Large-scale two-dimensional laboratory load tests of rock-socketed piles in synthetic rock-masses

Rock-socketed piles are a common foundation solution to transfer heavy loads from structures to the underlying rock mass. Their total capacity is largely governed by a skin friction mechanism (shaft resistance) developed at the rock-pile interface. The prediction of shaft resistance is a complex engineering problem and a traditional method to experimentally evaluate it is by in-situ load tests. Rock mass quality has a great influence on the shaft resistance, however the mechanisms and details of such influence are poorly understood since the rock mass quality is usually not defined during these load test programs. This paper presents a laboratory attempt to study the influence of two significant rock mass characteristics (joint orientation and infilling material) on the shaft resistance by a series of large-scale two-dimensional load tests. The tests were performed in four differently configured synthetic rock masses composed of concrete. The test results revealed that diagonal orientation of joint sets caused an approximately 150% reduction in shaft resistance when compared to what was measured in horizontal-vertical joint oriented rock masses. The soft and weak infilling material caused a dramatic reduction in shaft resistance, by an order of magnitude, when compared with clean and tight joints. Finally, the test results were evaluated using the micromechanical approach developed by researchers at Monash University.