Diaphragm Wall

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BENHAUNIVERSITY Faculty of Engineering Department Of Civil Engineering

DIAPHRAGM

WALL

A TECHNICAL REPORT SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE GEOTECHNICAL ENGINEERING GRADUATION PROJECT

Prepared by

Ahmed Saad El-Deen El-Sayed

Mahmoud Atta Ragab

Moustafa Atef Goda

Sabah El-Sayed Ahmed

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6.1 SLURRY TRENCH STABILITY ... Error! Bookmark not defined. 6.2 STABILITY ANALYSIS ... Error! Bookmark not defined. 6.2.1 Stability of UnsupportedTrenches... Error! Bookmark not defined. 6.2.2 Stability of Slurry- Filled Trenches in Clay ... Error! Bookmark not defined. 6.2.3 Stability of Slurry- Filled Trenches in Dry Sand Error! Bookmark not defined. 6.2.4 Stability of Slurry-Field Trenches in Sand W/WaterError! Bookmark not defined.

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6.3 MUD CAKE ... Error! Bookmark not defined. 6.3.1 Effects of Mud (filter) Cake on Sand... Error! Bookmark not defined. 6.4 Arching ... Error! Bookmark not defined. 6.4.1 Arching Effect on Short Trenches in Sand ... Error! Bookmark not defined.

CHAPTER 7 DESIGN OF DIAPHRAGM WALL ... 32

7.1 EARTH PRESSURE ... 32

7.1.1 Calculation of shear strength parameters (τ′, c′, φ′) ... 32

7.1.1.1 For cohesion soil ... 32

7.1.1.2 For cohesion less soil ... 33

7.1.1.3 For rocks ... 33

7.1.2 Lateral earth pressure calculation ... 34

7.1.2.1 Lateral earth pressure based on long-term, drained, effective stress values. ... 34

7.1.2.2 Lateral earth pressure based on short-term undrained stress values. .. 34

7.1.3 Water pressure ... 35

7.2 DESIGN OF DIAPHRAGM WALL... 35

7.2.1 Design of Cantilever Wall (Free Earth Support) ... 36

7.2.2 Design of Hinged Single Anchored System ... 37

7.2.3 Design of Fixed Single Anchored System ... 37

7.2.4 Design of Multi-prop System ... 38

7.3.1 Overall Stability ... 42

7.3.2 Basal Heave Failure... 45

7.3.3 Hydraulic Failure ... 50

7.4.1 Deformation of Wall ... 54

7.4.2 Deformation of Soil Behind the Wall ... 54

7.5.1 Ground Anchors ... 56

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IV

7.6.1 Factors Affecting Wall Movements ... 61

7.6.2 Instrumentation of Deep Excavations ... 63

7.7 FAILURE SHAPES OF DIAPHRAGM WALLS ... 64

CHAPTER 8 CASES OF STUDY ... 66

8.1 CASE STUDY 1 (QUAY WALL AT THE PORT OF CALAIS) ... 66

8.1.1 Introduction ... 66

8.1.2 Description of The Structure And Site ... 67

8.1.3 Geotechnical and Hydrological Context... 68

8.1.4 Construction Phases... 69

8.1.5 Instrumentation and worksite monitoring ... 70

8.2 CASE SYUDY 2 (MRT CHALOEM RATCHAMONGKHON LINE, BANGKOK) ... 71

8.2.2 Description of The Structure And Site ... 72

8.2.3 Construction phases ... 73

8.2.3.1 Diaphragm wall construction ... 73

8.2.3.2 Sequence of construction ... 74

8.2.3.3 Supporting fluid ... 74

8.2.3.4 Reinforcement ... 74

8.2.3.5 Concrete casting ... 75

8.2.4 Quality and Safety and Environmental Controls ... 75

8.3 CASE STUDY 3 (El-Azhar Road tunnels project) ... 77

8.3.2 Geotechnical Properties ... 78

8.3.3 Construction Phasing ... 79

Chapter 9 ConclusionS ... 80

APPENDIX : MULTI_ANCHORED DIAPHRAGM WALL ... 81

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WEB REFERENCES ... 103

LIST OF FIGURES

Figure 2.1 Soil slope reinforcing ... 3

Figure 3.1 Typical guide wall ... 4

Figure 3.2 trenching ... 6

Figure 3.3 End stops ... 6

Figure 3.4 Cage reinforcement ... 7

Figure 3.5 Slurry wall ... 8

Figure 3.6 construction of Ecofriendly Soil Cement Continuous Diaphragm Wall ... 9

Figure 3.7 Constructed pre-cast diaphragm wall construction ... 10

Figure 3.8 lifting a precast diaphragm panel ... 11

Figure 3.8 horizontal cross section jointing detail ... 12

Figure3.9 Jointing details for Prefasil diaphragm wall panels ... 12

Figure 3.10 Post-tensioned cantilever and single-propped diaphragm ... 13

Figure 3.11 Examples of post-tension ... 14

Figure 3.12 secant pile wall ... 15

Figure 3.13 constructed secant pile wall ... 15

Figure 3.14 thin diaphragm wall ... 16

Figure 4.1 Leaks in construction ... 21

Figure 5.1 SG series Hydraulic Diaphragm Wall Grab ... 22

Figure 5.2 shell grab ... 24

Figure 5.3 Mechanical graps ... 24

Figure 5.4 Hydromill grap ... 25

Figure 6.1 Stability of unsupported trenches ... 28

Figure 6.2 Stability of slurry- filled trenches in clay ... 28

Figure 6.3 Stability of slurry- filled trenches in dry sand ... 28

Figure 6.4 Stability of slurry-field trenches in sand W/Water... 29

Figure 6.5 Effects of mud (filter) cake on sand ... 30

Figure 7.1 trixial text ... 33

Figure 7.2 Relationship between standard penetration resistance and φ′... 33

Figure 7.4 stresses affect on cantilevered diaphragm wall ... 36

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Figure 7.6 stresses affect on fixed single anchored diaphragm wall ... 38

Figure 7.7 Empirical method in sand soil ... 39

Figure 7.8 Empirical method in soft to medium clays... 39

Figure 7.9 Empirical method in stiff clay ... 40

Figure 7.10 for shallow or wide excavation with (H/B) <1 ... 45

Figure 7.11 for deep excavation with (H/B)> 1 ... 46

Figure7.12 Factor of safety against basal heave in cohesion less soils ... 47

Figure 7.13 Factor of safety against basal heave in cut in clay ... 47

Figure 7.14 Factor of safety against basal heave in cuts in clay limited by hard stratum ... 48

Figure7.15 Stability of internally braced cut (circular arc method) ... 49

Figure 7.16 Potential failure surfaces ... 50

Figure7.17 the design charts for wall penetration ... 51

Figure 7.18 the design charts for wall penetration ... 52

Figure 7.19 the summary of the Japanese and Terzaghi methods ... 53

Figure 7.20 the equilibrium between overburden pressure and pore water pressure ... 54

