Applied Mechanics and Materials Vols. 256-259

Abstract: Nowadays, the safety effection study of the surface explosion operations on underground cavern safety become more and more important along with engineering construction's development. In this paper, effection of open stope surface explosive operations on underlying gap cavern as an example on studying the effection of blasting shock on underground cavern stability with the method of field monitoring and numerical simulation.When the explosion source and seismic gap are almost in the same level, the longitudinal wave leads the role of damage effect. The most dangerous part of the mined-out area is the spandrel. The collapse models of mined-out area manifest are as follows, cracks appear on 45. Inclined top of surface in mined-out area, the spandrels appear broken, surface cracks expand further, broken parts of spandrel are aggravated, arch waist are in jog and the side collapse inward in the end.

Abstract: Based on the engineering background of New Beijing-Zhangjiakou Inter-city railway Badaling underground station and tunnel transition section construction, the problem of tri-arch and large-span variable single arch construction schemes in the transition section launched research. This paper draws some basis and the law as reference in construction process by the simulate calculation of ABAQUS finite element analysis software. This thesis discuss the frequently-used methods(middle cell method, one-side wall drift heading method, CRD-4 holes method and CRD-6 holes method) that is used in large-scale variable cross-section tunnel engineering research and analysis the stress, deformation and plastic areas distribution of surrounding rock by the simulate calculation of construction process. By comparative analysis, confirm the best construction scheme of transition section: the middle cell method applies to tri-arch cross-section and the CRD-4 holes method applies to large-span single arch of variable cross-section. It can offer direct guidance to the Badaling underground station and tunnel transition section project and some reference to similar underground projects.

Abstract: Tunnel collapse causes serious casualties and economic losses. One typical case analysis of a collapse in deep-buried tunnel based on microseismic monitoring is presented. The results show that the number of microseismic event keeps increasing and the distribution of microseismic events becomes concentrated in space domain gradually during collapse nucleation process. And average distance squared decreases gradually during the imminent period time just before the collapse. The failure evolution mechanism of the collapse is analyzed by moment tensor method. It is noted that the failure mechanism between this kind of collapse and immediate strain-structure rockburst is similar. However, the proportion of shear and mixed fracture for collapse is higher than immediate strain-structure rockburst. It due to the rich structure planes in collapse zone.

Abstract: 2D boundary element method in time domain is used to investigate the screening effectiveness of open trenches on reducing vibration generated by a high speed train in this study. The parameter used in the study is the configurations of the trench. In order to evaluate the screening effectiveness of a wave barrier, a reduction of dB value is defined and used in this study. The maximum reduction of dB values is about 25 dB when an open trench is used as a wave barrier. The depth of open trench is a main influential parameter of screening effectiveness. The deeper the open trench, the better vibration reduction. The screening effectiveness increases slightly due to the increase of trench width. Current study facilitates the basics for the optimum configuration of the open trench as the wave barrier for reducing vibration.

Abstract: Pressure arch is a phenomenon of rock mass stress restructuring to display itself bearing capacity, one of the important aspects is determination of the pressure arch boundary, and now the main method to determine the pressure arch boundary is numerical analysis. In order to determine the pressure arch boundary theoretically, a circular tunnel is taken as analyzing model, and the secondary stress condition around the rock mass is analyzed, also the equations of horizontal stress and vertical stress are deduced, and then the variation regulation of horizontal stress and vertical stress are discussed. On this basis, 3 kinds of pressure arch boundary determination methods are researched, and the boundaries of each method are found out, finally, the differences of the methods are compared. The results show that every determination method of pressure arch boundary has its own rationality, and they can provide reference for engineering and new arch boundary determination method.

Abstract: To obtain reasonable subway vibration load is the key to many subway vibration problems. This paper uses a simplified method to determine subway vibration load in frequency domain analysis, based on ground vibration test induced by subway traveling and numerical simulation of soil-subway model. The operating steps are explained and one example for calculating subway vibration load is given. The result shows that this method is a certain degree of effective in analysis of ground vibration problems, since that it relies on ground vibration test. The operating steps of this method are simple, and also the method can reflect characteristic of randomness of subway vibration.

Abstract: In order to further study the law of surrounding rock deformation of soft rock-extremely soft rock double arch tunnel, resolve problem of tunnel excavation in complex geology conditions, based on project example, the central heading full section, central heading step and division method (three heading method) as research object, measured and simulated results were compared and analyzed, and used ANDIA software to do dynamic simulation. The results show that the characters of surrounding rock deformation are different with different excavation methods; Simulated and measured results are almost the same ,and the maximum difference has only 6%, reflecting simulated value has a certain reliability; The more the step numbers are excavated in soft rock-extremely soft rock tunnel, the smaller the area excavated is, the smaller the rock is disturbance, the smaller the surface subsidence and two state convergence value is, more be able to meet construction requirements; Compared with the other two methods, division method is more to reduce the deformation in the surrounding rock with class of V.

Abstract: This paper presents the combination method between geological radar and video surveillance in the tunnel geological prediction, in case the randomness in judgment for the target body prone in the current geological advanced prediction. In order to improve the accuracy, this method conducts geological advanced prediction by comprehensive of geological radar, geological and construction information. In order to verify the effect of this method, we conducted a field trial in the Yululing tunnel. The field trial results are very well. And the accuracy of geological advanced prediction has been improved. This method reached the expected target for the accuracy which we want to improve of geological advanced prediction.

Abstract: This study focuses on the basic electromagnetic theory of ground penetrating radar（GPR）and program composition with finite difference time domain (FDTD) to solve the Maxwell curl equations. The radar forward map for subsurface pipes in different diameter was simulated, and then the Matlab program is used to extract this different image feature, the Fourier transform is used for fitting curve in the corresponding region, as a result that the images curvature and radius data are obtained. Finally, the relationship between pipe diameter and curvature radius is achieved by contrasting this data, which provides accurate and reliable basis for non-professionals in radar image recognition for engineering pipe.

Abstract: Measurement of water inflow from borehole, drilling and coring, ultrasonic inspection, ground-penetrating radar and field excavation are all used to test effect of grouting water shutoff and reinforcement in F4 weathered slot of Xiamen Xiang’an submarine tunnel. The five test ways are inter-validated to determine the grouting effect accurately and reasonably. It can provide a reliable basis for grouting design, construction and grouting effect test in similar strata. The application and development of grouting in submarine tunnel can be promoted.