The distribution of the initial temperature field of a high-rock-temperature tunnel is critical for determining the tunnel line and the construction scheme. This study used model testing, numerical analysis, and field measurement to investigate the initial temperature field distribution of a tunnel with high rock temperatures. A model test system was developed, and the experimental results show that the boundary conditions set by the model are reasonable. The results show that the temperature along the tunnel line is high in the middle and low at both ends. Obviously, the periodic boundary conditions have a significant influence on the temperature field distribution. Then, the corresponding two-dimensional unsteady numerical model is established, and the numerical model is verified by the model test. Next, the numerical model is applied to the actual Jiwoxiga tunnel, which is a high-rock-temperature tunnel. The results show that the maximum ground temperature in the direction of the Jiwoxiga tunnel line is 52.5 °C, the tunnel lengths with ground temperatures above 28 °C account for 96.25% of the total tunnel length, and the tunnel length with a ground temperature above 45 °C comes to nearly 1200 m. In addition, this result is also verified by the field drilling data and field-measured data after excavation. The effectiveness and accuracy of the numerical model are fully demonstrated. This study provides theoretical support for the design and construction of high rock temperature tunnels.
Background: Part of tunnel of rail transit of line 1# in Lanzhou city passes through loess. Loess has obvious water sensitivity and anisotropy, these obvious characteristics will have different degrees of influence on different projects. Objective: To compare the differences of shear strength with the vertical and horizontal direction through triaxial and direct shear test, and permeability of samples in different directions. Method: The Q4 loess undisturbed sample respectively from vertical and horizontal directions near tunnel face were selected in order to study the physical mechanical properties of Lanzhou rail transit secent, many related experiments has been carried on. Results: The results show that the anisotropy of the shear strength of the surrounding rock (Q4 loess) is significant near the tunnel face with depth of 15m. The failure stress in the vertical direction is 1.33 times that in the horizontal direction, and the permeability coefficient in the vertical direction is 1.37 times that in the horizontal direction. In different directions, the internal friction angle of loess is basically the same. The cohesion force is different in different directions and different test methods. In general, the vertical strength of Q4 loess is greater than the horizontal strength. Conclusion: This characteristic is caused by the structural characteristics of loess. Therefore, in the design and construction of loess tunnel, the mechanical parameters in different directions of loess should be considered, and the influence of different test methods on the measured parameters should also be considered.
With the rapid development of rail transit, the excavation of new foundation pits will inevitably approach or pass through existing structures. Therefore, choosing a reasonable support scheme can effectively control the deformation of the foundation pit and ensure the safety of existing structures. This paper investigates the excavation of a typical foundation pit in Guangdong that underpasses a viaduct as the research object. This study uses field monitoring and numerical simulations to analyze the deformation characteristics of the supporting structure and introduces grey relational analysis (GRA) to investigate the key factors that influence the maximum horizontal deflection of the retaining wall. The results indicate that all monitored values are substantially less than the warning value specified in the code. Moreover, the horizontal deflection of the retaining wall and the horizontal displacement of the top of the wall at the measuring points near the existing bridge piles are smaller than at other measuring points. This support system has a high safety factor and a large space for optimization. The main factors affecting the maximum horizontal deflection of the retaining wall are as follows: second strut horizontal spacing > first strut horizontal spacing > layered excavation thickness > retaining wall thickness > retaining wall stiffness. The results of this study will provide technical guidance for the design of similar projects and optimization of their construction.
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