Systematic laboratory and field investigations on the soil-concrete interface of diaphragm walls and bored piles with focus on the influence of wall roughness-PPT Presentation

PPT Presentation

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The presentation examines how support fluids and wall roughness affect the soil–concrete interface of diaphragm walls, bored piles and barrettes, using field observations and laboratory direct-shear tests.<br /><br />Support-fluid rheology and clogging govern fluid penetration into the soil, pressure transfer, and the thickness and composition of the resulting filter cake. These outcomes depend on factors including fluid viscosity and gel strength, soil permeability, and the grading of both soil particles and solids in the fluid. Poorly graded materials can produce a permeable cake that does not fully transfer pressure; effective clogging can create a finer, less permeable layer and allow fuller pressure transfer.<br /><br />Field observations of bentonite-supported diaphragm walls show that interface conditions vary with soil type. In gravelly soils, filter cakes may be thick and discontinuous, with pebbles contacting the wall directly. Sandy soils tend to have thinner cakes, while clayey soils may have very thin or negligible cakes. Consequently, interface shear resistance may be governed by the filter cake, direct soil–wall contact, or the position and contact of pebbles.<br /><br />The interface’s wall friction angle depends on wall roughness, filter-cake thickness and composition, and soil shear strength. Laboratory direct-shear tests using gravelly sand, a bentonite-based filter cake and pebbles investigated how different pebble arrangements and wall roughness affect this friction angle.<br /><br />The central conclusion is that support-fluid properties and soil grading shape the interface, while wall roughness and filter-cake characteristics control its shear strength. This strength is important for the vertical bearing capacity of piles and barrettes and for earth-pressure loading and design of diaphragm walls.

Keywords

support fluids

wall roughness

soil-concrete interface

diaphragm walls

bored piles

barrettes

filter cake

bentonite

direct shear tests

wall friction angle