Numerical Study of Pile Raft Foundation Behavior Under Vertical Loads and Large Moments

• Published in: Geotechnical and geological engineering 2024-01, Vol.42 (1), p.97-119
• Main Authors: Al-Ne’aimi, Rafi’ M. Sulaiman, Hussein, Khalid Q.
• Format: Article
• Language: English
• Subjects: Bending moments; Civil Engineering; Deformation; Earth and Environmental Science; Earth Sciences; Finite element method; Geotechnical Engineering & Applied Earth Sciences; Groundwater; Hydrogeology; Load sharing; Loads (forces); Mathematical analysis; Mechanical properties; Multistory buildings; Original Paper; Parametric analysis; Pile foundations; Pile groups; Piles; Raft foundations; Rafting; Rafts; Ratios; Slenderness ratio; Soils; Subsoils; Terrestrial Pollution; Vertical loads; Waste Management/Waste Technology
• ISSN: 0960-3182; 1573-1529
• DOI: 10.1007/s10706-023-02558-7

Based on PLAXIS 3D finite element software, a 34-floor multi-story building piling group foundation under vertical loads and large moments is examined. It comprises seven different strata with different properties, with groundwater located 19.6 m below ground level. In drained situations, the soil is modeled as hardening soil, while piles are modeled as embedded beams. The study involved extensive parametric analysis. It includes pile spacing-diameter ratios, number of piles, pile slenderness ratios, square or triangular pile layout patterns with equal or variable pile length, raft, pile, and subsoil load sharing, pile modeling as an embedded or volume pile, gap effects between rafts and subsoils, and type of pile connections to evaluate their effects on rectangular unpiled and pile raft foundations in planning under large moments and vertical loads. Analysis results show volume piles yield less raft settlement and pile moment than embedded piles. Further, moment load effects increased raft bending moments by 2.2, 5.4, and 6.1 and absorbed loads by 1.4, 1.7, and 2.2 ratios for 24, 40, and 60 pile groups, respectively. In square and triangle pile configurations, at specified pile spacing, raft bending moments decrease with pile length. In contrast, it increases as pile spacing decreases. Thus, s/dpile = 4 gives the highest bending moment, with its variation along pile lengths depending on the pile head's hinge or fixation. A 0.2-m gap between raft and subsoil allows piles to absorb 71% of the load and rafts 29%, compared to 65% for piles, 29% for rafts, and 6% for subsoil without a gap.