Study On Surrounding Rock Stability Of Deep Tunnel By Double-Shield TBM Excavtion

Comparing with drill blasting method, TBM(tunnel boring machine) can have a little additional excavation and lesser disturbing for surrounding rock. TBM can sufficient protect surrounding rock itself strength, adjust and reinforce tunnel itself bearing capacity and stability, reduce the weight of lining structure, thrift the engineering material. There are remarkable characteristics of safe, high quality, efficiency and environmental for the TBM excavating method, so it has been widely used in hydropower projects, road projects, railroad projects, mine and national defense projects. But in deep tunnel around incompact, extrusion, much more groundwater and high ground-stress, how does the TBM construct with safe, continuum and high efficiency. It is one of the key question for TBM construction, and the surrounding rock stability of the tunnels during and after the construction becomes a concern. It is one of the research topics for TBM excavating tunnels.At the first time, in Jin Ping hydropower station left riverbank during the super tunnel construction, the microseismic monitoring is used for the surrounding rock stability estimating, and seismic events were recorded. The microseismic results have shown that rock fractures were developed at the intersection of the water, traffic and exploration tunnels where rock weakening between these tunnels might be developed, but after the super tunnel has be excavated the intersection would become more and more stability. Fracturing was also detected where a significant roof-fall occurred nearby. The microseismic results have provided good information for engineers to understand stress conditions in the rock mass and to assess the stability of the tunnels. Using the second derivative of the relation curve of microseismic frequency as a function of time,we may confer the surrounding rock that is stable or not. The study has also obtained the relationship between microseismicity and seismic transmission distance. At last, using the results colliqated microseismic interspace distributing, time distributing, power grade changing and scale domino offect, the tunnel surrounding rock stability can be set off four grades from stabilization to unstable estate, they are I , II, III and IV, this also is the results of tunnel microseismic prediction.Based on deformation characteristic and mechanical effect of the surrounding rock in deep tunnel by TBM excavating inland, a new concept of lining press discount coefficient for tunnel surrounding rock is presented according to elasticity mechanics principle and Hoek-Brown criterion. It is suggested some of calculating formulae for plastic radius, plastic displacement and the best lining press. The results of academic calculating were in good agreement with the site monitoring results, and it has shown that the academic calculating formulae were credible. At the same time, it is discussed the connection of TBM hob thrust for the uniaxial compressive strength, the style, the inteqrality, the airslake degree of the rock, and the displacement equation with TBM hob thrust is presented. The internal relation is set up about TBM excavating with surrounding rock quality, and it is very important for TBM constructing tunnel.The incompact surrounding rock and extrusion stratum are unfavorable geological conditions for TBM excavating, they might have huge influence to time limit for a project and cost . In order to understand their influence near the tunnel, it is suggested some of study for a craftwork flow, numerical simulation of polyurethane chemical grouting concreting incompact surrounding rock, a connection of deep extrusion stratum with TBM jamming and a mathematic mode of extrusion stratum. It is suggested a calculating formulae for the thickness of polyurethane chemical grouting, and a fine value of the decompress branch hole between the main tunnel. The theory study of the incompact surrounding rock and extrusion stratum infected the double-shield TBM constructing is very important, it has changed the old experiential method for chemical grouting concreting incompact surrounding rock and the analytical results might also channel off the double-shield TBM passing through unfavorable geological sections safely and quickly.According to different lining fashion, there are two kind of lining frames for double-shield TBM excavating tunnel, one is shield lining and the other is segment lining. In shield lining sect, the calculating method and influencing factor of frictional resistance to the shield between surrounding rock are discussed. Based on the Hoek-Brown criterion, the surrounding rock press around TBM shield is calculated in two kind of ideal state of elasticity and plastic, and explaining a little additional excavation of double-shield TBM is very importance. In segment lining sect, the beam-spring model for quadrangled segment is built, and to study internal force and deformation of the segment lining for three typical sections, which include fault fracture belt, squeezing strata and surrounding rock of class III. Following the study the structural stress zones where hexagon segment and pea gravel backfilling grouting and surrounding rock might be regarded as lining system, and the calculating results of a puoject example are shown that the richness intension of hexagon segment is 31%, so the segment is above safe intension, and it may be farther optimized.Based on principle of damage mechanics, the press damage variable of pea gravel backfilling grouting is defined. The damage evolution equations corresponding for subjection Weibull distributing is determined, and to discuss the parameter F₀ and m inside the damage evolution equations. To build the mathematic model of pea gravel backfilling grouting for damage effect, the main stress of pea gravel backfilling grouting was in good agreement with the test results.