In aggressive environments, including acidic environments, low and high-plasticity clays play an important role in transmitting and spreading dangerous pollution. Stabilisation of these types of soils can improve their characteristics. In this research, different ratios of two precursors with a low calcium percentage, for example, waste statiti-ceramic sphere powder (WS-CSP) and a high calcium percentage (e.g. ground granulated blast furnace slag [GGBFS], were employed to investigate the properties of soils with different plasticity indices [PIs]). Low and high-plasticity-stabilised and stabilised with 5 wt% Portland cement specimens were prepared and exposed to an acidic solution with a pH of 2.5 in intervals of 1, 3, 6 and 9 months. The long-term durability of specimens was evaluated using the uniaxial compressive strength test (UCS) and bending strength test (BS). Additionally, the microstructures of these specimens under various time intervals were analyzed using scanning electron microscopy and Fourier-transform infrared. According to the results, in an acidic environment, the reduction in UCS, BS, toughness and secant modulus of elasticity (E50) for low-plasticity-stabilised specimens and containing 100% WS-CSP was lower than that of other specimens. The Taguchi method and ANOVA were used to investigate the effect of each control factor on the UCS and BS.

High plasticity clay soils have low bearing and high swelling potential, which can lead to major problems if used in embankment layers. In current study, recycled concrete aggregates (RCA) were used as the most important part of construction and demolition (C&D) wastes in order to reduce the swelling potential and improve the mechanical strenght of high plasticity clay soil, and to achieve these goals, granulated blast furnace slag (GBS) was used as chemical additive. A set of laboratory tests including standard proctor, unconfined compression strength (UCS) and CBR tests were conducted to investigate the mechanical properties of the treated soil. Laboratory observations showed that by adding of RCA wastes to high plasticity clay, the UCS value increased up to 20% RCA content and then decreased with further RCA. Also, adding GBS and prolonged curing time improves the UCS of the clay - RCA mixture, and addition of 9% GBS can be suggested as the optimal content to achieve the design criteria of the subbase and subgrade layers. The use of RCA improves the secant modulus of elasticity (E50) and reduces the deformability index (DI), and these parameters are improved more significantly in the presence of GBS additive.

Inherent (fabric) anisotropy is one of the most important properties of earthen materials that significantly influences their strength and stiffness characteristics. In this study, a comprehensive series of unconfined and constrained compression tests is performed on normally consolidated (NC) clay samples with different plasticity indices to examine the effect of inherent anisotropy on their mechanical characteristics. Accordingly, several cylindrical clay samples with different proportions of kaolinite and bentonite are reconstituted at a wide range of deposition angles, and then subjected to both unconfined and constrained compressive loadings. The experimental results reveal that, for a clay sample with a particular plasticity index, the highest and lowest values of unconfined compressive strength (UCS), secant modulus (E50), and constrained Young's modulus (Eoed) are associated with deposition angles of 0 degrees and 90 degrees, respectively. The results also show that at a certain bedding plane angle, the sample containing 30 % bentonite (PI = 110 %) exhibits the highest UCS, E50, and Eoed values. Several practical empirical correlations are developed to estimate the strength and stiffness properties of NC clays based on their plasticity indices and bedding plane directions. Furthermore, Scanning Electron Microscopy (SEM) analysis is conducted to explore the microstructure of samples containing varying percentages of kaolinite and bentonite.

Deep soil mixing (DSM) is an established ground improvement technique employed in civil projects. Despite the superiority of field tests for understanding this technique, their high cost has directed researchers' focus on laboratory tests, resulting in limited attention given to operational factors. Consequently, in current research, a small-scale DSM setup was developed to investigate the influence of operational factors such as mixing time and execution procedure on strength and deformation characteristics of laboratory-scale DSM columns. For the installation of DSM columns, mixing times of 130, 190 and 250 seconds were used, together with normal and zigzag execution procedures, cement dosages (alpha) of 300, 400 and 500 kg/m(3), and total water-to-cement (W-total/C) ratios of 2.5, 3.0 and 3.5. Laboratory samples were also prepared using the same alpha values and (W-total/C) ratios for comparison with DSM columns. The sand bed was prepared with 5 % and 30 % moisture contents. Experimental observations showed that saturating the sand bed enhances the mixing quality by preventing slurry water infiltration into the soil surrounding the DSM columns. Results indicated that increasing mixing time and adopting zigzag execution procedure improved mixing quality, unconfined compressive strength (UCS), secant modulus (E-50), and strain at maximum stress (epsilon(Maximum Stress)), whilst reducing strength variability. Moreover, the outcomes showed that UCS and E-50 of samples have a direct and inverse relationship with alpha and (W-total/C), respectively, and that the nature of these relationships, not their magnitude, were not affected by mixing time and execution procedure. Additionally, findings indicated that the failure mode of DSM samples was influenced by operational factors, whereas (E-50/UCS) ratio was not.

Calcareous sands often display wide ring grain configurations, high intragranular porosity, a complex structure, and low grain hardness. These attributes typically do not meet the strength criteria necessary to sustain overlying infrastructure in civil engineering applications. This study investigates gel stabilization techniques, blending gel material with calcareous sand at concentrations ranging from 5% to 22%, followed by curing periods of 3 to 28 days to evaluate the load-bearing capacity. Subsequently, an unconfined compressive test is performed to determine the gel material content in stabilized specimens and investigate the influence of gel material types. The gel material-to-sand ratios employed are set at 5%, 10%, and 16% for Portland cement and 13%, 16%, and 22% for gypsum. After that, a triaxial consolidated undrained test is conducted to assess mechanical behavior, pore water pressure, and mechanical properties. The findings reveal increased dilation, stress-strain hardening, and softening post-yield, regardless of gel material type. Principal stress ratios, secant modulus, and cohesion show a positive correlation with maintenance duration and binder content, with implications for improved load-bearing capacity. The study also elucidates the qualitative relationship between secant modulus E50 and confining pressure.