Figure 7.21 Section of an anchored wall, details of anchors ... 56

Figure 7.22 Anchorage section ... 58

Figure 7.23 Free length section ... 58

Figure 7.24 Tie rod force ... 60

Figure 7.25 some examples for the geometry of strutted systems ... 61

Figure 7.26 Embedded wall cantilever failure by forward rotation ... 64

Figure 7.27 Bending moment failure of embedded wall ... 64

Figure 7.28 Failure of embedded wall by rotation about anchor ... 65

Figure 7.29 failure of yield of anchor or tie ... 65

Figure 7.30 Failure by rotation of soil mass ... 65

Figure 7.31 Overturning of soil mass ... 65

Figure 8.1 the Port of Calais ... 66

Figure 8.2 plan of the Port of Calais ... 67

Figure 8.3 Typical section cut of the completed structure ... 67

Figure 8.4 the Chaloem Ratchamongkhon line ... 71

Figure 8.5 subsoil profile ... 72

Figure 8.6 panel layout ... 74

Figure 8.7 El-Azhar Road tunnels project ... 77

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VII

Figure 8.9 Diaphragm wall for Attaba TBM arrival shaft being built under ... 79

LIST OF TABLES

Table7.1 Approximate values for the effective angle of shearing resistance of soft rocks ... 34

Table 7.2 Factors of safety for methods of analysis embedment (Padfield and Mair) ... 44

Table7.3 Summary of limiting deformation ... 55

Table 7.4 the minimum safety factors for design of individual anchors ... 59

Table 7.5 Maximum wall movements and vertical settlements behind walls ... 62

Table 7.6 Instrumentation of deep excavations ... 63

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CHAPTER1

INTRODUCTION

The purpose of this research is to identify thediaphragm wall systems andits common applications, construction processand design methods.

Diaphragm wallsare an underground concrete structural element commonly used for retention systems, permanent foundation walls,permanent basement wall solution,deep groundwater barriersand and add stability to landslides, highway cuts and deep building excavations.And also Diaphragm walls were first introduced in the United States in the1960.

The wide use of the diaphragm wall is due to its advantages such as small deformations with high loading, watertight to a large extent, gentle to the underground, economical, space saving, little noise during construction, Water bar can be incorporated, Less joints required than a piled wall, Top-down basement construction gives significant, Box outs can be incorporated in diaphragm walls to facilitate easy connections for slabs, stairs, etc But there were limitationsfor using diaphragm wall because of the extensive construction supplies, separate disposal of admixed soil excavations, block-outs for crossing pipes, tubes are often problematic to build.

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CHAPTER 2 SOIL RETENTION

2.1 BATTERED EXCAVATIONS

The stability of a cut slope in granular soils can be determined simply from knowledge of the angle of shearing resistance for the soil or the soil layers. In normally consolidated cohesive soils, the stability can be assessed by a repetitive calculation of disturbing and restoring moments for trial potential failure surfaces, the restoring force being based on quick undrained shear strengths of the soil on the failure surface. Where possible, it is usual to avoid the effects of disturbance on the measurement of clay strengths by measuring in situ shear strengths with a vane apparatus rather than relying on laboratory test values.

2.2 SLOPES IMPROVEMENT

There are six methods for improving the stability of a cut slope:

 Regarding the profile of the slope and, for example, weighting the toe of the slope locally with a soil berm to reduce the disturbing movement.

 Using tensioned ground or rock anchors to increase the effective stress on the potential failure surface, thereby improving soil strength.

 Intercepting potential failure surfaces with sheet piles or jet grouted columns installed from the face or the top of the slope.

 Increasing the effective vertical stress on the potential failure surfaces by reduction of pore-water pressure by drainage.

 Improving composite soil strength by regarding the slope and the inclusion of reinforcement to intercept the potential failure surface, using reinforced soil.

 Driving soil nails through potential failure surfaces.

2.3 SOIL REINFORCEMENT 2.3.1 Types of Reinforcement 2.3.1.1 Metal Strip Reinforcement

The metallic reinforcing strip currently recommended is galvanized milled steel, generally 5 mm thick and in standard widths of 40 or 60 mm. The surface of the strip is ribbed to improve soil-reinforcement friction as shown in figure 2.1. The strip is

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called high adherence strips. In permanent walls it is usual to allow a sacrificial thickness of the metal to be lost due to corrosion (from 0.5 to 2 mm depending on design life and exposure). It is also usual to place dummy strips through the wall face on aggressive sites in order that strips can be jacked out occasionally to monitor the rate of corrosion. The galvanized steel strip and precast concrete facing panel are competitive for vertically-faced walls of medium to large height, due to the high elastic modulus of mild steel and the low creep properties.

2.3.1.2 Polymer Geogrids

Tensergeogrids are high-strength polymer grids specifically made as tension-resistant inclusions in soils. The manufacturing process begins with an extended sheet of polyethylene or polypropylene which is punched with a regular pattern of circular holes. This sheet is then stretched under controlled heat conditions so that randomly long chain molecules are drawn into an aligned state. This process of stretching increases the tensile strength and stiffness of the polymer. The resulting geogrid structure of ribs and bars produces an effective means of transferring friction from soil to geogrid. The prime disadvantages of using a polymer grid is the low elastic modulus and high creep value compared with steel strip. The influence of long-term strength has been the subject of vigorous research, and the influence of load capacity on the design life of the geogrid can be predicted by extrapolation from laboratory curves of strain against load with increasing time at various temperatures.

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CHAPTER 3 DIAPHRAGM WALL SYSTEMS

3.1 SLURRY DIAPHRAGM WALLS

A slurry wall is technique used to build reinforced-concrete walls in areas of soft earth close to open water or with a high ground water table.

This technique is typically used to build diaphragm (cut-off) walls surrounding tunnels and open cuts, and to lay foundations. A trench is excavated to create a form for each wall. The trench is kept with full of slurry at all times.

The slurry prevents the trench from collapsing by providing outward pressure whichbalancesthe

inward hydraulic forces and prevents water flow into the trench. Then, rebar cage is lowered in and the trench is filled with concrete, which displaces the slurry.

3.1.1 Ordinary Construction of Slurry Walls 3.1.1.1 Fixing of Alignment For Diaphragm Wall

Alignment of Diaphragm Wall shall be fixed on the ground with the help of total station as per the relevant drawing. Proper alignment of Diaphragm Wall shall be maintained by means of guide wall.

3.1.1.2 Construction of Guide Wall

Guide wall of 1.20 m depth shall be made of reinforced cement concrete As shown in figure3.1. Distance between internal faces of guide wall shall be maintained 630mm. Dimensions of guide wall, whether in filled area or in excavation shall be same as specified in the above-referred drawing. Filled portion shall be compacted properly and then only excavation activity for guide wall shall be started.

