It is very important for an engineer to understand the evolution characteristics of pressure-arch of a highway tunnel under different stress conditions. After the numerical model of the highway tunnel being built, con...
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It is very important for an engineer to understand the evolution characteristics of pressure-arch of a highway tunnel under different stress conditions. After the numerical model of the highway tunnel being built, considering the lateral pressure coefficients varied from small to large, the forming process, distributional pattern and evolution characteristics of the pressure-arch of the highway tunnel under different stress states were analyzed. The numerical simulation of the step-bystep excavation was carried out along the tunnel axis, the distribution morphology and variation characteristics of the pressure-arches located in the front of working face and roof and floor of the tunnel during excavation were revealed. The results showed that the pressure-arch shapes of the tunnel mainly varied from spire, flat, convex, to sag top with the lateral pressure coefficient from small to large. And the stability of the surrounding rock near the tunnel working face became worse and worse with the principal stress difference increasing. The results are of great significance for the construction and reinforcing design of the similar engineering practice.
Due to the extreme complexity of mechanical response of soft surrounding rock(SR) around a tunnel under high geostatic stress conditions, the integration of physical and numerical modeling techniques was adopted. Base...
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Due to the extreme complexity of mechanical response of soft surrounding rock(SR) around a tunnel under high geostatic stress conditions, the integration of physical and numerical modeling techniques was adopted. Based on the similarity theory, new composite-similar material was developed, which showed good agreement with the similarity relation and successfully simulated physico-mechanical properties(PMP) of deep buried soft rock. And the 800 mm×800 mm×200 mm physical model(PM) was conducted, in which the endoscopic camera technique was adopted to track the entire process of failure of the model all the time. The experimental results indicate that the deformation of SR around a underground cavern possessed the characteristics of development by stages and in delay, and the initial damage of SR could induce rapid failure in the later stage, and the whole process could be divided into three stages, including the localized extension of crack(the horizontal load(HL) was in the range of 130 k N to 170 k N, the vertical load(VL) was in the range of 119 k N to 153.8 k N), rapid crack coalescence(the HL was in the range of 170 k N to 210 k N, the VL was in the range of 153.8 k N to 182.5 k N) and residual strength(the HL was greater than 210 k N, the VL was greater than 182.5 k N). Under the high stress conditions, the phenomenon of deformation localization in the SR became serious and different space positions show different deformation characteristics. In order to further explore the deformation localization and progressive failure phenomenon of soft SR around the deeply buried tunnel, applying the analysis software of FLAC3 D three-dimensional explicit finite-difference method, based on the composite strain-softening model of Mohr-Coulomb shear failure and tensile failure, the calculation method of large deformation was adopted. Then, the comparative analysis between the PM experiment and numerical simulation of the three centered arch tunnels was implemented and the rel
The general features of oscillations within a rectangular harbor of exponential bottom are investigated analytically. Based on the linear shallow water approximation, analytical solutions for longitudinal oscillations...
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The general features of oscillations within a rectangular harbor of exponential bottom are investigated analytically. Based on the linear shallow water approximation, analytical solutions for longitudinal oscillations induced by the incident perpendicular wave are obtained by the method of matched asymptotics. The analytic results show that the resonant frequencies are shifted to larger values as the water depth increases and the oscillation amplitudes are enhanced due to the shoaling effect. Owing to the refraction effect, there could be several transverse oscillation modes existing in when the width of the harbor is on the order of the oscillation wavelength. These transverse oscillations are similar to standing edge waves, and there are m node lines in the longshore direction and n node lines running in the offshore direction corresponding to mode（n, m）. Furthermore, the transverse eigen frequency is not only related to the width of the harbor, but also to the boundary condition at the backwall and the bottom shape.
In this research, the concrete specimens were prepared from C20 to C60, coupled effects of sulfate madefaction and dry-wet cycle were used to accelerate the rate of sulfate attack, and compressive strength of each spe...
