“Borehole Stabilization” for Deep Excavation, An Essentials Part in Bored Piling / Diaphragm Wall Construction-Paper

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Borehole stabilization is a critical temporary-work process in bored-pile and diaphragm-wall construction. It keeps excavations open, prevents collapse, and provides a clean, stable space for installing concrete and reinforcement. The chosen stabilization method affects safety, construction logistics, structural quality, cost, design assumptions, and environmental management.<br /><br />Support fluid must create a watertight boundary that retains sufficient hydrostatic pressure to resist soil and groundwater forces. Its properties must also allow it to be displaced evenly by concrete. Soil conditions, excavation depth, groundwater, and water chemistry determine which fluid is appropriate.<br /><br />Bentonite slurry is thixotropic and forms a filter cake in most soils, making it a reliable option across varied ground conditions. However, it requires extensive mixing and storage facilities, time to hydrate, and often substantial recycling before concreting—particularly at depth. Its filter cake can also reduce pile-shaft friction and reinforcement bond.<br /><br />Polymer slurry is lighter, faster to mix, easier to handle and dispose of, and generally easier to displace during concreting. It performs especially well in low-permeability soils. Because it does not form a filter cake, it may penetrate and be lost in permeable ground, creating instability risks. Polymers are also more sensitive to chemical, biological, and mechanical degradation, so careful product selection, slurry testing, and maintenance are essential. Maintaining adequate fluid overpressure is particularly important, including when drilling equipment is withdrawn.<br /><br />Three case studies—very deep piles in Malaysia, piles in coarse sand and gravel in Chechnya, and piles in soft clay using salt water in Indonesia—show that polymers can succeed in challenging conditions with suitable additives, monitoring, and construction controls. Hybrid bentonite-polymer fluids may be appropriate where soil layers require different properties. Overall, informed fluid selection and rigorous site supervision are essential to safe, economical, high-quality foundations.

Keywords

borehole stabilization

bentonite slurry

polymer slurry

bored pile construction

diaphragm wall

hydrostatic pressure

filter cake

groundwater control

soil conditions

foundation safety