| It is common that numerous rock engineering such as rock slope and underground cavern to be excavated in or on non-persistent jointed rock mass which is a kind of complex engineering medium. The existence and interaction of joints plays a decisive role in damage and mechanical characteristics of rock mass. To carry out a series of tests of uniaxial compression, biaxial compression and true triaxial compression on the jointed specimens, cement mortar was selected as the material to physically model the sandstone, and a set of specimens with non-persistent joints were made using the model materials. During the test, Multi-channel acoustic emission detector was used to dynamically monitor the destruction process of specimens. Through physical testing, theoretical analysis and numerical simulation test, the deformation, the mechanical properties and failure modes of the non-persistent jointed rock mass, mechanism of propagation and coalescence of branch crack and acoustic emission characteristics were analyzed. Through aforementioned analysis, the results and conclusions can be obtained as follows:(1) The failure modes of jointed specimens with multi non-persistent joints mainly depend on the crack type (e.g. wing crack and secondary-coplanar cracks) and the crack propagation path. As have been observed from tests, there are four failure modes, i.e., planar failure, stepped failure, rotation of new blocks, and mixed failure that influenced by the configuration of joints under uniaxial compression. With increasing the lateral pressure, the failure modes of jointed specimens change from breaking through joint plane to the compression-shear damage of rock mass. The failure will through the cater-corner plane for jointed specimens containing non-persistent joints with inclination of 45°under triaxial compression.(2) The configuration of non-persistent joints has significant influence on the characteristic of the stress-strain relationship curves. With respect to the uniaxial compression, according to the post-peak characteristic, the relationship curves of stress-strain of jointed rock specimens were divided into four types:falling with a single peak, strain hardening after yield, strain softening with zigzag fluctuation, and progressive strain softening. In terms of biaxial compression, the effect of lateral pressure eliminates the difference between stress-strain relationship curves in the post-peak phase. In the pre-peak phase, however, there is a stress hardening stage after yield. Under triaxial compression, stress-strain relationship curves turn to be relatively smooth with high residual strength in post-peak.(3) The anisotropic characteristics of uniaxial compression strength (UCS) ?max and elastic modulus E of jointed specimens are greatly influenced by the joint inclination ?and lateral pressure ?2-Under uniaxial compression, the amax decreases with the increasing of ? at beginning, then ?max increases as ? increases, which show a U-shaped in the relationship curve between ?max and ?. When ??60°, the value of E fluctuates in the range of 5-10 GPa. When ??75°, the value of E turns to be bigger than 19 GPa. Under biaxial compression, with the increase of ?2, the bottom of U-shaped curve of relationship between ?max and? gradually rises, which means that the influence of ? on ?max becomes non-significant as increasing the ?2.In addition, the lateral pressure ?2 shows no obvious effect on the elastic module E.(4) Due to the obvious periodic characteristic of the time series, the time series characteristic on acoustic emission of multi-joint rock specimens under uniaxial compression can appropriately reflect the initiation and propagation of crack in the jointed specimens. According to the active level and the characteristics of the cumulative count change events reflected by the acoustic emission event rates, the time series characteristic on acoustic emission can be divided into four stages during the whole loading process of jointed specimens.(5) The value of acoustic emission parameter b reflects the amplitude distribution ratio, and it also represents the relative scale of acoustic emission as the jointed rock mass under loading effect. In the present study, the value of b fluctuates between 2-3 in a stage of stable propagation of crack. The value of b will decreases as the crack starts unstable propagation. Significantly, the values of b of all the tested specimens with different joint inclinations will approach to a stable level that approximately is 1.66 as the stress reach its peak.(6) Taking the time as intermediate variable, a one-to-one relationship between the acoustic emission and the mechanical parameters of jointed rock specimens can be established. The damage model and constitutive equation were deduced using weibull probability density function of rock infinitesimal strength. The proposed damage model perfectly reflects the changes of damage with the loading process of the jointed specimens.(7) The failure process of jointed specimens under uniaxial and biaxial compression was numerically simulated by the improved rigid body spring method. The simulations can reproduce all the failure modes that observed in physical model tests, which deeply reveal the mechanism of the initiation and propagation of crack from a mesoscopic perspective. |
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