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5 3.1.1.3 Construction of Diaphragm Wall

Construction of Diaphragm Wall shall be done by alternate panel method. In this method primary panels shall be cast first leaving suitable gaps in between. Secondary panels & closing panel shall then be cast in this gap. The length of panel may vary from one location to another location depending upon the cut-off level and the termination depth. The changes shall be intimated in advance. Two stop end tubes shall be used at the ends of primary/secondary panels to support Cement Bentonite Slurry and to form suitable joints with the adjacent panel. The shape of the secondary panel end shall be such as to form proper joint with primary panel. 580 mm dia. MS hollow pipes shall be used as stop end tube. The semicircular shape shall provide the proper joint between adjacent panels. Length of panels shall be marked on the guide wall prior to start of trenching work.

a) Boring (Trenching)

Boring shall be carried out by wire rope grab As shown in Figure 3.2 operated by means of suitable crane. The crane shall control the vertical motion of grab. Initially grabbing/ boring shall be done from guide wall top up to water table level in dry conditions. After completing the dry boring, the bentonite slurry of minimum density 1.04 gm/cc shall be pumped to the partly excavated trench and bore shall be filled with bentonite slurry, and further grabbing shall be continued up to specified depth as mentioned in the relevant drawing. Continuous supply of bentonite slurry shall be maintained in bore during entire trenching process to have a constant head above the ground water level. Sodium based bentonite available at Bhuj/Bhavnagar shall be used for bentonite slurry. Necessary testing like density, PH value, viscosity shall be carried out at site until a consistent working pattern is established, taking into account the mixing process, blending of freshly mixed bentonite with previously used slurry etc. Contaminated bentonite shall be removed from site / bentonite tank by means of tankers / tractors and shall be disposed off at suitable location shown by client / consultant. Usually panel width shall vary from 4.0 m to 6.0 m, so that the entire trenching shall be completed in three cuts as per grab size. Panel width may vary as per site conditions. During trenching operation adequate care shall be taken to keep the bore vertical to such an extent so that it meets the permissible limits specified in the technical specification. To maintain verticality of trench following measures shall be adopted: Crane shall be placed on relatively firm and leveled ground and level of track chain of crane shall be checked by means of sprit level. During trenching grab shall be rotated by 180 degree after every three to four grabbing operation. To check the verticality

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distance between grab rope and guide wall face shall be monitored. After completion of boring up to specified depth, the boring equipment shall be shifted to another location.

Figure 3.2 trenching

b) Fixing of stop end tubes

Stop end pipes shall be lowered up to the bottom of trench maintaining pre specified distance marked on the guide wall. The center of stop end tubes shall match with the panel markings on Guide wall As shown in Figure 3.3Shutter release oil shall be applied on stop end tubes. During placing of stop end pipes, verticality shall be monitored by means of plumb bob to make the same vertical enough to meet the requirements specified in the technical specification.

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7 c) Cleaning of excavated trench

After trenching is completed, for flushing tremmie pipe of 200 mm dia shall be lowered in the trench keeping a gap of 300 mm to 500 mm from bottom of trench. Bentonite shall be pumped through the tremmie pipe so as to clean the bottom of trench. Bentonite level shall be maintained in trench by continuously pouring Bentonite from the Bentonite tank. Care shall be taken to avoid Bentonite level from going below bottom of Guide wall. Flushing shall be continued unless Bentonite density comes 1.15 gm/cc or below 1.15 gm/cc. For checking purpose the suitable bentonite sampler shall be used for collecting sample from the bottom of trench.

d) Trench Reinforcement

We put steel cage in side it, cage is fabricated on site as shown in Figure 3.4

Figure3.4 Cage reinforcement

e) Forming of cement-bentonite slurry diaphragm wall

After Flushing of Excavated trench re-circulation to be started for replacement by the Cement bentonite slurry as shown in Figure 3.5 with the help of suitable capacity of Vacseal/Electric Operated Pump s and Venture Mixer using high speed agitators. The Pumping out of Bentonite Slurry is to be done from the bottom of the trench and the Cement –Bentonite Slurry is to flow into trench by Gravity. Pumping out of the Slurry from

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the excavated Trench to Mixing tank and flow back to Trench till continue and cement to be added as per specifications. The Circulation of Cement Bentonite Slurry shall be continued for homogeneous mixing but mixing to be finished before initial setting time of Cement used and bulking time of Cement Bentonite Slurry.

Figure 3.5 Slurry wall

f) Bleeding of cement-bentonite slurry & top of trench

After one day Cement –Bentonite Slurry bleeding occurs which shall cause the top of the slurry to settle down to be top up by additional Cement Bentonite Slurry with required density to be pour to raised up to Cut-Off level.

g) Removal of stop end pipe

The end tubes shall be taken out gradually with the help of a Crane / Hydraulic Jacks. Adequate care shall be taken during removal of stop end pipe so that no damage is caused to the Slurry placed against them

3.1.1.4 Safety Precaution

Necessary safety precaution is the part of the job. All workers related with the construction shall be provided with PPE. Periodical checking of cranes, wire shall be done. After boring, the trench shall be covered with iron mesh till other activity starts. In the case of collapse of excavated trench, the same shall be back filled immediately with lean concrete.

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3.1.2 Ecofriendly Soil Cement Continuous Diaphragm Wall Method

Deep soil cement wall that can be excavated is built and up to 70 percent of the surplus soil reused in order to standardize the technology, quality control and construction method of continuous diaphragm wall methods, which recycle the surplus soil generated, as well as aiming to increase use of the method as shown in Figure 3.6

Takenaka Corporation (Head Office: Osaka; President: Toichi: Takenaka), jointly with Kajima Corporation and 11 other companies, has developed the "Continuous Diaphragm Wall Method Using Excavated Soil (Reducing the Amount of Construction Surplus Soil by Recycling the Excavated Soil)," and has received a Technical Inspection Certificate recognized by the Minister for Construction.

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Figure 3.6 construction of Ecofriendly Soil Cement Continuous Diaphragm Wall

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This is an earth retaining method able to be used deep underground to build a continuous diaphragm wall by reburying soil cement produced mainly with excavated soil (up to 70 percent recycling) into the groove excavated using stabilizing liquid by an excavator used in RC continuous diaphragm wall methods . This method takes strong consideration of the environment, and has superb quality, construction workability, safety and economic qualities required in this day and age.

3.2 PRE-CAST DIAPHRAGM WALL

There are some advantages for this type such as:

 General appearance: no cutting back is required and the finished surface is agreeably clean.

 The shape of the diaphragm can be tailored to form an integral part of the final structure, satisfying technical and economic consideration.

 Improved concrete quality and accuracy in placing reinforcement gives considerable savings on materials; prefabricated diaphragms are generally 30 % thinner than

conventional diaphragm walls.

 The prefabricated diaphragm can be built and installed in the ground to finer tolerances, and openings can be positioned more accurately.

 Watertightnees at the joints and in the wall itself is better than with conventional diaphragms.

 The improved finished surface can be obtained as shown inFigure 3.7.

