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1.
Plate anchors are extensively used in civil engineering constructions as they provide an economical alternative to gravity and other embedded anchors. The rate of loading is one of the important factors that affects the magnitude of soil resistance as well as soil suction force. This article outlines the effect of pullout rate on uplift behavior of plate anchors (70 mm diameter) buried in soft saturated clay by varying the pullout rate from 1.4 mm/min to 21.0 mm/min. The variation of breakout force and suction force with embedment depth and rate of pull are presented. A correlation between the rate of increase of undrained strength of clay and anchor capacity with rate of strain has been established. Finally an empirical equation has been proposed that includes the rate of pull in the estimation of breakout capacity of anchors. 相似文献
2.
板翼动力锚是依靠自重完成安装并靠自重和海床土的抗力来锚固的新型动力锚。板翼动力锚高速(15~25 m/s)贯入地基过程中涉及到高应变率、流固耦合、土体软化和大变形等难题,模型试验可避免上述计算困难,能直接得出不同的贯入速度所对应的沉贯深度。本文首先推导了模型相似关系,然后在常规重力条件下,进行了两组26个工况的板翼动力锚在均质黏土中动力安装过程的模型试验,根据试验结果确定了率效应参数的取值范围,并研究了每一项受力对沉贯深度的影响。最后提出了在均质黏土中预测板翼动力锚沉贯深度的经验公式。 相似文献
3.
A simplified analytical method is presented for the vertical dynamic analysis of a rigid, massive, cylindrical foundation embedded in a poroelastic soil layer. The foundation is subjected to a time‐harmonic vertical loading and is perfectly bonded to the surrounding soil in the vertical direction. The soil underlying the foundation base is represented by a single‐layered poroelastic soil based on rigid bedrock while the soil at the side of the foundation is modeled as an independent poroelastic layer composed of a series of infinitesimally thin layers. The behavior of the soil is governed by Biot's poroelastodynamic theory and its governing equations are solved by the use of Hankel integral transform. The contact surface between the foundation base and the soil is smooth and fully permeable. The dynamic interaction problem is solved following standard numerical procedures. The accuracy of the present solution is verified by comparisons with the well‐known solutions obtained from other approaches for both the elastodynamic interaction problem and poroelastodynamic interaction problem. Numerical results for the vertical dynamic impedance and response factor of the foundation are presented to demonstrate the influence of nondimensional frequency of excitation, soil layer thickness, poroelastic material parameters, depth ratio and mass ratio on the dynamic response of a rigid foundation embedded in a poroelastic soil layer. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
4.
鱼雷锚安装过程中,锚尖形状影响尖部贯入阻力进而影响贯入深度。基于塑性极限分析理论下限法分析不同锚尖长径比x的椭圆形锚尖的贯入阻力和贯入阻力系数,并考虑了贯入深度、锚-土界面摩擦对贯入阻力以及贯入阻力系数的影响。结果表明:(1)锚-土界面光滑时,锚尖贯入阻力系数随着锚尖长径比的增大而减小;锚-土界面粗糙时,锚尖贯入阻力系数随着锚尖长径比的增大而增大。(2)摩擦力对贯入阻力系数的影响随着ξ增大而增大。(3)随着埋置深度增加,贯入阻力系数受x影响最小时所对应的摩擦系数逐渐减小。(4)当锚-土界面摩擦系数ω 0.75时,工程中可选用ξ1的锚尖用以减小端部贯入阻力;当ω0.26时,ξ1的锚尖提供更小的端部贯入阻力。锚尖长径比ξ=0和ξ=1的下限解与前人研究的桩基和圆形结构的理论解较为一致,进一步验证了所提出的椭圆形锚尖下限法模型的可行性。 相似文献
5.
The results of a number of laboratory model tests for the short‐term ultimate uplift capacity of a circular plate anchor embedded in saturated soft kaolinite and montmorillonite are presented. The tests were conducted with and without venting the bottom of the plate anchor in order to determine the variation of the suction force with embedment ratio. The variation of the suction force is presented in terms of the undrained shear strength of the clay and also the net ultimate uplift capacity. 相似文献
6.
反压土对悬臂式支护结构嵌固深度的影响研究 总被引：3，自引：0，他引：3
基于Rankine土压力理论、滑移线场理论和Boussinesq解答在均布条形荷载作用下的表达式,建立了考虑反压土自重对坑底土体水平抗力的增强作用和反压土本身的嵌固作用两种机制时悬臂式支护结构嵌固深度的计算方法,并进行了算例分析。研究表明：虽然反压土能提供给支护结构的水平抗力较小,但由于其合力力臂较大,因此对支护结构有明显的嵌固作用;另外,反压土的自重能明显提高坑底土体的水平抗力。综合考虑反压土的以上效应后,支护结构的嵌固深度可以明显减小。基坑内侧预留反压土的施工方法可以省去水平支撑、降低支护结构深度,还可以节约投资和缩短工期,具有良好的经济效益、社会效益和环境效益。因此,在条件许可的情况下,该施工方法应优先选用 相似文献
7.
