Research On The Effect On The Porous Gases In The Weak Intercalated Layer Under The Seismic Load

By summarizing the results of previous studies on the development features of the of Daguangbao landslide during the time of the Wenchuan earthquake, the paper researched the "gap effect" found in the the landslip of Daguangbao. Firstly, according to the geological prototype, the paper established a theoretical model of gas ramp-rock interaction, and then used the physical simulation of the shaking table tests proved the existence of "gap effect", and initially obtained the mode of action and the variation of the effect. Then the paper used the method of the test of numerical simulation, and confirmed further the authenticity that the void gas effect exists, at the same time, the paper researched further the moving process of the cavity gas happened in the slope, as well as the mechanism that the excess cavity gas pressure effect on the surrounding rock and the mechanic damage effect work by excess cavity gas pressure to the weak intercalated layer under the seismic loads. This paper has obtained the following findings:(1)The generation of the excess cavity gas pressure:through the physical simulation test, the paper obtained that the excess cavity gas pressure could generate in the weak intercalated layer of the slope under vibration loads in a sudden, and there is a close relationship between the generation of the excess cavity gas pressure and the sudden vibration load and the extent of the closing of the cavity, whose condition the excess cavity gas pressure generated by. Through the numerical simulation test, the paper obtained that, under the seismic loads, the excess cavity gas pressure in the weak intercalated layer of the slope generated due to the aerodynamic response of the cavity gas under the seismic loads.(2)The reason of the cracks surrounding the cavity:through the physical simulation test, the paper found that, when the pressure changed, the crack could occur in the cavity side wall, and the splitting effect which the excess cavity gas pressure generated under the sudden vibration load effected on the rock and soil surrounding the cavity split the side wall of the weak intercalated layer, and extended the cracks even perforated. Through the numerical simulation test, the paper found that the change of the displacement surrounding the cavity in the weak intercalated layer occurred due to the mechanic effect which the excess cavity gas pressure effected on the rock and soil surrounding the cavity, and the effect of the excess cavity gas pressure could promote the deformation and failure of the model.(3)The mode of the deformation and failure of the cavity surrounding the cracks: through the physical simulation test, the paper found that the cracks in the cavity developed basically along the diagonal direction between the top and bottom, which is basically consistent with the slope inclination, and the crack opened and closed with generation and dissipation of the cavity gas pressure, and this closure is almost an closure without bond, in fact, that has become more loose surface. Through the numerical simulation test, the paper found that the cracks in the cavity of the weak intercalated layer of the slope developed most likely along the diagonal direction between the top and bottom, which is basically consistent with the slope inclination, and under the seismic loads, various types of responses occurred generation and dissipation, resulting in cracking and closure of the cracks repeatedly.(4)Features of the excess cavity gas pressure generated in the different cavities in the slope:through the physical simulation test, the paper found that, when the cavity gas in the weak intercalated layer is independent, the features of the excess cavity gas pressure generated in the rear of the slope are stronger than the front of the slope. Through the numerical simulation test, the paper found that, when the cavity locates in the rear of the weak intercalated layer, the aerodynamic response of the cavity gas is stronger than the front of the weak intercalated layer.(5)The influence that the excess cavity gas pressure effect on the shear strength of the rock mass:though the physical model test and analyzed the test results, then found that the shear strength of the rock mass was reduced Patanφ when there is cavity gas pressure, The shear strength is reduced from 4.4% to 12.8%.(6)The mechanism of the excess cavity gas pressure:though analyzing the physical model test. Crack tip is the gap of the gas pressure crushing of rock mass damage and crack expansion produced pull damage of the composite pattern, with the gap pressure generation and dissipation, and repeatedly stressed.(7) The splitting effect that the excess cavity gas pressure effect on the rock in the weak intercalated layer:through the physical simulation test, the paper found that cavity gas pressure plays a vital role on the crack extension, and plays a more vital role on the crake of the upper rock. Therefore, the role of gas pressure carried out from the splitting of the tip rock surrounding the crack and the loose of the upper rocks. Damaging effects on rocks with the formation of cracks at different propagation direction:when the crack developing direction is different with the angle of the weak intercalated layer, crack developing direction parallel with the weak intercalated layer.(8)Gas in different position of slope under the action of earthquake gap dynamic response is not the same, the cavity gap at 0.7 m high slope model the dynamic response of the gas is the most intense,0.8 m,0.9 m high. And, under the action of earthquake gap gas in different position of slope caused by the "gap effect", each time of surrounding rock strength reduction and the resulting speed of slope deformation and destruction also comply with the law.(9) Earthquake effect will make the overall stability of the slope from the natural state of K=1.15 (stable) down to K=0.94 (unstable), if the slope gas exists in the gap, in the earthquake under the action of the "gap effect" will aggravate slope overall stability is reduced, the reduced to K=0.8.