As a newly developed pile foundation, the snowflake shaped steel sheet pile is composed of three Y-shaped sections with an included angle of 120° and has a large specific surface area, which can give full play to the side friction of pile and improve the bearing capacity of single pile. At the same time, the snowflake shaped steel sheet pile has a high strength, relatively few materials, and it has good prospects with engineering applications. In order to accurately grasp the mechanical characteristics of the snowflake shaped steel sheet pile, this paper carried out the model test of snowflake shaped steel sheet pile based on OFDR (optical frequency domain reflector) distributed optical fiber sensor technology. The results show that: (1) OFDR distributed optical fiber sensing technology can effectively monitor the strain of snowflake steel sheet pile; (2) under the vertical load, the strain of snowflake steel sheet pile decreases along the length of the pile; (3) the strain of the same section of snowflake steel sheet pile is different at different positions, the strain at the junction between web and web is basically the same as the junction between web and flange, and the strain of the pile shaft on the flange edge is larger.

Microbially induced carbonate precipitation (MICP) technology holds great potential in enhancing soil properties. MICP can be employed to enhance the stability and strength of diverse sandy soil, but it has the shortcoming of low curing efficiency. In response to the identified problem, this study aims to investigate an optimized treatment protocol that involves formulating a cementing solution in a hydrochloric acid (HCl) solution to enhance the solidification rate in the MICP reaction and evaluate its effectiveness. The results indicate that when preparing a 1 M cementing solution in a 0.2 M HCl solution, it promotes the rapid bonding of calcareous sand particles, resulting in an unconfined compressive strength (UCS) of 1312.6 kPa in the sand column after five treatments. Compared to the conventional test group, the experimental group containing HCl exhibited an approximately 1357% increase in UCS. The analysis unveiled the pivotal role of metal ions dissolved from calcareous sand by HCl in enhancing the UCS of MICP-treated calcareous sand. The proposed experimental methodology serves as a valuable tool for designing treatment strategies for MICP-cemented calcareous sand in practical engineering applications.

In order to obtain a simpler and more reliable prediction model of unconfined compressive strength (UCS) of soil for application, the UCS data of synthetic fibre-reinforced clayey soil (FRS) were analyzed by statistical method, which were collected from previous studies. Based on the data sources, the failure modes of FRS were analyzed, it can be verified that the slippage of fibre is the major failure mode for UCS test. Six principal parameters of soil and fibre were selected for the new models. The α model and β model were proposed to predict the UCS values of FRS by means of multivariate nonlinear regression analysis. Moreover, the UCS data collected from different studies were used to evaluate the two models and the α–β model was proposed for modification. It was shown from the results that the three models were all reasonable in statistics. The α–β model can be considered as reference for application and the suggested value of a is less than 0.5.

To address the issues of low shear strength, susceptibility to eccentricity, and alignment difficulties in post-inserted core piles, a new type of steel tube concrete integrated mixing composite pile has been independently developed. This pile type replaces the conventional mixing pile shaft with a larger diameter steel tube equipped with mixing blades. After forming the external annular cement mixing pile, the steel tube is retained, and the hollow core is filled with concrete. To thoroughly explore the vertical compressive bearing characteristics of the steel tube concrete mixing composite pile and clarify its vertical compressive behavior, static load field tests and PLAXIS 3D finite element numerical simulations were conducted on four test piles of different sizes to analyze the vertical bearing performance of the steel tube concrete mixing composite pile. The research results indicate that for a composite pile with a length of 40 m, an outer diameter of 1000 mm, and a steel tube diameter of 273 mm, the ultimate bearing capacity of a single pile is 7200 kN, with the steel tube concrete core contributing approximately 81% of the vertical bearing capacity, while the cement mixing pile contributes around 19%. Based on the characteristic that the maximum axial force is concentrated in the upper half of the pile length, an innovative variable-diameter design with a reduced wall thickness of the steel pipe in the lower part of the pile was proposed. Practical verification has shown that, despite the reduced material usage, the load-bearing capacity remains largely unchanged. This effectively validates the feasibility of the “strong upper part and weak lower part” design concept and provides an effective way to reduce construction costs.