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Soldier Bored and Diaphragm
- 1. CONSTRUCTION TECHNOLOGY 2 CHAPTER1.1 DEEP EXCAVATION GROUP MEMBERS: LEE SU WEN LIM JIA YI CELINE CHONG YAP SUK PING KANG YING HONG
- 2. You arean engineer in a construction company which is awarded a tender in basement excavation and construction using the diaphragm wall method. The basement is designed for a three (3) storey car park below a multi-storey office block. You are assigned to prepare the method statements for this project which involves the following matters:-
- 3. WHAT IS ADIAPHRAGM WALL? A reinforced concrete structure constructed in-situ panel by panel. Constructed using a narrow trench excavated in ground and supported by an engineered fluid ( typically bentonite mud or polymer mud) until the mud is replaced by the concrete Walls generally range from 600 to 1500 mm thickness, in wide between 2000 and 3500 mm and can be excavated to depths of 60m or more. Used for decades to provide cost-effective, long-term solutions for many groundwater control problems
- 4. DIAPHRAGM WALL APPLICATIONS Commonlyused for retention systems and permanent retaining walls of the basement Used as deep groundwater barriers As a cut-off provision to support deep excavation Used in congested areas As a separating structure between major underground facilities As the final wall for basement or other underground structure
- 5. Q1. THE CONSTRUCTIONOF A PRE-TRENCH AT THE INITIAL STAGE OF DIAPHRAGM WALL.
- 6. GUIDE WALL Constructtwo temporary parallel concrete beams - guide the excavation tool and to stabilize the upper Maintain the horizontal alignment and wall continuity of a diaphragm wall while are adopted Help guide the diaphragm wall grabs vertically and aid in the positioning of the final structure The dimensions and shape - depending on the nature of the surface soil Shall be 100 to 250 mm thick, 1-2m deep and made of lightly reinforced concrete and shall represent the reference lines
- 7. TRENCH EXCAVATION Excavationis done by digging technique using clamshell or grabs to the desired depth. Sand and soft rock strata - excavation by cutting technique using reverse circulation trench cutters can be used. Carried out with the aid of several pieces of equipment, such as (in increasing order of cost): Mechanical clam-shell, Hydraulic clam-shell, Kelly bar Hydromill The choice of the equipment depends mainly on the characteristics of the soil to be excavated and on the depth to be reached.
- 8. EXCAVATION SUPPORT Preventedfrom collapsing - reinforcing and casting by the use of supporting bentonite slurry supporting slurry fluid must be cleaned - it's properties are within acceptable levels balances the inward hydraulic forces and prevents water flow into the trench The mud is usually pumped to a storage tank where it hydrates for up to 12 hours. The bentonite particles swell and absorb the water before it’s used to support the excavation.
- 10. REINFORCEMENT A prefabricatedreinforced cage is then lowered into the excavation between the stop ends. Reinforcement cage must have a sufficient transverse and diagonal reinforcement to withstand lifting and lowering handling forces Sufficient space must be left for at least two or three tremie pipes
- 11. CONCRETING Process ofreplacing the supporting slurry with the permanent concrete with the use of vertical pipes - tremies. Prevent the segregation of concrete Lift the tremies progressively as the concrete level raises Maintain a minimum depth of 0.6 meters of tremie pipe into the concrete. Overpouring might be required - make sure that all slurry is displaced Poor tremieing can result in slurry pockets getting entraped within the diaphragm wall concrete. Lead to excessive and costly groundwater leaks or even blowouts. Central Artery Project in Boston, MA (Big dig) and has led to costly repairs and delays.
- 12. JOINING FOR THEDIAPHRAGM WALL PANEL Purpose: to protect the rubber water stop during the excavation of the trench for the next panel It will be remove before the placing of reinforcement and concrete into the excavated trench • The steel pipes are installed at both panel fronts before concreting • The pipes rest on the excavation bottom and match the circular shape of the panel fronts • Concrete injected takes the shape of the stop end pipes • The panel has concave fronts 1. Stop End Pipes
- 13. 3. DISPOSABLE PIPES PVC Fixed to the cage and lowered to rest on the bottom A panel with two holes When concrete is cast in the secondary panel, it fills the recess and creates a joint with the primary panel. 2. Sheet Piling • Driven into the primary panel, before concrete is cast • Concrete on the fronts of the panel takes on the shape of the sheet pile and a recess is created. • Concrete has hardened - keep its shape, sheet piles are extracted. • Allows for the insertion of plastic elements - water stops between the panels -guarantee increased water tightness.
