Effect of Pile Section Shape on Bearing Capacity under Dry and Saturated Conditions

<ns7:p>Background Gypseous soil exhibits significant collapsibility when saturated due to the dissolution of gypsum bonds, resulting in substantial reductions in shear strength and settlement problems. Understanding the influence of pile morphology on shaft resistance under these conditions is essential for constructing foundations in collapsible soils. The load-settlement behavior of the pile foundation can be established through an empirical pile loading test after preparing the soil and installing the piles in the model. Methods A physical model measuring 37×80×80 cm was constructed to assess the performance of three aluminum floating piles (square, circular, and rectangular) with identical cross-sectional areas, embedded in loose gypseous soil containing 58% gypsum and exhibiting a relative density of 30%. Pile load experiments with a constant rate of penetration (1 mm/min) were conducted under both dry and saturated conditions. Twelve methods were employed to determine the ultimate bearing capacity, including Davisson, De Beer, Brinch Hansen's 80% and 90%, Chin-Kondner, Decourt, and ASTM D-1143. Results Soaking caused a significant decrease in capacity; the ultimate load dropped by approximately 45-55% for the square pile, 55-60% for the rectangular pile, and 60-65% for the circular pile, depending on the interpretation method used. The Chin-Kondner method is notable among interpretation methods, providing the most consistent and accurate estimates of ultimate capacity in both dry and saturated conditions, with the lowest variability across shapes (coefficient of variability &lt; 10%). Conclusions The shape of piles significantly influences load transfer in gypseous soils, especially when saturated. Square piles offer greater reliability and are less prone to strength loss due to collapse. In collapsible gypseous soils with high gypsum content, using square sections and Chin-Kondner interpretation is recommended for more accurate pile foundation design. Davisson's method provided the most conservative estimate of pile capacity among the twelve methods, particularly when saturated.</ns7:p>