Applied Mechanics and Materials Vols. 170-173

Abstract: Based on the analysis of influence of fissures and accumulation rainwater at toe of slope under rainfall condition on expansive soil slope, A limit equilibrium method was proposed based on former studies by dividing the slope into fully fissures area A , partially developed fissures area B , accumulation rainwater influence area B′, without fissures area C, and considering the top slope tension crack to reflect influence of fissures on expansive soil slope under rainfall condition. The depths of every layer and strength indexes were determined. The computed results of an engineering example using bishop method showed that the proposed method can not only reflect the characteristics of expansive soil landslide but also evaluate the long-term stability of the slope at ultimate state.

Abstract: Using similarity theory as guidance ,the paper designs the laboratory model test on foundation reinforcement by locating lime-soil pile at both side of strip footing, and researches foundation bearing capacity, p-s curve, the magnitude and distribution discipline of the foundation stress before and after reinforcement, and analyzes the load-bearing mechanism, strengthening mechanism and reinforcement effect of the strengthening technology. The results show that the lime-soil pile can effectively improve the foundation bearing capacity, and reduce the amount of ground settlement; under the role of the lime-soil pile, the stress spread lesser to the outside of pile in the ground, and causes the foundation stress to the deeper place.

Abstract: In recent years, more and more large-diameter and super-long steel pipe piles are widely used in bridge and port engineering. But so far, people know very little about their bearing characteristics and there is no suitable calculation method of their bearing capacity in the design specifications. In engineering design, computational theory of ordinary piles is referenced. We all know that carrying capacity of large-diameter and super-long steel pipe piles is very closely related to the surrounding soil stiffness, but we do not know how they influence each other. In the paper, the effect of soil stiffness on vertical bearing and settlement features are studied for large-diameter and super-long steel pipe pile based on the three-dimensional continuum medium fast lagrangian method (FLAC3D). The result shows that the settlement of pile top will be reduced and side friction resistance of large-diameter and super-long steel pipe pile can be increased effectively if the stiffness of soil around the piles become stronger under the unchanged load. But when the stiffness of soil exceeds a certain intensity, the rate of pile top settlement reducing decreases gradually. In other words, when the soil stiffness increases to a certain extent, continue to increase the stiffness of soil around piles can not effectively reduce the settlement of pile top. It is obvious that the stiffness of soil around pile has a direct impact on the pile settlement characteristics and bearing characteristics. The conclusion is of significance for the reasonable design of large-diameter and super-long steel pipe pile foundation in engineering applications.

Abstract: In recent years, more and more large-diameter and super-long steel pipe piles are applied in engineering project. But people just know little about the bearing characteristics of super-long piles as it is very difficult to study such type of super-long piles in the laboratory and the accumulated test data of super-long piles in actual projects is very few restricted by test conditions and test cost. In engineering work, design value of bearing capacity of large-diameter and super-long piles is still referred to the calculation theory of ordinary pile that cannot take into account engineering security and economic simultaneously. In this paper, SVM-Q which is an intelligent algorithm based on Support Vector Machines is developed for predicting side friction of large-diameter and super-long steel pipe pile. Result shows that the side friction of longer large-diameter and super-long steel pipe piles with similar bearing characteristics can be effectively predicted by the SVM-Q algorithm after fully learning enough side friction data samples of the limited testing piles with gradually larger length, and boundary length of super-long steel pipe pile in this actual engineering could be qualitatively judged by comparing predictive data with the measured data. This method is very meaningful for initiative predicting the bearing capacity of large-diameter and super-long steel pipe piles in the case that there is no suitable calculation method. The predictive bearing capacity also can be adopted to verify the bearing capacity of large-diameter and super-long steel pipe piles that donot be field-tested by static load tests in actual projects.

