Diaphragm Wall Presentation By Gagan

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Diaphragm wall Presentation by Gagan Goswami

gagangoswami@yahoo.co.in

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Diaphragm Wall Presentation By Gagan

  1. 1. Construction of Diaphragm Wall Presentation by: Gagan Goswami 1
  2. 2. Content Introduction Application Category of Diaphragm Wall Construction Procedure 2
  3. 3. Introduction Diaphragm Wall is generally reinforced concrete wall constructed in the ground using Underslurry technique which was developed in Europe. The technique involves excavating a narrow trench that is kept full of an engineered fluid of slurry. Walls of thickness between 300 and 1200 mm can be formed in this way up to a depths of 45 meters. 3
  4. 4. Conceptual sketch showing the RCC Diaphragm Wall 4
  5. 5. Diaphragm wall-Application Commonly used in congested areas -Can be Installed in close proximity to existing structure Practically suited for deep basements Used in conjunction with “Top Down” construction technique 5
  6. 6. Schematic section of Diaphragm Wall showing typical use 6
  7. 7. Schematic section of Diaphragm Wall showing typical use 7
  8. 8. Schematic section of Diaphragm Wall showing typical use 8
  9. 9. Schematic section of Diaphragm Wall showing typical use 9
  10. 10. Anchoring of Diaphragm Wall using Anchor Slab Anchor Slab 10
  11. 11. Anchoring of Diaphragm Wall using Anchor Blocks Diaphragm Wall Anchor Bars Anchor Blocks 11
  12. 12. Important Conditions Dictate the use of Diaphragm Wall Very unstable soil profiles below the water table Limited construction time Where deeper than normal cantilever support may be required 12
  13. 13. Positive facades of Diaphragm Wall Can be Installed to considerable depth Formation of walls with substantial thickness Flexible system in plan layout Easily incorporated into Permanent works Designable to carry vertical loads Construction time of Basement can be lowered considerably. Economic and Positive solution for large deep basement in saturated and unstable soil profiles. Can be used for seepage control in Dams. Noise levels limited to engine noise only. No vibration during installation. 13
  14. 14. Negative Facades of Diaphragm Wall Not economical for small, shallow Basements 14
  15. 15. Category of Diaphragm wall 1) In Situ Cement Bentonite Vertical Wall 2) In Situ RCC Vertical Wall 3) Precast RCC Vertical Wall 15
  16. 16. In Situ Cement Bentonite Vertical Wall Provides water tight barrier Used to prevent seepage/water loss from Natural reservoir and Dams 16
  17. 17. In Situ RCC Vertical Wall Underground Structural element Used for Retention systems and Permanent foundation walls Deep groundwater barriers 17
  18. 18. Procedure Diaphragm Wall construction begins with the trench being excavated in discontinuous sections or “panels”. Stop-ends are placed vertically at each end of primary panel to form joints for adjacent secondary panel or closing panels. Panels are usually 4 to 6 meters long. Stop-ends are used to form the joints between adjacent panels and a water bar can be incorporated across these joints. 18
  19. 19. Construction Method Secondary Primary Secondary Secondary Secondary Closing Secondary Construction Joint formed by Construction Joint Circular Stopend Pipe Schematic Diagram Showing Construction Joint between Adjucent Panels 19
  20. 20. Construction Method Secondary Primary Secondary Secondary Secondary Closing Secondary Construction Joint formed by Construction Joint Flat Stop end Schematic Diagram Showing Construction Joint between Adjucent Panels 20
  21. 21. Different Shapes of Diaphragm Wall Panel T-Shape Panel L-Shape Panel 21
  22. 22. Different stages of construction activities 22
  23. 23. Diaphragm Wall Construction Site 23
  24. 24. Construction Procedure Stage-1: Fixing of Alignment Stage-2: Guide wall Construction Stage-3: Trenching Stage-4: Trench Cleaning Stage-5: Stop ends fixing Stage-6: Reinforcement Cage lowering Stage-7: Placing of Concrete Stage-8: Withdrawal of Stop ends 24
  25. 25. Guide Wall Construction Guide Wall is constructed to fix the alignment of Diaphragm Wall in the field 25
  26. 26. Guide Wall Construction 26
  27. 27. Trenching Equipments Hydraulic Grab Kelly-mounted or Cable-hung cam buckets 27
  28. 28. Kelly-mounted Hydraulic Grab 28
  29. 29. Cable-hung cam bucket 29
  30. 30. Trenching Process Trenching usually carried out under bentonite slurry Bentonite Slurry – Key component. -This Slurry acts as shoring to prevent collapse by hydraulic pressure and thyrotrophic property. 30
