Undrained residual strength, s(ur), often termed remolded or postcyclic strength, is a critical input into embankment dam numerical deformation analyses. There are multiple methods available to assess s(ur) for fine-grained soils, each with advantages and disadvantages. Field tests, such as the vane shear test and the cone penetration test, can provide reliable in situ measurements of s(ur). In the laboratory, s(ur) can be estimated by measuring the shear stress mobilized at high strains in monotonic tests such as direct simple shear or triaxial shear. s(ur) is also frequently determined from postcyclic monotonic testing; however, the postcyclic stress-strain curves can be difficult to interpret because of high excess pore water pressure existing at the start of monotonic shear due to the sample being previously subjected to cyclic loading. Such analyses often have a significant amount of uncertainty. The work described here presents two new methods developed to quantify s(ur) through lab testing, namely, analysis of stress paths from postcyclic monotonic tests and iterative strain-controlled cyclic loading. This paper introduces the new approaches and presents results from testing performed on five fine-grained soils from the foundations of embankment dams. Values of s(ur) from the new approaches are compared with those from VST and monotonic and postcyclic monotonic direct simple shear testing. The paper details the new approaches and presents results and conclusions from five fine-grained soils from various sites across the western United States.

Landslides developing in bedding-plane sediments are predominantly controlled by basal shear zones, where clay-rich materials localize deformation along bedrock surfaces. The mechanical behavior of shear-zone soil is further influenced by the characteristics of soil-rock interface. This paper investigates the residual strength of the soil-rock interface samples through ring shear and large-scale direct shear tests under varying stress and rate conditions. Shear zone materials from two landslides sites are paired with manufactured base and natural rock to compose the interface samples. Experimental results find that the residual strengths of shear zone materials are altered by different interfaces. At a low normal stress level, the mechanical behaviors of soils show strong dependence on surface asperities. As driven by increasing shear stress, the smooth interface sample exhibits accelerated failure progression with significant loss of resistance. The surface morphology and rheological behavior explain that the basal shearing easily occur along a relatively smooth interface, resulting weakening at high velocity and stress states.

One of the prerequisites for the safe exploitation of surface mines is the stability of the working and final slopes of the mine. In order to ensure this, it is necessary to carry out detailed field and laboratory geomechanical tests of the soil and, based on the obtained results, make calculations related to stability analyses. The results obtained in this way are used for dimensioning the slope of exploitation slopes (excavation). Landslides occur when the ultimate shear strength is reached, and therefore, the adequate definition of shear strength parameters is one of the essential prerequisites for successfully solving the stability problem. Unlike earlier tests in Serbia, when the residual shear strength parameters were determined based on the usual conventional methods (direct shear apparatus, triaxial apparatus), this time, in addition to the direct shear apparatus, a ring shear apparatus was also chosen for testing. The paper shows the method of determining the residual shear strength parameters of high plasticity gray clays and siltstones of roof sediments from open pit mine Drmno, using direct and ring shear apparatus. The results show that the residual angle of internal friction for gray clays obtained with the ring shear apparatus is 9.9-10.8 degrees, and for the siltstone, it is 11.8-12.9 degrees, both of which are lower than the values obtained with the direct shear apparatus. In addition, correlations between the residual parameters of soil shear resistance and some physical indicators (plasticity index, clay content) are provided, showing high correlation coefficients. The proposed correlations should be used only when time and financial constraints prevent the execution of actual tests to determine residual shear strength, as concrete experimental procedures provide a much more reliable assessment of the residual strength properties of the soil.

February 6, 2023, Kahramanmara & scedil;-T & uuml;rkiye earthquakes caused widely scattered damage in southeastern T & uuml;rkiye. In this manuscript, liquefaction-induced failure of the Demirk & ouml;pr & uuml; bridge is discussed. The soil liquefaction triggering assessments and laboratory test results on surface ejecta suggested that the silty sand layer liquefied during the Pazarc & imath;k event. Back analyses of rotational failure surfaces revealed that the undrained residual strength and excess pore water pressure ratio values of the liquefied soil layer vary in the range of 17-30 kPa and 0.84 to 0.91, respectively. Comparisons revealed that the liquefaction induced instability would have been consistently predicted by available predictive models.

Freeze-thaw cycles are frequently overlooked as a pivotal factor contributing to leakage and structural failures in clayey soil-impermeable barriers used in landfills or tailings repositories in regions subject to seasonal freezing. This investigation explores the recovery and residual strength properties of Jilin ball clay undergoing six freeze-thaw cycles, and assesses the pore structure characteristics through a series of nuclear magnetic resonance (NMR) tests. The results indicate that normal stress has a greater impact on peak recovery strength than dry density and rest periods. Cohesion increases earlier and more significantly during rest periods compared to internal friction angle. Although the pore diameter remains consistent within the micropores during the freeze-thaw cycles, the soil's structural integrity undergoes notable changes. The concluding analysis provides valuable insights for the construction and management of impermeable barriers in landfills or tailings repositories within seasonally frozen areas.

