Dynamic Centrifuge Testing of Soil-Nailed Excavations
A series of dynamic centrifuge tests was conducted on models of soil-nailed excavations. The models were subjected to various levels of horizontal shaking to investigate the seismic stability of their prototypes. The scaling factor was 50 in all tests, the depth of the prototype excavation was H = 7.6 m, and the length of nails in each test varied between 0.33 H and 1 H. The tests revealed the most probable failure mechanism under strong shaking and at the same time showed that soil nailing is an excellent method for earth support in seismic regions. The paper describes details of the testing procedure. The procedure includes selection and preparation of the soil, selection and design of the nails and facing, step-by-step filling of the model box, rough simulation of possible geologic history of the soil, excavation and installation of the nails and facing, cyclic shaking, measurements of accelerations and displacements, excavation and incisions of the nailed soil after the tests, and data processing. The investigation showed that centrifuge testing can successfully simulate dynamic soil-structure interaction for complex geotechnical systems such as soil nailing. However, to incorporate pertinent details of the prototype into the model and to provide the proper boundary conditions, a carefully planned step-by-step testing procedure must be implemented. Limitations of the testing and problems encountered are also discussed.