| Filled joints are common in the overburden and surrounding rocks of coal mines,and after a long period of geological as well as tectonic evolution,there are many interlocking filled joints.It is of high value to study the propagation law of stress waves in filled joints at different angles under different surrounding pressures.In this paper,the propagation curves,dynamic mechanical properties,energy dissipation characteristics and transmission as well as reflection coefficients of stress waves in filled joints at different inclination angles under different surrounding pressures are studied using indoor tests and theoretical analyses,meanwhile the transmission and reflection coefficients of stress waves at the interface of two media partitioned by the oblique incidence and equivalent wave impedance of an interlayer are combined to study the transmission as well as reflection coefficients of stress waves in oblique incidence filled joints.It is hoped that this method can provide a reference for the maintenance of the stability of the surroundings and overlying rocks during coal mining.The main research contents and results are shown as follows.(1)The influence of dip angle and surrounding pressure on the dynamic mechanical properties of filling joints was analyzed.With the increase of the inclination angle,the reflected wave amplitude of the filled joint specimens increased and the transmitted wave amplitude decreased at different joint inclination angles(0°,15°,30°,45°);with the increase of the inclination angle(0MPa,4MPa,6MPa,8MPa),both the reflected wave amplitude of the filled joints and the transmitted wave amplitude decreased.According to the stress-strain curve,the maximum strain gradually increased while the maximum stress gradually decreased with the increase of the joint inclination at the same level of circumferential pressure,and the phenomenon of "strain rebound" was not obvious;at the same joint inclination,the maximum strain gradually decreased while the maximum stress gradually increased with the increase of circumferential pressure,and the phenomenon of "strain rebound" was not obvious.Under the same joint inclination,the maximum strain gradually decreased with the increase of the surrounding pressure,the maximum stress gradually increased,and the phenomenon of "strain rebound" gradually became obvious;under a joint inclination of 45°and a surrounding pressure of 0MPa,there was no "strain rebound" phenomenon.(2)The effect of dip angle and surrounding pressure on the energy dissipation characteristics of the filling joints was obtained.The reflected energy ratio was 0.442,0.538,0.617 and 0.835,the transmitted energy ratio was 0.463,0.369,0.306 and 0.111,and the dissipated energy ratio was 0.097,0.08,0.073 and 0.054 at the same circumferential pressure and different inclination angles.The reflected energy ratio increased,the transmitted energy ratio and the dissipated energy ratio decreased,the surrounding pressure remained unchanged,and the inclination angle increased,thus,all the above three had the above trend.For the same inclination angle and different surrounding pressures,the reflected energy ratio was 0.442,0.335,0.196 and 0.097,the transmitted energy ratio was 0.463,0.501,0.619 and 0.698,and the dissipated energy ratio was 0.097,0.163,0.183 and 0.203 with an inclination angle of 0°and a surrounding pressure of 0MPa～8MPa,for example.The transmission energy ratio and dissipation energy ratio both increased,the inclination angle was constant,and the surrounding pressure increased,thus,all the above three had the above-mentioned trends.(3)The oblique incidence of an equivalent wave impedance of the stress wave on the interlayer is proposed,and the results calculated based on the equivalent wave impedance are compared with the experimental results.By studying the wave impedance of the stress wave through the interlayer medium of the filling joints based on the propagation theory of the partition interface,it is equated to a wave impedance,and combined with the propagation theory of oblique incidence of the stress wave on the partition interface of both media,the transmission and reflection coefficients of the stress wave are analyzed theoretically through the filling joints;it is found through a theoretical analysis that the reflection coefficient gradually increases with the increase of the filling thickness;when the filling thickness is 0 and the incidence is vertical,the results of the theoretical analysis are consistent with the theories in previous studies.In the test,the reflection coefficient R increases from 0.603 to 0.911,the transmission coefficient T decreases from 0.569 to 0.255,and the reflection energy ratio increases from 0.442 to 0.835 when the incidence angle increases from 0° to 45° under a circumferential pressure of 0 MPa.In the theoretical analysis,the absolute value of reflection coefficient R increases from 0.504 to 0.846 when the incidence angle increases from 0° to 45°,the transmission coefficient T decreases from 0.528 to 0.098,and the reflected energy ratio increases from 0.454 to 0.785.Figure [44] Table [15] Reference [82]... |
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