---
title: "Bearing capacity from plate load curve"
subject: "Foundation Engineering"
chapter: 6
key: "semester_5/foundation_engineering:bc-from-load-settlement-sand"
source: https://www.bctengineer.com/q/semester_5/foundation_engineering/bc-from-load-settlement-sand
site: BCT Engineering
---

# Bearing capacity from plate load curve

Foundation Engineering · Chapter 6: Bearing Capacity and Settlement of Shallow Foundations

- Asked in: 2081 Bhadra, 2 marks
- Video: [The Plate Load Test Simplified | Foundation Engineering | Elementary Engineering](https://www.youtube.com/watch?v=8JnmHtjayI8) — Elementary Engineering
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/foundation_engineering/bc-from-load-settlement-sand
- Whole chapter: https://www.bctengineer.com/md/semester_5/foundation_engineering/chapter-6

## Question

How do you calculate bearing capacity from the load settlement curve obtained from a plate load test for sandy soil?

## Short answer

Plot pressure vs settlement. Determine ultimate plate capacity qup from peak or tangent intersection. For sand, footing qu = qup(B/Bp). Safe bearing capacity is qu/F. Also check settlement using plate–footing settlement relation; allowable pressure is the smaller of shear and settlement criteria.

## Answer

The load–settlement curve of a plate load test on sand is plotted as pressure $q$ against settlement $s$.

1. **Ultimate bearing capacity of the plate** $q_{up}$: take the pressure at the point of failure (peak). If the curve has no clear peak, use the intersection of tangents drawn to the initial and the final straight parts of the curve (or the break point on a log–log plot).
2. **Footing capacity:** in sand, $q_u$ increases with width, so $q_{u}(\text{footing}) = q_{up}\dfrac{B}{B_p}$.
3. **Safe bearing capacity (shear):** $q_s = q_u/F$ with $F = 2.5$ to $3$.
4. **Settlement criterion:** for the permitted settlement of the footing (25 mm), the equivalent plate settlement is found from $\dfrac{S_f}{S_p} = \left[\dfrac{B(B_p+0.3)}{B_p(B+0.3)}\right]^2$, and the pressure for that plate settlement is read from the curve.
5. The **allowable bearing pressure** is the smaller of the safe pressure by shear failure and the pressure by settlement.

## Check yourself

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

1. How does qu of a footing on sand relate to the plate qup?
   A. qu = qup * B/Bp
   B. qu = qup
   C. qu = qup * Bp/B
   D. qu = qup / 2
   Answer: A. Sand capacity increases with width. (Key point: Scaling to footing)

2. If the curve has no clear peak, how is failure load found?
   A. Take the maximum settlement load
   B. Intersection of tangents to initial and final straight parts
   C. Take half the final load
   D. Take load at 25 mm
   Answer: B. The tangent-intersection gives the break point. (Key point: No clear peak)

3. Which is adopted as allowable bearing pressure?
   A. The larger of the two
   B. Their average
   C. The smaller of the safe pressure by shear and that by settlement
   D. The shear value only
   Answer: C. Both criteria must be satisfied. (Key point: Allowable pressure)

## Related in Foundation Engineering

- [Footing size from plate load test curve](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Aplate-load-footing-size-3200kn) — Foundation Engineering, chapter 6
- [Pile capacity in sand, group effect, load test](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Apile-capacity-sand-group-load-test) — Foundation Engineering, chapter 8
- [Limitations of plate load test](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Aplate-load-test-limitations) — Foundation Engineering, chapter 6, asked 5×
- [Plate load test and limitations](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Aplate-load-test-description) — Foundation Engineering, chapter 6
- [Factors affecting bearing capacity; water table](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Abearing-capacity-factors-water-table) — Foundation Engineering, chapter 6, asked 5×
- [Mat bearing capacity: cohesive vs cohesionless](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Amat-bc-cohesive-vs-cohesionless) — Foundation Engineering, chapter 7, asked 2×

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