Load deflection prediction for laterally loaded piles in layered soils

Abstract

The present investigation has been conducted to study the load-displacement response and horizontal load capacity of vertical unrestrained piles subjected to lateral load using a finite difference method. Generally unifonn soil deposits are not found in nature and the piles are embedded in layered soils. The effect of two-layer cohesive soil system in the engineering behaviour of a laterally loaded pile is investigated analytically. Pile deflection often governs the design of laterally loaded piles, as such the possibility of reducing the pile head deflection using a stiff layer near the ground level has been investigated For piles subjected to a given horizontal load the deflection at pile head, is smaller for piles embedded in stiff soils than piles embedded in soft soils. Therefore the allowable capacity [the allowable horizontal load capacity according to BNBC (1993) is half of the horizontal load which produces I inch deflection at pile head] of a pile is greater if the . pile is embedded in stiff soil. However the maximum moment corresponding to allowable load increases with the increase of soil modulus. The reason behind this is the increase in allowable horizontal capacity in stiff soil. Higher horizontal load produces higher , maximum moment. To attain higher allowable capacity of a pile embedded in a better soil the reinforcement of the pile should be increased according to the value of maximum moment. The horizontal capacity and corresponding moment of a pile embedded in soft soil and tip resting on a stiff soil is similar to a pile embedded in a uniform soil having properties of the top soft layer. When a pile is subjected to a given horizontal load, the presence of a thin stiff layer at ground swface reduces the deflections and moments to a great extent. That is the horizontal capacity of a vertical pile can be increased significantly by replacing the upper soil with a thin stiff layer. The horizontal capacity depends on the modulus of subgrade reaction and thickness of the top stiff layer. When a pile is subjected to a given horizontal load the deflection of piles decreases with the increase of thickness of the top stiff layer. However effect of thickness on the values of maximum moment is negligible.