| With the continuous development of China’s economy, rapid development also appears in the construction of water conservancy and hydropower, road rail and so, thus resulting in the appearance of an increasing number of high and steep slope. Excavating tunnel in a slope is a common way in the construction of road. Especially excavating a double cave tunnel in a high and steep slope can cause a disturbance in the slope. We should pay close attention to the problems of slope stability and the distribution of displacement and stress in the slope, or the slope engineering will be unsafe once the problem occurs. However, when the tunnel space layout changes, or difference construction mode and construction sequence is adopted, there are more research efforts need to be done to reveal the influence of tunnel excavation to slope stability and the characteristics of displacement and stress distribution. The results are of high value for the optimization of tunnel construction mode and the reasonable layout of double cave tunnel in high and steep slope.This paper takes the Kayang double cave tunnel construction in landslide and high slope as the engeneering background. By use of investigation and document analysis, gray correlation method, theoretical analysis and numerical simulation methods, this paper studied the stability of the high and steep slope of Kayang, and the influence of excavation under different tunnel structure layout, or tunnel construction mode. The main contents and conclusions are as follows:(1) In connection with the stability problems of the high and steep slope with double tunnel undercrossing in the road construction of Kala and Yang fanggou hydropower station, according to the tunnel and slope engineering theory, combined with investigation and comprehensive analysis of the literature, this paper sumerized the main controlling factors of slope stability. They are the weight of soil, slope angle, cohesion, internal friction angle and the water table. Based on gray correlation analysis, the uniform experimental model of5factors and6levels was established. And then the sensitivity of these controlling factors for slope stability was analyzed by the use of grey correlation method. The result indicates that, the friction angle is the most sensitive factor, followed by the weight of soil, cohesion and slope angle, all of them are very important sensitive factors.(2) According to the complex condition of slope in Kayang construction district, the slopes are divided into three sections:tunnel portral section slope, tunnel deeply buried section slope and tunnel with the slope of landslide section. By the use of numerical simulation methods, the slope stability before tunnel excavation of Kayang was analyzed. The results showed that:slope with deep buried tunnel is stable, the excavation will not cause disturbances on the slope, the slope of landslide section is close to the limit equilibrium state because the stability coefficient is1.10, special attention should be paid to the supporting problems of slope before tunnel excavation, the tunnel portral section slope is in a stable state, but because of the shallow buried depth, excavating tunnel may affect the slope stability and close attention should be paid to the changes of slope deformation.(3) By use of numerical simulation methods, how the tunnel structure layout affect the slope stability was analyzed, and the characteristics of stress and displacement in slope were obtained. The results showed that:with the decrease of the horizontal spacing, slope stability tends to be unstable, the further the horizontal spacing is, the smaller impact of the excavation. When the spacing is too small,(as described spacing15m in this paper) the slope will have a great deformation, leading to sliding destruction. The excavation of the tunnel by the side of free surface have a controlling effect on slope stability, therefore, the further away from the free surface of the right tunnel, the smaller impact may create. When the vertical depth of tunnel changes, the deeply buried tunnel is superior to the shallow or medium depth tunnel. The shallow depth is the most unfavorable way to the slope stability. With the decrease of tunnel depth, the range of effects by excavation will gradually transfer from the bottom of the slope to the top. Shallow depth is likely to cause the collapse of rock and soil above the tunnel. Deeply buried tunnel only have an influence on slope the bottom, and the overall value of the final displacement has little difference from the other two sitiations. These can provide a theoretical basis for the reasonable choose of the tunnel spatial layout.(4) How the different modes of construction and construction sequence of the tunnel affect the slope stability is analyzed and the changing law of stress and displacement in slope under different circumstances was obtained. The results indicate that, the slope overall displacement is minimal by the use of bench cut method with excavating left tunnel first.The reason is that the stress deleased step by step during the excavation,and excavating left tunnel first can provide more space for adjustment of the second stress distribution. Therefore, this method is the most advantageous method for engineering safety. The full-face method with excavating right tunnel first is the most unfavaerable method for engineering safety. Because this method has less excavation step and the mode is excavating right tunnel first, both of them are unfavorable for the release and adjustment of stress. Especially after the excavation of right tunnel, the slope produced a large displacement,resulting that the impact of left tunnel excavation becomes non-negligible. This conclusion has a certain reference value for the choose of construction method in tunnel engineering. And in those project that the rock and slope conditions are similar to this paper’s condition, the bench cut method with excavating left tennel first should be adopted because it helps to control slope displacement. |
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