Final Project Winter 2013

11

Exchange student Civil Engineering Horsens, 25.09.2012

Daria Maria Biskupska (18 ECTS)

PROJECT NR 11

Foundation for Skyscraper in urban area.

Use diaphragm walls and top & down method

Supervisors:

Sara Kjrgaard 4/5 Sren Fisker 1/5

[email protected] [email protected]

Tele: + 45 87 55 42 82 Tele: +45 87 55 41 04

Table of Contents

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1. General introduction .................................................................................................. 5

1.1. The aim of the project........................................................................................................................ 5

1.2. Localization ....................................................................................................................................... 5

1.3. Construction and general characteristic of the building .................................................................... 6

1.4. Climate .............................................................................................................................................. 7

1.5. Project assumptions/Delimitation ...................................................................................................... 8

2. Geological Analyze .................................................................................................... 9

2.1.General information about soils in Poland .......................................................................................... 9

2.2. Local soils on the site ........................................................................................................................ 9

2.3. Previous drilling in the area ............................................................................................................. 10

2.3.1. Information according to Polish geo - engineering database ........................................................ 10

Information according to Geobad ................................................................................................. 13

3.Retaining structures analyze................................................................................. 15

Introduction ........................................................................................................................................ 15

3.1. Types of earth support systems ...................................................................................................... 16

3.1.1. Diaphragm walls ........................................................................................................................... 16

3.1.2. Pile walls ...................................................................................................................................... 19

3.1.3. Soldier pile with wooden lagging walls ......................................................................................... 20

3.1.4. Sheet pile walls ............................................................................................................................ 22

3.2. Comparison ..................................................................................................................................... 23

3.2.1. Best solution................................................................................................................................. 23

4. Types of diaphragm wall analysis and selection the best type ......................... 24

4.1. Cantilever diaphragm wall embedded in soil ................................................................................... 24

4.2. Strutted diaphragm wall .................................................................................................................. 25

4.3. Anchored diaphragm wall ................................................................................................................ 26

4.4. Conclusion ...................................................................................................................................... 27

5.Deep excavation methods analyze ....................................................................... 28

5.1. General introduction about deep excavations ................................................................................. 28

5.2. Types of deep excavations methods ............................................................................................... 28

5.2.1. Bottom-up method ........................................................................................................................ 29

5.2.2. Top and down method .................................................................................................................. 29

5.3. Conclusion ...................................................................................................................................... 34

6. Skyscraper in Wroclaw: underground garage stages of construction ............. 35

7.Geotechnical description ......................................................................................... 39

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7.1. Introduction to soil properties .......................................................................................................... 39

7.2. Soil physical properties ................................................................................................................... 41

7.3. Soil characteristics .......................................................................................................................... 42

7.3.1. Determination of weight density ................................................................................................... 42

7.3.2. Determination of characteristic undrained shear strenght ............................................................ 43

7.3.3. Determination of characteristic angle of shearing resistance ....................................................... 43

7.3.4. Determination of parameters for soils occurring in the project ..................................................... 43

8. Introduction to calculations .................................................................................... 45

8.1. Introduction Designing foundations by calculation according to Eurocode 7 ................................ 45

8.1.1. Partial factor safety ...................................................................................................................... 45

8.1.2. Geotechnical design by calculation .............................................................................................. 45

8.1.3. Designed values of actions .......................................................................................................... 46

8.1.4. Designed values of geotechnical parameters ............................................................................... 46

8.1.5. Designed values of geometrical data ........................................................................................... 46

8.1.6. Designed effects of actions .......................................................................................................... 47

8.1.7. EQU ............................................................................................................................................. 47

8.1.8. GEO ............................................................................................................................................. 48

8.1.9. STR .............................................................................................................................................. 48

8.1.10. GEO/STR Limit States ............................................................................................................... 49

8.2. Retaining wall design ...................................................................................................................... 49

8.2.1. Limit states ................................................................................................................................... 49

8.2.2. Future unplanned excavation ....................................................................................................... 50

9. Diaphragm wall calculations ................................................................................... 51

9.1. General assumptions for project ..................................................................................................... 51

9.2. Descriptions of calculations ............................................................................................................. 52

9.3. Geo5 calculations ............................................................................................................................ 75

10. Duration and prices ............................................................................................... 78

11. Safety and organization ......................................................................................... 79

11.1. Safety and organization the building site ....................................................................................... 79

11.2. Temporary dewatering ................................................................................................................... 80

12. Conclusion ............................................................................................................. 81

13. References .............................................................................................................. 82

ANNEXES ANNEX 1. Project description ANNEX 2. Pictures

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ANNEX 3. Soil profiles ( cut sections: I, II, III, IV) ANNEX 4. Soil classification system according to Eurocode 7 ANNEX 5. PN81-03020 ANNEX 6. PN EN 1997-1 Soil characteristics ANNEX 7. PN EN 1997-1 Factors for safety, Ultimate limit-State, coefficient ANNEX 8. PN EN 1997-1 Loss of static equilibrium (Examples) ANNEX 9. PN81-03010 ANNEX 10. GEO5 graphs for PHASE 5

DRAWINGS

DRAWING NR 1. LAND USE PLAN 1:500

DRAWING NR 2. LAYOUT DRAWING OF UNDERGROUND PARKING 1:100

DRAWING NR 3. CALCULATED CROSS SECTION WITH LOCATION 1:100

DRAWING NR 4. CONSTRUCTION DRAWING OF DIAPHRAGM WALL 1:50

1. General introduction

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1.1. The aim of the project

The aim of this project was to analyze geotechnical information about the area, to find proper

retaining structures, to design the construction for chosen structures, to find the best deep excavation

method and organization plan for excavation-works. After few analysis, the best solutions have been

found: diaphragm walls and top & down method. In order to have more clear understanding of the over-

all problem, there are some more studies in the following chapters of the project.

Equally important task was calculation and dimensioning of diaphragm walls by using software

and also doing calculations by hand. More-over, by doing the most of the calculations by GEO5, it was

possible to find all internal forces in diaphragm walls (in each step of garage building process) and

compare the results in a short period time.

In order to provide continuous work flow in urban area, it is very important to have an

organizational plan for the excavation works - the organization plan was prepared and it is included in

this project. Excavation as a process is a major challenge because of the extent of the work-area and

volumes. It is briefly analyzed and planned in this current project. Important issue in terms of this

particular case is drainage and it is analyzed and possible solutions are presented.

1.2. Localization

This project is about excavation works for Skyscraper in Wroclaw. Wroclaw is the third-largest city in Poland. More pictures from building site are enclosed as ANNEX 1.

Figure 1.1 Location of Wroclaw

The Skyscraper will be situated in the center of the down, which will make the construction more complex in many ways, including the excavation works.

Figure 1.2 Location of Skyscraper in Wroclaw.

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1.3. Construction and general characteristic of the building

The building is designed as in-situ reinforced concrete frame, with 2 under-ground stories and 11 above-

ground stories. The real name of the building is Office building of tax chamber. This Skyscraper is

designed by company AA Studio architects. The roof of the building is planned to be around at the

level of +40,0 meters. The area of the building is 1200m2 and the usable space is 5097m2. The

Skyscraper is established as Geotechnical Category 2. The building is a conventional structures (typical

multistory construction).

Figure 1.3 Skyscraper

1.4. Climate

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Study of the climate is very important when carrying out the works, because it changes the conditions of the works. If the works takes place in a rainy period the problems with the water will be higher, also if it is a snowy period it will be more difficult to work with the concrete/bentonite. The graph below shows the Temperature relations in the city of Wroclaw during the year, its essential that for designed excavation its necessary to pick the months with the temperatures above the freezing point

Figure 1.4 Average minimum and maximum temperature over the year. The monthly mean minimum and maximum daily temperature.

Figure 1.5 Average monthly precipitation over the year (rainfall, snow)

This is the mean monthly precipitation, including rain, snow, hail etc.

Precipitation is different throughout the year, Generally, Wroclaw experience precipitation from 2 cm to 8,4 cm with the maximum in July. Snowfall occurs mainly from late November until early March, but snow cover seldom lasts long. Snow during January and February is common and the average temperatures for these two winter months are near the freezing point.

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Figure 1.6 Average monthly hours of sunshine over the year. This is the monthly total of sunhour

To improve working conditions excavation work should be carried out in good light. The best time is

from May till August.

