黏土中鱼雷锚抗拔承载力数值分析

基于Abaqus软件,针对预埋在一定深度鱼雷锚的抗拔承载力进行3D数值分析,探讨了锚型、土体类型、拉拔荷载倾角、拉拔荷载水平分量与锚翼夹角等多种因素对拉拔承载力的影响。计算结果表明:在均质土、正常固结土和两层土体中,带4个锚翼鱼雷锚增加56.22 m2的锚翼侧面积,其拉拔承载力比无锚翼的提高1.9倍以上;当锚翼侧面积相同时,增加锚翼的宽度可以有效提高锚的承载力;拉拔荷载倾角α在30°～45°范围内,可获得较大拉拔承载力;锚翼宽度越大,拉拔荷载水平分量与锚翼间的夹角β对鱼雷锚水平承载力影响越明显;经归一化的V-H包络线公式对工程应用中预测鱼雷锚的承载力有一定参考价值。     

砂土中带裙板防沉板基础竖向承载力的上限解

防沉板是深海油气工程中水下生产系统的重要基础形式,因其埋深浅、水下施工方便等特点而具有广阔的应用前景。为了满足基础抗滑移的要求,可在防沉板底部设置裙板,裙板的存在增加了防沉板竖向承载力计算的难度。将防沉板基础简化为带裙板条形基础,考虑了内部土体与基础的相互作用,建立了竖向承载模式,即Terzaghi模式;运用极限分析法推导了该承载模式的上限解,引入了一个能够反映裙板与基础内部土体共同作用的经验参数—土体破坏率(η),其大小决定了地基中土体滑动面的范围;通过分析确定了在二维简化条件下带裙板防沉板基础的土体破坏率与基础高宽比的关系;并研究了土体破坏率不同时,地基承载力系数Nq和Nγ与土体内摩擦角之间的关系。     

基于边界面模型的砂土中板锚循环承载力数值分析

利用带误差控制的显式积分算法,将一种适用于饱和砂土排水循环动力分析的边界面塑性模型编写成可供有限元软件调用的用户自定义材料子程序。建立土体单元有限元数值模型对Toyoura砂的静、动排水三轴试验进行模拟,验证了模型具备合理描述砂土在不同荷载条件下力学响应的能力。建立饱和砂土中板锚循环承载分析的数值模型,针对板锚在砂土中的单调抗拔特性和循环承载特性进行数值分析,得到了与模型试验一致的荷载—位移响应规律。考察循环荷载要素对板锚循环承载特性的影响,结果发现,随着循环荷载的施加,板锚永久位移逐渐累积,循环荷载会导致板锚持续移动,循环幅值越大,初始位移和位移变化率越大;循环均值越大,初始位移越大,但位移变化率越小。     

Vertical uplift capacity of a group of shallow circular plate anchors in sand

ABSTRACT

The uplift capacity of a group of circular plate anchors buried horizontally in sand along a line has been determined. The uplift capacity of an interfering anchor is presented in terms of nondimensional uplift factors, F_γi and F_qi, due to components of soil unit weight and surcharge pressure acting on the ground surface, respectively. Theoretical solutions have been developed by applying the upper bound theorem of limit analysis based on a simple rigid wedge collapse mechanism. In the case of two and infinite number of anchors, closed-form solutions have been developed for computing the factor F_qi, whereas the factor F_γi is determined using a semianalytical approach. As expected, the interference of the anchors leads to a continuous reduction in the uplift resistance with a decrease in the spacing between the anchors, and the uplift resistance decreases with the increasing number of anchors at a given spacing. The results compare reasonably well with the available theoretical and experimental data from the literature.     

Evaluation of the uplift behavior of plate anchor in structured marine clay

The uplift behavior of a plate anchor in a structured clay (soft Ariake clay) is investigated through a series of laboratory tests and method of finite element analysis. The tests are adopted to identify the factors influencing the behavior of the anchor, including the thixotropic nature of Ariake clay, consolidation time, and embedment ratio of the anchor. A finite element method (FEM) is used to analyze and predict the uplift behavior of the anchor plate well in the elastic region and the yield load. The results from both the laboratory tests and the FEM analysis suggest that the embedment ratio for a deep anchor in Ariake clay is close to 4. Further increase in embedment ratio improves the capacity to a lesser extent. FEM overestimates the failure load of the uplift anchor in soft Ariake clay by about 20%. This may be ascribed to the hypothesis in the FEM analysis that there is continuous contact between the clay and the anchor until failure. Vesic’s theory for deep anchors, which may be used to predict the ultimate pullout resistance of the plate anchor in reconstituted Ariake clay, is verified to be applicable. In this paper, the plastic flow zone around the anchor is discussed using FEM which makes the behavior of anchor more understandable during the design stage.     

Behavior of a shallow plate anchor in clay under sustained loading

Laboratory model test results for the uplift of a shallow circular plate anchor embedded in a soft saturated clay are presented. For all tests the bottom of the anchor plate was vented to eliminate the mud suction force. The tests were divided into two categories: (1) short‐term tests to determine the variation of the net ultimate uplift capacity and hence the breakout factor with embedment ratio, and (2) creep tests with sustained uplift loads at varying embedment ratios. Based on the model test results, the variation with time, has been determined for the rate of strain of the soil located above the plate anchor. Empirical relationships for obtaining the rate of anchor uplift have been proposed.