The Experts below are selected from a list of 214356 Experts worldwide ranked by ideXlab platform
Penglu Gan - One of the best experts on this subject based on the ideXlab platform.
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Face stability analysis of shield-driven tunnels shallowly buried in dry sand using 1-g large-scale model tests
Acta Geotechnica, 2017Co-Authors: Wei Liu, Peixin Shi, Li Jiaoyang, Penglu GanAbstract:This paper investigates the face stability of shield-driven tunnels shallowly buried in dry sand using 1-g large-scale model tests. A half-circular tunnel model with a rigid front face was designed and tested. The ground movement was mobilized by pulling the tunnel face backwards at different speeds. The Support Pressure at tunnel face, settlement at ground surface, and internal movement of soil body were measured by load cells, linear variable differential transducers, and a camera, respectively, and the progress of face failure was observed through a transparent lateral wall of model tank. The tests show that, as the tunnel face moves backwards, the Support Pressure at the tunnel face drops sharply initially, then rebounds slightly, and tends to be stabilized at the end. Similarly, the ground surface settlement shows a three-stage variation pattern. Using the particle image velocimetry technique, the particle movement, shear strain, and vortex location of soil are analyzed. The variation of Support Pressure and ground surface settlement related to the internal movement of soil particles is discussed. The impact of the tunnel face moving speed on the face stability is discussed. As the tunnel face moves relatively fast, soil failure originates from a height above tunnel invert and an analytical model is developed to analyze such failure.
Magued Iskander - One of the best experts on this subject based on the ideXlab platform.
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evaluation of tunnel face stability by transparent soil models
Tunnelling and Underground Space Technology, 2012Co-Authors: Mahmoud Ahmed, Magued IskanderAbstract:Accurate estimation of tunnel face Support Pressure is necessary for economical and safe shield tunneling in cohesionless soils. This paper presents measurements of tunnel face Support Pressure and associated soil movements obtained using a transparent soil model that simulates shield tunneling in medium dense saturated sand. The use of a transparent soil surrogate permits measuring the internal soil deformations within the model soil. Soil deformations associated with various face Support Pressures are presented for 4 cover-to-diameter (C/D) ratios. Failure is found to be sudden with sand flowing into the tunnel leading to a prismatic wedge in front of the tunnel face and a vertical chimney of soil above. A minimum Support Pressure was achieved with Support Pressures as low as 10 ± 1% of the effective vertical stress at the tunnel axis. The stability of the tunnel face was related to the coefficient of active earth Pressure with C/D ratio having a small effect on the magnitude of required Pressure at collapse.
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Tunnel Face Support Pressure and Associated Risk
GeoRisk 2011, 2011Co-Authors: Mahmoud Ahmed, Magued IskanderAbstract:Prediction of ground movements and risk assessment of damage to adjacent buildings and utilities have become an essential part of the success of tunneling projects in urban environments. First stage assessment of risk in tunneling zones involved evaluation of face stability conditions and ground movement induced by tunneling. This paper presents experimental work on the stability of a tunnel face using transparent soil models to estimate the magnitude of tunnel face minimum Supporting Pressure, failure pattern and extension of failed zone which can further be applied to tunnel risk analysis. The model tunnel was installed in a plexiglas box filled with transparent soil and was Supported at the face by means of water Pressure. Tests were performed by reducing Supporting Pressure until collapse occurred. Model tests were sliced optically with a laser sheet and images were captured for every decrement in tunnel Supporting Pressure. Later, these images were analyzed by Digital Image Correlation (DIC) and vector fields of incremental displacements were obtained. The value of minimum Support Pressure was obtained and geometry of the failure zones was found to be of chimney shape with a limited extension in front of the face. Contour plots of resultant ground movement at pre-collapse and post failure indicated that a minimum distance equal to the tunnel diameter should be considered above and a way form the tunnel for underground utilities risk assessment. A minimum Support Pressure was achieved with Support Pressures as low as 10 % of the effective vertical stress at the tunnel axis. The stability of the tunnel face was related to the coefficient of active earth Pressure. In general, results of the study were in agreement with current knowledge of full-scale situations.
Changpeng Chen - One of the best experts on this subject based on the ideXlab platform.
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study on the regularity of ore Pressure in overburden hard rock working face of overburden mining on reverse faults
Geotechnical and Geological Engineering, 2020Co-Authors: Lianhai Tai, Zheng Liu, Tong Zou, Changpeng ChenAbstract:In order to study the mining Pressure on the upper coal seam in the fault, the working Pressure of the working face with a hard rock roof is based on the production geological conditions of the 3301 working face of Yiqiao Coal Mine. Use flac numerical simulation software to establish a three-dimensional numerical calculation model of mining face, and study the distribution characteristics of mining plastic area, the advance Support Pressure and elastic strain energy density. And the change curve is treated by origin software fitting function. In the end, it was found that the total volume of the plastic zone and the propulsive distance of the working face showed an exponential function. Before and after the "first square", the total volume of the plastic zone increased more significantly, and the hard roof failure was mainly bending failures; There is a logarithmic function between the advance Support Pressure and the advancing distance of the working face. The range of 5–14 m in front of the coal wall is a region where the Pressure increases sharply. The elastic strain energy density appears relatively high. During the mining process, the advance Support of the roadway should be strengthened, and the key monitoring should be carried out. If necessary, corresponding Pressure relief measures should be taken to ensure the safe production of the working face.
Da-jun Yuan - One of the best experts on this subject based on the ideXlab platform.
