Research On Physical Model Test And Numerical Simulation For Traffic Tunnel With High Geostress

Physical model test can qualitatively or quantitatively reflect the mechanics trait of crude rock-mass and interaction among complex engineering structures in underground engineering. Furthermore, it can simulate complex engineering structure, geologic conformation, stratum combination in the underground engineering because the test course and result can come into being automatically due to intrinsic mechanism indwelling in the physical entity by avoiding the embarrassment of expounding mechanism when the research on mechanism is not clear .The test course and result can provide foundation for new theories and mathematics models , gives solutions or reliable suggestions in the case of nowadays scientific and technology standard . So the rock mechanics model test has exclusive advantage for scientific research and settlement of practical engineering.This paper makes a systemic and deep research upon secondary stress state and bolt reinforcement mechanics in isotropic rock mass , upon deformation and failure mechanics of layered rock mass , upon optimizing design for bolt in layered rock mass, according to the simulation theory. All the research origion from the survey and measurement to deformation and support invalidation of GongHe Tunnel's rock mass with different geological characters and various buried depth . GongHe Tunnel lies in PengWu section of YuXiang Highway ,which is relied as typical sample engineer by the key article of the national natural scientific fund"stability and reliability of engineering construction in tunnel and underground space .The achievement is listed below:1. According to the elastoplastic and elastobrittle mechanical behaviors of the surround rock in different part of GongHe tunnel , 3 series of agglomerants are choosen .They are epoxy series , epory-silicone rubber series , rosin series. Adopting barite and silver sand as skeleton material ,successive various composition of every aggloment is made to form the mechanics character as elastoplastic behavior ,linear elastobrittle behavior and strong elastobrittle behavior of the model material .Finally pick out the composition of model simulation material whose mechanics resembles that of rock mass. Choose the modular E and compressive strengthσc as the main simulating parameters. 2. As prepairation for model test technology ,aiming at the research target we make sure of basic technics and technology about physical model when systemically design the project of test .Such as how to deal with the surface on the bottom of the strain gauge groove , how to get the bolt strain ,how to guarantee the loading mode of planar strain .3. Aiming at shale in part of tunnel ,the reinforcement mechanics of bolt in isotropic rock mass is gained by comparison of model test between excavation and bolt reinforcement case ,short and long bolt reinforcement case with elastoplastic model simulation material .That is that radial and tangent stress in bolt reinforcement case is higher than that in excavation .It illuminates that partial stress concentration appears because the resistance from bolt during the course of secondary stress forms so that the stress state of surround rock alters more stable with three dimentional compressive stress.4. Asynoptic transversely isotropic physical model is formed by layering model material whose interface is partially separated by mylar in order to decrease the friction olong it. Loading the model with simulating practical goestress the research can deduce the contribution trait of secondary stress and failure mechanics of low inclination angel layered rock mass. That is that the failure on the tunnel's tangent top happens for the sake of that the bedding is pressed to yield duo to the compressive stress within the bedding and then the interface seperates, while the surround rock of sidewall is extruded to failure due to the tangent compressive to the bedding . At the same time asymmetrical fractural rock ring forms.5. Based on the former research (article 4), system bolt reinforcement model with layered rock mass is made according to the practical design of whole-length cohesive bolt. Especially after the bolt measurement technology is solved, we can compare the strain of bolt and surrounding rock at the same position. The deformation trait and bolt reinforcement mechanics in layered rock mass presents that the bolt in tunnel's top area resists radial relaxation of surrounding rock and takes affect of radial bolt while the bolt resist tangential the fracture and relaxation and mainly takes affect of shear-bolt among the surrounding rock of tunnel's sidewall .The bolt beyond sidewall cannot be shorten or even be deleted.6. Based on the former research (article 4 and 5), system bolt design is altered to lengthen the bolt in feeble region and corresponding physical model is made. By comparison the strain of bolt and surrounding rock mass in the same point, redistribution of strain and failure trait after bolt optimized is analyzed and the bolt optimized design principle is discussed further. After optimized design in tangent top region the tension stain decrease in some degree so that the capacity of surrounding rock rises while relative feeble position presents in the foot of tunnel. In addition length optimization of bolt should be connected with the range optimization of bolt.7. Now take the load rank which simulates the practical geostress as O. C (overload coefficient) 1.0, then the O. C of initial cracking and the O. C of fracture in various cases correspondingly are: 1.38, 1.72 with isotropic surrounding rock, 1.30, 1.70 with layered surrounding rock, 1.8, 2.6 with system bolt reinforced surrounding rock, 2.4, more than 3.0 (fracture doesn't present in case of 3.0) with bolt optimized design case. The O. C with layered surrounding rock is less than that with isotropic one. After bolt reinforced to layered surrounding rock the O. C with the same deformation rises as well as the span of O. C between initial cracking and fracture becomes large which benefits for the safety of engineering.