Deformation-Failure Mechanisms And Stability Analysis Of A High-Speed Railway Tunnel Entrance Slope

Along with the large number of high-speed railway construction, how to correctly evaluate the stability of the railway cutting slope and tunnel import and export slope which significantly impacted by traffic load, and to take economic and reasonable control measures becomes an important topic for geologists.Take a tunnel entrance slope of a high-speed railway under construction for example, basing on field investigation and related data collection, this article analyzed the rock mass structural features and deformation-failure modes of the slope, and then evaluated the stability of the slope, and achieved the following results and understandings.1) This article analyzed the topography and geomorphology, formation lithology, geological structure, hydrogeology conditions and new tectonic activity and earthquake of the tunnel entrance slope.2) This article analyzed the lithologic features, weathering and unloading characteristics, structural planes and their combination features, development characteristics of unstable rock mass in the slope area.3) Laser range finder was used in the investigation of structural planes on high and steep slope. This article analyzed the principle of using laser range finder to measure and calculates the occurrence of structural planes, and derived the formula for occurrence calculation. This non-contact occurrence measurement method is an improvement and innovation of the traditional manner.4) Based on the study of the deformation and failure signs and influence factors, the deformation and failure modes of the slope can be divided into dumping - crack and slip– crack, and the modes of the unstable rock can be divided into dump, slump, and fall.5) Geological processes mechanism analysis and limit equilibrium method were used to evaluate the stability of the unstable rocks.6) Fast Lagrange Analysis of Continua in 3 Dimensions (FLAC-3D) was used to analyze the stress, strain and stability of the slope under natural, cavity and tunnel excavation and train loads conditions.7) Under natural conditions, the overall slope is stable, but stress concentration occurs in soft layer and at steep location,which may produce local instability.8) The cavity and tunnel excavation impact the nearby rock only, and the stability of the slope is slightly influenced by the excavation.9) Under train loads, shear strain increment zone may appear near the original joint planes, unloading joint planes, cavity surface and excavation surface, which will cause adverse effects to the slope stability, and may cause local instability, but the overall slope is stable under this condition.By the study of the engineering geological conditions and the deformation and failure mechanisms, we have an intuitive understanding of the stress and strain characteristics in the slope under different conditions, and the slope stability is also analyzed and evaluated, which can be referenced by similar slopes.