The Plate Load Test: Procedure, Methods, and Applications in Geotechnical Engineering

What Is Plate Load Test?

The Plate Load Test is a field method to identify the ultimate bearing capacity of the soil as well as the possible settlement under such a specified load. In essence, the test consists of taking a rigid plate only at the base level then deciding the settlement relating from each amount of the load.

The ultimate bearing potential is then assumed to be the load over which the plate begins to sink at such a quick speed. The bearing plate is square, with a minimum standard of 30 cm² as well as a max value of 75 cm². The width of the steel plate shall be not only about 25 mm.

Method of Plate Load Test

Plate Load Test has two method:

Gravity Loading Platform Method.
Reaction Truss Method.

1. Gravity Loading Platform Method

With this scenario, a frame is built over a vertical column lying mostly on test plate while loading is carried out using sandbags, stones including concrete blocks.

As loading is added to the test tray, it sinks or settles down. Settlement of the plate is meant by the use of sensitive dial gauges. 2 dial gauges should be used for the test specimen.

The dial gauges are placed on a data bar that is individually funded. As the plate settles, the branch of the dial gauges gradually decreases and the settling is suggested. The load is shown on the hydraulic jack load gauges.

2. Reaction Truss Method

Once the movement of the jack is supported by a truss reaction. The truss is fixed to the surface by the anchors of the earth. Mostly with aid of hammers, such anchors are securely anchored in the earth.

The truss reaction is normally constructed of mild steel parts. Guy ropes are also used to maintain the lateral tension of the truss. These days, any use of truss reaction is much more common because it’s basic, fast, and far less sloppy.

What Is Plate Bearing Test Procedure?

The plate bearing test procedure is as follows.

Plate Load Test Apparatus

Test Plate.
Hydraulic Jack & Pump.
Reaction Beam or Reaction Truss.
Dial Gauges.
Pressure Gauge.
Loading Columns.
Necessary Equipment for Loading Platform.
Tripod, Plumb Bob, Spirit Level, etc.

Procedure of Plate Load Test

The measures required to conduct a plate load test are listed below

Excave the test pit to the optimal depth. The scale of the pit would need to be at least five times the size of the test pan (Bp).
A tiny opening or gap is formed in the middle of the pit. The depth of penetration is the same as that of the steel plate. The lower depth of the hole should lead to the level of the real base. The depth of the cavity is formed so that perhaps the proportion of the depth to the width of the hole is equivalent to the total of the average depth to the impact overall of the hole.
The mild steel plate is often used as a load-bearing plate, the thickness of that should have at least 25 mm as well as the size of which can range between 300 mm to 750 mm. The plate may be square or oval. Usually, a square plate has been used for a square base and a circular plate will be used for a circular base.
The column is mounted in the middle of the plate. The load is passed to the plate via the central column.
The load may be moved to the column by both the Gravity Loading system or the truss method.
Also for gravity loading process, the platform is installed over the column and also the applied load to the platform by ways of sandbags or some other dead load. The hydraulic jack is mounted between both the column as well as the loading platform for incremental loading. This method of loading is named reaction loading.
At least 2 dial gauges must be mounted in the diagonal corners of the plate to track the settlement. The gauges are mounted on the platform ensuring that they do not rest on the counter.
Adjust the seating load of 7 T/m² then activate this before the actual loading begins.
The initial readings shall be remembered.
The load would then be applied through the hydraulic jack then gradually increased. For particular, the increase is one-fifth of the projected protected bearing capacity or one-tenth of the ultimate bearing capacity or some other smaller value. The load applied is recorded from the pressure gauge.
Settlement is detected with each increase and from the dial gauge. Increased load-setting must be detected at 1, 4, 10, 20, 40, and 60 minutes, then at hourly intervals, till the rate of settlement is even less than 0,02 mm each hour.
Upon finishing the data collection for a specific load, the next load increment is implemented as well as the readings are recorded under that new load. This increase and data collection is replicated until the final load is added. Maximum load is usually 1.5 times the expected final load or 3 times the expected permissible bearing pressure.

Plate Bearing Test Calculation

The plate load test only at jobsite be performed to assess the bearing capacity . A pit of scale 5 Bp X 5 Bp explores to a detailed results to the depth of the base in order to perform a plate load test only at location.

The plate must be made of 0.3 m² steel and therefore should be 25 mm wide. Circular plates are most often used sometimes. Often a wide plate of 0.6 m² is often used.

Throughout the pit, the central hole digs the size of Bp X Bp. The size of the central hole (Dp) can be obtained A plate load test is a field method to identify the ultimate soil bearing potential as well as the possible settlement under that specified load.

The test from the resulting relation.