1.5 Project assumptions/Delimitation This project is about a Parking under Skyscraper in Wroclaw, and it requires the design of the retaining structure of the parking basement. Designing process contains: analysis of different possibilities, calculations of structure and drawings. Also it will be designed the deep excavation method with steps of formations the structure. The construction process and management of the groundwater should be treated with special attention, so the environment is not compromised, following the environmental protection act. The life expectancy for the retaining structure is 100 years, with the first 25 years without important maintenance works. The safety of the construction should be guaranteed, as well as limitation for major deformations and stresses within the structure. The deformations of the retaining structure should be limited, hence not causing damage to the surrounding buildings. The used materials and design solutions should ensure proper water tightness. After the project finalization all interior surfaces have to appear dry and without signs of water intrusion. The basement slab has to be designed to act as a foundation, but it wont be calculated in this project.

References: [1] http://forum.investmap.pl/dolnoslaskie-infrastruktura-spoleczna-f77/nowa-siedziba-izby-skarbowej-t6129.html [2] http://www.weather.com/weather/today/Wroclaw+Poland+PLXX0029

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2. Geological Analyze

2.1 General information about soils in Poland

In Poland Eurocode 7 is obligatory. Soil classification system according to Eurocode 7 [ PN EN 1997-1:2004] is enclosed as ANNEX 4.

As this current project is about deep excavations, it is quintessential to have sufficient knowledge about

the soil and characteristics of it. By geological analysis the wider background of current area is briefly

introduced. Geological analysis according to existing information in some circumstances can point out

some aspects that should be focused on during geotechnical drillings.

Soils in Poland

Poland has many different soils. Sandy formations (20% of particles less than 0.2mm in diameter)

occupy about 50 % of the total area. Their water properties depend upon the depth of the ground-water

table, substratum soil profile layers, and content of silt particles less than 0.02 mm in diameter.

Appropriate agrotechnical and land reclamation (water conservation) measures are necessary for the

improvements of these soils. The main type of soils include swampy boulder loam, organogenic soils

developed on peat, alluvial soils, silty and loess formations. More data on soil types in Poland are

shown in Table 1.

Table 1 Parent rock soil types in Poland

2.2 Local soils on the site In this project, there are two bases of information about soils in the location of designed Skyscrapers

garage.

Sources of knowledge:

Internet : Polish geo-engineering database

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comment: datebase has a lot of information about the area of Wroclaw, but not very accurate. It

is not enough to design the foundation.

Geological documentation made by Polish Company GEOBAD

comment: documentation is very detailed, but it was made for other project and the building in

that project was in different location (the distance from that building to the Skyscraper in is less

than 1 km)

Unfortunately, it was impossible to get detailed information about soils in designed area from design

engineer who is engaged in designing Skyscraper in Wroclaw. That kind of documentation is prepared

by specialist and expensive.

It is necessary to assume soils according to available data ( details - point 2.3.1.)

2.3 Previous drilling in the area

2.3.1 Information according to Polish geo-engineering database The geo-engineering database and the geo-engineering atlas of the Wrocaw agglomeration were

prepared between 2007 and 2008 by Geological Enterprise of Wrocaw PROXIMA and the Polish

Geological Institute in the collaboration with Geological Enterprise of Katowice and the Geological

Company Geoprojekt Szczecin.

Figure 2.1 Wroclaw division of the city according to Polish Internet database.

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The Atlas of Wrocaw covers the area of Wrocaw City County (293 km2) as well as parts of the

neighbouring communes of Wrocaw County (Dugoka, Czernica, wita Katarzyna, rawina, Kobierzyce and Kty Wrocawskie Communes) and roda lska County (Mikina Commune). The total area covered by the maps is 719,8 km2.

The database of the geo-engineering atlas of the Wroclaw contains more than 50 000 boreholes that

come from archives and were also made especially for the purpose of this project. The average density

of survey points were 70 boreholes per km2 of the agglomeration area.

Borehole profiles collected in the database have been used to prepare 6 geo-engineering sections in the

scale of 1:5000 / 1:200 to present the geological structure synthetically.

Figure 2.2 Wroclaw location of building site Scale 1:10000(red place).

Figure 2.3 Wroclaw location of building site scale 1:1000(red place).

The geo-engineering database and the geo-engineering atlas of the Wrocaw shows soils at three levels:

at a depth of 1 meter

at a depth of 2 meters

at a depth of 4 meters

Maps (print screens) from the database with descriptions are given below:

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at a depth of 1 meter in Wroclaw city center is : fill (embankment)

Figure 2.4 Building site - soils at 1 meter according to Polish Internet database.

at a depth of 2 meters (Figure 2.5) and a depth of 4 meters (Figure 2.6) in Wroclaw city center is : glacial till

Figure 2.5 Building site - soils at 2 meters according to Polish Internet database

Figure 2.6 Building site - soils at 4 meters according to Polish Internet database

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2.3.1 Information according to GEOBAD

According to the GEOBAD Polish Company, there have been some previous drilling in the area near

designed skyscraper. GEOBAD is a geo-engineering company, which made research in Wroclaw for

one project in 2011. That project was about multistory building located less than 1 km from designed

Skyscraper. Based on given data, following information are assumed (adopted at my own discretion for

this project):

There are 4 boreholes assumed for this project:

- Borehole nr 1

- Borehole nr 2

- Borehole nr 3

- Borehole nr 4

Data for boreholes:

Borehole nr 1

Nr Deep [m p.p.t.] Layer Symbol Density Humidity

1 0 1,1 Embankment - Loose wet

2 1,1 2,0 Fine sand FSa ID=0,4 semi dry

3 2,0 5,2 Clayey silt saclSi IL=0,07 semi dry

4 5,2 6,4 silty sand siSa ID=0,5 wet

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5 6,4 clayey silt saclSi IL=0,29 wet

Borehole nr 2







Borehole nr 3




3 2,2 4,8 Clayey silt saclSi IL=0,09 dry


Borehole nr 4







Using information about boreholes , it is possible to prepare soil profiles, in problematic places where no drillings are made, it can be estimated what kind of soil is present at this place by using two closest holes and guessing what is between them. According to information above, four cut sections are assumed:

- Cut section I (between borehole nr 1 and borehole nr 2) - Cut section II (between borehole nr 2 and borehole nr 3) - Cut section III (between borehole nr 3 and borehole nr 4) - Cut section IV (between borehole nr 4 and borehole nr 1)

Cut sections are enclosed as ANNEX 3

Area of Wroclaw is very poor of water resources. This is a result of geological history. Ground waters are very deeply located under the ground level and surface waters appear very seldom. Due to the present conditions, ground water level for this project is assumed at depth of 11,8 meters.

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3. Retaining structures - analyze

In chapter different types of retaining walls wil l be described and compared

.In the end there wil l be the answer for question: Why diaphragm walls are the best solution according to site conditions?

4.1. Introduction

Urban settings pose unique challenge to the construction Industry. Special features of urban areas are restricted movements, inadequate space for equipment, soil heterogeneity (including fill and remains of old foundations or other unexpected obstructions); effects of changes in the water table; foundation interaction (the detrimental effects of construction of new structures on the surrounding buildings). Heavy traffic and lack of adequate space has compelled Civil engineers to excavate deeper into the ground to create additional floor space to meet increasing space requirements for amenities, parking and for housing of building utilities. As the number of deep excavations in city is seen to increase exponentially so are the problems associated with their construction. Structures in the immediate vicinity of excavations, dense traffic scenario, presence of underground obstructions and utilities have made excavations a formidable task to execute. Clearly, deep excavations are posing mounting problems that demand a site specific and tailor made retaining solution. Unsupported excavations pose several hazards, and the following list gives some of the important ones:

Very high risk potential of collapse or failure of excavation walls and consequently posing

hazard to workers and equipment

Hazards during excavation due to presence of public utilities, such as electricity, water, gas, or

natural gases and oxygen deficient atmosphere

Dewatering problems

Wet, slushy ground conditions, causing slips, trips, or falls, complicated by limited spaces in

which personnel work

Ground and/or ground water table changes affecting nearby structures.

Support provision for excavation depends on the type of soil in the area, the depth of the excavation, the type of foundation being built, and the space around the excavation. During excavation, some soil types pose greater problems than others. Sandy soil is always considered dangerous even when it is allowed to stand for a period of time after a vertical cut. The instability can be caused by moisture changes in the surrounding air or changes in the water table. Vibration from blasting, traffic and heavy machinery movement, and material loads near the cut can also cause earth to collapse in sandy soil. Clayey soils in general, present less risk than sand; however, soft clay can prove to be very treacherous. Silty soils are also unreliable and require the same precautions and support provision as sand.

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3.1. Types of earth support system

Several in-situ support systems have been deployed for containing deep excavations. The criteria for the selection of these systems are:

excavation depth,

ground conditions,

ground water level,

allowable vertical and horizontal displacements of adjacent ground,

availability of construction know-how,

cost factors,

subsequent

construction methodology,

working space limitations etc.

