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## What is Plate Load Test?

Plate load test is done at site to determine the ultimate bearing capacity of soil and settlement of foundation under the loads for clayey and sandy soils. So, plate load test is helpful for the selection and design the foundation. To calculate safe bearing capacity suitable factor of safety is applied.## Apparatus for Plate Load Test on Soil

- Mild Steel plate
- Hydraulic jack
- Reaction beam or reaction truss
- Dial gauges
- Excavating tools

## Procedure of Plate Load Test on Soil

A Pit is excavated in the ground at which foundation is to be laid. The size of pit is generally 5 times the size of the plate. The depth excavated should be equal to proposed foundation depth. The plate used is made of mild steel. It may be square (0.3m x 0.3m) or circular (0.3m diameter) with 25mm thickness. After excavation of pit, at center of excavated pit steel plate sized hole with âDpâ thickness is excavated and arrange the plate in it. The thickness of plate Dp is calculated by below formula^{2}is applied to set the plate and released after some time. Now load is applied with an increment of 20% of safe load. Dial gauges are arranged at bottom to record the settlement values. At 1min, 5min, 10min, 20min, 40min, and 60min and after that for every one-hour interval the settlement is observed and noted. The observations are made until the total settlement of 25mm has occurred.

## Calculation of Bearing Capacity from Plate Load Test

From the results obtained in plate load test, a logarithmic graph is drawn between loads applied to the corresponding settlement. Load is taken on x-axis and settlement is on y-axis. From the graph, we can find out the value of ultimate load for the plate, which is equal to the corresponding settlement of 1/5^{th}of plate width.

**Bearing Capacity Calculation for Clayey Soils**

Ultimate bearing capacity = ultimate load for plate
I.e. q_{u}(f) = q

_{u}(p)

**Bearing Capacity Calculation for Sandy Soils**

Ultimate bearing capacity = ultimate load for plate x {Width of pit (B_{f}) / Size of Plate (B

_{p})} q

_{u}(f) = q

_{u}(p) x B

_{f}/ B

_{p}Finally, safe bearing capacity = ultimate bearing capacity / factor of safety

**The factor of safety ranges from 2 to 3.**

## Calculation of Foundation Settlement from Plate Load Test

We can also calculate settlement for given load from plate load test as follows**Foundation Settlement Calculation on Clayey Soils**

Settlement of foundation (s_{f}) = s

_{p}x B

_{f}/B

_{p}

**Foundation Settlement Calculation on Sandy Soils **

Settlement of foundation (s_{f}) = s

_{p}[{B

_{f}(B

_{p}+ 0.3)}/{B

_{p}(B

_{f }+ 0.3)}]

^{2}Where B

_{f}and B

_{p}are widths of foundation and plate. Â

**Read More**What are the Needs and Functions of Pile Foundation? Soil Stabilization Methods with Different Materials Soil Tests Required for Shallow and Raft Foundations Pile Load Capacity Calculation for Single Pile and Group Piles