Valorization of the Use of Calcareous Tuff and Dune Sand in Saharan Road Design

This research objective is to propose a co-valorization of powdered tuff, containing a slight amount of clay and dune sand, by mixing the two substances at different rates such as 0%, 5%, 15%, 25% and 35% of sand. The adapted criteria formulas are those recommended by the technical Saharan road. The results of the proposed study showed that ＂tuff-sand＂ mixtures are denser with a lower optimum water content modified proctor, the fine rate decreases together with the plasticity index, whereas the bearing index （CBR： California bearing ratio test） increases. The intrinsic characteristics, cohesion and sensitivity of mixtures with respect to compactness are almost identical to those oftuffwithout addition. The optimal adapted sand incorporation rate is estimated at 25% at 96% of compactness. Under these conditions, the amount of fines decreases from 40% to an acceptable level of 25% and the plasticity index from 16.2 to 12. The compaction water content decreases by 36% and the CBR （bearing index） increases by 30% and the compressive strength and sensitivity, according to compactness, of the elaborated material are almost identical to those oftuffwithout addition.

A coupled strain softening and hardening model for completely weathered granite in a fault zone

his study focused on exploring the specificity of mechanical behavior for completely weathered granite,as a special soil,by consolidated drained triaxial tests.The influences of dry density(1.60,1.70,1.80 and 1.90 g/cm^(3)),confining pressure(100,200,400 and 600 kPa),and moisture content(13.0%,that is,natural moisture content)were investigated in the present work.A newly developed Duncan-Chang model was established based on the experimental data and Duncan-Chang model.The influence of each parameter on the type of the proposed model curve was also evaluated.The experimental results revealed that with varying dry density and confining pressure,the deviatoric stress–strain curves have diversified characteristics including strain-softening,strain-stabilization and strain-hardening.Under high confining pressure condition,specimens with different densities all showed strain-hardening characteristic.Whereas at the low confining pressure levels,specimens with higher densities gradually transform into softening characteristics.Except for individual compression shear failure,the deformation modes of the specimens all showed swelling deformation,and all the damaged specimens maintained good integrity.Through comparing the experiment results,the strain-softening or strain-hardening behavior of CWG specimens could be predicted following the proposed model with high accuracy.Additionally,the proposed model can accurately characterize the key mechanical indicators,such as tangent modulus,peak value and residual strength,which is simple to implement and depends on fewer parameters.