Piling & Foundation Glossary

The terms that appear on borelogs, method statements and load test reports — explained.

Foundation drawings and geotechnical reports are full of shorthand. This glossary explains the terms our engineers use across our piling services, project case studies and technical blog.

B C D I L M N P R S T U W

Bentonite Slurry: A clay-and-water suspension circulated during boring to hold the bore wall open by hydrostatic pressure and to carry cuttings to the surface. Its density and specific gravity are checked before every concrete pour.
Bored Cast In-Situ Pile: A pile formed by drilling a bore to design depth, lowering a steel reinforcement cage into the shaft and concreting it in place. Because the concrete is cast against the surrounding soil, shaft friction and load capacity are high, which makes it the default choice for multi-storey and industrial structures in Chennai.
Borelog: The record of a borehole: strata encountered, thickness, SPT N-values, water table level and sample details. The borelog is the single most important document in choosing a piling method.
Chiselling: Breaking through boulders, hard laterite or rock at the bore base using a heavy weighted chisel dropped repeatedly, until the specified founding level or socket is achieved.
Cut-Off Level: The design level to which the finished pile is trimmed after concreting, at which the sound concrete meets the pile cap. Concrete is always cast above this level and chipped back.
DMC (Direct Mud Circulation): A boring technique in which bentonite slurry is pumped down the drill rods and returns up the annulus, simultaneously stabilising the bore wall and flushing cuttings to the surface. Standard practice for bored cast in-situ piling in soft to medium strata.
Driven Cast In-Situ Pile: A pile formed by driving a temporary steel casing with a closed shoe into the ground, placing reinforcement, then concreting as the casing is withdrawn. Fast and economical for residential and low-rise work where soils are reasonably uniform.
Initial Load Test: A test carried out on a sacrificial test pile, loaded up to 2.5 times the design working load in increments, to establish the safe working load before the production pile schedule is finalised.
Lateral Load Test: A test applying horizontal load to a pile head to measure deflection, relevant for retaining structures, jetties, bridge piers and any structure resisting wind or earth pressure.
Load–Settlement Curve: The plot of applied load against measured pile head settlement recorded during a load test. Its shape — and the residual settlement after unloading — determines whether the pile passes.
Marine Clay: Soft, high-plasticity clay deposited in a coastal environment, common along the ECR belt. It has very low shear strength near the surface, so piles are usually carried through it to a competent layer below.
Negative Skin Friction: Downdrag load imposed on a pile when surrounding soil settles more than the pile does, typically in recent fill or consolidating clay. It reduces the pile's usable capacity and must be allowed for in design.
Pile Cap: The reinforced concrete slab cast over a pile or group of piles that transfers column load into the piles and ties the group together.
Pile Integrity Test (PIT): A low-strain test in which a small hammer blow sends a stress wave down the pile; reflections reveal necking, bulging or discontinuities in the shaft without excavating.
Pull-Out Test: A tension test that measures a pile's resistance to uplift, used where structures are subject to buoyancy, overturning moments or heave from expansive soils.
Reinforcement Cage: The fabricated assembly of longitudinal bars, spiral or lateral ties and cover blocks lowered into the bore before concreting. Cover blocks ensure the cage sits centrally with the specified concrete cover.
Rotary Hydraulic Rig: A tracked hydraulic drilling rig with high torque output, capable of forming large-diameter piles and socketing into weathered and hard rock with far less noise and vibration than percussion methods.
Routine Load Test: A verification test on a working pile, normally loaded to 1.5 times the design load, carried out on an agreed percentage of piles to confirm the executed piles perform as designed.
Safe Bearing Capacity (SBC): The pressure a soil can carry with an adequate factor of safety against shear failure and excessive settlement. Where the SBC at shallow depth is too low for the structural load, a piled foundation is used instead of a raft or footing.
Socketing: Extending a pile a specified depth into rock or hard strata so that load is carried by end bearing and rock-socket friction. Socket length is set by the structural designer against the borelog.
SPT (Standard Penetration Test): An in-situ test where a split-spoon sampler is driven into the base of a borehole by a 63.5 kg hammer falling 750 mm. The blow count (N-value) indicates soil density or consistency and feeds directly into pile capacity calculations.
Tremie Concreting: Placing concrete through a pipe whose tip stays submerged in the fresh concrete already in the bore, so the pour displaces slurry upward without segregating or mixing. Any break in the pour risks a defect, so tremie concreting is always continuous.
Under Reamed Pile: A bored pile with one or more enlarged bulbs formed along its length by an under-reaming tool. The bulbs anchor the pile against uplift and heave, which is why under-reamed piles are widely used in the expansive black cotton and clay soils around Tambaram and Chengalpattu.
Working Load: The service load a single pile is designed to carry, derived from the ultimate capacity divided by a factor of safety, and confirmed by load testing.

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