Response of granular pile-anchors under compression

Abstract

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.