Applied Mechanics and Materials Vol. 188

Abstract: The vertical bearing capacity of a special pile group of platform in an offshore gas field has been studied. Large diameter d (2.134 m), deep penetration l (96 m), small spacing sa (3.507 m), and only one row piles are the usual characteristics of the pile group foundation in offshore engineering. According to the requirements of the related design code, the super pile group effect has to be considered. However, with the usual design code, when sa/d, the ratio of spacing to diameter, is less than 2.0, there is no way to consider the pile group effect. In this paper, considering the occlusion effect of soil plug of pipe pile, several methods have been introduced to study the super pile group effect of the vertical bearing capacity. These methods include linear elastic theory method, the method recommended by the Code of Pile Foundation in Port Engineering (JTJ254-98), and the method with virtue of the existing pile group model test results. Meanwhile, the plugged and unplugged conditions have been considered, respectively. Through the analysis, the factors of safety in extreme and normal operation states are obtained, and the results satisfy the design specifications.

Abstract: The combined effects of the rate-dependent behavior of both the backfill soil and the geosynthetic reinforcement have been investigated, which should be attributed to the viscous property of material. A nonlinear finite element method (FEM) analysis procedure based on the Dynamic Relaxation method was developed for the geosynthetic-reinforced soil retaining wall (GRS-RW). In the numerical analysis, both the viscous properties of the backfill and the reinforcement were considered through the unified nonlinear three-component elastic-viscoplastic model. The FEM procedure was validated against a physical model test on geosynthetic-reinforced soil retaining wall with granular backfill. Extensive finite-element analyses were carried out to investigate the tensile force distributions in geosynthetic reinforcement of geosynthetic-reinforced soil retaining wall under the change of loading rate. It is found from the analyses that the presented FEM can well simulate the rate-dependent behavior of geosynthetic-reinforced soil retaining wall and the tensile force of geosynthetic reinforcement arranged in retaining wall.

Abstract: Numerical and experimental studies including different soft and hard layer thickness were conducted under different pressures for analyzing the effect of interlayers on stability of salt cavern considering shrinkage rate, plastic zone and displacement vectors. The results indicate that: Cavern shrinkage rate is increased appreciably with increased of soft layer thickness and decreased significantly with increased of hard layer thickness. The plastic zone change is not obviously with increased of soft layer thickness but obviously with hard layer and plastic zone are significant differences at layer while cavern including soft layer and hard layer, the soft layer effect on plastic zone is less than hard layer and it is more sensitive to pressure increasing, the fracture of hard layer is more easily than soft layer. Maximum displacements happen at layer while cavern including soft layer and at salt rock while cavern including hard layer. Comprehensive differences effects of soft layer and hard layer to stability of salt cavern storage find that fine hard layer and heavy soft layer are more unfavorable. The results are important to oil-gas storage cavern modeling analysis in laminated salt rock.

Abstract: Based to the geometric and mechanical parameters of the typical high-speed railway, the settlement values on the foundation and the subgrade face with different structure layer load are obtained by the numerical calculation. According to these numerical results, the power functional relationship between Sst / S∞ and Pst /hγ is found, and a new evaluation method of the subgrade face settlement caused by the structure layer using the measure data is put forward. Through analyzing the settlement data of different conditions, the parameters of the formula are discussed, and some conclusions and suggestions are given. This new evaluation method will provide some reference for the design and the evaluation of the subgrade settlement caused by the structure layer of the high-speed railway.

Abstract: Time-dependent brittle deformation is a foundational process operating in the underground engineering. So, the study of its characterization is essential to the design and construction of excavations in the rocks for high level radioactive waste disposal repositories. In this study, three constant stress tests under different confining pressures were performed on specimens of Beishan granite. Based on the laboratory results, we investigated mechanical creep behavior of Beishan granite under low confining pressures and compared the results with previous investigations.

Abstract: To use slag in high subgrade reasonably and effectively, the filling height limit was investigated. The viscoelasticity parameters of slag in a ascertain graduation were gained by viscoelasticity constitutive model and indoor creep test. The differential settlement values (DSV) of subgrade surface at various filling heights were obtained by the finite element modelling. The research results show that the DSVs on subgrade surface increase with the filling height. According to the effects of DSV on pavement structures, four grades of differential settlement from low to high were divided, the ultimate filling heights of slag were evaluated correspondingly.

Abstract: The Richards equation is applied to describe the unsaturated soil moisture movement. The Lattice Boltzmann method is developed to solve this partial differential equation. The accuracy and efficiency of the Lattice Boltzmann method in modeling unsaturated soil moisture movement are compared to the Philip series method as well as Crank-Nicolson finite difference scheme. The results reveal that all three methods provide solutions of comparable accuracy. The computation efficiency, accuracy and simplicity of the Lattice Boltzmann method indicate that it has the capacity to model unsaturated soil moisture movement.

Abstract: The numerical simulation using DDARF was carried out to analysis the rock samples with two and four cracks under uniaxial loading condition. Contrastive research was made about the fracture process analysis of rock mass with joints sets at the three different angles. The rock stability with difference of joint rock mass was compared when the lateral coefficient of initial stress varied. It is shown that distribution of joint groups will bring effects on rock surroundings in controlling deformation, stress status and stability.

Abstract: The hydraulic fracturing technology is widely used in the forefront of engineering and production, the mechanisms of hydraulic fracturing crack initiation and propagating are the core content of hydraulic fracturing research. We explain the tensile mechanism of rock under the hydraulic effect, give the two forms of the crack initial water pressure (total stress and effective stress expression) in detail. From the results of theoretical analysis, experiment and numerical simulation we discriminate the mechanisms of hydraulic fracturing crack propagating, which show that cracks are distributed in the minimum principal stress plane under different stress situations. Furthermore, the injection rate is an important influencing factor. The study is valuable to the engineering design of hydraulic fracturing.

Abstract: A large number of reinforced concrete (RC) buildings constructed in the 1970s, whose main structural form is fish-bone shear wall, are still used in Qiansanmen area of Beijing. Due to the economical and technical limitation at the time, both the concrete strength and reinforcement ratio are far from satisfying the requirements given in the current seismic design code for concrete structures. In order to investigate the seismic performances of the wall with the low concrete strength and reinforcement ratio, four RC shear wall specimens were constructed and tested. Quasi-static tests considering large axial compression ratio were carried out, and the stiffness, the strength and the energy dissipation capacity of the RC shear walls are investigated. Test results suggest that the wall with low concrete strength and reinforcement ratio has low strength and poor deformation capacity, indicating the necessity of strengthening.