Study On Damage Mechanics And Stability Of The Surround Rock Mass Of Branched Tunnel

The highway branched tunnel is one kind of new tunnel structure pattern.It is being exploited in order to reduce the project construction cost and construction difficulty in the area which the terrain and geology condition are complicated while the bridge connected the tunnels,especially in canyon mountainous area. The highway branched tunnel is composed commonly of four-lanes big span tunnel, multi-arch tunnel,small spacing tunnels and standard spacing separation tunnels.Researches on the design methods,construction techniques,damage mechanics and stability of the surround rock mass of the highway branched tunnel are nearly blank currently as it's new.Therefore, it is in urgent need of studying on damage mechanics and stability of the surround rock mass for branched tunnel when the branched tunnel structure used first in Baziling supper long tunnel in Yichang-Enshi expressway.Hence the mainly characteristics of the branched tunnels can be studied in the thesis.The discontinuous jointed rock mass in Baziling branched tunnels are considered as the studying background. The mechanics test about the damage mechanics property of jointed rock mass is carried on. Upon such tests, corresponding damage analysis in theory is developed. Applying principle of irreversible thermodynamics theory, elasto-plastic damage constitutive equations and damage evolution equations of fractured rock mass is developed which are the theory basic of next analyses step -reasonable spacing of the branched tunnels and stability of surrounding rock mass; On the foundations of theory analyses, through modeling test of the branched tunnel, reasonable spacing and damage failure mechanism of the branched tunnel is developed, which provides failure configurations and damage evolution property of transition section under complex stress condition where large arch to double arch and double arch to small interval tunnels; reasonable interval that are determinated by theory analyses and modeling test must be validated by in-situ measurement, so in-situ measurement technique and back analysis method for the branched tunnels are introduced, which ensure the safety and information for the construction; Applied above researched results, built the theory analysis method and rational construction procedure of preserving rock pillar in the branched tunnels; Key issues in tunnel design and construction are finally solved through above research and in-situ measurement analysis.Aiming at the property of jointed rock mass in Baziling branched tunnels, mechanics test of the damage of the jointed rockmass is carried on at firstly, and proportioning of rock-like materials is studied, provided new modeling experiment materials, which provide essential conditions for similar test of jointed rock mass. By AE (Acoustic Emission) monitoring and uniaxial compress test of mortar specimen with cracks, AE full process curve of compress failure process in crack propagation region of brittle material with cracks, as well as distribution of AE and sound source points, is menstruated. Full rock specimen, and uniaxial compress experiment of specimen with initial damage and that with double-crack initial damage are imposed, and full stress-strain curve is gained.By the relationship between AE accumulative number and damage variable, for the first time critical thresholds for each phases of damage and breakage of jointed rock mass are quantificational determined. Five phases of jointed rock mass breakage are first brought forward: initial cracks close phase; linear elastic damage phase; elasto-plastic damage phase; cracks create and macroscopically cracks stably expand and unstably expand phase; material failure and softening phase caused by damage.Full specimens and critical theshold for each phases of material failure of single initial crack and double initial cracks specimen are quantificational analyzed, which are the experimental foundations for determinations least space of the branched tunnels.Aiming at mechanics test of the damage characteristic, with geometry damage method imposed for the first time, failure mechanism of rock-like materials with initial damage and occurring process of full stress-strain curve are amply described, which provide experimental foundations and theory background for next step that constructs damage constitutive equation of energy dissipation of jointed rock mass. Here damage constitutive equations of the energy dissipation of jointed rock mass are studied, and corresponding numerical analysis method is developed, which provides effective instrument for rationally evaluating stability of surrounding rock mass and reasonable interval of the branched tunnels.Based on the theory study, such large-scale geological mechanics experiment is for the first time carried on, providing experiment foundations for damage characteristic and stability of surrounding rock mass of the Baziling branched tunnels.On the basic of modeling experiment, aiming at the characteristics of the Baziling branched tunnels, for the first time in-situ monitoring and measurement as well as back analysis research of each phases of the tunnel, and design method of tunnel in-situ monitoring and measurement system is introduced; By omnidirectional tracing monitoring on surrounding deformation, loosening area, supporting internal force, partition wall and lining stress, deformation and force characteristic of surrounding rock mass and supporting system is analyzed; Based on the monitoring result, back analysis of tunnel stability is developed.For the sake of the better evaluating surrounding damage characteristics and reasonable interval of the Baziling branched tunnels, based on the above researches and experiments, the finite element method for elasto-plastic damage is developed to provide experience and analysis method for the similar engineering.The finite element method of coupling elasto-plastic with damage is introduced. damage characteristic of the surrounding rockmass and reasonable interval of the branched tunnels are simulated. By comparing the result of FLAC3D with that of DFEM and that of modeling experiment, the method introduced here is proved correct and effective for the jointed rock mass.