Chapter 3 Retaining wall and Retaining Systems.pptx

retaining wall is a structure designed to hold back or retain soil, rock, or other materials at different elevations on the two sides of the wall. Retaining walls are commonly used to prevent soil erosion, stabilize slopes, and create usable spaces in hilly or uneven terrain.

1. www.huawei.com Geotechnical Engineering Design - I I Chapter 3 Retaining Systems By: Fenta Nebiyou (MSc. in Geotechnical Engineering) 1

2. Lecture Outline 3.1 Introduction 3.2 Rigid Retaining Walls Gravity retaining walls Semi-gravity retaining walls Cantilever retaining walls Buttress retaining walls Counter-fort retaining walls Design of retaining walls P roportioning of retaining walls Stability Analysis Provide reinforcement, if required 3.3 Flexible Retaining Walls Sheet Pile Walls Braced Cuts 3.4 Mechanically Stabilized Earth (MSE) Walls 3.5 Shoring Pile 3.6 Cofferdams 2

3. Introduction The design and construction of retaining structures forms an integral part of many civil engineering projects. They comprise a number of elements and may restrain the soil by virtue of their mass , or because they are embedded, propped and/or anchored. To design a retaining structure it is necessary to understand the soil and its behavior, the ground water conditions, how wall is constructed and how the soil and the structure interact. 3

4. Introduction Retaining structures are structures used to provide stability of earth or other material where conditions disallow the mass to assume its natural slope . Common application of retaining structure include: Highway and railroad projects where the required grade is significantly above or below the ground and the right of way is not large enough to accommodate a slope Bridge abutments Building sites on sloping ground where earth retaining structures are used to create level building pads. Flood control activities Unstable ground, where the earth-retaining structures provide the needed resistance to prevent landslide . Retaining water under off-shore construction. As a basement wall 4

5. Types of Retaining Structures 5

6. Sample Retaining Structures 1 2 6

7. Sample Retaining Structures Gravity RW Counterfort RW Cantilever RW 7

8. Sample Retaining Structures Crib Walls 8

9. Gabion wall Sample Retaining Structures 9

10. Anchored Pile Walls Shotcrete Common in A.A tall buildings Sample Retaining Structures 10

11. In-situ Walls Sample Retaining Structures 11

12. Sheet pile wall (Cantilevered or Anchored) 12

13. Reinforced Earth and Soil Nailing & Shotcrete & Grouting [internally stabilized] 13

14. 3.1 Externally stabilized Retaining Walls (Rigid) 14

15. Common Types of Externally stabilized Retaining Walls 1.Gravity walls M ade of plain concrete or stone masonry. D epends upon its weight for stability . T rapezoidal in section with the base projecting beyond the face and back of the wall. N o tensile stress in any portion of the wall. E conomically used for walls less than 6m high. Wc Pp Pa Ws 15

16. Typical Gravity walls 16

17. 2. Cantilever walls Made of reinforced concrete material. Reinforcements takes tensile load & minimizes concrete volume as compared to Gravity Wall. Inverted T-shaped in section with each projecting acts as a cantilever. Economically used for walls 6 to 7.5m high . Vertical stem Heel Toe Wc Pp Pa Ws Base 17

18. Typical Cantilever Wall 18

19. 3. Counterfort walls: M ade of reinforced concrete materials C onsists of cantilever wall with vertical brackets known as counterfort placed behind face of wall O rdinarily used for walls height greater than 6.0m Counterfort 19

20. Typical Counterfort Wall 20

21. 4. Buttress walls S ame as counterfort except that the vertical brackets are on the opposite side of the backfill Vertical stem Heel Toe 21

22. Typical Buttress Wall 22

23. Proportions of Retaining Walls The usual practice in the design of retaining walls is assign tentative dimensions and then check for the overall stability of the structure. The soil properties on side and below foundation should be determined to determine BC & Lateral Earth Pressure. i ) Gravity Wall B = H/2 to ⅔ H 30cm to H/2 H D f = H/8 to H/6 l t = D f /2 to D f l h = 10 to 15cm 50 1 23

24. ii) Cantilever wall D f = H/12 to H/10 H b s = H/12 to H/10 Min. 30cm B = 0.4 to 0.7H 50 1 l t = B/3 24

