Study On Aseismic Structrue For Tunnel Passing Through Active Fault

Based on major project (No.51038009) of National Natural Science Foundation of China, by using methods of field investigation, theoretical analysis, numerical analysis and model test, the prominent problem of tunnel damage by earthquake is summarized. Focused research is aimed at tunnel passing through active fault, reliable methods as model test to simulate tunnel damage when passing through active fault and study aseismic measures are established, test result of different aseismic measures is give. Finally, a new type energy absorption lining structure for tunnel is proposed and studied. The main conclusions and outcomes are as following:(1) Based on field investigation and document research, serious seismic damage zone of long and large depth tunnel are three categories:portal section, week and broken zone of tunnel body and tunnel passing through active fault.(2) Numerical analysis of tunnel body dynamic response by seismic load is made, indicating dynamic response of tunnel passing through week and broken zone is obviously larger than that in hard rock zone, tunnels are more likely to earthquake damage.(3) A reliable method as model test to simulate tunnel damage when passing through active fault and study aseismic measures is established, test result is reliable, testing apparatus and design fulfil basic requirements of simulating mechanical behavior when tunnel passing through active faults, tunnel damage characteristics are obviously coincided with actual damage.(4) By measures of setting aseismic joint, damping effect by aseismic joint for tunnel passing through active fault is analyzed. The test shows setting aseismic joint may control longitudinal damage distance influenced by fault movement and control internal force increment. By reducing aseismic joint separation distance, different damping effect of different joint separation distance are studied, the test shows that reducing aseismic joint separation distance may further control longitudinal damage distance influenced by fault movement, but monocyclic ring in the centre may more likely to damage, due to short longitudinal length, the seismic problem may be more prominent. By contrast test, primary support is expected to set aseismic joint, rather than serious fracture and peeling phenomenon, as well as aggravating secondary lining damage. (5) Adopting expanded section and setting aseismic joint are able to guarantee tunnel effective clearance after fault movement, the design of expanded section should be related to estimated final static slippage and combined use with setting aseismic joint to guarantee tunnel effective clearance. The bigger intersection angle between fault and tunnel axial, the bigger loss of tunnel clearance. To guarantee designed tunnel clearance after earthquake, the expanded section should be bigger. The smaller intersection angle between fault and tunnel axial, the bigger range of influence by fault in the same fault displacement, the range of aseismic joint should be greater. The expanded section dimensions and aseismic joint distance should be reasonable arrangement due to the fault direction and fault displacement to guarantee damping effect and control engineering cost of projects.(6) Setting aseismic joint design is a effective damping method for tunnel passing through active fault, but due to material characteristics defect of concrete lining, the lining cannot bear severe impact and load during fault movement, and possess not the ability of buffer and absorbing energy. Material characteristics is in urgent need to be improved to solve lining homeostasis.(7) Compared with tradition lining, rubber lining can bear larger deformation in the same fault movement, growing no crack or damage, the lining structure is in favourable elastic deformation state. The rubber lining has the buffer of dynamic response during fault movement. Cooperated with setting aseismic joint, internal force increment of lining near fault zone may greatly reduced. Cooperated with short distance aseismic joint, influence region is more reduced, faulting of slab ends is less. When aseismic joint distance are20cm,10cm,5cm and2.5cm, lining slide60cm,40cm,30cm,25cm, the zone is more tend to fault zone.(8) Dynamic additional load on tunnel structure in section are influenced by earthquake magnitude and stiffness ratio, based on simulation of fault movement, the higher the earthquake magnitude and the severer the fault movement, the more serious the tunnel earthquake damage. The bigger the stiffness ratio, the severer the internal force response of lining. When the stiffness ratio is less than1, the tunnel is more flexible than surrounding rock, dynamic response is less.(9) elasticity of rubber lining is good and has larger deformation in same load, compared with common lining, continuous deformation capability is far larger than common lining. Tunnel can keep no collapse in large load and deformation, when the load is gone, the rubber lining is even able to recover and will have no permanent damage. From the energy point of view, energy absorption capability of rubber lining is far larger than common lining, being a new type endergonic and flexible aseismic structure.(10) The use of rubber lining should in accordance with possible fault movement and lining stiffness, and cooperate with setting expanded section. Obligate clearance design is sum of final fault movement and self-deformation, material performance requirement of rubber lining is according to maximum displacement during fault movement.