Abstract
Recently, environment-friendly microbial biopolymer has been widely applied as a new construction material in geotechnical engineering practices including soil stabilization, slope protection, and ground injection. Biopolymer is known to exhibit substantial improvements in geotechnical properties, such as shear strength enhancement and hydraulic conductivity reduction, through the formation of direct ionic bonds with soil particles, especially clay particles. Moreover, the rheological characteristics (e.g., pseudoplasticity, shear-rate dependent thixotropy) of biopolymers render distinctive behaviors such as shear thinning and lubrication effect under a high strain condition, while recovering their viscosities and shear stiffnesses when they are at rest. To ensure the practical applicability of biopolymer-based soil treatment, it is important to understand the interfacial interaction (i.e., friction) between biopolymer-treated soil and adjoining structural members which can be constructed in a biopolymer-treated ground. Thus, in this paper, interfacial shearing behavior of biopolymer-treated soil along solid surfaces as well as internal shearing on biopolymer-soil matrix were explored via direct and interface shear test. Experimental results show a predominant effect of the soil moisture content on the interfacial shear behavior of biopolymer-treated soil which attributes to the rheology transition of biopolymer hydrogels. At low moisture content, condensed biopolymer biofilm mobilizes strong intergranular bonding, where the interfacial shear mainly depends on the physical condition along the surface including the asperity angle. In contrast, the biopolymer induced intergranular bonding weakens as moisture content increases, where most interfacial failures occur in biopolymer-treated soil itself, regardless of the interface condition. In short, this study provides an overall trend of the interfacial friction angle and adhesion variations of xanthan gum biopolymer-treated sand which could be referred when considering a subsequent structural member construction after a biopolymer-based ground improvement practice in field.
Highlights
Studying the shear behavior at the interface between the exterior surface of solid structures and the surrounding earth material is essential for understanding the soil–structure interaction, which plays an important role in the geotechnical engineering design of various structures including deep foundations, retaining wall structures, landfills, and slope stability [1]
Interfacial shearing of soil has been investigated by several researchers using various laboratory testing methods such as the interface direct shear, ring shear, simple shear, and resonant-column torsional shear tests [2,3,4,5,6]
State representative direct shear stress (τ)-horizontal displacement (δ) behavior of xanTheThe representative direct shear stress (τ)-horizontal displacement (δ) behavior of xanthan gum-treated sand according to different normal stress, moisture state, and than gum-treated sand according to different normal stress, moisture state, and MXG/MS XG
Summary
Studying the shear behavior at the interface between the exterior surface of solid structures and the surrounding earth material is essential for understanding the soil–structure interaction, which plays an important role in the geotechnical engineering design of various structures including deep foundations, retaining wall structures (e.g., anchored, reinforced, soil nailing), landfills, and slope stability [1]. The particle shape, which includes angularity and size distribution, surface roughness, cementation, and normal stress, mainly influences the interfacial shearing behavior of soil [7]. These factors induce variations in the apparent adhesion and interface friction angle (δ), which are considered as the main parameters for the design and analysis of the actual soil–structure interaction. In the general design of geotechnical structures having shear resistances or frictional behaviors between soil and solid materials, δ is considered to be in the range of 1/2–2/3 times the internal friction angle (φ) of soil, and the magnitude of interface adhesion (ca ) is typically considered to be a fraction of the soil cohesion (c) [8,9]
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