Investigating the behavior of silty soils reinforced with geotextile layers in terms of shear strength and deformation in a laboratory setting is the study's objective described in this paper. This work includes an experimental study based on a series of undrained monotonic triaxial tests, which were carried out on clean sand from Chlef, medium dense (Dr = 50%), mixed with silt content fluctuating between 0 and 30%. The mechanical behavior was examined and discussed in this paper by varying the number of geotextile layers (Ng = 1, 2, 3) and the fines content where the samples were consolidated under 100 kPa confining pressure. Experimental results on unreinforced and reinforced silt/sand soils by geotextile layers show that the quantity of geotextile layers is growing in the studied samples improves the shear strength characteristics of the soil, nevertheless, lessen the radial deformations cause the pore water pressure to rise instead. However, the pore water pressure increases while the deviatoric stress decreases as the percentage of fines increases.

In this study, the undrained mechanical behavior of saturated completely decomposed granite (CDG) with different weathering degrees is investigated. To this end, a series of consolidation undrained (CU) triaxial compression tests are conducted on saturated CDG, and the effects of weathering degree on the main undrained mechanical properties are analyzed. Based on the experimental results, a poromechanical model is then established with the concept of effective plastic stress in a poroplasticity framework. Plastic distortion is described using a particular yield surface and a nonassociated plastic potential, which are both functions of the effective plastic stress and a subtly unified smooth hardening/softening variable. As an original contribution, an enhanced semi-implicit return mapping (ESRM) algorithm is developed to integrate the proposed model. This algorithm is based on a semi-implicit return mapping procedure and is combined with a new adaptive substepping technique. The model is subsequently implemented and validated by comparing the numerical simulation results with the experimental data. The main undrained mechanical characteristics of saturated CDG with different weathering degrees are well reproduced. A discussion follows regarding the parameter sensitivity analysis and robustness of the ESRM algorithm. Interestingly, the high accuracy of the ESRM algorithm is almost step-size independent, and the computational efficiency is also greatly improved.