BEHAVIOUR OF SAND DEPOSIT TREATED WITH MINIGROUTED PILES

Abstract

The present study refers to 25mm diameter minigrouted model piles installed into loose sand (R.D. = 26.3%) deposit and cast through an aluminium casing pipe with a 60° wooden conical shoe. The pile is provided with a 4 mm diameter reinforcing mild steel rod and grouted through cement sand grout which is made to flow under gravity only. The casing pipe is gradually' withdrawn after placing of cement sand grout, and while withdrawing the casing additiOnal cement sand grout was poured. In the study, the following aspects have been studied related to minigrouted piles : (i) effect of length to diameter variation of minigrouted piles an load (compressive) settlement behaviour. Comparative load-settlement behaviour of minigrouted pile with driven pile is also observed. (ii) comparative study of load settlement behaviour and group action of free standing and piled foundation. (iii) effect of length and spacing of minigrouted piles on strength-deformation characteristics of loose sand, considering the minigrouted piles as vertical in-situ reinforcing elements. All the tests have been carried out in the laboratory. On the basis of the test data and its analysis it has been observed that the ultimate capacity of single and groups of four minigrouted piles increase with increase in pile length. At a spacing of two times the pile diameter, the free standing and piled foundations of the minigrouted piles have almost the same ultimate capacity; while ultimate capacity of piled foundation is significantly higher than the corresponding free standing pile group as the spacing is increased to four to six times the pile diameter. Group efficiency of free standing minigrouted pile groups is observed to have increased with decrease of spacing, while group efficiency of piled foundations increase with increase in spacing. As vertical reinforcing elements, the minigrouted piles contribute significantly in improving the strength-deformation behaviour of loose sand deposit.