[Dp/Bp] = [Df/Bf]

Dp = [ (Df/Bf) x Df ]

Test Result Plate Load Test

The ultimate capacity of the planned foundation qu(f) could be achieved by the use of the following factors.

For clay soils,

qu (f) = qu(p)

For sandy soils,

qu (f) = [ { qu(p)} X { Bf/Bp}]

The plate may be used to assess the settlement for a specific loading strength (q0). The relationship between the positioning of the plate (sp) and those of the base (sf) at the same load strength as seen below-

For sandy soil,

Sf = Sp X { Bf/Bp}

Assess the determination of a given loading strength (q0).

Limitations of Plate Load Test

Size Effect.
Scale Effect.
Time Effect.
Interpretation of Failure Load.
Reaction load.
Water-Table.

1. Size Effect of Plate Load Test

The strength and settling properties of the materials inside the pressure bulbs represented the effects of the plate load examination. Because as pressure bulb depends on the amount of the filled field, it becomes much deeper for the specific base.

If the soil isn’t really homogeneous and isotropic to a significant depth, the plate load test often does not reflect the actual circumstances.

2. Scale Effect of Plate Load Test

Throughout the case of saturated clays, the ultimate bearing capacity is directly proportional to the size of the layer, although in the case of cohesionless soils, the ultimate bearing capacity rises only with size of the plate.

In order to reduce the scale effect, it is preferable to replicate the plate load test for plates of two or more different dimensions and also to generalise the bearing potential for the actual base and to use the average value provided.

3. Interpretation of Failure load of Plate Load Test

Other than in the situation of general shear failure, the failure load was not very well specified. There may be an inconsistency in personal perception of some forms of errors.

4. Time Effects of Plate Load Test

Basically, a plate load test is a limited term test. It should not send the final settlement to clay soils. The load-setting curve is not strictly descriptive.

5. Water Table of Plate Load Test

Potential of sandy soils influenced by the water table level. Whenever the water table is over the height of the base, it must be lowered by pumping until the plate is placed.

6. Reaction Load of Plate Load Test

It is not feasible to have a response of more than 250 kN. It is also impossible to measure on a wide plate of more than 0.6 m width. Only at depth of the water table, the measurement must be carried out when it is less than 1 m just below base.

Advantages of Plate Load Test

Bearing able to evaluate the actions of the base under loading conditions.
Assessing soil capability at a certain depth and predicting settlement over a certain load.
A shallow foundation could be determined on the basis of the permissible bearing size, which can be estimated in the context of a plate load test.
Time and cost-effective
It’s easy to execute.

Disadvantages of Plate Load Test

Depth of impact is small and can hardly offer soil power.
It does not have details on the prospects for long-term consolidation of the base soil.
The scale of the test plate is smaller than the real base, hence why there is a scale impact.
Significant land disturbance happens after drilling is finished.

Frequently asked questions (FAQs) that could be included in your article about the Plate Load Test:

What is a Plate Load Test?

A Plate Load Test is a field test used to determine the bearing capacity and settlement characteristics of soil beneath a foundation by applying a specified load to a steel plate placed at the foundation level.

Why is a Plate Load Test performed?

It is performed to assess the soil’s ability to support a foundation under realistic loading conditions and to predict settlement under those loads.

What are the methods of conducting a Plate Load Test?

The two primary methods are the Gravity Loading Platform Method and the Reaction Truss Method. The former uses incremental loading via sandbags or dead loads, while the latter employs a reaction truss anchored to the ground.

What equipment is used in a Plate Load Test?

Equipment includes a test plate (steel), hydraulic jack and pump, reaction beam or truss, dial gauges for settlement measurement, pressure gauge, and necessary loading apparatus.

How is settlement measured during a Plate Load Test?

Settlement is typically measured using sensitive dial gauges placed on the test plate. These gauges record vertical displacement as the load is applied and increased incrementally.

What factors influence the results of a Plate Load Test?

Factors include soil type (clay, sand), depth of the water table, size and shape of the plate, and the loading procedure used (gravity loading or reaction truss).

What are the advantages of conducting a Plate Load Test?

Advantages include its ability to simulate real-world loading conditions, cost-effectiveness, relatively simple execution, and providing valuable data for designing shallow foundations.

What are the limitations of the Plate Load Test?

Limitations include the scale effect due to the smaller size of the test plate compared to the actual foundation, limited depth of impact, and the inability to predict long-term settlement characteristics.

How are results from a Plate Load Test interpreted?

Results are interpreted to determine the ultimate bearing capacity of the soil and predict settlement under various loads, providing crucial information for foundation design and construction.

What are the key considerations before conducting a Plate Load Test?

Key considerations include site preparation (excavation depth, soil conditions), ensuring proper equipment calibration, and adherence to safety protocols during testing.