Study On Surrouding Rock And Applying In Engineering Of Super Shallow Large-span Double-arch Tunnel

Double-arch tunnel is an important structure tunnel, compared with the separated tunnel, because of its shape and smooth, small occupation area, high space utilization rate, to avoid the entrance road or bridge framing, convenient connection with outside line; at the same time to adapt to the terrain conditions, the number of environmental protection and engineering has the superiority, in recent years Double-arch tunnel, along with China’s rapid economic development, has been hitherto unknown development, also appeared a lot of new challenges and problems. The Great Wall green near the highway tunnel is a two-way six lane double-arch tunnel, the maximum depth of less than5meters, the maximum span of17meters, is the super shallow buried large span Double-arch tunnel. At the same time, the surface has a history of over2000years the ruins of the Great Wall, which puts forward higher requirements for the project construction, and the current research on this kind of tunnel is very small, there is no experience, in order to make the project proceed smoothly, while ensuring that the national cultural safety of the site, the the Great Wall tunnel as the engineering background, based on the analysis of surrounding rock of shallow buried large span Double-arch tunnel, on the basis of theoretical analysis, through the development of similar test platform for materials and3-D geological model, geological mechanical model test, combined with field monitoring, the main contents are as follows:(1) Because of the special engineering condition, relates to the historical and cultural relics protection important, put forward very strict requirements on ground surface settlement, so according to the city underground engineering surface current settlement standards and relevant state regulations for the protection of cultural relics, the ground surface settlement control standard of value.(2) Based on the failure mode of shallow tunnel on the comprehensive analysis, based on the Hoek-Brown nonlinear failure criterion, the limit of plastic analysis, establishment of shallow tunnel surrounding rock collapse and failure mode, and the the Great Wall tunnel collapse failure shape diagram calculation.(3) According to the similarity theorem, development of the similar material model, the super shallow buried large span Double-arch tunnel geological model of platform, the establishment of three-dimensional geomechanical model test of large scale under the action of gravity, with a variety of monitoring means, a comprehensive analysis of the CRD1, plastic zone distribution of three kinds of construction schemes for CRD2and CD, distribution of pressure of surrounding rock, and the ground settlement data of horizontal convergence and vault settlement, the effect of CRD1and CRD2two excavation methods on the surrounding rock is no great difference, and the surface of two kinds of construction methods of settlement value lower than30mm, can be used as construction scheme. Compared with CRD1and CRD2two kinds of excavation scheme, to a large number of CD the influence of excavation on surrounding rock, that temporary horizontal support to play in the super shallow buried large span tunnel’s role is critical. Compared with the theoretical calculation of the tunnel collapse surface shape, get take CRD1and CRD2two kinds of excavation methods in surface shape scope bigger, illustrates the influence of surrounding rock affected by construction factors, damage range will increase.(4) For super shallow large-span tunnel wall overlying rock special structure and force, mode of the arched, expansion of geomechanical model test failure mode and mechanism of the overlying rock in the partition, and simulated by using UDEC, fully reveal the partition wall overlying surrounding rock failure mechanism, and put forward the construction measures.(5) The comprehensive theoretical analysis and experimental study, improve the surrounding rock and supporting force chose surface grouting and shed as auxiliary construction method based on enhanced advance, through field tests, field monitoring results indicate that, compared with the crown settlement and horizontal convergence on model test to become much smaller, the maximum surface subsidence control in30mm within that auxiliary construction measures, improve the surrounding rock, reduce the loose range of surrounding rock, and then illustrates the rationality of the auxiliary measures. Study site monitoring, surface transverse cracks with the site construction process, found that horizontal displacement control formation is also a key factor, and the horizontal displacement problems occurring in the field, formulate effective measures.(6) The electrical resistivity testing can be drawn, the Great Wall mountain tunnel engineering itself, partition wall approx.5m above the range of rock burst is serious, large vault of about2.8m range of rock burst is serious, which come with the numerical range of the plastic zone is basically a induced by resistivity testing can also reflect; out of the wall above the region affected by the excavation disturbance effect of stress state of frequent regulation, surrounding rock failure.