Search Results (7)

A large set of undrained compression triaxial tests was carried out on different types of cohesionless soils, from sands to silty sands and silts. Shear wave velocity measurements were also carried out. These tests exhibit distinct state transitions ranging from flow liquefaction to strain softening or strain hardening. With the purpose of defining a framework to assess soil liquefaction, it was found that the ratio between the shear wave velocity (V_S0) and the peak undrained deviatoric stress (q_peak), V_S0/q_peak, could be accurately used to define a boundary between liquefaction and strain hardening for sands and between strain softening and strain hardening for silty sands and silts. Since this ratio is a function of the tested material, the prediction of these boundaries can be made as a function of soil grading, namely via the coefficient of uniformity, C_U. Despite not being regarded as a strong geomechanical parameter, C_U is easily determined from a grain-size distribution test and has an empirically proven correlation with critical state parameters. Full article

This is the first study on “ribbed smoked sheets (RSS)” as a geogrid reinforcement in geotechnical engineering. An RSS is a kind of natural para rubber. RSS (grade 3) was designed as a biaxial geogrid with an aperture size of 20 mm × 20 mm and a spacing of 20 mm. The RSS was found to be a significant functional layer when applied to the subbase lateritic soil layer. The lateritic soil with an RSS reinforcing layer was greatly improved regarding the California bearing ratio (CBR). Numerical simulation using two-dimensional finite element software was used to determine the optimal number and positions of the RSS reinforcing layers in road embankment stabilization. The simulation data in terms of horizontal displacement of unreinforced road embankments was validated by the collected data from the actual construction site. The RSS reinforced layer was varied from one to three layers under 61 analysis conditions. The highest safety factor was obtained with two layers of RSS at 0.1H below the top of the road embankment and 0.4H below the first RSS layer, suggesting a suitable installation of the RSS reinforcing layer. The RSS is thus strongly recommended as a reinforcing material in low CBR lateritic soil for the road embankment. Full article

Clay–gravel mixture has been widely used in high embankment dams and understanding its seepage characteristics is critical to dam safety. From the instrumental perspective, the realization of continuous pressurized water supply becomes a key technical challenge, significantly restricting the working conditions replicated in previous seepage apparatuses. To this end, a novel water provision system, relying on parallel-disposed sensor-based pressure devices, was introduced, so that the application of an existing large-scale stress-controlled apparatus can be expanded to long-term seepage tests regarding coarse-grained cohesive soils. Constant-head permeability tests were conducted on original-graded clay–gravel mixtures to investigate their hydraulic properties, incorporating the influence of stress relaxation. Test results show that with 35% gravel content, the clay–gravel mixture is suitable for dam construction as the core material. The stress relaxation holds a marginal effect on the hydraulic conductivity of soil. The functionality of this improved apparatus is verified, especially under long-term seepage conditions. Full article

Colloidal nano-silica (NS) hydrosols are electrochemically stabilized, polymerized amorphous silica in low viscosity solutions, and in the form of hydrated gels, silica globules or pellicles. Compared to applications in concrete technology, the use of silica-based binders for groundwork applications has received little attention. Silica-based hydrosols impose no known direct risks to humans and are generally courteous to the soil health and ecosystem service functions. Their localized impact on microorganisms however needs to be further investigated. To this end, NS hydrosols have a scope for use as an alternative low-viscose material in groundworks. The current understanding of interactions between NS hydrosols and soil (sand) is, however, confused by the limited availability of experimental evidence concerning undrained static flow and large strain behavior. The contributions, presented in this paper, advance the knowledge through experimental testing, molecular modelling, and micro-analytical measurements. Four grades of colloidal NS (1–15 wt.%) were synthesized for grouting medium-dense sub-angular fine siliceous sand specimens. Consolidated-undrained triaxial compression testing was performed on the base and treated sand for isotropic consolidation over the effective stress range 100–400 kPa. Overall, silica impregnation produced improvements in yield and residual undrained shear strengths, restricted unwelcomed impacts of excess pore water pressure, and led to the formation of generally more dilative, strain-hardening behavior. Steady states and static flow potential indices are also studied as functions of confinement level and viscosity of the NS grout. Full article

