Applied Mechanics and Materials Vols. 353-356

Abstract: Horizontal freezing induces ground frost heave and ground displacement happens. Excessive uneven displacement or deformation may be dangerous to the surrounding building. The stratum that a Nanjing subway tunnel will traverse through is the soft and silt clay. The artificial freezing construction method is proposed to help the tunnel to traverse through the worse stratum. To control the ground building deformation and displacement due to the ground frost heave, the frost heave effect for the artificial freezing construction should be predicted before the construction process. The stochastic media theory is proposed to predict the frost heave effect due to the artificial freezing construction in the paper. The basic analysis procedure for analyzing frost heave effect is introduced and ground deformations such as ground vertical displacement, ground curvature are analyzed. The analysis result shows that the ground deformation due to the frost heaves is in the limit of ground displacement control requirement.

Abstract: With the rapid development of city subway, subway disaster problems aroused people's attention. Subway fire especially priority among priorities in subway disaster. This research mainly rely on the way of questionnaire survey, conducted a statistical study on metro fire evacuation behavior. The author has carried on questionnaire investigation to the passengers of some subway station in Tianjin Metro Line 1. The author sent out 116 questionnaires, received effective questionnaires 100 copies. The questionnaire content mainly includes the basic personal information, the surrounding environment and the passenger behavior in fire condition. The author analyzes the first behavior survey of different sex, different age, different education, different frequency and different subway fire experience reaction. Management departments according to the behavioral responses of passengers improve and optimize the subway facilities and fire evacuation passage.

Abstract: A three-story underground structure shaking table test had been carried on to study the earthquake damage mechanism of underground structure in layered foundation. The test model was similar to typical subway station according to a certain similarity ratio, and the soils were disturbed sandy soil and silty clay dug from the site of Harbin subway. Shaking table tests to this typical model in silty clay and alternating layers of clay and sand were performed to reveal the effect of different layered soils. Results show that the sandy soil layer can reduce the damage of the soil and underground structure, the damage of underground structure is mainly controlled by displacement of the surrounding soil, and the response of shallow buried underground structure is larger than deep buried.

Abstract: Simplified plane strain model and 3-D model were used to research the influence of pit excavation on the stability of underground openings using the finite element method (FEM). Conclusion from the 3-D FEM study is that the central region of the pit will have a large springback deformation and the openings will also float up at the same time because of large ranges of pit excavation. When using the simplified two-dimensional plane strain model for the analysis of this problem, the size of the excavation region leads directly to two completely inconsistent results. If the excavation region was wider than the openings the springback deformation would be obtained, while the settlement would be obtained if the opening was wider than the excavation region. Therefore the two-dimensional plane strain model is not proper for the analysis of the stability of the openings under this condition.

Abstract: Stability of rock stratum between concealed karst cave and tunnel is evaluated by the catastrophe theory. The numerical simulation method of safe distance between concealed karst cave and tunnel is proposed based on catastrophe theory energy catastrophe. Through array of rock stratum energy change and distance change between concealed karst cave and tunnel, a cusp catastrophe model of safe distance between concealed karst cave and tunnel is built. The simulation of safe distance between concealed karst cave and tunnel can be finished by Ansys program and Matlab, and automatically calculates the safe distance by a compile interface program, which is verified by engineering example.

Abstract: The excavation of foundation pit will change the initial stress state in surrounding soils, which induce the superimposed stress and uneven settlement to the adjacent existing tunnels. Based on the pit excavation engineering in Shenyang, which sits atop the existing tunnels, the risk factors and failure type of shield segment lining were studied through risk analysis theory. According to the uncertainty and spatial variability of soil parameters, the risk accident of existing tunnel was calculated by means of stochastic finite element which is combined Monte Carlo simulation with FEM. The risk of existing tunnel during the pit excavation stage was evaluated respectively under multi-failure patterns. The framework is used to estimate and minimize risks at pit excavation engineering in Shenyang.

Abstract: Taking some deep buried immerse tunnel as background, deformation characteristics of foundation gravel bed is discussed by physical model test. The results show that small particle size gradation is not suitable for the foundation gravel bed, and compared with the non-groove gravel, compression modulus is greatly reduced in case of gravel with groove, and in case of pile foundation, gravel crushing phenomenon is obvious at the end of loading, and the ultimate bearing capacity of gravel bed is about 480kPa. If pile and gravel bed are used as the immerse tunnel foundation plan, it needs to take measure to control the stress level under the ultimate bearing capacity of gravel bed.

Abstract: Kinetic research of Small spacing tunnel blasting excavation is always the hot issue both at home and abroad. In this paper, the entrance section of a small spacing tunnel is chose as an example, the Explicit dynamic finite element model and the Euler method is adopted to accurately simulate the process of blasting vibration, and the peak vibration velocity response of the tunnel is gotten. Studies has shown that, the peak velocity is more sensitive to space change when clear distance is less than 1.5 times of the hole diameter; various depth of tunnel causes different clamping action of surrounding rock, thus has different effects on peak velocity; vibration velocity at head-burst side is 5-8 times more than that at back side, vibration velocity at tunnel waist is 1.98-2.23 times more than that at up side, vibration velocity at tunnel shoulder is 1.68-1.85 times more than that at up side, so the waist position at head-burst side should be given exclusive attention.

Abstract: Groundwater flow into mountain tunnel can lead to drawdown and groundwater loss in tunnel construction and operation stages under drainage and limited drainage principle conditions. The author defines groundwater recovery degree of drawdown and volume change, and simulate drawdown and groundwater recovery process adopting nonhomogeneous and anisotropic equivalent tunnel flow model, and study influencing effect of various factors to groundwater recovery by numerical method. The results show that the essential condition of groundwater recovery in tunnel is that groundwater recharge is greater than groundwater inflow volume, which can be controlled by efficient waterproof and drainage measures. The efficient measures include curtain grouting, radial grouting and high impermeability performance of shotcrete.

Abstract: The Beijing East 2nd Ring underground road is one of the three horizontal and four vertical underground expressways, and it is an important part of Beijing's expressway system. Technical standards, engineering line location, geological conditions, construction methods, construction organization, controlling conditions of the project are illustrated in the paper. Research and demonstration of the feasibility of the projects is carried out. The conclusions are as follows: (1) The overall line location conform to the city's underground transportation system planning. (2) The overall project layout is correct. Underground space is used reasonably. The urban expressways system can be improved. The technical standards of the expressway project can be satisfied. (3) The project connects Puhuangyu Expressway and Beijing-Chengde Highway. Cross-border traffic is solved. That plays an important role to ease the traffic pressure of city center road network. (4) Large diameter shield construction program is feasible. (5) The large cross-section of proposed tunnel, complex construction environment, high technical difficulty, could be included in the forefront of the construction of city tunnel at home and abroad. Scientific and technological research and research projects are proposed to carry out, laying a solid foundation for the smooth implementation.