25. 1 B = 0.4 to 0.7H Min. 30cm 50 D f = H/14 to H/12 H Min. 30cm l=0.3 to 0.6H iii) Counterfort wall bs = H/14 to H/12 25

26. Forces on Retaining Walls The forces that should be considered in the design of retaining walls include Active and passive earth pressures [Pa, Pp - from property of soil to be retained ] (Use Coulomb/ Rankine theory) Dead weight including the weight of the wall and portion of soil mass that is considered to act on the retaining structure (W1, W2, W3, W4). Surcharge including live loads, if any (q & P) Water pressure, if any (Pw) Contact pressure under the base of the structure ( q min, q max) Consider 1m in analysis & all loads are applied at centroid P q W1 W2 W3 W4 Pp Pa Pw GWT Pav Pah toe qmax qmin 26

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28. Stability of Retaining Walls A retaining wall may fail in any of the following ways : It may overturn about its toe . It may slide along its base. It may fail due to the loss of bearing capacity of the soil supporting the base. It may undergo deep-seated shear failure . It may go through excessive settlement. 28

29. Basic Requirements of Retaining Walls a. External Stability of Retaining Walls Retaining walls should be designed to provide adequate stability against Sliding , Overturning about the toe, Foundation bearing failure and Overall or deep foundation failure. 29

30. 1.Sliding stability Factor of safety = Factor of safety  1.5 for granular soils Factor of safety  2.0 for cohesive soils 30

31. Stability Cont… M aximum resisting force that can be derived from the soil per unit length of the wall along the bottom of the base slab is; 31

32. What if sliding stability is not satisfied? Fs<1- failure Extend the heel of the footing Add a key beneath the footing Use a stronger backfill soil Install tieback anchor Install tiedown anchor Stability Cont… 32

33. 2. Overturning Stability Factor of safety = Driving Moment = P ah * H/3 Resisting Moment ∑ M r about toe Factor of safety  1.5 for granular backfill Factor of safety  2.0 for cohesive backfill * Use table format to sum all moments 33

34. Overturning Stability Cont.… Using Rankine’s Theory The factor of safety against overturning about the toe that is, about point C 34

35. 3. Foundation Stability (Bearing Failure) Here, the base of the retaining wall can be treated as a strip foundation that is subjected to a line load, which can act eccentrically and with some inclination to the vertical . The resultant must avoid tension [foundation separation ]. The foundation must not be subjected to bearing capacity failure. It must not settle excessively. 35

36. Foundation Stability Cont…. Taking moments about C Treating the base of the retaining wall as a continuous foundation , using Meyerhof’s Bearing Capacity equation Generally, a factor of safety of 3 is required. 36

37. 4. Deep foundation failure ( Overall stability) If layer of weak soil is located within a depth of about 1 ½ times the height of the retaining wall the overall stability of retaining wall should be investigated. The failure surface may be assumed to have cylindrical shape and critical failure surface for sliding may be determined through analysis. If for sliding Fs> 1.5 this type of failure wouldn’t occur 37

38. Internal Stability [Structural Design] A trial section is selected & after satisfying external stability requirements structural design follows. Proper design of the retaining wall stem , heal and toe considering the ultimate and serviceability limit state criteria . Flexural & Shear Requirements 38

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40. Take as Fixed end Cantilever Beam & Draw SFD & BMD Thickness can be determined from V max Reinforcement can be determined from M max SFD BMD Vmax A S =100% M/2 Mmax A S =50% Net factored load Pressure on heel, toe or stem 40

41. Moment & shear capacity of concrete M = 0.32 * f cd * bd 2 V ud = 0.25f ctd k 1 k 2 b w d k 1 = ( 1+50  ) k 2 = 1.6 – d 41

42. Reinforcement cut AS=100% AS=50% Secondary Reinforcement Minimum reinforcement [per 1m] Pa Main Reinforcement Main Reinforcement H Secondary Reinforcement Minimum reinforcement 42

43. Construction Joints and Drainage [ every 1m fill concrete & compact before next ] 43

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45. Drainage of the backfill 45

46. Summary Major conditions have to be consider in design of retaining wall; Stability Strength Drainage Drainage facilities are provided in design of retaining wall; To reduce lateral earth pressure by eliminating or reducing pore pressure 46

47. Summary There are two phases of design in retaining wall: 1 st the LEP known, the structure as a whole is checked for stability , overturning , sliding , and bearing capacity failures. 2 nd each component of the structure is checked for strength , and the steel reinforcement . 47

