Measurement of Strain Distribution Along Precast Driven Pile During Pile Load Test

Abstract

One of the basic parameters required for forecasting pile deformation under loads is the characteristics and profile of the shaft load transfer from the pile to the surrounding soil.  This parameter can be obtained by measuring the strain distribution along the pile during full-scale pile load test.  For cast-in situ bored pile, the strain measurement can be easily done by fixing the sensors to the reinforcement cage before pouring the concrete. For precast driven / jack-in piles, the application of instrumented full-scale static load tests is far more challenging than their bored pile counterparts due to significant difference in method of pile installation. Due to practical shortcoming of conventional instrumentation method instrumented full-scale static load tests are in fact rarely used in driven pile application in this region.  For hollow precast spun concrete piles attempts have been made by geotechnical engineers to measure the strain distribution by installing either an instrumented reinforcement cage or instrumented pipe into the hollow core of spun piles followed by cement grout. However in this method, known as approximate method, the measured characteristics cannot be considered to represent the working piles because the presence of reinforcement/pipe and the grout would alter the stiffness of the test pile.  In this paper a method to measure the strain distribution along the installed precast spun concrete pile during full-scale pile load test is described. The method utilizes the hollow core of the spun pile without changing the physical properties e.g. stiffness, of the pile. The main advantages of this method are: the measurement can be done at any location along the pile, the sensors can be retrieved and the measured characteristics are representative of those of the working piles