---
title: "Plate load test and limitations"
subject: "Foundation Engineering"
chapter: 6
key: "semester_5/foundation_engineering:plate-load-test-description"
source: https://www.bctengineer.com/q/semester_5/foundation_engineering/plate-load-test-description
site: BCT Engineering
---

# Plate load test and limitations

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

- Asked in: 2082 Bhadra, 4 marks
- Video: [Plate Load Test | Soil Bearing Capacity | Soil Mechanics | ASTM D 1194 | All About Civil Engineer](https://www.youtube.com/watch?v=MNQuBqhHKu8) — All About Civil Engineer
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/foundation_engineering/plate-load-test-description
- Whole chapter: https://www.bctengineer.com/md/semester_5/foundation_engineering/chapter-6

## Question

Describe plate load test and its limitations.

## Short answer

A rigid steel plate (30–75 cm) is loaded in increments at foundation level, and settlement is recorded. The ultimate load is obtained from the load-settlement curve. For sand, qu(footing) = qu(plate) × B/Bp and settlement is scaled; for clay, qu is the same. Limitations: only shallow stressed depth is tested, no long-term consolidation measurement, size effects prevent direct extrapolation to large footings, and it is expensive and represents a small area.

## Answer

The **plate load test** is an in-situ test used to find the ultimate bearing capacity of soil and the settlement of a footing at a given load. A rigid steel plate is loaded in stages and the settlement is recorded at each stage.

#### Procedure
1. A pit is dug to the foundation level, with width at least 5 times the plate size. A square or circular plate of 30 to 75 cm (about 25 mm thick) is bedded on the levelled soil.
2. A load is applied through a hydraulic jack acting against a reaction (a loaded platform or a kentledge, or an anchored truss). The jack load is measured by a pressure gauge or proving ring.
3. Load is applied in increments of about one-fifth of the estimated safe load. Settlement is read on dial gauges (usually 2 to 4, supported on an independent datum beam) at set time intervals, until the rate of settlement falls to $0.02$ mm/min (or 24 h in clay) before the next increment.
4. The test continues until failure or until the settlement is 25 mm or more (about 1.5 times the proposed design load).

```text
        Jack + gauge
           |   Dial gauge
  ====Reaction beam====
           |
        [Plate]    <- test pit
  ///////////////
```

#### Results
- The load–settlement curve is plotted. The ultimate load is the point of failure, or the intersection of tangents on the initial and final parts. For sand, $q_u(\text{footing}) = q_u(\text{plate}) \times B/B_p$ and settlement $S = S_p\left[\dfrac{B(B_p+0.3)}{B_p(B+0.3)}\right]^2$. For clay, $q_u$ is the same for plate and footing.

#### Limitations
- The stressed depth is small (about $2B_p$), so deeper weak layers are not tested.
- Only immediate settlement is measured, not long-term consolidation in clay.
- Size effects: results cannot be extrapolated directly to large footings.
- Represents only a small area, and is expensive and slow.

## Check yourself

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

1. What does the plate load test find?
   A. Water content
   B. Ultimate bearing capacity and settlement at a given load
   C. Pile capacity only
   D. Permeability
   Answer: B. It is an in-situ test giving bearing capacity and settlement from a load-settlement curve. (Key point: Purpose)

2. How is load applied?
   A. Dropped at once
   B. In increments of about one-fifth of the estimated safe load, waiting until settlement rate falls to 0.02 mm/min
   C. Continuously without readings
   D. In one increment
   Answer: B. Each increment is held until the rate of settlement falls to 0.02 mm/min (or 24 h in clay). (Key point: Loading procedure)

3. How is footing capacity obtained from the plate in sand?
   A. Same as plate
   B. q_u(footing) = q_u(plate) x B/B_p
   C. Divided by B/B_p
   D. Square of B/B_p
   Answer: B. In sand q_u scales with width; in clay q_u is the same for plate and footing. (Key point: Scaling to footing in sand)

4. Which is a limitation?
   A. It tests deep weak layers
   B. Only immediate settlement is measured, not clay consolidation
   C. It measures long-term settlement
   D. It is cheap and fast
   Answer: B. Stressed depth is small (about 2B_p) and consolidation is not captured. (Key point: Limitation)

## Related in Foundation Engineering

- [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×
- [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
- [Bearing capacity from plate load curve](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Abc-from-load-settlement-sand) — 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

## Related in other subjects

- [Limitations of direct shear test](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Adirect-shear-limitations) — Soil Mechanics, chapter 10
- [CST steel plate: stiffness, load vector, displacements](https://www.bctengineer.com/question.md?key=semester_8%2Fcomputational_techniques_in_civil_engineering%3Acst-stiffness-load-displacement-c8) — Computational Techniques in Civil Engineering, chapter 4
- [CST plate: stiffness, load vector, displacements](https://www.bctengineer.com/question.md?key=semester_8%2Fcomputational_techniques_in_civil_engineering%3Acst-stiffness-load-displacement-k8) — Computational Techniques in Civil Engineering, chapter 4
- [Timber-steel plate composite member: permissible load](https://www.bctengineer.com/question.md?key=semester_3%2Fstrength_of_materials%3Atimber-steel-composite-permissible-load) — Strength of Materials, chapter 3