The Research On Mechanical Effect Of Excavation Of Deep Tunnel Under Tectonic Stress Field

In highway construction, in order to improve the line shape, shorten the mileage, improve operational efficiency, avoid diseases and protect environment, the construction of highway tunnels is increasing. Tunnel excavation is changing process damaging the initial stress state of rock mass in time and space. Though the tunnel in the shallow buried depth, geological environment which is under surrounding low grade, only considered self-weight stress field also can satisfy the engineering demand. Under the deep buried depth the surrounding rock uniaxial compressive strength lower, in the complex situ stress state, considered the tectonic stress to the stability of tunnel surrounding is essential, can help reducing construction cost and prevent geological disaster which is unnecessary. Studying the process of tunnel excavation through restoring the original rock mass stress state will have theoretical and practical significance.The article summarizes numerical simulation method of the tectonic stress effect in geological engineering and underground engineering, as well as numerical simulation methods of the process of tunnel excavation, take the Luoping tunnel as background ,which is the second phase project of highway from Hangzhou to Lanzhou in Wufeng, use the large-scale finite element ANSYS software to do numerical simulation analysis of the runnel excavation process.Carrying out numerical simulation analysis of the simplified two-dimensional model under the self-processing stress state and different tectonic stress state respectively, Then, come to conclusion: (1) Applied the constraint condition can influence the stress state of model. Based on the stress state can see, when subtract boundary constraint, adding smaller structure stress, its stress state influenced by gravity is more significantly, the result also not accord with practical. Along increased the structure stress, gradually close to the practical stress state, the stress state has significantly regularity changes. (2) Judging from the stress vector diagram, in the gravity constant circumstance, with the increase of horizontal tectonic stress, the size and direction of maximum principal stress have been continuous changed, until horizontal tectonic stress become maximum principal stress. The whole stress state is controlled by horizontal tectonic stress. The tunnel surrounding rock deformation be controlled by large principal stress, when the self-stress exceed the principal stress, control the surrounding deformation is gravity stress. (3) The vault sedimentation decrease and the plane constringency increase with the tectonic stress increasing. Tectonic stress will be the maximum principal stress when be greaten to a certain extent. Structure stress can substitute gravity stress control the surrounding deformation.It can be seen from three-dimensional numerical simulation analysis on the excavation process in Luoping K4 +903-K+933 tunnel paragraph that: (1) Considering self-weight stress on both sides means increasing restriction in the X, Z direction of the model, thus limiting the unit's displacement in the X direction, in other words, in the horizontal direction. Considering the tectonic stress is not only to restore the true stress environment but also do not limit the displacement in X direction, numerical calculation will be much closer to the actual works. By calculating. (2) Because the number simulation process is at the time of excavation to activate cauling ring and to jet concrete, supporting structure have never considered disturblance of blasting etc and deformation of constructure process of supporting structure.Therefore, the data of simulation is a little smaller than the date of measured data.through the simulation compare analysis of crown settlement, crown settlement based the effect of tectonic stress is greater than based effect of gravity stress.The results of vault settlement numerical simulation can consistent with the trend of field monitoring measurement data. The numerical simulation data under structure stress close to measured data. Which means: It is necessary to consider the effect that tectonic stress impact the process of tunnel construction in the tunnel which is great in depth.