R 3.1.3 Boundary between Serpentinite and Mudstone (Open Channel)

- Un-weathered sandstone are found in red weathered clayey soil on rare occasions.- Boundary between mudstone and serpentinite (N35E, 40-80E) might exist near the thrust

which is located at downstream of northern dam, running along the road (Ref. Picture R 3.1.4).

Picture R 3.1.4 Boundary between Serpentinite and Mudstone (Northern Dam)


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- Boundary of mudstone and serpentinite is found near the northern dam, running across theditch. This boundary is fault and its inclination is N40E, V.

- Low-angle fracture zone was found at the outcrop located at downstream of northern dam,which is considered to be thrust (low-angle fault, N30E, 20). Some serpentinite are fractured in

low angle, or 20 degree, and brecciated.

- Although geological survey has been done at this dam site, geological structure cannot bechecked because the boring core has already been disposed. Therefore, it is important to

re-confirm the status of rocks, degree of weathring and permeability for standard soil at river

bed.

3.1.2 Topography and Geology of ReservoirTopography and geology of reservoir are listed below.

- The area of dam reservoir is now used for siltation pond, which is called “Magas-MagasSiltation Pond”. Moreover, lot of mine is piled at the left bank of northern dam, which makes it

difficult to check the planned dam axis with eyes.

Picture R 3.1.5 Magas-Magas Siltation Pond

- Details of geographical condition is not clear at reservoir area because of no outcrop.According to existing survey and observation, geology at bottom of reservoir (bottom of Tuba

River) is considered to be sandstone or mudstone and those of right and left bank is consideredto be serpentinite.

- Boundary between sandstone/mudstone and serpentinite is considered to be the fault, whichruns along the Tuba River, from northern dam to southern dam. That fault exists at the

foundation rock of northern and southern dams in a transversal direction. Conditions of the

fault is required to be studied with geology survey.

- Deposition of mud was found at the bottom of Magas-Magas Siltation Pond. Depth or someother details of this mud layer is not clear.


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3.1.3 Fault at Right Side of southern Dam siteFault located at right side of the southern dam site was confirmed at three locations, which is

mentioned as a boundary between serpentinite and mudstone in HATCH Report (Ref. Fig. R

3.1.3).

Fig. R 3.1.3 Estimated Fault at right side of Southern Dam

Fault between serpentinite and mudstone at right side of the southern dam was observed at three

locations as follows:

- At location A in Fig. R 3.1.3, excavated slope of drainage near northern dam site (Ref. PictureR 3.1.6). Serpentinite has been strongly weathered.

Picture R 3.1.6 Fault between Serpentinite and Mudstone observed at Location A

- At Location B in Fig. R 3.1.3, excavated temporary channel bed (Ref. Picture R 3.1.7).

TSF-1 Reservoir

Southern Dam Axis (Plan)

Mt. BulanjaoExisting

Magas-MagasSiltation Pond

1,000m0 200 400 600 800

HPAL Plant

Estimated FaultFault ???

Ser entinite

MudstoneSer entinite

Location A

Location B

Location C

Serpentinite Mudstone

Fault


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Serpentinite and mudstone have been strongly weathered.

Picture R 3.1.7 Fault between Serpentinite and Mudstone observed at Location B

- At Location C in Fig. R 3.1.3, existing borrow area for TSF-1 embankment (Ref. Picture R3.1.8). Strength of serpentinite and mudstone have been lowered by slaking phenomenon.

Picture R 3.1.8 Fault between Serpentinite and Mudstone observed at Location C

- Fault between serpentinite and mudstone at left side of the southern dam has not yet observed.

Serpentinite Mudstone

Fault

SerpentiniteMudstone

Fault


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3.2 STAGED CONSTRUCTIONThe staged embankment design is the most common construction technique used in tailing storage

facilities. It can minimize up-front capital works and improve overall economies. Depending on

the quality of tailings, there are three main methods for constructing tailings embankment using

the tailings as a major construction material 5

:

- Upstream Method,- Downstream Method,- Centerline Method.

