Applied Mechanics and Materials Vols. 353-356

Abstract: Economic development and urbanization give rise to the excavation complexion, and higher requirements on design work are put forward. The risk of excavation in soft clay area is high and the design shall be comprehensive. While in practice, the dynamic characteristic of vehicle loads is seldom calculated. In this paper, conventional one-side plane method (beam on elastic foundation method) and three-dimensional finite element method were adopted to analyze the effects of vehicle loads on the retaining strutting system of braced excavation. Moreover, the reinforcement scheme of excavation after collapse was given as references for similar situations.

Abstract: In order to determine shearing strength parameters of triaxial tests(cohesion and friction angle), nonlinear programming solution was suggested based on “minimum square sum of distance”. After proving that the vertical distances between Mohr circles and the regressed strength line are distributed normally, data with gross error would be excluded; moreover, the only strength line, as well as cohesion and friction angle, could be determined. Combining with Matlab, the solution process became rapid, precise and intuitive. Some examples verified the applicability of suggested method finally.

Abstract: The excavation of deep foundation pit by numerical simulation is researched in this paper. Different locations of soil are selected to be as test points. Under two velocities, the law of total displacements that reflect the test points in the same locations is discussed. The variation tendency of the pore pressure under the rapid construction and tendency of the volume change under the normal construction are compared. The soil is divided to three parts in numerical simulation: the side, the bottom I and the bottom II of the foundation. The numerical results are as follows: the total displacement of the rapid construction is double for ones of the normal construction, which is on the side and the bottom I of deep foundation pit. Under the different drainage conditions, the soil on the side of deep excavation experiences the dilatancy, and then the shear-contraction, and then the dilatancy; the soil on the bottom II of deep excavation experiences the dilatancy and then the shear-contraction. The soil on the bottom I experiences the dilatancy under the normal construction; but it experiences the dilatancy and then the shear-contraction under the rapid construction.

Abstract: A new method of displacement back analysis, named SVM-CTS, was proposed based on support vector machine (SVM) and continuous tabu search (CTS). On the one hand, SVM-CTS used SVM to build the nonlinear mapping relationship between the measuring point displacements and rock and soil mechanics parameters of positive analysis based on the study samples. On the other hand, SVM-CTS used the global optimization performance of CTS to catch the optimal rock and soil mechanics parameters in the global space. The nonlinear mapping relationship built by SVM can fit and forecast the measuring point displacements under different parameters with high accuracy. CTS can prevent object function from trapping in local optimum and improve precision of back analysis. Case study shows that SVM-CTS can be well applied to the displacement back analysis in geotechnical engineering.

Abstract: Because various lithologic rock present very obvious differences in many aspects (such as: the apparent lumpiness, longitudinal wave velocity, mechanical property etc), the results of the rock mass structure classification by using current specification or general methods can not reflect the true engineering geological properties. Based on a large number of onsite structural surface investigations, acoustic measurements and field and laboratory tests, this paper discusses the related issues on division of rock mass structure using single lumpiness indicators and analyzes the impact of the structural body property and structural surface effect on the rock mass structure. At the same time, the related issue on the integrality coefficient is discussed in the evaluation of rock mass integrity degree. Finally, the proposal which rock structure classification should consider the structure bodys strength and stiffness, the structure surfaces extension length and closed degree, the structure body block size and the rock mass compression wave velocity is put forward.

Abstract: It mainly reviewed the current research status of the bearing characteristic of rock-socketed piles. From reading all kinds of calculation model in different code, it pointed out the disadvantages. It concluded the present work on the two main factors which influence the bearing capacity of rock-socketed pile most. Based on this work, it figures out the deficiencies of the research presently and prospects the future research. In the end, it suggests that the bearing behavior and failure mechanism of rock-socketed piles with thick sediments remains need to be further discussed.

Abstract: Under the combined effects of various external factors, such as temperature, seepage, alternate wetting and drying and so on, the mechanical properties of rock mass are susceptible to be deteriorated, and its strength characteristics are significantly degraded with time. The mesoscopic damage accumulated inside the rock, contributing the rock slope instability with weak structure planes, generate the time-dependent deformation, and eventually lead to the slope failure. Given the time-dependent deformation of the rock, numerical simulations are conducted to investigate the key factors influencing the long-term stability of slopes. Numerical results show that the catastrophic failure time of slopes is linear to its cohesion, and the bigger cohesion and friction angle increase catastrophic failure time, i.e., the stability of rock slope increase. In addition, the configuration of the intact rock bridge can also influence the time-dependent slope stability. Slope height can significantly affect the slope stability and the maximum horizontal displacement. Differences in rock mass storage environment play an important role in the long-term stability of slopes.

Abstract: The influence of hydroxyl aluminium on the mechanical and physical characteristics of montmorillonite clay was examined in this study. Hydroxyl aluminium-modified and unmodified montmorillonite samples were examined using X-ray diffraction (XRD), scanning electron microscopy (SEM), hydrometer analysis, unconsolidated undrained (UU) triaxial strength tests, unconfined compressive strength tests, Atterberg limit tests, swelling potential tests and other evaluation techniques. The results indicated that the hydrophilic nature and the swelling and shrinkage properties of the montmorillonite clay changed drastically as a result of modification with hydroxyl aluminium. The free swelling ratio of the clay was reduced sharply, and its particle size gradation and strength characteristics were greatly improved by modification with hydroxyl aluminium. The proportion of clay-sized particles decreased dramatically, and the proportion of silt-sized particles increased. The results of this study suggest that hydroxyl aluminium influences the mechanical and physical properties of montmorillonite clay by physicochemical interactions.

Abstract: Building up the 3D numerical analysis and computing model, force properties of buried pipelines under vibration loads induced by bridge pile foundation construction were researched, to evaluate and control the influence of construction vibration on adjacent buried pipeline. It was concluded that the most adverse position of impact loads effect on pipeline appeared in the upper right and lower left parts of the pipeline closed to the side away from the pile hole about a quarter of an arc. And the peritubular stress distribution curve with the change of the vibration source location were approximately sinusoidal line, parabola and the cosine line changes. Another, under the same conditions, the vibration velocity of ground above the pipeline was significantly greater than the pipeline itself vibration velocity, so through a reasonable assessing and controlling the vibration velocity of ground above the pipeline, it could be made security decisions for buried pipelines. Finally, according to the horizontal spacing of the buried pipeline and shock vibration source, the pipeline grading protection measures were proposed, with achieving better results in engineering application. Research results could provide some evidence both for the force calculation and design construction of the pipeline project, and support for scientific decision-making of the bridge pile foundation construction. It has an important social and economic efficiency.

Abstract: A pre-stressed lattice frame is an effective structure of reinforced slope. The purpose of this paper is concerned chiefly with the study of the internal force distribution and calculation methods of the pre-stressed anchor lattice frames, and analyzed calculation methods advantages and disadvantages. It is concluded that the design and calculation of the lattice frames should consider the common deformation of the beam and the soil. It can make result especially approaching the force condition of the lattice frames.