Effect of Sample Preparation on Saturated and Unsaturated Shear Strength of Cohesionless Soils

Abstract

The geotechnical behavior of cohesionless soils is governed by field conditions. Such soils exist in two distinct forms, namely: disintegrated, such as fresh sediments under no overburden and/or no suction, and intact, such as old deposits with overburden and/or suction. The main contribution of this research was the successful capture of field conditions in laboratory samples, and the determination of shear strength under saturated and dried states. Results indicated that disintegrated samples possess identical soil behavior under both saturation states. Shear stiffness and peak shear increased with increasing normal stress, and no clear failure peaks were observed, similar to loose soils. Both samples showed an initial contraction followed by dilation at low normal stresses and mostly contraction at high normal stresses. Apparent cohesion was non-existent, and the friction angle measured 44.5° in the saturated state and 48° in the dried state. The intact sample exhibited behavior similar to the disintegrated sample when saturated. Under the dried state, clear failure peaks followed by residual shear were observed, similar to dense soils. Soil response was primarily dilative at low normal stresses and largely contractive under high normal stresses. Apparent cohesion was zero, and friction angle was 42° in the saturated state and changed to 91 kPa and 36°, respectively, in the dried state. Finally, structural cohesion increased with normal stress, and the friction angle due to suction was between 0.05° and 0.02°.

A Transient Seepage–Thermal Stability Model for Cohesionless Soil Slopes in the Semi-Arid Continental Climate of the Canadian Prairies

“…For NP-NL (Figure 8a), the initial FS fluctuation extended by two months till end of June (due to saturated conditions arising from excess precipitation compared to evaporation), followed by an increase up to 1.5 (similar to mean climate conditions) till the end of September, an abrupt change to 1.1 during October (because lower the temperature reduces evaporation, thereby ensuring close to saturation), and a gradual reduction to 0.9 by the end of December (owing to continuous temperature reduction). Under the same conditions with TL (Figure 8b), the FS trend and values were quite similar to mean climate conditions (increased sliding moment), along with a reduction in resistance due to the collapse of the soil structure in wet climate conditions [99]. For US-NL (Figure 8c), the trends and FS values are similar to their counterparts for mean climate conditions such that the period for FS < 1 was extended till the end of June, and the period for FS > 1 was reduced till the end of September; the reasons for these observations are the same as before.…”

“…The reported shear strength parameters (c = 0 and ϕ = 42 • ) for intact cohesionless soil under full saturation was used [99]. The unsaturated shear strength parameters were estimated using Equation (3).…”

Determination of the Basic Geotechnical Parameters of Blast-Furnace Slag from the Kremnica Region

“…In Figure 7, we also see dilatancy curves; the slag samples increased their volume with increasing shear. For the practical purposes of designing building structures, the dilatancy angle ψ is given by Equation ( 4) [41][42][43]. Excellent determination coefficients of R 2 = 0.997 were achieved for both slag samples.…”