This Express Letter reports three methane explosion accidents during tunnel construction in Southwest China. In recent years, tunnel construction of China is developing rapidly. The geological conditions of the tunnel passing through are extremely complex, especially, tunnels in coal strata increase rapidly, what's worse, many methane explosions occur during the tunnel construction. The backgrounds, causes and rescue operation of three methane explosion accidents situation are studied. Furthermore, we proposed relevant measures to prevent methane explosions of tunnels. ARTICLE HISTORY

e recycling and reuse of waste materials is a topic of global concern and great international interest for those interested in sustainable development and protecting the environment. In recent decades, global production of construction and demolition waste (C&D waste) has signi cantly increased and became a worldwide problem. is research proposes to evaluate the feasibility of using aggregate from recycled C&D waste for urban road embankment applications based on the Sanhuan road construction project in eastern Xi'an. An extensive suite of laboratory and eld compaction tests were carried out to determine the physical properties and engineering characteristics of the C&D waste. e e ect of curing on the strength of the C&D waste was investigated using uncon ned compression strength (UCS), California bearing ratio (CBR), and de ection tests. e results show that the C&D waste has the characteristics of high strength and signi cant stability after simple treatment and further suggest that the use of these materials for paving urban road embankments is feasible. is study is of value for the reasonable and e ective promotion of using C&D waste recycled materials in road subgrade applications.

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Over the past couple of decades, root piles as the new tool for addressing a number of tough problems have been gaining a continually increasing interest in tunnel, especially for complex geological conditions. Therefore, in order to promote the development and application of root piles in tunnel engineering, this paper systematically sorts out the research status and development prospect of root piles from the application in foundation underpinning to reinforcement of tunnel foundation. Firstly, the type and development process of root piles are discussed. Secondly, the reinforcement mechanism of the root piles in the tunnel base is refined and combed: the reinforcement mechanism analysis focuses on frictional resistance of soil around pile, soil among piles, and piles. Thirdly, the calculation method of reinforced tunnel foundation is studied from the bearing of vertical load, horizontal load and pile reinforcement design. And through the engineering case, the paper illustrates the reinforcement effect of the root pile in ensuring the stability of the tunnel and the concrete process of the root piles in the tunnel construction. Finally, the problem and development prospect of root piles are discussed, so as to provide new perspectives and fundamental data for the research on tunnel engineering.