Shear strength of Bremanger sandstone rockf ill at low stress

Abstract

The Bremanger Sandstone rock fill is used to form a cobble beach, to build an underwater foundation layer of a sea water breaker and to construct a run -way for a large crane in construction of Maasvlakte 2 (MV2), the extension of Rotterdam harbor. The main purpose of this work is to determine in the laboratory the strength of Bremanger rock fills under low stress. Tests are conducted on rock fills with a finer particle size distribution than that used at MV2. Results obtained cannot be directly used in the design of MV2 project. The influence of the testing equipment, for a given ratio of the equipment size to the particle size, of the degree of compaction and of the particle strength on the strength of the Bremanger rock fill are investigated. The effect of the test boundary conditions is researched by conducting tests with a triaxial cell apparatus, medium and small scale shear boxes and a tilt apparatus. The movement of particles was also studied during medium scale shear box testing to get a better insight into this effect. Emphasis is put on determining the contribution of dilatancy to the shear resistance of the Bremanger sandstone rock fills with respect to the contribution to resistance to rolling of particles. For this purpose, dilatancy is measured during testing and the basic friction angle of the Bremanger rock fill is determined on sandblasted rock discontinuities with a Golder shear box. The basic friction angle controls the resistance to rotation of smooth particles. Test results are fitted using empirical models. The performance of these models at predicting the strength of the tested materials is assessed.