| In this paper, Partridge Mountain Tunnel belonging to highway from Wenchuan to Maerkang acts as a project basis. By SEM-EDS analysis test on the samples of slate and phyllite, the author trys to learn the chemical elements and microstructure features of the two kinds of rock; Analysising on-site monitoring measurement data, the author summarizes the law of rock deformation; By the finite difference software-FLAC3D, the author simulates four excavation construction method (entire section method, bench method, core soil reserved method and CD method) determined by the design company, and prefers the stress, deformation and plastic zone of the surrounding rock as indicators to determine the most reasonable construction method; On this basis, the author optimizes the construction sequence of bias tunnels with small clear distance.The main conclusions are obtained:(1) By SEM-EDS analysis test on the samples of slate and phyllite,we can see that there are more micro-cracks on the surface of phyllite than the surface of slate.(2) The law reflected by on-site monitoring measurementThe subsidence of surface:The excavation of the curved pit guide surface plays a big influence on the surrounding rock above the woking face,the surface subsidence rate of the monitoring section reachs a peak; The ups and downs of the surface determines subsidence is symmetrical or not,and when the surface has a gentle slope, subsidence is more symmetrical and when the surface has a rigid slope, subsidence is not and the subsidence in a higher point is larger than the lower point.The subsidence of dome:In general, as the distance to the entrance openning increases (the depth of tunnel gradually increases), the subsidence of dome is gradually reduced. As excavation face advanes continuously, the effect-excavation face binding on the surrounding rock is gradually weakened and the subsidence of dome is gradually increasing.Horizontal convergence:Horizontal convergence is not monotonously increasing,some section may expansion during a short time.(3) Though the simulation of four excavation construction method.we can see that entire section method and CD method have advantages in terms of final deformation value.However,as for the instant deformation of surrounding rock,the extrude deformation of excavation face and the depth of plastic zone,entire section method has a big disadvantage but CD method performs very well.So the security of entire section method is worst although it has advantage of controlling the final displacement.Therefore considering the deformation and stability of surrounding rock, CD method is the best method. Of course, if you take into account the cost of project, core soil reserved method is also feasible if you can insure the security of construction.(4) Though the simulation of four construction sequence,we find:When we first excavate shallow-buried tunnel, the deformation of surrounding rock around shallow-buried tunnel is smaller than that when we first excavate deep tunnel.So is for deep tunnel.And thus if you want to control the surrounding rock displacement of deep tunnel, we should first excavate deep hole;As for excavation of a single tunnel, the first side of the rock excavation in shallow dome subsidence caused by deep excavation side than the first rock to be small, and thus in the construction, if you want to control the surrounding rock displacement of deep hole, then should be used after the first period (first excavated in the folder next to the inner rock and soil, and then the outside of the excavation of rock and soil; in the first and then the outer contrast) of the process of construction; when using the first light after dark, first after the excavation process when the outer, upper part of the clip in the negative horizontal displacement maximum, the lower part of the rock in the folder forward horizontal displacement is the largest in the folder to the rock pillars in shallow side overturning trend relative to the other three processes is the most obvious; using the first light after dark when you step in the folder surrounding rock plastic zone does not penetrate, using the first light after dark through the process; from surrounding rock plastic clip area size, the adoption of the first step outside after using smaller inside than outside inside after the first. Considering that the stability of middle surrounding rock is crucial for the design and construction of tunnels with small clear distance,we should first excavate shallow-buried tunnel and first excavate inner rock.That is the most reasonable construction sequence. |
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