--- title: "Specification of earthwork for isolated footing" subject: "Construction Management" chapter: 12 key: "semester_8/construction_management:detailed-spec-earthwork-footing" source: https://www.bctengineer.com/q/semester_8/construction_management/detailed-spec-earthwork-footing site: BCT Engineering --- # Specification of earthwork for isolated footing Construction Management · Chapter 12: Specification - Asked in: 2079 Jestha, 6 marks - Video: [Earthwork Excavation For Building Foundation as per CPWD | Excavation | Reinforce QST](https://www.youtube.com/watch?v=I6zkecR_HDk) — REINFORCE - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/construction_management/detailed-spec-earthwork-footing - Whole chapter: https://www.bctengineer.com/md/semester_8/construction_management/chapter-12 ## Question Prepare detailed specification for earth work in sandy soil for isolated footing of multi-storey building. ## Answer #### 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. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How is excavation size decided? A. Equal to footing size B. Footing size minus 300 mm C. Footing size plus 300 mm working space on each side D. Twice the footing Answer: C. Working space of 300 mm each side allows formwork and construction. (Key point: Excavation size) 2. Why are side slopes or shoring needed in sandy soil? A. Sand is loose and can collapse; slopes 1:1 or shoring beyond 1.5 m depth B. Sand is too hard to dig C. To increase excavation volume D. To protect trees Answer: A. Loose sand collapses, so stable slopes and timbering are required for depths over 1.5 m. (Key point: Sandy soil stability) 3. What happens if the bottom is over-excavated? A. Filled with loose soil B. Ignored C. Filled with lean concrete at the contractor's cost D. Paid extra Answer: C. The bottom must not be disturbed; over-excavation is made good with lean concrete at contractor's cost. (Key point: Over-excavation) 4. What is the backfilling requirement? A. Clean moist soil in 150-200 mm layers compacted to at least 95% MDD B. Dumped in one layer C. Uncompacted organic soil D. Compacted to 50% MDD Answer: A. Layered compaction to at least 95% of maximum dry density is specified. 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