The problems existing in the stability analysis of tunnels and the design concept and method were put forward, and three limit analysis methods were introduced and put forward according to the principle of elastic-plastic mechanics. It is pointed out that the numerical limit method is the only way to solve the tunnel design problem. The reliability of three limit analysis methods and their feasibility in tunnel engineering are illustrated by examples. In order to solve the uncertainty in tunnel stability analysis and to provide more scientific and reasonable mechanical parameters of surrounding rock, it is necessary to do a good job of surrounding rock classification combining theory, investigation and experience. Taking the surrounding rock classification of rail transit tunnels as an example, the level and scientificity of classification were improved including the coordination and optimization of qualitative and quantitative classification, the improvement of strength and integrity index, the compilation of classification table of surrounding rock of interval tunnel and station tunnel, the judgment of self stability ability of surrounding rock and the determination of physical and mechanical parameters of surrounding rock. A classification method with two kinds of tunnel spans is proposed, which provide more scientific and reasonable mechanical parameters and improve the level of quantitative classification method.

Tunnelling and underground excavations involve the removal of soil or rock mass from their initial locations. This process may be accurately modelled by the unloading of a cavity from the in-situ stress state. In the past decades, for the purpose of controlling ground deformation and maintaining tunnel stability, cavity contraction theory had been used to predict ground reaction curves, to estimate ground settlements due to tunnelling and to design tunnel support systems. This paper presented a comprehensive review of analytical cavity contraction solutions for these typical applications. For illustration, a new finite strain analytical solution was derived for the unloading analysis of a cylindrical spherical cavity in non-associated Mohr Coulomb materials with a finite radial extent. This paper would be beneficial for the future development of cavity contraction theory and its application to practical tunnelling problems.

There are many problems during shield/TBM construction, such as the difficulty of muck removal, tool wear, shield tail failure, ground settlement, which seriously affected the safety and efficiency of tunnel construction and become important issues for shield construction at present. The key to solve these problems is to carry out the research on shield/TBM soil conditioning and tail sealing technology. This study described the causes of the above problems. Based on the common construction technology of shield tunnel, this study focused on the current research status of soil conditioning and shield tail sealing technology at home and abroad, and summarized the shortcomings of current common construction methods and construction technology. Relying on the combination of laboratory test and field test, new shield materials and supporting construction technologies were developed, such as high-efficiency soil conditioning agent, anti-dust and wear-resistant agent, high-performance shield tail sealing grease, synchronous grouting filling agent. The theoretical analysis and effect comparison test were carried out to solve the technical problems related to the shield/TBM tunneling process, ensuring the safe and rapid construction of the tunnel, and providing the theoretical basis and technical support for soil conditioning and shield tail sealing in the complex environment with high water pressure in the future.

The discontinuity layout optimization is a novel numerical method for upper bound limit analyses, proposed in 2007. It is widely used in analyzing the limit load and stability of geotechnical and plate/shell-like structures. In this method, a large number of nodes are introduced into the domain, the lines(2D)and surfaces(3D)formed by the nodes are considered as potential discontinuities. Based on the minimization of dissipated energy, the target function is built. The restraints equations are generated by geometric compatibility conditions, Mohr-Coulomb flow rules, and load/work conditions. Not only the limit load/factor of safety but also the activated discontinuities and displacement jumps are obtained. The method is theoretically clear, whose pre- and post-processing is easy for implementing and its computational efficiency is very high. However, there are only a few researches and applications about this method in China. This work is the first Chinese paper introducing DLO, which presents basic concepts, engineering applications especially in geotechnical and tunneling engineering of this method in details, which will hopefully promote its further developments in China.

The large-diameter single-pile foundation is the main form of offshore wind turbine. It is of great significance to evaluate the horizontal bearing capacity of the pile foundation and the 1^st natural frequency of the wind turbine to optimize the design. The numerical analysis method of the strength degradation of soft clay based on non-linear kinematic hardening model was developed. The comparisons with triaxial tests and centrifuge test results showed that the method had reliabilities in analyzing the strength degradation of the soil and interaction of pile-soil system. The method analyzed the effects of cyclic loading on the stiffness of pile-soil system, the bearing capacity of pile foundation and the 1^st natural frequency of the wind turbine. The results showed that the effect of cyclic load amplitude was greater than the number of cycles when the number of cycles was small. The bending stiffness and flexural bearing capacity of the pile-soil system were attenuated more than the horizontal stiffness and the lateral bearing capacity. Due to the limited degree of stiffness attenuation, the overall first-order natural frequency of the wind turbine was not significantly reduced.

