Investigating the Deformation and Failure Mechanism of a Submarine Tunnel with Flexible Joints Subjected to Strike-Slip Faults

Knowledge from historical earthquake events indicates that a submarine tunnel crossing active strike-slip faults is prone to be damaged in an earthquake. Previous studies have demonstrated that the flexible joints are an effective measure for a submarine tunnel crossing a strike-slip fault. The background project of this paper is the second submarine tunnel of Jiaozhou bay. In this work, model tests and numerical simulations are conducted to investigate the deformation and failure mechanism of a submarine tunnel with flexible joints under a strike-slip fault dislocation. The influence of strike-slip faults on a tunnel with flexible joints has been investigated by examining the deformation of rock mass surface, analyzing lining stains, and crack propagation from model tests. Numerical simulations are conducted to study the effects of the design parameters of a tunnel with flexible joints on the mechanical response of the lining. The results showed that the ‘articulated design’ measure can improve the ability of the tunnel to resist the strike-slip faults. In terms of the mechanism of design parameters of a tunnel with flexible joints, this paper finds that increasing the lining thickness, decreasing the lining segment length, and decreasing the tunnel diameter to a reasonable extent could effectively improve the performance of this faulting resistance measure for a tunnel under the strike-slip fault zone dislocation. Compared with the horseshoe tunnel cross-section, the circular tunnel cross-section can improve the ability of the faulting resistance of a tunnel with flexible joints, while the optimal angle of the tunnel crossing the fault zone is 90º. It is concluded that the wider fault zone, smaller flexible joint width, and less stiffness of the flexible joint could make lining safer under a strike-slip fault dislocation. The above research results can serve as a necessary theoretical reference and technical support for the design of reinforcement measures for a submarine tunnel with flexible joints under strike-slip fault dislocation.

Fire behaviors along timber linings affixed to tunnel walls in mines

Timber linings are applied as primary supports in the tunnel fault and fracture zones of mines. These linings are essential to prevent broken rock from falling during the occurrence of exogenous fires. In this study, experiments and numerical simulations were carried out using a fire dynamics simulator to investigate the flame-spread rate, flame characteristics, smoke movement, and spread process of timber-lining fires under different wind speeds of 0, 0.25, 0.5, and 0.75 m/s. It was found that cross-section flame spreading follows the three-stage sidewall-ceiling-sidewall pattern. Moreover, the average flame-spread rate increases along the vertical flame-spreading direction and decreases when the flame reaches the timber-lining corners. Moreover, the flame lengths underneath the timber-lining ceiling in the x-direction are longer than those in the y-direction. As the wind speed increases, the normalized flame lengths R(f) in the two directions decrease, and the maximum temperature underneath the ceiling decreases. In addition, the maximum temperature in the three tunnel sections of interest is first recorded in the tunnel cross-section in the initial fire stage. Higher wind speeds correspond to farther distances of the maximum-temperature points of the three timber-lining sections from the fire source.

Tunneling in Various Shapes Using Numerical Analysis

Tunnelling has gained popularity in the recent times due to lack of space and the rapidly increasing population. Thus, going underground is the only option to provide the infrastructure facilities which will meet the need of increasing population. The shape and dimensions of the tunnel cross section usually depends on certain parameters like purpose for which the tunnel is provided, drainage & maintenance requirements, requirement of escape route, etc. Geology plays an important role in deciding the shape of the tunnel. The ground behaves in a complex manner, when a tunnel is excavated in it as new stresses are developed. Based on the ground types, the shape is selected in such a way that the stresses developed in the ground should distribute properly around the tunnel periphery and should not cause convergence of the tunnel boundary. Also, requirement of support system should not be too heavy, as it will increase the cost. Apart from the above parameters, the availability of the equipment & the construction method also decides the shape of the tunnel. There are various shapes of tunnels like D-shape, Circular, Elliptical, Egg-shape, Box type, Horseshoe & Modified Horseshoe shape. In the present course of work three shapes of tunnels viz. Horseshoe Shape, Modified Horseshoe Shape & D-Shape tunnels are considered. By hypothetical assumption the geology and overburden are taken into account for the tunnels and the tunnels are simulated for roof collapse and shear failure case by using RS2 FEM based software.

Numerical Modelling of The Behavior of Tunnel in Soft Surrounding Rock. A Case Study of Djebel El-Ouahch Tunnel, Algeria.

