Granular Pile Anchor Research Articles

Reducing heave of expansive clay beds through granular pile–anchor groups

The granular pile-anchor (GPA) foundation system, a more recent technique, has also been found to be quite successful in controlling heave of expansive clay beds. This paper presents experimental data obtained from laboratory-scale heave tests conducted on an unreinforced expansive clay bed (n = 0) and expansive clay beds reinforced by a single GPA (n = 1), twin GPAs (n = 2) and a group of GPAs laid in equilateral triangular pattern (n = 3). The thickness of all the test clay beds was 200 mm. Heave was monitored at different depths of clay beds as they were inundated. Ground heave (or surface heave) was also monitored at different radial distances (r) from the centre of the test tank. The unreinforced clay bed and the GPA-reinforced clay beds were identical with regard to thickness (H), placement water content (w%) and dry density (γd). Heave decreased at all depths of the clay beds as the number of the GPAs (n) increased. Furthermore, heave decreased with increasing depth (z) from the top of the clay beds. Heave was measured to be 56·5, 48, 28·5 and 24 mm at the top of the clay bed, respectively, for n = 0 (unreinforced expansive clay bed), n = 1, 2 and 3, indicating increased resistance to heave with increasing number of GPAs. The factor of safety of the GPA foundation system against uplift also increased with increasing number of GPAs.

Swell–consolidation characteristics of artificial sand clay mixes

Many remedial measures have been devised to lessen the damage caused by expansive soils. Physical alteration, chemical stabilization, innovative foundation techniques like belled piers, drilled piers, under-reamed piles and granular pile anchors are some of these remedial measures. Mixing a non swelling material such as gravel or sand to expansive soil is one of the methods of physical alteration. This paper presents experimental data on artificially prepared sand-clay mixes. Swell and consolidation characteristics of these artificially prepared sand-clay mixes were studied in one dimensional consolidometer. Fine sand content and fines content in the expansive soil were arbitrarily varied in the investigation. The fines content was varied as 425–300 μm and 150–75 μm, separated from the same expansive soil based on the grain size. Swell potential and swelling pressure decreased with increasing fine sand content but increased with increasing fines content. Coefficient of compressibility, coefficient of volume compressibility and compression index of the samples decreased initially up to a sand content of 15% and thereafter increased at higher sand contents.

Finite Element Modeling of Innovative Shallow Foundation System for Reactive Soils

Granular pile anchor foundations (GPAF) are a promising foundation system that can be used to mitigate the serious consequences of volumetric changes of reactive soils, both during expansion and shrinkage. This paper presents results from 3D finite element analyses, using PLAXIS software, undertaken on a typical double-story building constructed over a system of GPAF in a reactive soil. The study investigates the ability of the GPAF system to resist the forces induced by soil movement due to moisture variation, and the impact of this resistance on the straining actions affecting the superstructure. The results confirm the efficiency of the GPAF system in arresting the movement of the reactive soil, which in turn improves the structural responses of the building in terms of induced deformations, angular distortions and internal forces.

Field behaviour of granular pile-anchors in expansive soils

Different innovative foundation techniques have been suggested for controlling the detrimental volume change behaviour of expansive soils. The efficacy of a recent innovation in the form of granular pile-anchors in controlling heave of expansive clay beds and improving the engineering behaviour of the ambient soil has also been reported, based on results obtained from laboratory model tests. Before suggesting granular pileanchor foundations for installation in field practices, however, an in situ study of the behaviour of granular pile-anchors is also required as a support to the laboratory study. This paper describes an extensive field study of the behaviour of granular pile-anchor foundations of expansive clay beds. The field study was performed to study the rate of heave, reduction of heave and variation of heave with radial distance and with depth. Heave was found to be reduced by about 90% upon installation of granular pile-anchors. Final heave was reached in just about half the time required for final heave in the case of an unreinforced expansive clay bed. Improvement in the engineering behaviour of the ambient clay was studied through Proctor needle penetration tests and unconfined compression tests. It was found that a maximum increase of about 120% was observed in penetration resistance in the case of expansive clay beds reinforced with granular pileanchors.

Response of granular pile-anchors under compression

The granular pile anchor (GPA) is an innovative foundation technique, devised for mitigating heave of expansive clay beds and improving their engineering behaviour. It is a modification of the conventional granular pile wherein an anchor is provided in the pile to render it tension-resistant. This paper presents the results of a field-scale test programme conducted to study the response of anchors embedded in expansive clay beds. Plate load tests were conducted on unreinforced expansive clay beds and clay beds reinforced with GPAs to compare the compressive load response. The bulging pattern of the anchors was also studied. It was found from the field load tests that expansive clay beds reinforced with GPAs showed higher load-carrying capacity and improved compressive load response than unreinforced clay beds. Whereas the stress required to cause a settlement of 25 mm in the unreinforced expansive clay bed was 200 kN/m2, the clay bed reinforced with a GPA 1000 mm long and 150 mm in diameter (lgp/dgp=6·67) required 500 kN/m2to cause the same settlement, showing an improvement of 150%. Of the various single anchors with lgp/dgp values between 2.5 and 10, that of length 1000 mm and diameter 100 mm (lgp/dgp=10) showed the best load response when tested alone, resulting in an improvement of 440%. The maximum bulge diameter increased with increasing diameter and length of the GPA. The effect of GPA length is more pronounced in the increase in maximum bulge length than that of diameter.