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In this research, the concrete specimens were prepared from C20 to C60, coupled effects of sulfate madefaction and dry-wet cycle were used to accelerate the rate of sulfate attack, and compressive strength of each specimen was tested. The results showed that, compared to the same age of water curing specimens, the strength of the dry-wet cycle specimens increased 4%-10% within 30 days. After 30 days, with the age increased, strength began to decrease. In 120 days, C20 decreased 16.3%, C30 decreased 23.1% and C40 decreased 18.9%, C50 and C60 decreased about 7%. The higher strength grade of concrete is, the better the performance of concrete in sulphate corrosion is.
Similar to other metropolitan cities in China, urban rail transportation has been highly emphasized in Beijing in the past decades. However, the growing subway system is seriously challenged by several critical issues...
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In this work, the Eshelby tensor of a finite spherical domain is employed to construct an interphase model to evaluate elastic properties of concrete composites. Explicit formulations of the interphase model via multi...
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We explore how Swedish Local Planning Authorities perceive standardized housing construction and attempt to use an ideal type typology of institutional logics to describe how Local Planning Authorities make use of the...
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ISBN:
(纸本)9780955239090
We explore how Swedish Local Planning Authorities perceive standardized housing construction and attempt to use an ideal type typology of institutional logics to describe how Local Planning Authorities make use of the multiple institutional logics available to them. Increased standardization in Swedish housing construction has been suggested as a means to meet the growing need for housing with reasonable rent levels. However, housing contractors that use standardization and repetition of processes and components claim that the variation of requirements set by Local Planning Authorities prevents them from taking full advantage of their standardization. A recent empirical study of standardized housing contractors' perceptions suggests that Local Requirement Setting, the requirement setting practices of Local Planning Authorities, are interpretational responses to a lack of familiarity with standardized housing construction. Yet, Local Planning Authorities' perceptions of standardized housing construction have never previously been explored. Empirical material for this on-going study was collected through in-depth exploratory interviews with local planning officers from three municipalities situated in Swedish population growth regions. Findings suggest that Local Planning Authorities perceive potential benefits with standardization, but ultimately expect standardized housing concepts to adapt to local standards for processes and products. In projects with high ambitions for architectural quality standardized housing concepts need to be highly flexible. Conversely, highly standardized housing concepts benefit from project ambitions that favour reasonable rent levels. Therefore, Local Requirement Setting is indicative of a mismatch between the Local Planning Authority's project ambitions and the standardized housing contractor's degree of product standardization.
An anisotropic damage model is developed based on conventional rotating crack approach. It uses nonlinear unloading/linear reloading branches to model the hysteretic behavior of concrete. Two damage variables, determi...
An anisotropic damage model is developed based on conventional rotating crack approach. It uses nonlinear unloading/linear reloading branches to model the hysteretic behavior of concrete. Two damage variables, determined by the ratio of accumulated dissipating energy to fracture energy, are introduced to represent the stiffness degradation in tension and compression. Three cyclic tests are simulated by this model and sensitivity analyses are conducted as well. The numerical responses calculated by the damage model are consistent with those obtained from the experiments. The numerical results reflect the nonlinear behavior observed in those tests, such as the damage-induced stiffness degradation, accumulation of residual deformation, energy dissipation caused by hysteretic behavior and stiffness recovery effect due to crack closure. Sensitivity analyses show that the damage exponents have significant influence on the computational accuracy. It is concluded that the anisotropic damage model is applicable to the nonlinear analyses of concrete structures subjected to cyclic loading.
Evaluation of basal heave stability is one of important design checks for excavations in soft clays. The commonly used classical calculation method based on limit equilibrium theory and the safety coefficient formula ...
Evaluation of basal heave stability is one of important design checks for excavations in soft clays. The commonly used classical calculation method based on limit equilibrium theory and the safety coefficient formula recommended by the current code, do not consider the influence of supporting structure of foundation pit depth heave stability, which results in conservative. Considering the wall stiffness and strength, the effective stress changes in different depth of soil, the frictional resistance between the retaining wall and the passive zone, the vertical shear resistance of the soil behind the wall and other factors. The modified safety factor calculation formula of foundation pit stability is presented, comparison analysis of calculation method combined with examples. The calculation results show that the safety factor of foundation pit stability is improved considering the influence of supporting structure depth, the calculation results are more reasonable.
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