Effects of the installation parameters on the compressive performance of helix stiffened composite piles in soft clay

Abstract

The Helix Stiffened Cement Mixing (HSCM) pile is an innovative type of composite pile, and the installed technique can affect the load-bearing performance and bond diameter of the pile. To verify the feasibility of the simultaneous drilling and grouting techniques for HSCM piles in soft clay and to investigate the influence of the installation parameters on the compressive load bearing performance, two sets of model tests were designed in this study, including HSCM piles with the different helix number and drilling speed and comparative helical piles. The test piles were installed in soft clay prepared from kaolinite clay and tested for compressive load-bearing performance and pile geometry to analyze the relationship between the installation parameters of the HSCM piles and the soil-cement column. The test results showed that the simultaneous drilling and grouting techniques were able to form the soil-cement column with the shape of an inverted frustum of a cone around the helical pile, with the average bond diameter of the soil-cement column being approximately 1.17 to 1.36 times the helix diameter. An appropriate increase in the helix number could enhance the integrity and continuity of the soil-cement column by mixing the cement with the soil adequately to improve the installed quality of HSCM piles. Excessive drilling speed could result in inadequate grouted, which reduces the bond diameter and stiffness of the soil-cement column. The compressive ultimate bearing capacity of HSCM piles under the conditions of this paper is 3.83 to 3.93 times that of helical piles. The enlargement of the pile diameter increased the skin resistance. The grouting technique was able to reinforce the soil and increase its strength, thus compensating for the reduction in strength caused by the disturbance of the soil by the helix plate during the rotary process.