During the global coronavirus (COVID-19) pandemic, a huge amount of personal precautionary equipment, such as disposable face masks, was used, but further usage of these face mask leads to adverse environmental effects. Here, we evaluated the feasibility of using mask chips to reinforce clayey soil, testing this with static and impact loading, including uniaxial compression, diametral point load, and drop-weight impact loading tests. The concurrent influences of shape, size, and percentage of waste material were considered. Generally, the contribution of shredded face mask (SFM) was majorly attributable to its tensile reinforcement. As a consequence, the strength of the mixture, measured by the static tests, was increased. This property was enhanced by the addition of rectangular mask chips. We determined the optimum percentage of SFM, beyond which the uniaxial compression strength and the point load strength index decreased. An increase in the percentage of SFM in the soil produced a higher damping coefficient and lower stiffness coefficient, causing greater flexibility. This trend increased beyond 1.2% of SFM (by volume of clay soil). Generally, based on our results, 1-1.5% of SFM was the optimum content.

In this study, impact compression tests on low-temperature concrete were conducted using a split Hopkinson pressure bar. The impacts of low temperatures on the strength, fractal, and energy characteristics of concrete were analyzed. The damage evolution mechanism of the microcrack density was discussed based on microscopic damage theory and microscopic tests. The results demonstrated that the impact fractal dimension and energy dissipation density of low-temperature concrete were positively correlated with the strain rate. The strain rate sensitivity of the impact fractal dimension was significantly affected by low temperature at low strain rates; however, low temperature had little effect at high strain rates. The pore water transformed into ice at negative temperatures, the fracture energy of the concrete increased, and the energy dissipation density increased. More than 50 % of the capillary and free water inside the concrete was frozen at -10 degrees C; approximately 30 % of the capillary and free water and 65 % of bound water did not freeze when the temperature was -30 degrees C. The macropores did not collapse under the action of ice filling at high strain rates; however, microcracks were generated around them. With a decreasing temperature, the threshold stress for microcrack propagation increased, crack propagation required more energy, and the microcrack density decreased.

The complex multiphase composition of frozen soil induces significant coupling interactions between the thermal, hydrological, mechanical, and damage fields during deformation, particularly under dynamic loading conditions. This study presents a hybrid decomposition phase-field model to investigate the multi-field coupling behavior and damage mechanisms of frozen soil. Unlike the spectral decomposition model, the proposed framework integrates isotropic degradation and the spectral decomposition methods, thereby enabling the simulation of damage evolution under compressive-dominated loading conditions. The model incorporates the viscous effects and strain rate sensitivity to accurately capture the dynamic response of frozen soil and establishes governing equations for coupled displacement, temperature, and fluid pressure fields. The applicability of the model was validated through confined compression experiments on frozen soil, demonstrating its capability to predict distinctive damage features, such as compaction bands oriented perpendicular to the loading direction, which represent the competitive interaction between the softening mechanism of pore collapse and the hardening mechanism of microstructural densification. This study provides significant advancements in the theoretical understanding and numerical simulation of the dynamic mechanical behavior of frozen soil.

The frozen moraine soil is geographically distributed across the Qinghai-Tibet Plateau and its surrounding areas, serving as a fundamental substrate for engineering projects such as the Sichuan-Tibet Railway and the ChinaPakistan Highway. As an economical and efficient construction technique, blasting is a commonly employed in these projects. Understanding the dynamic mechanical response, damage, and failure characteristics of moraine soil is crucial for accurately predicting the impact of blasting. Therefore, this study utilizes the Split Hopkinson Pressure Bar (SHPB) equipment to conduct impact tests on moraine soil under different temperatures and strain rates. Additionally, a model for predicting the dynamic mechanical response of frozen moraine soil has been proposed based on peridynamic theory, decohesion damage theory, and the ZWT model, in which the debonding damage and the adiabatic temperature rise are considered. This model focuses on considering the bonds between different substances within frozen moraine soil. By defining the mechanical response of these bonds, the impact deformation mechanism of frozen moraine soil is unveiled. Within this, the modeling of icecemented bonds contributes to a deeper understanding of the crack propagation characteristics in frozen moraine soil. The model prediction results demonstrate its capability to predict various aspects of the dynamic response of frozen moraine under impact loading, including the macroscopic stress-strain behavior, the mesoscopic crack initiation and propagation, and the influence of adiabatic temperature rise on the damage mechanism, as well as evaluate the damage state of frozen moraine soil under impact loading.

