Role of special feature in side resistance of a model steel pile

Abstract

The steel piles have the advantages of being robust, light to handle, capable of carrying high compressive and tensile loads when driven to a varied stratum, capable of being driven to a deep level to reach a bearing stratum and to develop a high frictional resistance, although, their cost per metre run is relatively high compared with precast concrete piles. The frictional resistance of pile is known as side resistance of pile in the literatures on piles.The main contribution of this work to the body of knowledge is introducing invented special feature which resulted in increase in side resistance of a model steel pile and that, too, with almost minimum disturbance of the soil (air and sun dried sand has been considered in the present wok) while introducing a special feature. Described herein is a slotted holes, mesh-filtered; mesh-plugged steel pile (patented by Kumar and Trivedi, 2013a, b) having a pattern of regular or zig-zag orthogonal spikes (spiking out from the lateral surface of the pile in orthogonal or in inclined direction at varied angles) that can be used in a variety of soil conditions as well as in apparatus and associated methods. In saturated and submerged soils (pore pressure measurements are not considered in the present thesis), slotted holes helps in increase of effective stresses in soil-steel pile surface interaction by draining out extra build-up of pore water pressure in the immediate and longer run of time under the structural loading pressure. Flow of water at higher potential will not be outwards from the lateral surface of the steel pile, but, inwards to inside of steel pile through slotted holes of steel pile. These slotted holes are on the entire lateral surface of steel pile except conical surface at the bottom of steel pile. It reduces the chances of build-up of excess pore water pressure for liquefaction of soils in the radial stressed zones of interaction of soil-steel pile. As effective stresses are directly proportional to shear strength of the soil mass so, any reduction of pore water pressure through slotted holes of mesh- filtered steel pile or lead to increase of side-resistance on soil-steel pile surfaces. The side-resistance which is a part of load carrying capacity of steel piles tend to increase to a large extent due to increase of effective stresses on soil-steel pile interface. This is further increased due to presence of slotted holes on the outer lateral surface of the steel pile which not only drains out pore water to inside of the steel pile through mesh filter slotted holes, mesh-filtered; mesh-plugged steel pile but also increase frictional forces due to roughness induced on the surface. Further, this work considered the effect of orthogonal as well as inclined spikes, which in totality due to interlocking arrangement of spikes with the soil, lead to increase in side resistance. The whole arrangement of providing slotted holes, spikes along with doubly sloped circular fins on lateral surface at regular intervals, increased the side resistance of the steel pile, increased the density of adjoining soil mass, and consolidated the soft soil, thereby, improving the safety factor for designed loads of super-structures, making it usable for construction of deep foundation unit. The dewatering unit (not discussed in this thesis) as patented by Kumar and Trivedi (2013 a, b)is attached through a pipe from the top-most slotted hole of the steel pile which act to remove the drained out water collected in-side the conical-tip of slotted hole-cum-spiked steel pile. This special feature of slotted holes-cum-spikes was provided throughout the vertical lateral surface of the model steel pile. This work has introduced an improvement factor, ξ, which numerically captures the potential increase in the load carrying capacity of a model steel pile in the context of in side resistance due to special feature i.e. slotted holes, spikes and fins. The side resistance increased due to length of spike, diameter of spike and inclination of spike (maximum at 60º in the direction of application of force). The following parameters were kept fixed w.r.t. number of spikes, spacing between the spikes in a row, vertical spacing between the spikes, pattern of the spikes (i.e. zig-zag or regular pattern), shape of the spikes (cylindrical), taper of the spikes (0º in the present work because of cylindrical spikes), surface roughness of the spikes in the form of threaded pattern on the surface on the spikes coming through welded nuts. The spike inclination, β, w. r. t. vertical plumb line is defined as any angle at a point on a model steel pile between outside upward plain surface of a model steel pile and inclined spike and varies in the range 0º< β <180º for the vertical direction at specified constant angular intervals of 30º, where β=30º, 60º, 90º, 120º and 150º) were considered in increasing order in the clockwise direction when spikes were to be seen on the right of the vertical axis of upright direction of the model steel pile. There was an increase in side-resistance of a model steel pile which leads to significant increase of load carrying capacity of the model steel pile. Providing a special feature such as, whole arrangement of providing slotted holes, spikes and that, too, at various inclinations from 30º to 150º, along with doubly sloped circular fins on lateral surface at regular intervals, on a model steel pile, not only increased side resistance but also increased load carrying capacity of a model steel pile. It made the specially featured i.e. slotted-cum-spiked-cum-doubly sloped finned (facing vertically upwards) model steel pile is not only a user-friendly but an economical one also (due to lesser overall cost of per meter run of a special featured steel pile when compared for an equivalent load carrying capacity of per meter run of a plain model steel pile).