Study On Support-Surrounding Rock Interaction For PDL Tunnel

ABSTRACT:Railway tunnel construction has achieved great achievements in our country. During the 11th Five-Year Plan period (2006-2010), railway network construction which focuses on PDL (Passenger Dedicated Lines) is in a comprehensive way, and the number of railway tunnels has been growing rapidly. In the next 10 years, the length of railway tunnel to be built is more than the total length of railway tunnel that are completed. Meanwhile, the contradiction between tunnel construction scale and tunnel construction technology is becoming increasingly conspicuous. The confusion exists in tunnel design has seriously constrained the scientification, precision and standardization in tunnel construction. In response to this series of contradictions, systematic studies are made on tunnel deformation control, surrounding rock failure modes, rock-support interaction in this paper and yield the following key findings:(1) Analysis of the mechanical characteristics of tunnel structure system:The concept of the tunnel structure system is put forward, and the interaction between surrounding rock and tunnel support is deeply studied. According to the principle of tunnel deformation control, the deformation features of each sub components in this system are studied. Based on these analyses, theoretical model of the tunnel structure system which includes "surrounding rock-grouting circle-preliminary lining-secondary lining" and safety evaluation method for tunnel structure system are set up.(2) Theoretical analysis on surrounding rock failure modes:Based on elastic-plastic theory,5 failure zone modes of surrounding rock as well as the definition of each mode are given. It reveals that the V-shaped shearing wedge block is the major failure mode for zoneâ…¡and III. According to theoretical analysis, the analytical method for shearing wedge block is given and the possible failure modes in three-dimensional state are also proposed.(3) Micro-mechanism analysis using PFC:PFC is adopted to simulate the failure process of tunnel surrounding rock that involves the initiation, growth and accumulation of micro-cracks. So as to use PFC in a better way, gray correlation analysis is introduced to establish the relationship between macro mechanical parameters of rock and micro parameters used in PFC. Neural network is also utilized to achieve the calibration of macro mechanical parameters for surrounding rock.(4) Laboratory study on tunnel excavation:Barite powder, quartz sand and vaseline are selected as the components of similar material based on investigation and research. A large number of laboratory tests are made to study the mechanical properties and strength properties of similar material that affected by similar ratio. The relationship between similar material and geotechnical material is finally established according to similar ratio. Tunnel excavation laboratory simulation system is designed under the instruction of author. The system consists of test platform, contact monitoring system and non-contact monitoring system. Cohesive similar material and sandiness similar material are used to simulate different kinds of surrounding rock, connected with these two materials two kinds of failure modes are achieved. Damage mechanism and progressive failure characteristics of these two failure modes are also elaborated.(5) Study on the interaction between preliminary lining and surrounding rock: According to the specific situation of PDL tunnel in China, ground response curve is studied under different mechanical parameters of surrounding rock and different stress state. Support characteristic curves of shotcrete, grid steel frame and section steel frame are analyzed in a theoretical way. The deformation characteristics and failure regularity of grid steel concrete and section steel concrete are studied using ANSYS software. FLAC3D software is also used to analyze the ability of rockbolt in deformation control of surrounding rock(6) Study on the interaction between preliminary lining and secondary lining:4 typical PDL tunnels are selected to monitor the contact pressure between preliminary lining and secondary lining. Combined with on-site monitoring, time-space regulations on contact force are studied. It reveals that the most unfavorable stress state for secondary lining is in the moment when the tunnel lining trolley removes. The stress acts on secondary lining is actually deformation pressure which is totally different from loose pressure prescribed in China Tunnel Standard. The safety factor of secondary lining under measured load is higher than that under standard pressure and it satisfies safety requirements. The measured contact force is roughly in a same level under different geological conditions, so it is possible to reduce the thickness of secondary lining as well as reinforcement.