The response of a massif to stresses generated by tunnel excavation depends essentially on the geological conditions, the geometry of the tunnel and its underground position. The major problem related to the construction of these structures is to ensure the stability of the whole tunnel-ground, by controlling the various deformation generated during the constructionIn this context, the present paper examines the effect of these conditions on the behavior of tunnels and the surrounding soil. The study is applied to a real tunnel, in this case the tunnel of Djebel El Ouahch, Algeria was taken as a reference model. The research includes a parametric study to evaluate the effect of several parameters on the behavior of the tunnel and surrounding soil such as the tunnel anchoring depth, the tunnel-soil interface rate, and the shape of the tunnel cross section. The analysis is performed using the PLAXIS 3D TUNNEL calculation code with an elastoplastic Mohr-coulomb model for the soil behavior. The results show that the strongest and most stable position is the mid-deep tunnel with a circular section, with a non-slip interface between the tunnel and the ground. These outcomes can help to understand the effects of various influences parameters which control the stability of the tunnel in a soil with bad characteristics.

A Novel Contact Tunnel Profile Monitoring System: Concept and Application

The displacement of the cross section directly reflects the stress state and stability of the surrounding rock and structure, so the monitoring of it is essential during the construction and operation of the tunnel and underground engineering, particularly under the conditions of earthquake and other geological disasters. This paper introduces a new contact tunnel profile monitoring system (TPMS) in detail that uses a tilt sensor and a displacement sensor as data acquisition devices. According to the relation between the sensing physical quantity and displacement change, the displacement calculation formulas of the tunnel cross section measuring points based on the two-dimensional plane coordinate system were deduced, and in order to eliminate the actual installation and positioning deviation of the monitoring system, the method of obtaining the optimal monitoring plane and converting coordinates of the measuring points was proposed, thus establishing the theoretical basis for the application of the TPMS. With the Beishan exploration tunnel (BET) in China as the test platform, the TPMS was successfully applied for long-term monitoring. The application experience showed that the TPMS can realize continuous monitoring, automatic collection and transmission of the monitoring data, remote access whenever necessary, without affecting the transportation in the tunnel, and high accuracy, which reaches 0.01 mm. This system provides a new simple and effective method with good generality and applicability for the deformation monitoring of the tunnel and underground engineering.

Experimental Study on the Temperature Field of Cold Region Tunnel under Various Groundwater Seepage Velocities

Groundwater seepage significantly affects the temperature field of a cold region tunnel. Laboratory model tests are carried out to evaluate its effects, yielding four main results. First, groundwater seepage can increase tunnel air temperature and decrease the thickness and length of the tunnel insulation layer. Second, groundwater seepage and tunnel ventilation exert a coupling effect on the surrounding rock temperature. This effect is related to the surrounding rock depth. Third, the influence of the groundwater seepage velocity on the temperature of the interface between the lining and surrounding rock demonstrates a spatial difference, and the groundwater seepage leads to an uneven temperature distribution at the interface between the lining and surrounding rock. Furthermore, under groundwater seepage, the shape and size of the tunnel cross section have significant effects on the interface temperature. Fourth, the cold region tunnel has an antifreezing capability that is mainly related to the frost heaving of the surrounding rock and the groundwater seepage velocity. This capability should be fully utilized in the design of cold region tunnels. The experimental data presented can be used to verify the reliability of the theoretical calculation model for tunnel temperatures in cold regions.

Effect of Seismic P-Waves Propagation on Circular Tunnels in Layered Ground

During propagation of the compression seismic P-waves, the tunnels are subjected to ovaling deformations. In cases where the soil stiffness is varying along the tunnel cross-section, tunnel lining may take sharper deformed shapes and subjected to magnified bending moments and thrust forces. This paper investigates the effect of the soil stratification on the seismic behavior of circular tunnels under P-waves loading. A 2D finite element models with time history earthquake (EQ) analysis were performed accounting for different tunnel/soil interface slippage conditions. The finite element analysis results were compared with recent analytical solution for calculating the seismic forces of the tunnel lining. The study proved that soil stratification has a great effect on the tunnel seismic forces and it should be considered in the analysis and design. Illustrative curves were presented in this paper to give approximate magnification factors for the anticipated forces. It should be used as a guide in the preliminary design stage.