Abstract: The pile-soil interactions are constrained by the pile cap in pile groups with cap, while mutually independent in pile groups without cap. The mechanism of negative skin friction variation in pile groups with cap is analyzed briefly. Under the condition of groundwater level falling, the negative skin friction behaviors of pile groups with cap are analyzed by three-dimensional finite element method. The analytical results show that the negative skin friction of pile groups with cap is generally similar to that of a single pile: as the loads on cap increasing, the neutral point moves up, additional settlement increases and the downdrag decreases, though there are differences between piles in different positions. The constraints of settlement of piles in various positions by the cap are significant when the load is not large; so that the neutral point of piles are almost coincident. As the load increasing, the deformation of the cap increases and the neutral points of piles become more various, lowest for the corner pile, second for the perimeter pile and highest for the center pile. The negative skin friction of each pile in pile groups with cap mobilizes differently along the depth. It is mobilized most fully for the corner pile, second for the perimeter pile and least for the center pile.

Key words: pile groups with cap, groundwater level falling, negative skin friction, behavior, finite element method