Search

• Using spring sets and built-in water bag to simulate aquifer; embedding guide lift hose and branch conduit as prefabricated water-conducting channel; Using "cutting-support-blocking" integrated device to simulate key equipment of ARFMP. • The floor failure characteristics of ARFMP are obtained and its effectiveness in preventing water inrush is verified. • An engineering treatment scheme combining ARFMP and floor regional control is proposed, and reliability of the model test results is verified after field application. The coal mining in North China is seriously threatened by floor water inrush from the Ordovician limestone, so it is particularly important to explore failure characteristics. Automatic roadway formation mining without pillars (ARFMP) provides an effective method for reducing floor failure. To explore failure characteristics above confined water, a two-dimensional model test system is built up. Such a system can be applied to compare the difference of floor failure between ARFMP above confined water and traditional retained coal pillar mining, and to intuitively analyze the lifting law of confined water under dynamic disturbance. The core features of this system include the customized spring sets and water bag adopted as materials to simulate the floor aquifer, the guide lift hose and branch conduit used as the lifting channel of confined water, and the flow rate and cumulative volume monitored in real time. The customized "cutting-support-blocking" integrated device is the key equipment to simulate ARFMP. Then, the model test is conducted on a typical engineering case. By comparing stress, displacement, and water inrush characteristics of floor in different areas, failure characteristics of the roof-cutting side, the middle of working face, the collapse column area, and the coal pillar side were obtained, and it was clarified that ARFMP can effectively prevent floor water inrush. According to the results of model test, a comprehensive treatment scheme combining ARFMP with the floor regional control is proposed to ensure the safe mining of working face. [ABSTRACT FROM AUTHOR]

The urban transit system is vulnerable to various types of hazards and failures, where the failure of a system component may lead to a redistribution of the pressure and result in cascade failures. It is of great significance to develop an efficient approach to model and assess the system vulnerability for achieving a sustainable transit system. This research develops a novel holistic approach to assess the vulnerability of the urban transit system toward sustainable development. The cascading failure mechanism is incorporated in the established complex network to simulate the process in a dependent system, where the failure of one or a few system components can trigger the failure of other components. Several attack strategies (i.e., static and dynamic intentional attack and random attack strategies) are used to test the system vulnerability, and the impacts of the tolerance parameter and passenger transfer rate on the loss of transport capacity are explored. A complex network consisting of 198 nodes and 415 edges is constructed to model the urban transit system with cascade failures. A realistic urban transit system in China is used as a case to testify the applicability and effectiveness of the developed approach. Results indicate that: (1) The interchange stations display high vulnerability in the network and Xianggang Rd station, Hongtu Boulevard station, Taipingyang station, and Zhongnan Rd are the most vulnerable stations, which should be paid more attention in the operation management; (2) The damage of the attacks in the intentional attack strategies are much more significant than that in the random attack, indicating that the proposed approach presents the ability to identify the important nodes; (3) The metric of node betweenness would be more efficient to identify the vulnerable nodes in the intentional attack; (4) The optimal value of the tolerance parameter is the range [0.8, 0.9], while keeping the passenger transfer rate in the range [0.3, 0.4] can effectively reduce the effect of cascade failures with minimum resources. The developed approach can be used as a decision tool to not only assess the vulnerability in the existing transit system but also optimize the planning of the new transit system. • A holistic approach with detailed procedures to assess vulnerability of transit system is presented. • Several attack strategies are used to test the system vulnerability considering cascade failures. • A complex network with 198 nodes and 415 edges is built to model a realistic metro system. • Impacts of tolerance parameter and passenger transfer rate on transport capacity loss are explored. • The developed approach can be used to optimize the planning of the new transit system. [ABSTRACT FROM AUTHOR]

The large section tunnel support is facing tremendous challenges. They are large in span and poor in self-stability of surrounding rocks. Traditional I-steel arches are easily subject to buckling failure. As a result, safety accidents always occur, such as the failure of supporting system and the collapse of tunnels. To solve the problems, a new support technology of confined concrete and corresponding arches are invented. With high strength and rigidity, it can effectively control the deformation of surrounding rocks on large section tunnels. To clarify the bearing capacity and failure mechanism of the new arch, a mechanical testing system for the combined arches in large section tunnels is developed. Comparative tests were carried out on the mechanical mechanism of the combined arches of confined concrete and traditional I-steel. The tests took Longding Tunnel, one of the largest city road tunnels in China, as engineering background. In the test, the following results were found. The in-plane flexural buckling occurred on the vault of the combined I-steel arch first, and then out-plane flexural-torsional buckling occurred on the hance and bottom of the arch. It resulted in the overall loss of its bearing capacity and the entire arch being flattened. In the other hand, the confined concrete combined arch showed no severe deformation; its bearing capacity was 2.63 times that of the I-steel arch; and its average rigidity at the coordinated bearing stage is 2.51 times that of the I-steel arch. It is superior in bearing capacity and stability to the I-steel arch. Based on the experimental research conclusions, the engineering suggestions are put forward for the application of the confined concrete support technology in tunnels and the field application was carried out. The control effect is excellent on surrounding rocks. The results can provide a reference for the future research and design in this field. [ABSTRACT FROM AUTHOR]