Bridge scour is recognized as one of the key factors that causes structure failures, which in turn leads to economic and life loss. In this study, flume tests of four typical arrangements of pier groups embedded in sand under steady clear water conditions were carried out to observe the process and maximum depth around piles of scour. The investigation included single pile, tandem piles, side-by-side piles, and 3 × 3 pile groups. Different conditions including different pile spacing, flow velocity, and water depth are considered. Moreover, the evaluation of design methods from the United States, New Zealand, and China was analyzed and compared through experimental and mathematical methods. The experimental results show that shielding and jetting effects are obvious in pile groups, which become less obvious with the increase of pile spacing. The dynamic process of scour around single pile and pile groups are quite different. Meanwhile, most of the predicted scour depths by these equations tend to be much larger than those from field data, which may lead to overdesign and consequently high construction cost. In addition, data from this study and some laboratory experiment data from previous work were used to derive the correction factors of a new scour prediction equation, which can be used to estimate the scour in a sand bed and agree well with the observations. 相似文献
In a piled raft, the length and arrangement of piles has a significant effect on the stresses and deflections of the raft. The use of piles with different dimensions and properties below a raft is an innovative concept and can optimize the design of a piled raft. In this study, an integral equation method with a fictitious pile model was adopted to analyze the piled raft foundation with dissimilar piles. The Fredholm integral equations of the second kind were obtained for this problem. The loads shared by piles and subsoil, the load transfer, and the settlement of the piled raft were obtained using numerical calculation. The results from the present method were compared with those in the literature. An optimization technique was introduced to design piled rafts with dissimilar piles. The stiffening effect of piles on the surrounding soil is also discussed as compared the conventional interaction factor approach. 相似文献
To provide appropriate uses of nonlinear ground response analysis for engineering practice, a three-dimensional soil column with a distributed mass system and a time domain numerical analysis were implemented on the OpenSees simulation platform. The standard mesh of a three-dimensional soil column was suggested to be satisfied with the specified maximum frequency. The layered soil column was divided into multiple sub-soils with a different viscous damping matrix according to the shear velocities as the soil properties were significantly different. It was necessary to use a combination of other one-dimensional or three-dimensional nonlinear seismic ground analysis programs to confirm the applicability of nonlinear seismic ground motion response analysis procedures in soft soil or for strong earthquakes. The accuracy of the three-dimensional soil column finite element method was verified by dynamic centrifuge model testing under different peak accelerations of the earthquake. As a result, nonlinear seismic ground motion response analysis procedures were improved in this study. The accuracy and efficiency of the three-dimensional seismic ground response analysis can be adapted to the requirements of engineering practice. 相似文献
Natural clays usually show anisotropic stiffness due to their deposition process and anisotropic in situ stress state. The stiffness anisotropy depends on both of the stress anisotropy and fabric anisotropy, while the latter can be quantified by the stiffness anisotropy at isotropic stress states. This paper measures the K0 value (i.e., stress anisotropy) and elastic shear stiffness anisotropy of natural Shanghai clay in a triaxial apparatus with horizontal and vertical bender elements. The results show that the K0 value of Shanghai clay lies in the range of 0.40–0.66, and an empirical equation is proposed to estimate the K0 value based on the plasticity index and initial void ratio. The fabric anisotropy of natural Shanghai clay lies in the range of 1.2–1.4 with a stronger fabric in the horizontal plane. Moreover, the experimental data of the stiffness anisotropy and fabric anisotropy of different clays in the literature are reviewed and analyzed. It reveals that the stiffness anisotropy generally increases, while the fabric anisotropy remains nearly the same during K0 consolidation. For normally consolidated clay, the fabric anisotropy generally lies in the range of 1.1–1.7. For overconsolidated clays, the fabric anisotropy generally increases as the overconsolidation ratio increases. Empirical equations are proposed to approximately estimate the fabric anisotropy of clays based on its stress normalized elastic shear stiffness.
Earthquake Engineering and Engineering Vibration - Research to reliably predict the seismic response of nuclear power stations with a pile-raft foundation is needed to meet the high safety... 相似文献
This paper presents both experimental study and numerical simulation to investigate the effects of an innovative sacrificial piles concept to reduce local scour surrounding service piles. These sacrificial piles are placed upstream of the pile groups, which serves to change the flow field and reduce the erosive force before it reaches the service piles. Four types of pile group arrangements were considered in the experimental and simulation analyses, including single pile, double pile in tandem arrangements, double pile with side-by-side arrangements, and pile array of 2 × 2 arrangements. Scaled experiments were conducted in flume for each group of design, and local scour around piles with and without sacrificial piles was monitored. It was found that the sacrificial piles effectively reduced the development of local scour surrounding the service piles, especially at their heels. The results also showed that the use of sacrificial piles reduced the time required for the scour depth to reach the equilibrium conditions than those without the sacrificial piles. To corroborate the experimental observation, numerical simulation with three-dimensional computational fluid dynamics model has also been carried out with commercial code with verified erosion model. The development of dynamic scour process and maximum scour depth were obtained by the computational simulations. Comparison of experimental and computational results both indicates that the use of sacrificial pile is effective in reducing the scour depth. The extent of reduction in the maximum scour depth varied with the arrangement of sacrificial piles. 相似文献