Grain-size effect on uplift capacity of plate anchors in coarse granular soils

Abstract

This letter investigates the uplift capacity of plate anchors in granular soils. Simulations based on a discrete-element method are used to measure the uplift capacity of anchors of differing widths to embedment B/H and width to grain-size B/d ratios. Results confirm that the uplift capacity of anchors with a large B/d ratio is well described by existing models developed from continuum mechanics, with no grain-size effect. In contrast, results reveal a strong deviation from these models for anchors with relatively small B/d ratios. A semi-empirical model is introduced that captures this strong grain-size effect. This model is further supported by a micro-mechanical analysis, indicating that anchor uplift capacities are not only governed by a frustum mechanism predicted by continuum mechanics but also involve the mobilisation of grains surrounding this frustum. These results and model are particularly important to rationalise uplift capacities measured in small-scale experiments, typically involving small B/d ratios, and to safely upscale them to larger anchor size relevant to field applications.

Inertial drag in granular media

“…We refer to these regimes as quasistatic regime and inertial regime, respectively. As in [18], we observed that the quasi-static maximum drag is given by Eq. (1) with:…”

“…There is no interstitial fluid in the pores or long range interaction. Grain translation and rotation are simulated over time using a discrete element method similar to that introduced in [18,34,35]. The plate moving through the packing is made of grains that are similar to the free grains described above.…”

“…For vertical uplift loadings, the maximum drag F s is proportional to the vertical hydrostatic normal stress σ h at the object depth: reported values ranging from 1 to 100. Several studies have shown how this parameter varies with the internal friction angle φ of the packing [3,[7][8][9][10][11], the object shape [12][13][14][15][16] and the grain size [17][18][19]. The experimental method used to measure this parameter consists of uplifting the object at a constant and relatively slow velocity and monitoring the drag force during the uplift.…”

Three-Dimensional Simulations of Plate Anchor Pullout in Granular Materials

“…DEM models predict the emergent behavior of particulate assemblies (e.g., sands) based on simulation of independent particle behaviors. Athani et al (2017) used DEM to conduct two-dimensional simulations of plate anchors embedded into granular soils, specifically considering the influence of the ratio of embedment depth to anchor width and grain size on the holding capacity. They found that the anchor width to grain size ratio and internal friction angle influenced the uplift capacity of the plate anchor.…”

Size-dependent finite strain analysis of cavity expansion in frictional materials

“…It is generally observed that the smaller the structure size is, the stiffer soil response may be experienced. For example, greater tip resistances are often measured by smaller penetrometers in CPTs (Balachowski, 2007;Bolton et al, 1999;De Beer, 1963;Eid, 1987;Lima and Tumay, 1991;Wu and Ladjal, 2014), the shaft friction and toe resistance of piles tend to increase with decreases of the pile diameter (Balachowski, 2006;Chow, 1996;Lehane et al, 2005;Meyerhof, 1983;Turner and Kulhawy, 1994;Wernick, 1978), the normalised uplift bearing factor of earth anchors may increase with an decreasing ratio of anchor-to-soil grain size (Athani et al, 2017;Sakai et al, 1998;Tagaya et al, 1988). In general, it is found that the size effects existing in these non-dimensional results of the soil resistance closely relate to the ratio of the structure size over the grain size.…”