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Panel widths and lengths are limited to the capacity of mobile lifting equipment suitable for operation on construction sites, and in practical terms this is of the order of 30 ton. The panels are usually cast on site; some additional site area may be needed to do this although less space is needed to store reinforcement since prefabrication of reinforcement cages is not necessary with pre-casting. Panel being lifted as shown in Figure 3.8

Figure 3.8 lifting a precast diaphragm panel

There are two mechanical connections between panels and the timing of the use of cementation slurry to surround the precast unit and support the subsoil:

 Soletanche's Pansol method:

The panel is dug under cementations slurry containing retarding and regulating additives, the slurry being removed without difficulty from the smooth face of the wall during bulk excavation of the site. Slurry between the rear face of the precast panel and the subsoil remains permanently as an inert filler material between wall unit and subsoil, the final strength of the set slurry being designed to exceed neighboring soil strength.

 Bachy's Prefasil method:

The panel is dug under a conventionalbentonite mud which is later displaced by the introduction of a cementations grout just before the precast unit is positioned in the panel excavation. It gives

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flexibility in site operations, allows a wide range of grout strengths to be used, is particularly convenient when large vertical loadsare being carried by the panels, and the process also avoid risk of contamination of the grout bysoil during the excavation process.

The methods of panel connection for the Soletanche system are shown in Figure 3.8 where types (a) and (b) are standard joints ; types (c) –(e) use temporary metal guides; types (f) and (g) use preformed water bars (courtesy of Soletanche).

Figure 3.8 horizontal cross section jointing detail

The technique used by Bachy.Shown in Figure 3.9 where

Joint type (a) uses a preformed water bar, type (b) uses a reinforcing key, and type (c) uses grout only (courtesy of Bachy)

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13 3.3 POST-TENSION DIAPHRAGM WALL

The feature of post-tension is that stressing of the panel is undertaken before bulk excavation

is carried out. Figure 3.11 shows examples of post-tensioned diaphragm wall and while the wall panel is fully embedded. Tendon forces and eccentricities are calculated on

loading on the final structure with no tension across the concrete section, the panel movement during stressing being minimized by the surrounding soil, the soil restrain varying between full passive pressure and earth pressure at rest. The cable profiles for a cantilever wall and a propped diaphragm wall are shown in Figure 3.10, shows earth pressure, bending moments and stresses in a typical wall unit before removal of the surrounding soil, the applied to the wall section by the prestressing force being effectively reduced by the soil stiffeners preventing tension developing a cross the section due to pre-stress.

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14 Max prestress (N/mm2) b (m) h (m) H (m) Type Site 3.6 60 2.7 7.0 A Centrale PTT Bellinzona 3.5 80 5.10 7.6 A Admiral SA,Paradiso 3.1 90 5.70 9.6 A German Embassy, London 3.7 80 6.20 13.2 B ETA-WerkeGrenhen 3.6 60 4.60 11.6 C Propr.Fabriane, Lugano 2.1 80 -15.0 C Centrale TT , Moralto

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15 3.4 SECANT PILES WALL

Secant piles wall can be both temporary and permanent wall for excavation. Usually secant piles wall is used in stiff soil and lower water table. The advantages of secant piles wall are lower cost and speed in construction for temporary or permanent wall where drilling conditions are conducive as shown in figure3.12. The system has higher capacity to overcome obstructions like rock compared to other system. However additional works are needed to form an acceptable surface to the wall.

Figure 3.12 secant pile wall 3.4.1 Construction of Secant Piles

Secant pile walls are formed by constructing intersecting reinforced concrete piles as shown in Figure 3.13.The piles are reinforced with either steel rebar or with steel beams and are

constructed by either drilling under mud or angering. Primary piles are installed first with secondary piles constructed in between primary piles once the latter gain sufficient strength. Pile overlap is typically in the order of 3 inches (8 cm). In a tangent pile wall, there is no pile overlap as the piles are constructed flush to each other.

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16 3.5 THIN DIAPHRAGM WALLS

This kind of diaphragm wall has been formed by ramming steel sheet panels into the soil as shown in Figure 3.14.. The hollow cavity created when extracting the profiles is filled under pressure with a special building material. The overlapping sequencing of these elements creates a sealing barrier in the subsoil, as is often used in damming for flood protection.

Figure 3.14 thin diaphragm wall 3.5.1 Thin diaphragm wall building materials

Thin diaphragm wall building materials are mixes comprising cement, limestone filler and bentonite. Due to the procedure, these materials are required to exhibit a very much higher density (high specific gravity) by comparison with diaphragm wall building materials. Thin diaphragm wall building materials are also available as ready-to-use dry mixes.

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CHAPTER 4

OBSTACLES OF CONSTRUCTION

Diaphragm wall construction is to use the Trench equipment on the ground, under the action of the Slurry Wall, along the perimeter of deep excavation, excavation of a narrow groove, placing the reinforcement cage in the tank and pouring concrete, building into a reinforced concrete wall construction process.

Diaphragm Wall technology, complex, into the wall can be divided into by: pile row type, tank plate, combined, according to excavation: The underground continuous wall,

underground cutoff wall. Underground continuous wall has many advantages, such as

stiffness, both retaining and retaining, the construction of no vibration, low noise, can be used for the construction of any soil, but the construction of high cost and technical complexity.

4.1 TYPES of OBSTACLES

Diaphragm wall construction including: guide wall construction, steel cage production, production and control of the mud, into the slot, the next locking pipes, reinforced steel cage and lower cage dipping, pulling locking pipe and other PROCESSES.

4.1.1 The Guide Wall Construction

Guide wall construction of diaphragm wall construction is the first step, it is the role of retaining walls, storage, mud, play a significant role on the chamfer. Guide wall

construction generally the following problems.

4.1.1.1 Guide Wall Deformation

The main reason this occurs is the guide wall did not increase after construction of the vertical support; lateral stability deficiencies occurred guide wall guide wall deformation.

Solution

After form removal guide wall, 1m intervals along the vertical guide wall located two Cricket support, will be supported by two guide wall up in the guide wall did not meet the design strength of concrete before the heavy machinery in the guide wall against the side of road, to prevent guide wall deformation.

4.1.1.2 Guide And Inner Wall Are Not Parallel To The Axis

Conduction within the wall of the diaphragm wall and not parallel to the axis of the wall will cause the diaphragm wall does not meet the design requirements.

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18 Solution

Be sure to ensure the guide wall centerline axis coincides with the underground

continuous wall, inside and outside the guide wall clearance should be equal to the design of diaphragm wall plus the width of 50mm, spacing error is less than 5mm. Guide wall and outside wall vertical.

4.1.1.3 Guide Wall Backfill.

Backfill easy to collapse, resulting in dorsal hollow guide wall, increasing the amount of concrete square.

Solution

Use a small dug-based guide wall excavation, backfilling earthwork to reduce, and then instead of using plain miscellaneous fill backfill soil.

4.1.2 The Production of Steel Cage

The production of steel cage construction of diaphragm wall is an important part of the reinforcement cage making a direct impact on the speed of construction progress. Reinforcement cage made of the following general problem.

4.1.2.1 The Progress of Issues

Affect the speed of the reinforcement cage made many factors, such as by site conditions, construction site does not allow setting the two steel production platforms, and when entering the rainy weather, the welding class can only stop the construction.