- 14. WHAT IS EXCAVATIONSUPPORT SYSTEM? keep the sides of deep excavations stable 1 To withstand soil pressure and water pressure (hydrostatic pressure) 2 ensure that movements will not cause damage to neighbouring structures 3 Preliminary analysis has to be carried out for many options of wall and support system 4
- 15. TEMPORARY EXCAVATION SUPPORT: •Only for temporary construction • can be taken out after constructed • Reused • Example: 1. Cantilever wall 2. Soldier pile and lagging 3. Sheet pile- to provide safe access for construction PERMANENT EXCAVATION SUPPORT: • Remain in the site • Example: 1. Diaphragm wall 2. Bore pile 3. Sheet pile- serve as permanent retaining structures
- 16. Q2. THE SELECTIONOF SUITABLE TEMPORARY EXCAVATION SUPPORT
- 17. Cantilever wall • onetype of retaining structure • suitable for situation when the excavation relatively shallow and the ground is stiff • A structure to withstand the soil pressure and water pressure.
- 18. Soldier pile andlagging • An earth retention technique that retains soil, using vertical steel piles with horizontal lagging • pile can be from the UB (universal beam) or UC (universal column) • and are inserted into the pre-bored holes at the perimeter of the excavation site for basement
- 19. Interlocking sheet pile •H-piles with infilling horizontal sheeting have also been used successfully • Driven in side by side with interlocking ends • Light weight • Can be reused serval times
- 20. CONSIDERATION OF EXCAVATIONSUPPORT Soil characteristic Depth of the project Cost management Neighbourhood conditions of a site Construction procedure
- 21. Soil characteristic • Canbe used in most type of soil Depth • Suitable for 3storey basement Water table • Required dewatering Costing • Cheap Neighbour disturbance • Relatively quiet Construction procedure • Easy and fast to construct SOLDIER PILE AND LAGGING Dewatering: • A process to remove the over-saturated water in ground • Keep the subsoil within a non-saturated condition.
- 22. Q3. LIST OUT6 ADVANTAGES OF THE DIAPHRAGM WALL SUPPORT
- 23. ADVANTAGES OF THEDIAPHRAGM WALL SUPPORT Reduced number of joints in the wall •Improves the walls water tightness •Little effects on adjacent structure Great depth Lee Tunnel Project Diaphragm wall with 98m depth Quiet and little vibration Low environmental impact * Sound pollution * Land disturbance Shorten working period
- 25. Saving Cost Less temporarysupports Eg: Labour Cost, Specialist Contractors Take Heavy Loads Used as permanent structure wall Foundation of the superstructure Time Management Faster execution Prevent liquidated damage
- 26. PRIMARY & SECONDARY& ENDING PANELS
- 27. DISADVANTAGES OF DIAPHRAGM WALLSUPPORT Less flexible High cost for short term project
- 28. Q4. STATE 2OF EXCAVATOR MACHINES
- 29. EXCAVATOR MACHINES Suitablefor different kind of works such as rock excavation, trenching, etc. Suitable for hard surface and soil Control high degree of verticality Hydraulic rock cutter
- 30. HYDRAULIC DIAPHRAGM WALLGRAB Suitable for most of soil conditions Controlled by monitoring system High accuracy to verticality Excavate over 50m depths Free of noise and vibration
- 31. Q5. WHAT ARETHE SUITABLE STEPS AND PRECAUTIONS TO TAKE IF RUBBER WATER STOPS ARE TO BE CAST AT BOTH SIDES OF THE DIAPHRAGM WALL?
- 32. • Mainly toblock the passage of liquid within concrete joints • PVC is the most commonly used material for water stops • Copper and stainless steel and natural rubber can also be used • Fundamental object for construction works to exclude water RUBBER WATERSTOP
- 33. PRECAUTIONS • Pay particularattention to the underside of horizontally placed waterstops • Intimate contact between the concrete and waterstop is necessary for full performance of a waterstop • Maintain adequate clearance between reinforcing steel and the waterstop • To promote the formation of voids due to aggregate bridging • Waterstop should never be cut or modified to allow reinforcement to pass through
- 34. Q6. THE SUITABLETYPE OF ADDITIONAL SUPPORT FOR THE COMPLETED DIAPHRAGM WALL
- 35. ADDITIONAL DIAPHRAGM WALLSUPPORT Commonly used for the stabilization of steep slopes which consist of softer soils Tendon the steel rods is connected to the bearing plate Help preventing excessive erosion or landslide GROUND ANCHOR
- 36. Q7. THE FUNCTIONOF TREMIE TUBE AND PRECAUTION TO BE TAKEN WHEN USING THE TUBE
- 37. PRECAUTIONS Transfer concreteunder bentonite slurry which will displace bentonite slurry when the concrete is filled from the bottom Pour concrete underwater in a way that avoids washout of cement from the mix due to turbulent water contact with the concrete while it is flowing Tremie tube has to be cleaned every time after using, to prevent any excess concrete to stick on to the tube, that will cause blockage Concrete should be coherent, rich in cement and of slump between 150 and 180mm Lower end of tremie tube should be kept embedded in the wet concrete When a large number of concrete are required to be placed over an extensive area, it is advisable to use a number of tremis FUNCTION