Numerical study on the lateral behavior of pile groups in Toyoura sand using the hypoplastic constitutive model.

A pile group under lateral loading is a complex pile‒soil-pile interaction problem. In this study, numerical analysis was used to investigate the lateral behavior of pile groups arranged in a 3 × 3 configuration with varying piles spacings. The hypoplastic constitutive model embedded into ABAQUS software through the UMAT subroutine was used to characterize the stress‒strain relationship of Toyoura sand. The effects of the pile spacing on the load‒displacement relationship of the pile group, the bending moment-depth relationship of each pile in the pile group, the deflection-depth relationship, and the soil resistance distribution were investigated. The results indicate that the lateral bearing capacity of the pile group decreases by more than 50% when the pile spacing is reduced from 7D to 3D. When the pile spacing is greater than 5D, the "edge effect" of the laterally loaded pile group gradually decreases, and when the pile spacing is greater than 7D, the "shadowing effect" can be negligible, and the wedge-shaped failure zone of the pile group occurs within a depth of 5D below the mud surface.

Effects of clay in a sandy soil on saturated/unsaturated pore water flow and dissolved chloride transport from road salt applications.

Saturated/unsaturated pore water flow induced by rainwater infiltration in a soil column composed of a mixture of Toyoura sand and a small amount of clay (kaolin minerals) and the rinsing rate (mass transfer) of dissolved NaCl accumulated in the pore system from previous road salt application were investigated by experiments and simulations. Experiments were conducted with variable kaolin minerals mass contents (mixing ratios) in the soil columns. Measured saturated hydraulic conductivity (Ks) diminished with increased clay contents, i.e., Ks=0.00771, 0.00560, 0.00536, 0.00519, and 0.00314 cm s-1, for clay contents = 0.2, 0.5, 1, 2, and 5%, respectively. Experimental NaCl concentrations in the effluent from the bottom of the soil columns were about constant for times t ≈ 800, 1200, 1300, 1400, and 3400 s from the beginning of a rinsing experiment for the clay contents = 0.2, 0.5, 1, 2, and 5%, respectively. These NaCl concentrations then decreased with time quickly, and finally, approached zero. The presented model can reproduce experimental time variations of NaCl concentration in the effluent from the soil column reliably. Simulated salt mass left in the soil column with time also matches the experimental results for the clay contents = 0.2 and 0.5%. An inconsistency between simulated and experimental salt mass left in the soil columns becomes more significant as the clay content increases. These results suggest that the soil-water retention curve for the pure Toyoura sand can be applied to the soil column composed of kaolin minerals/Toyoura sand mixture when the clay content is small, i.e., less than 1%. Prediction of rinsing process becomes more difficult with increased clay content. However, the time required to remove saline water from the soil column to less than 1% of its initial value simulated by the model agrees closely with experimental results of 1000, 1500, 1700, 2100, and 5400 s, respectively.

Visualization of Toyoura sand-grown plant roots by X-ray computer tomography.

Plants establish their root system as a three-dimensional structure, which is then used to explore the soil to absorb resources and provide mechanical anchorage. Simplified two-dimensional growth systems, such as agar plates, have been used to study various aspects of plant root biology. However, it remains challenging to study the more realistic three-dimensional structure and function of roots hidden in opaque soil. Here, we optimized X-ray computer tomography (CT)-based visualization of an intact root system by using Toyoura sand, a standard silica sand used in geotechnology research, as a growth substrate. Distinct X-ray attenuation densities of root tissue and Toyoura sand enabled clear image segmentation of the CT data. Sorghum grew especially vigorously in Toyoura sand and it could be used as a model for analyzing root structure optimization in response to mechanical obstacles. The use of Toyoura sand has the potential to link plant root biology and geotechnology applications.