A New Rod Shear Device for the Measurement of the Degradation of Soil-Pile Interfaces

Abstract

Abstract A laboratory model pile testing apparatus (Rod Shear) was developed toobtain a better understanding of the behavior of soil/pile interfaces under awide range of loading conditions. The instrumented model pile is capable ofmeasuring the frictional resistance mobilized during loading and the porepressures generated at the soil/pile interface. This article presents adescription of the Rod Shear, the method used to prepare the sample, and theprocedure to conduct the test. Preliminary results on Kaolin clay are included. Finally, a discussion regarding further research possibilities using this newRod Shear is given. Introduction Laboratory model pile tests are an inexpensive, versatile means of studyingthe behavior of cyclically loaded piles in clay. Safe and economical piles canbe designed without relying on expensive pile load tests or empiricalcorrelations, if the critical factors affecting pile capacity under static andcyclic loading can be determined. An optimum design is especially important foroffshore structures which require costly, large diameter, very long piles whichare subjected to cyclic wave storm loading and possibly earthquake loading. Laboratory model pile tests can be performed on a variety of soils undercontrolled conditions of lateral stress, vertical stress, degree ofconsolidation, and degree of saturation. The purpose of this research was to develop an improved Rod Shear device, atriaxial-type test apparatus using an instrumented model pile, for determiningthe mechanism of degradation of skin friction in clays under cyclic axialloading. The amount of load that the soil can support without failure is known as thesoil resistance or pile capacity. During cyclic loading, the ability of thesoil to carry a load may decrease. Less load is transferred from the pile tothe soil as the skin friction, i.e. the shear transfer, degrades. Past researchhas shown that the pile capacity under cyclic loads may be significantly lessthan the static capacity (Matlock and Holmquist [1]; Bogard and Matlock [2];Briaud and Felio [3]; Poulos [4,5,6]). The degradation of skin friction may bedue to changes in pore water pressure and the migration of pore water and/ordue to realignment of clay particles (Bogard and Matlock [2]).