---
title: "Factors in construction stage of trench excavation"
subject: "Building Technology"
chapter: 2
key: "semester_6/building_technology:trench-excavation-factors"
source: https://www.bctengineer.com/q/semester_6/building_technology/trench-excavation-factors
site: BCT Engineering
---

# Factors in construction stage of trench excavation

Building Technology · Chapter 2: Foundations

- Asked in: 2070 Magh
- Video: [Trenching and Excavation](https://www.youtube.com/watch?v=7Ou4BhxWPPc) — Job-Site Safety Institute
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/building_technology/trench-excavation-factors
- Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-2

## Question

Discuss factors to be considered in construction stage of trench excavation.

## Short answer

Set out lines, fix depth and width, assess soil type, provide shoring or slopes, dewater, ensure safety, dispose spoil, protect services, level the bottom, avoid rain, choose method, and get engineer approval before concreting.

## Answer

Factors to be considered in the construction stage of trench excavation:

1. **Setting out and alignment**: Mark the trench lines with pegs, string and lime from the approved drawing; check dimensions and levels (profile boards, sight rails).
2. **Depth and width**: Excavate to the required foundation level; width is the footing width plus working space of 150 to 300 mm for formwork.
3. **Type of soil**: Soft soil needs slopes or shoring; hard soil or rock needs picking, drilling or blasting.
4. **Side stability and shoring**: Timber planking and struts for trenches deeper than 1.5 m in loose soil to prevent collapse and for the safety of workers.
5. **Ground water**: Dewatering by sumps, ditches, or well-point system; the bottom is kept dry.
6. **Safety**: Barricades, warning signs and lights, ladders for exit, spoil heaped at a safe distance from the edge (at least 1 m), no heavy loads near the trench, and inspection after rain.
7. **Disposal of spoil**: Store for backfilling and remove surplus; do not block drainage.
8. **Existing services and adjacent structures**: Locate underground pipes and cables; support nearby foundations.
9. **Trench bottom**: Level, clean, and compact; remove loose soil; do not over-excavate (fill with PCC if so).
10. **Weather**: Avoid the rainy season; protect the trench from rain run-off by diversion bunds.
11. **Method and equipment**: Manual or machine; cost and time.
12. **Inspection and approval** of the trench bed by the engineer before concreting.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Trench lines are first marked using:
   A. Dumpy level only
   B. Water level
   C. Guesswork
   D. Pegs, string and lime from the approved drawing
   Answer: D. Alignment and dimensions are checked with profile boards and sight rails. (Key point: Setting out)

2. Timber planking and struts are used for trenches:
   A. Deeper than 1.5 m in loose soil
   B. Shallower than 0.3 m
   C. Only in rock
   D. Never
   Answer: A. To prevent collapse and protect workers. (Key point: Shoring)

3. If a trench is over-excavated, it should be:
   A. Filled with loose soil
   B. Left open
   C. Filled with water
   D. Filled with PCC
   Answer: D. Over-excavation is filled with PCC, not loose soil, to keep a firm bed. (Key point: Over-excavation)

4. Before concreting, the trench bed needs:
   A. Inspection and approval by the engineer
   B. Nothing
   C. Painting
   D. Flooding
   Answer: A. The engineer inspects and approves the bed. (Key point: Approval)

## Related in Building Technology

- [Formwork and timbering for trench excavation](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Atrench-formwork) — Building Technology, chapter 8, asked 3×
- [Foundation selection factors, excavation in wet areas](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aexcavation-selection-wet-080c) — Building Technology, chapter 2
- [Formwork for excavation, timbering, RCC formwork](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aformwork-timbering-062p) — Building Technology, chapter 8
- [Factors for selecting roof covering](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aroof-covering-factors) — Building Technology, chapter 4, asked 2×
- [Configuration factors for seismic safety](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aconfig-factors-seismic) — Building Technology, chapter 11, asked 2×
- [Repair versus retrofit; configuration factors](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aretrofit-vs-repair-config) — Building Technology, chapter 11

## Related in other subjects

- [Factors for selecting construction materials](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Afactors-selection-construction-material) — Civil Engineering Materials, chapter 1, asked 9×
- [Factors in selecting construction equipment](https://www.bctengineer.com/question.md?key=semester_8%2Fconstruction_management%3Aequipment-selection-factors) — Construction Management, chapter 4, asked 6×
- [Trench bottom heave safety factor](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Atrench-heave-rock) — Foundation Engineering, chapter 4
- [Tyre construction, types and factors affecting life](https://www.bctengineer.com/question.md?key=semester_5%2Fautomotive_technology%3Atyre-construction-bias-radial-life) — Automotive Technology, chapter 8