Excavation Support & Bracing Systems

Comprehensive vocabulary flashcards covering shoring methods, internal and external bracing systems, and excavation dewatering strategies from Lecture 2 of the Foundations module.

Foundation Soil Testing

A mandatory series of laboratory tests performed to establish foundation design parameters, consisting of shear strength, compressibility, permeability, chemical and mineralogical composition, and soil classification.

Soldier Beams and Lagging

A slope-support shoring method using vertical steel I-beams driven or drilled at intervals, between which horizontal wood or reinforced concrete (R.C.) lagging boards are inserted as excavation proceeds; best suited for simple, accessible sites of moderate depth with low water-tightness.

Sheet Piling

A shoring system formed by driving interlocking sheets of steel, timber, or precast concrete before excavation commences to create a continuous retaining wall; suitable for water-bearing soils at moderate depth, though joints tend to leak.

Guide Wall

A temporary surface-level concrete wall constructed to establish accurate alignment and positioning for the equipment digging a slurry (diaphragm) wall panel.

Bentonite Slurry

A dense fluid suspension introduced during trench excavation that hydraulically supports the trench walls against collapse prior to concrete placement in slurry wall construction.

Tremie Pipe

A pipe through which concrete is pumped in a continuous operation starting from the bottom of an excavated trench, keeping the discharge tip submerged in fresh concrete as it rises to upwardly displace bentonite slurry.

Slurry Wall (Diaphragm Wall)

A high water-tightness shoring system built panel-by-panel using surface guide walls, grab or trench cutter excavation under bentonite slurry support, insertion of steel reinforcement cages, and bottom-up tremie concreting; ideal for deep, urban excavations adjacent to sensitive structures.

Secant Pile Wall

A shoring and cutoff wall constructed from interlocking, overlapping bored concrete piles that can be combined with tieback anchors for additional lateral resistance.

Soil Mixing

An in-situ ground improvement method where modifying substances (such as cement, fly ash, or lime) are blended directly into native soil via vertical rotating augers or paddles, transforming the earth into a soft rock-like mass for cantilevered or circular shaft retention.

Crosslot Bracing

An internal bracing system employing compressive horizontal struts that span from one excavation wall to the opposite wall to transfer lateral earth and hydrostatic pressures directly across the excavation footprint.

Strut

A structural compression member engineered to resist axial force along its length, spanning across an excavation to prop opposing retaining walls.

Buckling Prevention in Horizontal Struts

The installation of bracing members perpendicular to horizontal crosslot struts to reduce their effective length and suppress lateral buckling under severe axial compression.

Rakers

Diagonal shores inclined typically between $45^{\circ}$ and $60^{\circ}$ that transfer lateral wall loads downward to the excavation floor or a heel block/sole plate, leaving the upper-central interior largely open.

Waler

A horizontal structural beam attached along the face of a shoring wall to distribute earth pressures from soldier beams or sheets to individual rakers, crosslot struts, or tiebacks.

Tieback

A tensile wall-anchoring system composed of a tendon, rod, or helical shaft anchored deep into soil or bedrock behind the wall, eliminating interior structural obstructions.

Grouted Tiebacks

High-strength steel rods drilled at an angle through retaining walls into competent soil or bedrock and grouted under pressure along a fixed bond length to resist tensile pullout forces.

Helical Anchors

Screw-in ground anchors whose load resistance is directly proportional to the torque required during mechanical installation, deployed for short-run low loads or in continuous long runs for heavy loads.

Deadman Anchor

A buried anchoring body (such as a mass concrete block) embedded in stable earth behind a wall to anchor a tieback rod and resist overturning forces caused by lateral soil or water pressures.

Construction Dewatering

The removal or drainage of groundwater or surface runoff from an excavation site, riverbed, caisson, or shaft via pumps or evaporation prior to and during foundation construction.

Well Points

A perimeter dewatering system consisting of closely spaced, small-diameter vertical suction pipes linked to vacuum pumps to draw down the water table locally below the excavation subgrade.

Deep Well System

A dewatering installation comprising drilled wells equipped with electric submersible pumps, designed for large water volumes and significant drawdown depths exceeding suction lift limits.

Watertight Barrier Wall

A continuous cutoff wall (such as a slurry wall or soil-mixed wall) socketed into an impermeable stratum beneath the site that prevents groundwater ingress without requiring drawdown of the exterior water table.

Settlement Hazard of Dewatering

The risk of damage to neighboring structures during groundwater drawdown caused by soil consolidation settlement or by exposing previously submerged untreated timber foundation piles to atmospheric decay.