扩径率和入岩深度是影响岩基挖孔基础抗拔承载特性的两个重要因素。通过开展8个不同扩径率、不同入岩深度挖孔基础的现场真型上拔静载试验,从荷载位移变化规律、抗拔承载力和地基岩体破坏模式三方面分析了扩径率与入岩深度对基础抗拔承载特性的影响,结果表明扩径率对荷载位移曲线初始线性阶段影响显著。采用图解法分别获得代表基础低、中、高3种承载能力的抗拔承载力QL1、QDLI、QL2,分析表明,随着扩径率与入岩深度的增加,基础抗拔承载力均有不同程度提高,但两种因素对基础承载力影响机制不同,扩径率可明显提高初始弹性阶段的承载力QL1,而入岩深度可明显提高塑性阶段的承载力QDLI和QL2。通过分析地基破坏时地表岩体裂缝的分布特征,得出岩基中上拔岩体的破坏模式与基础结构型式无关,均是从基底开始出现裂缝,沿着一定角度的开口延伸至地面,直至地基发生破坏,并且破坏范围随着入岩深度的增加而减小。综合考虑基础施工安全性、经济性和机械化程度,建议优先选择加深入岩深度的措施来提高基础抗拔承载力。 相似文献
8.
《Geomechanics and Geoengineering》2013,8(2):145-154
Plate anchor is one of the most common varieties of anchors used in the construction and maintenance work of various on-land and offshore structures. An accurate estimation of the uplift capacity of anchor foundations is necessary for an economical design as well as for the safety and stability of structures. This paper outlines the effect of shape of anchor plates on their breakout capacity, through a series of model tests. Both shallow and deep anchor behaviours were investigated under conditions developing suction force and without suction force. The results of these tests are presented in terms of load-displacement behaviour, variation of breakout factors (with and without suction force) with depth of embedment, the critical embedment depth of anchors and variation of suction force with embedment ratio. Further, the variations of breakout factor ratio with aspect ratio and embedment ratio are reported. Based on the experimental results and the model test results of other investigators an empirical relationship has been suggested to determine the shape factor and holding capacity of plate anchors buried in saturated cohesive soils. 相似文献
9.
Gravity installed anchors (GIAs) are released from a height of 30–150 m above the seabed, achieving velocities up to 19–35 m/s at the seabed, and embed to depths of 1.0–2.4 times the anchor length. Challenges associated with GIAs include the prediction of anchor initial embedment depth, which determines the holding capacity of the anchor. Based on the coupled Eulerian–Lagrangian approach, a numerical framework is proposed in this paper to predict the embedment depth of GIAs, considering the effects of soil strain rate, soil strain-softening and hydrodynamic drag (modeled using a concentrated force), with the anchor-soil friction described appropriately. GIAs are influenced by the hydrodynamic drag before penetrating into the soil completely, hence the anchor accelerates less than the previous investigations in shallow penetration, even decelerates directly at the terminal impact velocity. The hydrodynamic drag has more influence on OMNI-Max anchors (with an error of ∼4.5%) than torpedo anchors, and the effect becomes more significant with increasing impact velocity. An extensive parametric study is carried out by varying the impact velocity, strain rate and strain-softening parameters, frictional coefficient, and soil undrained shear strength. It is concluded that the dominant factor affecting the penetration is the soil undrained shear strength, then are the impact velocity, strain rate dependency and frictional coefficient, and the minimal is the strain-softening of soil. In addition, although the strain rate dependency is partly compensated by the softening, the anchor embedment depth accounting for the effects of strain rate and strain-softening is lower than that for ideal Tresca soil. Strain rate dependency dominates the combined effects of strain rate and strain-softening in the dynamic installation of GIAs, on which should pay more attention, especially for the calibration of the related parameters and the measured solutions. In the end, the theoretical model based on the bearing resistance method is extended by accounting for the hydrodynamic drag effect. 相似文献
10.
Bearing capacity of strip foundation on geogrid-reinforced sand 总被引：1，自引：0，他引：1
E. C. Shin B. M. Das E. S. Lee C. Atalar 《Geotechnical and Geological Engineering》2002,20(2):169-180
Results of small-scale laboratory model tests to determine the ultimate bearing capacity of a strip foundation supported by sand with multiple layers of geogrid reinforcement are presented. Tests were conducted with only one type of geogrid and a sand compacted to one relative density. The embedment ratio of the foundation was varied from zero to 0.6. It is found that, for the given reinforcement-depth ratio, the bearing capacity ratio with respect to ultimate load increases with embedment. The relationship between the bearing capacity ratio at ultimate load and at limited levels of settlement (less than or equal to 5% of foundation width) is also presented. The bearing capacity ratio at limited levels of settlement is smaller than the value at ultimate load. 相似文献