Dimensionless Reaction Coefficients for Embedded Piled Raft Foundations in Soft Clays under Vertical Loads

Abstract

Although three-dimensional finite-element analysis has been introduced to foundation design for years, simplified computer-based calculations based on the spring analogy of soils and structural elements are also frequently used in many engineering projects. Using coefficients of subgrade reactions and pile stiffness is a straightforward way to design and analyze a piled raft foundation. This paper discusses the determination of the coefficients of pile reactions for embedded piled raft foundations in soft clays subjected to vertically uniform loads through a series of finite-element analyses. The geologic property was assumed to be composed of homogeneous soft clays with the shear-wave velocities varying at 100–140 m/s. The foundations with a square raft ranging from 16 to 36 m and embedment depths of 8 and 12 m were studied. Load intensity approximating 1.5 times the excavated soil pressures was considered where the maximum uniform load was applied to the foundation. The foundation settlements and reactions of the piles were obtained first from a three-dimensional finite-element analysis. For design convenience, the dimensionless pile displacements, pile reactions, and coefficients of pile reactions were developed and presented in plots. The embedment depth-to-raft size ratio, pile slenderness ratio, and pile-to-pile spacing distance-to-pile diameter ratio were examined to find their optimized correlation. Finally, a design example was given to verify the proposed suggestions. We conclude that the proposed method can be an alternative to the piled raft foundation design.