An Analysis of the Influence of the Diameterto-Depth Ratio on the Bearing Capacity of Single and Group Bored Piles in Cohesive Soil

Abstract

The load-bearing capacity of both single and group piles is influenced by the diameter-to-depth ratio (D/L), especially in soil with high plasticity and saturation, such as clay. Selecting an appropriate D/L ratio is crucial for the foundation design, ensuring structural stability and efficiency. The objective of this study is to evaluate the impact of varying D/L ratios on the allowable bearing capacity of bored pile foundations, examine how these variations affect the pile group efficiency, and formulate technical recommendations for the optimal D/L range. A quantitative approach was performed using the Meyerhof (1956) empirical method, which was supported by borehole examination data and laboratory soil testing, with pile diameters ranging from 0.6 m to 2.0 m and depths from 10 m to 20 m, resulting in D/L ratios between 0.03 and 0.20. The findings indicate that a lower D/L ratio significantly increases the bearing capacity, particularly when the depth increases from 10 m to 12 m. There was an increase of over 50% for diameters of 1.5–2.0 m and over 70% for diameters of 0.6–1.2 m. The average efficiency ranged from 64% to 73%, and the optimal D/L ratio depended on the pile diameter.

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