A model test designed for measuring negative friction response of an end bearing pile

This paper presents a design of model test for measuring the negative friction response of an end bearing pile. A half bridge connection of strain gauges is proposed to eliminate the influence of temperature fluctuation during the long term test. A dummy model pile embedded in the same environment as the test pile is used. Test results show that the negative friction response is closely related to the relative displacement on the pile-soil interface. Most of negative friction occurs during primary consolidation stage. The negative friction increases slowly with the secondary compression of soil. As the primary consolidation proceeds, neutral point gradually moves to the bottom of the compressible layer. The final position of neutral point is close to a depth of 0.9 times the thickness of compressible layer. The downdrag force caused by the compressible layer is fully balanced by the increased positive friction on the pile segment between neutral point and pile bottom as well as the end bearing capacity of the pile.