Solution

the construction site conditions can be set to alternate operation of two construction platform. To ensure that one day one of the construction progress. When entering the rainy days, you can use sub-erection of scaffolding and color steel shed, the welding in the shed construction, to be reinforcement cage can be directly used to use when hanging from the crane shed

4.1.2.2 Welded Steel Cage

As the heavy workload and lack of concentration and other workers, will cause steel joint dislocation, and many joints after welding is still in the high-temperature weak state, in the handling or stacking will not pay attention to, it will reinforced joints caused by stress and deformation.

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this problem is mainly caused by man-made, thus enhancing the technical management and improve the quality of construction workers, the problem can be completely resolved.

4.1.3 Production and Control of Slurry

Mud production is the key to underground continuous wall if making bad mud, the surface of the tank wall cannot form a layer of solid granular cements Ying (slurry) and loss of

adhesion. Slurry liquid column pressure will result in the same time, cannot Soil excavation SLOT balance inside and outside wall of earth pressure and water pressure, leading to instability in maintaining vessel wall, causing landslides.

Solution

According to hydro geological data, the use of bentonite, soda ash and other raw materials, prepared by a certain percentage as mud. Slurry production process should also note the following issues

 the use of mud slurry timely indicators of the state inspection. Slurry of recycled tests for determining if time will cause deterioration in the quality mud

 Mud convergence of production and project as a whole. The new preparation of the slurry should be placed in the pool fully fermented be put into use.

 The amount of slurry produced by the general to the specific side mixing amount of 1,5 times the theoretical side more appropriate

4.1.4 Diaphragm Wall Trench Construction

Diaphragm wall trench construction is an important part. Mainly into the slot machine construction, slurry liquid level control, low clearance, brushes the wall and so on.

 Into a slot machine construction. Into a slot machine is the most important issue in the construction bias problem.

 Liquid level control and ground lift mud. In the process into the slot and should be carried out after the slurry liquid level control, when faced with rain and so the rapid rise in the groundwater, the need to control the movements of underground water, if not handled the wall will affect the quality of a good groove. or even collapse.

 The work of clearing at the end. Ching result of low sediment is not too much time, will cause the concrete diaphragm wall reduces the strength, steel cage floating, affecting its capacity as water seepage, it can lead piping. At the same time too much sediment will affect the steel cage the sinking.

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 Brush the wall. If the brush is not timely may result in the wall between the two walls there are the earth, will have serious leakage, the integrity of underground continuous wall.

Solution

The rapid rise in groundwater level, it can reduce some or all of the groundwater. Or raise the mud surface, to at least 0.5-1.0 meters above the water table to ensure the vessel wall stability. Moreover, you should do the work of technical tests , correct attitude towards the construction workers, in a timely manner and brush the wall with low clearance work

4.1.5 The Delegation of The Reinforcement Cage Lifting

 Steel cage lifting. Steel cage in the dipping process, because the central lifting point does not coincide with the trough section of center steel cage will deform.

 Decentralization of reinforcement cage. Tank requirements or substandard vertical slurry leakage and other reasons, the reinforcement cage of concrete blocks in the lower levels encountered, resulting in elevation of the reinforcement cage around inconsistency or lateral

Solution

technical personnel to operate carefully, to ensure the absolute safety of lifting steel cage, steel cage to the lower levels, to make the center line of the reinforcement cage and the slot segment overlap as much as possible the vertical axis. In addition, make sure to compact the backfill slurry leakage prevention.

4.1.6 Pulling Locking Pipe

Pulling locking pipe must to time, when the concrete did not freeze when operating, will cause plasma leakage at the bottom of the wall, this time locking tube if not dense backfill, concrete pipe will bypass the locking, the next one the construction of diaphragm wall caused great obstacles.

Solution

Mastering the initial setting time of concrete, concrete at the conclusion of the use of hydraulic jacking frame pulling locking pipe.

4.1.7 Leaks in Construction

When making underground structures using diaphragm walls, leaks can arise at the joints between the diaphragm wall panels as shown in figure 4.1. Also in the diaphragm or wall

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panels themselves, as a result of problems when casting the concrete there may be pockets of gravel that can cause leaks in a construction pit. And after the diaphragm wall is completely excavated and a floor has been cast then there may be leaks at the connection of the floor to the wall as a result of the high water pressure.

B&W Grondinjectie has extensive experience in solving these problems using injection and therefore also guarantees the solution to every type of leak in diaphragm walls.

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CHAPTER 5

TYPES OF MACHINES

There are different types of machines will mention as follow:

5.1 SERIES HYDRAULIC DIAPHRAGM WALL GRAB

The Hydraulic Diaphragm Wall Grab which shown in figure 5.1 can be used in the deep pit wall of subway, underground works, garage and street, as well as in underground

transformer substation and high building's basement.It especially can be used in deep pit wall in dense buildings of cities.

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5.1.1 Working Principle of hydraulic diaphragm wall grab  Making guide wall.

 The machine digs along the guide wall; and at the same time, using inclinator to measure the verticality.

 Adjust the grab verticality to keep the wall precision

 Slurry should be used to prevent wall collapse

 And finally clean the wall bottom, place the cage and then concrete the cement

5.1.2 Features of hydraulic diaphragm wall grab

 Low vibration and noise, so it can also work during night

 Electron detector, inclinometer and hydraulic push-plate are equipped to control the depth and verticality.

 High wall strength: thus the walls can bear huge side pressure and avoid groundsill sinking and landslip.

 Good penetration resistance.

 Cost Saving: functions like soil retaining, water stealing and weight bearing, etc are all integrated.

 Can be used as the rigid foundation to replace shafts, and other foundation. 5.2 SHELL GRAB (MECHANICAL GRAB APPLIED in OVERHEAD CRANE)

Mechanical grabs are the best solution to excavate diaphragm walls in all soil conditio ns up to soil hardness of 70 mPA as light chiseling work is possible. The SWG series of diaphragm wall grabs is available with grab extensions for a total length of 10 or 12 m and also with extra ballast to reach a total weight of up to 22550 kg for even the most demanding projects.

Jaws may be rectangular or round shape. Jaws, ropes, pulleys and different teeth can be quickly replaced on site without any problems As shown Figure 5.2. All rope and guide pulleys have adequately dimensioned, maintenance-free bearings filled with grease. We also supply hydraulic diaphragm wall grabs with inclination measuring and monitoring systems to guarantee a verticality of the diaphragm wall of 1: 800. The recorded data of the complete excavation procedure can be stored and printed out for further use.

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The grab is widely used in ship, port, railway station, factory, mine and other transport departments. It is an ideal tool in handling bulk cargo such as coal, ore powder, fertilizer and sand.

Figure 5.2 shell grab 5.2.1 Features of Shell Grab

 Grab Advantages: Simple structure, good performance, high productivity.

 Grab's capacity 3 cbm to 30 cbmwith reducing capacity system.

 Supplied with removable spill plates, giving the capability to work light and heavy cargos with the one grab.