One of the key governing factors is the requirement of water tightness of the retaining structure. Following types of deep support systems are commonly used in metropolitan cities.

1. Diaphragm walls 2. Pile walls (Contiguous, Tangent or Secant) 3. Soldier pile with wooden lagging walls 4. Sheet pile walls 5. Composite supporting systems that is, any of the retaining systems (1) to (4) above

strengthened by Anchors, internal strutting etc.

3.1.1. Diaphragm walls

Diaphragm walling is a technique of constructing a continuous underground wall from the ground level. Diaphragm walls provide structural support and water tightness. These reinforced concrete diaphragm walls are also called Slurry trench walls due to the reference given to the construction technique where excavation is made possible by filling and keeping the wall cavity full with bentonite-water mixture during excavation to prevent collapse of vertical excavated surfaces.

These retaining structures find following applications:

earth retention walls for deep excavations;

basements,

tunnels;

high capacity vertical foundation elements;

retaining wall foundations;

water control.

permanent basement walls for facilitating Top-down construction method.

Typical wall thickness varies between 0.6 to 1.1m. The wall is constructed panel by panel in full depth. Panel width varies from 2.5m to about 6m. Short widths of 2.5m are selected in less stable soils,

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under very high surcharge or for very deep walls. Different panel shapes other than the conventional straight section like T, L are possible to form and used for special purposes. Slurry wall technique is a specialized technique and apart from the crane mounted Grab, other equipment involved are cranes, pumps, tanks, desanding equipment, air lifts, mixers etc.

Steps involved in the construction of diaphragm wall can be broadly listed as follows:

1. Guide wall construction along alignment

2. Trenching by crane operated Grab/ hydraulic grab

3. Bentonite flushing

4. Lowering reinforcement cage

5. Concreting using tremie

The sequence of construction of diaphragm wall panel has been schematically illustrated in Fig. 3.1

It must be remembered that Diaphragm walls are constructed as a series of alternating primary and secondary panels. Alternate primary panels are constructed first which are restrained on either side by stop-end pipes. Before the intermediate secondary panel excavation is taken up, the pipes are removed and the panel is cast against two primary panels on either side to maintain continuity. Water stoppers are sometimes used in the construction joints between adjacent panels to prevent seepage of ground water.

Diaphragm wall construction is relatively quiet, and minimum noise and vibration levels make it suitable for construction in urban areas. The water tight walls formed can be used as permanent structural walls and are most economical when used in this manner. The finished structural wall formed prior to excavation allows subsequent construction of the basement in a water tight and clean environment. Once the diaphragm walls are constructed, work can be planned to proceed simultaneously above and below the ground level. There is a minimum of space wasted. Work may be carried out right against existing structures and the line of wall may be adjusted to any shape in plan.

Diaphragm walls however, require the use of heavy construction equipment that requires reasonable headroom, site area, and considerable mobilization costs. In limited headroom conditions, smaller cranes can be used though this could compromise efficiency. They are not considered efficient means in hard and rocky grounds, where the conventional grabs are undeployable.

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Figure 3.1 The sequence of construction of diaphragm wall panel

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3.1.2. Pile walls (Contiguous, Tangent or Secant) Contiguous Pile walls will be described as an example.

There are different types of pile walls (Fig.3.2). Diameter and spacing of the piles is decided based on soil type, ground water level and magnitude of design pressures. Large spacing is avoided as it can result in caving of soil through gaps. In Contiguous bored pile construction, center to center spacing of piles is kept slightly greater than the pile diameter. Secant bored piles are formed by keeping this spacing of piles less than the diameter. Tangent piles are used when secant piling or diaphragm walling equipment is not available.

Figure 3.2 Schematic Arrangement of Contiguous Piled Retaining System

Contiguous piles serving as retaining walls are popular since traditional piling equipment can be resorted for their construction. They are considered more economical than diaphragm wall in small to medium scale excavations due to reduction in cost of site operations. Common pile diameters adopted are 0.6, 0.8 and 1.0m. These piles are connected with a Capping beams at the top, which assists equitable pressure distributions in piles. These retaining piles are suitable in areas where water table is deep or where soil permeability is low. However, some acceptable amount of water can be collected at the base and pumped out.

Contiguous piles are suitable in crowded urban areas, where traditional retaining methods would otherwise encroach the adjoining properties. Provision of Contiguous piles restricts ground movements on the backfill side, and thus protects the neighboring structures, foundations and boundary walls from the detrimental effects of the excavation. Contiguous piles facilitate deployment of several independent sets of equipment and gangs along its alignment which can speed up its execution. They can be constructed using even the conventional piling equipment, and can be constructed in hard and rocky sub-soil conditions where diaphragm wall construction is difficult. Such retaining systems has advantage of employing varying diameter of piles in lieu of change in sub-surface conditions, or on encountering competent stratum at a depth which is different than that anticipated during design. Further, unlike the diaphragm wall which relies on the orthogonal geometry of the excavated area contiguous pile retaining system can constructed to form any shape in the excavated area.

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They are however, not considered suitable for construction in areas of high water table, as retention and containing water is not possible in contiguous piles. Perfect alignment of piles is often difficult to achieve at site, and this in turn is found to affect the dimension and alignment of the Capping beams. In design parlance, only the portion of concrete and steel away from the neutral axis is known to offer resisting moment. As a result, some concrete and steel area remains under-utilized.

Figure 3.3 Contiguous piles supporting excavation at Worli, Mumbai 3.1.3. Soldier pile with wooden lagging walls

Soldier pile and lagging walls are some of the oldest forms of retaining systems used in deep excavations. These walls have successfully been used since the late 18th century in metropolitan cities world over. This type of retaining system involves the following broad based activities:

1. Constructing soldier piles at regular intervals (1 to 3m on center typically)

2. Excavating in small stages and installing wooden lagging.

3. Backfilling and compacting the void space behind the lagging.

Soldier piles are driven/ bored at regular interval and allowed to gain strength. Excavation proceeds step by step after placement of Soldier piles at the periphery of the excavation. Depending on the ground conditions, wooden laggings are placed spanning from one soldier pile to another. At some predetermined levels, horizontal Waling beams and supporting elements (struts, anchors or nails) are erected. Ground anchors are increasingly used in such supports due to easy access to equipment.

Moment resistance in soldier pile and lagging walls is provided solely by the soldier piles. Passive soil resistance is obtained by embedding the soldier piles beneath the excavation grade. The lagging bridges and retains soil across piles and transfers the lateral load to the soldier pile system.

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Figure 3.4 Soldier Pile and Wooden Lagging System

Soldier pile and lagging walls are the most inexpensive systems compared to other retaining walls. They are also very easy and fast to construct. These are found to be suitable for soils with some cohesion and without water table. They are commonly preferred in narrow excavations for pipe laying or similar works, but are also used for deep and large excavations in conjunction with struts. The major disadvantages of soldier pile and lagging systems are that they are primarily limited to temporary construction. They cannot be used in high water table conditions without extensive dewatering. Poor backfilling and associated ground losses can result in significant surface settlements. They are not as rigid as other retaining systems. Because only the flange of a soldier pile is embedded beneath subgrade, it is very difficult to control basal soil movements.

Figure 3.5 Soldier Piles and Wooden Lagging System at Udyog Bhawan, New Delhi

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3.1.4. Sheet pile walls

A pile is designed to be beaten into the ground next to other piles already set up. Each sheet pile are set between themselves via lateral veins called locks. The material can be wood, but mostly steel. Once planted into the ground, their assembly may form a retaining wall or a waterproof screen. There are several shapes of sheet pile. These differences come from the performance of their joints. In an urban context, it is more interesting to drive the piles with a hydraulic cylinder: this method, silent and resulting in no vibration on adjacent structures, requires soil differential settlement in long term state. The nature of steel sheet tends to concentrate the leak rates in the locks. The locks are the weaknesses of the sheet pile walls. Use of sheet pile walls to retain contaminated soil requires very low leakage rates and therefore must necessarily use special fixing at the locks. Besides welding, these devices are based on the use of bituminous materials, wax or water blowing. Generally the following permeability is expected: - Greater than 10-7 m/s with joints without sealant - 10-7 m/s with tar or wax seals - 5x10-10 m/s with hydro swelling joints Traditional sheet pile shapes are Z type and U type. Z-Type (Z): Used for intermediate to deep wall construction, Z sections are considered one of the most efficient pile available today. Z- piles are commonly used for cantilevered and tiedback systems. Additional applications also include load bearing bridge abutments. U Type (U) sheet piles are used for the applications similar to Z- Type.

