RESPONS OF SCREW PILE GROUP TO LATERAL CYCLIC LOAD EMBEDDED IN TWO CLAY LAYERS

Abstract

ABSTRACT Screw piles or helical piles are deep foundation elements used to resist forces exerted by tension, axial compression, and lateral loading. Despite the great development in the manufacture of the helical pile and the development of their use, especially in transmission towers and wind turbines, there is a little research on their lateral behavior. In this study, the investigation of the behavior of screw pile group (1×2), (2×1), and (2×2) with the pile spacing to the helix diameter ratio (S/Dh =1.5, 3, and 4.5) having a diameter (10 mm) and different embedded length to shaft diameter ratio (L/d = 40, 33, and 26) by using single and double helix is carried out. In addition, ordinary pile group (2x2) with the same three spacing's between the screw piles and have the same shaft diameter of screw piles and with embedded length (L/d= 40) is also investigated. The entire pile group embedded in experimental model content soft clay in the top with thickness equal to 200 mm and extends to stiff clay with thickness 450 mm and tests under the influence of pure two way symmetrical lateral cyclic load with environmental frequency of (0.2 Hz). VI In this work, different parameters has been studied such as the effect of configuration and spacing between piles group, the effect of number of helix in screw pile and compare with ordinary pile, and the effect of embedded length for screw pile under the influence of different level in cyclic load ratio (CLR) and by use number of cyclic equal to 100. The results showed that increasing the distance between the piles had a great effect on increasing the lateral resistance. For the same embedded length the increase of screw pile spacing in the all groups model from (1.5 Dh) to (3 and 4.5 Dh) increases the lateral resistance about (25-39)% and (49-64)% respectively at cyclic load ratio of 80%. Also, the arrangement of the same piles number in the group affects the lateral resistance; the group (2×1) gave a lateral resistance more than the group (1×2) about 11% for single helix and about 6% for a double helix. From the results also found that the screw piles performance is better than ordinary piles under lateral cyclic load impact, as the ordinary piles gave lateral displacement more than the screw piles with a ratio of (20-88) % at different cyclic load ratio, and for the same spacing and configuration the screw pile with double helix gives an increase in lateral resistance about (4- 19) % from the single helix. As well, the results showed that, reducing the embedded length of the screw piles has a significant effect on increasing the lateral displacement, as reducing the embedded length by 17.5% leads to an increase in lateral displacement by a rate ranging between (14-50) % at low cyclic load ratios (CLR= 20 and 40) %, while it increases by rates ranging between (50-150) % at a high cyclic load ratio (CLR= 50, 60, and 80) %.