Effect of asymmetry pile’s length on piled raft foundation system under earthquake load

Abstract

Abstract In light of the global development of construction, particularly tall buildings and skyscrapers, researchers have spent years studying and developing types of foundations that are suitable in terms of endurance in heavily loaded and economic terms, particularly in weak soils under dynamic loading. In the event of high-rise buildings or weak soil media, the piled-raft foundation system is considered an efficient system that fits the design criteria. Several factors influence the performance of the piled-raft foundation system, among pile length, which was taken into account in the numerical study using the Plaxis 3D program. Four pile length scenarios are explored using 28 piles in a pattern 4 × 7 group with a rectangular raft of 10 × 20 and 1.5 m thickness. The central piles 3 × 2 are all the same length of 12 m or 20 m, but the others vary to 10 m, 8 m, and 6 m. In addition to the El-Centro seismic loading, a uniform static load of 300 kN/m2 was applied to the weak C- ϕ soil. The results reveal that the length of the asymmetric pile has a substantial effect on the behavior of the piled raft foundation. The symmetry pile’s length has greater static and dynamic load sharing than the asymmetry pile’s length. Static load sharing is greater than dynamic load sharing in all models, with static sharing values of 73.2% for the uniform pile’s length group L12 + 12 and 68.82%, 63.33%, and 55.96% for the asymmetry groups L12 + 10, L12 + 8, and L12 + 6, respectively. With decreasing external pile length, the dynamic load sharing values under 0.1 g intensity are 72.3%, 67.4%, 60.6%, and 55.2%, respectively. When the seismic intensity increases to 0.2 g, these values decrease by around 3%, and so on for 0.3 g. Vertical settlement increases as the exterior pile length decreases and the seismic energy increases. The maximum settlement values for L12 + 12, L12 + 10, L12 + 8, and L12 + 6 at 0.3 g seismic intensity are 137.9, 158.1, 169.7, and 171 mm, respectively. The differential settlement caused by seismic load is greater in the case of the asymmetry pile length group (L12 + 10). The differential settling increases with increasing seismic intensity in all models. The maximum lateral displacement increases as seismic intensity increases, whereas the length of the pile has no impact on the lateral displacement. When compared to a 12-m pile length, a 20-m pile will have a larger load sharing and less settlement, but exhibit a similar trend. The external pile’s length has a slight effect on the factor of safety where the reduction under the seismic load by about 18% for the both symmetry and asymmetry cases respectively in comparison to static case.

Keywords

• Piled-raft foundation system
• Seismic load
• Pile’s length
• Horizontal seismic coefficient