Abstract: In accordance with the occurrence behavior of roof strata and the fracture characteristics of key stratum in shallow seam longwall mining, this paper studied the post-buckling behaviors of key roof stratum in the process of mining by using initial post-buckling theory, which derived a critical load and a breaking span of the main roof during the first weighting, determined the final subsidence for broken key stratum, and presented an application with the example of Daliuta 1203 face. The results indicate that the rock blocks a in are state of non-equilibrium after main roof breaking, the equilibrium path of main roof is unstable from breaking to final subsidence; thick unconsolidated layers above roof have effect on post-buckling behaviors of key stratum; the stability for bifurcation point equilibrium configuration and post-buckling equilibrium path of roof strata could be revealed and an effective method for determining displacement field of imperfection structure could be provided by using initial post -buckling theory.

Abstract: Based on the unified solution of shear strength in terms of double stress state variables for unsaturated soils, whilst considering the effect of the intermediate principal stress rationally, the unified solution of Coulomb’s active earth pressure for unsaturated soils without cracks is developed. Comparability of the solution is analyzed and influencing characteristic of each factor is obtained. The research result indicates that: the intermediate principal stress and matric suction have obvious impacts on Coulomb’s active earth pressure for unsaturated soils; Coulomb’s active earth pressure has been decreasing until zero with the increase of unified strength theory parameter and matric suction; Coulomb’s active earth pressure increases with the increase of grading angle of retaining wall and slop angle of backfill, but decreases with the increase of matric suction, effective internal friction angle and matric suction angle, while external friction angle has no obvious influence. The proposed unified solution of Coulomb’s active earth pressure enjoys a wider application, and unified solution of Rankine’s active earth pressure is just the special case. The results are of great significance to soil pressure determination such as slope and foundation pit, and to retaining structures design.

Abstract: With a certain actual lime-soil pile composite foundation project for background, the Finite Element Method (FEM) model of composite foundation was carried out by using the Drucker-Prager theory and ANSYS FEM procedure. By imitating the status of composite foundation under the construction load and analyzing the factors such as stress, settlement, stress ratio between pile and soil, carrying capacity of composite foundation with lime-soil pile has been gained. The conclusions offer some beneficial references to design and construction of actual projects.

Abstract: Soil is divided for finding the ultimate bearing capacity of foundation with given buried depth and size. Supposing a uniform load acts on the foundation, Mindlin’s integral formula and corner points method are used to get extra stress of every mesh knot by MATLAB program, then the principal stress is found. Combining with failure criterion, MATLAB program is used to find coordinates of points which are destroyed. Using graphic processing function of MATLAB, the failure points are showed in the coordinate. Increasing the rectangular uniform load, the failure points are found until these points can form a continuous failure surface. This rectangular load is the ultimate bearing capacity of the foundation. The method can avoid errors brought by unreasonable hypotheses of the empirical formulas; and the three-dimensional failure surface of the foundation soil is obtained.

Abstract: Uniaxial compression creep tests have been performed on a kind of rock salt similar material and laminated salt rock similar material on the base of salt rock gas-storage in Jintan. The creep tests show that the rheological property of the similar material is basically the same with the original rock. Under the uniaxial compression, the deformation gradually approaches to be constant after the early short stage of creep attenuation. The similar material shows stress-dependent behavior obviously under different stress stage, the greater the load the higher the creep ratio and creep deformation. A creep constitutive equation which is suitable to rock salt is used to the similar material, and it fits with the obtained creep data very well. The results show that the similar material developed in this passage has the same creep property as the original salt rock,and this material can be used to simulated the deformation and failure of underground gas storage constructed in bedded salt deposits.

Abstract: Dynamic analysis of structure of rock-soil material is a difficulty in structure analysis of rock-soil material. Dynamic analysis referred here is equivalent to plasticity analysis in classical elasticity/plasticity theory. But, for the structure of rock-soil material, the granules form a structure in the form of network, which makes dynamic analysis especially complex. We attempt to simplify granular form in this study, and construct a Markov model of structural evolution of system according to finite connection modalities between granules. Connection modality distributions for each structural state are obtained using recursion technique. Next, depending on connection modality distribution, we obtain the mechanical and geometric parameters of the system, thus stiffness-strength-displacement relation can be established. This relation serves as the basis for building dynamic constitutive relationship for rock-soil material. Literature on relevant subjects has been rarely found so far, and our discussion is only a tentative exploration.