Figure 3.6 U-Type sheet piles

Figure 3.7 Z-Type sheet piles

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3.2. Comparison

The following table is suitable to summarize the above.

Sheet pile walls Soldier pile

with wooden

lagging walls

Diaphragm

walls

Pile walls (contiguous,

tangent, secant)

COST medium medium medium medium

WEIGHT small medium hight medium

NOISE/ VIBRATION medium high small medium

WATER TIGHTNESS + - +

+

TRANSFORMING INTO

BASEMENT WALLS

- - + +

TIME OF IMPLEMENTATION medium medium medium medium

3.2.1. Best solution

The problem is that we are in an urban area, with close buildings surrounding, so vibration has to be avoided. The best solution taking all features into consideration are diaphragm walls and that is why they will be used in this case (from north, south and west and east site). Parameters of sheet pile walls and diaphragm walls are almost the same but diaphragm walls are more common in Poland, and that makes them less expensive. Benefits of Diaphragm Walls:

Installed to considerable depths

Walls with substantial thickness can be formed

Flexible in plan layout

Easily incorporated into permanent works

Wall (sections) can be designed to carry vertical load

Basement construction time reduced

Economical solution for large, deep basements in saturated and unstable soil profiles

Noise levels limited to engine noise

Vibration-less

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4. Types of diaphragm wall- analysis and

selection the best type

In chapter different types of diaphragm walls will be described.

In the end there will be the answer for question: Which type of diaphragm wall is the best solution according to underground building construction ?

Calculations of three standard designed problems are performed in this point. These cases are:

Cantilever diaphragm wall embedded in soil

Strutted diaphragm wall

Anchored diaphragm wall

Third example concerns an excavation within strutted diaphragm wall method of support of excavations walls very common in Poland.

4.1. Cantilever diaphragm wall embedded in soil

Cantilever walls are walls that do not have any supports and thus have a free unsupported excavation. Cantilever walls restrain retained earth by the passive resistance provided by the soil below the excavation. Many engineers use the cantilever wall term to actually describe gravity walls. In reality both gravity and vertical embedded walls types can be categorized as cantilever if no lateral bracing support is provided by means of tiebacks, struts, etc. This sections examines vertical cantilever walls and the basic design methods used for cantilever wall analysis.

Figure 3.8 Cantilever diaphragm wall with maximum dimensions.

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Figure 3.9 Example of cantilever diaphragm wall with stress distribution. Cantilever diaphgram wall is impossible in this case because as we can see in the Figure 3.8,the maximum length of wall above the ground (Hn) is 4 meter or less. In this project there are 2 floors of underground garage, so the dimension Hn will be more than 4 meters.

4.2. Strutted diaphragm wall

Figure 3.10 Single and double strutted diaphragm wall with maximum dimensions.

Figure 3.11 Example of single strutted diaphragm wall and stress distribution.

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Strutted diaphgram wall is recommended for this project. The maximum dimension of the wall above the ground (Hn) is 12 meters, that means that it is ideal dimension for 2 floors of underground garage. In this project retaining wall could be strutted by floor slabs. 4.3. Anchored diaphragm wall Anchored diaphragm walls are often used when securing deep foundation pits, e.g. in built-up areas or under groundwater levels

Figure 3.13 Anchored diaphragm wall with dimensions

Figure 3.14 Anchored diaphragm wall

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Anchored diaphgram wall is also recommended for this project. The maximum dimension of the wall above the ground (Hn) is 12 meters, that means that it is ideal dimension for 2 floors of underground garage. 4.4. Conclusion In sum we have to choose between strutted and anchored method. Cantilever diaphragm wall was excluded. Due to the construction of floors in garage (reinforced concrete slabs), it seems to be the better idea to use strutted method. The construction of garage will be used in two ways slabs can take to loads from cars and other object in garage, and slabs can take over the role of struts. The connection between diaphragm wall and each slab is designed as fixed (rotation of the slab towards diaphragm wall is impossible) The best method is strutted diaphragm wall.

Figure 3.15 Under-ground construction Basement reinforced concrete slabs roles:

1. To transform the load from cars and other objects, to the columns, and next to the ground.

2. To act as 'strut' and be the support for diaphragm wall.

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5. Deep excavations methods- analyze

In chapter different types of deep excavations methods (concern diaphragm walls) wil l be described and compared.

.In the end there wil l be the answer for question: Why top & down method is the best solution in this case?

5.1. General introduction about deep excavations

The construction of deep excavations in the urban environment is a technically challenging problem. Design and construction typically involves many steps including site characterization, design of excavation support systems, specification of responses to construction difficulties, preconstruction surveys of adjacent properties and utilities, field observations during construction, excavation installation, and structure construction. Adjacent construction may be a nuisance to neighboring property owners (e.g., right of entry agreements, shoring, underpinning, and/or alterations to operations, dust, noise, felt vibrations, traffic congestion). Frequently, adjacent property owners claim construction-induced damage. For deep excavations, this damage may include a combination of building settlement because of a loss of lateral support, loss of use, business interruption, cosmetic finish distress, and structural damage.

Although excavations are regulated by federal, state, and local building codes, problems occur in the process of developing a site due to many factors including design errors, construction errors, construction accidents, striking unknown utilities, differing site conditions, unforeseen natural events, or delays in completion.

Correct analyze of deep excavation includes:

Pre- and post-construction condition surveys

Emergency response in the event of a failure

Analysis of the cause of failure

Evaluation of differing site conditions claims

Evaluation of the suitability of temporary shoring and dewatering systems

Analysis of building or ground deformation resulting from a loss of lateral support

Vibration analysis

Evaluation of construction activities and response to construction difficulties

Review proposed excavation plans

5.2. Types of deep excavations methods

It is already known that diaphragm walls are the best solution for this project. Walls can be made extremely stiff and therefore better resistant to deflection. It is also possible to use effective internal propping with a diaphragm wall rather than the normal ground anchors. Temporary cut-offs can also be created using this technique.

There are two main methods of building construction with underground garage:

1. bottom-up method

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2. top and down method

5.2.1. Bottom-up method

Conventionally, buildings with underground basements are built by bottom-up method where sub-structure and super-structure floors are constructed sequentially from the bottom of the sub-structure or lowest level of basement to the top of the super-structure. Though this conventional method, also called as bottom-up method, is simple in both design and construction, it is not feasible for the gigantic projects with limited construction time and/or with site constraints.

5.2.2. Top and down method

Top-down construction method as the name implies, is a construction method, which builds the permanent structure members of the basement along with the excavation from the top to the bottom. Top-down method is mainly used for two types of urban structures, tall buildings with deep basements and underground structures such as car parks, underpasses and subway stations. In this case the basement floors are constructed as the excavation progresses. The top/down method has been used for deep excavation projects where tieback installation was not feasible and soil movements had to be minimized. Top-down construction method which provides the significant saving of the overall construction time has been adopted for some major projects where time factor is of primary importance. The sequence construction begins with retaining wall installation and then load-bearing elements that will carry the future super-structure. The basement columns (typically steel beams) are constructed before any excavation takes place and rest on the load bearing elements. These load bearing elements are typically concrete barrettes constructed under slurry (or caissons).

PROCEDURE

The typical construction procedure of top down construction is as follows

1. Construct the retaining wall.

2. Construct piles. Place the steel columns or stanchions where the piles are constructed.

3. Proceed to the first stage of excavation.

4. Cast the floor slab of first basement level

5. Begin to construct the superstructure

6. Proceed to the second stage of excavation; cast the floor slab of the second basement level.

7. Repeat the same procedure till the desired depth is reached

8. Construct the foundation slab and ground beams, etc. Complete the basement

9. Keep constructing the superstructure till it gets finished.

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Figure 4.1 Top and down construction method

Step nr 1: Installation of retaining wall

Figure 4.2 Installation of retaining wall

The underground retaining wall which is usually a diaphragm wall, is installed before excavation commences.

Step nr 2: Excavation and installation of steel strut

Figure 4.3 Excavation and installation of steel strut

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The soil is excavated just below roof slab level of the underground structure. Struts are installed to support the retaining walls, which in turn support the soil at the sides

Step nr 3: Construction of underground structure

Figure 4.4 Construction of underground structure part I

The roof slab is constructed, with access openings provided on the slab for works to proceed downwards. The roof slabs not only provides a massive support across the


Figure 4.4 Construction of underground structure part II

The next level of slab is constructed, and this process progresses downwards till the base slab is completed


Figure 4.5 Construction of underground structure part III

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The side walls are constructed upwards, followed by removal of the intermediate struts. The access openings on the roof slab are then sealed

STRUCTURAL MEMBERS REQUIRED FOR TOP-DOWN CONSTRUCTION

Design and construction principles for top-down method primarily call for two major structural elements. Columns with sufficient capacity must be pre-founded in bored piles or barrettes to sustain the construction load and to utilize as part of bracing system. Excavation for basement must be carried out with the support of permanent retaining wall so that basement floor slabs can be utilized as lateral bracing.

