Lateral load capacity of underreamed piles - An analytical approach

Underreamed piles having one or more bulbs at specified locations along their depths have been extensively used in India to support a wide variety of structures in almost all types of soil strata. In many situations, these piles are also required to resist considerable amount of lateral loads besides vertical compressive and uplift loads. However, the behaviour of these piles under lateral loads has not been properly investigated and the present guidelines for their design under lateral loads are mainly empirical. In this paper, an analytical procedure has been suggested to predict the ultimate lateral load capacity of the underreamed piles incorporating the influence of (i) size of bulb, (ii) position of bulbs, (iii) number of bulbs, (iv) length to diameter ratio of piles and (v) type of soil strata. The point of rotation and ultimate lateral resistance of underreamed piles have been computed in terms of passive resistance along the shaft and additional resistance on the surface of bulb(s) as well as bearing on the bottom and uplift resistances on the top of bulb(s). Non-dimensional relationships and design coefficients have been established for the estimation of improvement in lateral load capacity of underreamed piles over straight shafted piles. The limiting lengths of the underreamed piles to decide them as either rigid or flexible under lateral loads have also been brought out. An illustrative example followed by comparison with a few reported field cases demonstrates the effectiveness of the developed approach.