48. Design Elements to Prevent Failure Relieve water pressure (for all 3 types of failure) Crushed stone Weeps Overturning Cantilevered Footing Reinforcing Sliding Key 48

49. Flexible Retaining Walls Sheet Pile Walls [ Sheet Pile Structures] 49

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52. Uses of sheet piles 52

53. W ooden sheet piles Used only for temporary, light structures that are above the water table. The most common types are ordinary wooden planks, which are about 50mm x 300mm in cross section and are driven edge to edge . (b) Precast concrete sheet piles Precast concrete sheet piles are heavy and are designed with reinforcement to with stand the permanent stresses to which the structure will be subjected after construction and to handle the stresses produced during construction. In cross section, these piles are about 500-800mm wide and 150-250mm thick. 53 Types of sheet piles commonly used in construction

54. (c) Steel sheet piles A re convenient to use because of their resistance to high driving stress that is developed when they are being driven into hard soils. And also they are light weight and reusable. They may be Z, deep arch, low arch or straight web sections. The inter locks of the sheet pile sections are shaped like a thumb and finger or a ball and socket for watertight connections Steel sheet piles are about 10-13mm thick . (d) Aluminum sheet piles are also marketed. The interlocks of the sheet pile sections are shaped like a thumb-and finger or ball-and-socket joint for watertight connections. 54

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60. Sheet pile walls may be basically divided into two categories: Cantilever Sheet pile and Anchored Sheet pile Generally, the construction methods can be divided into two: Backfilled the structure Sheet pile driven in to the ground and then backfill placed on the land side. b) Dredged structure Sheet pile driven into the ground and the soil in front of the sheet pile dredged. 60 Sheet pile Types and Construction methods

61. The sequence of construction for a backfill structure Step1. Dredge the in situ soil in front and back of the proposed structure Step2. Drive the sheet piles. Step3. Backfill up to the level of the anchor, and place the anchor system, Step4. Backfill up to the top of the wall 61

62. The sequence of construction for a dredged structure Step1. Drive the sheet piles Step2. Backfill up to the anchor level, and place the anchor system, Step3. Backfill up to the top of the wall, Step4. Dredge the front side of the wall. 62

63. General In either case, the soil used for backfill behind the sheet pile wall is usually granular. The soil below the dredged line may be sandy or clayey. The surface of soil in front of the sheet pile is referred to as mud line or dredge line. 63

64. Cantilever sheet pile walls Cantilever sheet pile walls are usually recommended for walls of moderate heights about 6m or less , measured above the dredge line. In such walls, the sheet piles act as a wide cantilever beam above the dredge line. Hydrostatic pressure at any depth from both sides of the wall will cancel each other ; the effective lateral soil pressures only considered. 64

65. 65 Cantilever sheet pile walls

66. A) Cantilever sheet pile penetrating sandy soils Figure: Cantilever Sheet pile penetrating sand: (a) variation of pressure diagram; (b) variation of moment 66

67. Step by step procedure for obtaining the pressure diagram Calculate K a and K p Calculate P 1 and P 2 (Note that L 1 and L 2 are given) Calculate L 3 Calculate P. Calculate Ž (i.e., center of pressure for the area ACDE) by taking the moment about E Calculate P 5 . Calculate A 1 ,A 2 ,A 3 ,and A 4 Solve eqn. by trial and error to determine L 4 Calculate P 4 Calculate P 3 Obtain L 5 Draw a pressure distribution diagram. Obtain the theoretical depth of penetration as L 3 + L 4 .The actual depth of penetration is increased by about 20 – 30% 67

68. It may be noted that some designers prefer to use a factor of safety on the passive earth pressure earth pressure coefficient at the beginning. In that case, in step1, K p (design) = Where F.S = factor of safety (usually between 1.5 and 2) For this type of analysis, follow steps 1-12 with the values of K a = tan 2 (45 – ϕ’/2) and K P (design) . The maximum moment will occur between point E and F’. Obtaining the maximum moment ( M max ) per unit length of the wall requires determining the point of zero shear. 68

