A stiffened deep cement mixing (SDCM) pile is a type of composite pile that has a rigid pile at the core that reinforces the deep cement mixing (DCM) pile. An SDCM pile combines the advantages of both a DCM pile (i.e., high lateral friction resistance) and a rigid pile (i.e., high stiffness and strength). This work presents four sets of laboratory model tests that were aimed at investigating the vertical bearing capacity of SDCM piles with different cement contents by monitoring the pile top load, the axial force, the pile settlement, and the pile end resistance. Two failure modes of the SDCM piles were observed during the tests––pile failure (the pile ruptured at the section below the core pile) and punching failure (the pile penetrated into the underlying soil). It was found that the vertical bearing capacity of the SDCM piles increased with cement content, up to the point of punching failure. The pile end resistance increased with the pile top load. When the ultimate bearing capacities of the SDCM piles were reached in the model tests, the ratio between pile end resistance and pile top load ranged from 19.4% to 54.2%, indicating that pile end resistance cannot be ignored.

Induced Trench Installation (ITI) is a viable option to reduce the load on rigid culverts buried under high embankments. However, reliable design methods are limited, which restricts further applications of this technology. Based on Marston's formula, a modified analytical solution is proposed, in which the vertical stress across the width of the soil column immediately above the compressible layer is assumed to be distributed in a parabolic shape, and the effects of the geometry and stiffness of the soft layer on load reduction are considered explicitly. Comprehensive comparisons are made between field monitored results and the calculations from different design methods. Parametric studies are subsequently conducted to investigate the influence of different distribution patterns of vertical stress and the properties of the soft layer. It is found that compared to Marston's theory, the proposed method yields a closer estimation to the field measured data. Finally, a simplified design chart is introduced, which can facilitate use of the proposed method.

This study aimed to determine the effect of circulating fluidised bed bottom ash (CFB-BA) content on the mechanical properties and drying shrinkage of cement-stabilised soil. Experiments were performed to study the changes in unconfined compressive strength and expansibility of cement-stabilised soil with different CFB-BA contents and the underlying mechanisms based on microscopic properties. The results show that CFB-BA can effectively increase the unconfined compressive strength of the specimen and reduce the amount of cement in the soil. When the combined content of CFB-BA and cement in the soil was 30%, the unconfined compressive strength of the specimen with C/CFB = 2 after 60 days of curing was 10.138 MPa, which is 1.4 times that of the pure cement specimen. However, the CFB-BA does not significantly improve the strength of the soil and cannot be added alone as a cementing material to the soil. Additionally, swelling tests showed that the addition of CFB-BA to cement-stabilised soil can significantly reduce the drying shrinkage. This research project provides reference values for the application of CFB-BA in cement–soil mixing piles, including compressive strength and the reduction in the shrinkage deformation of specimens.

Buried lined-corrugated high density polyethylene (HDPE) pipes have been applied to transport sewage for decades. During its service life, a pipe of this kind could suffer from differential ground motion as a result of various geohazards (e.g., differential settlement induced by tunneling, basement excavations, changes in water table). However, studies of this kind of behavior of thermoplastic sewers have largely been absent in the pipe research literature. A full-scale test was conducted to investigate the structural response of 600-mm diameter lined-corrugated HDPE pipe subjected to differential ground movements associated with a normal fault having dip angle of 90°. This normal fault was simulated in a facility called the Split Box, where half of the floor of the test pit rests on screw jacks that allow it to be lowered in a stepwise process. Strain gauges and optical fibers were used to measure strains in the longitudinal and circumferential directions on the inner or outer surfaces of the pipe. Vertical displacement and cross-section distortion of the pipe were monitored using digital images analyzed using particle image velocimetry (PIV). Test results show that pipe strains were distributed nonlinearly around the pipe cross sections, especially for those measured proximal to the fault. Maximum pipe diameter changes were also observed at pipe cross sections close to the fault. The test results were compared with two current calculation approaches (i.e., the three-beam method and the Kappa method) and it is found that these two methods both overestimated peak bending strains in the pipe relative to those observed in the test.

Stiffened deep cement mixing (SDCM) piles have been applied in practice for decades. The bearing capacity of this kind of pile is closely related to the compaction and expansion of the deep cement mixing (DCM) pile and surrounding soil during penetration of the core pile. However, studies on driving behavior are scarce in the literature. Two sets of laboratory model tests will be conducted to facilitate the understanding of the response of an SDCM pile. The penetration depth of the core pile and the excess pore water pressure of the surrounding soil will be monitored using a string potentiometer and pore pressure transducers (PPTs). Diameter changes in the DCM pile before and after penetration of the core pile will be analyzed. Unconfined compressive strength (UCS) tests will be performed to investigate the mechanical properties of cement-treated soil with different densities. The results show that the excess pore water pressure of the surrounding soil increased during penetration of the core pile until the end of the core pile reached the depth of that position. The radius of influence was <7.90 times the diameter of the core pile. The normalized diameter of the DCM pile by its original diameter after penetration of the core pile was <1.05 at a depth of two times the core pile diameter below the end of the core pile, which indicated that the expansion effect that was caused by the penetration of the core pile was insignificant below that depth. In addition, the UCS and elastic modulus of the cement-treated soil increased linearly with density and the peak strain decreased.