Plate Load Test
(Bearing Capacity of Soil)
In-situ static load test using a rigid plate to determine the bearing capacity and load-settlement behaviour of soil or rock at foundation level — essential for shallow foundation and pavement design.
What is the Plate Load Test?
The Plate Load Test (PLT) applies an incremental static load to a rigid steel plate placed on the test surface at the proposed foundation level. The resulting settlement is measured at each load increment to produce a load-settlement curve from which the ultimate bearing capacity, safe bearing capacity and modulus of subgrade reaction are determined.
Conducted as per IS 1888, the plate load test is one of the most reliable in-situ tests for bearing capacity determination. It is widely used for shallow foundation design, pavement sub-base assessment and ground improvement verification. Global Lab conducts PLT with 300mm, 450mm and 600mm diameter plates per IS 1888.
The plate load test (IS 1888) loads a rigid steel plate at foundation level in steps and records the settlement at each step. The load–settlement curve gives the soil’s ultimate and safe bearing capacity, the settlement expected under the design load, and the modulus of subgrade reaction (k-value).
Plate Load Test — Site Images
How the Plate Load Test is Conducted
-
1Test Pit ExcavationTest pit is excavated to proposed foundation or sub-grade level. Base is trimmed level and cleared of loose material.
-
2Plate & Reaction SetupSteel plate (300mm dia.) is placed on prepared surface. Kentledge or anchor reaction system is set up above.
-
3InstrumentationDial gauges or LVDTs are installed at minimum 3 points on the plate to measure average settlement.
-
4Incremental LoadingLoad applied in increments of approximately 1/5th of estimated failure load per IS 1888. Settlement recorded after stabilisation.
-
5Bearing Capacity & K-Value CalculationLoad-settlement curve plotted. Ultimate and safe bearing capacity determined. K-value calculated. NABL report within 3 days.
How Bearing Capacity is Worked Out from a Plate Load Test
Each load step is plotted as load intensity (kN/m²) against settlement (mm). The shape of that curve tells the engineer how the soil will behave under a real footing.
- Ultimate bearing capacity: the pressure at which settlement starts increasing rapidly. Where the curve has no sharp break, it is commonly read where tangents to the early and late parts of the curve intersect.
- Safe bearing capacity: the ultimate value divided by a factor of safety, commonly 2.5 to 3 in shallow-foundation practice (IS 6403).
- Allowable bearing pressure: the lower of the safe bearing capacity and the pressure that keeps settlement within the limit permitted for the structure.
- k-value: pressure divided by settlement, read at the settlement the design method specifies. IS 9214 uses 1.25 mm on a 750 mm plate; smaller plates need a size correction.
From a 300 mm plate to a real footing
A small plate stresses only shallow soil, so its settlement cannot be applied to a wide footing as-is. For granular soils the commonly used Terzaghi–Peck relation scales it:
Worked example: a 0.3 m plate on sand settles 6 mm at the design pressure. For a 1.5 m wide footing: Sf = 6 × [1.5 × 0.6 / (0.3 × 1.8)]² = 6 × 2.78 ≈ 16.7 mm. In clays, settlement is usually scaled in direct proportion to width (Sf = Sp × Bf/Bp), and long-term consolidation must be checked separately.
Which Soils is the Plate Load Test Suitable For?
The test gives the most dependable results on sands, gravels, compacted fills, granular sub-bases and stiff to hard clays: soils that respond within the duration of the test.
It has three limits worth planning for. A plate only stresses soil to a depth of roughly 1.5–2 times its width, so a soft layer deeper down can be missed. In saturated soft clays, the short test does not capture long-term consolidation settlement. A high water table changes the result and must be recorded. That is why the plate load test is best read alongside borehole logs or SPT data for the full soil profile.
Plate Load Test vs EV1/EV2 Test
Both load a plate, but they answer different questions. The IS 1888 plate load test finds bearing capacity and settlement for foundation design. The EV1/EV2 test (DIN 18134) uses two loading cycles to measure strain moduli, the acceptance check for compacted railway formation and subgrade layers.
Applicable Test Standards
| Standard | Title | Scope | Type |
|---|---|---|---|
| IS 1888 | Method of Load Test on Soils | Plate Load Test | Indian Standard |
| IS 6403 | Code of Practice for Determination of Bearing Capacity of Shallow Foundations | Bearing Capacity | Indian Standard |
| IRC 37 | Guidelines for the Design of Flexible Pavements | Pavement Design | IRC |
| ASTM D1196 | Standard Test Method for Nonrepetitive Static Plate Load Tests of Soils | Load Test | ASTM |