Soil-rock mixtures (SRM) from mine overburden form heterogeneous dump slopes, whose stability relies on their shear strength properties. This study investigates the shear strength properties and deformation characteristics of SRM in both in-situ and laboratory conditions. Total twelve in-situ tests were conducted on SRM samples with a newly developed large scale direct shear apparatus (60 cm x 60 cm x 30 cm). The in-situ moist density and moisture content of SRM are determined. Particle size distribution is performed to characterize the SRM in laboratory. The bottom bench has the highest cohesion (64 kPa) due to high compaction over time while the other benches have consistent cohesion values (25 kPa to33 kPa). The laboratory estimated cohesion values are high compared to in-situ condition. It is further observed that for in-situ samples, the moist density notably affects the cohesion of SRM, with cohesion decreasing by 3 to 5 % for every 1 % increase in moist density. At in-situ condition, internal friction angles are found to be 1.5 to 1.7 times compared to laboratory values which is due to the presence of the bigger sized particles in the SRM. The outcomes of the research are very informative and useful for geotechnical engineers for slope designing and numerical modeling purpose.

This work presents an analysis of the relationship between strength parameters determined in the laboratory and the results of a cone penetration test with pore water pressure measurement (CPTU) of waste soils in the White Seas area in Cracow. Anthropogenic soil is an alkaline waste formed during the production of soda ash and deposited in the area of the former Solvay Sodium Plant factory in Cracow, Poland. Due to the large area of the land and numerous investment plans and completed buildings, there was a need to identify reliable functional relationships enabling the determination of the strength parameters of these soils based on the results of the CPTU. Statistical analysis showed that the best correlation with the test results was provided by two logarithmic functions in which the dependent variables were the effective friction angle and effective cohesion. The dependent variable for both cases was the corrected cone resistance qt. The functional relationship combined data from labour-intensive, long-lasting and costly laboratory measurements with quick and less expensive measurements, i.e., in situ CPTUs. The obtained relationships enable the determination of the strength properties of the subsoil of these anthropogenic soils.

This study examines the application of nano-colloidal silica (NCS) in enhancing the mechanical properties of sandy clay soils. Consolidated undrained (CU) triaxial tests were performed on specimens containing varying percentages of NCS (0 %, 5 %, 10 %, and 20 %), which were then cured for different curing periods (1, 7, and 28 days) and subjected to three different confining pressures (50, 100, and 200 kPa). The findings revealed that the inclusion of 10 % NCS resulted in a significant 65 % increase in strength after 28 days compared to the untreated sample. However, higher NCS percentages, exceeding 10 %, led to a decline in strength as the excess NCS was not effectively utilized. The inclusion of NCS and increased curing time led to an increase in the brittleness of the soil and the application of confining pressure was able to reduce this brittleness.Furthermore, the use of 10% NCS and a curing period of 28 days significantly increased the stiffness and absorbed energy of the soil. Despite boosting the peak shear strength, NCS reduced the residual strength. Finally, polynomial modeling (Poly4) provided an excellent fit, enabling the characterization of the stress-strain and pore pressure-stain responses from the triaxial test.

Temporal variability in the macro-mechanics and microstructure induced by periodic water fluctuations during reservoir operation is widespread but adverse for slip zone soils. Herein, taking the slip zone soils of Huangtupo No. 1 landslide in the Three Gorges Reservoir area as a research case, the consolidation undrained (CU) triaxial tests coupled with wetting-drying cycles are organized to address macroscopic temporal variability of shear strength parameters. Then, quantitative microscopic characterizations are performed based on X-ray diffraction (XRD) and scanning electron microscopy (SEM) combined with mercury compression test (MIT). Eventually, the macro and micro connections are identified via gray rational analysis (GRA) and dynamic time warping (DTW) to be thus mathematized. Moreover, the weakened constitutive model is constructed. The test results show that the temporal variability of macroscopic shear strength parameters can be quantified as negative exponential decay. The wetting-drying cycles prominently contribute to the generation of intra-agglomerate pores (0.9-35 mu m). Besides, the inter-granular pores (0.007-0.9 mu m) and porosity are the connections to bridge microstructural parameters and macroscopic shear strength parameters. Furthermore, empirical equations for macro and micro connections are tentatively derived; the temporal variability of slip zone soils is invited to appropriately model the weakening laws of stress-strain. This study is expected to provide ingenious perspectives and promising references in stability evaluation and even disaster prevention of reservoir landslides.