In many cases of shield tunnel collapse accidents occurred both domestically and internationally, the development process of the collapse showed the characteristics of progressive collapse, leading to serious economic losses and casualties. However, the research is still in its primary stage. The lack of understanding of the triggering conditions, development process, and effective prevention measures of the progressive collapse of shield tunnels restricted the high-quality development of urban rail transit in China. Based on the statistical analysis of nearly one hundred cases of tunnels accidents all over the world and focused investigation into 23 typical cases of progressive collapse from 2003 to 2020, the characteristics of progressive collapse of shield tunnels was analyzed. Using statistical methods, the initial damaged location, stratum, damage degree and other factors of shield tunnel progressive collapse accidents and their relationships were categorized and evaluated. The main characteristics were clarified. Based on the comprehensive analysis of multiple cases, the development process of the shield tunnel lining structure damage in the accident was generalized, and it corresponded to the damage degree of the tunnel structure. Finally, considering the interaction between the tunnel structure and the surrounding stratum, the response of the surrounding water and soil during the collapse was analyzed, and it was pointed out that the progressive collapse of the shield tunnels was a fluid-solid coupling dynamic problem. The research results are helpful to improve the relevant understanding of the progressive collapse of shield tunnels, and provide guidance for the prevention and control of the progressive collapse of shield tunnels.

The interaction between the hob and the rock mass is the core of TBM technology, and numerical simulation plays an important role in studying this process. In this paper, a hob and a soft-strong inter-bedded rock model was built based on further development of discrete element software MatDEM, which contained 502 thousand particles. By simulating the process of the rock breaking by a hob, as well as recording and analyzing, including boundary and hob force, particle connection, energy conversion, heat distribution and so on. The simulation results showed that, when strong rock breaked, the force of boundary and hob changing obviously, and the particles had greater force in the direction perpendicular to the hob and layer, but when weak rock layer was breaking, the inner boundary and the hob bore less stress, and the force of the hob was uniform; There were a few of broken joints in strong rock layer, and breaking volume of rock mass was small; During this process a lot of frictional heat was produced, and the accumulate of energy in strong rock was larger. MatDEM could simulate rock breaking process by hob effectively. By modifying the shape of hob and parameter of rock, this method could be further used for simulation of large-scale rock breaking by hob in other engineering conditions. It also provided a new way for numerical simulation of large-scale hob breaking rock.

The main academic thoughts and achievements of Academician Mengshu Wang in the tunnel and underground engineering were summarized. The new Austrian tunnelling method(NATM)was introduced and innovated, and successfully applied in Dayaoshan Tunnel and thus forming the shotcrete anchor construction method of railway, breaking through the outdated tunnel construction technologies, which had milestone significance in the history of tunnel development. The shallow underground excavation method for the urban subway engineering was established, which changed the construction status of subway construction that must be “open cut” from the ground, and could effectively protect the safety of the building structures and promote the rapid development of urban subway construction. In terms of undersea tunnel construction, the determination method of minimum roof thickness and design value of hydraulic pressure of the tunnel were established, and the waterproof and drainage technology and corresponding key construction technologies of undersea tunnel were put forward, all of which could provide technical support for the construction of the first undersea 2019年 - 第1卷第2期 谭忠盛:隧道与地下工程建设理念及关键技术——记王梦恕院士的主要学术思想和科研成就 \=-tunnel in China. A new mode of tunnel construction by TBM+ drilling and blasting method was put forward, and the auxiliary tunnelling technologies were established, compression concrete shield with a diameter of 7.3 m cutter head was firstly developed in China, which promoted the nationalization of shield. For the complexity of geology and environment in our country, the construction concept and basic principle of tunnel and underground engineering were put forward. Academician WANG Mengshus academic thoughts and scientific research contributions have had a profound impact on the development of the discipline, and has made a significant historical contribution in promoting the development of tunnel and underground engineering technology in China.

Natural gas, as a clean energy, is one of the main energies fueling the green economic development of China. It is one of the main tasks to develop underground gas storage facilities so as to increase the natural gas storage capacity and to improve the quick access to large volume of natural gas during high demand periods. The state-of-the-art of the three principal types of underground gas storage, i.e., in depleted oil/gas fields, aquifers and salt caverns and the basic information on underground gas storage facilities used in USA and Europe were reviewed. The development of underground gas storage facilities in China was compared with that in other countries. Root causes for three typical accidents on three underground gas storage facilities were analyzed. The statistical results on the accidents on underground gas storage facilities documented in literature were summarized. The differences on the root causes of accidents on different types of underground gas storage facilities were analyzed. Some suggestions on the plan and construction of underground gas storage facilities in China were presented according to the experiences and lessons from the review on the development in other countries.

