---
title: "Foundation on hard rock"
subject: "Building Technology"
chapter: 2
key: "semester_6/building_technology:foundation-hard-rock"
source: https://www.bctengineer.com/q/semester_6/building_technology/foundation-hard-rock
site: BCT Engineering
---

# Foundation on hard rock

Building Technology · Chapter 2: Foundations

- Asked in: 2077 Chaitra, 4 marks
- Video: [Footing on bedrock - tips and tricks](https://www.youtube.com/watch?v=2uNa-3uXQ5A) — The Cheap Bastard
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/building_technology/foundation-hard-rock
- Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-2

## Question

What type of foundation will you recommend for the foundation on hard rock? Justify.

## Short answer

For hard rock, recommend a shallow foundation, either a strip or spread footing placed directly on cleaned, levelled rock. The rock has a safe bearing capacity of about 3240 kN/m², negligible settlement, and this option is economical because no deep foundation is required.

## Answer

For a foundation on hard rock, a **shallow foundation** is recommended: a simple **strip or spread footing** (or a footing directly on the cleaned, levelled rock), with the rock benched or stepped if the surface is sloping.

#### Justification
1. **High bearing capacity**: Hard sound rock has a safe bearing capacity of about 3240 kN/m² (IS 1904), far more than the pressure from ordinary building loads, so no deep foundation is needed.
2. **Negligible settlement**: Rock is nearly incompressible, so differential settlement is not a problem.
3. **Economy**: Deep excavation, piles or rafts are not needed, so the cost and time are lower.
4. **Excavation**: Only the top weathered layer is removed. If the rock is sloping, it is benched into steps, or anchor bars (dowels) are grouted into the rock to prevent sliding.
5. **Bonding**: The cleaned, roughened rock surface is bonded with a PCC bed or the footing concrete for firm contact; any cracks or fissures are grouted.

```text
   column
    | 
  [footing] 
 ///rock/// (benched, cleaned)
```
If the rock is weathered or fractured, the excavation is deepened until sound rock is reached, or the cracks are grouted.

## Check yourself

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

1. Recommended foundation on hard rock?
   A. Deep pile
   B. Shallow strip or spread footing
   C. Well foundation
   D. Raft with piles
   Answer: B. Hard rock has high bearing capacity so a shallow footing suffices. (Key point: Recommendation)

2. Sound rock SBC per IS 1904 is
   A. 30 kN/m2
   B. 100 kN/m2
   C. 440 kN/m2
   D. 3300 kN/m2 or more
   Answer: D. It exceeds usual building loads. (Key point: SBC)

3. How is sloping rock treated?
   A. Left smooth
   B. Filled with piles
   C. Benched into steps or doweled with anchor bars
   D. Covered by sand only
   Answer: C. Benching or dowels prevent sliding. (Key point: Sloping rock)

4. Why is settlement negligible?
   A. Rock is soft
   B. Water table is high
   C. Footing is large
   D. Rock is nearly incompressible
   Answer: D. Incompressibility prevents settlement. (Key point: Settlement)

## Related in Building Technology

- [Earthwork excavation in soft soil, hard rock, wet soil](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aexcavation-soft-hard-wet) — Building Technology, chapter 2
- [Earthwork excavation in soft soil and hard soil](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aexcavation-soft-hard-compare) — Building Technology, chapter 2
- [Excavating foundation trenches in water-logged ground](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aexcavation-wet-methods) — Building Technology, chapter 2, asked 2×

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