Importance of anisotropy in dam foundation, estimated by in-situ dilatometer tests

摘要

Rock mass anisotropy can be found in volcanic rocks and sedimentary formations consisting of alternating layers or beds of different rock types. Rock mass cut by one or several joint sets are anisotropic in addition to being discontinuous. This paper deals with the subjects of rock mass anisotropy and rock mass deformability. Both topics are important in rock engineering and are interrelated. The rock mass deformability is currently evaluated by means of different types of in situ tests, i.e. the plate loading tests, the borehole expansion loading test, the chamber tests and so on. In this paper, borehole expansion tests (dilatometer) have been used to characterize the deformability of anisotropic rock masses in different directions. The analyses of field tests is usually done assuming that the rock mass behaves linear elastically when subjected to the applied loads. The modulus of deformation is determined for different loading directions. The rock mass modulus of deformation is determined with dilatometer tests at different dam foundations located in a sedimentary formation in Iran. Finally, it is noteworthy that the analysis of the dilatometer tests in anisotropic rock mass was carried out to identify the major and minor axes of rock mass anisotropy. From data processing of in situ tests result it is also pointed out that most useful direction for dam axes could be estimated by borehole dilatometer tests.