Abstract:
Abstract: This paper presents the experimental investigations on the behaviour of a group of single, double and
triple helical screw anchors embedded vertically at the same level in sand. The tests were carried out on one, two,
three and four numbers of anchors in sand for different depths of embedment keeping shallow and deep mode of
behaviour in mind. The testing program included 48 tests conducted on three model anchors installed in sand whose
density kept constant throughout the tests. It was observed that the ultimate pullout load varied significantly with
the installation depth of the anchor and the number of anchors. The apparent coefficient of friction (f*) between
anchor and soil was also calculated based on the test results. It was found that the apparent coefficient of friction
varies between 1.02 and 4.76 for 1, 2, 3 and 4 numbers of single, double and triple helical screw anchors. Plate load
tests conducted on model soil showed that the value of ф increases from 35o for virgin soil to 48o for soil with four
double screw helical anchors. The graphs of ultimate pullout capacity of a group of two, three and four no. of
anchors with respect to one anchor were plotted and design equations have been proposed correlating them. Based
on these findings, it has been concluded that the load-displacement relationships for all groups can be reduced to a
common curve. A 3-D finite element model, PLAXIS, was used to confirm the results obtained from laboratory
tests and the agreement is excellent.
