Numerical investigation on the penetration of gravity installed anchors by a coupled Eulerian–Lagrangian approach

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.     

Use of evolutionary computing for modelling some complex problems in geotechnical engineering

In this paper, the feasibility of using evolutionary computing for solving some complex problems in geotechnical engineering is investigated. The paper presents a relatively new technique, i.e. evolutionary polynomial regression (EPR), for modelling three practical applications in geotechnical engineering including the settlement of shallow foundations on cohesionless soils, pullout capacity of small ground anchors and ultimate bearing capacity of pile foundations. The prediction results from the proposed EPR models are compared with those obtained from artificial neural network (ANN) models previously developed by the author, as well as some of the most commonly available methods. The results indicate that the proposed EPR models agree well with (or better than) the ANN models and significantly outperform the other existing methods. The advantage of EPR technique over ANNs is that EPR generates transparent and well-structured models in the form of simple and easy-to-use hand calculation formulae that can be readily used by practising engineers.     

深基坑桩锚支护体系变形实例分析

通过分析基坑桩锚支护系统变形机理及其影响因素，讨论了支锚刚度及预应力对深基坑桩锚支护体系变形的影响，并结合工程实例，阐述了合理确定支锚刚度及预应力控制深基坑桩锚支护体系变形的方法。     

美国加利福尼亚海岸出水石锚的地质学考证

通过对加利福尼亚海岸出水石锚的岩石学和古生物学的研究,初步推断了其原岩的产地,并用14C同位素测年测定了保存于石锚内的现代贝壳的年龄,由此大致推断出石锚的入水年龄。以上研究结果表明:(1)这些石锚石料非采自美洲本土,就世界范围而言,其产地分布于环太平洋的新阿尔卑斯皱褶带内,包括日本、台湾、马来西亚、印度尼西亚及中东、西亚乃至地中海沿岸地区;(2)这些石锚至少在1500年前就已落入海中,也就是说这些石锚的主人要比哥仑布发现美洲新大陆早1000余年。     

系统锚杆对地下厂房洞室群稳定性影响的数值分析

以某水电站地下厂房工程为实例,采用数值分析方法,通过对比厂房洞室群是否施加系统锚杆的差别,获得系统锚杆对洞室群稳定性的影响.结果表明,施加系统锚杆对围岩主应力影响小,但能平均降低围岩位移28.07％,降低拱顶和拱角处围岩位移34％以上,降低主厂房和尾闸室边墙塑性破坏区深度2.2～4.8m,在一定程度上提高洞室群的整体稳...     

The inspection of retaining walls using GPR

In hilly regions, retaining walls along roads, motorways and railway lines are numerous. In some cases the knowledge of the details of the construction is limited. If rehabilitation work becomes necessary, a detailed knowledge of the construction is desirable for the improved planning of maintenance and repair. This paper describes the application of Ground Penetrating Radar (GPR) for the inspection of retaining walls. The work was carried out in two steps. First, an investigation was carried out on large retaining walls at a Swiss motorway within the framework of a service contract. This included the development of an apparatus enabling high precision positioning of the antennas on the walls. Second, a pilot study was performed on a smaller wall with optimized acquisition and processing parameters. This included the use of antennas with different orientations and the fusion of the two corresponding datasets as well as true 3-D data processing. This paper describes the approaches to data acquisition and processing in the form of the two case studies. Results from different acquisition and processing strategies are compared and the benefits and limits are discussed.     

土层锚杆模型试验研究

针对土层锚杆应力分布的复杂性,进行室内模型试验,利用所得数据,绘制了拉力型锚杆和压力型锚杆杆体全长上的应变分布曲线、同列锚杆锚固段末端点以及坡面处的应变分布曲线。在所得曲线的基础上,对坡体中锚杆的应力分布特征以及变化规律进行了分析及讨论,从而对其工作性能和加固机理进行初步研究。介绍了锚杆上剪应力分布的理论解,并将试验结果与理论分析结果进行了对比,两者基本吻合,验证了本试验结果的合理性和可靠性。     

板翼动力锚水中自由下落过程数值模拟

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。板翼动力锚在水中自由下落的阻力决定了锚到达海床表面时的速度,进而直接决定了锚贯入海床中的深度以及它能提供的承载力。板翼动力锚的形状比较复杂,采用计算流体动力学的方法研究板翼动力锚的下落速度、水平位移和转角与下落位移的关系。计算结果表明:板翼动力锚的拖曳阻力系数约为0.93~1.12之间;在沉贯过程中应使加载臂与翼板共面以减少阻力;板翼动力锚的终端速度约为28 m/s。     

Stability of anchored sheet wall in cohesive‐frictional soils by FE limit analysis

This study extends the limit analysis techniques used for the computation of strict bounds of the load factors in solids to stability problems with interfaces, anchors and joints. The cases considered include the pull‐out capacity of multi‐belled anchors and the stability of retaining walls for multiple conditions at the anchor/soil and wall/soil interfaces. Three types of wall supports are examined: free standing wall, simply supported wall and anchored wall. The results obtained are compared against available experimental and numerical data. The conclusion drawn confirms the validity of numerical limit analysis for the computation of accurate bounds on limit loads and capturing failure modes of structures with multiple inclusions of complex interfaces and support conditions. Copyright © 2012 John Wiley & Sons, Ltd.     

Pullout capacity of embedded suction anchors in sand

An analytical solution has been developed to estimate the horizontal, vertical, and inclined loading pullout capacities of embedded suction anchors in sand. Validation of the analytical solution on pullout capacities has been made through comparisons with the centrifuge model test results. Primary variables for the centrifuge model tests are the depth to the loading point, the load inclination angle, and the addition of flanges. The results indicate that both the horizontal and vertical pullout capacities of the embedded suction anchor in sand increase, reach the peak and then start to decrease as the loading point moves downward. The inclined loading pullout capacity is very much dependent on the load inclination angle and the loading point. The effect of flanges on the pullout capacities is also found to be significant.