A New Semi-Analytical Method for Elasto-Plastic Analysis of a Deep Circular Tunnel Reinforced by Fully Grouted Passive Bolts

The use of fully grouted passive bolts as a reinforcement technique has been widely applied to improve the stability of tunnels. To analyze the behaviors of passive bolts and rock mass in a deep circular tunnel, a new semi-analytical solution is presented in this work based on the finite difference method. The rock mass was assumed to experience elastic–brittle–plastic behavior, and the linear Mohr–Coulomb criterion and the nonlinear generalized Hoek–Brown criterion were employed to govern the yielding of the rock mass. The interaction and decoupling between the rock mass and bolts were considered by using the spring–slider model. To simplify the analysis process, a bolted tunnel was divided into a bolted region and an unbolted region, while the contact stress at the bolted–unbolted interface and the rigid displacement of the bolts were obtained using two boundary conditions in combination with the bisection method. Comparisons show that the results obtained using the proposed solution agree well with those from the commercial numerical software and the in situ test. Finally, parametric analyses were performed to examine the effects of various reinforcement parameters on the tunnel’s stability. The proposed solution provided a fast but accurate estimation of the behavior of a reinforced deep circular tunnel for preliminary design purposes

Intelligent Classification of Surrounding Rock of Tunnel Based on 10 Machine Learning Algorithms

The quality evaluation of the surrounding rock is the cornerstone of tunnel design and construction. Previous studies have confirmed the existence of a relationship between drilling parameters and the quality of surrounding rock. The application of drilling parameters to the intelligent classification of surrounding rock has the natural advantages of automatic information collection, real-time analysis, and no extra work. In this work, we attempt to establish the intelligent surrounding rock classification model and software system driven by drilling parameters. We collected 912 samples containing four drilling parameters (penetration velocity, hammer pressure, rotation pressure, and feed pressure) and three surrounding rock (grade-III, grade-IV, and grade-V). Based on the python machine learning toolkit (Scikit-learn), 10 types of supervised machine learning algorithms were used to train the intelligent surrounding rock classification model with the model parameter selection technology of grid search cross validation. The results show that the average accuracy is 0.82, which proves the feasibility of this method. Finally, the tunnel surrounding rock intelligent classification system was established based on three models with better comprehensive performance among them. The classification accuracy of the system was 0.87 in the tunnel test section, which indicates that the system has good generalization performance and practical value

Experimental Study on Bond-Slip Behavior between Corroded I-Shaped Steel and Concrete in Subsea Tunnel

Degradation of the bond between I-shaped steel and concrete due to the corrosion of I-shaped steel significantly affects the durability of steel reinforced concrete (SRC) structures. This study carried out the accelerated corrosion test and push-out test to study the bond-slip behavior and characteristics considering the corrosion of I-shaped steel, and test results indicated that: (1) The performance degradation of the bond-slip accelerated when the corrosion ratio reached 12%. (2) The corrosion failure pattern of SRC experienced slip phase and destruction phase in the rising stage. (3) Based on the principle of minimum potential energy, the bond stress was obtained only with the load and the displacement in the free end and the loading end. (4) Meanwhile, a new bond-slip degradation model was developed using the interface damage theory. Finally, the proposed model agreed with the experimental results

Energy-Saving Network Ventilation Technology of Extra-Long Tunnel in Climate Separation Zone

Saving energy is a major challenge for the development and safety of the world. Researchers at home and abroad have been continuously working on energy saving technology in the tunnel ventilation for decades. Based on segmented longitudinal ventilation for extra-long road tunnels, the main ventilation mode and utilization method of natural wind energy in extra-long road tunnel were analyzed in this paper. In addition, the possible velocity distribution of natural wind in each section under wind pressure was investigated. Principles of natural wind in each tunnel section were studied based on long-term monitored meteorological factors. Accordingly, a fan equipment configuration method with high guaranteed rate during tunnel operation was proposed. A calculation method for energy-saving network ventilation in the tunnels was established. A feasible and efficient optimized energy-saving ventilation strategy was proposed, which utilizes natural wind and reduces the operation energy consumption. Thus, the annual energy saving in ventilation can reach up to 43.2% compared to previous energy costs when the intelligent ventilation system works. The research results can properly combine natural wind energy with mechanical ventilation to realize the smart self-energy saving in extra-long tunnels

Research on the Earth Pressure and Internal Force of a High-Fill Open-Cut Tunnel Using a Bilayer Lining Design: A Field Test Using an FBG Automatic Data Acquisition System

When there are railway tunnels on both sides of a valley, a bridge is usually built to let trains pass. However, if the valley is very close to an urban area, building an open-cut tunnel at the portal and then backfilling it to create available land resources for the city and to prevent excavation slag from polluting the environment would be a wise choice. This has led to the emergence of a new type of structure, namely, the high-fill open-cut tunnel. In this paper, by performing an automatic long-term field test on the first high-fill open-cut tunnel using a bilayer design in China, the variations of earth pressure and structural internal force during the backfilling process were obtained, and different tunnel foundation types were studied. The results showed that the earth pressure significantly exceeded the soil column weight, with a maximum earth pressure coefficient between 1.341 and 2.278. During the backfilling process, the earth pressure coefficient increased at first and then decreased slowly to a relatively stable value, and a stiffer foundation would make the structure bear higher earth pressure (1.69 times the normal one observed during monitoring). The change of internal force had two stages during backfilling: before the backfill soil reached the arch crown, the internal force of the lining changed slowly and then grew linearly as the backfill process continued. Moreover, the axial force ratio of the inner and outer linings was close to their thickness proportion, and the interaction mode between the two layers was very similar to the composite beam