Diaphragm wall of 0.8m to 1.2m in thickness with sufficient embedment in firm soil layers is commonly used as a retaining wall whereas prefabricated steel columns known as Stanchions embedded in either large diameter deep-seated bored piles or barrettes are utilized as structural columns. Figure 4.6 illustrates the top-down construction method with utilization of stanchions and diaphragm wall.

Figure 4.6 Top-down construction with stanchion and diaphragm wall

TYPES OF STANCHION AND THEIR APPLICATION

TYPES OF STANCHION General information

Material & Example Size Application Light stanchion Steel H-beams

350x350x137kg/m For semi top-down

construction For temporary decking

Medium sized stanchion Steel H-beams 350x350x390 kg/m

For semi and full top-down construction of shallow to

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medium deep excavation Heavy stanchion Steel H-beams

508x457x738kg/m Composite steel columns built up by 2 or more small to medium size H-beams

Large section pre-cast RC column (seldom use)

Full top-down construction in deep excavation

STANCHION INSTALLATION METHODS

Stanchion installation method is usually selected by the piling contractor who takes into consideration three main factors such as installation depth, size of stanchion and size of bored or barrette piles. Though installation details may be different from one contractor to another, stanchion installation can be categorized under two main methods, post-concreting or plunging installation and pre-concreting installation or placing stanchion prior to concreting.

Post-concreting installation or plunging method

In this method, stanchion is installed immediately after completion of bored pile concreting process. General construction sequence involved in this method is demonstrated in Figure 4.7.

Guide frame is used to install the stanchion at the correct position.

Figure 4.7 general construction sequence of pre-concreting installation method

Pre concreting method

In this method, stanchion is installed immediately after completion of drilling and reinforcement lowering prior to concreting process. In some projects stanchion is attached to the last section of reinforcement and installed together with the reinforcement. General construction steps involved in this method are demonstrated in Figure 4.8.

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Figure 4.8 general construction sequence of pre-concreting installation method

Advantages and disadvantages

Advantages:

1. The shortened construction period due to simultaneous construction of the basement and the superstructure.

2. More operational space gained from the advanced construction of floor slabs.

3. The higher stiffness of floor slab compare to steel struts improves the safety of excavation.

4. It is highly suitable for construction for tall buildings with deep basements to be constructed in urban areas.

Disadvantages:

1. Higher cost (due to the construction of pile foundation)

2. Since the construction period of the basement is lengthened, the lateral displacement of retaining wall or ground settlement may possible increase due to the influence of creep if the soil layers are encountered.

2. The construction quality may influence because of worsened ventilation and illumination under floor slab.

3. It requires highly skilled supervision and labour force.

5.3. CONCLUSION

From the above chapter we can conclude that top down construction has its suitability for certain kind of

mega structures. It is suitable for structures with deep basements like underground rails, car parks etc. It

is also very efficient way of doing two way construction to save time.

Skyscrapers with deep basements in urban areas should be constructed using top down

method.

But top down construction needs very efficient planning and designing and skilled supervision and

labour force. Top down construction is the need of the hour as it is highly time efficient and is becoming

popular and is coming more and more in practice with every passing day.

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6. Skyscraper in Wroclaw: underground garage stages of construction

According to previous chapter, following steps of construction were prepared by GEO5 software.

OPERATIONS PRIOR TO EXCAVATION The sequence construction begins with retaining wall installation and then load-bearing elements that

will carry the future super-structure.

Retaining wall installation:

First step of retaining wall installation: Guidewall construction , dimensions: height :120 cm, weight 80-

100 cm , long depending on the building

Second step of retaining wall installation: Panel (vertical segments) excavation

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Third step of retaining wall installation: Installation of the reinforcement

The last step of retaining wall installation: Bentonite filling

During diaphragm wall installation, the basement columns (steel beams) and concrete barrettes are

made. Basement columns and the concrete barrettes are load-bearing elements that will carry the future

super-structure. The construction process of those elements is beyond the scope of this project.

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EXCAVATION: STEP NR 1

The top floor slab is constructed with at least on construction (glory) hole left open to allow removal of

spoil material (Figure 4.9)

Top-down construction involves casting the ground floor slab and excavating the ground below while

work on the superstructure above can continue

Figure 4.9 Excavation - Step nr 1 -Ground floor construction

Figure 4.10 Example of whole in a top floor slab

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The excavation starting at the glory hole begins once the top floor has gained sufficient strength. Soil

under the top basement floor is excavated around the basement columns to slightly lower than the first

basement floor elevation in order to allow for the installation of the forms for the first level basement

slab. Glory holes are left open within each newly formed basement floor slab and the procedure is

repeated. Each floor rests on the basement columns that were constructed earlier

Figure 4.11 Excavation - Step nr 2 - First level basement slab construction


Figure 4.12 Excavation - Step nr 3 - Second level basement slab (foundation slab) construction

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7. Geotechnical description

7.1. Introduction to soil properties Geotechnical description is the last step of 'theoretical part' before the calculation. The geotechnical

description is important in all kind of project in civil engineering. In this part the subsurface conditions

and materials are investigated. It is necessary to determine the physical and mechanical properties of

materials.

It is really important to have an overview on the surrounding buildings because the Skyscraper

will be located in an urban area, in the heart of Wroclaw. The building site is surrounded by other

buildings, and road - located next to the area which will be excavated and possibly causing the collapse

to these road and buildings as a result of the excavation or dewatering.

Water level is between at depth 11,8 meters under the ground level. So it is not necessary to

perform a temporary dewatering for the excavation (the deep of excavation is 7 meters). In case when

the excavation is at depth e.g. 11 meters, the dewatering should then be arranged so that the water

table is lowered at least 1 meter below the excavation level. There will probably be a dug in clay, in

which case the dewatering of the excavation possibly will be done by simple drainage.

The safety of any geotechnical structure is dependent on the strength of the soil. Understanding shear strength is the basis to analyze soil stability problems. If the soil fails, the structure founded on it can collapse.

Figure 4.13 Foundation failure by liquefaction after the 1964 Niigata Earthquake.

Shear strength is a term used to describe the magnitude of the shear stress that a soil can sustain. The shear resistance of soil is a result of friction and interlocking of particles, and possibly cementation or bonding at particle contacts. Due to interlocking, particulate material may expand or contract in volume as it is subject to shear strains. If soil expands its volume, the density of particles will decrease and the strength will decrease; in this case, the peak strength would be followed by a reduction of shear stress. The stress-strain relationship levels off when the material stops expanding or contracting, and when interparticle bonds are broken.

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According to BS EN ISO 14688-2:2004,5.3,Table 5 the shear strength of soils when measured by Field or Hand Shear Vane Apparatus, or in the laboratory by Quick Undrained Triaxial compression test, shall be expressed as below:

Table 4 shear strength of soils

Term based on measurement Undrained Shear Strength classification definition C

u, in kPa

Extremely low

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Figure 4.15 Internal friction angle

7.2. Soil physical properties

There are different types of soil in the designed area.

Fill

From the building demolition or base course (mix concrete, sand or asphalt)

Humus

It's the layer of organic matter in soil. Humus, which ranges in colour from brown to black, consists of about 60 percent carbon, 6 percent nitrogen, and smaller amounts of phosphorus and sulfur. As humus decomposes, its components are changed into forms usable by plants. Humus is classified into mor, mull, or moder formations according to the degree of its incorporation into the mineral soil, the types of organisms involved in its decomposition, and the vegetation from which it is derived.

Sand

Sand is a naturally occurring granular material lcomposed of finely divided rock and mineral particles.

The composition of sand is highly variable, depending on the local rock sources and conditions, but the

most common constituent of sand in inland continental settings and non-tropical coastalsettings

is silica (silicon dioxide, or SiO2), usually in the form of quartz.

The second most common form of sand is calcium carbonate, for example aragonite, which has mostly

been created, over the past half billion years, by various forms of life, like coral and shellfish.

ISO 14688 (International Organization for Standardization) grades sands as fine, medium and coarse with ranges 0.063 mm to 0.2 mm to 0.63 mm to 2.0 mm. In the United States, sand is commonly divided

into five sub-categories based on size: very fine sand (16 mm diameter), fine sand ( mm mm), medium sand ( mm mm), coarse sand ( mm 1 mm), and very coarse sand (1 mm 2 mm).

