In municipal solid waste landfills (MSWL), the center and peripheral regions of the basal compacted clay liner (CCL) often experience steady elevated temperatures due to waste biodegradation and cyclic temperatures similar to the seasonal atmospheric temperature patterns, respectively. In the present study, the negative effects of cyclic elevated temperatures on the desiccation behaviour of a MSWL basal CCL was examined by subjecting CCL samples to multiple wet-dry cycles with different drying temperatures. It was observed that the extent of desiccation cracking experienced by the CCL rose as the drying temperature and number of wet-dry cycles increased. The present study also assessed the effect of different thermoplastic cooling pipes on the reduction of temperature rise and desiccation experienced by CCLs exposed to constant elevated temperatures (CETs). It was observed that the introduction of thermoplastic cooling pipes led to a significant attenuation of the final temperature (FT) and desiccation magnitude along the CCL depth in the face of all applied CETs, irrespective of the cooling pipe material employed. A comprehensively analysis of the final temperature distributions within the entire CCL, coolant and sand layer surrounding the cooling pipe was also carried out via the conduction of a numerical simulation. Overall, the present study revealed the adverse effects imposed by cyclic elevated temperatures on a CCL and the potential that thermoplastic cooling pipes possess to successfully reduce the temperature rise and desiccation experienced by a CCL in the face of different CETs.

In this study, the size effect on the tensile properties of compacted clay was investigated by using deep beam specimens. The equation for calculating tensile strength considering the effect of specimen thickness was established based on the results of finite element analyses. By using deep beams, Brazilian discs, and three-point bending beams, the tensile strength of compacted clay was tested to verify the rationality of deep beam specimens. Furthermore, differences in the tensile properties of deep beams of different sizes (widths of 50, 75, 100, and 125 mm) were explored. The results showed a significant size dependence of the peak load and peak displacement. As the specimen size increased, the tensile strength of the soil exhibited a linearly decreasing trend, whereas the energy required for tensile damage gradually increased. The Ba & zcaron;ant size effect model was used to predict the strengths of compacted clays, and a peak load prediction model that considers the structural parameters of the specimens was developed.

The long-term performance of pavement structures is heavily reliant on the sustained load-carrying capacity of the subgrade soil. Under repetitive traffic loads, permanent deformation (PD) gradually accumulates in the subgrade due to plastic yielding and soil particle rearrangement, which can compromise the serviceability and durability of overlying pavement layers. This study aimed to enhance the understanding of compacted clay response under long-term cyclic loads through a systematic repeated load triaxial (RLT) testing approach. The proposed approach considered depth-dependent static and dynamic stresses exerted on compacted clay beneath pavement structures and traffic loads. A series of RLT tests were conducted to investigate the impact of key factors, including soil properties (moisture content and compaction degree), stress conditions (confining pressure and deviator stress), and load characteristics (load duration and rest period), on the PD behaviour of compacted clay subgrade. Stress-strain hysteresis loops and damping ratios were analyzed to enhance the fundamental understanding of subgrade PD evolution. The results showed that higher moisture content and lower compaction degree significantly increased PD, with the PD response transitioning from plastic shakedown to plastic creep. Greater deviator stress also exacerbated PD accumulation. Variations in loading duration and rest period influenced the PD behaviour, demonstrating the importance of accurately simulating the stress history experienced by subgrade soil elements under traffic loading. The findings provide valuable insights to optimize subgrade design and implement performance-based management of pavements.

The stable and safe operation of highway/railway lines is largely dependent on the dynamic behavior of subgrade fillings. Clay soils are widely used in subgrade construction and are compacted at different remolding water contents and compaction degrees, depending on the field conditions. As a result, their dynamic behaviors may vary, which have not been fully investigated until now. To clarify this aspect, a series of cyclic triaxial tests were carried out in this study with three typical remolding water contents (w = 19%, 24%, and 29%), corresponding to the optimum water content as well as its dry and wet sides, and two compaction degrees (Dc = 0.8 and 0.9), which were selected according to the field-testing data. Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) tests were also conducted on typical samples to investigate the corresponding soil fabric variations. The findings indicate the following: (a) The soil fabric at the optimum remolding water content and its dry side was characterized by a clay aggregate assembly with a bimodal pore size distribution. In contrast, the soil fabric on the wet side of the optimum water content consisted of dispersed clay particles with a unimodal pore size distribution. (b) As the compaction degree increased, to ensure the optimum water content and its dry side, large pores were compressed to make them smaller, while small pores remained unchanged. Comparatively, all the pores on the wet side were compressed to make them smaller. (c) For each compaction degree, as the remolding water content increased, a non-monotonic changing pattern was identified for both the permanent strain and resilient modulus; the permanent strain first decreased and then increased, while, for the resilient modulus, an initial increasing trend and then a decreasing trend were identified. In addition, a larger changing rate of the permanent strain (resilient modulus) was observed on the dry side, indicating a larger effect of the remolding water content. (d) For each remolding water content, as the compaction degree increased, the permanent strain exhibited a decreasing trend, but an increasing trend was identified for the resilient modulus. Moreover, the rate of change in the permanent strain (resilient modulus) on the dry side of the optimum water content was larger than that on the wet side. In contrast, the minimum rate of change was identified at the optimum water content. The obtained results allowed for the effects of the remolding water content and compaction degree on the dynamic behavior to be analyzed, and they helped guide the construction and maintenance of the subgrade.

Compacted clay liners are an integral part of the waste landfills, which are provided to contain the leachate within the landfills and protect the surrounding environment. Generally, locally available natural soils are used for the construction of compacted clay liners if they satisfy the design criteria. However, not all soils in their natural state satisfy all the design criteria for the liner materials. Thus, there is a definite need to modify the locally available natural soils by blending with bentonite to meet the required design criteria for the liners. In view of this, the present study evaluates the suitability of an Indian red soil enhanced with bentonite as a liner material. To achieve this, a series of experiments were carried out using locally available red soil and bentonite. First, the suitability of the red soil was evaluated as a liner material. The experimental results showed that the red soil met all the selection criteria stipulated by the Environmental Protection Agencies (EPAs) for the liners except the hydraulic conductivity criterion. Therefore, the red soil was mixed with bentonite contents of 10%, 20% and 30%, and the red soil-bentonite mixtures were evaluated for their suitability for liners in their compacted state. Further, as the liners in the arid and semi-arid regions are subjected to moisture variations due to seasonal moisture fluctuations and other factors, the red soil-bentonite mixtures were subjected to wetdry cycles, and their suitability was evaluated after wet-dry cycles. The experimental results revealed that all the red soil-bentonite mixtures met the stipulated EPA criteria for the liners in the as-compacted state. However, the red soil-bentonite mixtures with 20% and 30% bentonite contents only satisfied the hydraulic conductivity requirement even after wet-dry cycles. The experimental findings were supplemented with the microstructural insights captured through digital camera images, scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) studies. O 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/).