Effect of Screw Piles Spacing on Group Compressive Capacity in Soft Clay

Abstract

Screw piles are considered as one of the solutions in different complications projects. Performance of circular screw piles group subjected to compressive load and embedded in two layers; soft clay and compacted sandy soils is investigated in this study. The thickness of two layers soft clay and sand soil is 250 mm and 350 mm respectively which are prepared after compacted to sub layers in the container. By choosing different slenderness ratios of L/ D 25, 32 and 39, many model tests were achieved on screw piles group. Single and double helix plates were used in screw piles with constant of helix spacing 60mm. A square pattern of screw piles group with different spacing between piles (1.5Dh, 3Dh, 4.5Dh), where Dh is diameter of helix is adopted in this study. The results of this study showed that the ultimate capacity of piles group was increased by increasing the spacing between the piles until reached spacing 3Dh then begin to decrease when piles extended in sandy soil, while in soft clay the ultimate capacity increase with decrease piles spacing in two cases single and double helix. The increasing percentages for pile spacing 3Dh and 4.5Dh are (55.3% and 39.4%) respectively for L/D ratio 32 and (27.2% and 23.8%) respectively for L/D ratio 39. Also, it is recommended to use screw piles group in case of deep layer of soft clay laying on sandy layer due to high increase in compressive resistance capacity of group when extended in sandy layer.