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An in-situ slurry fracturing test for slurry shield tunneling *
Journal of Zhejiang University Science, 2014Co-Authors: Da-jun YuanAbstract:When performing a slurry shield excavation in the shallow earth cover under a waterway, the Support Pressure is difficult to calibrate. If not carefully monitored, slurry fracturing or even slurry breakout can occur; water from the river can rush into the slurry circulating system, threatening the security of the project. In this study, an in-situ slurry fracturing apparatus was created to analyze the phenomena of slurry fracturing and fracture propagation. First, the fracturing test procedures and the method of identifying slurry fracturing are introduced. Then, mechanical models of the slurry fracturing and fracture propagation are described and validated with in-situ tests. The models provide fairly good predictions: the driving Pressure is related to the properties of both the soil and slurry. Slurry with large parameters for bulk density and viscosity is beneficial for preventing slurry fracturing propagation. However, such parameters have little influence and can be neglected when determining the initial fracturing Pressure. Preventing slurry fracturing and breakout is important for not only shield tunnel preparation, but also shield tunneling under dangerous conditions. A crucial factor is setting and limiting the maximum Support Pressure values. These Pressures can be obtained through the in-situ tests and mechanical models described here. These results provide useful references for the Weisan Road Tunnel to be built under the Yangtze River in Nanjing, China.
Bibhash Kumar - One of the best experts on this subject based on the ideXlab platform.
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Stability of Square Tunnels in Two Layered Clayey Soil
Lecture Notes in Civil Engineering, 2020Co-Authors: Bibhash Kumar, Jagdish Prasad SahooAbstract:The Support Pressure offered by means of lining for maintaining the stability of a square tunnel driven in a layered clay medium under undrained condition has been determined. Finite element lower bound limit analysis and linear programming are used for performing the analysis. The Support Pressure is assumed to be uniform on the periphery of tunnel. The influence of undrained shear strength of upper layer relative to that of lower layer on the magnitude of Support Pressure has been studied. The magnitude of Support Pressure required to maintain the stability in the layered clay medium as compared to that of homogeneous clay layer has also been examined. Corresponding to a given cover of the tunnel, the magnitude of required Support Pressure is found to be decreasing continuously with an increase in the ratio of undrained shear strength of upper clay layer to that of lower clay layer.
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Support Pressure for circular tunnels advanced below water bodies
Tunnelling and Underground Space Technology, 2020Co-Authors: Bibhash Kumar, Jagdish Prasad SahooAbstract:Abstract The limiting Support Pressure required to be exerted by a Support system for maintaining stability of circular tunnel driven in granular soils below water bodies has been computed. The analysis was performed on the basis of lower bound theorem of plasticity in conjunction with finite elements and second order cone programming. The effect of anisotropy in both strength and hydraulic properties of granular soil on the magnitude of required Support Pressure has been examined. The required Support Pressure is defined in terms of non-dimensional factors normalized with respect to unit weight of soil and diameter of tunnel. The variation of Support Pressure for different combinations of strength and hydraulic properties of soil, height of water level above bed of water body, and diameter and cover of tunnel has been established. The magnitude of Support Pressure is observed to be substantially influenced by strength anisotropy of soil; whereas, the influence of hydraulic anisotropy is shown to be insignificant on the Support Pressure. Moreover, the Support Pressure is found to be increasing with increase in the height of water level and is found to be higher in the case of tunnel driven below water bodies than that advanced in dry soil.
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Support Pressure for circular tunnels in two layered undrained clay
Journal of Rock Mechanics and Geotechnical Engineering, 2020Co-Authors: Bibhash Kumar, Jagdish Prasad SahooAbstract:Abstract To estimate the required Support Pressure for stability of circular tunnels in two layered clay under undrained condition, numerical solutions are developed by performing finite element lower bound limit analysis in conjunction with second-order cone programming. The Support system is assumed to offer uniform internal compressive Pressure on its periphery. From the literature, it is known that the stability of tunnels depends on the overburden Pressure acting over it, which is a function of undrained cohesion and unit weight of soil, and cover of soil. When a tunnel is constructed in layered undrained clay, the stability depends on the undrained shear strength, unit weight, and thickness of one layer relative to the other layer. In the present study, the solutions are presented in a form of dimensionless charts which can be used for design of tunnel Support systems for different combinations of ratios of unit weight and undrained shear strength of upper layer to those of lower layer, thickness of both layers, and total soil cover depth.
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Support Pressure for stability of circular tunnels driven in granular soil under water table
Computers and Geotechnics, 2019Co-Authors: Jagdish Prasad Sahoo, Bibhash KumarAbstract:Abstract In this paper, the internal Pressure required to be offered by a Support system to Support the periphery of circular tunnels excavated in granular soils in the presence of groundwater seepage towards the tunnel has been computed. The optimal value of Support Pressure is computed with the application of finite element limit analysis based on lower bound theorem of plasticity and second order cone programming. The seepage forces generated due to flow of ground water towards tunnel periphery are computed from the distribution of total head in the ground by solving the two-dimensional flow equation under steady state seepage condition. The forces acting on the Support system due to effective overburden Pressure and seepage are incorporated as body forces in the analysis. The solutions are presented in the form of non-dimensional charts which will be used in practice to estimate the required Support Pressure in terms of soil properties, elevation of groundwater table, and diameter and cover of tunnel. For the tunnel driven under water table, a significant increase in the magnitude of required Support Pressure has been observed as compared to that excavated in dry soil from the solutions obtained in the present analysis.
