Yinghui Tian

Expansive soil is prone to significant swelling and shrinkage deformation with changes in moisture conditions, posing serious safety hazards to engineering construction. This study focuses on alkali-activated self-compacting fluid-solidified soil (ASFS) and systematically explores the regulatory effect of expansive soil with different dosages (0–100%) on its properties. This study analyzes the influence of expansive soil on the setting time, hydration characteristics, autogenous shrinkage, and compressive strength of ASFS while verifying the feasibility of this method for solidifying expansive soil through microstructural analysis. The results show that, with the increase in content of expansive soil, the initial and final setting times of ASFS were prolonged by 0.08–1.58 times and 0.08–1.29 times, respectively. Although expansive soil inhibited the hydration of ASFS, it could compensate for autogenous shrinkage through the expansion effect of clay minerals, reducing the autogenous shrinkage by 13.4–51.2%. Furthermore, the optimal dosage of expansive soil in ASFS is 60%. Compared with the control group, the 7d compressive strength of ASFS increases by 52.4%, the strength after 3d water immersion rises by 62.6%, and the strength after eight wet–dry cycles still remains 10% higher. This optimal dosage achieves the best balance between mechanical properties, water stability, and shrinkage resistance of ASFS, providing a reliable technical reference for the efficient utilization of expansive soil in engineering.

Static pile ended with cone apex angle is widely used in practical engineering. However, the corresponding penetration resistance is still impossible to be predicted accurately. To address this, the penetration process of static pile is simulated by using the coupled Eulerian-Lagrangian (CEL) method in this study. During the penetration process of static pile in clay, the effect of cone apex angle and soil rigidity index on pile-end resistance and the distribution of the plastic zone of the soil around the pile-end are analyzed. The corresponding results indicate that the pile-end resistance is positively correlated with the size of cone apex angle and soil rigidity index, and the pile-end resistance rises with the increase of penetration depth until reaching a certain depth. Besides, the expansion process of the plastic zone near the pile-end is characterized by the expansion of spherical cavity. Since the position of expansion cavity center is different from the traditional theory, the corresponding radius in the traditional theory of cavity expansion is modified according to the corresponding numerical results. Finally, a semi-empirical method, in which the effect of cone apex angle and the soil rigidity index are considered, is proposed to predict the ultimate pile-end resistance of static pile.

Helical piles are utilized worldwide as foundations for onshore infrastructure, providing fast installation and high capacity. Their unique advantages have led to their potential as an alternative to monopile foundations for offshore wind turbines. One challenge in their service life is dealing with combined loading caused by wind, waves, current, and the weight of the structure itself. While research has focused on helical piles’ capacity for uniaxial tensile loads, there is limited knowledge regarding their performance under combined loads. This study used FEM analysis to investigate the impact of aspects such as helix-to-shaft diameter ratios and helix position on the capacity and failure mechanisms of hollow shaft single-plate helical piles in clay. With 561 analysis cases under both uniaxial and combined loading, failure envelopes were evaluated for various helix-to-shaft diameter ratios and positions. The study revealed a linear positive correlation between helix-to-shaft diameter aspect ratios and load-bearing ability, while the effect of helix positioning on failure envelopes was more complex and nonlinear. The outcomes from this comprehensive analysis enabled the development of a formula to predict the bearing capacity of helical anchors under combined loading.

Helical piles with small sizes are widely used in traditional civil engineering infrastructure application, especially in onshore electrical power industry. The floating offshore wind power industry has taken an interest in helical piles because of their rapid installation and ability to support immediate loading. Compared with onshore structures, wind power structures suffer larger external load and it becomes necessary to increase the overall size of helical piles, leading to considerable load capacity provided by the shaft, which is typically neglected for a light structure. In this paper, the undrained uplift capacity of helical piles was studied using finite-element limit analysis. The analysis explored various diameter ratios of the shaft to the plate and embedment depths, as well as different interface conditions. The local bearing capacity on the plate was also explored for attached and vented interface conditions. The failure mechanisms of a helical pile were presented to explain the mutual influence between plate anchor and shaft on the uplift capacity. Algebraic expressions for the uplift capacity of a helical pile were proposed. Engineers may use these expressions to improve the accuracy of their estimates for the uplift capacity of helical piles.