Clay Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilical minerals containing variable amounts of water trapped in the mineral structure. Clay minerals are typically formed over long periods of time by the gradual chemical weathering of rocks, usually silicate-bearing, by low concentrations of carbonic acid and other diluted solvents. These solvents, usually acidic, migrate through the weathering rock after leaching through upper weathered layers. In addition to the weathering process, some clay minerals are formed by hydrothermalactivity. Clay deposits may be formed in place as residual deposits in soil, but thick deposits usually are formed as the result of a secondary sedimentary deposition process after they have been eroded and transported from their original location of formation. Clay deposits are typically associated with very low energy depositional environmentssuch as large lakes and marine basins.

Sandy clay Soil material that contains 35 % or more clay and 45% or more sand.

Gravel

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Is composed of unconsolidated rock fragments that have a general particle size range and include size classes from granule- to boulder-sized fragments. Gravel is sub-categorized by the Udden-Wentworth scale into granular gravel (>2 to 4 mm or 0.079 to 0.16 in) andpebble gravel (>4 to 64 mm or 0.2 to 2.5 in). One cubic yard of gravel typically weighs about 3000 pounds (or a cubic metre is about 1,800 kilograms).

Gravel is an important commercial product, with a number of applications.

Many roadways are surfaced with gravel, especially in rural areas where there is little traffic. Globally,

far more roads are surfaced with gravel than with concrete or tarmac; Russia alone has over 400,000

km (250,000 mi) of gravel roads. Both sand and small gravel are also important for the manufacture

of concrete.

7.3. Soil characteristics

According to Eurocode 7 and Polish National Standards PN-81 B-03020 (Annex 5) the following

geotechnical parameters have to be known to calculate the underground structure (in this case

underground parking):

g weight density [kN/m3]

cu,k characteristic undrained shear strength of soil [kPa] fk characteristic angle of shearing resistance [0]

7.3.1. Determination of weight density (g)g)g)g) Density represents weight (mass) per unit volume of a substance. Soil density is expressed in two well accepted concepts as particle density and bulk density.

Particle Density: The weight per unit volume of the solid portion of soil is called particle density.

Bulk Density: The oven dry weight of a unit volume of soil inclusive of pore spaces is called bulk density. The bulk density of a soil is always smaller than its particle density.

According to PN-81 B-03020 (ANNEX 5) :

Table for cohesionless soils:

SOIL HUMIDITY

Particle density

ggggS

Bulk density gggg depending on the ID

ID = 1,0 0,68 ID = 0,67 0,24 ID = 0,33 0,0

FSa

siSa

dry

2,65

1,7 1,65 1,6

semi dry 1,85 1,75 1,7

wet 2,0 1,9 1,85

Example:

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For Fine Sand (dry, ID = 0,5) the particle density equals 2,65 g*cm3 and the bulk density equals 1,65

g*cm3

Table for cohesion soils:

SOIL

Particle density

ggggS

Bulk density gggg depending on the IL

IL < 0 ID = 0,0 0,25 IL = 0,25 0,5 IL = 0,5 1,0

saclSi 2,68 2,15 2,10 2,00 1,9

7.3.2. Determination of characteristic undrained shear strength [cu,k]

Drained condition occurs when there is no change in pore water pressure due to external loading. In a drained condition, the pore water can drain out of the soil easily, causing volumetric strains in the soil.

Undrained condition occurs when the pore water is unable to drain out of the soil. In an undrained condition, the rate of loading is much quicker than the rate at which the pore water is able to drain out of the soil. As a result, most of the external loading is taken by the pore water, resulting in an increase in the pore water pressure.The tendency of soil to change volume is suppressed during undrained loading.

The shear strength of a fine-grained soil under undrained condition is called the undrained shear strength.

Based on Annex 5, picture nr 5 the characteristic undrained shear resistance can be assumed from the graph.

7.3.3. Determination of characteristic angle of shearing resistance [0]

Angle of shearing resistance is also called internal angle of friction or angle of frictional resistance.

Definition: Angle representing the relationship of shearing resistance to normal stress acting on the

sliding surface within a soil mass during shear; angle between the axis of normal stress and the tangent

to the Mohr envelope at a point representing a given failure-stress condition for the solid material.

Based on Annex 5, picture nr 3,4 characteristic angle of shearing resistance can be assumed from the

graphs.

7.3.4. Determination of parameters for soils occurring in the project.

Borehole nr 1

Nr Layer Symbol Density Humidity g[kN/m3] cu,k [kPa] fk [0]

1 Embankment - Loose wet 18,0 0 22

2 Fine sand FSa ID=0,4 semi dry 16,5 0 30

3 Clayey silt saclSi IL=0,07 semi dry 21 35 20,7

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4 Silty sand siSa ID=0,5 wet 17,5 0 30,5

5 Clayey silt saclSi IL=0,29 wet 20 28,3 16,6

Borehole nr 2




3 Clayey silt saclSi IL=0,12 semi dry 21 36 20

4 Silty sand siSa ID=0,8 wet 18,5 0 30,5

5 Clayey silt saclSi IL=0,22 wet 21 30 17,5

Borehole nr 3




3 Clayey silt saclSi IL=0,09 dry 21 36 22,5

4 Clayey silt saclSi IL=0,27 wet 20 27 16,5

Borehole nr 4




3 Clayey silt saclSi IL=0,07 semi dry 21 35 22

4 silty sand siSa ID=0,5 wet 17,5 0 30,5

5 clayey silt saclSi IL=0,29 wet 20 28,3 16,6

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8. Introduction to calculations

In chapter fol lowing rules wil l be described and explained: partial factors of safety, method of geotechnical design by calculation, method of retaining wall design by

calculation.

8.1. Introduction Designing foundations by calculation according Eurocode 7

8.1.1 Partial factor of safety

There are different partials of safety according to EN 1997-1:

Polish Standard PN 81 B 03020 (ANNEX 5) use g for unit weight (weight density)

In calculations designed values are used by combining the characteristic value with the appropriate factor of safety.

8.1.2. Geotechnical design by calculation

The algorithm below shows the steps of calculations

The algorithm was prepared by Dr Ian Smith from Edinburgh Napier University

8.1.3. Designed values of actions

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To determine design effects of action we follow the steps:

8.1.4. Designed values of geotechnical parameters

To determine design value of geotechnical parameter we follow the rule:

8.1.5. Designed values of geometrical data

In cases where deviations in the geometrical data have a significant effect on the reliability of a structure, design values of geometrical data (ad) shall either be assessed directly or be derived from nominal values using the following equation ( 6.3.4 of EN 1990:2002):

8.1.6. Designed effects of actions

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During the verification of geotechnical strength (i.e. GEO limit state) some effects of the actions will depend on the strength of the ground in addition to the magnitude of the applied action and the dimensions of the structure. Thus, the effect of an action in the GEO limit state is a function of the action, the material properties and the geometrical dimensions.

During the verification of static equilibrium (i.e. EQU limit state) some effects of the actions (both destabilising and stabilising) will depend on the strength of the ground in addition to the magnitude of the applied action and the dimensions of the structure. Thus, the effect of an action in the EQU limit state, whether it be a stabilising or a destabilising action, is a function of the action, the material properties and the geometrical dimensions.

8.1.7. EQU

EQU: loss of equilibrium of the structure or the supporting ground when considered as a rigid body and where the internal strength of the structure and the ground do not provide resistance.

Limit state is satisfied if the sum of the design values of the effects of destabilising actions (Edst;d) is less than or equal to the sum of the design values of the effects of the stabilizing actions (Estb;d) together with any contribution through the resistance of the ground around the structure (Td),

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8.1.8. GEO

GEO: failure or excessive deformation of the ground, where the soil or rock is significant in providing resistance.

This limit state is satisfied if the design effect of the actions (Ed) is less than or equal to the design resistance (Rd),

8.1.9. STR

STR: failure or excessive deformation of the structure, where the strength of the structural material is significant in providing resistance.

As with GEO limit state, the STR limit state is satisfied if the design effect of the actions (Ed) is less than or equal to the design resistance (Rd),

There are also UPL and HYD limit states.

UPL: This limit state is verified by checking that the sum of the design permanent and variable destabilising vertical actions (Vdst;d) is less than or equal to the sum of the design stabilizing permanent vertical action (Gstb;d) and any additional resistance to uplift (Rd).

HYD: This limit state is verified by checking that the design total pore water pressure (udst;d) or seepage force (Sdst;d) at the base of the soil column under investigation is less than or equal to the total vertical

stress (sstb;d) at the bottom of the column, or the submerged unit weight (G'stb;d) of the same column.