Fig. R 3.2.1 Construction of a tailings embankment using Upstream Method

Fig. R 3.2.2 Construction of a tailings embankment using Downstream Method

5 Geotechnical Engineering of Embankment Dams, Robin Fell, Patrik MacGregor and David Stapledon


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Fig. R 3.2.3 Construction of a tailings embankment using Centerline Method

One of the earliest and the most common types of construction is by the upstream method.

However, the upstream method is the most common design to fail. The low relative density of the

tailing, if saturated, may liquefy and lead to slope failure and flows of the tailings. There are more

incidents with dams built by the upstream method than with other types

The centerline method is a compromise between the upstream and downstream methods. It is more

stable than the upstream method but still have a risk of failure during earthquake condition.

The tailings produced by HPAL plant are very fine. Therefore, they can not support loads of next

stage embankment. In this study, the downstream method is selected as an optimum staged

construction method.

3.3 DAM TYPE3.3.1 Southern DamHeight of southern dam is more than 50m at final stage.

Fill type dams are largely classified into two (2) types, namely, rockfill dam and homogeneous

earthfill dam based on the materials comprising the dam body. Structural characteristics of rockfill

dam and homogeneous earthfill dam are given as follows:

Rockfill Dam

Rockfill dam has a smaller restraint from the strength of foundation rock because it transmits the

external loads onto the broader area of the foundation. The dam body can be divided into at least

three (3) zones, namely, impervious, semi-pervious and pervious zones. Impervious zone filled


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with earth materials provides watertightness. Pervious zone filled with rock of all sizes supports

the less stable impervious material and provide the stability of the dam body.

Homogeneous Earthfill Dam

Homogeneous earthfill dam is constructed entirely or almost entirely of a single embankment

material. It has been built since the earliest times and is used today whenever only one type of

material is economically available. However, the possible height is limited within 30 m in general,

because it is usually composed of impervious or semi-pervious soil with small shear strength,

especially internal friction angle. In addition, when fine material such as silt/clay is used, it can not

be avoided to increase excess pore pressure in embankment. The excess pore pressure affects the

safety of dam. Since southern dam has about 50m in height, if applied, upstream and downstream

slopes shall be much gentler than those of rockfill type dam. Finally, It will be much costly.

Rockfill Dam with Center Core or Sloping Upstream Core

In rockfill dam, the impervious zone is placed in a vertical position near the center of the

embankment or sloped upstream. Generally, they are called the center core type and sloping

upstream core type respectively.

Both types can be adopted as water retention dam. However, considering the following matters,

rockfill type with sloping upstream core type is selected as an optimum dam type for southern dam

of TSF-2:

- Staged construction is facilitated by positioning the impervious core at near the upstream slope,- The impervious core material and filters may be placed after the downstream rockfill, allowing

rock fill construction to proceed in wet weather when placement of earthfill may be

impracticable,

- The downstream slope of the dam may be steepened.3.3.2 Northern DamAlthough height of northern dam is about 20m at final stage, homogeneous earthfill type can not

be adopted for northern dam. Available embankment material near the dam site is silt/clay with

gravel, which is used as embankment material for TSF-1 raising (Ref. Picture R 3.3.1). As

mentioned in the previous section, when fine material such as silt/clay is used, it can not be

avoided to increase excess pore pressure in embankment. If applied, in order to secure the dam

safety, upstream and downstream slopes shall be much gentler than those of rockfill type dam.

From the above consideration, rockfill type with center core type is selected as an optimum dam

type for northern dam of TSF-2


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Picture R 3.3.1 Available Embankment Material for Homogeneous Earthfill Type Dam

3.4 DAM FOUNDATIONAlthough geological survey has been done at this dam site, geological structure cannot be checked

because the boring core has already been disposed.

3.4.1 Additional Boring TestResulting from the site investigation in January 2009, Geological structures such as highly

weathered mudstone were observed at the riverbed around the southern dam site. However, faults

and fracture zone mentioned in the geological section prepared by HATCH could not be

investigated.

From these conditions, in order to clarify the thickness of alluvial formation and status of

foundation rock, additional boring tests and soil tests has been carried out at southern dam site in

February, 2009. Additional investigations have been done at four points and length of boring test

is about 20m. Location of additional tests is shown in Fig. R 3.4.1.

Fig. R 3.4.1 Location of Additional Boring Test at Southern Dam Foundation

Result of additional boring tests and soil tests are shown below.

