An Experimental Study on Bearing Capacity of Steel Open Ended Pipe Pile with Exterior Wings Under Compression Load

The present study investigates the increasing in ultimate pile capacity and studied the soil plugging phenomenon and the incremental filing ratio for a modified type of open-ended pipe pile. The modification performed by adding steel plates as wings with special dimensions and fixed on the exterior face of the pipe pile wall at a location near the pile tip with specified dimensions. Five wings have used for each new model of pipe pile. These wings distributed in equal spacing along with the circumstances of the exterior wall of the open-ended pipe piles. The efficiency of the proposed type studied by modelling and manufacturing twelve piles (40 mm diameter, L/D = 15 and L/D = 20). Complete setup manufactured for installing and loading the piles in a constant rate of penetration. The model piles installed in poorly graded loose dry sand. The obtained results show that the proposed type has a higher ultimate bearing capacity. The percentage of increase reaches more than 50%. The development of the load capacity is due to the three effects. The first is increases of the exterior shaft friction, and the second effect creates a new end-bearing capacity under the constrained soil between the exterior wings. And the third effect is developing the end-bearing capacity under the soil plug inside open-ended pipe pile due to the first and the second effects.

     

Estimation of bearing capacity of open-ended model piles in sand

The plugging of pipe piles is an important phenomenon, which is not adequately accounted for in the current design recommendations. An open-ended pipe pile is said to be plugged when the soil inside the pile moves down with the pile, resulting in the pile becoming effectively closed-ended. Plugging is believed to result in an increase in the horizontal stresses between the pile and the surrounding soil, which results in an increase in skin friction. A total number of 60 model pile tests are carried out to investigate the behavior of plugs on the pile load capacity and the effects of plug removal. Different parameters are considered, such as pile diameter–to–length ratio, types of installation in sands of different densities, and removal of the plug in three stages (50, 75, and 100 %) with respect to the length of plug. The changes in the soil plug length and incremental filling ratio (IFR) with the penetration depth during pile driving show that the open-ended piles are partially plugged from the outset of the pile driving. The pile reached a fully plugged state for pressed piles in loose and medium sand and partially plugged (IFR = 10 %) in dense sand. For driven piles, the IFR is about 30 % in loose sand, 20 % in medium sand, and 30 % in dense sand. The pile load capacity increases with increases in the length of the plug length ratio (PLR). The rate of increase in the value of the pile load capacity with PLR is greater in dense sand than in medium and loose sand. Based on test results, new empirical relation for the estimation of the load carrying capacity of open-ended piles based on the IFR is proposed.