Applied Mechanics and Materials Vols. 638-640

Abstract: Normal triaxial apparatus is suited to the loading stress path test, some stress path triaxial apparatus can be used to unload radial load smaller than the axial load, but it is difficult to unload axial load smaller than the radial load or even unload the axial load to zero. Using the iso-diameter headgear, different axial-radial unload ratio tests were done on the GDS triaxial apparatus, and the axial load was unloaded smaller than the radial load. During the test, it was found there are some deficiencies in the GDSLAB system. The results conformed to the characteristics of unloading test, which well verified the correctness of the test method and test results.

Abstract: The shear wave scattering due to an elliptical cavity in an infinitely long strip of orthotropic graded saturated porous (OGSP) media is studied with the boundary element method (BEM). The shear modulus and the mass density of the OGSP are assumed to have exponential forms. Using Biot's theory, the governing equations are developed for OGSP. The fundamental function is obtained by separating variables in terms of the Dirac delta function. A system of linear equations describing the displacement on the ellipse is obtained by applying the linear BEM. The numerical results for the normalized boundary surface displacements in the scattering field are presented with different OGSP coefficients. The effects of many parameters are evaluated with numerical examples. These results are expected to have great technical interest for determining boundary stability when elastic waves interact with OGSP cavities.

Abstract: The density of the sand is important factor for its engineering properties, There are many methods to evaluate the sand density, just the results may be differences, usually means, this is the test error of the different test methods. In fact, the reasons of the sand formation and buried conditions, sand particle shape and size, sand gradation, groundwater etc. are also the important factors for its engineering properties, but these factors are often ignored. Bearing pressure of confined water will change the distribution of the effective weight stress in soil and the abnormal phenomenon of sand density will appear. In the project, the cause analysis of sand density require attention. According to theoretical knowledge, to identify applicable conditions of the various evaluation methods and their advantages and shortcomings.

Abstract: Unconsolidated sandstone is a kind of formation with low strength and large deformation property. Deeper unconsolidated sand formations have larger geostress and perform the plastic and rheological characteristics. After the borehole has been drilled into, this kind of sandstone will creep, which will cause some problems such as pipe stuck and casing deformation failure etc. Therefore, creep parameters of unconsolidated sandstone are critical for designing drilling fluid density and choosing casing material. Through indoor experiments, creep data of unconsolidated sandstone from Zhujiang group of X oil field in the west of South China Sea was get. The experiments results indicate that creep law of this sandstone conforms to Nishihara’s model, and the creep parameters were calculated based on experiments data. According to Nishihara’s model, using numerical simulation method, this paper analyzes the relationship of sandstone creep shrinkage rate with time of Zhujiang group reservoir sandstone and determines the drilling fluid density that ensures the safety of horizontal wells drilling, which has guiding significance for well design and drilling.

Abstract: The shear strength of rock joints is highly depended upon the failure mode of joint asperity. At lower normal stress slide-up of one asperity up over another mode, however at high normal stress the joint asperities are sheared off at the base. This research uses pressure measurement film to directly measure the contact normal stress between smooth joint surfaces. It demonstrates that the density of color impression is capable of capturing the normal stress distribution behavior. The contact normal stress distribution during shearing is changed. After shearing, the contact stress becomes large. This increase in contact normal stress is to fracture the joint wall material.

Abstract: Using finite element software ANSYS/LS-DYNA, dynamic response of pile-soil-structure interaction (PSSI) system under blasting load was analyzed, and the effects of blasting load on surrounding buildings foundation and superstructure were studied. This can provide a reference for structural and seismic reinforcement under blast loading. The results show that the every floor’ acceleration of superstructure of PSSI system along the vertical direction is usually larger than the value along the horizontal direction under horizontal explosion load. Peak-acceleration along the vertical direction decreases from the lowest layer to the top and peak-acceleration along the horizontal direction decreases and then increases with the increase of layer. The top peak-shear stress of piles is larger than the tip of piles, and the distribution laws are inverted triangles. The maximum values of peak of pile-soil contact pressure are located on the top of the piles. With little change in height and contact pressure plummeted. Contact pressure increases more near the tip of the piles.

Abstract: During the construction of excavation, adopting top-down method and taking steel sheet piles as maintenance structure, some projects involving surface subsidence, surface displacement, deep horizontal displacement, underground water level and steel bracing internal force are monitored. Based on monitoring data, prompt feedback and early warning can prevent excessive displacement, deformation and engineering accident. Every monitoring indicator under control effectively achieves safety assurance of excavation engineering and surrounding building, realizes informatization construction of excavation engineering and guides similar engineering forcefully.

Abstract: The experiment on foundation improvement by dynamic compaction in Collapsible Loess foundation of the power plant was made. Before and after the experiment, kinds of in-situ and laboratory tests were performed .Through these tests, the influence of the dynamic compaction on the character of the soil, such as dry density, collapsibility, bearing capacity is analyzed. The effective depth of improvement of foundation is calculated and the conclusion of the efficiency of the foundation treatment by dynamic compaction is made. The choosing of techniques and parameter of the dynamic compaction also is elaborated in the paper, which make an example for other similar construction in the future.

Abstract: This paper conducts an experimental study on the variable modulus foundation for frame-tube structure. The base reactions are measured and its correlation with deformation characteristic is analyzed. The following conclusions are summarized: (1) soil cement (volume ratio is 1:4) is used to strengthen the foundation soil at core tube area. The ratio of moduli of foundation soils at core tube area and external frame column is 2.23. The vertical deflections of medial axis and diagonal are 0.08‰ and 0.1‰. (2) Under the working loads, the base reaction at core tube area is highest and distributed uniformly. The base reaction at the area between the core tube and the external frame column decreases gradually. The overall distribution of base reaction shows a basin shape. (3) The ratio of foundation modulus at core tube area and external frame column area is 2.35. The ratio of base reactions at these two parts is 3.31, which shows a good correlation with the foundation modulus.

Abstract: Through the one dimensional consolidation of creep test, the paper presents and analyzes the deformation law of reloading under different stress level, the variation of the coefficient of consolidation and the relation between the secondary consolidation deformation and loading history. These test results show that the secondary compression during previous loading has great influence on the subsequent deformation of soil.