A new in situ thermal piezocone penetration test (T-CPTU) system is developed to determine the thermal properties of soil. It is expected to overcome most of the shortcomings observed in existing in situ test techniques. Based on Fourier's heat conduction equation and pore pressure dissipation theoretical equation, a method for calculating the thermal conductivity, namely the predicted temperature method, was proposed. The accuracy of the T-CPTU probe testing process and thermal conductivity calculation results were verified by numerical simulation, laboratory large-scale model tank tests, and thermal needle tests. Finally, the field data of T-CPTUs at three sites in Nanjing, China, were collected and compared with the laboratory thermal needle tests. The results indicated that the thermal conductivities obtained using T-CPTU were accurate and closer to those of laboratory thermal needle tests for most soils. The thermal conductivities of the undisturbed soil samples measured in the laboratory were lower than those obtained by T-CPTU.

The thermal conductivity of soil is an important parameter that determines the geothermal properties of geotechnical engineering structures. In this research, a series of thermal needle tests were conducted to investigate the effects of water content, dry density, degree of saturation, and porosity on the thermal conductivity of mucky silty clay. Three models were used to predict the thermal conductivity of mucky silty clay in Nanjing, China. The results indicate that the critical water content of 25% can be attained by mucky silty clay, while its thermal conductivity is related linearly and exponentially to dry density and degree of saturation, respectively. Similarly, thermal conductivity is exponentially related to porosity. A modified predictive model of mucky silty clay that considers its high water content was established based on a parallel-series mixed model. By comparing it with three classic models and three sets of measured data from three sites in Nanjing, it is demonstrated that the modified predictive model can accurately estimate the thermal conductivity of mucky silty clay. This research contributes to a more comprehensive understanding of the heat transfer mechanism in mucky silty clay and provides thermal parameters for the design of geothermal-related structures in such soils.

Technical challenges associated with the treatment of silt subgrades frequently arise in coastal and river delta areas. Given the importance of environmental sustainability, the selection of efficient, cost-effective, and eco-friendly techniques for silt subgrade stabilization is paramount. While recycled polyester fibers primarily sourced from discarded polyester bottles have not yet been systematically employed in silt subgrade reinforcement, their potential is considerable. This paper offers a comprehensive review of the existing literature on the microstructural, physicochemical, and mechanical properties of silt, summarizing prior advancements in silt stabilization methodologies. Building upon this foundation, we introduce a novel approach utilizing recycled polyester fibers for silt subgrade improvement, outlining both its application prospects and challenges, which require further investigation. The findings of this study serve as a robust scientific foundation for the broader adoption and engineering implementation of this technology.