Dense prehydrated geosynthetic clay liners (DPH-GCLs) are a particular type of GCL which, unlike conventional GCLs manufactured with dry bentonite, contain bentonite prehydrated during manufacturing. DPH-GCLs are produced by a patented process that includes bentonite prehydration with a polymer solution and vacuum extrusion. This paper describes the results of permeability tests that were carried out using flexible-wall permeameters to investigate the hydraulic conductivity of a DPH GCL to water, natural seawater and a 12.5 mmol/l CaCl₂ solution. Moreover, the efficiency of the 0.1 m overlap seams between DPH-GCL panels has been investigated by means of a medium-scale permeameter able to accommodate specimens 0.305 m in diameter. Test results showed that the DPH GCL has very low hydraulic conductivity to water (10⁻¹²–10⁻¹¹ m/s) and preserve low permeability, of the order of 10⁻¹¹ m/s, in the presence of relatively high calcium concentration in the permeating liquid. However, the efficiency of overlap seams can be affected by the permeant type. In the presence of permeant liquids that inhibit swelling (e.g. seawater), the hydraulic efficiency of the seams needs to be improved by adding bentonite paste at the overlap interface. The hydraulic performance of the DPH-GCL is attributed to the combination of prehydration, densification and chemical amendment.

Reusing construction and demolition wastes for geotechnical and geo-environmental purposes has already become a research hotspot. This study was carried out to evaluate the feasibility of using recycled construction and demolition wastes in a partial substitution of cement to enhance the mechanical properties of soft soil. The strength and stiffness development of two types of recycled material (RM1 and RM2), incorporated with peat and clayey soil under 7, 14, and 28 days’ curing time, was investigated based on unconfined compressive strength and free–free resonance frequency test methods. The findings demonstrated that clayey soil showed an average of 2.5 times higher strength than peat with the addition of recycled materials, regardless of the type. However, after 14 days of curing, the strength remained constant for peat soil. Moreover, it is concluded that the studied granular recycled materials could be used to replace a part of the cement content to improve the strength and stiffness properties.

Bentonite clay is widely used as a hydraulic barrier in geosynthetic clay liners (GCLs) due to its low hydraulic conductivity, but in an aggressive environment, such as interaction with electrolytic solutions and higher temperature variations and number of wet and dry cycles, the performance of bentonite deteriorates. Polymerised bentonite clay (hyper clay) has shown better performance than untreated bentonite under these conditions, possibly due to better water retention, thus highlighting the need to investigate the water retention capacity. Therefore, the water retention behaviour of hyper clay GCLs was studied and compared with that of untreated clay GCLs. This paper presents the soil water retention curves of untreated bentonite GCL and hyper clay GCLs treated with 8% carboxymethylcellulose measured by filter paper tests. Different electrolytic solutions were used as permeation fluids along with deionised water to represent a more aggressive environment. The results showed that a hyper clay GCL has 7% higher water retention capacity near the air entry value than an untreated clay GCL in deionised water. In other words, a hyper clay GCL can be considered a potential alternative to conventional bentonite GCLs due to its improved water retention capacity.

Cement-clay mixtures are regularly employed as cut-off walls to isolate polluted soils or in ground improvement technologies. In this research, an alternative method to monitor the mechanical and hydraulic behavior of cement-clay mixtures is proposed. Bender elements were installed in a hydraulic conductivity cell, to monitor simultaneously the small-strain shear modulus (G₀) and the hydraulic conductivity of a cement-treated kaolin clay mixed with blast furnace slag cement. During permeation with deionized water, an increase of G₀ with time was observed, due to cement hydration (hardening). Conversely, after permeation with a sulfate solution, a sudden decrease of G₀ and a gradual increase of the hydraulic conductivity were noticed. The interparticle cementation of the mixture was probably affected by contact with sulfates, which are particularly aggressive to cement. Monitoring of G₀ was shown to provide valuable additional information to study the impact of sulfate attack on the mechanical and hydraulic behavior of cement-clay mixtures.

This study investigates the feasibility of landfill expansion using the limit equilibrium and finite element methods. A 15.5 m high reinforced fill structure (RFS) was analyzed to assess how fill type, consolidation rate, geometric configuration, waste strength, compaction and the inclusion of banquettes affect horizontal displacement, differential settlement, reinforcement strain and facing behavior. The baseline configuration demonstrated acceptable settlement, reinforcement strain, and gabion performance but exceeded allowable horizontal displacement limits. The scenarios including increasing consolidation rate and substitution with sand fill further aggravated displacements, whereas banquettes significantly reduced lateral movement and settlement, demonstrating their effectiveness in stabilizing slopes. Enhancing the industrial waste properties decreased displacements substantially improving overall stability. Geometric modifications, such as widening the reinforced zone, enhanced displacement control, while higher compaction achieved the best global performance, albeit with increased gabion compressibility. Extending geogrid length provided only marginal improvements beyond a certain threshold. Overall, banquettes, enhanced waste properties, and improved compaction were identified as the most effective strategies for stable efficient landfill expansion, emphasizing the importance of displacement control and reinforcement–facing interaction.