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.

In the process of earth pressure balance(EPB)shield tunneling at silty clay stratum, it is easy to occur shield clogging with cutterhead and poor plasticity characteristics of the muck, so it is necessary to carry out soil conditioning to ensure the safe and efficient tunnel-construction of the shield. Taking one construction section of Hangzhou Metro Line 10 as an example, this study conducted liquid and plastic limit tests for soil conditioner selection, and then applied for the improvement of silty clay. The validity of selected conditioner and its parameters was verified through the slump test and compressive strength test of conditioned soil, and field soil conditioning test on the basis of the laboratory test. It was found that foam could significantly reduce the plastic limit of silty clay. Silty clay stratum was more sensitive to the increase of water content(w)and foam injection ratio(FIR). The slump value of conditioned soil increased with the increase of water content and foam injection ratio, and its compressibility also improved with the increase of foam injection. After optimizing the improvement parameters of conditioned soil, the torque of the shield cutter plate was significantly reduced, and the driving parameters of the shield remained stable,which indicated that the optimization and improvement parameters of the stratum were set reasonably, and that the improvement effect of the silty clay stratum using foam agent was significant.

With development of railway transportation, shield tunneling technology has been widely used. As a key component of shield tunneling, the working efficiency and failure form of hob were directly related to the geological conditions and had an important influence on construction schedule and safety. Based on a subway tunneling project, its geology related was analyzed firstly, then the failure types and corresponding causes of the disc cutters were also explained. Finally, a brief discussion was given about the material properties of disc cutters. The results showed that the failure forms were mainly partial grinding, edge curl, fracture of disc cutter ring, cutter ring off, fracture of cutter shaft.

Based on the analysis of the tunnel TBM construction process and technology, using the three-dimensional geological modeling technology and engineering simulation technology, a construction cycle network simulation model was established, which could achieve the prediction and visual analysis of TBM tunnel construction process. Taking the DXL tunnel project in Tibet as the research object, coupled with the three-dimensional geological model of the DXL tunnel, an optimized analysis of the TBM construction schedule of the DXL tunnel was performed through simulation calculations. The relationship between the completion probability and the construction time was fitted, and the expected completion probability was determined. The construction process was visualized and suggestions to guarantee the construction progress were proposed.

With the rapid development of underwater shield tunnel construction in China, the waterproof problem of segment joints is becoming more and more prominent, and the hydraulic pressure on shield tunnel is also increasing, which poses a severe challenge to the waterproof safety of the tunnel. The waterproofing of shield tunnel with high hydraulic pressure has gradually become a hot topic at home and abroad. Aiming at the possible problems in the design stage, construction stage and long-term operation stage of segment joint waterproofing of shield tunnel with high hydraulic pressure, the relevant important research at home and abroad were summarized, mainly including: material selection, section design, corner processing, arrangement of multi-channel sealing gasket, waterproof of bolt hole, numerical simulation and test analysis of sealing gasket, waterproof performance of sealing gasket under earthquake action and long-term durability evaluation of aging sealing gasket material. The existing problems and the research trend of related waterproof problems were discussed.

On the basis of theoretical analysis in the framework of specific energy, the main factors of such an interaction were summarized as: the size and the spacing distance of cutters, mechanical properties of stratum, and penetration. A method for design of scaled model tests of tunneling process, by means of shield boring machines, was proposed. The diameter of cutterhead was reduced, while the size and the spacing distance of cutters, the stratum, and the penetration were kept as the same as they were on site. Such a method was applied to a model test of the tunneling of the Cancer Hospital Metro Station of Shenzhen Line 14. This station was the first application of a new construction method which was characterized by that the station was firstly excavated by a small shield boring machine and then re-excavated by a larger one. The results of the model test allowed for predictions of the axial forces and the torque moments of the prototype cutterhead. The predicted values agree well with the monitored ones on site. This underlines the reliability of the proposed method for design of the model test. The originality of this work was highlighted by the quantitative relations between the quantities of the model and the prototype shield boring machines, which provides a reliable method for design of a model test of tunneling by means of shield boring machines.