Comparison of Numerical Methods for Piled Raft Foundations

Abstract

The methodologies used to calculate piled raft foundations are normally more complex than conventional foundations due to the large number of variables involved in the problem. In the conventional block, the interaction variables considered are only between the pile and the soil. In the piled raft, all the interaction effects must be considered, as follows: plate-soil, plate-piles and piles-soil, simultaneously. The Finite Element Method (FEM) has proven to be a useful tool in analyzing these types of problems. This study aims at assessing the behavior of piled rafts using the Cesar-LCPC numerical tool, version 4.0, which is based on the finite element method. Literature cases of rafts supported by 9, 15 and 16 piles were analyzed. The results obtained were compared with analysis methods presented in the bibliography. The following parameters were assessed: relative spacing (S/D), relative length (L/D), relative stiffness between piles and the soil (KPS), and settlement of piles and the raft. The spacing between piles has a significant influence on load distribution between piles and the raft. Very small spacing provides stiffness to the foundation, which then functions as a conventional pile foundation, in which only the piles absorb the load from the superstructure. The larger the L/D ratio, the lower the settlement and for a given modulus of elasticity of the pile, the increase in relative stiffness (KPS) causes an increase in settlement. In all analyses, the data obtained corroborated the results presented by other methods published in the literature.

Behavior of Defective Cast in Place Piles

“…Various studies have been conducted on the subject of defective piles. In general, however, these studies are mainly of theoretical, numerical or associated with experiments on reducedscale models studies, for example the studies of Makarchian and Poulos (199 4), Xu (2000), Novak et al (2005), Cunha et al (2010), and Freitas Neto et al (2013, 2020.…”

Numerical Simulation of Combined Pile Raft Foundation under Horizontal Loading

“…Combined Pile raft foundation (CPRF) term was coined by Katzenbach et al [4] which consists of pile, raft and subsoil as the load bearing elements. After idealizing the various soil profile for combined pile raft foundation, Poulos [5,6] concluded that a uniform soil profile of relatively stiff clay or dense sand would be the favorable situations for CPRF. Analysis techniques for pile group was first developed by Butterfield and Banerjee [7] as mentioned by Randolph [8], then the analysis technique was developed for pile raft foundation by Davis and Poulos [9] and further simplified analysis methods were also developed by Hooper [10], Sommer et al [11], Franke at al.…”

Behavioral Evaluation of Small-Diameter Defective and Intact Bored Piles Subjected to Axial Compression

“…Several studies have been conducted on blocks with defective piles; however, these studies are exclusively theoretical, numerical or associated with experiments on reduced-scale models. Among the most significant studies are those of Makarchian & Poulos (1994), Abdrabbo (1997), Xu (2000), Prakoso & Kulhawy (2001), Petek et al (2002), Kong & Zhang (2004), Novak et al (2005), Zhang & Wong (2007), Cordeiro (2007), Cunha et al (2007), Cunha et al (2010), Chung et al (2010), Leung et al (2010), Omeman (2012) and Freitas Neto et al (2013). Full-scale experimental studies are rare, especially those including pile defects.…”