69. B) Cantilever sheet piling penetrating clay 69

70. Step-by-step procedure for obtaining the pressure diagram ; Calculate K a for the granular backfill Obtain P 1 and P 2 Calculate P and Ž Use eqn.to obtain the theoretical value of D Using eq., calculate L 4 Calculate P 6 and P 7 Draw the pressure distribution diagram as shown in the Figure above. The actual depth of penetration is D actual = (1.4 to 1.6) D theoretical The maximum moment (zero shear) will be between (L 1 + L 2 )<Z<( L 1 + L 2 +L 3 ). 70

71. Anchored sheet pile walls/ anchored bulkhead When the height of a backfill material behind a cantilever sheet pile wall exceeds about 6m , tying wall near the top to anchor walls, or anchor piles become more economical. Anchors minimize the depth of penetration required by the sheet piles and also reduce the cross sectional area and weight of the sheet piles needed for construction. However, the tie rods and anchors must be carefully designed. The two basic methods of designing anchored sheet pile walls are : a ) The free earth support method and ( b) The fixed earth support method. 71

72. Figure; Nature of variation of deflection and moment for anchored sheet piles (a) free earth support method and (b) Fixed earth support method 72

73. A) Free earth support method for penetration of sandy soil 73

74. B) Free Earth Support Method for Penetration of Clay 74

75. Fixed Earth Support method for Penetrating into Sandy soil 75

76. 20 Introduction to Cofferdams

77. Cofferdams A cofferdam is a temporary structure constructed to divert water in a river or to keep away water from an enclosed area in order to construct a permanent structure such as a bridge pier. When construction must take place below the water level, a cofferdam is built to give workers a dry work environment. The word "cofferdam" comes from "coffer" meaning box, in other words a dam in the shape of a box. 77

78. Types of Cofferdams Earth ‐ Type Single wall Braced Double ‐ Walled Cellular 78

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86. Cell Fill 86

87. Advantages of Cofferdams 87

88. Types of Imposed Loads A typical cofferdam will experience several loading conditions as it is being build and during the various construction stages. The loads imposed on the cofferdam structure by construction equipment and operations must be considered, both during installation of the cofferdam and during construction of the structure itself. The significant forces are hydrostatic pressure, forces due to soil loads, water current forces, wave forces, ice forces, seismic loads and accidental loads. In order to over come the displaced water buoyancy, the seal thickness is about equal to the dewatered depth. 88

89. Types of Imposed … Cont’d Waves : due to wind, passing ships & boats. Ice Forces: due to static ice forces (the forces exerted by expansion of frozen water) and dynamic ice forces (the forces exerted moving ice. Seismic Loads: These have not been normally considered in design of temporary structures in the past. For very large, important, and deep cofferdams in highly seismically active areas, seismic evaluation should be performed. Accidental loads: These are the loads usually caused by construction equipment working alongside the cofferdam and impacting on it under the action of waves. 89

90. 34 Fig. Cofferdam- the inside part

91. Fig. Cofferdam for the Sidney Lanier Bridge, Oregon 91

92. Fig. Installation of wale and strut system 92

93. Fig. Installation of wale and strut system and driving the sheet pi l 3 e 7 s

94. 38 Excavation nearby structures Introduction to Braced Cuts

95. Braced Cuts Many building sites extend to the edges of the property lines. Under these circumstances, the sides of the excavation have to be made vertical and must usually be supported by bracings to avoid failure. Uses of braced cuts: To avoid considerable settlement or bearing capacity failure of nearby structure. To stabilize cuts To prevent water seepage into excavation

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97. Lateral Earth Pressure in Braced Cuts 40

98. Apparent Pressure Diagrams The pattern of deformation differs so greatly from that required for Rankine's state that the distribution of earth pressure associated with retaining walls is not a satisfactory basis for design. Peck (1969) presented pressure distribution diagrams on braced cuts. These diagrams are based on a wealth of information collected by actual measurements in the field. Assumptions :

99. Peck (1969) after a great deal of study of actual pressure measurements on braced cuts used for subways, he presented pressure distribution diagrams on braced cuts. Apparent Pressure Diagrams … Cont’d

100. Cuts in Stratified Soils It is very rare to find uniform deposits of sand or clay to a great depth. Many times layers of sand and clays overlying one another are found in nature. When layers of sand and soft clay are encountered , the pressure distribution shown in Fig(d) may be used if the unconfined compressive strength q u is substituted by the average q u and the unit weight of soils by the average value (Peck, 1969).