Study on Oxygen Supply Standard for Physical Health of Construction Personnel of High-Altitude Tunnels

The low atmospheric pressure and low oxygen content in high-altitude environment have great impacts on the functions of human body. Especially for the personnel engaged in complicated physical labor such as tunnel construction, high altitude can cause a series of adverse physiological reactions, which may result in multiple high-altitude diseases and even death in severe cases. Artificial oxygen supply is required to ensure health and safety of construction personnel in hypoxic environments. However, there are no provisions for oxygen supply standard for tunnel construction personnel in high-altitude areas in current tunnel construction specifications. As a result, this paper has theoretically studied the impacts of high-altitude environment on human bodies, analyzed the relationship between labor intensity and oxygen consumption in high-altitude areas and determined the critical oxygen-supply altitude values for tunnel construction based on two different standard evaluation systems, i.e., variation of air density and equivalent PIO2. In addition, it has finally determined the oxygen supply standard for construction personnel in high-altitude areas based on the relationship between construction labor intensity and oxygen consumption

Prediction Method of Tunnel Natural Wind Based on Open-Source Meteorological Parameters

The rational use of natural wind in extra-long tunnels for feedforward operation ventilation control can dramatically reduce tunnel operation costs. However, traditional tunnel natural wind calculation theory lacks a prediction function. This paper proposes a three-stage tunnel natural wind prediction method relying on the Yanglin Tunnel in Yunnan, China based on the massive meteorological parameters provided by the open-source national meteorological stations around the tunnel, which make up for the partial deficiency of the meteorological parameters of the tunnel portal. The multi-layer perceptron model (MLP) was used to predict the real-time meteorological parameters of the tunnel portal using the data from four national meteorological stations. The nonlinear autoregressive network model (NARX) was used to predict the meteorological parameters of the tunnel portal in the next period based on the predicted and measured real-time data. The natural wind speed in the tunnel was obtained by a theoretical calculation method using the predicted meteorological parameters. The final tunnel natural wind prediction results are in good agreement with the field measured data, which indicates that the research results of this paper can play a guiding role in the feedforward regulation of tunnel operation fans

Analysis of the Mechanical Characteristics of Different Track Bed Types in Heavy-Haul Railway Tunnels

Based on field measurement data from the Fuyingzi Tunnel and Hongshila Tunnel on the Zhangtang Railway, a comparative analysis was conducted on the characteristics of a ballast bed and ballastless slab track, which are commonly used in the track structures of heavy-haul railway tunnels. According to the relevant domestic standards and the theory of the stress diffusion angle, a wheel-rail sharing ratio and theoretical calculation method for the added value of the trainload on the surface and bottom of different track bed types was proposed. In accordance with the measured data, the dynamic load thresholds and distributions on the surface and bottom of different track bed types were analysed and compared with the theoretical results. The results show that the theoretical equation has high accuracy and good applicability. The ballast bed can better cushion the heavy loads, while the ballastless slab track is better able to accomplish train load attenuation. In addition, the distribution on the bottom of the ballastless slab track is “triangular”, while the distribution at the surface or bottom of the ballastless track and ballast bed is “saddle-shaped.” The ballast bed is subjected to a greater load from the vehicle, and the long-term effect is more pronounced. These results can provide a theoretical basis for the stress analysis and design parameters of heavy-haul railway tunnel track beds

Investigation of the failure mechanism and theoretical model of bolt-reinforced shallow tunnel faces with different bolt lengths

Using fiberglass bolts to reinforce a tunnel face is a practical auxiliary technology for ensuring tunnel face stability in soft ground. The reinforcing effect and the economics of this technology are significantly affected by bolt length. However, to date, the failure mechanism of bolt-reinforced tunnel faces with different bolt lengths has rarely been investigated. To reveal the failure mechanism of bolt-reinforced shallow tunnel faces, in this study, the stability of bolt-reinforced tunnel faces with different bolt lengths was investigated by using laboratory tests and numerical simulations, and a simplified theoretical model for practical engineering was proposed. The face support pressure and failure pattern for different bolt lengths during the face collapse process were obtained, and the influence of bolt length on face stability was clearly revealed. More specifically, the results show that face stability increases with increasing bolt length, and the reinforcing effect of face bolts is governed by the shear failure at the soil-grout interface first in the stable zone of the tunnel face and then in the failure zone. Once the bolt length in the stable zone is larger than that in the failure zone, face stability will not be improved with increasing bolt length; thus, this bolt length is referred to as the optimal bolt length Lopt. The Lopt value is slightly larger than the initial failure range (in the unreinforced condition) and can be approximately calculated by Lopt = (1 − 0.0133φ)D (φ is the friction angle of the soil, and D is the tunnel diameter) in practical engineering. Finally, a simplified theoretical model was established to analyse the stability of reinforced tunnel faces, and the results are in good agreement with both laboratory tests and numerical simulations. The proposed model can be used as an efficient tool for the design of face bolts