Ancient landslides tend to reactivate along pre-existing slip zones that have reached a residual state. On the eastern margin of the Tibetan Plateau, previous research has indicated that the slip zone of ancient landslides is primarily composed of clayey soil with gravel, known as gravelly slip zone soil. However, the relationship between the macromechanical behavior of gravelly slip zones and the mesostructure of the shear surfaces affected by gravel is still unclear. Herein, ring shear tests and reversal direct shear tests were performed on gravelly slip zone soil, and the 3D morphology and shear surface roughness were quantitatively characterized by using 3D laser scanning technology and the power spectral density method. The results showed a significant correlation between the friction coefficient of the shear surface and its roughness. Gravel played a crucial role in influencing the macromechanical behavior of slip zones by altering the mesomorphology of the shear surfaces. By analyzing the mechanical properties of the contact unit on the shear surface, the residual strength of the gravelly slip zone was found to be jointly controlled by the basic strength of the fine-grained soil and the undulations caused by the gravel. Finally, a residual strength model was developed for the gravelly slip zone considering both the strength of the fine-grained soil and the shear surface roughness caused by the gravel. The reactivation of ancient landslides has caused serious casualties and economic losses. Field investigations have revealed that the slip zones of ancient landslides commonly contain gravel. However, we still have limited knowledge regarding the effects of gravel on the behavior of slip zones. We carried out shear tests on gravelly slip zone soils and quantitatively characterized the shear surface morphology. Our results showed a strong correlation between the friction coefficient of the shear surface and its roughness. We found that the presence of gravel significantly influenced the macromechanical behavior of the slip zone by altering the mesostructure of the shear surface. Based on our findings, we developed a residual strength model for the gravelly slip zone that considers both the strength of the fine-grained soil and the roughness of the shear surface caused by the gravel. Our study provides valuable insights into the behavior of ancient landslides along pre-existing slip zones and improves our understanding of the role of gravel in influencing their macromechanical behavior. The friction coefficient of the slip zone is positively correlated with the shear surface roughness The gravel controls the macromechanical behavior of the slip zone by altering the morphology of the shear surface A residual strength model for the gravelly slip zone soil considering the shear surface roughness caused by gravel is proposed

A modelling approach consisting of best -fit relations to estimate the post -yield strength parameters is presented for simulating post -peak behavior beyond the point of residual strength of coal pillars having different w/h ratios. The model was developed based on back -analysis of the complete stress -strain behavior of specimens belonging to six different Indian coal seams with different w/h ratios of 0.5 -13.5. It was found that the simultaneous degradation of the cohesion and friction angle of the MohrCoulomb rock material characterizes the post -peak strength behavior of the rock. The resulting expressions are simplistic as they require parameters that can be easily determined using uniaxial and triaxial compression results. Eventually, the developed model was validated by simulating the triaxial tests of coal specimens with different sizes under varying confining stresses and comparing its findings with the published test results. The study showed that its implementation in the numerical model could reproduce laboratory -observed mechanical response, deformation behavior, and failure mechanism very closely. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY -NC -ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).

The mechanical properties of the concrete-frozen soil interface play a significant role in the stability and service performance of construction projects in cold regions. Current research mainly focuses on the precast concrete-frozen soil interface, with limited consideration for the more realistic cast-in-place concrete-frozen soil interface. The two construction methods result in completely different contact surface morphologies and exhibit significant differences in mechanical properties. Therefore, this study selects silty clay as the research object and conducts direct shear tests on the concrete-frozen soil interface under conditions of initial water content ranging from 12% to 24%, normal stress from 50 kPa to 300 kPa, and freezing temperature of -3 degrees C. The results indicate that (1) both interface shear stress-displacement curves can be divided into three stages: rapid growth of shear stress, softening of shear stress after peak, and residual stability; (2) the peak strength of both interfaces increases initially and then decreases with an increase in water content, while residual strength is relatively less affected by water content; (3) peak strength and residual strength are linearly positively correlated with normal stress, and the strength of ice bonding is less affected by normal stress; (4) the mechanical properties of the cast-in-place concrete-frozen soil interface are significantly better than those of the precast concrete-frozen soil interface. However, when the water content is high, the former's mechanical performance deteriorates much more than the latter, leading to severe strength loss. Therefore, in practical engineering, cast-in-place concrete construction is preferred in cases of higher negative temperatures and lower water content, while precast concrete construction is considered in cases of lower negative temperatures and higher water content. This study provides reference for the construction of frozen soil-structure interface in cold regions and basic data support for improving the stability and service performance of cold region engineering.

Recently, stability analyses of structures built of granite residual soils, for example, earth dams or other urban structures, particularly when under vibration, are being recognized as much more important than previously imagined. In such analyses, it is emphasized that the residual strength should be utilized considering the seismic effect. Therefore, the residual strength of granite residual soils must be evaluated accurately in order to reduce the damage to structures built on them. This paper presented a laboratory study designed to examine the effect of fine-grained particles (FGPs; particle size = 0.075 mm), such as the quartz particles in the granite residual soils. It was also found that the amplitude of fluctuation was smaller when the FGP fraction was greater. In addition, under the same normal stress, the peak strength and residual strength decreased with an increase in the ratio of FGPs. Then, they remained almost the same when the ratios of FGPs were equal to 85% and 90%, respectively, and the post-peak attenuation tended to increase initially with an increase in the FGPs and then remained almost the same. Moreover, based on the sensitivity analysis, the order of influence of physical indexes on the residual frictional angle was also ranked for the granite residual soils.