Previous experimental studies on laterally loaded pile groups usually applied loading along the direction parallel to the edge of the pile cap. This study aims to determine the effects of the loading direction on the response of laterally loaded pile groups through a comprehensive experimental investigation. Model pile groups with different configurations embedded in sand were subjected to lateral loads along various horizontal directions. The results show that the loading direction has a predominant effect on the evolution and eventual distribution of force among piles in the pile group, the bending responses along the piles, and the total lateral resistance of the pile group. These results can be attributed to different group-interaction effects under different loading directions. For both square and rectangular configurations, the pile groups provide the largest total lateral resistance along the diagonal direction. The effect of the loading direction on the response of the pile group is affected by the configuration of the group. The pile group at medium spacing (5D) is more sensitive to changes in the loading direction. Back-calculated p-multipliers indicate a substantial difference in p-multipliers of individual piles when the pile groups are loaded along different directions. The p-multipliers of the front-row pile can be approximately 67% larger when loaded along the diagonal direction than when loaded along the direction parallel to the edge of the pile cap. The effects of both the pile group configuration and the loading direction on the values of p-multipliers should be considered in analyzing the responses of pile groups under lateral loads.
Abstract Lateral loads applied to pile foundations in some cases are multidirectional. However, most of the past studies only considered soil-pile interaction under unidirectional horizontal loadings. This paper describes a comprehensive experimental study on a pile-sand system under both unidirectional and multidirectional horizontal loadings using a computer numerically controlled biaxial motion platform. The displacement paths at the pile head include unidirectional regular paths, cross paths, figure-8 paths, and unidirectional and multidirectional irregular paths with different displacement amplitudes and different aspect ratios of the displacement amplitudes along two horizontal directions (α). The test results indicate that the preloading along one horizontal direction influences the subsequent response along the orthogonal horizontal direction, in terms of the pile resistance and the direction of the force increment vector. In the figure-8 tests, the shapes of the force-displacement curves in most cases differ significantly from that obtained from the unidirectional regular test and different from the unidirectional regular test, the maximum forces appear before the displacements reach the maximum values. In these tests, the direction of the force increment vector always deviates from the direction of the displacement increment vector. According to the results of the regular and irregular loading tests, the lateral resistance of the pile under the multidirectional paths is generally lower than that under the unidirectional path, and the degree of reduction increases with the aspect ratio (α). The ratio of force (rF), defined as the maximum force in the multidirectional tests to that in the unidirectional test, can be expressed as an exponential function of α. Considering that the reduction in the resistance can reach as large as about 30%, overlooking the multidirectional loading effect can lead to unconservative analysis or design in some cases.
We establish an elaborate numerical model with which to investigate the deformation characteristics of segmental lining. The numerical model contains reinforcement and connecting bolts that previous numerical studies have generally neglected. We validated the model parameters using a full-scale model test result. Based on this numerical model, we studied the deformation characteristics of segmental lining. Convergence, joint deformation, bolt stress, and reinforcement stress were systematically analyzed under different loading conditions. Furthermore, we discuss the relationships between convergence and joint opening, bolt stress and joint opening. The deformation characteristics of segmental lining are revealed. When the lining is deformed by earth pressure, plastic hinges form at the joints. The segment rotates around the plastic hinge, which is the main reason for segmental lining deformation under earth pressure. Horizontal convergence is a single index to reflect the deformation of tunnel rings, representing the overall deformation of the ring to a certain extent but not the deformation characteristics of the joint. When the loading conditions differ, the relationship between joint opening and horizontal convergence is consistent for some joints and inconsistent for others.
This article presents nondimensional solutions for laterally loaded piles in sand considering nonlinear soil–pile interactions. A nonlinear elastoplastic p–y model, termed the H-model, is introduced, and its ability to model the responses of laterally loaded piles in sand is demonstrated. Nondimensional forms of both the H-model and the governing equation for laterally loaded piles are then derived, after which the nondimensional responses of free-head piles subject to lateral forces and moments and that of fixed-head piles subject to lateral forces are evaluated using the finite-element method. It is found that (1) the pile responses are significantly affected by the nondimensional pile length; and (2) using nonlinear soil–pile interaction, the critical length of the pile increases with increasing normalized displacement and is noticeably larger than that utilizing linear soil–pile interaction. The quantitative nondimensional relationship between force and the moment responses of free- and fixed-head long piles is also obtained. Two design curves, normalized force against normalized displacement and normalized force against maximum normalized moment, are presented. Illustrative examples are given to show the step-by-step procedure for how the curves could be used in practice to estimate the behavior of piles.
The interaction mechanism between grouted anchor cables and the surrounding rock mass or soil are complicated and difficult to investigate using conventional monitoring technologies. This study focuses on the in-situ pullout behavior of grouted anchor cables using Brillouin Optical Time-Domain Analysis technique. A series of pullout tests were conducted on anchor cables with five different anchor lengths and three grouting methods. Distributed fiber optic sensors were used to measure the strain distribution of cable bolts from tip to top. The in-situ pullout test results show that both ultimate pullout resistance and ultimate displacement at the ultimate pullout resistance increase with anchor length. The bond strength suffers a slight variation with an increase in anchor length. Both ultimate pullout resistance and the ultimate displacement for Type-B grouting (grouting with reaming) and Type-C grouting (secondary grouting) are larger than those for Type-A grouting (one-time grouting). The shear bond strength of Type-C grouting is greater than that of Type-A grouting. Results from Gaussian functions analysis show that it is feasible to use the function to characterize the axial stress of anchor cables. Furthermore, the overall mobilized percentage η was evaluated. The anchor cables with smaller anchor lengths will result in greater η. The η for the anchor cables of 6 m reaches 92% at the last load, whereas the anchor cables of 18 m were mobilized by only 29% at the last load. The grouting method has a negligible effect on the η, increasing from 22% to 29% in process of the pullout test.
Abstract Centrifuge model tests have been widely used to validate analytical procedures, with the assumption that variations of parameters from the prototype to the model are governed by the scaling law. However, the coefficient of permeability in dynamic centrifuge tests seems to be much larger than the value calculated from the scaling law. Permeability may significantly affect the rate of pore-pressure buildup in liquefiable soil and associated deformation during earthquake loading. Therefore, proper estimation of the actual coefficient is very important in interpreting experimental data and validating analytical procedures. Based upon the physical law of conservation of mass, this paper presents an approach for backanalysis of the permeability of saturated sand in the dynamic centrifuge test. The ability and necessity of such an approach was demonstrated by comparing the experimental and numerical results.
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