Advanced Materials Research Vols. 243-249

Abstract: Considering the co-action of micro-pile and soil nailing, the state equation of limit equilibrium and the performance function of inner global stability of foundation pit supported by the micro-pile composite soil nailing is set up with the slope limit equilibrium theory and the circular sliding slice method. The calculating model of sliding surface for inner global stability of foundation pit is established with the geometry controlling method and the optimization searching of the most dangerous sliding surface is achieved. Then with the shear strength indexes of soil as random variables, the partial derivatives of the performance function to all random variables is deduced and the reliability index of inner global stability of foundation pit supported by micro-pile composite soil nailing is calculated with the design checking point method. Finally, the effects of coefficients of variability of the random variables on reliability index are analyzed.

Abstract: Soil improvement by foam is a key technique to control formation damage in shield construction. The half-life of three kinds foam was obtained by test self-developed foam and other two types. Meanwhile, their characteristics of stability and dissipation were analyzed. The physical-mechanical characteristic of red clay which was improved by foam was tested. Test result show that as the foam concentration increasing, the cohesion and plastic fluidity of soil increases firstly and then decreases, but the internal fiction angle decrease always. The permeability of red clay was measured by penetration test. The impregnation depth of foam in red clay was analyzed. The results provide key parameters for shield construction to prevent engineering accidents, such as, flowing, sand gushing, mud boiling, collapse and so on.

Abstract: Using a double-layer horizontal strata model, a simplified time-history analytical method which considers liquefiable layer existence is proposed for calculating ground motion acceleration and displacement. Solutions in frequency and time domains under arbitrary loading are given. By the cycle-by-cycle method, the calculating results of ground acceleration and displacement time histories under arbitrary loading are presented. Adopting a proper pore-water pressure ratio incremental model, shear modulus of the liquefiable layer is modified cycle by cycle that the nonlinearity of the liquefiable layer induced by soil liquefying is proximately simulated. Through numerical analysis, ground displacement on liquefied sites is much larger than that on non-liquefied sites during liquefaction process. Before initial liquefaction, ground displacement and acceleration on liquefied sites are obviously higher than those on non-liquefied sites. After initial liquefaction, ground acceleration remarkably decreased but displacement remains much larger than that on non-liquefied sites. Normalized acceleration response spectra are calculated. It shows that the low period components on liquefied sites are lower than those on non-liquefied sites, but long period components are higher than those on non-liquefied sites.

Abstract: The current study was implemented to evaluate the backfilled gravel subgrade slope stability of a highway, China. Typical crossing section in Jiling Province was evaluated by using the finite element based strength reduction method. The calculation code was developed based on BCF, which was programmed for 2D finite element analysis on soil stress-strain analysis. The Duncan-Chang nonlinear constitutive model was employed to describe the stress and strain relationship of the soils. The safety factor calculated by the strength reduction method was compared with traditional limit equilibrium slice Bishop Method.

Abstract: The composite foundation with capped rigid piles and geo-synthetics is a new technology. A plane of equal settlement exists in the fill through soil arching. The horizontal membrane can restrain the lateral deformation of the pile and subsoil. Most loads can be effectively shifted to the piles and the deep layer. The total settlement and differential settlement can be controlled. The technology is particularly fit for soft soil ground treatment engineering. The mechanism of interaction among fill, foundation soil, geo-synthetics and pile (caps) was analyzed. A theoretic design method of the composite foundation with capped piles and geo-synthetics has been presented and a project case was cited in the paper. This study will improve the design theory of ground treatment.

Abstract: Stress state of soft soil foundation under vacuum preloading is completely different from its counterpart under surcharge preloading, and the method of calculating the final settlement of soil mass by means of surcharge preloading (positive pressure) is unreasonable in present design. According to a case of soft foundation stabilized with vacuum preloading and through consolidated-undrained triaxial (CU) test on the specimens sampled in situ, the stress paths under different confining pressure are obtained. The settlement of soft foundation treated with vacuum preloading is calculated by strain isoline method. Compared with the practically measured field data, the errors are analyzed and discussed.

Abstract: In terms of the physical mechanism and features of the dynamic soil-structure interaction during earthquake excitation, a simplified procedure for evaluating the earthquake-induced differential settlement of buildings on natural subsoil is presented. It takes into account of the irregularity of incident seismic waves and the different distribution of vertical dynamic stresses caused by seismic loading under the two sides of building base. Instead of FEM the simplified method based on the layer-wise summation method is used to calculate the settlement of the subsoil with building presence. The cone model proposed by Meek and Wolf is adopted to calculate the dynamic stress distribution under the building. The residual strain potential model of soil under irregular loading and the modulus-softening model are employed to calculate the permanent deformation of subsoil. The simplified method can consider the combined effect of soil, structure and seismic wave reasonably and describe the developing process of differential settlement. The results of large shaking table tests are consistent with the corresponding calculated results.

Abstract: The pore water pressure variation during the process of dynamic drainage consolidation is calculated and analyzed with numerical simulation method, using constitutive model of Finn. The pore water pressure in mud presents transient vibration process, and decreases with depth. The pressure in mud is always higher than in sang bag well, which reveals that sang bag well is an effective vertical drainage channel in process of dynamic drainage consolidation. In addition, seen from the characteristics of pore water pressure variation, effective consolidation depth can be accurately forecasted.

Abstract: Experiments of unloading confining pressure of rock were conducted to reveal deformation characteristics of rock mass under different excavation intension in thigh geostress condition. It were concluded from tests that volumetric strain of rock is inverse proportional to unloading rate. The smaller the unloading rate, the bigger the ductility of rock. Energy release are bigger under high unloading rate than that under low unloading rate. That means that tendency of rock burst turn smaller when unloading rates decrease.

Abstract: The pile ground heat exchanger is devised to overcome the shortcomings in configuration of existing ground heat exchangers. In view of its engineering applications of the spiral tubes ground heat exchanger inside foundation piles, the effects of them on the loading capacity features of the pile are studied. Firstly, a spiral tube model is proposed for the energy pile system and the model is proved correctly compared with engineering practice of the piles.Then，in the FEM software the model is applied in the comparasion between the piles with and without buried tubes .As a result, the effects of buried tubes on the loading capacity features of the piles are found.