Tunneling beneath driven or jacked end-bearing piles in sand

This paper presents centrifuge model test data that relate to the problem of tunneling beneath driven or jacked end-bearing piles in sand. The centrifuge model consisted of a tunnel and two piles and allowed for the acquisition of subsurface digital images throughout the tests. Soil and pile displacements were measured using particle image velocimetry and close-range photogrammetry techniques. The piles were jacked into the ground in-flight prior to tunnel volume loss to obtain ground stress profiles representative of conditions around driven or jacked piles. Patterns of displacements and calculated soil strains are presented to illustrate mechanisms of displacement and soil behavior. The measured soil and pile displacements are compared against greenfield test measurements. The results indicate that driving the piles significantly alters greenfield conditions and that greenfield displacements should not be used as an input for analytical tunnel-soil-pile interaction analyses for driven or jacked piles. Large pile displacements were observed to occur suddenly in the tests, illustrating the brittle nature of the soil in the areas affected by pile installation. A relationship between relative pile-tunnel location and the volume loss at which large pile displacements occurred is presented, which provides useful guidance to tunnel design engineers.