This code details essential procedures and requirements for designing and constructing diaphragm walls, which serve as earth-retaining and cutoff barriers in various engineering fields. It encompasses specifications for materials, excavation processes, slurry characteristics, reinforcement configurations, and construction methodologies to ensure stability and impermeability under challenging soil and groundwater scenarios.
Overview
This code details essential procedures and requirements for designing and constructing diaphragm walls, which serve as earth-retaining and cutoff barriers in various engineering fields. It encompasses specifications for materials, excavation processes, slurry characteristics, reinforcement configurations, and construction methodologies to ensure stability and impermeability under challenging soil and groundwater scenarios.
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Frequently Asked
For diaphragm wall construction, aggregates should comply with IS 383-1970, utilizing well-graded coarse aggregates around 20 mm for reinforced concrete walls. Cement selection generally involves Ordinary Portland Cement (OPC) per IS 269 or Portland Pozzolana Cement (PPC) as per IS 1489, ensuring durability and strength suited for underground and water-exposed environments. Water-cement ratios typically range from 0.45 to 0.55 to balance workability and strength.
Bentonite slurry preparation requires sodium-based bentonite mixed with water in suitable tanks, followed by a minimum gelation time of 12 hours before application. Testing involves assessing concentration, viscosity, pH, and groundwater hardness. Equipment like vibrating screens and centrifuges assist in maintaining slurry quality by removing impurities. The slurry density must be calculated to provide sufficient hydrostatic pressure, ensuring trench stability with a safety factor close to one, using relevant soil and trench parameters.
Selection of excavation equipment depends on soil type, wall depth, and project specifics. Soft to medium soils are suited for rotary boring rigs, trenching buckets, and hydraulic grabs. Gravelly or bouldery soils require percussion rigs, mechanical grabs, and chiselling tools. Rock formations necessitate percussion rigs and submersible mortar drills. Often, a combination of equipment is employed to address heterogeneous strata, with attention to minimizing vibrations and adapting to site constraints.
Reinforcement cages must be fabricated as rigid assemblies matching panel joint configurations, maintaining a minimum clear spacing of 100 mm to allow proper concrete flow. During installation, cages are lowered carefully into the trench, supported with spacers to preserve concrete cover, and aligned within longitudinal and vertical tolerances of ±75 mm and ±50 mm, respectively. Inserts or boxes for recesses and anchors are incorporated at designated levels to maintain integrity and facilitate structural continuity.
To avoid defects, concreting is generally performed using special tremie pipes that facilitate continuous underwater concrete placement from the bottom up, minimizing segregation and slurry contamination. Panels are constructed sequentially with reinforcement cages inserted prior to concreting. Joints between panels utilize form tubes or chiselled edges to ensure proper bonding. Maintaining uninterrupted tremie concreting and monitoring slurry and groundwater conditions is essential for producing impermeable, defect-free diaphragm walls.
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