For quotation of grab, there are detailed informations as following:

 Capacity and volume.

 Application.

 Handling Material

 Working Temperature..

Double Rope Clamshell Grab Single Rope Bulk Grab Figure 5.3 Mechanical graps

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25 5.3 Diaphragm Wall Hydromill Grap

The hydromill which shown in figure 5.4 is a hydraulically operated excavating machine which operates on the principle of reverse circulation. The cutting chains are used to transfer the power of the motors (positioned in the upper section of the Hydromill body) to the cutting wheels.This system utilized exclusively by the CasagrandeHydromill, insures a continuous cutting impact along the entire width of the excavation, increasing productivity, especially, when excavating hard/very hard and difficult geological formations. The Hydromill chain cutting system modified to form a key joint into the concrete (removed from the primary panels), greatly improves the verticality control while insuring a more efficient overlapping between panels.The “key joint” system may be used, if specified by engineers and owner, as an extra requirement to insure a superior (structural and waterproof) final wall result.

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The submersible pump

A powerful submersible pump mounted above the mill wheels conveys the soil/rock cuttings together with the trench support fluid to the surface and then to the desanding plant.

The long guide

A long guide frame is fitted on top of the cutting wheel assembly to steer the machine down the diaphragm wall trench. The guide frame incorporates a series of trim plates (optional) with which adjustments can be made to the machines inclination in order to maintain the desired verticality. The guide frame also incorporates the electronic control instrumentation and the descent control cylinder (optional) which enables the operator to vary the pressure on the cutting teeth so as to optimize their efficiency in the different soils which are encountered along the excavation.

The power pack

The hydro mill may be powered directly off the support crane’s hydraulic system if this has sufficient capacity; alternatively it may be driven by an independent power pack, mounted to the base carrier.

The instrumentation

Excavation with the hydromill is a continuous operation which is free of vibration; this characteristic makes the machine ideal for instrumentation. The Casagrandehydro mills are therefore fitted with a full set of instruments which measure and transmit to the operator or to a remote station, parameters such as: the cutting wheel torques and speeds; the weight acting on the cutting wheels, the performance of the fl using pump; the depth of the machine and its inclination on two axes.

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CHAPTER 6

COLLAPSE OF SLURRY TRENCH DURING CONSTRUCTION

Primarily, it is the fluid pressure of the slurry in combination with arching in the ground that maintains trench stability in cohesion less soil. In addition, some local penetration into the pervious, soil will impart cohesion to the soil and will prevent spalling. The bentonite slurry in the trench is maintained at a higher elevation than the surrounding ground water table. By a combination of hydrostatic pressure, osmotic pressure, and electrolytic properties of the colloid, a membrane or “mud cake” forms against the walls of the trench. The effect of this “mud cake” is to prevent fluid loss and to maintain the fluid pressure against the trench wall

6.1 SLURRY TRENCH STABILITY  Fluid pressure + arching in the ground.

 Local penetration of the slurry into pervious soil imparts. Cohesion to the soil and prevents spalling.

 Bentonite slurry is kept higher than the ground water table.

 Hydrostatic pressure, osmotic pressure, electrolytic properties of the colloid, membrane or (mud cake) forms against the walls of the trench.

 Electro – osmotic phenomena, migration of colloidal particles to the trench wall by electrical potential at the slurry, soil interface.

 Penetration of slurry into cohesion less soil, forming of the mud cake by seepage force affected by the depth and permeability of the soil.

6.2 STABILITY ANALYSIS  Fluid pressure + arching.

 Analysis mostly based on experience.

6.2.1 Stability of Unsupported Trenches

There are stability takes place in case of cut in clay soil due to cohesion properties which it has by resisting earth pressure. Figure 6.1 shows (a) section through cut (b) Horizontal earth-pressure diagram

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Figure 6.1 Stability of unsupported trenches 6.2.2 Stability of Slurry- Filled Trenches in Clay

As shown in figure 6.2 Stability takes place between slurry pressure, earth-pressure and soil cohesion in clay soil.

Figure 6.2 Stability of slurry- filled trenches in clay 6.2.3 Stability of Slurry- Filled Trenches in Dry Sand

As shown in figure 6.3 Stability takes place between slurry pressure and earth-pressure in sand soil.

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6.2.4 Stability of Slurry-Field Trenches in Sand W/Water

As shown in figure 6.4 Stability takes place between slurry and earth-pressure in sand W/water

Figure 6.4 Stability of slurry-field trenches in sand W/Water 6.3 MUD CAKE

The extent of fluid penetration into the soil voids depends upon the permeability of the soil and the properties of the colloid. 'With very pervious soils such as sands and gravels, having permeability greater than 10 Am/set, there could be free penetration of the slurry into the soil without the formation of a “mud cake”. With soil shaving permeability between low2 and lb -1 cm/set, there may be some time lag associated with the development of an impervious “mudcake”.With soils having permeability less than 1V2cm/sec, the depth of penetration for formation of an impervious “mud cake” is minimal and there is essentially no time lag (Hutchinson, 1974).

With impervious soils, such as clay, the bentonite need not form a “mud cake” because the clay itself is essentially impermeable. In these cases the bentonite protects against fluid loss through pervious seams that may be interbedded within the parent clay formation.

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30 6.3.1 Effects of Mud (filter) Cake on Sand

Figure 6.5 Effects of mud (filter) cake on sand 6.4 Arching

In order to understand arching, the redistribution of stresses away from plane strain conditions, two conditions must be examined:

 The strain conditions at great depth below the surface.

 The strain conditions near the surface.

At great depth, strain is essentially two-dimensional condition acting in the horizontal plane outside the influence of Local conditions. Horizontal strain is less near the ends of the panel thinner the center of the panel. As a result, load concentrates at tends of the excavated panel, thus relieving the stress condition near the center and improving stability. The very top of the trench is restrained by a guide wall which is used to align the excavation and to introduce circulated slurry.

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So that arching develops in the vertical plane. Arching also occurs in -the horizontal plane. Experience has shown that a rigidly placed guide wall is an extremely important element in maintaining the stability of the top part of the trench.

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CHAPTER 7

DESIGN OF DIAPHRAGM WALL

This chapter addresses the key design items of earth and water pressure on a vertical wall and the analysis of the wall to resist these pressures. Cantilevered, single anchored and multi-anchored walls represent the different systems of diaphragm walls.

7.1 EARTH PRESSURE

Mohr's circle of stress can be used to illustrate graphically the horizontal soil pressures which can be generated in active or passive states at either side of retaining wall.The problem of assessing earth pressures can be solved using the coulomb equation for shear strength

(τ′ = C′+ϭ′ tanφ′) Where:

C′ represents effective soil cohesion. ϭ′ represents effective vertical stress.

φ′ represents the angle of shearing resistance in terms of effective stress.

Mohr's circle is seen to touch the failure envelope to give values in the extremes of minimum and maximum horizontal stresses. The active and passive earth pressure according to horizontal stress is less than or greater than vertical stress.

