Deformation Anisotropy Study Of Columnar Jointed Rock Masses

Columnar jointed basalt is distinct in structure and mechanical features from general rockmasses. Its deformation rule is complicated. The results of field deformation tests that carried outin Baihetan Hydropower Station, Jinshajiang River, and reveal that its horizontal deformationmodulus is larger than the vertical one. However, the column is nearly vertical to the water level.There is a contradiction between this special phenomenon and general mechanical viewpoint.The study on anisotropic deformation characters is helpful to solve the problem in rockengineering, also to develop basic theory for rock mass mechanics.Researches on columnar jointed basalt in Baihetan Hydropower Station, which based onmethods such as field surveys, datum collecting, theoretical analysis and numerical calculus,bring out good fit. Based on classifying basis datum and generalizing the mechanical featuresand distributions of geological planes, such aspects of the research are accomplished. First, theresults of field plate-loading tests were analyzed, the causes of deformation anisotropy ofunderground cavities'mother rock were figured out. Second, the result of in-situ true triaxial testwas studied. Then the deforming characteristics of columnar basalt under diverse stress levelsand via different directions were summarized. Third, the report of the Test-Cavity in BaihetanHydropower Station was analyzed and studied, then modulus of the mother rock around theTest-Cavity were obtained using back-analysis method by'FLAC'software.The cognition about deformation anisotropy of columnar basalt was more in-depth throughall the studies showed above. The major conclusions show as follows:a. The steep dip longitudinal joints, the lateral fissures and gently dipping structural planesformed in columnar jointed rock mass are the causes of deformation anisotropy.b. The columns are intermittent mosaic between each other. The joints and fissures split ifthe pressure is very low or non-homogeneous, then the rock masses loosened and deteriorated.Accordingly, the cock mass can be calculated as continuous elastic media under wellproportionedstress condition, and displays intact rock mass deforming characteristics.c. The field plate-loading test showed that horizontal deformation modulus is larger than thevertical one in the survey cavities. The important reason for this special phenomenon is thatthickness of loosened annulus in vertical direction is larger than the horizontal one in the surveycavities. The in-situ true triaxial test reveals that horizontal deformation modulus is smaller thanthe vertical one, and this is an objective value. d. The horizontal deformation modulus of intact columnar jointed rock masses is smallerthan the vertical one. Therefore, it is consistent to general mechanical viewpoint. Anyway, thecolumnar jointed basalt can be considered as transversely isotropic media, of which isotropicplane is parallel to the cock formation layers.