101. Design of Various Components of Braced Cuts 101

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107. Stability of Braced Cuts A braced- cut may fail as a unit due to unbalanced external forces or heaving of the bottom of the excavation. If the external forces acting on opposite sides of the braced cut are unequal, the stability of the entire system has to be analyzed. If soil on one side of a braced cut is removed due to some unnatural forces the stability of the system will be impaired. However, we are concerned here about the stability of the bottom of the cut. Two cases may arise. They are Heaving in clay soil & Piping in cohesionless soil

108. Heaving in Clay Soil The danger of heaving is greater if the bottom of the cut is soft clay. Even in a soft clay bottom, two types of failure are possible. Case 1: When the clay below the cut is homogeneous at least up to a depth equal 0.7 B where B is the width of the cut. Case 2: When a hard stratum is met within a depth equal to 0.7 B.

109. Case 1: Formation of Full Plastic Failure Zone Below the Bottom of Cut

110. Case 2: When the Formation of Full Plastic Zone is Restricted by the Presence of a Hard Layer If a hard layer is located at a depth D below the bottom of the cut (which is less than 0.7B), the failure of the bottom occurs as shown in the figure. The width of the strip which can sink is also equal to D.

111. Piping Failures in Sandy Cuts Piping is a phenomenon of water rushing up through pipe- shaped channels due to large upward seepage pressure. When piping takes place, the weight of the soil is counteracted by the upward hydraulic pressure and as such there is no contact pressure between the grains at the bottom of the excavation. Therefore , it offers no lateral support to the sheet piling and as a result the sheet piling may collapse. Further the soil will become very loose and may not have any bearing power. It is therefore, essential to avoid piping.

112. Piping Failures in Sandy Cuts … Cont’d Sheet piling is used for cuts in sand and the excavation must be dewatered by pumping from the bottom of the excavation. Sufficient penetration below the bottom of the cut must be provided to reduce the amount of seepage and to avoid the danger of piping.

113. Example 2.4 In trench excavation, the braced cut shown in figure is used. The struts are placed at 4 m horizontally. Determine the following: T he pressure on walls, T he strut loads, T he maximum bending moment in the wales, and T he maximum bending moment in the sheet piles. 113

114. Mechanically Stabilized Earth (MSE) Walls Mechanically stabilized earth (MSE) walls consist of facing elements, soil mass and reinforcement combined to form a composite solid structure. In a typical MSE wall, compacted granular soil is reinforced by horizontal layers of steel strips or geosynthetic materials. The use of reinforced elements significantly increases the strength of the system . Facing elements are relatively thin components, usually made out of pre-cast concrete, welded wire mesh panels or shotcrete. 114

115. 115 Mechanically Stabilized Earth (MSE) Walls

116. Their structural objective is to hold the soil between the reinforcement layers. A facing system enables the construction of a steep or even a vertical MSE wall . Soil material is also placed without a reinforcement between the stabilized zone and the natural surface of the ground . A complete MSE wall is a gravity-based structure. 116 Mechanically Stabilized Earth (MSE) Walls

117. It relies on its mass to bear the applied forces including lateral earth pressures, water pressures, seismic loads or loads related to human activity. MSE walls are cost-effective structures that may withstand larger total and differential settlements compared to concrete walls . Moreover, their construction is simpler and quicker as there is no need for support structures (e.g. scaffoldings) and curing time. They also exhibit high resistance in continuous and dynamic loads (e.g. earthquakes ). 117 Mechanically Stabilized Earth (MSE) Walls

118. Regarding the downsides of MSE construction, the wall must obtain a minimum width in order to acquire adequate stability. Moreover, the reinforced soil mass must consist of granular material which may be costly if it is not readily available. Finally, the reinforced component must be designed to withstand erosion and corrosion processes which can highly deteriorate the mechanical behaviour of the composite structure. 118 Mechanically Stabilized Earth (MSE) Walls

119. MSE Wall systems are designed for two categories: 1. External Stability (deals with composite structure) a. Sliding b. Bearing Resistance c. Overturning (Eccentricity) d. Overall (Global) Stability 2. Internal Stability (deals with soil reinforcement) a. Reinforcement Pullout (pullout from reinforced soil mass) b. Reinforcement Strength (tension rupture) c. Reinforcing to Facing Connection 119