Aiming at the common problems of tunnel excavation in coal-bearing strata in road construction at present, taking Taoziya Tunnel of Zhengxi Expressway as an example, the whole construction process of three construction methods for coal-bearing strata excavation was simulated. The stability of the surrounding rock and the supporting structure were analyzed, and the variation rules of stress, displacement and other parameters during the construction process were obtained and the construction suggestions were put forward. The results showed that the excavation method and temporary structure affected the stress distribution and deformation of surrounding rock and tunnel structure: for the step method, the temporary structure might be appropriately arranged to control the deformation in the lower half section; at the interface of the inclined rock strata, the CRD method and the core soil method should adjust the surrounding rock of each section to stabilize the rear surrounding rock according to the working conditions, and control the surrounding rock deformation during excavation. According to the above results, the construction scheme and supporting design could be optimized, which has reference significance for similar tunnel construction.

By collecting the data of collapses and landslide disasters at the mountain tunnel mouth, ten factors were summarized to two major aspects of collapses at tunnel mouth and instability in heading slope in this paper. Classification of disaster factors were suggested, math model of the membership degree of disaster factors which could achieve qualitative to quantitative mathematical was established, mathematical principles on disaster factors in fuzzily integrated analysis method was explained, thus, the mathematical model for engineering geological hazard risk assessment of mountain tunnel mouth was established. Ttaking the engineering practice of the mouth section of Zishi Tunnel and Ganggou tunnel as two cases, the application method of the model was described in detail, and the engineering geological risk of the project was evaluated, which provided theoretical tools and methods for tunnel workers to strengthen the safety control of the construction at the mountain tunnel mouth.

At present, more research had been done on the indoor model test of the influence of soft soil circular tunnel construction on adjacent structures. However, the indoor model test for the deformation of adjacent underground pipelines caused by the excavation of quasi-rectangular-irregular section tunnel was still rare to study. Based on the quasi-rectangular-shaped section tunnel excavation convergence displacement mode, a model test system for the deformation of adjacent underground pipelines induced by quasi-rectangular tunnel excavation was established, including quasi-rectangular tunnel excavation simulation device, pipeline simulation device, pipeline displacement measurement system, and model test data collection system, etc. The excavation process of quasi-rectangular tunnel was simulated by four liquid bags drainage, and the settlement deformation of adjacent underground pipelines, the internal force of pipeline section, and the surface contact force of excavation-like tunnel excavation and the earth pressure of pipeline surface were recorded in real time. Tunnel excavation induced settlement deformation of adjacent underground pipelines and internal force distribution and development of pipeline sections. It was found that the settlement value of pipelines increased slowly with the drainage of tunnel sacs, and the soil pressure on the surface of tunnels and pipelines increased slowly and then stabilized. In addition, a variety of working condition model tests were carried out for different pipeline depths and pipeline outer diameters. The results showed that under the same working conditions of pipeline outer diameter, as the pipeline depth increased, the distance between the tunnel and the pipeline became smaller, as the settlement deformation of the pipeline increased, the internal force of the pipeline increased. Under the same working conditions of the buried depth of the pipeline, as the outer diameter of the pipeline increased, the settlement deformation of the pipeline decreased, and the internal force of the pipeline increased. At the same time, the numerical model of the corresponding working conditions was established and compared with the model test results, and good consistency was obtained.

The dissertation carried out researches on parameters of internal force, displacement of pile top and stability against overturning of deep excavation in Xuzhou Rail Transit Line 2, by means of FRWS software, to determine the support form of the base pit of the station foundation pit suitable for the over-consolidated stratum. The research focused on the settlement of the retaining structure in the precipitation construction and the impact on the surrounding surface. Through the monitoring of displacement of pile top, surface settlement and water level in the pit, the maximum horizontal deformation of the retaining structure at the standard section was 14.60 mm, and the surface settlement at the standard section was 21.00 mm. This met the specification design requirements. A joint design method was formed. The method was to insert the over-consolidated stratum to cut off the aquifer through the bite pile, and arrange the precipitation and dewatering well in the pit to control the consolidation settlement. It could effectively control the settlement of over-consolidated soil and provide a reference for similar projects.

In order to give full play to the role and value of monitoring and measurement in the tunnel construction process, the Nalang Tunnel was used as the background of the engineering example.The support vector machine was used as the theoretical basis, and its model parameters were optimized by using particle swarm optimization and chaos theory. A chaos optimized PSO-SVM model was constructed to achieve accurate prediction of tunnel deformation. The re-calibration range method was used to judge the development trend of tunnel deformation to prove the accuracy of the aforementioned prediction effect. The case study showed that the model parameters of the support vector machine could be effectively optimized by the trial algorithm and the particle swarm algorithm, and the chaos theory could effectively weaken the residual sequence of the prediction results. The average relative errors of the prediction results were less than 2%, which validated the research. The validity of the prediction model; at the same time, the re-standard range analysis showed that the tunnel deformation will continue to increase, but the increase rate tended to decrease. The obtained results were consistent with the prediction results, which verified the accuracy of the former analysis results. The study found that it provided a new idea for tunnel deformation prediction and was worth further promotion and application.