Current Issue : July - September Volume : 2020 Issue Number : 3 Articles : 5 Articles
Analyses of catastrophic collapse of some adjacent precast concrete box beam bridges reveal the fact that the hinge joints between\nthe adjacent beams were not sufficiently designed. The joint failure caused by deterioration is the result of system reliability\ndeficiency of this type of bridges............................
Accurately evaluating the ground pressure on the tunnel lining greatly helps the structure design of a tunnel. In this study, the\nearth pressure and water pressure on the tunnel lining of four cross sections of a metro tunnel were measured and analyzed and\nthen compared with the theoretical values. Results show that the values and distribution of observed ground pressure acting on the\nlining are different for different overburden depths. The water pressure measured on-site is approximately equal to the theoretical\nhydrostatic pressure.Thewater pressure acting on the shield tunnel lining does not fluctuate with the shield tunnel excavation.The\nmaximum ground pressure was measured in the process of backfill grouting, and the maximum values are approximately larger\nthan 30% of the stable value of the measured pressure. For a shield tunnel under a river with deep water, the water pressure on the\nlining is dominant and the observed total ground pressure is nearly equal to the water pressure. The findings presented in this\npaper can provide a reference for the structure design of similar tunnel projects....
The study aims to research the influence of salt fog corrosion cycles on seismic performance of reinforced concrete (RC) frame\nbeam-column joints in coastal atmosphere. Based on low cyclic loading tests of six RC frame beam-column joint specimens, this\nstudy analyses the failure patterns, hysteresis loops, load carrying capacity, displacement, backbone curves, and energy dissipation\ncapacity of corrosion-damaged RC frame beam-column joints. The effect of salt fog corrosion cycles and axial compression ratios\nare tested repeatedly.................................................
The deformation of Muzhailing deep tunnel is about 2.3m in the process of construction, which is difficult to be controlled by the\ntraditional â??anchor-grouting integrationâ? support system. This paper deeply analyzes the geological characteristics, rock mechanics\ncharacteristics, and surrounding rock failure characteristics of Muzhailing tunnel. The deformation mechanism and the\nfailure of the support system are analyzed through the numerical simulation, theoretical analysis, and field test. The authors\npropose support measures suitable for Muzhailing tunnel based on the analysis results. The maximum buried depth is 600 m, and\nthe engineering rock mass at the depth has nonlinear physical and mechanical phenomenon. The maximum principal stress of\nMuzhailing tunnel is 25.7 MPa, which belongs to high-stress joint swelling soft rock tunnel. The NPR cable can achieve large\ndeformation under the condition of constant support resistance. The authors put forward the coupling support mode of â??NPR\ncable + steel arch frame + concrete,â? which is based on the idea of transforming the composite deformation mechanism to a single\ntype. The stress concentration appears in the range of 12m in the surrounding rock circle, and the lateral and vertical stress\ndistributions are relatively symmetrical after the improved support. The circumferential strain of the surrounding rock is greatly\nreduced, and the range of strain is reduced by 10%. The field monitoring results show that the new support system can well control\nthe large soft rock deformation of Muzhailing tunnel (0.5 m). The support strategy proposed can effectively control the large\ndeformation and promote the formation of new support concept for deep tunnel....
The stability of tunnels has mainly been evaluated based on displacement. Because displacement due to the excavation process is\nsignificant, back analysis of the structure and ground can be performed easily. Recently, the length of a segment-lined tunnel\ndriven by the mechanized tunneling method is increasing. Because the internal displacement of a segment-lined tunnel is trivial, it\nis difficult to analyze the stability of segment-lined tunnels using the conventional method. This paper proposes a back analysis\nmethod using stress and displacement information for a segment-lined tunnel. A differential evolution algorithm was adopted for\ntunnel back analysis. Back analysis based on the differential evolution algorithm using stress and displacement was established and\nperformed using the finite difference code, FLAC3D, and built-in FISH language. Detailed flowcharts of back analysis based on\nDEA using both monitored displacement stresses were also suggested. As a preliminary study, the target variables of the back\nanalysis adopted in this study were the elastic modulus, cohesion, and friction angle of the ground. The back analysis based on the\nmonitored displacement is useful when the displacement is significant due to excavation. However, the conventional displacement-\nbased back analysis is unsuitable for a segment-lined tunnel after construction because of its trivial internal displacement\nsince the average error is greater than 32% and the evolutionary calculation is finalized due to the maximum iteration\ncriteria. The average error obtained from the proposed back analysis algorithm using both stress and displacement ranged within\napproximately 6â??8%. This also confirms that the proposed back analysis algorithm is suitable for a segment-lined tunnel....
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