Surrounding Rock Deformation And Reliability Study On Jinjishan Two-to-four In-situ Expansion Tunnel

In recent years, with the increase of amount of travel, more and more demand for transportation is growing. Not only the demand of the roads and Bridges, but also the demand of the tunnel and underground structure, especially the development of large section of small clear distance tunnel is the trend of The Times. And the two-to-four tunnels are more and more common in the practical engineering, but So far the research achievement of the two-to-four tunnels is not much. So the research of the two-to-four tunnels need urgently researchers dedicate time and effort to put into.There has been no relevant reliability research achievement about the comparison between the two-to-four tunnels. Thus, make comparative analysis between several four-lane in-situ expansion tunnels, complement each other, validate each other.Perfect the terms of reliability research on tunnel expansion. Such scientific research studies have important implications.In this paper, take Fuzhou Jinjishan two-to-four in-situ expansion tunnels project as research background. Based on the four-lane in-situ expansion tunnels field data analysis and various parameters of the surrounding rock, launched two research ideas:One is do 3d numerical simulation of in-situ expansion tunnels based on the theory of the unloading on the common software ANSYS, to complement field data verification;Second, on the basis of large amounts of data obtained from the numerical simulation,expand reliability research on surrounding rock, research results of Jinjishan tunnel and Tai Mo Shan tunnel were compared and analyzed. The main results are as follows:1. Take expanding tunneling and new four-lane section tunnel as a construction mechanics and Displacement behavior comparative study. Jinjishan two-to-four in-situ expansion tunnels represent for expanding tunneling and Guangzhou Longtoushan tunnels represent for new four-lane section tunnel. The maximum of the final contact stress and cumulative stress of steel support in the four-lane section of in-situ expanded tunnel is greater than that in the new four-lane section tunnel. But,the conversion process between tensile stress and pressure stress at 45 degrees of the first excavation guide hole in the new four-lane section tunnel is more frequent.2. Compared with the three dimensional numerical simulation results of a new four lane(Qianou tunnel): The later tunnel plastic zone of the two-to-four tunnels is finally distributed in hance, while the new four lane and the front four lane of the two-to-four tunnels plastic zone is eventually concentrated on the arch foot; first lining von mises stress maximum of the two-to-four tunnels is larger than the new four lane.3. Deformation effect on in-situ tunnel is different from the influence on adjacent existing four lanes from two-to-four tunnels construction process. Peripheral convergence is dominant in situ tunnel, and vertical settlement is dominant in adjacent existing four lanes. And the bias of the adjacent tunnel left side is obvious.4. By unloading simulation under different excavation sequences and different penetrations, we get different disturbance radius. Thus, the construction scheme with ABCD sequence and footage of 2m is the best scheme.5. Using FOSM, based on the GA-SVM,determined by the function and then come to a final Jinjishan excavation tunnel reliable indicator of 4.9697, function checking function value at the point is only 0.0029. The accuracy of the model is proved.6. By reliability of research results Comparison between Jinjishan and Tai Mo Shan expanding tunneling, analyzed and summarized the factors affecting the reliability index value as follows: sample factors(mean and variation coefficient),way of tunnel excavation, form of tunnel support, predict randomness of GA-SVM the rock strata distribution in the study section selected, etc.