8.1.10 GEO/STR Limit states

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Three Design Approaches are offered. The design approach followed reflects whether the safety is applied to the material properties, the actions or the resistances.

Design Approach 1: Combination 1: A1 + M1 + R1

Combination 2: A2 + M2 + R1

Design Approach 2: A1 + M1 + R2

Design Approach 3: A* + M2 + R3

A*: use set A1 on structural actions, set A2 on geotechnical actions

For axially loaded piles, DA1, Combination 2 is: A2 + (M1 or M2) + R4

POLISH NATIONAL ANNEX STATES THAT DESIGN DESIGN APPROACH NR 2 SHALL BE USED

8.2. Retaining wall design

8.2.1. Limit states

The limit states are:

loss of overall stability;

failure of a structural element such as a wall, anchorage, wale or strut or failure of the connection between such elements;

combined failure in the ground and in the structural element;

failure by hydraulic heave and piping;

movement of the retaining structure, which may cause collapse or affect the appearance or

efficient use of the structure or nearby structures or services, which rely on it;

unacceptable leakage through or beneath the wall;

unacceptable transport of soil particles through or beneath the wall;

unacceptable change in the ground-water regime.

And for :

- Gravity walls:

bearing resistance failure of the soil below the base;

failure by sliding at the base;

failure by toppling;

- Embedded walls:

failure by rotation or translation of the wall or parts thereof;

failure by lack of vertical equilibrium.

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EN 1997-1:2004 9.2(1)

Examples:

8.2.2. Future unplanned excavation

In ultimate limit state calculations in which the stability of a retaining wall depends on the ground

resistance in front of the structure, the level of the resisting soil should be lowered below the nominally

expected level by an amount Da.

for a cantilever wall, a should equal 10 % of the wall height above excavation level, limited to a

maximum of 0,5 m;

for a supported wall, a should equal 10 % of the distance between the lowest support and the

excavation level, limited to a maximum of 0,5 m.

EN 1997-1:2004 9.3.2.2

9. Diaphragm wall calculations

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In this chapter one panel of diaphragm wall wil l be calculated and designed. The method of calculations wil l be explained using cut section I as an example.

Calculations wil l be made for each step of construction process.

9.1. General assumptions for project.

With the vertical cross section of the soil and the characteristics values, it is possible now to calculate the necessary diaphragm wall. Calculations will be performed using following methods:

Dependent pressures method, according to Polish Code PN-83/B-03010 Design of retaining walls,

Dependent pressures method, according to Eurocode 7. Dependent pressures method was chosen because of its simplicity and as it is very common in European and Polish design practice. According to Eurocode 7 retaining walls should be designed at limit states (GEO). Point 2.4. of Eurocode 7 specifies 3 Design Approaches with combinations of partial safety factors referring to surcharges, material coefficients and soil resistance (Previous chapters). Calculations will be performed using one combination of partial safety factors from the second Design Approach DA2 (practiced in Poland). Third DA(DA3) was ignored, because of the similarity in the values of partial safety factors, as well as First DA (DA1) Calculations employing dependent pressure method were performed using software GEO5 Sheeting check. The method of evaluation of subgrade reaction modulus (kh) based on nomogram of Chaidesson was chosen. Representative values of actions were calculated assuming the value of coefficient = 1.00, according to PN EN 1990 Basis of structural design. Design values of actions were calculated applying partial safety factors according to Polish Code (PN) or Eurocode 7. Analysis were performed determining minimum penetration of the diaphragm wall below the bottom of the excavation (D) and maximum bending moments (Mmax). In addition, maximum lateral displacements of the wall (Umax) were calculated and compared. Important information about the project:

The deepest excavation is 7,5 meters measured from the existing ground. There are four retaining walls in the project. All are designed as diaphragm walls. Water level for designed area is assumed as at the depth 11,8 meters. Surrounding buildings are in the danger zone.

It is considered the load distribution angle in soil is 45o, so danger zone is around 10 meters around the perimeter of construction area. As can be seen from in Annex A2 ( Pictures from the building site) the surrounding buildings are in the danger zone. It is necessary to strengthen the construction or surrounding buildings ( this is not a part of this project)

There can be some temporary distributed load right behind the retaining structure. It can me machinery on the construction site, normal traffic on streets and so on. Therefore additional load p=5 kN/m2 (characteristic value) is applied in every calculation. The safety factor for temporary distributed additional load is 1,5.

9.2. Description of calculations.

The geometry of the analyzed case is shown on Figure 9.1 In this example following soil parameters are considered:

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Nr Layer Symbol Density Humidity Depth Thickness

1 Embankment - Loose wet 0,0 1,1 1,1

2 Fine sand FSa ID=0,4 semi dry 1,1 2,0 0,9

3 Clayey silt saclSi IL=0,07 semi dry 2,0 5,2 3,2

4 Silty sand siSa ID=0,5 wet 5,2 6,4 1,2

5 Clayey silt saclSi IL=0,29 wet 6,4 great depth

Characteristics values of: soil parameters, active earth pressure coefficient (Ka), passive earth pressure coefficient (Kp) are given below in the table. Earth pressure coefficient are taken from ANNEX 7 page 126.

Nr Layer Symbol g[kN/m3] cu,k [kPa] f'k [0] Ka Kp

1 Embankment - 18,0 0 22 0,48 2,5

2 Fine sand FSa 16,5 0 30 0,31 3,2

3 Clayey silt saclSi 21 35 20,7 0,46 2,3

4 Silty sand siSa 17,5 0 30,5 0,31 3,2

5 Clayey silt saclSi 20 28,3 16,6 0,41 2,0

Table : Characteristic values of soil parameters for DA2 9.3. Designed values.

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In the DA2 (A1 + M1 + R2 ) partial safety factor for reduction of soil resistance in front of the wall

gR = 1,4 will be considered in further calculations.

Soil nr 1 Embankment

1,k= 18,00 kN/m3

1,d= 1,k/ 1, = 18/1,0 = 18,00 kN/m3

f1,k = 22,00o

f 1,d =arc(tg f 1,k / )= arc(tg22,00 / 1,00 ) = 22,0 o

C1= 0,00 kPa

Soil nr 2 FSa

2,k= 16,50 kN/m3

2,d= 2,k/ 2, = 16,5/1,0 = 16,50 kN/m3

f 2,k = 30,00o

f 2,d =arc(tg f 2,k / )= arc(tg30,00 / 1,00 ) = 30 o

C2= 0,00 kPa

Soil nr 3 saclSi

3,k= 21,00 kN/m3

3,d= 3,k/ 3, = 21,0/1,0 = 21,00 kN/m3

f 3,k = 20,70o

f 3,d =arc(tg f 3,k/)= arc(tg20,70 / 1,00 ) = 20,70 o

C3,k= 35,00 kPa

C3,d= C3,k/ 3,c = 35,00/1,00 = 35,00 kPa

Soil nr 4 siSa

4,k= 17,50 kN/m3

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4,d= 4,k/ 4, = 17,50/1,0 = 17,50 kN/m3

f 4,k = 30,50o

f 4,d =arc(tg f 4,k/ )= arc(tg30,50 /1,00 ) = 30,50 o

C4= 0,00 kPa

Soil nr 5 saclSi

5,k= 20,0 kN/m3

5,d= 5,k/ 5, = 20,00/1,0 = 20,00 kN/m3

f 5,k = 16,60o

f 5,d =arc(tg f 5,k/ )= arc(tg16,60 /1,00 ) = 16,6 o

C5= 2Sp8,30 kPa

C5,d= C5,k/ 5,c = 28,30/1,00 = 28,30 kPa

Following construction stages are considered:

Stage 1: excavation to level 0,3 m b.g.s.

Stage 2: installation of reinforced concrete slab at level 0,3 m b.g.s. PHASE 1

Stage 3: excavation to level -3,55 m b.g.s.

Stage 4: installation of reinforced concrete slab at level -3,55 m.b.g.s PHASE 2

Stage 5: excavation to level -7,00 m.b.g.s.

Stage 6: installation of reinforced concrete slab at level -7,00 m.b.g.s. PHASE 3

All phases will be calculated by GEO5 software. PHASE 3 will be calculated manually.

