Advanced Materials Research Vols. 671-674

Abstract: Environment pollution and exhaustion of mineral resources aroused strongly research and development of fly ash utilization. As a kind of foundation treatment method, improved by fly ash is more and more used in highway, railway roadbed construction. With the increase of speed of vehicles and vehicle load, the influence of dynamic load on the subgrade has caused people's concern. In this paper, based on fly ash modified loess, dynamic property of modified fly ash loess is discussed through the dynamic triaxial test of the unsaturation disturbed loess. The effect of the dynamic elastic modulus and the damping ratio with different amount of fly ash loess is studied. The results show that the difference of dynamic properties in dynamic load and static load is large. It mainly presents the hysteresis quality and nonlinear relationship between dynamic stress and dynamic strain. And the dynamic elasticity modulus increases with fly ash mixed amount.

Abstract: The studies application of deep foundation pit decompression technology focusing on special engineering geological and hydrogeological conditions. Taking foundation pit dewatering of certain rail transit station as an example, designs deep foundation pit decompression precipitation technology scheme with hydrogeological parameters obtained through pumping test, and assesses and monitors its impacts on surrounding environment according to measured data on project site, which has achieved good results in practical engineering application and provides foundation for construction of rail transit lines.

Abstract: Foundation Pit Dewatering always arouses surrounding land subsidence that has significant influence on the neighboring environment and even leads to serious natural disasters. So an accurate prediction of the settlement is the precondition of forecasting and evaluating the Foundation Pit Dewatering environment influence. Using the distance from settlement points to Foundation Pit, Equivalent compression modulus, the drawdown, Supporting structure stiffness and equivalent permeability coefficient as the independent variables, adopting the 38 groups of Engineering practical monitoring datas as the samples to establish the prediction model of Land Subsidence caused by Foundation Pit Dewatering based on Support Vector Machine theory. The project trial result shows that compared with traditional empirical method, the model possesses bigger forecast precision.

Abstract: The importance of analysis of stability of slope during rapid drawdown of water table is firstly introduced in this paper. Through summary of the current theoretical and model test research on stability of slope during rapid drawdown of water table, the important of considering the matric suction in unsaturated soils, the analysis method of transient unsaturated seepage and safety of slope and the changes of slope safety was summarized and introduced in this paper. In addition, the problems existing in the analysis of stability of slope during rapid drawdown of water table are pointed out and some ideas for its further development are suggested.

Abstract: Based on the impact of deep foundation pit excavation to the adjacent history style construction, FLAC3D was adopted to establish the excavation and supporting calculation model of a pit in Tianjin. The excavation deformation was analyzed, and the contact slip effect of the supporting structure and soil was considered. The results of study are as follows. (1) The pit has been dig to the third layer, and the values calculated are consistent with the monitored ones by comparing simulation values and measured results on B1 section. (2) Digging to the bottom of the pit, we can predict the biggest horizontal displacement of soil is 34.6 mm, and the value is 11.2mm in the history style construction. Therefore, the results of the study can play a guiding role in the engineering construction safety.

Abstract: Base on the parallel-bond model in PFC2D(Particle Flow Code in two Dimension) used to describe the contact between coal micro-particles, DEM(Discrete Element Method) model of coal has been established, so that the coal uniaxial compression test could be investigated. By comparing the simulation result and experimental result, it is clear that DEM is suitable to simulate the mechanical characteristics and failure mode of coal. The effects of micro-parameters on the constitutive behaviors of coal simulation sample are discussed, they can provide basis for designing DEM model of other analogous coals with differenet mechanical characteristics. The microparameters of coal DEM model obtained in simulation test could be a guilding role for further developing the applicability of the DEM in coal mining, crushing and some other aspects.

Abstract: A study on the soil layer settlement of the aeolian sand foundation treatment by dynamic compaction is reported. The site soil conditions and the dynamic compaction settlement test were introduced. The change curves of the ground surface settlement on the impact point in the course of tamping and the soil layer settlement beneath the impact point after tamping were given. It was found that the ground surface settlement along with number of drops can be described by the hyperbolic function, and the soil layer settlement along with the depth can be described by exponential function. Other some meaningful conclusions were also obtained.

Abstract: Gradient algorithm is difficult to obtain explicit analytic function of the optimization model, at the same time heuristic algorithm is computationally intensive with low speed and less efficient in soil nailing optimization. To overcome these problems, a new optimization method based on improved response surface (IRS) which constructed by uniform design (UD) and non-parametric regression (NR), is proposed. The soil nailing optimization is adopted by the combination of explicit analytic model based on IRS and composing program. The optimization process is explained and a soil nailing is optimized to verify the feasibility of the proposed method. The optimum results show that the introduction of UD and NR to construct the IRS calculate fast, do not need solving the specific analytic solution and can obtain global optimal solution.

Abstract: A non-linear numerical method of composite foundation with rigid-flexible piles in the stratified soil under the vertical load was established in this paper. The analytical model of the pile-soil-pile interaction was used to imitate the pile-soil system and the finite element method was applied to simulate the cushion (the cushion cap). The corresponding calculation program was programmed. Computation results show that the method is reasonable and feasible, and can be applied to the analysis of practical composite foundation.

Abstract: In order to study the slope stress-deformation characters and stability of foundation pit after excavation, analyzed the examples based on the FEM theory, the results show :both the horizontal displacement of slope edge and settlement of slope top are small after support, and they are within the standard, deformation is not the reason for fissure: safety factor of slope is smaller than 1 after excavation, while the safety factor reaches require after support.