A Study on the Triaxial Shear Behavior of Geosynthetic Reinforced Soil by Discrete Element Method

A 3D DEM model using Particle Flow Code (PFC3D) software was developed utilizing a bonded-ball flexible membrane approach to study cohesionless soil as a discontinuous discrete material. The 3D model was calibrated and verified with experimental data, and a sensitivity analysis was carried out for the microparameters. Triaxial tests were simulated to observe the stress-strain curves and volumetric changes, as well as the strength parameters of soils consisting of spherical particles with different gradations but the same porosity. One important finding is that the relationships between particle size and deviatoric stress, internal friction angle, and dilatancy angle were found to be linear. Geosynthetics were added to the developed model to study the stress-strain behaviors of reinforced soil in a geosynthetic reinforced soil (GRS) mass, which have important applications that can improve the design of the structures. Results indicate that geosynthetics improve the cohesion to the granular soil

Modeling Triaxial Testing with Flexible Membrane to Investigate Effects of Particle Size on Strength and Strain Properties of Cohesionless Soil

A 3D DEM model using Particle Flow Code (PFC3D) software was developed utilizing a bonded-ball flexible membrane approach to study cohesionless soil as a discontinuous discrete material. This approach is not yet widely used because of its complexity and high computational cost, but it allowed the authors to observe the stress-strain curves of triaxial specimens, to single out effects of individual factors on the strength and strain properties, and to observe the formation of the shear band and failure surface. The 3D model was calibrated and verified with experimental data, and a sensitivity analysis was carried out for the microparameters. Triaxial tests were simulated to observe the stress-strain curves and volumetric changes, as well as the strength parameters of soils consisting of spherical particles with different gradations but the same porosity. The authors investigated the effects of mean particle size, larger particle size, smaller particle size, and soil gradation on three soil parameters: peak deviatoric stress, internal friction angle, and dilatancy angle. Four different cases with different soil gradations and particle sizes were studied: a uniform soil, a soil with randomly created particle sizes, and two soils each contains two particle sizes. For two out of the four cases studied, peak deviatoric stress, internal friction angle, and dilatancy angle increased when the mean particle size D50 increased. For the other two cases, the parameters decreased when the mean particle size D50 increased. One important finding is that the relationships between particle size and deviatoric stress, internal friction angle, and dilatancy angle were found to be linear. These relationships can provide predictions on soil strength and strain properties when the particle size changes. Observations and discussions on the formation of shear bands during shear testing are also presented. A step-by-step delineation of the DEM model development is also presented with the development process of a flexible membrane carefully described

Evaluating Wettability of Geotextiles with Contact Angles

Geotextiles have been used for drainage purposes in pavements for many years. To drain water out of road sections, the geotextiles need to get wet first. In this study, the wettability of three different types of geotextiles, namely wicking woven (WW) geotextile, non-wicking woven (NWW) geotextile, and nonwoven (NW) geotextile, was investigated in terms of their contact angles dependent on water-geotextile interaction. Contact angle was observed by the VCA Optima XE tensiometer for up to 12 s after a water droplet was dropped at the center of a geotextile\u27s surface. Water droplets of two different sizes (2 μL and 5 μL) were used to demonstrate the droplet size effect on the contact angles of water on undisturbed geotextiles. Test results show that the contact angle decreased to smaller than 90° and the droplet disappeared on the wicking woven geotextile within a few seconds after water dropping, while the contact angle remained larger than or approximately equal to 90° on the other two types of geotextiles within the observation period. This comparison indicates that water penetrated faster into the wicking woven geotextile than other geotextiles. Furthermore, this study investigated the effects of soil particle intrusion and geotextile or fiber deep groove flattening associated with compaction on the wettability of geotextiles

Evaluating Wettability of Geotextiles with Contact Angles

Geotextiles have been used for drainage purposes in pavements for many years. To drain water out of road sections, the geotextiles need to get wet first. In this study, the wettability of three different types of geotextiles, namely wicking woven (WW) geotextile, non-wicking woven (NWW) geotextile, and nonwoven (NW) geotextile, was investigated in terms of their contact angles dependent on water-geotextile interaction. Contact angle was observed by the VCA Optima XE tensiometer for up to 12 s after a water droplet was dropped at the center of a geotextile\u27s surface. Water droplets of two different sizes (2 μL and 5 μL) were used to demonstrate the droplet size effect on the contact angles of water on undisturbed geotextiles. Test results show that the contact angle decreased to smaller than 90° and the droplet disappeared on the wicking woven geotextile within a few seconds after water dropping, while the contact angle remained larger than or approximately equal to 90° on the other two types of geotextiles within the observation period. This comparison indicates that water penetrated faster into the wicking woven geotextile than other geotextiles. Furthermore, this study investigated the effects of soil particle intrusion and geotextile or fiber deep groove flattening associated with compaction on the wettability of geotextiles

Technical Review of Development and Applications from Wicking Fabric to Wicking Geotextile

Moisture-wicking fabrics first appeared in the market more than 20 years ago and have been mostly used for the clothing industry to improve comfort by soaking sweat when they are worn on human body. Extensive research has been conducted in this industry to improve properties and behavior of wicking fabrics. In recent years, wicking fabrics have been increasingly used as wicking geotextiles to remove moisture from soils to mitigate frost heave, poor drainage, and soil expansion problems. This paper provides a comprehensive literature review of the development of wicking fabrics in the clothing industry and the applications of this technology as wicking geotextiles in geotechnical engineering. The review first discusses the basics of wicking fibers including types of polymers, geometries of fibers, fiber-water surface interaction, water transportation in fibers, water evaporation from fibers, fiber-water-soil interaction, and their influence factors, and then summarizes recent research and advances in the use of wicking geotextiles to solve moisture-related problems in geotechnical engineering, especially for roadways

Impact of Tidal Phase on Inundation and Thrust Force Due to Storm Surge

Impact of storm surge largely varies depending on the tidal phase during the landfall of a tropical cyclone. This study investigates comparative variance in inundation condition and thrust force for an identical cyclone during low tide and high tide by applying a numerical model (Delft3D) and a semi-analytical model (DFM). A moderate strength cyclone, Mora, which made landfall on Bangladesh coast in May 2017 is selected to study its impact on land during low tide and high tide. Actual landfall time of Mora was during low tide. To study the impact of storm surge during high tide, a synthetic cyclone is created which has similar strength and track to that of Mora but makes landfall during high tide. The results show that inundation depth, inundation extent, and thrust force increase when a cyclone makes landfall during high tide compared to the condition when the cyclone makes landfall during low tide. But the relation between storm surge impact and tidal phase is not linear. It depends on the land topography of the location, direction of cyclone movement, direction and magnitude of water velocity and wind velocity, gradients of water surface and wind velocity, and proximity and position of the location with respect to cyclone track