Geological disposal repositories for high-level nuclear wastes or storage caverns for storing oil and natural gases should be sited in such rock masses as without significant continuous fracture which may cause leakage of radioactive materials or oil and gases. However, mechanism of crack developments in rock masses due to fault rupturing is not fully understood so far. As compared to dip-slip faulting, strike-slip faulting is more complicated as its three dimensional nature. The purpose of this study is to understand the mechanism of crack development due to strike-slip faulting. A series of model fault tests were conducted using two kinds of shear boxes with double shear planes. An artificial model ground placed on the sliding base plates was sheared along two parallel planes simulating strike-slip movements, and crack developments on the surface of the overlying model ground were observed and measured to investigate the types of cracks, their configurations, geometries and sizes.
Geological disposal repositories for high-level nuclear wastes or underground caverns for storing oil and natural gases should be sited in continuous rock masses avoiding significant discontinuities which may cause leakage of the radioactive materials or oil and gases. To conduct efficient geological and geotechnical investigation around the potential sites, knowledge regarding the mechanism of crack developments in rock masses due to fault rupturing is of great help. However, this rupturing mechanism in rock ground is not fully understood so far. Moreover, as compared to dip-slip faulting, strike-slip faulting is more complicated as its three dimensional nature. The purpose of this study is to understand the mechanism of crack development due to strikeslip faulting.
Two types of strike-slip fault model tests were performed [1.2]. The one using mortars as the model ground whose surface could be observed while the fault displacements were increased as the tests were conducted on the laboratory floor. While the other using a tuff could not be observed during faulting, the tests were performed under confining pressures in triaxial cell. By comparison of these two test results, type, process, configuration, size and orientation of cracks were studied.
Figure 1 shows the shear box with double shear planes. Two model grounds, those of length L = 638mm, width W = 150mm and thickness H = 20mm or 30mm are placed together parallel to each other in the shear box. The bottom plate of the shear box is divided into three parts by parallel fault planes. By sliding the center plate along two fault planes using the loading device placed on the reaction frame, strike-slip fault movements were given to the model ground. The model ground was made of mortar; the mixing proportion of cement: siliceous-sand: water = 1:5:1. The fresh mortar was placed into the shear box directly and was cured under the 468 wet condition for seven days before shearing.