Where:

Ϭ′ҥ=Ҡa* Ϭ′ѵ&Ϭ′ҥ=Ҡp* Ϭ′v

Ҡa =(1-sin φ′)/(1+sin φ′) &Ҡp =(1+sin φ′)/(1-sin φ′)

7.1.1 Calculation of shear strength parameters (τ′, c′, φ′) 7.1.1.1 For cohesion soil

The values of C′ and φ′ from drained triaxial tests or undrained tests with pore-water pressure measurement as shown in fig 7.1.The effects of stress level, rate of strain for testing, the degree of weathering and of sample swelling before the test, will all influence the test result.

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Figure 7.1 trixial text 7.1.1.2 For cohesion less soil

The values of (φ′) based on in situ tests where possible. The relationship between standard penetration resistance and (φ′) in shown in Fig7.2.

Figure7.2 Relationship between standard penetration resistance and φ′

7.1.1.3 for rocks

Table7.1 gives approximate values for the effective angle of shearing resistance of soft rocks considered.

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Table7.1 Approximate values for the effective angle of shearing resistance of soft rocks φ′ Stratum 35 Chalk 2 Clayey marl 33 Sandy marl 42 Weak sandstone 35 Weak siltstone 2 Weak mudstone

7.1.2 Lateral earth pressure calculation

7.1.2.1 Lateral earth pressure based on long-term, drained, effective stress values.

Active and passive earth pressures acting on the wall at depth (Z) given by: P'a=Ҡa* Ϭ′ѵ= Ҡa(γz+q-u)&P' p=Ҡ p * Ϭ′ѵ= Ҡ p (γz+q-u)

And for a soil with cohesion intercept P'a=Ҡa*Ϭ′ѵ=Ҡa(γz+q-u) - 2 C′(Ҡa)0.5

&P' p =Ҡ p*Ϭ′ѵ=Ҡ p (γz+q-u) +2 C′(Ҡp)0.5 Where:

γ is the bulk soil density.

q is the surcharge on ground surface. U is pore-water pressure.

These values known as Rankin values.

The pore-water pressure is added to the effective lateral earth pressure to give the sum of earth and water pressure

Pa = P'a+U&Pp = P' p + U

7.1.2.2 Lateral earth pressure based on short-term undrained stress values.

In terms of undrained conditions Active and passive earth pressures acting on the wall at depth (Z) given by:

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Pa=Ҡa* Ϭѵ = Ҡa(γz+q) &Pp=Ҡp* Ϭѵ = Ҡp (γz+q)

7.1.3 Water pressure

Average hydraulic pressure at toe (B): U = (U1+U2)/2 > UB

HYDRAULIC PRESSURES: U1 = (d-i)*γW

U2 = (h+d-j)*γW Steady seepage:

In case of uniform dissipation of head difference along the flow path adjacent to the wall UA = (2(d-i)(h-j+i))/(2d+h-j-i)

UB = (2(d-i) (d+h-j))/(2d+h-j-i)

7.2 DESIGN OF DIAPHRAGM WALL

In the design of earth retaining system for deep excavation, it requires both ultimate limit states and serviceability limit states to be considered. An ultimate limit state of a structure is seemed to have been reached when sufficient parts of the structure, the soil around it, or both have yield to result in the formation of a failure mechanism in the ground or severe damage in the principal structural components. A serviceability limit state of a structure is seemed to have been reached with the onset of excessive deformation or deterioration.

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7.2.1 Design of Cantilever Wall (Free Earth Support)

Fully fixity must be obtained to prevent a rotation and collapse of the wall .the penetration depth is control the fixity. Certain simplifying assumptions are made due to the relative complexity of the calculations.Fig7.4 shows an actual pressure diagram , shear, bending moment and wall deflection diagrams.

Figure 7.4 stresses affect on cantilevered diaphragm wall

Design procedure

1) Ʃ Ma = zero to Find (Penetration depth). 2) Find Point of zero shears.

3) Find max bending moment (Mmax ) at point of zero shear 4) Actual penetration depth = 1.4*(calculated penetration depth).

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37 7.2.2 Design of Hinged Single Anchored System

Fully fixity must be obtained to prevent a rotation and collapse of the wall .the penetration depth anchored system is control the fixity.

1) Ʃ Ma = zero.

2) Ʃ H = zero EP+T- Ea=0. 3) From 1, 2 find D, T. 4) Find Point of zero shear.

5) Find max bending moment (Mmax ) at point of zero shear.

Fig 7.5 shows an actual pressure diagram and shear, bending moment and wall deflection diagrams.

Figure7.5stresses affect on hinged single anchored diaphragm wall 7.2.3 Design of Fixed Single Anchored System

This structure can be subdivided into two parts (AB & BC). AB part can be solved as cantilever.

BC part can be solved as single anchored free earth support

Fig 7.6 shows an actual pressure diagram and shear, bending moment and wall deflection diagrams.

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Figure7.6stresses affect on fixed single anchored diaphragm wall

7.2.4 Design of Multi-prop System

For deep excavation, usually the multi-anchored walls are used instead of cantilever or singly supported walls. The design requirements and analyses for multi-anchored walls are different from cantilever or singly supported wall. The earth pressures that act on multi-level strutted walls or multi-multi-level tied-back walls depend on the wall stiffness relative to the soil, the support spacing and the acting pressure. The method of construction of these walls is usually sequential, installing the wall and excavation in stages followed by installation of support like anchor or prop at each installation stage. The available methods for analysis and design of multi-level supported walls can be categorized as follows:

A. Empirical method

Usually based on strut load envelopes recommended by Terzaghi and peck (1967) or peck(1969) for three categories of soil: sands, soft to medium clays and stiff clays.

a) For sand

Sands are assumed "drained". If no permeable wall is used, hydrostatically distributed water pressure should be added to strut loads. Wall can be designed using the Coulomb earth pressure distribution with hydrostatic water pressure except full drainage occurs through the wall.

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Pt = .65*Ka*γ*H2 → empirical value pA = .5*Ka*γ*H2 → exact value pt/pA = 1.3

Figure 7.7 Empirical method in sand soil

b) For soft to medium clays

Clay is assumed "undrained" and only considers total stresses.

Pt = . 75*γ*H2

(1-4/N) PA = .5*γ*H2(1-4/N) Pt/PA =1.75

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40 c) For stiff clays

Pt = .15*γ*H2

to .3*γ*H2 PA/N = 4 PA = 0 N4 PA4

Figure 7.9 Empirical method in stiff clay

Gue and Tan (1998) observe that for anchored diaphragm walls in Kenny Hill residual soils in Kuala Lumpur, the apparent lateral earth pressures that were obtained from the load cells indicated that for anchors at depths greater than 60% of the maximum excavation depth of more than 20m, the apparent earth pressure obtained is larger than the values suggested by Terzaghi& Peck (1967).

B. Beam spring approach (beam on elastic foundation)

The earth pressures are modeled with a series of independent spring supports similar to Winkler elastic foundation model. At the start of the model, the springs are compressed to create an initial load equal to represent a state of at-rest pressure. At each stage of excavation or support system, the spring loads change as soil, water, and support system loads are applied or removed and lateral wall displacement occurs. The soil springs load-displacement relationship (modulus of subgrade reaction) is determined by the input soil stiffness and governs the spring displacement until the limiting value of active or passive pressure is reached.

