Specification of earthwork for isolated footing

Detailed specification: earthwork in excavation in sandy soil for isolated footings

Scope: Excavation in sandy soil for isolated footings of a multi-storey building to the lines, levels and dimensions shown in the drawing, including shoring, dewatering, disposal, backfilling and compaction.

1. Site preparation and setting out

• The site is cleared of vegetation, debris and obstructions. The centre lines and excavation limits are set out with pillars/pegs and lines by a surveyor, and approved by the engineer before work begins.
• Excavation size = footing size + a working space of 300 mm on each side (or as directed).

2. Excavation

• Excavation is done by hand or by a backhoe excavator to the depth shown in the drawing, and not less than the depth recommended in the soil report; the bearing capacity of the sandy soil must be confirmed by tests.
• Since sandy soil is loose, side slopes are kept stable (typically 1:1 or flatter). Vertical sides are allowed only with timbering/shoring, which is also required for depths over 1.5 m or wherever there is a risk of collapse. Neighbouring structures are protected.
• Excavated soil is stacked at least 1.5 m from the edge, or removed to the place directed, and never on the building area. Usable soil is stacked for backfilling.
• The bottom is levelled, trimmed and cleaned. It is not disturbed or over-excavated; any over-excavation is filled with lean concrete at the contractor's cost.
• Water is removed by pumping and the pit is kept dry; ground water is drained away from the foundation.
• The bottom is compacted (e.g. with a rammer) before PCC, and the soil is checked by the engineer against the design bearing capacity.

3. Safety: barricades, warning lights, safe access (ladders), no workers under unsupported sides, and a safe distance for vehicles.

4. Backfilling: after the footing and plinth work, selected, clean and moist sandy soil is placed in layers of 150–200 mm and compacted with a rammer or plate compactor to at least 95% of the maximum dry density.

5. Tolerances: ±25 mm in level, ±50 mm in lateral dimensions.

6. Measurement and payment: the work is measured in cubic metres of net volume to the specified lines (footing size plus the allowed working space) and paid at the contract rate per m³. The rate includes excavation, shoring up to the specified level, dewatering, disposal within a lead of 50 m and a lift of 1.5 m, trimming and backfilling.