PHASE 3 - MANUALLY CALCULATION

STATIC MODEL

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Designed wall height:

According to Eurocode 7 point:{9.3.2.2(2)} the designed height of the diaphragm wall (Ho) equals:

Active earth pressure from weight of the soils (permament load):

characteristic values of active earth pressure : eak

designed values of active earth pressure : ead Formulas according to PN EN 1997 - 1:

eak = i,d * z * Kai [kN/m2] for cohesive-less soil

ea, k, i = i,d * z * Kai 2 * Ci,d* [kN/m2] for cohesive soil for z= 0,0m ( top of the first soil layer) ea,k, (0,0) = 18 * 0 * 0,46 = 0 kN/m2

ea,d,(0,0)= ea,k,0 * E = 0 *1,35 = 0 kN/m2

for z=1,10m ( the bottom of the first layer)

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ea,k, (1,1) = 18 * 1,1 * 0,46 = 9,11 kN/m2

ea,d, (1,1) = ea,k,1* E = 9,11 *1,35 = 12,29 kN/m2

for z=1,10m ( top of the second soil layer) ea,k,(1,1) = 18*1,1 * 0,31 = 6,14 kN/m2

ea,d,(1,1)= 6,14 *1,35 = 8,28 kN/m2

for z=2,00m ( the bottom of the second layer) ea,k, (2,0) = (18*1,1+16,5*0,9) * 0,31 = 10,74 kN/m2

ea,d,(2,0)= 10,74*1,35 = 14,5 kN/m2

for z=2,0m (top of the third soil layer) ea,k (2,0) = (18,0*1,1+16,5*0,9) * 0,46 2 * 28,30 * = 2,47kN/m2

ea,d(2,0)= 2,47 *1,35 = 3,33 kN/m2

for z=5,20m ( the bottom of the third layer) ea,k (3,2) = (18,0*1,1+16,5*0,9+21,00*3,2) * 0,46 2 * 28,40 * = 38,52 kN/m2

ea,d(3,2)= 38,52*1,35 = 52,01 kN/m2 dla z=5,20 m ( top of the fourth soil layer) ea,k (5,2) = (18,0*1,1+16,5*0,9+21,00*3,2) * 0,31 = 31,58 kN/m2

ea,d(5,2)= 31,58 *1,35 = 42,64 kN/m2

dla z=6,4 m (the bottom of the fourth layer) ea,k (6,4) = (18,0*1,1+16,5*0,9+21,00*3,2+17,5*1,2) * 0,31 = 38,08 kN/m2

ea,d(6,4) = 38,08 *1,35 = 51,41 kN/m2 dla z=6,4 m (top of the fifth soil layer) ea,k (6,4) = (18,0*1,1+16,5*0,9+21,00*3,2+17,5*1,2) * 0,41 2 * 28,30 * = 14,12 kN/m2

ea,d(6,4) = 14,12 *1,35 = 19,07 kN/m2 dla z=7,5 m (the bottom of the fifth layer) ea,k (7,5) = (18,0*1,1+16,5*0,9+21,00*3,2+17,5*1,2 + 20,00*1,1 ) * 0,41 2 * 28,30 * = 23,14 kN/m2

ea,d(7,5) = 23,15 *1,35 = 31,24 kN/m2

for z=7,5 m + t

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IMPORTANT : t is the dimension of the wall under the excavation level, that means that 7,5 m +t = total height of the wall.

ea,k (7,5 +t) = 14,12 + 0,41 * 20,00 *(t + 1,1) = 8,2 t + 23,14 kN/m2

ea,d (7,5 +t) = 14,12 + 1,35 *0,41 * 20,00 *(t + 1,1) = 8,2 t + 31,24 kN/m2

To calculate the resultant value of active earth pressure from permanent load (RBg,k )we assume

static model with one strut : Graph 1. Active soil pressure from permament load

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-(0,5*9,11*1,1*2,66) (6,14*0,9*1,85) ((10,74-6,14)*0,5*0,9*1,7) (RBgk * (4,1+0,5t)) + (2,47*3,2*0,2)+((38,52-2,47)*3,2*0,5*0,73)+(31,58*1,2*2,4)+((38,08-31,58)*1,2*0,5*2,6)

+(14,12*(t+1,1)*(3,6+0,5t) +(((8,2t+23,14)-14,12)*(t+1,1)*(4,1*0,67t) = 0 RBgk * (4,1+0,5t) = 185,71 + 139,19t + 52,76t2 + 5,49t3

the resultant value of active earth pressure from permanent load

RBgk = (5,49t3 + 52,76t2 + 139,19t + 185,71)

Active earth pressure from weight of the surrounding buildings and machines (temporary load):

load from the surrounding buildings = 115 kN/m2

load from the machines = 5 kN/m2

Total temporary load = 120 kN/m2

characteristic value of active earth pressure : eakn

designed value of active earth pressure : eadn Formula according to PN EN 1997 - 1:

eakn = pk* Kai [kN/m2]

In first soil layer:

eakn,1 = 120 * 0,48 = 57,6 kN/m2

eadn,1 = 57,6 * 1,5 = 86,4 kN/m2

In second soil layer:

eakn,2 = 120 * 0,31 = 37,2 kN/m2

eadn,2 = 37,2 * 1,5 = 55,8 kN/m2

In third soil layer:

eakn,3 = 120 * 0,46 = 55,2 kN/m2

eadn,3 = 55,2 * 1,5 = 82,8 kN/m2

In fourth soil layer:

eakn,4 = 120 * 0,31 = 37,2 kN/m2

eadn,4 = 37,2 * 1,5 = 55,8 kN/m2

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In fifth soil layer

eakn,5 = 120 * 0,41 = 49,2 kN/m2

eadn,5 = 49,2 * 1,5 = 73,8 kN/m2

Graph 2. Active soil pressure from temporary load

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Water pressure was ignored, because of the high depth of ground water level (- 11 m GWL). Passive earth pressure from weight of the soil layers (permanent load):

Formula according to PN EN 1997 - 1:

eph,k=Kph (*z +p)+2ck(Kph )0,5

where p=0 For fifth soil layer (saclSi) following parameters are assumed: 5,k= 20,0 kN/m3 , f 5,k = 16,60o , C= 28,30 kPa , Ka,5 = 0,41, Kp,5 = 2,0

eph1,k=2*28,30*(2,0)0,5=80,04 kN/m2

eph2,k=2,0*20,0*t+80,04= 40t+80,04

Eph,k=(eph1,k+eph1,k)*0,5t=80,05t+20t2

Determination of requirement anchorage length t

Model:

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To find dimension 't' formula according to PN EN 1997 1 is used:

RB,d < Eph,d For Second Designed Approach (DA2) the formula assumes the form :

RB,d = Rbg,k* ggggG + RBp,k* ggggQ + RBp,w* ggggW < Eph,k / ggggR

According to DA2:

ggggG = 1,35

ggggQ = 1,5

ggggW= 1,4

RBp,w* ggggW was ignored, because of the high depth of ground water level (- 11 m GWL). Formula above assumes the form:

Using Mathcad software 't' is searched by method of successive approximations :

t=2 F(t) = 18,83 t=2,5 F(t) = 7,29 t=2,8 F(t) = 0,25 t=2,9 F(t) = -2,10 t=3 F(t) = -4,46

Assumed value t=2,8m,

According to Eurocode PN EN 1997-1, assumed value should be increased by:

t= 2,8 m + hn=2,8+0,5= 3,2 m

Checking the compatibility between earth pressure and wall displacement

The scheme of wall displacement is shown in picture below :

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scheme of wall displacement

According to PN-83/B-03010 Designing of retaining wall formule nr 20 : [Annex 9]

f=p;gr*t/2=0,5p*t/2 According to PN-83/B-03010 graph nr 9 :

for:

f 5,k = 16,60o and for : t = 2,8 m

f=(0,5*0,072*280)/2=5,04 mm The minimum value of the wall displacement in relation to the soil behind the wall:

A=5,04/(410+280)=0,0073 For soils, appearing behind the wall according to graph 8 PN-83/B-03010: for:

f = 30,50o and for: h = 10,7 3,4 = 7,3 m Referring to obtain parameters:

A=0,0073 > a=0,002

CONCLUSION Wall anchorage length can be considered as sufficient.

Determination of earth pressures for total length of the wall :

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Requirement anchorage length t is assumed as 3,2 m according to previous calculations, that gives

the total length of diaphragm wall equals 10,7 m.

Active earth pressure from weight of the soil layers (permanent load) at level z=7,5 m + 3,2 m

ea,k (6,4 +3,2) = 8,2 *3,2 + 23,14 = 49,38 kN/m2

ea,d (6,4 +3,2) = 49,38 * 1,35 = 66,66 kN/m2

Passive earth pressure from weight of the soil layers (permanent load) at level z=3,2 m under the excavation level

eph2,k= 40t+80,04=40*3,2+80,04=208,04 kN/m2

Final Project Winter 2013

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