SETTLEMENT OF SAND DEPOSITS REINFORCED WITH GRANULAR MATERIAL UNDER VIBRATIONS

Abstract

Saturated loose sand deposits are known to be prone to liquefaction. Many a times, the strength deformation characteristics of loose sand deposits are improved by using techniques of ground improvement. One such technique is use of granular piles. However, the settlement characteristics of loose saturated sand deposits, reinforced with granular material walls are not fully known. The present investiga-tion is aimed to study the influence of granular material walls on the settlement characteristics of a saturated sand deposit under varying vibratory loads. Studies were carried out on a horizontal shake table. Samples of saturated sand were prepared at two different initial relative densities of 30% and 50% in a tank 105 cm x 60 cm x 61 cm high mounted on the shake table. Granular material walls of thickness, t of 5 cm, were installed at three different spacings of 2.5 t, 3.5 t and 5 t by specially fabricated installing device. Tests were conducted on the saturated sand samples, with and without granular walls, under steady state horizontal vibrations at different accelerations of 0.10 g, 0.15 g,, 0.20 g and 0.30 g at a constant frequency of 1.833 cps. Settlements of the deposit have been computed after 10, 20, 40 and 80 cycles of motion, in each test, by measuring the quantity of water collected on the surface of the sample. The test data has been analysed to bring out the influence of granular material walls on settlement characteristics of sand deposit subjected to vibrations. The analysis of data indicates that with increase in number of cycles, settlement of the composite deposit increases at all magnitudes of accelerations and spacings of granular material walls. However, the settlements are larger at higher accelera-tions and at larger spacings, keeping other parameters constant. The introduction of granular wall in the deposit brings down the settlement significantly. However, the magnitude of decrease in settlement of reinforced deposit to unreinforced deposit depends upon the spacing of the reinforcing granular material walls. Closer the spacing of the walls, 'larger is the reduction in settlement, keeping other parameters constant. Comparisons made with the data obtained by previous investigators reveals a common trend of variation of settlement with no. of cycles and accelerations • for uniform sand deposit. Based on the study suggestions for further study have also been made