Optical Model Test on Work Mechanism of Single Pile with Cap

A deformation measurement system based on the digital image correlation method has been developed for studying the work mechanism of a single pile with a cap. A digital camera with high resolution is used to capture the gradual deformation failure process of the pile foundation under vertical load. Reliability and precision of this measurement system are validated by an example, which presents sub-pixel precision. The test results indicate that the settlement of the pile foundation varies gradually with total load. As the load increases, the ultimate state of the pile is earlier reached than that of the soil under the cap, and the additional increase in load is taken mainly by the soil. The displacement pattern of a pile with a cap is similar to that of a single pile without a cap. The plastic region of soil beneath the cap is developed after the pile reaches the ultimate state and the plastic region is transformed from cap edge to center as the load increases. A triangular compression zone beneath the cap occurs and is similar to those proposed by Terzaghi using the limit equilibrium method. The pile foundation is presented as the general shear failure. The test results indicate that this deformation measurement system is a useful tool for geotechnical physical model test to study global and localized deformation problems.