Correlated UCS values from PLI

It is a general practice to carryout Point load test for 2-3 specimens retreived from Pile bores and convert to UCS and evaluate the socketing depths with other criterias, such as CR/RQD of adjacent boreholes, sample sizes, angularity/shape of samples, weathering conditions, rock condition and depths of adjacent piles etc. However as per the ASTM D 5731 to obtain accurate PLI values for lump samples at least 20 specimens shall be tested for a sample, and which is not possible/practicle with samples from bored piles. However it is understood testing 2-3 specimens are carried internationally and an accepted criteria and since it is not the sole parameter which determines the socketing the accurancy of the test results are not required to a manner it is requested to carry out as per ASTM D 5731. 

However I would like to know from any expert who dealt in this area, the reliability of UCS recieved from PLI test if we test only 1 specimen, 2 specimen or 3 specimen.



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