| With the further development of China's western development strategy, the speed of economic development in the western region has reached an unprecedented state,but also more and more needs a better transportation network system to support the development of the economic industry. Due to the western mountains and valleys,undulating terrain larger, in order to better show line wiring, traffic route through the mountains to place more, making highway bridge and tunnel engineering higher proportion, and the construction difficulty increases. Mountain tunnel engineering geological environment is changeable, in the area of soft rock construction of tunnel surrounding rock large deformation is always the question in the course of design and construction more difficult. Due to large deformation of soft rock tunnel generally have large deformation and deformation rate is fast and deformation for a long time,disturbance of surrounding rock in a wide range of pressure and fast growth, so from the tunnel excavation to the completion of the construction, even including the whole process of post operation are accompanied by surrounding rock and supporting supporting structure of a series of mechanical behavior, the study of the variation of the mechanical behavior for the construction of tunnel and underground caverns has an important role. In view of this, the Syrian railway in Xuyong County, Village)Engineering in typical soft rock bias tunnel- Hetao Wan Tunnel Engineering Based on, based on actual needs in the soft rock of the bias tunnel construction, from the change of tunnel excavation section geometric forms of the angle of the soft surrounding rock deformation control technology. Mainly based on the principle of orthogonal test of multiple sets of numerical model, the geometric parameters by means of single factor effect curve analysis, range analysis, variance analysis and other methods of soft rock deformation is studied. The selected factors between the best combination as the optimal condition.Located in southern Sichuan Xuyong to village railway walnut Bay Tunnel in theconstruction process, the bedded and cataclastic rock mass structures appear tunnel face instability, landslides, initial lining failure and other engineering problems. These problems has occurred frequency high, affecting a wide range, characteristics of serious disaster induced by, construction and safe operation of walnut Bay tunnel project brought huge risk. Therefore, the stability of surrounding rock in tunnel excavation is analyzed in this paper, and the construction technology of deformation control for tunnel excavation in this kind of rock mass is explored:(1) Through the analysis of the engineering geological survey data and the indoor test data, it shows that the primary structure and the secondary structure in the surrounding rock of the walnut Bay Tunnel are very developed. Among them, bedding with a spacing of about 1cm continuity is good, a micro state; joint and crack spacing is generally 2 ~ 6cm, with a penetrating, length with the thickness of rock block,usually in the form of open state, clip calcite vein and thin mud mask. The direction of rock strata in the tunnel area is NE direction, which is basically consistent with the direction of the tunnel excavation. The angle of the inclined rock stratum is about 45 degrees, which constitutes the internal cause of the bias of the tunnel. In a large number of structural planes, the control of the stability of the surrounding rock is very obvious. The weak surrounding rock has the characteristics of high plasticity, strong expansion, strong disintegration, strong anti disturbance, strong bias and weak rheological properties. The deformation of surrounding rock of tunnel has many kinds of failure mechanisms, including four aspects: plastic flow, expansion, bending of beam and slab, and deformation of the wedge.(2) The numerical analysis results show that the influence of tunnel excavation on the mechanical behavior of rock mass is more than 3 times. The larger surrounding rock stress is mainly concentrated in the left lower part and the upper right of the tunnel, and the lower right and left lower right high. The plastic zone range from the tunnel excavation is obviously irregular in the shape of the tunnel. In the bedding direction about 3 times of the hole diameter in the range of plastic zone has an obvious extension, mainly to shear failure; and in the vertical direction of the levels,hole week plastic zone scope is about 1.5 times the hole diameter, plate girder bending failure mode. On the whole, the existence of the weak layer blocks the continuity of stress and displacement, and has great influence on the mechanical properties and deformation characteristics of surrounding rock.(3) Under the condition of no support excavation, the longitudinal deformationcurve has obvious stage, and there are three stages in the ahead deformation section,the sharp increase section and the slow deformation stage. Among them, in front of the tunnel face super characteristics of the displacement front is mainly distributed in front of tunnel face about 1.5 times of the hole diameter range, slow deformation and at the tunnel face reaches the maximum value, accounting for about 30% of the final deformation of. The range shift tunnel face after the dynamic characteristics is: the initial stage displacement increases the speed to be quick, displacement also large deformation increases rapidly with the trend, mainly distributed in 0 ~ 1.5 times of the hole diameter range, displacement accounted for 60% of the final deformation; late stage displacement changes slowly, or gradually stabilized, mainly distributed in 1.5to 3 times of the hole diameter range, accounting for about 10% of the final deformation of. With the advancing of the excavation face, the stage of the displacement of the tunnel is moving forward. Therefore, the purpose of support is mainly in each excavation cycle, the control of the lead deformation and the convergence distance of the latter.(4) On Walnut Bay bias tunnel with weak surrounding rock bench excavation method of sectional geometric parameters based on the principle of orthogonal test design are analyzed. The results show that the tunnel face vertical slope and step height is deformation of surrounding rock is the most sensitive factor that effect the next is tunnel face lateral ramp rate and step length, step slope is the minimum of the influencing factors. Orthogonal synthesis analysis and the actual situation of the construction point of view, the optimal excavation section geometric parameters: 4m step length and step height 4.95 M, slope ratio 1:5, tunnel face vertical slope 0.25, the transverse slope of tunnel face 1:0.5, at this time of tunnel with weak surrounding rock deformation control is the best. |
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