What Is Plate Load Test | Method of Plate Load Test | Limitations of Plate Load Test | Advantages & Disadvantages of Plate Load Test
Table of Contents
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
Here, the two different methods of plate load test are as follows.
- 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.
Apparatus of Plate Load Test
Here, the list of apparatus used in plate load test are as follows.
- 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
Some limitations of plate load test are as follows, please look out.
- Size Effect.
- Scale Effect.
- Time Effect.
- Interpretation of Failure Load.
- Reaction load.
- Water-Table.
We have detailed all the limitations of the plate load test as follows.
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
Here, the list of different pros of plate load tests are as follows.
- 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
Here, the list of different cons of plate load tests are as follows.
- 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.
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What Is Plate Load Test?
The Plate Bearing Test (or Plate Loading Test) is an insitu load bearing test of soil used for determining the ultimate bearing capacity of the ground and the likely settlement under a given load. The Plate Bearing Test is normally carried out at foundation level, either on the surface or in a shallow pit.
Method of Plate Load Test
The plate load test, which is used to determine bearing capacity and settlement, may be carried out by either using a gravity loading or truss loading method. A test pit of the same depth as the foundation and width equal to five times the size of bearing plate is dug in the ground.
Plate Load Test
The plate load test basically consists of loading a steel plate placed at the level where the actual load is to be applied, and recording the deformation (settlement) corresponding to successive load increments. From: Soil Improvement and Ground Modification Methods, 2015.
Plate Bearing Test Procedure
The general procedure of plate bearing test is very simple. It basically consists of loading a steel plate of known diameter and recording the settlements corresponding to each load increment. The test load is gradually increased till the plate starts to settle at a rapid rate.
Plate Bearing Test Calculation
The load-settlement curve is plotted from which the settlement and bearing capacity of the soil can be determined. The total value of the load on the plate divided by the area of the steel plate gives the value of the ultimate bearing capacity of soil.
Plate Load Test Results Interpretation
Having determined the total value of the load required to induce settlement, we can then calculate the ultimate bearing capacity of the ground (the maximum vertical pressure that can be applied before shear failure occurs).
Plate Load Test Method Statement
Plate load test method statement is a description that ensures necessary precautions, health & safety risks have been identified and safety systems are put in place during the testing activity in determining the ultimate load bearing capacity of soil over the in-situ condition.
Plate Load Test Calculation
From the graph, we can find out the value of ultimate load for the plate, which is equal to the corresponding settlement of 1/5th of plate width. The curve breaks at one point, the load corresponding to that break point is considered as ultimate load for plate.
How to Calculate Cbr from Plate Bearing Test?
The data generated from plate bearing tests also allows for a fairly accurate calculation of CBR, derived from the subgrade reaction.
CBR plate load test results
- Settlement = ρ;
- Plate Diameter = B;
- Ground Stiffness = E;
- Plate Pressure = q;
- Poisson’s Ratio = v;
- So that ρ = (((q x B x (1 – v2))/ E) x (π/ 4).
How Is Plate Load Test Done?
The plate load test, which is used to determine bearing capacity and settlement, may be carried out by either using a gravity loading or truss loading method. A test pit of the same depth as the foundation and width equal to five times the size of bearing plate is dug in the ground.
What Is Limitation of Plate Load Test?
- It has limited depth of influence. It could only give the bearing capacity of soils with depths up to two times the diameter of plate.
- It may not provide information on the potential for long-term consolidation of foundation soils
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