Abstract
This study uses the uniaxial compressive strength (UCS), the indirect tensile strength (ITS) and the point load tests (PLT) to determine the strength and deformation behavior of previously deformed and altered tonalite and anorthosite. In general, veined samples show higher strength because the vein material has both cohesive and adhesive properties while fractures have no cohesion, only frictional resistance. This implies that each rock category has to be treated independently and absolute strength predictions are inaccurate. Thus, the conversion factor k is a sample specific parameter and does not have a universal value. The ratio of UCS/ITS appears to be related to the rock strength and can be used to classify rocks based on their strength. The shear strength parameters, the friction angle and the cohesion, cannot be calculated for rocks with pre-existing planes of weakness. Reactivation is favoured only for planes oriented less than 20° to the maximum stress. For planes oriented between 20° and 50° to the maximum stress, failure occurs by a combination of reactivation and newly formed fractures, while for orientations above 50°, new shear fractures are favoured. This suggest that the Byerlee’s law of reactivation operates exclusively for planes oriented ≤10° to the maximum stress.
Highlights
Rock strength and rock deformation mechanisms are important parameters for understanding geological processes in general and for geohazards as well as geotechnical problems.For example, pluton emplacement and volcanism are structurally controlled so that magma [1] takes advantage of pre-existing structures [2,3] to migrate through the crust
Five different failure modes were identified for the point load tests (PLT) test (Table 2), five different failure modes were identified for the uniaxial compressive strength (UCS) test (Table 3), and four different failure modes were identified for the indirect tensile strength (ITS) test (Table 4) The failure mode and strength results for each test were correlated using bar charts (Figure 7)
The results results of of this this study study show show that that because because deformed deformed and and altered are highly highly anisotropic, anisotropic, The altered rocks rocks are there is no mathematical solution for predicting rock failure modes accurately, making it difficult to to there is no mathematical solution for predicting rock failure modes accurately, making it difficult understand deformed rock behaviour under an applied load
Summary
Rock strength and rock deformation mechanisms are important parameters for understanding geological processes in general and for geohazards as well as geotechnical problems.For example, pluton emplacement and volcanism are structurally controlled so that magma [1] takes advantage of pre-existing structures [2,3] to migrate through the crust. That leads to redistribution of heat within the crust, which, in turn, affects the deformation behavior of the rock [4,5]. It is worth noting that there is a tendency for older structures to get reactivated during younger deformation events, which leads to prolonged tectonic activity along the same structures [10,11]. This has been observed along active seismic zones with the occurrence of earthquakes preferentially occurring along pre-existing fault zones [12]
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