Peak State Friction Angles Research Articles

Large-scale triaxial tests of reinforced coral sand with different grain size distributions

The strength, deformation and particle breakage behaviors of reinforced coral sand were analyzed by performing a series of large-scale consolidated drained triaxial tests on unreinforced and two-layer geogrid reinforced samples. Two grain size distributions, namely, the natural coral sand in the South China Sea (ISG) and the uniformly graded coral sand (UG), were used to investigate the effect of gradation on unreinforced and geogrid-reinforced specimens under dry and saturated conditions. The results indicated that the inclusion of geogrid offered a great improvement to the coral sand with respect to increasing its shear strength and reducing the shear dilation. The reinforcement effect of geogrid on dry sample was better than that on saturated one. Moreover, the UG sample exhibits high compressibility and distinct strain hardening behavior due to the significant particle breakage resulting from the lack of fine content compared with the ISG sample, which induced the better reinforcement effect of geogrid on ISG sample. The increase of particle breakage further led to the decrease of peak-state friction angle.

Experimental and Numerical Studies on the Direct Shear Behavior of Sand-RCA (Recycled Concrete Aggregates) Mixtures with Different Contents of RCA.

Recycled concrete aggregate (RCA) is a typical construction and demolition (C&D) material generated in civil engineering activities and has been widely used as the coarse-grained filler added to sand for roadbed fillings. The effect of RCA content on the mechanical behavior of sand–RCA mixtures is complicated and still not fully understood. To explore the effect of RCA content on the macroscale and microscopic behavior of the sand–RCA mixtures with various RCA contents, laboratory direct shear tests and numerical simulations using the 3D discrete element method were performed. Experimental direct shear tests on sand–RCA mixtures with different contents of RCA were first carried out. Numerical direct shear models were then established to represent the experimental results. The particle shape effect was also considered using a new realistic shape modeling method to model the RCA particles. Good agreement was observed between the DEM simulation and experimental results, verifying the ability of the numerical direct shear models to represent the direct shear behavior of sand–RCA mixtures. The macroscopic responses of both experimental and numerical tests showed that all samples presented an initial hardening followed by a post-peak strain softening. The peak-state friction angles increased with the RCA content for samples under the same vertical stress. The effect of RCA content on the microscopic behavior based on DEM simulation was also found. The microscopic properties of RCA–sand mixtures, such as coordination numbers, PDFs and contact force transformation features, were analyzed and related to the macroscopic results.

The effect of temperature on the drained shear behavior of calcareous sand

In answer to the growing demands for temperature-related engineering applications in marine geotechnical engineering, this article explores the effect of temperature on the drained shear behavior of calcareous sand. Sixteen drained triaxial shear tests were therefore performed on calcareous sand under various temperatures, and in addition, a further eight were carried out on Fujian standard quartz sand by way of comparison. The results showed that an increase in temperature aggravated the particle breakage of calcareous sand in shear. Increasing the temperature improved the strength and dilatancy of quartz sand but weakened them in calcareous sand. This aggravation of particle breakage at high temperature seems to be one of the main reasons behind the decrease in the strength and dilatancy of calcareous sand. Increasing the temperature led to a decrease in the peak-state friction angle φps, the maximum dilatancy angle ψps, the critical-state friction angle φcs and the critical-state void ratio of calcareous sand. A stress-dilatancy equation for the impairment of the stress-dilatancy behavior caused by increasing the temperature was proposed for calcareous sand, and an empirical model for estimating φcs was then put forward. An increase in the temperature caused the increase in relative particle breakage Br of calcareous sand. φps and ψmax decreased with Br as a negative correlation power function. Additionally, the effect of particle breakage on φcs had a correlation with the stress state. This study may be helpful in reducing the deterioration of structural stability in projects with an inadequate design due to the lack of a full understanding of the effect of temperature on calcareous sand.

Particle Breakage and the Drained Shear Behavior of Sands

This paper presents particle breakage and the drained shear behavior of sands. A series of drained shear tests were conducted on Silica Sand No. 5 and Coral Sand No. 3 under a 3-MPa confining pressure to produce the precrushed sands that were reused in triaxial tests to detect the influence of particle breakage. It was revealed that, for a given initial void ratio, particle breakage resulted in the impairment of the dilatancy of sands to become more contractive in influencing the shear behavior of the precrushed sands. Particle breakage resulted in the reduction of the peak-state friction angle and dilatancy angle, but the peak-state basic friction angle (the difference between peak-state friction angle and peak-state dilatancy angle) experienced first an increase and then a decrease with increasing particle breakage. For estimating the dilatancy angle by the excess friction angle (the difference between the peak-state friction angle and the critical-state friction angle), particle breakage was shown to have a significant influence on the friction-dilatancy behavior, including the accuracy of the excess friction angle to assess the peak-state dilatancy angle. The relations of the strengths and the void ratios of the precrushed sands were discussed as well. In addition, particle breakage resulted in a decrease of the critical-state void ratio but had a complex influence on the critical-state friction angle. (C) 2017 American Society of Civil Engineers.

Strength–dilatancy relation of sand containing non-plastic fines

Bolton's stress–dilatancy equation is mainly used for clean sands. It needs to be investigated whether this equation could be used for sand with non-plastic fines or not. A series of drained triaxial compress tests were conducted for the sand with non-plastic fines. It was observed from these tests that the peak-state and critical-state friction angles increased with increasing the fines content. The peak-state friction angle and maximum dilatancy angle increased with decreasing the confining pressure. It was also found that the relationship between the excess friction angle (i.e. the difference between the peak-state and critical-state friction angles) and maximum dilatancy angle was unchanged with the non-plastic fines content. This has illustrated that the Bolton's stress–dilatancy equation proposed for clean sands could still be applied to sands with non-plastic fines.

Strength and Dilatancy Behaviors of Dense Modeled Rockfill Material in General Stress Space

AbstractThe strength and dilatancy behaviors of modeled dense rockfill material were systematically investigated through a series of true triaxial compression tests at different minor principal stress and intermediate principal stress ratios. It was found that the intermediate principal stress ratio had great influence on the critical-state friction angle, peak-state friction angle, and maximum dilatancy of the modeled rockfill material. Both the critical-state and peak-state friction angles at a given confining pressure first increased and then decreased with an increase in the intermediate principal stress ratio. An increase in the minor principal stress led to a decrease in both the critical-state and peak-state friction angles at a given intermediate principal stress ratio. The maximum dilatancy decreased with an increase in the minor principal stress or the intermediate principal stress ratio. It was also found that the intermediate principal stress ratio significantly affected the relationship betwe...

Strength and Deformation of Rockfill Material Based on Large-Scale Triaxial Compression Tests. II: Influence of Particle Breakage

AbstractThe amount of particle breakage of Tacheng rockfill material (TRM) in the process of shearing was quantitatively measured by a relative breakage index. The fractal dimension of TRM at the final state of the tests was found to be linearly related to the void ratio and logarithm of the confining pressure. The influences of the relative breakage index on the friction angle, modulus, and deformation were investigated based on a series of large-scale triaxial compression tests on TRM. An increase in the relative breakage index leads to an increase in the volumetric strain and to decreases in the peak state friction angle, critical state friction angle, deviatoric strain, and critical state void ratio. The test results were used to propose simple formulations pertaining to the relative breakage index for the strength and deformation indexes (e.g., peak state friction angle, critical state friction angle, initial elastic modulus, secant modulus at 50% of the peak strength, volumetric strain, deviatoric s...