• Geomechanics and Engineering
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• v.29 no.2
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• pp.183-192
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• 2022

Piled raft foundations are widely used and effective in supporting high-rise buildings around the world. In this study, a piled raft system was numerically simulated using PLAXIS 3D. The settlement comparison results between the actual building measurements and the three-dimensional (3D) numerical analysis, were in good agreement, indicating the usefulness of this approach for the evaluation of the feasibility of using a piled raft foundation in Ho Chi Minh City subsoil. The effects were investigated of the number of piles based on pile spacing, pile length, raft embedment on the settlement, load sharing, bending moments, and the shear force of the piled raft foundation in Ho Chi Minh City subsoil. The results indicated that with an increased number of piles, increased pile length, and embedding raft depth, the total and differential settlement decreased. The optimal design consisted of pile numbers of 60-70, corresponding to pile spacings is 5.5-6 times the pile diameter (D_p), in conjunction with a pile length-to-pile diameter ratio of 30. Furthermore, load sharing by the raft, by locating it in the second layer of stiff clay, could achieve 66% of the building load. The proposed model of piled raft foundations could reduce the total foundation cost by 49.61% compared to the conventional design. This research can assist practicing engineers in selecting pile and raft parameters in the design of piled raft foundations to produce an economical design for high-rise buildings in Ho Chi Minh City, Viet Nam, and around the world.

• Geomechanics and Engineering
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• v.32 no.4
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• pp.387-396
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• 2023

Ground subsidence, which is a current concern that affects piled raft foundations, has occurred at a high rate in Ho Chi Minh City, Viet Nam, due primarily to groundwater pumping for water supply. In this study, the groundwater level (GWL) change affect on a piled raft foundation was investigated based on the three-dimensional finite element method (3D-FEM) using the PLAXIS 3D software. The GWL change due to global groundwater pumping and dewatering were simulated in PLAXIS 3D based on the GWL reduction and consolidation. Settlement and the pile axial force of the piled raft foundation in Ho Chi Minh subsoil were investigated based on the actual design and the proposed optimal case. The actual design used the piled foundation concept, while the optimal case applied a pile spacing of 6D using a piled raft concept to reduce the number of piles, with little increased settlement. The results indicated that the settlement increased with the GWL reduction, caused by groundwater pumping and dewatering. The subsidence started to affect the piled raft foundation 2.5 years after construction for the actual design and after 3.4 years for the optimal case due to global groundwater pumping. The pile's axial force, which was affected by negative skin friction, increased during that time.