Ultimate Soil Pressures for Pile Groups in Soft Clay Subjected to Lateral Soil Movements-Article

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The study investigated ultimate soil pressures on pile groups subjected to lateral soil movement in soft clay. Laboratory model tests used rigid, 16 mm diameter piles with pinned heads and tips, embedded in clay with an average undrained shear strength of about 24 kPa. Tests examined groups of 2, 3, 4, 6, and 9 piles, with different arrangements and spacings of 3 or 6 pile diameters.<br /><br />Single-pile tests produced an ultimate soil pressure of approximately 11 times the undrained shear strength, consistent with earlier studies. In groups, individual pile pressures were generally lower than for an isolated pile. Front-row piles typically had group factors close to 1, while middle- and back-row piles experienced substantially greater reductions, reflecting soil-pile interaction and shielding by piles ahead of them. Individual-pile group factors increased with wider spacing and varied considerably with pile position and arrangement.<br /><br />For the group as a whole, the group factor generally decreased as the number of piles increased and increased with pile spacing. Groups with the same number of piles showed no significant difference in overall group factor solely due to arrangement, although arrangement strongly affected the pressure on individual piles. A two-pile row spaced at 6 diameters behaved nearly like two isolated piles.<br /><br />The authors note that these findings come from model tests under specific soil and pile conditions. Further research is needed to assess other soil types, pile fixities, scales, and group behavior at specified displacements rather than only at ultimate pressure.

Keywords

pile groups

lateral soil movement

soft clay

ultimate soil pressure

undrained shear strength

pile-soil interaction

group factor

pile spacing

laboratory model tests

soil shielding