| Frequent happening earthquakes and densely distributed faults in China(especially in the provinces like Taiwan,Sichuan,and Tibet)resulted from complicated and frequent intra-plate tectonic activities.Correspondingly,China holds the largest amounts,the biggest scale,and the fastest speed of construction of the transport tunnel projects over any other countries.Specifically,after the design and construction of the Sichuan-Tibet Railway project,many tunnels are located in the zone of seismogenic faults.Lots of realistic tunnel damages have proven that the active fault-crossing tunnels would suffer severely when subject to the fault dislocation.Thus,the fault dislocation is a nonnegligible hazard to transport tunnels.The main objective of this thesis is to establish the mechanical model of an active fault-crossing tunnel and the anti-fault effectiveness of the sectional design based on the Basalt fiber reinforced concrete(BFRC).The main researches are as follows:(1)A three-dimensional FE model was established to study the influence of reverse active fault with 60° dip angle on a tunnel structure constructed with conventional method.Through this model,the seismic response of the tunnel was revealed.Thereafter,this soil-structure system was simplified to be a plane stress problem.The load model of tunnel structure under fault dislocation was established based on the load distribution pattern obtained in the abovementioned FE model.The stress function of a beam under random loads was derived,and several particular excitation functions were adopted to simulate the load distribution pattern.Thus,the elasticity solution of tunnel structure under fault dislocation was calculated through Matlab,and this solution was validated by comparing with numerical analysis.The fault influential range was obtained based on the elasticity stress function,which was determined as the anti-fault fortification range and could serve as the basis of subsequent studies in content(4).(2)Based on the three-dimensional FE model established in(1),the crack behavior and failure mechanism of tunnel structure after subjecting to the fault dislocation were analyzed after applying the Extended finite element method(XFEM).The anti-fault measure,“Articulated design”,that practically applied in domestic and foreign tunnel projects were introduced.Based on the Articulated design,the“Sectional Design” was proposed(3)Through employing the fiber volume ratio method,standard-sized BFRC concrete specimens were tested.During the test,scanning electron microscopy(SEM)was initially applied to observe and analyze the microscopic structure of BFRC and the bonding between basalt fiber and cement matrix.Thereafter,the connection between basalt fiber volume content and concrete mechanical properties(compressive strength and tensile strength)was analyzed through the uniaxial compression tests and splitting tensile tests.According to the comprehensive comparison of the BFRC specimens’ strength and their failure modes,0.5% was determined as the optimal volume content of the basalt fiber.The split tensile stress of 0.5% BFRC is 4.25 MPa while its compression stress is 43.3 MPa.The elastic modulus and Poisson ratio of 0.5% BFRC were measured,which is 26900 MPa and 0.18,separately.(4)According to the length of anti-fault fortification derived in(2),the key parameters of “Sectional Design” such as the length of the sectional section and the length between two of them was determined.The anti-fault effect of 0.5% BFRC sectional design was analyzed after applying the 0.5% BFRC sections to tunnels under2 different surrounding rock conditions.The results showed that the length and width of lining cracks were declined significantly,the highest values of which reached 36.59%and 16.92% separately,and the influential range of cracks were also shortened. |