120. The following wall facing systems and soil reinforcement types are most commonly used and can be accommodated by the MSE Wall Design; Wall Facing Systems: Precast Concrete Panels Modular Block (not to be confused with Prefabricated Modular Block Walls which rely on gravity to remain stable) Welded or Twisted Wire Mesh Geotextile Wrap Soil Reinforcement Types: Metal Strip Steel Bar Grid Mat Welded Wire Geosynthetics (Geotextile Sheets or Geogrids) 120

121. MSE Wall Element Dimensions Needed for Design 121

122. Shoring Pile Introduction Shoring is used to support a structure to prevent a collapse. The most common shoring techniques that we encountered are during the early stage of construction which is an excavation. Shoring is intended to support a deep excavation to prevent the retained soil overturns and eventually cause a project mishap. Depending on the soil type, shoring support is usually provided when we need to support an excavation with at least 1.20-meter difference in levels from our gate level or the +/- 0.00 level. In construction, shoring is completely different from a retaining wall, as this is used only to retain the soil during the excavation and as far as the structural design is concern; it is not used primarily for the purpose of a retaining wall. 122

123. The five common types of shoring that we usually encountered in the construction project are: H or I-Beam Shoring H or I-Beam Shoring also known as soldier pile walls are the most common type of shoring that we usually encountered in a construction project. It is constructed by driving prefabricated steel I or H sections into the ground. Soil conditions may allow for the sections to be vibrated directly into the ground instead of the pre-drilling of the soil before installing the beam. The full wall is formed by installing a pre-cast concrete panel between the driven steel beams to construct the shoring walls. 123

124. The use of this type of shoring ranges from supporting excavation with a depth between 1.2 meters to that of a depth of 5 meters. However, it can exceed 5 meters, as long as it’s design accounts for the surcharge load along its perimeter.. 124

125. 2. Secant Pile Shoring Secant Pile Shoring was formed of intersecting two combinations of piles, with a “reinforced”, also called as secondary and “un-reinforced” or primary pile interlocking each other to form a continuous wall. A guide beam is constructed first prior to installation to keep the alignment in place. This is usually used in deep excavations. After casting the “primary” pile, the temporary casing is extracted while the concrete has not fully set and the heavy casing is then driven into the intervening pile location cutting into the fresh concrete of the adjacent pile. The “secondary” piles are then immediately drilled. The steel cages of the “secondary” pile are inserted and the structural concrete is poured to form a continuous wall. 125

126. Secant Pies are the best choice to use when there is no room for open excavation or when space is limited because of an existing structure that was too close in proximity. In this case a surcharge loads due to the neighbouring structure is considered in the design. 126

127. 3. Contiguous Pile Shoring Contiguous or Tangent Pile Shoring is composed of closely spaced piles wherein the faces of the piles are almost touching or tangent with each other. This is used in areas where water is not significant or the water pressure is very minimal.   This is usually proposed in clay soils and can use to retain dry granular material or fills. Although water seepage between the gaps of the pile is more likely to occur when used in water-bearing granular soils, it can be prevented by grouting these gaps to form a water-tight retaining wall.  This type of shoring is not recommended to use in high ground water table without dewatering works. 127

128. Construction of contiguous pile is very similar to that of the secant piles as prior to the installation, a guide beam should be constructed to serve as a guide for the contiguous wall to install in place. Contiguous Pile Shoring Guide Beam for Contiguous Pile Shoring 128

129. 4. Sheet Piles Although it can be used to retain soil to soil excavations, this type of shoring is best to use when we need to isolate our excavation from the bodies of water specifically a creek, a pond or on a sea-side. It is commonly seen in a port and harbour construction. Similar to soldier piles, it can be constructed by driving prefabricated Z or U steel sections into the ground using a Vibro hammer. The full wall was formed connecting the Z or U steel sections or the sheet piles. Depending on the depth of excavation, the end of the sheet piles if not long enough can be welded together to reach the desired depth in the ground. 129

130. Typical details of sheet piling works and drawing 130

131. 5. Diaphragm Walls When the excavations are too deep for the type of shoring that is above mentioned above, diaphragm walls can be used. It is made of reinforced concrete designed primarily according to loads that needs to be resisted. It can be the element for a temporary or permanent retaining wall or both.   For the deep excavation of the basement and tunnels, the diaphragm wall is the best option. 131

132. Thank You!