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111.
112.
The design of spread footings on granular soils is generally governed by serviceability requirements. Recent studies have utilized databases of load tests to investigate the use of normalized load-settlement curves to model the behavior of footings on sands. A major limitation of available databases is that they are based primarily on data from plate load tests or footings that have an equivalent width smaller than 1.0 m. There is a need to confirm the applicability of these curves to footings of practical scale. The main objective of this paper is to update available normalized load-settlement curves using point measurements of settlement and load from full-scale footings. Bayesian techniques are employed in the updating process. Results indicate that the updated normalized load-settlement relationship is slightly more conservative but less uncertain than the current relationship. Results from an illustrative example involving serviceability limit state reliability analyses using footings with widths ranging from 1.5 to 3.0 m indicated that the updated relationship resulted in a slightly higher reliability level compared to the prior relationship. 相似文献
113.
In India, rural roads are constantly being constructed. To ensure proper design of rural roads, it is desirable to have an appropriate selection of design parameters. The California bearing ratio (CBR) method of pavement design is the most commonly used method employed for the foundation design of rural roads. In the CBR method, the CBR value of the subgrade soil is critical in deciding the overall thickness of the pavement. Additionally, for good drainage, a typical specification for the pavement foundation design requires the value of permeability coefficient of the subgrade material to be specified. Thus, permeability and CBR constitute two important parameters in the design and assessment of long-term performance of the pavement. In this study, laboratory investigation has been carried out on a number of soil samples procured from a roadwork project site. Preliminary tests, such as index tests and particle size distribution tests, useful for soil classification, were followed by light compaction, CBR and variable head permeability tests. Further, observations from the laboratory investigation are statistically analysed to study correlations among various parameters. Because the predominant soil type found in the study area is alluvial, this study also highlights the suitability of alluvial soils as pavement subgrade material. 相似文献
114.
M. F. Bransby M. C. R. Davies A. El Nahas S. Nagaoka 《Bulletin of Earthquake Engineering》2008,6(4):607-628
The propagation of reverse faults through soil to the ground surface has been observed to cause damage to surface infrastructure.
However, the interaction between a fault propagating through a sand layer and a shallow foundation can be beneficial for heavily
loaded foundations by causing deviation of the fault away from the foundation. This was studied in a series of centrifuge
model tests in which reverse faults of dip angle 60° (at bedrock level) were initiated through a sand layer, close to shallow
foundations. The tests revealed subtle interaction between the fault and the shallow foundation so that the foundation and
soil response depend on the foundation loading, position, breadth and flexibility. Heavily loaded rigid foundations appeared
best able to deviate fault rupture away from the foundation but this deviation could be associated with significant foundation
rotations. However, a lightly loaded foundation was unable to deviate a reverse fault and the fault emerged beneath the foundation.
This led to gapping beneath the foundation as well as significant rotations and may cause severe structural distress. As well
as providing insight into the mechanisms of behaviour, the data from the tests is used to validate finite element analyses
in a separate article. 相似文献
115.
基坑开挖不仅改变了半无限空间体边界条件,卸载时还会引起周围地层移动,导致既有建筑物地基承载力的附加损失。在临近基坑既有建筑物地基承载力计算中,其抗剪强度参数的选取有别于斜坡上地基计算参数的常规取值方法。通过探讨临近基坑既有建筑物地基抗剪强度指标的取值问题,建议以地基土的完全软化强度与残余抗剪强度的平均值作为临近基坑既有建筑物地基抗剪强度指标,并据此估算了临近基坑既有建筑物地基承载力。所得结果与斜坡上地基承载力的试验值和理论解对比分析后显示出其具有一定的合理性。所建议的抗剪强度指标取值方法,还有待于试验的进一步验证。 相似文献
116.
The transient response of large embedded foundation elements of length-to-diameter aspect ratio D/B=2–6 is characterized by a complex stress distribution at the pier–soil interface that cannot be adequately represented by means of existing models for shallow foundations or flexible piles. On the other hand, while three-dimensional (3D) numerical solutions are feasible, they are infrequently employed in practice due to their associated cost and effort. Prompted by the scarcity of simplified models for design in current practice, we here develop an analytical model that accounts for the multitude of soil resistance mechanisms mobilized at their base and circumference, while retaining the advantages of simplified methodologies for the design of non-critical facilities. The characteristics of soil resistance mechanisms and corresponding complex spring functions are developed on the basis of finite element simulations, by equating the stiffness matrix terms and/or overall numerically computed response to the analytical expressions derived by means of the proposed Winkler model. Sensitivity analyses are performed for the optimization of the truncated numerical domain size, the optimal finite element size and the far-field dynamic boundary conditions to avoid spurious wave reflections. Numerical simulations of the transient system response to vertically propagating shear waves are next successfully compared to the analytically predicted response. Finally, the applicability of the method is assessed for soil profiles with depth-varying properties. The formulation of frequency-dependent complex spring functions including material damping is also described, while extension of the methodology to account for nonlinear soil behavior and soil–foundation interface separation is described in the conclusion and is being currently investigated. 相似文献
117.
This paper presents a new practical modeling approach, based on the beam-on-a-nonlinear Winkler foundation (BNWF) model, to simulate the 3D rocking, vertical and horizontal responses of shallow foundations using structural elements that are readily available in the element library of commercially available structural analysis programs. An assemblage of a moment-rotation hinge, shear hinge connected in series with an elastic frame member attached to the bottom end of ground story columns was proposed to model the response of the footing under combined action of vertical, horizontal and moment loading. To couple the responses of these hinges, two bounding surfaces equations were introduced and derived mathematically: a surface that defines the interaction between the rocking and vertical capacities of the footing along its width and length; and a surface that defines the interaction between the horizontal capacities of the footing along its width and length. Simple calculation steps to evaluate the geometric and mechanical properties of the proposed assemblage of structural elements are provided. The proposed modeling approach was verified using experimental results from large scale model foundations subjected to cyclic loading. Based on this study, it was found that the proposed assemblage can be reliably used in modeling the rocking and horizontal responses of shallow foundations under cyclic loading. 相似文献
118.
119.
路堑边坡开挖对邻近既有隧道影响研究 总被引:5,自引:2,他引:3
设计中的承德迎宾大道路堑边坡邻近既有京承铁路21号隧道,边坡开挖后会对既有隧道产生不利影响。根据现场试验取得的围岩及隧道衬砌的力学参数,对边坡开挖进行了静力学和动力学数值分析,研究了路堑边坡可开挖的最大范围及爆破振动对隧道的影响。结果表明:当路堑二级边坡坡脚距离隧道中心线距离大于等于30 m时,边坡开挖后隧道衬砌内力虽有增加,但仍可保证结构安全。进行边坡爆破开挖时,如考虑3倍的安全系数,当京承铁路21号隧道衬砌振速小于1.5 cm/s时,隧道衬砌内产生的动拉应力小于衬砌极限抗拉强度,可按此控制指标进行现场监测。 相似文献
120.