Smart Risk Assessment Model of Water Inrush in Submarine Tunnel through AHP-TOPSIS and Intelligent Computing

In tunnel construction, water and mud inrush disasters are prone to occur when the tunnel traverses water-rich faults, which leads to structural damage and tunnel instability, which is one of the most severe hazards in tunnel excavation and construction. This paper proposes a method of combining AHP and TOPSIS. The weights are determined through the analytic hierarchy process utilizing expert scoring. The determined weights are evaluated and predicted by TOPSIS for water inrush risk. The Jiaozhou Bay Subsea Tunnel is used as a case to carry out the tunnel crossing the fault zone. Water inrush risk prediction provides a new idea for water inrush risk prediction.

Optimization for U-Shaped Steel Support in Deep Tunnels under Coupled Static-Dynamic Loading

With the effects of high geostress and intensive dynamic disturbances in deep mining, the stability and safety of tunnels are seriously affected. The optimization for U-shaped steel support is of vital significance and can solve the problems of cost reduction and tunnel instability. Based on the perturbation equation, a coupled formula for U-shaped steel and the surrounding rock mass was proposed to evaluate the practical stability of a U-shaped steel support. Through a numerical simulation method, the characteristics of U-shaped steel support can be obtained under coupled static-dynamic loading. Furthermore, the field test was carried out and compared with the numerical simulation, which was discussed. The results show that there will be a stress concentration when the contact area is small. In addition, the concentrated stress will release with the increase in contact area. With the increase in the lateral stress coefficient, the deformation exhibits a downward trend under static loading, indicating that the lateral stress is the dominant force driving the deep geostress activity. The support requirement of this section of surrounding rock can be satisfied by a U-shaped steel group with 1.5 m spacing under dynamic disturbance.

Predicting Tunnel Squeezing Using Multiclass Support Vector Machines

Tunnel squeezing is one of the major geological disasters that often occur during the construction of tunnels in weak rock masses subjected to high in situ stresses. It could cause shield jamming, budget overruns, and construction delays and could even lead to tunnel instability and casualties. Therefore, accurate prediction or identification of tunnel squeezing is extremely important in the design and construction of tunnels. This study presents a modified application of a multiclass support vector machine (SVM) to predict tunnel squeezing based on four parameters, that is, diameter (D), buried depth (H), support stiffness (K), and rock tunneling quality index (Q). We compiled a database from the literature, including 117 case histories obtained from different countries such as India, Nepal, and Bhutan, to train the multiclass SVM model. The proposed model was validated using 8-fold cross validation, and the average error percentage was approximately 11.87%. Compared with existing approaches, the proposed multiclass SVM model yields a better performance in predictive accuracy. More importantly, one could estimate the severity of potential squeezing problems based on the predicted squeezing categories/classes.

Risk Assessment of Geological Hazards in a Tunneling Project Using Harmony Search Algorithm (Case Study: Ardabil-Mianeh Railway Tunnel)

During the design and implementation of underground constructions, the risk assessment and management of geological hazards are important due to the hazards such as the water inflow, collision with crushed fault zones, squeezing and instability around excavation zones. In the present research, it is attempted to study and assess the risk of geological hazards in 378+021 km of the route of Ardabil-Mianeh railway tunnel using the harmony search algorithm (HSA). In the first section of research, after studying structural and geological characteristics during 24 sections of the excavation route, the risk relating to geological hazards including the tunnel instability, squeezing, water inflow and swelling was assessed in three separate classes using HSA. In order to study the accuracy of results, geological hazards recorded during the implementation of excavation operations were used. Studies obtained from the comparison of observed and predicted results indicate the high accuracy of HSA in the assessment and prediction of geological risks in the tunnelling project.

Stability analysis of a shallow depth metro tunnel: a numerical approach / Analiza stabilności płytkiego tunelu metra z wykorzystaniem metod numerycznych

In this paper, an attempt has been made to use numerical modelling for simulating a long halt in construction process at a shallow depth metro tunnel and investigate the effects of soil nailing to increase the tunnel face strength. Finite difference software FLAC with high applicability in a continuum environment was adopted for this study. The tunnel is being excavated for Tehran metro project. Shield tunnelling with roadheader and back hoe cutting tools is applied in the excavation process. Mohr-Coulomb elasto-plastic constitutive law is considered to model the ground. After two months halting in excavation process, tunnel instability and ground subsidence were recorded in thirteen different monitoring points. Numerical simulation results showed a close approximation (11-16%) between measured and FLAC computed displacements of the tunnel crown in case of unsupported face, which is in close proximity and a proof indicates the reliability of simulation. Also, simulation results exhibit a significant reduction in the ground subsidence and tunnel instability in case of supported face by means of the soil nailing.

Back calculation of in-situ rock stresses for a tunnel project in Himachal, India

Determination of in-situ stresses in the rock mass is necessary for stability assessment and proper design of underground openings. It is important to know the state of stress surrounding the opening so that right and optimum rock support is assigned as preliminary and permanent rock support. However, the majority of long tunnels with high rock cove r face severe tunnel instability problems related to rock stresses. The headrace tunnel of Parbati II hydroelectric project is one of such tunnels, especially the tunnel segment passing through Manikaran quartzite. It is known fact that the extent and type of stress induced instability vary greatly upon rock type, deformability properties, jointing and inter-bedding characteristics in the rock mass. This paper back calculates the state of stress using Phase 2 finite element model in a TBM bored segment of the tunnel and also briefly reviews mechanical properties of the intact rock that may have direct link on the nature of stress induced instability. It is believed that back calculated stress magnitude may be useful for the stability assessment in other segment of headrace tunnel.

Numerical Analysis of Faults on Deep-Buried Tunnel Surrounding Rock Damaged Zones

Fault is one of the most important factors affecting tunnel instability. As a significant and casual construction of Jinping II hydropower station, when the drain tunnel is excavated at depth of 1600 m, rockbursts and water inrush induced by several huge faults and zone of fracture have restricted the development of the whole construction. In this paper, a progressive failure progress numerical analysis code-RFPA (abbreviated from Rock Failure Process Analysis) is applied to investigate the influence of faults on tunnel instability and damaged zones. Numerical simulation is performed to analyze the stress distribution and wreck regions of the tunnel, and the results are consistent with the phenomena obtained from field observation. Moreover, the effects of fault characteristics and positions on the construction mechanical response are studied in details. Some distribution rules of surrounding rock stress of deep-buried tunnel are summarized to provide the reasonable references to TBM excavation and post-support of the drain tunnel, as well as the design and construction of similar engineering in future.