Advanced Materials Research Vols. 671-674

Abstract: Based on the problems of the saturated silt foundation, the failure reasons of dynamic consolidation on saturated soft foundation in the past will be analysized. Combining with some successful experiences of dynamic consolidation, authors present some notices of dynamic consolidation on saturated soft foundation.

Abstract: Numerical simulation method and on-site dynamic monitoring are used to study a railway laneway disturbed by excavation of neighboring roadways under high in-situ stress in a deep coal mine of Huainan region. The paper presents a series of variation trend about stress state, deformation, plastic zone and tension of cables under disturbance effects based on the simulation results, and the evolution of surface displacement of railway laneway is also discussed according to on-site monitoring data. The analysis shows that disturbance effects have spatiotemporal characteristics and support structure should be installed in a short time which helps to reduce disturbance by construction of adjacent caverns.

Abstract: The problems of compacted loess roadbed utilization are closely related to the characteristics of compacted loess and long-term vehicle loads. According to the characteristics of compacted loess in different degree of compaction, the distribution and deformation change rules of the dynamic stress under dynamic load are studied through the finite element program numerical analysis of vehicle loads roadbed dynamic response. The data is acquired by field test and laboratory experiment. In lighting of the influence of the subgrade deformation by degree of compaction and pavement structures, the influence models are given which are used for estimating the roadbed vertical displacement in different conditions.

Abstract: Traffic safety in existing railway has strict demands to the subgrade deformation, and the subgrade deformation caused by foundation pit excavation should be under the limit value. In this paper, steel sheet pile cofferdam supporting system is introduced, as well as its construction process. 2D numerical simulation is adopted to simulate the construction process, the deformation of subgrade at different cases are discussed. At last, the field monitoring data is provided to verify the validity of supporting system and numerical simulation results . Research results indicate that steel sheet pile cofferdam supporting method can well control the subgrade deformation, and can be took as a precedence technique in similar engineering. To ensure the traffic safety, it’s necessary to prevent the trains crossing near the excavation, and the train speed should be limited.

Abstract: Environmental vibration problem caused by rail transport is always a crucial problem for the development of rail transport harmoniously and favorably. Lots of legislations have formulated to constrain this problem in many countries, however, most of them are worked out based on the analysis results and measured data from only single rail line. With the further development of rail transportation in China, more and more engineering will cross the others inevitably, which will cause a more complicated problem with multi-vibration source. And obviously, the multi-vibration source problem is not the linear superposition of several single vibration source problems. Focusing on two being planned overlapping shield tunnels, the computation model is established and the environmental vibration is calculated and analyzed by considering the running mode and running number of subway train. Fitting analysis is conducted and empirical formulas for vibration attenuation and then, the vibration range is determined accordingly. The research results in the paper can provide guide for the pre-design of overlapping engineering and also can offer references for the completion of relative legislations.

Abstract: This paper presents a self-made apparatus which has been used for estimating the adverse influence induced by some factors. There are two main factors that can make significant impact on the result of slope model tests: boundary effect and porosity effect. The relationship between the sliding angle and boundary effect can be achieved when the soil is at a loose condition of packing. The angle will decrease as the slope thickness increases and it will keep at a rough constant value when the thickness is relatively big, namely, the influence induced by the boundary effect which can be ignored at that time. In this paper, a theoretical method is employed to quantify and confirm this relationship. Corresponding predicted results agree well with the experimental results. But this conclusion is not suitable to dense soil. Special attention is also given to dense soil within a given porosity range, and a comparison between boundary effect and porosity is described. It could be seen clearly that the porosity is a stronger factor to the variation of the sliding angle than the boundary condition. These conclusions are valuable to a practitioner in taking modification work for such type of apparatus to get an optimal resolution for the latter experiment.

Abstract: Large-scale deep excavation may affect the bearing capacity of piles inside the excavation zone. It does not only cause the loss of friction, but also change the stress state of the subsoil. In this paper, nonlinear finite element technique is employed to investigate the bearing capacity of piles influenced by the deep excavation. Parameters of soil are obtained by back analysis on the pile static load test results. The bearing capacity of the piles during excavation is analyzed by performing FEM modeling under three conditions using the calibrated parameters. The numerical study shows that the loss ratio of vertical bearing capacity of pile foundation caused by excavation unloading is 34%.

Abstract: In order to study the supporting of deep surrounding rock with zonal disintegration tendency, the zonal disintegration phenomenon of deep surrounding rock under three supporting forms is analyzed by the ABAQUS finite element software in this paper, and three supporting forms are un-supporting, bolting and grouting, and combined “Bolting and grouting plus Anchor rope” supporting. The results show that the different effects to zonal disintegration under different supporting forms will occur. Supporting can help to restrain the zonal disintegration of the reinforcement part advantageously, and also lower rupture degree of zonal disintegration and reduce the size of rupture zone. Meanwhile, the stability of surrounding rock is improved. But zonal disintegration may occur outside reinforcement part under greater ground stress. The results are great importance to a better understanding of the deep roadway supporting.

Abstract: In order to reduce the cost of soil nail supporting to deep foundation pits and ensure safety as well as stability, a model is established to optimize the design parameters for soil nail wall. This paper is concerned with the analysis of soil nail channel number, diameter, length, horizontal spacing, vertical spacing and dip angle. For parameter optimization design of soil nail wall is a complex problem, the traditional method is easy to fall into local optima. The genetic algorithm is a global optimization method. To some extent it has the drawback of appearing premature convergence and oscillation so as to slow iterative process. Therefore, a forward and backward search algorithm is proposed, which is combined with genetic algorithm. Furthermore some improvement measures are put forward by means of improved hybrid genetic algorithm. As a result engineering studies arrive at an optimum design. It shows that the optimized design results of IHGA not only ensure the stability of foundation, but greatly reduce the cost of engineering materials.

Abstract: Traditional analysis methods of reliability in the foundation pit engineering have larger error and larger amount of calculation. Therefore, the response surface method has attracted much attention because it can effectively use the finite element analysis method (FEAM) and reduce the number of the numerical simulation. This paper combines uniform design (UD) with support vector machine (SVM). On this base, a reliability analysis method of the foundation pit is put forward based on the response surface of support vector machine (RSSVM). The UD structures random samples and the FEAM is used to obtain corresponding response parameters including the lateral displacement of wall, settlement of ground, safety factor of overall stability and safety factor of against overturning. Then, SVM trains the above random samples and corresponding response parameters to get response surface (RS) respectively. The probability density distribution of each response parameter is obtained by combining the Monte Carlo method with RSSVM. The instance analysis shows that the method has high computing efficiency and less amount of calculation, and the result is reasonable. It provides an effective way for the reliability analysis of the foundation pit engineering.