Existing

Magas-Magas

Siltation Pond

BH09-4 BH09-3

BH09-2 BH09-1

250m0 50 100 150 200


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Fig. R 3.4.2 Results of Additional Boring Test at Southern Dam Foundation

Table R 3.4.1 Results of Additional Boring Test at Southern Dam Foundation

BH09-3 (Left Bank) BH09-1 BH09-2 BH09-4 (Right Bank)

Ground EL RL.32.140m Ground EL RL.31.036m Ground EL RL.32.400m Ground EL RL.31.712mDepth

(m)

USCS PI N Vlaue USCS PI N Value USCS PI N Value USCS PI N Value

1 SM 9 8 MH - 5 MH 22 10 SC 40 21

2 SM - - MH - 8 MH 32 8 CH 51 13

3 SM - - MH - 10 CH 30 10 CH 30 9

4 SC 25 5 MH 24 12 CH 31 14 CH 26 4

5 CH 48 4 CL 20 14 CH - - RK - 9

6 CH 27 8 CL 18 27 RK - - RK - 80

7 ML 19 30 CL - - RK - - RK - -

8 ML 10 60 RK - - RK - - RK - -

9 RK - RK - - RK - - RK - -

*1 USCS: Unified Soil Classification System ASTM D2487

*2 PI: Plasticity Index

SM

SC

CH

ML

RK

MH

CL

RK

MH

RK

CH

SC

RK

CH


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Table R 3.4.2 Unified Soil Classification System (ASTM D2487)

Picture R 3.4.1 Siltstone Boring Core (Sedimentary Structure is Broken)

Table R 3.4.3 Falling Head Permeability Test Results at Borehole

Test BH09-3 (Left Bank) BH09-1 BH09-2 BH09-4 (Right Bank)

No. 1 4.9 x 10-6

cm/s 7.4 x 10-7

cm/s 1.6 x 10-7

cm/s 3.1 x 10-6

cm/s

No. 2 1.6 x 10-5 cm/s 1.7 x 10-7 cm/s 4.8 x 10-8 cm/s 1.8 x 10-7 cm/s

3.4.2 Test Pit InvestigationIn April 2009, two test pit excavations have been done at foundation of southern dam, at the

bottom of valley. Pit excavation was done by backhoe. Location of pit excavation is shown below.


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Fig. R 3.4.3 Location of Test Pit Excavation at Southern Dam Foundation

Table R 3.4.4 Test Pit Excavation Result at FTP-1

Depth(m)

Condition Picture

0.0

0.5

1.0

1.5

2.0

Existing earth fill to the depthof 2.0m

2.5

3.0

Black colored sandy silt with yellow

patch to the depth of 3.0m, includingroot of plants, groundwater at 3m

depth from surface

3.5

4.0

Brownish yellow clay to the depth of

4.0m

Table R 3.4.5 Test Pit Excavation Result at FTP-2

Depth (m) Condition Picture

0.0

0.5

Surface soil to the depth of 0.5m,

including root of plants

1.0

1.5

2.0

2.5

Black silty sand to the depth of 2.5m,groundwater at 2m depth from thesurface

3.0

3.5

Fawny sandy silt with yellow patch to

the depth of 3.5m

4.0

4.5Ash gray clay to the depth of 4.5m

3.4.3 Geological Investigation ResultFindings of geological investigation are listed below.

- Bedrock at the boring location is siltstone, and no boundary between siltstone and serpentinitewas observed.

BH09-3BH09-4

BH09-2 BH09-1

Existing

Magas-Magas

Siltation Pond

FTP-1FTP-2

250m0 50 100 150 200

Brownish Yellow Clay


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- Sedimentary structure of the siltstone has been once broken by fault movement thenre-connected firmly, which is found by the boring core observation. Permeability of the

siltstone is small.

- Depth of the bedrock from the ground is 4m at the right bank, and 8m at the left bank, which isgoing deeper gradually.

- Alluvial formation over the bedrock consists of sandy silt, silt and clay, and thickness of thealluvial formation is 4m to 8m. Clay layer over the siltstone is considered to be highly

weathered siltstone, not the alluvial formation. N value of the silty layer and clayey layer

ranges 4 to 14, which is not so weak.

