Plate load test IS 1888
This procedure may be adequate for light or less important structures under normal conditions, relevant laboratory tests or field tests are essential in the case of unusual soil types and for all heavy and important structures. Plate load test method used for determination of ultimate bearing capacity of soil in place which assumes that soil strata is reasonably uniform. The load test included in the standard is also used to find modulus sub grade reaction useful in the design of raft foundation -and in the design of pavements. The test results reflect only the character of the soil located within a depth of less than twice the width of the bearing plate. Since the foundations are generally larger than the test plates, the settlement and shear resistance will depend on the properties of a much thicker stratum.
Moreover this method does not give the ultimate settlements particularly in case of cohesive soils. Apparatus :Circular or square bearing plates of mild steel, not less than 25 mm in thickness and varying’in size from 300 to 750 mm with grooved bottom of 1 mm depth 2 mm pitch.
Increment of load is 20 % of ultimate load bearing capacity of soil. Settlements should be observed for each increment of load after an interval of 1, 2.25, 4, 6.25, 9, 16 and 25 min and thereafter at hourly intervals to the nearest 0.02 mm. In case of clayey soils the ‘time settlement’ curve shall be plotted at each load stage and load shall be increased to the next stage either when the curve indicates that the settlement has exceeded 70 to 80 percent of the probable ultimate settlement at that stage or at the end of 24 hour period.For soils other than clayey soils each load increment shall be kept for not less than one hour or up to a time when the rate of settlement gets appreciably reduced to a value of 0.02 mm/min. The next increment of load shall then be applied and the observations repeated. The test shall be continued till, a settlement of 25 mm under normal circumstances or 50 mm in special cases such as dense gravel, gravel and sand mixture, is obtained or till failure occurs, whichever is earlier. Alternatively where settlement does not reach 25 mm, the test should be continued to at least two times the estimated design pressure. If needed, rebound observations may be taken while releasing the load.
Moreover this method does not give the ultimate settlements particularly in case of cohesive soils. Apparatus :Circular or square bearing plates of mild steel, not less than 25 mm in thickness and varying’in size from 300 to 750 mm with grooved bottom of 1 mm depth 2 mm pitch.
Increment of load is 20 % of ultimate load bearing capacity of soil. Settlements should be observed for each increment of load after an interval of 1, 2.25, 4, 6.25, 9, 16 and 25 min and thereafter at hourly intervals to the nearest 0.02 mm. In case of clayey soils the ‘time settlement’ curve shall be plotted at each load stage and load shall be increased to the next stage either when the curve indicates that the settlement has exceeded 70 to 80 percent of the probable ultimate settlement at that stage or at the end of 24 hour period.For soils other than clayey soils each load increment shall be kept for not less than one hour or up to a time when the rate of settlement gets appreciably reduced to a value of 0.02 mm/min. The next increment of load shall then be applied and the observations repeated. The test shall be continued till, a settlement of 25 mm under normal circumstances or 50 mm in special cases such as dense gravel, gravel and sand mixture, is obtained or till failure occurs, whichever is earlier. Alternatively where settlement does not reach 25 mm, the test should be continued to at least two times the estimated design pressure. If needed, rebound observations may be taken while releasing the load.
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