A pressure-grouted helical pile (PGHP) is a stiffened helical pile installed by using the simultaneous drilling and grouting technique. The formation of the soil-cement column surrounded by the helical pile is influenced by the multiple installation parameters, including helix number, helix size, and drilling speed. A series of small-scale model tests was carried out in clay to investigate the influence of installation parameters on axial behavior of PGHP and the load transfer mechanism. The model piles were pulled out after the loading tests, and the dimensions of the soil-cement columns were measured. The ultimate compressive bearing capacities of the PGHPs were 260% to 293% higher than the un-grouted helical piles. The ultimate bearing capacities of the PGHPs were proportional to the increase of the helix number and helix size and decreased with the drilling speed. The average bond diameter of the soil-cement column was 1.26 to 1.35 times the helix size. The adhesion between the soil-cement column and the surrounding clay was in the range of 0.8 to 1.2. The overall results examine the feasibility of the simultaneous drilling and grouting technique in clay and the improvement of the axial bearing performance compared to un-grouted helical piles.

The Helix-Stiffened Cement Mixing (HSCM) pile is a composite pile constructed by grouting the soil–cement during the installation of the helical pile. A series of 3-D Finite Element Method (FEM) models were developed to investigate the uplifting behavior of HSCM piles installed in marine soft clay. The uplifting behavior of HSCM piles was compared to the Stiffened Deep Cement Mixing (SDCM) piles and the difference was discussed. The FEM results showed that the uplifting ultimate bearing capacity of the HSCM piles and SDCM piles increased with the soil–cement-strength-to-clay-adhesion ratio (Cref/su) until the ratio reached 20 and 40, respectively. The failure mode influenced the uplifting behavior of HSCM piles. At Cref/su ∈ 40,80, the HSCM pile incurred damage at the pile–soil interface, which gradually shifted to the steel pipe and soil–cement interface as the Cref/su was further decreased. Based on the FEM results, the empirical formula for estimating the uplift ultimate bearing capacity of HSCM piles under different failure types was proposed, which provided reliable guidance for designing HSCM piles.

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