A new nano-soil stabilizer (N-MBER, Nanometer Material Becoming Earth into Rock) material was developed in this research by using the high activity and ultrafine properties of nano-SiO₂ (NS), which were able to improve the properties of cement-based soil stabilizer and had broad application prospects. The results showed that (1) the strength of N-MBER obeyed a compound function relation with curing period and additive amount of NS. The relationship between strength and curing period obeyed an exponential function when the additive amount was constant. The strength and additive amount were a power function when the curing period was fixed. The compressive strength of N-MBER increased by more than 15% compared with MBER at day 28 of the curing period, and 50% compared with grade 32.5 cement. (2) The pozzolanic catalytic activity of NS significantly increased the amount of calcium silicate hydrate gel (C–S–H) in the N-MBER colloid. NS was also able to make the distribution of the network structure of colloidal space more uniform and improved the fractal dimension of particles by 0.05. The above results provide theoretical data for exploring the mechanism of soil stabilizer strength growth and for promoting the application of solid waste utilization. Full article

Binary soil mixture, containing large silica particles (sand) mixed with variable content of very fine silt or clay, is an example of a functionally graded material that is important for several science and engineering applications. Predicting the porosity (or void ratio), which is a fundamental quantity that affects other physical properties, of such material as function of fines (clay or silt) fraction can be significant for sediment research and material design optimization. Existing analytical models for porosity prediction work well for binary mixed soils containing multi-sized non-cohesive particles with no clay, while such models frequently underestimate the porosity of sand-clay mixtures. This study aims to present an analytical model that accurately predicts the porosity of mixed granular materials or soils containing sand and very fine silt or clay (cohesive particles). It is demonstrated that accounting for the cohesive nature of very fine particles, which exists due to the effect of inter-particle forces, is a major missing aspect in existing packing models for mixed soils. Consequently, a previously developed linear packing model is modified so that it accounts for fines cohesive packing in sand-fines mixtures. The model prediction is validated using various experimental published data sets for the porosity of sand-fines mixtures. Improvement in the prediction of permeability and maximum packing dry density when incorporating cohesive packing behavior is discussed. The current model also provides important insights on the conditions under which, the lowest permeability and maximum packing state are expected. Full article

To design holographic and impulse ground penetrating radar (GPR) sensors suitable for humanitarian de-mining in the Donbass (Ukraine) conflict zone, we measured critical electromagnetic parameters of typical local soils using simple methods that could be adapted to any geologic setting. Measurements were recorded along six profiles, each crossing at least two mapped soil types. The parameters selected to evaluate GPR and metal detector sensor performance were magnetic permeability, electrical conductivity, and dielectric permittivity. Magnetic permeability measurements indicated that local soils would be conducive to metal detector performance. Electrical conductivity measurements indicated that local soils would be medium to high loss materials for GPR. Calculation of the expected attenuation as a function of signal frequency suggested that 1 GHz may have optimized the trade-off between resolution and penetration and matched the impulse GPR system power budget. Dielectric permittivity was measured using both time domain reflectometry and impulse GPR. For the latter, a calibration procedure based on an in-situ measurement of reflection coefficient was proposed and the data were analyzed to show that soil conditions were suitable for the reliable use of impulse GPR. A distinct difference between the results of these two suggested a dry (low dielectric) soil surface, grading downward into more moist (higher dielectric) soils. This gradation may provide a matching layer to reduce ground surface reflections that often obscure shallow subsurface targets. In addition, the relatively high dielectric deeper (10 cm–20 cm) subsurface soils should provide a strong contrast with plastic-cased mines. Full article