Experimental Evaluation of Rockfill Alteration

摘要

A methodology for evaluating the alteration of rock fill materials is proposed in this paper. The study focuses on the mechanical behavior of a basalt rockfill from Marimbondo Dam in Brazil, which has been in operation since 1975. Consideration is given to the process of natural alteration in the field. Details of design and performance of a large Soxhlet device are presented. This equipment promotes the accelerated weathering of large rockfill samples by continuous lixiviation. Soxhlet results allow interpretation of natural rockfill alteration in the field. The results indicate that lixiviation produces a change of chemical element concentrations, an increase of dimensions of discontinuities and an increase of deformability of the basalt rock. Laboratory direct shear tests were performed on weathered rockfill specimens in a large shear box. Significant reduction of shear strength of both laboratory and field altered materials has been observed when comparing to the intact rockfill strength. The results show that the weathering conditions imposed by the Soxhlet device simulate adequately the natural weathering in the field, making possible a prediction of the long-term mechanical behavior of rockfills.