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Failure Mechanisms and Modes of Tunnels in Monoclinic and Soft-Hard Interbedded Rocks: A Case Study
Jianxun Chen,Weiwei Liu,Lijun Chen,Yanbin Luo,Yao Li,Haijiang Gao,Daochuan Zhong 대한토목학회 2020 KSCE JOURNAL OF CIVIL ENGINEERING Vol.24 No.4
The issue of large deformation mechanism in soft rock tunnels has puzzled tunnel scholars for decades. Previous studies have not evolved a clear and common understanding. Therefore, detailed on-site measurement, full investigation and statistical analysis have been conducted on the instability and failure of Muzhailing Tunnel since its construction, whose length is beyond 15 km. The study aims at systematically analyzing the failure mechanisms and modes of Muzhailing Tunnel in monoclinic and soft-hard interbedded rock strata. Study results show that the angle between strata strike and tunnel axis greatly determines the magnitude of deformation, the dip direction significantly controls the bias direction and maximum deformation direction, and the dip angle deeply affects the deformation form. The failure modes of surrounding rock mainly include four types: spalling and overturning failure, bending failure, shear slip failure and buckling failure. Large deformation characteristics are summarized from six aspects: failure form, groundwater, sensitivity to influencing factors, deformation degree, deformation speed and deformation duration. The instability modes of primary lining include in-plane (transverse) instability and out-plane (longitudinal) instability. Finally, the causes of large deformation are analyzed from geological, structural, engineering and human factors.
Qi Liu,Rongchang Li,Qingling Zhang,Jianxun Li 제어·로봇·시스템학회 2019 International Journal of Control, Automation, and Vol.17 No.12
This paper considers the problem of sliding mode control (SMC) design for a class of nonlinear singular systems with time-varying delay and uncertainties, especially with uncertainties in the derivative matrix. By taking uncertainties of the derivative matrix into account, the state augmentation transformation is constructed such that uncertainties of the derivative matrix are eliminated. Then an appropriate integral-type sliding surface function is designed. And the resulting sliding mode dynamics is an uncertain singular time-varying delay system. A delaydependent sufficient condition which guarantees the sliding mode dynamics to be admissible with H∞ performance is established. A new version of stabilization solvability condition is then proposed in terms of linear matrix inequality (LMI), which determines the undetermined parameter K in both the sliding surface function and the SMC laws. Moreover, two distinctive controllers (i.e., an SMC law and an adaptive SMC law) are synthesized such that the finite-time reachability of the predesigned sliding surface can be ensured. Finally, simulation examples are given to demonstrate the effectiveness and the merits of the proposed theory.
Criteria for evaluating working fluids in loop gravity-assisted heat systems
Chen Jianxun,Liu Jinping,Xu Xiongwen,Liang Lingjiao,Yu Yinhao 한국화학공학회 2023 Korean Journal of Chemical Engineering Vol.40 No.9
A loop gravity-assisted heat pipe (LGHP) is characterized by passive heat dissipation and extensive application prospect. Dissimilar working fluids give rise to noticeable differences in their working performance (Critical heat flux (CHF)). Consequently, it is of great significance to evaluate the performance of LGHP working fluid for its design. In accordance with the basic theories of CHF and hydrodynamics, the pressure drop models of laminar, smooth turbulence, and completely rough turbulence flows were established, and an extensible two-phase composite property parameter was obtained. On this basis, the physical property parameter of transitional rough turbulent flow was also derived. Finally, as persuasively illustrated by the experimental results, there was almost a linear association between CHFs and the derived physical parameter. As a result, the physical parameters derived in this paper can be employed as favorable criteria for the selection of LGHP working fluid.
Peng Deng,Jianxun Guo,Yan Liu,Boyi Yang 한국강구조학회 2021 International Journal of Steel Structures Vol.21 No.1
Owing to seismic, wave, or wind actions, tubular joints used in onshore and off shore civil infrastructures may require retrofi tting to withstand both static and cyclic loadings. In the present study, bearing capacities, failure modes, and ductilities of damaged tubular T-joints retrofi tted with carbon fi ber reinforced polymer (CFRP) were investigated. Two-step loading was applied: fi rst, a pre-determined load was applied to induce chord deformation; this was followed by unloading and CFRP retrofi tting. Subsequently, the specimens were reloaded to failure. Results showed that the retrofi tted specimens exhibited a maximum capacity similar to and a plastic deformation slightly larger than that of the bare specimen when these subjected to static loading; the retrofi tted specimens, which were not severely damaged, exhibited a higher compressive ductility index than that of the bare specimen when these subjected to cyclic loading.