  31. 31. Bentonite Slurry Used as a support fluid The bentonite suspension used in bore holes is basically a clay of montmorillonite group having exchangeable sodium cations (Na+). The action of bentonite in stabilizing the sides of bore holes is primarily due to the thixotropic property of bentonite suspension. The bentonite suspension when undisturbed forms a jelly which when agitated becomes a fluid again. 31
  32. 32. Functions of Bentonite In case of granular soils, the bentonite suspension penetrates into the sides under positive pressure and after a while forms a jelly. The bentonite suspension gets deposited on the sides of the hole resulting in the formation of a filter cake in contact with soil against which the fluid pressure acts. In case of impervious clay, the bentonite does not penetrate into the soil, but deposits only a thin film on the surface of the hole. 32
  33. 33. Factors affecting stability of Trench Level of the supporting fluid -Level of the bentonite slurry should be maintained preferably at least 1.5m above the ground water level to avoid problem of instability. Density and Viscosity of supporting fluid Loss of shear strength with time Suction effect during trenching 33
  34. 34. Specification of Bentonite (as per IS:2911-Part1:Sec2) Liquid limit : 300 to 450 % (in accordance with IS:2720-part V ) Sand content : Less than 7 % Density: 1.12 Marsh viscosity : About 37 second, tested by Marsh cone Swelling index: Swelling index at least 2 times of dry volume. pH value : Less than 11.5 34
  35. 35. Tests and compliance values for support fluid prepared from bentonite (as per IS9556-1980) Property Test method As Before supplied concret to the ing bore Density Mud balance 1.04- <1.15g/ 1.10g/m ml l Viscosity Marsh cone 30 - 90 seconds Shear Shearometer / 1.4 to 10 strength Vane shear N/sq.m apparatus pH Digital pH 9.5-12 meter 35
  36. 36. Schematic Diagram of Bentonite Setup •Storage tanks Settling Circulation Fresh T3 T2 T1 Mixer •Mud Pump Diaphragm Wall Construction area 36
  37. 37. Bentonite Setup 37
  38. 38. Preparation of Bentonite Slurry Bentonite slurry made by passing dry powder through water jet. A conical hopper is used with bottom nozzle through which water is pumped under pressure. The bentonite powder is poured directly from top and when it falls down the hopper, it gets agitated in the water. After getting circulated, the mixed bentonite thus falls in the tank. 38
  39. 39. Trench Cleaning Joints of adjacent panels to be cleaned to obtain watertight bond Loose materials to be lifted by suitable air lifting method 39
  40. 40. Fixing of Stop ends Stop ends to be fixed at the proper position keeping it truly vertical Distance between two Stop ends to be fixed as per prefixed Panel Layout 40
  41. 41. Reinforcement Cage Excavation of panel is followed by placing of steel reinforcement cage in center of the panel. 41
  42. 42. Reinforcement Cage fabrication 42
  43. 43. Reinforcement Cage shifting 43
  44. 44. Lowering of reinforcement cage in the excavated panel 44
  45. 45. Lowering of reinforcement cage in the excavated panel 45
  46. 46. Resting of reinforcement cage in the excavated panel 46
  47. 47. Different stages of construction 47
  48. 48. Placing of Concrete Placing of concrete having slump 150mm to 190mm by tremmie method Concrete to be placed through a top metal hopper and into a rigid leak proof tremmie pipe (2 sets), sufficiently large enough to permit free flow of concrete. Initially there should be a suitable plug at the bottom of metal hopper, which will not discharge concrete until sufficient concrete accumulate in the metal hopper. concrete displaces the slurry from bottom and rises in such a manner that mixing of concrete with slurry does not occurs 48
  49. 49. Placing Concrete 49
  50. 50. Placing of Concrete Pouring shall be continued till it accumulates in vertical Tremmie pipe up to top of funnel. Tremmie pipe shall be raised so as to release the concrete in a single continuous flow. Concrete to be discharged in the trench without any lateral movement of Tremmie pipe. 50
  51. 51. Placing of Concrete Caution - Bottom end of Tremmie pipe must remains immersed in concrete. Operation to be continued till good concrete reaches 300mm above the cut-off level of Diaphragm Wall. This concrete above cut-off shall be removed when green Chipping of concrete is not to be permitted. Length of Tremmie pipe shall be reduced by removal of Tremmie segment stage by stage. 51
  52. 52. Withdrawal of Stop ends Withdrawal of Stop ends just after the Initial setting of concrete. If retarders are not added, Stop End Pipes shall be moved up & down not later than 45 minutes from the time of placing of concrete. 52
  53. 53. Thank You If any Query please mail me- gagangoswami@yahoo.co.in 53

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