Plate bearing test procedure and calculation

Plate bearing test is an activity carried out by design engineers in the field to determine the bearing capacity with regards to the soil underneath. This test is normally carried out during the design of traffic surfaces or in shallow foundations. The results achieved after the test is carried out can be utilized as the design parameter or can be used for design assumption confirmation. The test is required to be carried out with the general accordance of BS 1377 contained in part 9 of the 1990 In-Situ Teats.

This is the procedure of carrying out the load test with regards to soil and the determination of settlements from the test and bearing capacities. This procedure assumes that down towards the depth and in relation to the influence of stresses, soil strata is uniformly reasonable. Please contact us to discuss your site investigation requirements on 0333 5670 754.

Apparatus

The apparatus used include loading equipment, bearing plates, and instruments that will be used to measure the resulting settlements and applied loads.

Loading equipment

Loading equipment consists of a hydraulic jack and a dead or reaction load. The reaction framework can be appropriately be loaded to provide the required reaction load towards the plate. The load utilized can either be measured by using a dial gauge assembly and proving ring or by a pressure gauge that is connected to on the output end on the hydraulic jack.

Bearing plates

Bearing plates include a mild steel 1.5 to 3 centimeters thickness and 75 cm in diameter and other few plates that are of the same thickness, but with smaller diameters. They are usually 22.5,30,45 and 60 centimeters in diameter used like stiffeners.

Settlement measurements

Settlement measurements can be made up with four or three dial gauges that are fixed to the periphery of the bearing plate but from a free datum frame. The datum frame is normally supported from a distance to the loading area.

Procedure

The plate bearing test site is prepared, and any loose materials are removed to make sure that the seventy-five-centimeter diameter plate can rest horizontally and by full contact to the soil subgrade.in case there is need of natural ground for reaction modulus of sub-grade, the topsoil can be removed to a depth of not more than twenty centimeters before testing.

The plate is then seated perfectly, and a seating load equal to the pressure of 0.07 kg/cm2 (320 Kgs for 75-centimetre diameter plate) is used and then released a few seconds later. The dial reading settlements are now recorded corresponding to the zero load. The load is then applied by using the jack, enough to make a typical settlement of 0.25 mm. In case there is not enough settlement increase or the settlement rate is less than or equal to 0.025 millimeters per minute (in the case of clay soils or soils with significant moisture content) the dial reading on the load and on the settlement are recorded. The average of the four or three dial readings on the settlement is taken as the total average settlement on the plate consistent with the applied load.

The load is thereafter increased until the average settlement increases to about 0.25 millimeters, and the average settlement and load reading are recorded. This procedure is repeated until the settlement reaches the desired reading of 1.75 millimeters or more.

Calculating the bearing capacity

From the recording and results achieved from load plate test, a graph is drawn logarithmically between the loads applied in correspondence with the settlement. The load is indicated on the X-axis, and the settlement is indicated on the Y-axis. The value of the ultimate load to be used on the plate can be found on the graph that is equal to a corresponding settlement equal to one-fifth of the plate Width. The point at which the curve break, the load matching that breakpoint is determined to be the ultimate load required for the plate. From this ultimately determined load required for the plate, the ultimate value of bearing capacity and the best safe bearing soil capacity can be determined for the foundation.