Taking cement-improved frozen soil as the research object, this paper, based on uniaxial unconfined compressive tests of improved-frozen soil under the conditions of different cement contents (6%, 12%, 18%) and curing ages (7 d, 14 d, 28 d), analyzed the results and probed the relationship between the strength and elastic modulus of cement-improved frozen soil and cement content and curing age. In combination with laboratory test results, numerical simulations were set with the PFC^3D group, building on the samples with 6% and 18% cement content at 14 days of curing, respectively, and the mesoscopic parameter values of the two different amounts were calibrated, which proved the simulation of cement with PFC^3D reliable to improve frozen soil, and from the microscopic view, the crack development, stress field, and the particle displacement field of the two samples were analyzed. The result shows that the force is not evenly distributed in the samples; with the main force chain on the cement particles, an increase in particles can lessen the cracks, and the failure of the 6% sample is a tensile plastic failure and that of the 18% sample is a tensile shear failure.

Volatile organic compounds (VOCs), as a primary pollutant in industrial-contaminated sites or polluted soils, cause severe damage to the soil. Therefore, a comprehensive understanding of the transport of VOCs in soil is imperative to develop effective detection means and removal methods. Among them, biochar possesses potential advantages in the adsorption of VOCs, serving as an effective method for removing VOCs from soil. This review provides an overview of the VOCs within soil, their transport mechanisms, monitoring technology, and removal approach. Firstly, the historical development of the VOC migration mechanism within the capping layer is described in detail. Secondly, the in situ monitoring techniques for VOCs are systematically summarized. Subsequently, one of the effective removal technologies, a capping layer for polluted sites, is simply introduced. Following this, the potential application of a biochar-modified capping layer for the removal of VOCs is comprehensively discussed. Finally, the major challenges in the field and present prospects are outlined. The objective of this study is to furnish researchers with a foundational understanding of VOCs, their relevant information, and their removal approach, inspiring environmental protection and soil pollution control.

Using the coda wave interferometry (CWI) method to obtain the ultrasonic coda wave characteristics of loaded concrete is an important method to evaluate the mechanical response of concrete. In this paper, the ultrasonic coda wave characteristics of C40–C70 concrete specimens (four strengths of concrete) under uniaxial compression were tested by laboratory experiments. Furthermore, to clarify the relationship between the internal damage process of concrete and the change rate of coda wave velocity, an ultrasonic coda wave discrete element simulation model combined with digital image processing technology was established. The results show that the coda wave is very sensitive to small changes in the compressive damage to concrete, and the change in coda wave velocity can correspond to the development process of concrete damage. This research is conducive to a better understanding of the complex material behavior of compressive concrete and proves the feasibility of ultrasonic field simulation and processing by using numerical simulation images of concrete damage.