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Abstract Underground grouting is a concealed project, and it is difficult to test the strength of grouting stones in engineering practice. Aiming at the problems of high confined water pressure and strong water-richness of the roadway floor, a pressure filtration test device was developed, and a PFC2D uniaxial compression model was established to study the variation law of stone strength and crack evolution mechanism of grouting materials under different grouting pressures. The results show that with the increase of pressure filtration value, the amount of slurry dehydration increases, the pore water pressure dissipates, the pores between particles are tightly compressed, the contact force between particle skeletons increases, and the strength of stone body increases. Under the condition of the same cement powder ratio (mass ratio of cement to stone powder) or stone powder particle size, the strength of stone body of stone powder-cement grouting material increases with the increase of pressure filtration value. The stress-strain curves of the stone body with different pressure filtration values all experienced three stages: continuous elasticity, fracture expansion and strength failure. Before the peak, the number of cracks increases slowly; after reaching the peak, the micro-cracks extend rapidly and the number increases rapidly, resulting in the final tensile failure of the specimen. This study can provide a basis for the selection of grouting engineering material ratio and grouting pressure parameters.

Objectives: This study aimed to investigate factors associated with sleep quality in healthcare students and to determine whether depressive and anxiety symptoms may explain some of the associations between sleep quality and self-rated health. Study design: This is a cross-sectional study at wave one. Methods: A total of 637 healthcare students were recruited via a stratified random sampling method in Hangzhou, China. The Sleep Quality Questionnaire (SQQ) and the four-item Patient Health Questionnaire (PHQ-4) were used to assess sleep quality and depressive and anxiety symptoms, respectively. Self-rated health was assessed via a self-developed questionnaire of both physical and psychological health. Structural equation modeling was used to examine the direct and indirect effects of sleep quality on self-rated health through depressive and anxiety symptoms. Results: Students engaged in part-time employment (p = 0.022), with poor perceived employment prospects (p = 0.009), and who did not participate in recreational sports (p = 0.008) had worse sleep quality. Structural equation modeling revealed a significant total effect of sleep quality on self-rated health (b = 0.592, p < 0.001), a significant direct effect of both sleep quality and depressive and anxiety symptoms on self-rated health (b = 0.277, 95% CI: 0.032–0.522), and a significant indirect effect of sleep quality on self-rated health through depressive and anxiety symptoms (b = 0.315, 95% CI: 0.174–0.457). Conclusions: Depressive and anxiety symptoms partially explain the association between sleep quality and self-rated health. Intervening upon sleep quality, depressive, and anxiety symptoms may bolster the self-rated health of healthcare students.

Clay cement grout is frequently employed in geotechnical reinforcement projects. However, laboratory test revealed that clay cement slurry does not consolidate in a closed environment for an extended period of time, with cracks forming during the consolidation process under natural conditions, indicating that the geotechnical reinforcement poses dangers. Stone powder is a powdery solid waste similar to clay materials. Stone powder particle surfaces provide an attachment point for cement reaction, which can speed up cement hydration, with the ability to substitute clay cement slurry. According to our findings, the bleeding rate of clay cement slurry is 14.80% at 290 mm fluidity, and that of the same mass ratio (1:3) as stone powder cement slurry is 11.09%. The bleeding rate is minimal, which promotes the creation of an integral structure after setting between the slurry and lose rock and soil. Mechanical test results show that the strength of the stone powder cement slurry hardened body is 1458 kPa, whereas the strength of the clay cement slurry hardened body is 436 kPa. Microstructural analysis shows that the stone powder cement hardened body has more hydration products and is porous than the clay cement hardened body. The hardened body of stone powder cement slurry has high strength and resistance to external loads, which can increase the bearing capacity and improve the geotechnical reinforcement effect.

The grouting method is often used to strengthen the bearing capacity of building foundations. In the process of grouting, the stress structure of slurry and rock and the soil mass under the condition of high permeability and high stress (“double height”) is complex, and the strength mechanism of slurry stone under different double-height conditions is not clear. Therefore, stone samples of grout under the curing pressures of 2 MPa, 4 MPa, 6 MPa, 8 MPa and 10 MPa were prepared for the uniaxial compression test to analyze the influence of curing pressure on compressive strength. The microstructure of the slurry stone was observed by scanning electron microscope, and the development law of microcracks was further studied using the particle flow program. The research shows that the strength of the slurry stone body increases with the increase of curing pressure. When the curing pressure increases from 2 MPa to 10 MPa, the compressive strength of the stone powder-cement slurry stone body increases from 8.3 MPa to 22.7 MPa, an increase of nearly 2.7 times, and the compressive strength of the clay-cement slurry stone body increases from 5.7 MPa to 16.8 MPa, an increase of 2.9 times. According to the axial compressive stress-strain curve of the specimen, the failure process goes through three continuous stages: continuous elasticity, crack propagation, and strength failure. When the stress peak is reached, the number of cracks increases slowly; when the stress peak is reached, the cracks expand rapidly, the number increases exponentially, and a penetrating main crack is finally formed, which destroys the specimen. This study provides a reliable basis for the selection of grouting parameters and grouting materials in stratum-grouting engineering.

The green disposal of tailings solid waste is a problem to be solved in mine production. Cemented tailings filling stoping method can realize the dual goals of solid waste resource utilization and mined-out area reduction. However, the volume of the mined-out area of the open-pit method is larger than the filling capacity, resulting in the complex stratification of the underground backfill, and the strength of the backfill cannot meet the requirements. In this paper, according to the delamination situation, the specimens of horizontal and inclination angle layered cemented tailings backfill (LCTB) is made for a uniaxial compression test, and the failure process of delamination backfill is reduced by PFC. The results show that the corresponding reduction factor φ of horizontal LCTB is 0.560-0.932, and the corresponding φ value of inclination angle LCTB is 0.338-0.772. The failure mode of backfill in different layers is mainly manifested as a tensile failure. The PFC numerical simulation results are consistent with laboratory test results, which verifies the correctness of backfill failure. The research results provide a reliable theoretical basis for the strength design of backfill in goaf, which is of great significance for solid waste utilization and environmental protection. [ABSTRACT FROM AUTHOR]