This paper describes recent advances in stability analysis that combine the limit theorems of classical plasticity with finite elements to give rigorous upper and lower bounds on the failure load. These methods, known as finite-element limit analysis, do not require assumptions to be made about the mode of failure, and use only simple strength parameters that are familiar to geotechnical engineers. The bounding properties of the solutions are invaluable in practice, and enable accurate limit loads to be obtained through the use of an exact error estimate and automatic adaptive meshing procedures. The methods are very general, and can deal with heterogeneous soil profiles, anisotropic strength characteristics, fissured soils, discontinuities, complicated boundary conditions, and complex loading in both two and three dimensions. A new development, which incorporates pore water pressures in finite-element limit analysis, is also described. Following a brief outline of the new techniques, stability solutions ...

Geotechnical stability analysis

Helical piles are increasingly used to support and rehabilitate structures subjected to both tensile and compressive axial loads This paper presents a detailed investigation into the axial perform

Axial testing and numerical modeling of square shaft helical piles under compressive and tensile loading

This paper presents an experimental investigation on soil deformation around uplift plate anchors in sand by using digital image correlation (DIC). The experimental setup consists of a camera, loading frame, plexiglass mold, and computer, which is developed to capture soil deformation during anchor uplifting. A series of model tests are performed to investigate the influence of particle size, soil density, and anchor embedment depth on soil deformation. A set of images captured during anchor uplifting are used to calculate soil displacement fields by DIC. The failure surface is studied by tracking the points with maximum shear strain values. On the basis of this study, it is found that soil deformation and the pullout resistance of plate anchors are substantially influenced by soil density and anchor embedment depth, whereas particle size within the studied range has limited influence. In dense sand, the shape of the failure surface changes from a truncated cone above a shallow anchor to a combine...

Sand Deformation around an Uplift Plate Anchor

Offshore wind turbines play a key part in the renewable energy strategy in the UK and Europe as well as in other parts of the world (for example, China). The majority of current developments, certainly in UK waters, have taken place in relatively shallow water and close to shore. This limits the scale of the engineering to relatively simple structures, such as those using monopile foundations, and these have been the most common design to date, in UK waters. However, as larger turbines are designed, or they are placed in deeper water, it will be necessary to use multi-footing structures such as tripods or jackets. For these designs, the tension on the upwind footing becomes the critical design condition. Driven pile foundations could be used, as could suction-installed foundations. However, in this paper, we present another concept-the use of helical pile foundations. These foundations are routinely applied onshore where large tension capacities are required. However, for use offshore, a significant upscaling of the technology will be needed, particularly of the equipment required for installation of the piles. A clear understanding of the relevant geotechnical engineering will be needed if this upscaling is to be successful.

https://royalsocietypublishing.org/doi/pdf/10.1098/rsta.2014.0081

Helical piles: an innovative foundation design option for offshore wind turbines.

Soil anchors are commonly used as foundation systems for structures that require uplift or lateral resistance. These types of structure include transmission towers, sheet pile walls and buried pipelines. Although anchors are typically complex in shape (e.g. drag or helical anchors), many previous analyses idealise the anchor as a continuous strip under plane strain conditions. This assumption provides numerical advantages, and the problem can be solved in two dimensions. In contrast to recent numerical studies, this paper applies three-dimensional numerical limit analysis and axisymmetrical displacement finite element analysis to evaluate the effect of anchor shape on the pullout capacity of horizontal anchors in sand. The anchor is idealised as either square or circular in shape. Results are presented in the familiar form of break-out factors based on various anchor shapes and embedment depths, and are also compared with existing numerical and empirical solutions.

/pdf/three-dimensional-lower-bound-solutions-for-the-stability-of-1rvneehck7.pdf

Three-dimensional lower-bound solutions for the stability of plate anchors in sand

An experimental investigation of the uplift behaviour of relatively large scale model circular plate anchors up to 400 mm in diameter embedded in loose, medium-dense, and dense dry sand is describe...

K Muthukrisnaiah

Papers

Experimental investigation of the uplift behaviour of circular plate anchors embedded in sand