Evaluation On The Stability Of Front Slope And Study On Control Technique At The Tunnel Entrance

With the rapid development of China's highway industry, the construction and application of tunnel is more and more popular. In recent years, a large number of highways tunnels have been builded continuously. When start to construct a tunnel,the first problem must be encountered and resolved is the stability and treatment of front slope under the tunnel entrance construction. The geology and topography conditions of the tunnel entrance are generally so poor,which is the one of spots always make collapse and craze destroy.In this case,the stability of front slope at the entrance become the issue must be taken seriously during tunnel design and construction stages.The research content of this thesis relied on the project the Part of Erenhot in Inner Mongolia to Guangzhou Highway from Yongzhou to Lanshan in Hunan Province. According to related slope failure theory, the influence factor of front slope stability at tunnel entrance is analyzed, the failure patterns and mechanism of the front slope is studied.Then based on the corresponding monitoring data, the development process of slope failure is summarized. After that, the comprehensive analysis and determine method of a tunnel front slope stability is summarized too. Meanwhile, some processing technology that can improve the stability of front slope at tunnel entrance is discussed.At last, combining with engineering example which called Xiaoniutang tunnel front slope in the third contract section of Yonglan Highway, the actual situation on tunnel site is described in detail,such as environmental geological conditions, tunnel entrance enter way and entrance processing program.According to the reality, the stability of front slope is analyzed qualitatively by using Stereographic Projection Method.Then based on Strength Reduction, this front slope's stability is imitated respectively by using FEM software named MIDAS under three operating conditions like state of nature, excavation without regard to rainfall and excavation to consider rainfall,obtained slope stability safety factor under different operating conditions. At the same time, based on Limit Equilibrium Theory, the front slope stability is analyzed again by using Geo-Slope software due to Bishop method under the three same operating conditions, verified the accuracy of the FEM imitation,then the reasonable treatment plans are proposed.