This study conducts several triaxial cyclic and plane strain cyclic impact tests on fissured soil under varying effective consolidation pressures, impact peak loads, and frequencies through the true triaxial test system to investigate the mechanical response characteristics. The results indicated that, under plane strain conditions, the specimens' shear resistance increases compared to that under triaxial loading. Moreover, the influence of fissures is challenging to quantify under triaxial loading compare to the mechanical response to fissure failure under the plane strain condition. As a result of the lateral confinement under plane strain conditions, the excess pore pressure, stress path, and lateral stress coefficient exhibit changes in sensitivity due to fissure damage, facilitating the analysis of the fissures' influence. Lower consolidation stress tends to increase the likelihood of fissure failure. As the peak impact stress escalates, the specimen deformation and excess pore pressure rise. When the impact peak stress reaches a critical value, the sample undergoes substantial deformation and fails rapidly. The impact of the frequency on specimen deformation correlates with the peak impact stress. Under low-impact peak stress, higher frequencies result in smaller deformations. However, under high-impact peak stress, a critical frequency exists. As the frequency increases, the difference between the maximum and minimum pore water pressure expands, with the change in this difference relating to fissure damage. Inherently, fissures in the soil significantly affect the mechanical properties under the impact load in the plane strain condition. The findings from this study can provide technical support for determining and evaluating the mechanical parameters of the fissured soil layer in light of the impact load.

Improvement of the mechanical properties of soil, such as density, compressibility and shear strength, is typically due to the variation in its inherent microstructure. This paper presents a microscopic study of the densification mechanism in granular soils subjected to impact loading. Both model test and discrete element simulation were carried out to quantitatively analyze the fabric evolution from a particle-scale perspective. Irregularly shaped particles were used in the simulation, on basis of which realistic packing structural information such as average contact number, contact area and branch vector length could be learned. The results reveal the microscopic densification mechanism that impact loading not only promotes the increase of contact number, but also enhances the contact area around per particle. Increasing of contact area has enriched the distribution of sutured contacts to form more steady mechanical status of soil.

In the rockfall prevention and control project, the reinforced concrete (RC) slab and sand (gravel soil) soil cushion layer are commonly used to form the protection structure, thereby resisting the rockfall impact. Considering that the oversized deformation of the cushion layer under impact load using the finite element simulation cannot converge, this article establishes a numerical calculation model using smoothed particle hydrodynamics-finite-element method coupling (SPH-FEM). First, the standard Lagrange finite -element mesh is established for the whole model using ABAQUS, and then the finite -element mesh of the soil cushion layer is converted to SPH particle at the initial moment of the calculation, and finally the calculation results are solved and outputted. The results indicate that, compared with the results of the outdoor rockfall impact test, the relative errors of the rockfall impact force and the displacement of the RC slab are within 10%, which proves the rationality of the coupling algorithm; moreover, in terms of the numerical simulation, the SPH-FEM coupling algorithm is more practical than the finite element for reproducing the mobility of the rockfall impacting the sand and soil particles. In addition, at an impact speed of less than 12 ms(-1), the cushion layer is able to absorb more than 85% of the impact energy, which effectively ensures that the RC slab is in an elastic working state under small impact energy and does not undergo destructive damage under large impact energy; the peak impact force of the rockfall is approximately linear with the velocity, and the simulated value of the peak impact force is basically the same as that of the theoretical value of Hertz theory; the numerical simulation is good for reproducing the damage process of the RC slab in accordance with the actual situation. The SPH-FEM coupling algorithm is more justified than the FEM in simulating the large deformation problem, and it can provide a new calculation method for the design and calculation of the rockfall protection structure.