FINITE ELEMENT ANALYSIS OF DIFFERENTIAL SETTLEMENT IN CEMENT FLY ASH GRAVEL PILE COMPOSITE FOUNDATIONS ON SATURATED TAILINGS USING PLAXIS 3D

Abstract

This study presents a finite element analysis of Cement Fly-ash Gravel (CFG) pile composite foundations under saturated soil conditions, using PLAXIS 3D. The research aimed to develop a representative numerical model, simulate staged surface loading, and 
validate the results against field and laboratory data reported by Lai et al. (2016). The soil profile was modelled with four distinct layers subgrade fill, gravel cushion, saturated tailings sand, and loess foundation while the groundwater table was assigned at 6.5 m 
depth to replicate in-situ conditions. A uniform grid of 35 CFG piles, each 0.5 m in diameter and embedded to 15 m depth, was incorporated into the model, with mesh refinement applied around the pile group to capture stress transfer and settlement behavior accurately. Staged surface loadings of 50, 100, and 150 kN/m² were applied to evaluate total and differential settlement responses. The results indicated progressive increases in settlement with higher loading stages, accompanied by lateral expansion of settlement zones. Time settlement curves demonstrated coupled consolidation behavior, with primary settlement occurring rapidly and secondary consolidation developing over time. Differential settlement analysis confirmed the effectiveness of CFG piles in controlling deformation between reinforced and unreinforced zones. Validation against field data showed close agreement, with simulated settlements (2.1 mm, 4.9 mm, and 8.5 mm) falling within the ranges reported by Lai et al. (2016). The findings confirm that CFG piles significantly enhance the load-bearing capacity of soft saturated soils and that the PLAXIS 3D model provides a reliable tool for analysing composite foundation performance.