- Permeability of alluvial formation is very small, 1.6 x 10-5 cm/s at a maximum, 5 x 10-6 cm/sother than the maximum. It was measured by the falling head permeability test at the borehole.

- Water retention dam normally founded on rock and grouting is often required, whereas tailingsdams normally are founded on soil and do not require grouting. This is because the deposited

tailings constitute an extensive and effective source of fine material for self sealing of cracks.

Foundation of southern dam is soil with comparatively low permeability. Therefore special

seepage control measures for foundation are not necessary.

- Looking at all these conditions, it is considered that silty layer and clayey layer can be used asfoundation for core zone, not to remove or replace. However, methodology of compaction of

core zone should be carefully examined to avoid insufficient compaction. If vibration roller is

used for compaction of core materials, compaction may be insufficient due to waving. It is

recommended to use tamping roller to avoid this problem.


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3.5 DAM AXISSouthern Dam

Due to the geological shape of right bank and left bank, planned location for southern dam axis is

considered to be appropriate. Weathered rock at the embankment of right bank is relatively thin.

Although fault is expected to exist at alluvial bedrock, it seems to be no problem because the fault

seems to be adhered firmly. Weathered layer at the abutment of left bank is thick. Since laterite is

under mining at this location, foundation rock is expected to appear in the near future.

Northern Dam

According to the 1/50,000 map, hill is located at the northern dam axis. However, the hill was not

observed because of huge amount of stockpile.

Fig. R 3.5.1 Layout of Southern and Northern Dams (from HATCH Report)

Picture R 3.5.1 Axis of Southern Dam

Axis of Southern Dam

Northern Dam

Southern Dam


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Picture R 3.5.2 Axis of Northern Dam

3.6 ZONING AND EMBANKMENT MATERIALS3.6.1 Zoning of Rockfill Dam1) General

Rockfill dam with sloping upstream core consists of three major zones within the proposed

embankment, namely Core Zone, Filter Zone and Rock Zone, depending on the range of

variation in the character and gradation of the available material. The permeability of each

zone is designed to increase toward the outer slopes.

Fig. R 3.6.1 Typical Section of Rockfill Dam with Sloping Upstream Core

The purpose of each zone are given as follows:

- Core zone filled with impervious earth material provides watertightness.- Rock zone filled with rock of all sizes support the less stable core material and provide

the stability and durability of the dam body. Selected rock zone shall be filled with hard

Axis of Northern Dam


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and durable rock, which are slightly weathered to fresh rock, and provide the stability and

especially durability of the dam body.

- Filter zone is further classified into 2 zones, namely fine filter zone and coarse filter zone.Fine filter zone shall be filled with well graded sand which will form a fine filter on the

downstream face of the clay core to prevent piping of fines within core zone. Coarse filter

zone shall be filled with well graded gravel which is grading compatible with fine filter

material.

2) Core ZoneGenerally, core zone constructed of most fine-grained soils is impervious. Such fine-grained

soil normally has less shear strength. Consequently, from the standpoint of stability, the

thinner the core zone is made the better. On the other hand, a thick core zone has more

resistance to piping, especially to piping that may develop in differential settlement cracks. In

addition, core zone with a thickness of 30 % to 50 % of the water head have proved

satisfactory at existing many dams under diverse conditions.

Considering the above discussion, horizontal width of core zone is designed to 4.0 m at the

top and inclined shape with 1.0 vertical to 1.3 horizontal on upstream side and 1.0 vertical to

1.0 horizontal on downstream side. The width corresponds to about 35 % of the water head at

the bottom.

3) Filter ZoneFilter zone consists of 2 zones, namely fine filter zone and coarse filter zone. These zones

shall be embanked between core zone and rock zone to serve as a transition and filter.

Theoretically, protective layers of properly graded filter material can be very thin. The

minimum width is usually that which can be constructed by common method and it is most

often the case that the horizontal widths are more than 2.5 m. However, sand and gravel for

filter zone are distributed in the very limited area near the dam site. They may be purchased

from a supplier and be much costly. Therefore, the horizonta

Rio Tuba FR Vol_I Main Report 090618

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