The Winkler elastic foundation model approximates the wall-soil interaction with a one-dimensional model instead of a two-one-dimensional model that includes the soil mass, and hence doesn't include the effects of arching within the soil mass.

Typically, the required soil parameters include: unit weight; at-rest, active, and passive earth pressure coefficients; and values for the modulus of subgrade reaction for the various soils

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that may affect the system. The modulus of subgrade reaction is not a true soil property, but rather depends on both the soil conditions and the geometry of the excavation being modeled. To be representative, the modulus of subgrade reaction needs to be adjusted based on the effective influence zone, which varies with the size of the loaded area.

Typically, the predicted wall displacements are much more sensitive to the values of sub grade modulus used in the analysis than the predicted brace loads and wall bending moments. Hence, conservative selection of the modulus of subgrade values should provide conservative estimates of ground movements, without significantly increasing the structural demand of the wall and bracing system.

C. Soil-structure interaction method (Finite Element method)

This method will be able to model wall and soil deformation and stress in realistic stages of operations that follow actual construction sequence. Pre-judged failure modes are not required in the analysis. This method can be carried out in two or three-dimensional depending on the computer codes used. Usually two-dimensional is sufficient.

This method is particularly useful in predicting deformations of wall and soil for serviceability checks especially there are deformation sensitive structures around the excavation. Use of soil stiffness at low strain value is essential in this approach. Tan (1997) has presented correlation to acquire the stiffness of Kenny Hill residual soils at low strain. Some of the computer packages in this category include Finite Element program CRISP90 (Brittoand Gunn, 1987) and Plaxis, and the finite difference package FLAC (ITASCA, 1991).

Comparison of BEF and FE Results

For the United States Capital Visitor Center (Pearlman et.al. 2004 and Bonita (2005)), the analyses for the structural design of the support system were performed using both BEF and FE models The BEF program (WALLAP, 1997) was easier and quicker to run than FE programs, so it was used for the structural design of the wall system by using the BEF model, the design team could evaluate more design profiles FE models were run to verify that the BEF model loadings and stresses were conservative and to provide ground deformation predictions.

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42 7.3 ULTIMATE LIMIT STATES

The check on the ultimate limit states of the wall includes check on the following: A. Overall Stability the provision of sufficient embedment depth to prevent

overturning of the wall and overall slope stability.

B. Basal Failure the wall penetration depth must be sufficient to prevent basal failure in front of the wall after excavation to formation level.

C. Hydraulic Failure the penetration of the wall must be sufficient to avoid piping or

blow out' in front of the wall after excavation to formation level 7.3.1 Overall Stability

The overall stability of both retaining walls is often evaluated using limit equilibrium methods of analysis in which the conditions of failure are postulated, and a factor of safety is applied to prevent its occurrence. There are a number of ways of applying the factor of safety for the overall stability. They are:

a) Factor on embedment:

A factor of safety is applied to calculate embedment depth at limiting equilibrium. The method is described in the US Steel Sheet Piling Design Manual (United States Steel Corporation, 1975), the British Steel Corporation Pilling Handbook (1988) and by Symons (1983).

b) Factor on moments of gross pressure:

This method applies a factor of safety to moments of gross pressure on the passive side only. Water pressure is not factored. The method is described in NAVFAC Design Manual 7.2 by US Navy (1982).

c) Factors on moments of net total pressure:

The net horizontal pressure distribution acting on the wall is calculated and the factor of safety is defined as the ratio of moments of the net passive and active forces.

d) Factors on net passive resistance or Potts and Burland Method

Developed by Potts and Burland (1983) and is analogous to the calculation of the bearing capacity for a strip load. This method defines the factor of safety as the ratio of the moment of the net available passive resistance to the moment activated by the retained material

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including water and surcharge.

e) Factors on shear strength on both active and passive sides:

Soil shear strengths are reduced by dividing c' and tanφ′ by factor of safety, and the active and passive pressure diagrams are calculated using these reduced values. The reduced values approximate to mobilized values. Bending moments and prop loads derived from the calculation can be used for wall design if they are treated as ultimate limit state values. This method is recommended in BS8002, 1994.

f) Factor on shear strength of passive side only:

The passive resistance is factored but no factor is applied to the active side.

Comparative studies show that there is no relationship between factors of safety applied to methods listed. There are little that the preferred method is really defined by personal use and experience, but some useful observations were made as follows:

 The factor on embedment is empirical and should be checked by applying a second method (Factor on moments of gross pressure).

 The method of factoring moments on gross pressure may give excessive penetration at low angles of shearing resistance (φ′ less than 20 ), so use varying factors for different ranges of φ′ .

 The factoring of net passive pressure moments tends to give high penetration values.

 The factors on modified net passive resistance give consistent results in a reasonable range of soils and wall dimensions.

Factors of safety recommended by Padfield and Mair for use in stiff clays with methods for factoring embedment, moments of gross pressure, net passive resistance, shear strength on both active and passive sides, are produced in table 7,2.

Two approaches are used:

 Approach A is based on moderately conservative parameters.

 Approach B uses worst credible soil parameters, geometry and loading in design .while applying to stiff clays, the factors of safety listed can also be taken as indicative values in granular soils.

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Table 7.2 Factors of safety for methods of analysis embedment (Padfield and Mair)

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45 7.3.2 Basal Heave Failure

Usually base failure to an excavation by upward heave applies particularly in very soft and soft clays and silty clays.Stiff soil less prone to encounter this problem. The basal heave failure is analogous to a bearing capacity failure, only in reverse being that stresses in the ground are relieved instead of increased.

There are many methods to examine the basal heave failure and may be broadly divided according to basic concepts such as those based on bearing capacity formulae and those based on examination of moment equilibrium. It is recommended that in the design, both methods are to be used for basal heave check.

A) Method based on Bearing Capacity Formulae:

The first method based on bearing capacity formulae are presented by Terzaghi (1943) for shallow and wide excavation shows in Fig 7.10.

The second method introduced by Bjerrum&Eide (1956) is suitable for deep and narrow excavations shows in Fig 7.11.

Both methods neglect the effect of wall penetration below foundation level and results may be conservative especially where stiffer clays exist with depth

Diaphragm Wall

DIAPHRAGM

WALL

Prepared by

Ahmed Saad El-Deen El-Sayed

Mahmoud Atta Ragab

Moustafa Atef Goda

Sabah El-Sayed Ahmed

TABLE OF CONTENTS

LIST OF FIGURES

LIST OF TABLES

CHAPTER1

INTRODUCTION

CHAPTER 2

SOIL RETENTION

CHAPTER 3

DIAPHRAGM WALL SYSTEMS

CHAPTER 4

CHAPTER 5

The submersible pump

The long guide

The power pack

The instrumentation

CHAPTER 6

CHAPTER 7