Evaluation of Horizontal Stresses in Soil during Direct Simple Shear by High-Resolution Distributed Fiber Optic Sensing

Abstract

This paper presents an approach for evaluating the horizontal stresses that develop in geotechnical Direct Simple Shear (DSS) tests through the use of high-resolution distributed fiber optic sensing. For this aim, fiber optics were embedded in 3D printed rings used for confining the soil in the test procedure. An analytical approach linking the measured spatially-distributed strain profile and the internal soil-ring contact stresses is developed in the paper. The method is based on representation of the contact stresses by a Fourier series expansion, and determining the coefficients of the series by minimizing the difference between the measured strain and the analytical strain within the linear elastic ring. The minimization problem results in a linear set of equations that can easily be solved for a given measurement. The approach is demonstrated on a set of drained DSS tests on clean sand specimens. Stress paths using the evaluated horizontal stresses are plotted together with Mohr circles at failure. These illustrate how, in these specific tests, the horizontal stress increases and principal stress direction rotates, until failure occurs along horizontal planes.

Cyclic Direct Shear Testing of a Sand with Waste Tires

“…Sand controls the behavior if the volumetric proportion of tire crumbs is less than 30% in the mixture, and rubber forms the skeleton, if the volumetric proportion of tire crumbs is above or equal to 60% [44]. These results are similarly observed by previous researchers [66,[75][76][77][78]. The summary of the maximum and minimum horizontal stresses measured at the end of each loading cycle for tested specimens is given in Table 4.…”

Long-Term Response of Sand Subjected to Repetitive Simple Shear Loading: Shakedown, Ratcheting, and Terminal Void Ratio

“…The initial normal stress σ 0 o and deviatoric stress τ o (Chang and Whitman 1988;Lekarp and Dawson 1998;Liu et al 2018;Gu et al 2020), as well as the cyclic stress amplitudes Δσ 0 and Δτ , control the accumulation of volumetric and shear strains (Silver and Seed 1971;Drnevich and Richart 1970;Youd 1972;Cai et al 2015;Klar et al 2019). Various stress ratios defined in terms of normal effective stress σ 0 or p 0 , shear stress τ or q, or stress obliquity η ¼ q=p 0 have been used to analyze experimental results including (p 0 -q quadrant in Fig.…”

“…This situation prevents the computation of stress invariants. Previous efforts to overcome this limitation have considered instrumented shear rings using fiber optics to measure lateral stress σ h and the radial strain field (Uchida et al 2015;Klar et al 2019), complementary triaxial and simple shear tests to estimate model parameters (Wood et al 1979), or assumptions such as coaxiality between principal stresses and strain increments at the maximum shear stress (Li et al 2018), although this approach may underestimate noncoaxiality and is less accurate when the stress state is lower than the failure state (Li et al 2021).…”

Special Issue “Fibre Optic Sensors for Structural and Geotechnical Monitoring”

“…Paper [3] reports the use of fibre optic distributed monitoring to investigate properties of geomaterial samples according to the laboratory procedure named direct simple shear test. A new procedure is proposed to evaluate some component of the stresses in the sample, taking advantage of the very high-resolution measurements that can be done by use of a proprietary implementation of the optical frequency domain reflectometry.…”