Experimental Study of the Bearing Characteristics of a Novel Energy-Saving and Environmentally Friendly Pile: Drilling with Prestressed Concrete Pipe Cased Piles

Abstract

Drilling with prestressed concrete pipe cased piles (DPC piles) introduces a novel methodology in the domains of energy conservation and environmental protection, utilizing nondisturbed, high-strength, prestressed concrete pipe piles with diameters ranging from 800 to 1,400 mm. The distinctive construction method intrinsic to DPC piles creates an annular gap, roughly 10 mm thick, between the pile shaft’s wall and the drill hole’s wall. Grouting within this pile–soil gap constitutes an effective strategy to recover and augment the skin friction of DPC piles. Although an innovative design, the grouting mechanism and its implications on the load-bearing attributes of DPC piles are still under investigation. To explore this, on-site experiments and laboratory physical model assessments were performed, focusing on DPC piles’ load-bearing performance. The principal findings are as follows: (1) DPC piles serve as friction end-bearing piles, where a DPC pile of 1.0 m diameter consistently exceeds a load-bearing capacity of 20,000 kN; within this, lateral friction accounts for 67.84%–72.85%. The primary failure mode of DPC piles is identified as shear failure at the contact interface between the grouting stone and adjacent soil. Remarkably, in comparison with cast-in-place piles and pile-driven pipe piles, DPC piles demonstrate load-bearing capacity increments of 33.42% and 23.16%, respectively. (2) Both the coverage extent of the pile area by grouting stone and the per-unit-area shear strength of the pile–slurry–soil contact interface have substantial impacts on the load-bearing performance and load transmission characteristics of DPC piles. (3) After grouting, the ability of DPC piles to withstand upper loads in silty clay layers exceeds that in sandy soil layers; moreover, their vertical load-bearing capacity within silty clay layers outperforms their capability in sand layers. (4) The presence of voids within the pile–soil gap or infiltration of parts of this gap by sand may alter the grout’s flow trajectory, consequently changing the thickness of the grouting stone and the area covered by it. These variations underlie the effect on the skin friction of DPC piles. (5) And, the primary aspect contributing to the enhancement of shear strength at the contact interface through postgrouting resides in the increase of cohesion or the internal friction angle at this interface.