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Undrained instability in sandy soil containing fine particles such as liquefaction has remained a troublesome challenge in geotechnical research. Soil reinforcement could be taken as an approach to enhance its engineering properties like shear strength, cohesion, and bearing capacity. The present paper aims to evaluate the capability of geotextile reinforcement in improving undrained shear strength and diminishing undrained brittleness of loose clayey sands. A series of consolidated undrained triaxial tests were carried out on clayey sands containing 0, 5, 10, 15, 20 and 30% fines content (F.C.) under 100, 150 and 200 kPa confining pressures. To investigate the effect of geotextile reinforcement, experiments were performed in three reinforcement arrangements. The results indicate that geotextile reinforcement increases the steady state shear strength and decreases liquefaction potential and softening behavior. Geotextile reinforcement leads to decrease brittleness index of clayey sand specimens. It can also be pointed out that the presence of clay fines changes the dilative behavior of clean sand to contraction, and consequently reduces its undrained shear strength. Also, it is found that by increasing the clay content up to 10%, the undrained shear strength of reinforced and unreinforced clayey sand are decreased and brittleness index increased. With further rises in clay content, the undrained shear strength increases and brittleness behavior decreases. [ABSTRACT FROM AUTHOR]

In this study we investigate the effect of prior seismic shaking on the monotonic shear strength of saturated Ottawa Sand 20/30. We perform a series of stress-controlled undrained cyclic triaxial tests with different seismic intensities intentionally without causing failure, followed by drainage of the excess pore pressure and an undrained monotonic loading test to determine the undrained shear strength. The experimental data show that small to moderate seismic events that do not fail the specimen can significantly increase undrained shear strength without much change in relative density. One prior seismic event with peak ground acceleration ~ 1.3 m/s2 may increase the undrained shear strength of a specimen at ~ 10 m depth by around 30%. The results also show that as the intensity of the shaking increases, the increase in the monotonic shear strength increases. However, the strengthening effect does not increase with the number of seismic events although a small degree of global densification in the sample is observed. The results of this paper will help assess the change in static slope stability after a single or multiple small to moderate events occurred without causing initial instability. • Investigation of post-cyclic monotonic undrained shear strength of Ottawa Sand. • The strengthening effect increases as the seismic intensity increases. • The strengthening effect does not increase with the number of seismic events. • The change of shear strength does not depend on the change of relative density. • Shaking may induce non-homogeneity in the sample that influences its shear strength. [ABSTRACT FROM AUTHOR]