Shear Strength Behavior of Sand Reinforced by Kraft Paper Using the Ring Shear Apparatus

To explore the reinforcement effects of different reinforcement methods, kraft paper was used as reinforcement material, and shear tests were carried out in sand to study the reinforcement effects of kraft paper perpendicular and parallel to the shear plane. The test results show that the two reinforcement methods can effectively improve the strength of sand and the orthogonal reinforcement form is more superior. The existence of reinforced materials greatly improves the cohesion of sand, but does not significantly improve the internal friction angle. The width of reinforcement material has little effect on the reinforcement effect and shows different variation laws under different reinforcement forms.

Experimental evaluation of the shear behavior of large landslide slip zone using Multistage - Multiphase shearing method.

Abstract The study of shear behaviors comprises of the analysis of shear deformation characteristics and strength parameter determinations. Understanding the constitutive behaviour of shear zone soil samples is essential for evaluation of the critical shear behaviors of reactivated landslides, through considerate experimental tests. The experiment was carried out based on the multistage - multiphase shear technique via ring shear apparatus. The main advantage of this new method is to examine the same soil specimen for progressive loading and the continuous phases of shearing. The result shows that two major shear characteristics under the multiphase shear mode; the first is a post-peak shear weakening behavior of the soils on the last phase shear process, it indicated a decrease in friction resistance on fast rate effects, which enables to narrate with fastly moved coseismic landslide behaviors. The other one is a practical increase in friction coefficient values (hardening behavior) on the entire shear process as the rate increases. This shear resistance scenario can also be related with the stabilization mechanism of landslide slip surface soils against sliding.

Effects of Polypropylene Fiber on the Liquefaction Resistance of Saturated Sand in Ring Shear Tests

This study focused on investigating the effects of polypropylene fiber on the liquefaction resistance of saturated sand. We performed a battery of tests with a state-of-the-art ring shear apparatus on fiber-reinforced saturated sand, considering the influences of fiber content and sand density. Two different shearing methods named shear-torque-controlled (STC) and cyclic-torque-controlled (CTC) were considered for carrying out the tests. An energy approach was chosen to evaluate the results, and the fiber reinforcement mechanisms were analyzed. Our test results showed that in STC tests, the shear strength and shearing time of saturated sand increased proportionally to an increase of fiber content and sand density. The cycles required for liquefaction in CTC tests also increase with an increase in sand density and fiber content. The presence of fibers clearly increases the shear energy required for liquefaction. The shear energy increases with an increase in sand density and fiber content. Greater total shear energy is required in specimens with a higher density or larger fiber content. Fiber reinforcement in sand has acted as a spatial network in interlocking soil grains, thereby resulting in the necessity of more energy for overcoming the resistance during the shearing process. After performing the shearing test, the unreinforced specimen with loose structure collapsed totally, and the one with a dense structure collapsed partially, while fiber reinforcement specimens still maintained structural stability.

Laboratory investigation of interface shearing in chalk

Chalk, a soft fine-grained Cretaceous limestone, is encountered across northern Europe where recent offshore windfarm, oil, gas and onshore developments have called for better foundation design methods, particularly for driven piles whose shaft capacities are controlled by an effective stress Coulomb interface failure criterion. Interface type and roughness is known to affect both interface friction angles, δ′ and the magnitude of dilation required for shaft failure to develop. Site-specific interface ring-shear tests are recommended for offshore pile design in sands and clays to account for driven pile shaft materials, roughnesses and shear displacements. However, few such tests have been reported for chalks and it is also unclear whether δ′ angle changes contribute to the striking axial capacity increases, or set-up, noted over time with piles driven in chalk. This paper describes an interface shear study on low-to-medium density chalk from the St. Nicholas-at-Wade research test site in Kent, UK, where extensive field driven pile studies have been conducted [1, 2]. Direct shear and Bishop ring shear apparatus were employed to investigate the influences of interface material and surface roughness, as well as ageing under constant normal effective stresses (σn'). It is shown that the high relative roughness of the interface compared to the chalk grain size results in the ultimate interface shearing angles falling close to the chalk-chalk shearing resistance angles. The δ′ angles also increased by up to 5° over 38 days of ageing.