Advanced Materials Research Vols. 243-249

Abstract: This paper presents a theoretically study on the time-dependent characteristic of soil-nail axial force in the whole construction process of foundation pit. Firstly, the time-varying performance of axial forces of soil nails is analyzed according to the measured lateral deformation curves of pile-anchor and soil-nail composite supporting deep foundation pit. Then combined with a soil rheological model, a time-dependent formula of soil nail axial force is put forward, and the simulated results are compared to the back-analyzed ones. Finally, a formula to predict the time-dependent axial force of soil nail in the whole construction process of foundation pit is established and an example is investigated to validate the method.

Abstract: As a new type of building envelope, Gcrw is mainly used for excavation of foundation pit. It can stand by itself without the help of bracing, especially in soft soil area. Its stressed characteristic hasn’t been known yet. By using advanced big finite element software Abaqus/Cae, a simulation was made on model of Gcrw under soil pressure when a foundation pit is dug, while the whole excavation is divided into three continuous independent excavation stages. The result shows that Gcrw is a rather good building envelope, Gcrw and soil in the gridding form an integral earth-retaining structure and keep balance under soil pressure before or behind the structure, and have little displacement in horizontal direction. It is like a gravity-type retaining wall in its entirety, but takes on an elastic characteristic. The soil pressure presents a linear change, but its value is less than the theoretical value of calculation. The front wall of Gcrw, like a sheet, is the main flexural construction element, which is subjected to the pressure from side wall of foundation pit and produce curve deformation. The back wall of Gcrw has little displacement and almost is built in the clay. The partition wall endures the effect of the tensile force, its horizontal deformation increases with the build-in depth’s increasing. The back wall and the partition wall play a very important role in dragging back the front wall, the role of them is similar to a pair of anchor tie. The soil in the gridding not only provides soil pressure, but also can fix the back wall, so it is seen as a part of Gcrw and in favor of the Gcrw’s anti-overturn.

Abstract: In the design process of the earth-rock dam, the slope stability problem was always focused on. The shear strength of rockfill in the earth-rock dam had strong nonlinear characteristics. The characteristic directly affected the factor of safety (FOS) of stability of dam slope and the determination of the critical slip surface. The shear strength parameter of rockfill was related to the minimum principal stress σ3 closely. And the value of σ3 had close relationship with the deformation characteristics of filling material and the process of dam filling etc. Strength reduction method has been widely used in solving the FOS of slope stability, and this method has the advantage on the searching of the critical slip surface. Combining the deformation and stress analysis of earth-rockfill dam filling process and the strength reduction method, this paper proposes a comprehensive method of dam slope stability analysis.

Abstract: Granite is generally composed of the minerals such as quartz, feldspar and mica. Distinguishing types and distributions of these meso-compositions are of significantly importance in analyzing the properties of granite in practice. In the current study, the Bayes rule was used to classify the compositions in granite images. The grayscale threshold based technique was used to initially distinguish the meso-compositions in the original image. Six parameters, including the average, variance, contrast, correlation, energy, homogeneity of grayscale values, were extracted from the granite images and selected as the variables characterized minerals in the classifier. A linear discrimination function is then obtained. The meso-compositions of the granite images from different sites were used for the purpose of validation. The image processing was coded into a program and can be automatically run. The result shows that the grayscale threshold based technique and Bayes classifier proposed herein may provide a lot of valuable information both in distinguishing the meso- compositions in rock materials and in analyzing those in the field of the civil engineering.

Abstract: In the framework of critical state soil mechanics, a simple constitutive model for overconsolidated clays is proposed based on subloading surface and normal consolidation yield surface. A more rational hardening law is used to describe the change between subloading surface and the normal consolidation surface with plastic deformation and an associated flow rule is adopted. The model can describe many characteristics of overcaonsolidated clays, such as stress-strain relationship, strain hardening and softening, and stress dilatancy. Compared with the Cam-clay model, two more parameters are required which represents specific physical meanings. Numerical simulation is compared with data from triaxial drained compression test, indicating that the proposed model can rationally describe overconsolidated properties.

Abstract: Considering reinforcement zone and natural foundation as a whole, the displacement component formulas satisfy with the displacement boundary conditions were constructed based on some hypotheses. Considering friction influence under foundation, a approximate analytical algorithm of foundation deformation was established under embankment loads by the variational method of displacement, and the approximate analytical formula on the relationship between the load and the average settlement was derived. The static load model tests were carried out in laboratory to verify the feasibility of this method proposed in this paper.

Abstract: Combined with two-order gradient theory, the least square inversed analysis of the soil parameter for the foundation is studied and put forward in detail. After the mechanical theory for the plate on the foundation is introduced, the controlling differential equations of the plate on the foundation which is subjected to vertical loads are deduced. Through utilizing Fourier transformative theory, the corresponding solutions to the plate on the foundation are gained. Linear algebra controlling equations for the plate are achieved which leads to solve the original differential equations more easily. The least square error function for the soil parameter on the plate is established and applied with the two-order gradient method. The inversed steps on the least square error function for the soil parameter are listed. The calculation results verify the conclusions that the soil parameter of the foundation can be efficiently inversed by applying the least square theory. When different initial soil parameter is set, the iterative computations can be convergent to the true value of the soil parameter. And this least square method can also be applied for the problem of inversed analysis of parameters for other foundation models.

Abstract: In order to study the impact of pile modulus variation on the long-short-pile composite foundation,the relation between bearing capacity and settlement, distribution of the axial force and skin friction along pile, pile-soil stress ratio, load sharing ratio and the bearing mechanics of long-short-pile composite foundation with long and short piles were studied based on laboratory tests in three different conditions: Long pile(Aluminum) with short pile (pentatricopeptide repeats, PPR), Long pile(polyvinyl chloride, PVC) with short pile (PPR), and Long pile(Aluminum) with short pile (PVC). Conclusions were as follows: The settlement of long-short-pile composite foundation decreased with the increasing of long piles modulus, meanwhile, the value of long piles axial force increased, and the value of short piles axial force decreased, and the pile-soil load sharing ratio(LSR) increased. On the other hand, there are few influence on settlement, long piles axial force, and pile-soil load sharing ratio when the modulus of short piles modulus changed, except that the value of short piles axial force and short piles modulus increased or decreased on the same direction.

Abstract: The slope stability analysis is of importance for the practical engineering, and has received widely attention. Generally, the calculation process of the traditional methods is complex. In this paper, a new method was presented to analyze stability of the simple homogeneous slope, in which the safety factor and the max slip displacement of the slope under seismic excitation can be derived based on the principle of the minimal potential energy. The proposed method was efficient and did not require any iterative process for calculation. In order to evaluate its performance, a numerical example was studied to analyze the slope stability. The numerical results show the proposed method is valid and feasible by comparing with the numerical method.

Abstract: Water is an important factor that influences the mechanical properties of rock. Uniaxial compressive experiments have been carried out on sandstone under different cyclic times of drying and wetting. The corresponding complete stress-strain curves are obtained, and characteristics of deformation and failure are analyzed. Test results show that when sandstone samples are submitted to cyclic of drying and wetting, the uniaxial strength and Young's modulus of sandstone obviously decrease. Then, the improved Duncan constitutive model is developed, which can do better in describing sample’s deformation behaviors subject to different cyclic times of drying and wetting. Introduction