Adding fibers into cement to form fiber-reinforced soil cement material can effectively enhance its physical and mechanical properties. In order to investigate the effect of fiber type and dosage on the strength of fiber-reinforced soil cement, polypropylene fibers (PPFs), polyvinyl alcohol fibers (PVAFs), and glass fibers (GFs) were blended according to the mass fraction of the mixture of cement and dry soil (0.5%, 1%, 1.5%, and 2%). Unconfined compressive strength tests, split tensile strength tests, scanning electron microscopy (SEM) tests, and mercury intrusion porosimetry (MIP) pore structure analysis tests were conducted. The results indicated that the unconfined compressive strength of the three types of fiber-reinforced soil cement peaked at a fiber dosage of 0.5%, registering 26.72 MPa, 27.49 MPa, and 27.67 MPa, respectively. The split tensile strength of all three fiber-reinforced soil cement variants reached their maximum at a 1.5% fiber dosage, recording 2.29 MPa, 2.34 MPa, and 2.27 MPa, respectively. The predominant pore sizes in all three fiber-reinforced soil cement specimens ranged from 10 nm to 100 nm. Furthermore, analysis from the perspective of energy evolution revealed that a moderate fiber dosage can minimize energy loss. This paper demonstrates that the unconfined compressive strength test, split tensile strength test, scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) pore structure analysis offer theoretical underpinnings for the utilization of fiber-reinforced soil cement in helical pile core stiffening and broader engineering applications.

Bilateral helix-stiffened cement mixing piles (BHCMPs) are a new type of robust composite pile. In this paper, the influence of design parameters, such as the diameter of inner helix plates and the number and size of outer mixing helix plates, on the vertical bearing performance of the pile foundation and the behavior of the pile diameter are investigated through laboratory model tests. The results indicate that incorporating a reverse-mixing process in the pile formation of helix-stiffened cement mixing piles can enhance the overall ultimate bearing capacity and strengthen the soil-cement of the piles. In the case of the same double-blade inner drill pipe, for every 22 mm increase in the blades, its ultimate compressive load-bearing capacity was increased by 10% to 25%, and its pullout load-bearing capacity was increased by 15% to 45%. With further increases in the blades, the percentage increase in the compressive and pullout load-bearing capacity was reduced. With an increase in the number of external mixing blades, its compressive load capacity increased in the range of 5% to 20%, and the elevation load capacity increased in the range of 10% to 25%. Increasing the number of reverse-mixing helix plates on the outer casing enhances the soil-cement strength of the pile body by approximately 15–20% for each additional plate. The average strength of the pile-body soil-cement for each additional plate is estimated to be 1 to 1.4 times that of the previous set, indicating that increased mixing iterations can enhance the perimeter soil-cement strength of the pile. The average bond diameter of soil-cement piles with double-blade internal drilling rods could be seen from the diameter of the piles formed, which was 1.02 to 1.21 times the diameter of the blades.