Deep Foundations and Caissons

Caissons are selected when competent bearing lies below weak or variable surface soil, settlement limits are tight, uplift or lateral loads are significant, scour or future excavation is possible, or shallow foundations would become impractically large. The structural and geotechnical engineers choose the system and capacity from project-specific ground and loading data.

The specified reviewer confirms depth, bearing material or rock socket, cleanliness, water condition, and absence of loose cuttings using the approved inspection method. Harrowgate provides safe access or remote inspection arrangements, cleans the base, and places reinforcement and concrete promptly. A design depth alone does not prove an acceptable founding surface.

Casing supports unstable soil, isolates water-bearing layers, limits ground loss, and protects the shaft profile while drilling and concreting proceed. It can be temporary or permanent according to design. Harrowgate coordinates casing diameter, toe depth, extraction rate, concrete head, and reinforcement clearance so removal does not neck the shaft or lift the cage.

Where water cannot be removed without destabilizing the hole, concrete is placed by an approved tremie method that keeps the discharge end embedded in fresh concrete and maintains continuous upward displacement. Harrowgate plans uninterrupted supply, tracks concrete level and volume, and avoids cycling the tremie through contaminated water or breaking its seal during placement.

Actual volume above theoretical shaft volume can result from overbreak, cavities, loose ground, casing geometry, or measurement variation. It is a field indicator, not a diagnosis by itself. Harrowgate records delivery volume and concrete level by time, compares them with drilling observations, and alerts the engineer when the pattern suggests loss or abnormal geometry.

The foundation specification may require static load tests, dynamic methods, low-strain integrity testing, cross-hole sonic logging, concrete cylinders, or only documented inspection. Each method answers different questions. Harrowgate prepares test elements and access, preserves tubes or heads, supplies installation records, and does not assume one passing test validates unrelated shafts.

Provide the foundation schedule, structural loads, geotechnical report and boreholes, shaft diameters and toe criteria, rock sockets, reinforcement details, casing assumptions, groundwater, working-platform design, spoil and excess-soil rules, concrete procedure, inspection and testing plan, access limits, obstructions, cut-off elevations, and measurement rules for variable depth or concrete overrun.