PARAMATRIC STUDY OF VERTICAL AND BATTER PILE GROUPS UNDER THE UPLIFT LOAD IN SAND

Pile foundations are frequently used to transmit the superstructure loads to deeper strata if the subsurface soil is of inadequate strength. In cohesionless soils, the shaft resistance is an important source of pile capacity under axial loading, especially when the pile is subjected to uplift loading. Foundations of structures like transmission line towers, tall chimneys, offshore structures, jetty structures, Mooring system, submerged platform, etc. are subjected to overturning moments due to wind load, seismic effect, wave load, ship impacts, etc. For foundations in such structures, generally a combination of vertical and batter piles are used. Batter piles provide a much stiffer resistance to horizontal and inclined loads than would be possible with vertical piles. Experimental model tests have been conducted on pile groups embedded in sandy soil and subjected to pure axial uplift loading. In the present study an attempt has been made to estimate the uplift capacity of combined vertical and batter pile groups embedded in sandy soil of uniform relative density of 63%. The model piles used in this investigation are mild steel solid shaft. The pile groups consisting of 2x2 piles (2 vertical and 2 batter piles), c/c spacing is 3d (d is diameter of pile) and slenderness ratio (L/d) of 8, 12 and 16. In pile groups the angle of batter piles is varied as 10˚, 20˚, 30˚, 35˚ and 40˚. The influences of pile embedment depth, batter angle on the uplift capacity of piles are investigated. Results indicate that the uplift capacity of pile group increases about 2 to 2.5 times with increase of slenderness ratio from 8 to 12 and 12 to 16. The pull out capacity of these pile groups increases with increasing the batter angle up to the 35˚ and after that it reduces drastically.