Stress Testing And Inversion In Galongla Tunnel Of Motuo Highway

Galongla tunnel is located in southern Tibet, with complex geological conditions, bad climate, active tectonic movement, various geological disasters . Initial geostress field and surrounding rock secondary stress field plays a vital role of construction of tunnel. Based on the analysis of the geological condition of galongla tunnel, and through the field test, laboratory test , theoretical analysis and numerical simulation, the initial stress field and surrounding rock secondary stress were studied.①Three-dimensional initial geostress state of 2 measured points is got by three holes intersection stress release method, making clear the characteristics of initial geostress field. Rock stress field is the result of joint action of tectonic stress and gravity, not a single gravity stress or tectonic stress field.②Three-dimensional initial geostress state of 8 measured points is got by kaiser effect method. Testing results of three holes intersection method and kaiser effect method in the same position are close, showing kaiser effect method′s practicability, also proving the correctness of the other point′s test results.③Combining with engineering practice, 6 kinds of influence factor of geostress are determined. Six working models are established. The initial geostress value measured is translated by elastic mechanics formula for geostress components in calculating coordinates. Initial geostress field of tunnel is got by multiple linear regression analysis method, combining with the initial geostress data measured, and tunnel initial geostress field distribution rule is obtained.④Surrounding rock's second stress of six points is got by modified stress recovery method. Combining with initial geostress inversion results, numerical simulation of the surrounding rock secondary stress field is done by side pressure coefficient method. Characteristic of the secondary stress field of surrounding rock is obtained after tunnel excavation. The relationship of secondary stress and the buried depth of tunnel, and the characteristics of secondary stress cross the tunnel section are analyzed. And the distribution of the secondary stress field caused by excavation is got.