HOW TO PERFORM PLATE LOAD TEST OF SOIL ON SITE?

Objective

Perform plate load testing to obtain the load-disposal curve of the soil at a particular depth so as to estimate the ultimate bearing capacity.

Device

  1. Square shaped test plate (300mm or 450mm or 600mm or 750mm)
  2. Hydraulic Jack (50T Capacity)
  3. Hydraulic Pump (50T Capacity)
  4. Pressure gauge (for reading 50 T load with a sensitivity of 0.5 T)
  5. Proving Ring or Load Cell (50T Capacity)
  6. 4 numbers of dial gauge (with a sensitivity of 0.01 mm and travel of 50 mm)
  7. loading column
  8. Dial Gauge Supporting Channel
  9. dial gauge stand
  10. magnetic base for dial gauge
  11. Truss with loading platform equipment (girder, plate, sand bag etc.) or anchor rod
  12. plumbob
  13. spirit level
  14. Tripod (for erecting the platform or truss frame)
  15. Pulley block (for lifting girders or truss frames)

Process

  1. Excavate the test pit. The size of the test pit should be 5 times the size of the test plate (B.)P) and the depth equal to the depth of the foundation.
  2. The loading platform should be erected above the test pit in such a way that the vertical line drawn through the center of gravity of the load passes through the center of the base of the test pit. This can be achieved by positioning the reaction girder (truss) with the help of plumb bob and spirit level. The load on the platform must be at least 50% more than the estimated load to be transferred to the plate. This will ensure the safety of the platform for any small variation of the CG of the loading platform from the vertical axis of the pit.
  3. Center the test plate at the base of the pit. Ensure that the ground surface under the test plate is completely horizontal and level so that no stress concentration occurs under the plate during loading. If the ground surface is slightly uneven then a thin layer of sand is spread under the test plate.
  4. Place the hydraulic jack on top of the plate so that when hydraulic pressure builds up, the jack pushes against the loading platform. If necessary, place a loading column between the test plate and the jack to ensure that the jack reaches the loading platform.
  5. Place at least two dial gauges diagonally at the corners (preferably 4 at all corners of the test plate) to record the plate’s settlement. The dial gauge must be carefully supported on a stable base that does not settle with the plate. This can be achieved by placing two cross beams at ground level, on which the dial gauges are supported with the help of magnetic bases. The settling of the plate is transmitted through the dial gauge stand to the dial gauge.
  6. The dial gauge should be placed such that the plunger of the dial gauge is at the beginning of the rebound (ie the plunger is initially pushed upwards) so that it is released when the plate is frozen and the reading changes and the difference in reading is provided Go. plate disposal. (See fig-1 for plate load setup)
  7. A load is applied to the plate by pumping hydraulic pressure into the jack. The upward motion of the plunger of the jack tries to push the loading platform up. Since the pressure built into the jack (eg 1 or 2 T) is much less than the load on the platform, the pressure in the jack will push the test plate down, assuming the loading platform (say 30 to 40 T) is rigid. Cooperation. It is a similar case to the extension of a system between two supports. Expansion causes weak support (ground) yields.
  8. 0.7 t/m. apply a seating load of2 which is issued before the actual loading begins.
  9. Note the initial reading of the dial gauge.
  10. The load is applied by means of hydraulic jacks in convenient increments. The load increase may be one-fifth of the expected safe bearing capacity or one-tenth of the final bearing capacity or any other smaller load. The applied load is read either from the pressure gauge mounted on the hydraulic pump or from the proving ring fixed between the jack and the reaction platform.
  11. The settlement of the plate is seen from the dial gauge reading. Settlement should be observed for each increase of load after 1, 4, 10, 20, 40 and 60 minutes and thereafter at hourly intervals until the rate of settlement is less than approximately 0.02 mm per hour. Enter readings in table form. (see fig-2)
  12. After completing the recording of the settlement reading under load, the next load increment is applied and the dial gauge reading is noted under new load.
  13. Recording of loading increments and settlements under each load continues until the maximum load is reached. The maximum load to be applied corresponds to 1.5 times the estimated final load or 3 times the proposed allowable bearing pressure.

observation and calculation

The load intensity and settlement observations of the plate load test are plotted. The figure shown below (Figure-3) shows a set of typical load settlement curves. The ultimate bearing capacity is taken as the load at which the plate begins to sink rapidly, i.e. when the curve descends to a vertical line. It can be seen from Figure 3 that failure is not pronounced in dense sand or hard soil. In such cases a plot of load and settlement, both being taken in logarithmic scale, gives two straight lines. The intersection of these lines is taken as the ultimate bearing capacity of the soil (see fig. 4).

Figure-1 (Plate Load Test Setup)
Figure-1 (Plate Load Test Setup)

plt observation sheet
Figure-2 (PLT Observation Sheet)

PLT load-disposal curve
Figure-3 (PLT load-disposal curve)

PLT load-disposal logarithmic curve
Fig-4 (PLT load-disposal logarithm curve)

also read post Uncertainties involved in plate load testing.


Also read: How To Calculate Soil Bearing Capacity From Plate Load Test

Er. Mukesh Kumar

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Er. Mukesh Kumar is Editor in Chief and Co-Funder at ProCivilEngineer.com Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.