Rock mass characterisation for rock dredging projects
This chapter discusses general aspects of the characterisation of rock for dredging projects. The following subjects are treated: intact rock strength, discontinuities and block size, rock mass strength, weathered rock mass and rock cementation. The information that is needed to arrive at meaningful engineering geological units for a project relates to useful description methods of the rock mass. The effect of mineralogical composition, rock microstructure, homogeneity and anisotropy on the mechanical behaviour of intact rock should be considered. If the rock is anisotropic, strength tests should always be carried out in at least two directions: normal and parallel to the anisotropy. In site investigation for rock excavation projects, normally the unconfined compressive strength of rock is the standard used to define rock strength. Many dredging projects take place on the boundary of weathered rock and overlying soil. In many dredging projects in coastal areas the phenomenon of cementation of soils is encountered.