MODIFICATION TO IS CODE ON INTERPRETATION OF PILE LOAD TEST DATA

Abstract

Pile load tests are carried out in almost all major projects and the estimates based on these tests are often taken as the final word on carrying capacity of piles. Pile-soil conditions at the time of load test may not remain the same under the working load conditions. For example, (1) thickness of various soil layers at different locations of the same site may/ vary; (2) a part of the ground support may be lost due to scour in foundations of river bridges, (3) loss of shear strength in clays due to remoulding during the construction process and the subsequent thixotropic strength gain in soil with time etc. The results of the load test may become inapplicable under these changed conditions. The IS procedure ignores the above aspects and assumes that the observed load-settlement curve provides a valid representation of actual behaviour of the pile under working load conditions. Here, a computer aided procedure based on Hazarika and Ramasamy (2000) accounting the above aspects is recommended for the interpretation of the pile load test data. This method provides a realistic approach for the estimation of the load-settlement behaviour of piles. However, the accuracy of the method depends upon the appropriate choice of soil parameters such as Ks, Ng, a, 6, Zt, Zs etc which have to be chosen based on available literature. In the present case, these critical, soil parameters are chosen by a process of matching the observed load-settlement in the load test with the one predicted for the test condition. Reanalysis of the pile adopting these parameters for the actual pile-soil situation occurring under the working load gives a moderated load-settlement curve. Estimation of safe load using this moderated curve is expected to provide a better estimate. The above procedure has been translated into a user friendly package in Visual Basic 6.0 incorporating suitable knowledge base. Using this package, the results of a number of pile load tests have been analyzed and the results are evaluated to assess the reliability of the suggested procedure.