Expansive soils have significant characteristics of expansion by water absorption, contraction by water loss. Under the freeze-thaw (F-T) cycles, the engineering diseases are more significant, and the serious geotechnical engineering incidents are induced extremely easily. The aim is to investigate the mechanical response characteristics of geogrid-reinforced expansive soils (GRES) under F-T cycles. Based on a series of large-scale temperature-controlled triaxial tests, influencing factors were considered, such as the number of F-T cycles, the geogrid layers, and the confining pressure. The results showed that: (1) Friction between the expansive soil and geogrid and the geogrid's embedded locking effect indirectly provided additional pressure, limited shear deformation. With the increase in reinforced layers, the stress-strain curve changed from a strain-softening to a strain-hardening type. (2) Elastic modulus, cohesion, and friction angle decreased significantly with increasing number of F-T cycles, whereas dynamic equilibrium was reached after six F-T cycles. (3) The three-layer reinforced specimens showed the best performance of F-T resistance, compared to the plain soil, the elastic modulus reduction amount decreases from 35.7% to 18.3%, cohesion from 24.5% to 14.3%, and friction angle from 7.6% to 4.5%. (4) A modified Duncan-Zhang model with the confining pressure, the F-T cycles, and the geogrid layers was proposed; the predicted values agreed with the measured values by more than 90%, which can be used as a prediction formula for the stress-strain characteristics of GRES under freeze-thaw cycling conditions. The research results can provide important theoretical support for the practical engineering design of GRES in cold regions.

The degradation of soil structure in sandy regions undermines soil functionality and poses a significant threat to environmental sustainability. The incorporation of Pisha sandstone, a natural soil amendment, has been recognized as an effective intervention to reduce soil erosion and expand arable land in the Mu Us Sandy Land, China. However, the microstructural stability and resilience of amended sandy soil formed by mixing Pisha sandstone with sandy soils remain inadequately understood. This study aims to evaluate the effects of Pisha sandstone addition on the microstructural stability of sandy soils. Four amendment rates of Pisha sandstone (16.7 %, 33.3 %, 50 %, and 100 % w/w) and five water content levels (40 %-80 %) were tested. Key parameters related to microstructural stability and structural resilience were assessed using amplitude sweep and rotational shear tests via a rheometer. Results indicated that soil shear resistance (tau LVR, tau max, tau y), storage modulus (G'YP) and viscosity (eta 0) decreased with the addition of Pisha sandstone, attributed to its lubricating effect and swelling properties. Additionally, Pisha sandstone enhanced physical elasticity (gamma LVR) and structural recovery of sandy soil under conditions of low disturbance. However, when water content exceeded 50 %, the fluidity of the amended sandy soil increased with Pisha sandstone addition. The sandy soil with a Pisha sandstone addition rate of 16.7 % exhibited optimal structural elasticity, shear resistance, and stiffness. These findings provide valuable insights into the enhancement of sandy soil structural stability using Pisha sandstone, offering a scientific foundation for refining amendment ratios and advancing agricultural management practices.

In slopes where high pore water pressure exists, deep counterfort drains (also called drainage trenches or trench drains) represent one of the most effective methods for improving stability or mitigating landslide risks. In the cases of deep or very deep slip surfaces, this method represents the only possible intervention. Trench drains can be realized by using panels or secant piles filled with coarse granular material or permeable concrete. If the trenches are adequately socket into the stable ground (for example sufficiently below the sliding surface of a landslide or below the critical slip surface of marginally stable slopes) and the filling material has sufficient shear strength and stiffness, like porous concrete, there is a further increase in shear strength due to the shear keys effect. The increase in shear strength is due both to the intrinsic resistance of the concrete on the sliding surface and the resistance at the concrete-soil interface (on the lateral surface of the trench). The latter can be very significant in relation to the thickness of the sliding mass, the socket depth, and the spacing between the trenches. The increase in shear strength linked to the shear keys effect depends on the state of the porous concrete-soil interface. For silty-clayey base soils, it is very significant and is of the same order of magnitude as the increase in shear resistance linked to the permanent reduction on the slip surface in pore water pressure (draining effect). This paper presents the results of an experimental investigation on the shear strength at the porous interface of concrete and fine-grained soils and demonstrates the high significance and effectiveness of the shear keys effect.

Compacted granular material, integral to geotechnical engineering, undergoes translation, rotation, and interlocking when subject to shear displacements or external loads. The present study focuses on the interlocking of heterogeneous granular materials, a complex behavior influenced by gradation, compaction, and varying particle geometry, and has consequently received limited attention in existing research. To address this research gap, we conducted an analysis on the effect of grain interlocking on the shear resistance of granular assemblies, using a combination of laboratory testing and the discrete element method (DEM). Initially, large-scale direct shear tests were conducted on gravel-sand mixes with varying degrees of compaction and normal pressure. One of the mixes also underwent subsequent shear reversal to explore the differences in grain interlocking between the two shearing processes on the shear plane. After analyzing the laboratory results, a mesoscopic scale investigation was performed by replicating the test using discrete element simulations. To facilitate this, granular particle geometries were measured using 3D laser scanning based on the physical lab tests. Subsequently, based on these scans, discrete element R-block and ball models were utilized to construct both the coarse and fine particles within the mix. Surface vibro-compaction was employed to regulate the degree of compaction. The results indicate that an increase in vertical pressure, coupled with a zero dilatancy angle, results in a rising stress ratio, indicative of grain interlocking. This interlocking exhibits a positive correlation with both the coarse content and the degree of compaction, and varies depending on the shear displacement. As interlocking progresses, the shear band, induced by particle movement, expands and is associated with reduced particle rotation near the shear band. The study further reveals a consistent positive correlation between interlocking and the principal orientation angle of strong normal contact forces, as well as a correlation between interlocking and mobilized contacts. (c) 2024 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

Oil sludge exhibits a compositional similarity to bitumen, a pivotal constituent in asphalt concrete mixtures. This similarity underscores the potential applicability of oil waste in the production of asphalt concrete, serving not only as an organic binder to fortify indigenous soils but also as a binding agent for the fabrication of organomineral mixtures. The incorporation of oil sludge in road construction endeavors holds promise for the conservation of natural resources, the amelioration of the environmental landscape, and a concurrent reduction in the cost of construction materials. The focus of this study encompasses a comprehensive examination of the physical and mechanical properties pertaining to asphalt concrete of Grade I, Type B. To enhance the performance attributes of asphalt concrete, an additive in the form of oil sludge sourced from ZhaikMunay LLP (Uralsk) was introduced. Various proportions of oil sludge, namely 5%, 10%, and 15%, were incorporated into the asphalt concrete mixture. The utilization of 5% oil sludge elicited negligible alterations in the properties of the asphalt concrete. However, with a 15% addition of oil sludge, discernible reductions were observed in maximum compressive efficiency (0.03% by volume) and shear resistance, indicated by the internal friction coefficient efficiency (0.01% by volume).