Compressive Behavior of Damaged Tubular T-joints Retrofitted with Collar Plate
Peng Deng,Jianxun Guo,Yan Liu,Zhongying Wang 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.9
The static bearing capacity and failure modes of damaged tubular T-joints retrofitted with collar plates under axial compression were investigated. Two-step loading was applied: First, the chord deformation was loaded to the pre-designed degree, followed by unloading and collar plate installation. Subsequently, the specimens were reloaded. The maximum capacity and corresponding displacement (Δ1,m) were determined, and the ratio of the chord deformation of the other joints to Δ1,m was utilized to define the damage degree. The maximum capacity of retrofitted tubular T-joints could be up to 13 – 77% in second step loading, compared with that of unreinforced T-joints; however, the capacity decreased by 2 – 10% compared to that of directly reinforced T-joints. Sixty-nine finite element models were generated. The effects of chord wall thickness, chord diameters and collar plate lengths on the bearing capacity under different damage degrees were analyzed. A satisfactory effect could be obtained by using a suitable size of expanded collar plates under a constant damage degree. Retrofitting with collar plates could mitigate the development of equivalent plastic strain in the joint intersection, even for considerably damaged tubular T-joints. A modified formula considering the damage degree was proposed for bearing capacity prediction of retrofitted tubular T-joints.
Yanbin Luo,Yunfei Wu,Jianxun Chen,Fangfang Dong,Weiwei Liu,Lijun Chen,Yao Li,Zhou Shi 대한토목학회 2022 KSCE JOURNAL OF CIVIL ENGINEERING Vol.26 No.1
Rock mass pressure has always been a research hotspot in the field of tunnel engineering, especially in the super large-span tunnel, which is characterized by flat section, large excavation span, and complex stress field. Based on the Letuan Tunnel (a bi-directional tunnel with eight traffic lanes) of Binlai expressway expansion project in Shandong Province, China, this paper focused on the calculation method of rock mass pressure and the evolution law of load release in the construction process of the super large-span tunnel excavated by upper-bench central diaphragm (CD) method. Based on field measured data of Letuan Tunnel, the deformation behavior of primary lining and the distribution state of rock mass pressure during the tunnel construction were analyzed. According to the bearing mode of supporting structure, the mechanical models of different construction stages were established. Then, the rock mass pressures in different construction stages were back-calculated using mechanical models and compared with the measured values, and the evolution law of load release during the tunnel construction was discussed. The study results show that the tunnel deformation and rock mass pressure were significantly affected by the construction process and support form, and the excavation span was the key factor affecting the stability of rock mass. For the shallow-buried super large-span tunnel constructed by upper-bench CD method, the primary support of upper bench was under eccentric pressure. The comparison between the back-calculated value and the field measured value indicated that they were similar, and the average relative error was 17.23%. According to the concept of load release coefficient proposed in this paper, the load release coefficient after the pilot tunnel ahead (Part I) excavation reached 63%, and the load release coefficient after the pilot tunnel behind excavation (Part II) was 37%, which means that the rock mass pressure of Part I is increased about 59% due to the excavation of Part II.
Space-Stretch Tradeoff Optimization for Routing in Internet-Like Graphs
Tang, Mingdong,Zhang, Guoqiang,Liu, Jianxun The Korea Institute of Information and Commucation 2012 Journal of communications and networks Vol.14 No.5
Compact routing intends to achieve good tradeoff between the routing path length and the memory overhead, and is recently considered as a main alternative to overcome the fundamental scaling problems of the Internet routing system. Plenty of studies have been conducted on compact routing, and quite a few universal compact routing schemes have been designed for arbitrary network topologies. However, it is generally believed that specialized compact routing schemes for peculiar network topologies can have better performance than universal ones. Studies on complex networks have uncovered that most real-world networks exhibit power-law degree distributions, i.e., a few nodes have very high degrees while many other nodes have low degrees. High-degree nodes play the crucial role of hubs in communication and inter-networking. Based on this fact, we propose two highest-degree landmark based compact routing schemes, namely HDLR and $HDLR^+$. Theoretical analysis on random power-law graphs shows that the two schemes can achieve better space-stretch trade-offs than previous compact routing schemes. Simulations conducted on random power-law graphs and real-world AS-level Internet graph validate the effectiveness of our schemes.