Analysis and comparison of displacement granular pile anchors

Granular piles can resist only compressive and shear loads owing to their inherent nature. By a simple modification of providing a pedestal/geogrid at the bottom and attaching a cable to the same, they are made to resist pullout/uplift forces. This paper presents an analysis of granular pile anchor (GPA), considering it and the in situ soil to behave linearly and the in situ ground to be semi-infinite. A parametric study presents results in the form of variations of normalised shear stress, displacement influence coefficient and axial uplift force with depth with relative stiffness factor. Two methods for the estimation of deformation moduli of the GPA and the in situ soil are proposed. Based on the estimated values of the moduli, the displacements of GPA were estimated and the results compared with test results of Kumar (2002). The predicted displacements compare well with the measured ones.

Pullout Behavior of Granular Pile-Anchors in Expansive Clay Beds In Situ

Granular pile anchors (GPA) are one of the recent innovative foundation techniques devised for mitigating the problems posed by swelling clay beds. In a granular pile anchor, the footing is anchored to an anchor plate at the bottom of the granular pile. This makes the granular pile tension resistant and enables it to absorb the tensile force caused on the foundation by the swelling clay. An understanding of the amount of uplift resistance offered by the GPA is important in the design of granular pile-anchor foundations in field situations causing tensile forces on foundations, such as in expansive clay beds. This paper presents the results of a field-scale test program conducted to study the pullout response of GPAs embedded in expansive clay beds. Pullout load tests were conducted on GPAs of varying lengths and diameters. It was found from the field pullout load tests that granular pile anchors of larger surface area resulted in higher pullout capacity. Of the various single granular pile anchors with l∕...

Granular Pile Anchor Foundation (GPAF) System for Improving the Engineering Behavior of Expansive Clay Beds

Abstract Several innovative foundation techniques have been suggested for reducing the detrimental heave of foundations in expansive clays. This paper presents another innovative technique in the form of a granular pile anchor-foundation (GPAF) system for arresting heave and for improving the overall engineering behavior of expansive clay beds. In the GPAF system, the foundation is anchored at the bottom of the granular pile to an anchor plate through an anchor rod. As a result, heave of the foundation is reduced. The laboratory model tests using this new concept of the GPAF system revealed that the heave of the expansive clay beds was reduced by about 96 %. The development of final heave was faster in the case of the expansive clay beds reinforced with the GPAF system. The undrained strength of the clay surrounding the granular pile anchor improved by about 20 %. The tests on two-group granular pile anchors indicated that heave was reduced to a minimum value when the spacing between the granular pile anchors was kept at twice the pile diameter. The compressive load response of the expansive clay bed reinforced with granular pile anchors also improved. The pull-out load of the granular pile anchors increased with increasing diameter and the relative density of the pile.

Increasing pull-out capacity of granular pile anchors in expansive soils using base geosynthetics

Granular pile anchors are innovative and effective in resisting the uplift pressure exerted on the foundation by a swelling expansive soil. In a granular pile anchor, the foundation is anchored at the bottom of the granular pile to an anchor plate with the help of a mild steel rod. This renders the granular pile tension-resistant and enables it to offer resistance to the uplift force exerted on the foundation by the swelling soil. This resistance to uplift or pull-out load depends mainly upon the shear parameters of the pile-soil interface and the lateral swelling pressure of the soil, which confines the pile radially and prevents it from being uplifted. The resistance to uplift can be increased by placing a base geosynthetic above the anchor plate so that it forms an integral part of the granular pile anchor. The increase in resistance is due to the friction mobilized between the geosynthetic and the confining media when the uplift load acts on the pile and the geosynthetic moves along with the pile. Hence it depends on the friction between the geosynthetic and the confining media and the area and stiffness of the geosynthetic. This paper discusses the effects of these parameters on pull-out load, rate of heave, and relative ground movement near the pile surface.Key words: expansive soil, granular pile anchor, base geosynthetic, ground movement, rate of heave, pull-out load.

Increasing pull-out capacity of granular pile anchors in expansive soils using base geosynthetics

Increasing pull-out capacity of granular pile anchors in expansive soils using base geosynthetics