Research on Ultimate Behavior of Steel Group Piles Based on Lateral Loading Tests

摘要

In order to evaluate the maximum horizontal capacity of pile foundation against large earthquakes, it is extremelyrnimportant for group piles to clarify the relationship between the lateral load and the lateral displacement until the ultimaternstate. This paper describes the outline and the results on the lateral loading tests for steel pile groups in large deformation.rnThe numerical simulations on the tests were also performed. The test specimens for the group piles were composed of two,rnthree, four, six and nine piles rigidly connected with reinforced concrete foundations. The behaviors of the group piles inrnlarge deformation, the strain distributions of each pile, the share of the total force to each pile, the estimated coefficients ofrnhorizontal subgrade reaction and group pile effects on both the initial stiffness and the maximum horizontal capacity wererndiscussed in details. It was recognized from the test results that the peak of the pile strain distribution in the soil appearsrnaround 1.5 m and 2.0 m below the ground surface for all loading steps. The average load and horizontal displacementrnrelationships as well as the initial stiffness and horizontal displacement relationships could be clearly clarified between thernsingle pile and the group pile. It was also found that the maximum horizontal capacity per pile was constant, about 0.8,rnregardless of the number of the piles. Furthermore no significant difference was observed for the maximum horizontalrncapacities between the cyclic loading tests and monotonic loading tests. Numerical simulations on the tests were performedrnbased on the method of Specifications for Highway Bridges in Japan I~1. For the single pile specimens, using 4 times largerrnmaximum capacity correction coefficient than the value computed by the Specifications, the numerical results agreed wellrnwith the test results. For the group pile specimens, the pile group effect and the influence of the pile pullout on both therninitial stiffness and the maximum horizontal capacity were numerically investigated. It was found that the group pile effectrncould be evaluated by correcting the upper limit of subgrade reaction for the single pile and the influence of the pile pulloutrnon the maximum horizontal capacity could be estimated to take the non-linearity of the axial stiffness of the pile-soil systemrninto consideration.