Distributed Fiber Optics Measurements of Rock Deformation and Failure in Triaxial Tests

Abstract

Constitutive models are used to describe the mechanical behavior of materials (Karev et al., 2020;Nadai, 1963;Puzrin, 2012). These consist of mathematical equations that can be used to relate physical quantities and are defined by material-specific constants (Davis & Selvadurai, 2005). The design of civil engineering structures relies on the precise calibration of these constants (Alonso et al., 2010;. Triaxial tests are commonly carried out to obtain the constitutive parameters of geomaterials (Jaeger et al., 2007). It is generally assumed that the triaxial test is a representative volume test, meaning that the developed stresses and strains are uniform in the sample. Accurate detection of a sample's strain is important for the determination of the mechanical properties. Linear variable differential transformers (LVDT) and strain gauges are common technologies to measure the strain response. The drawback is that the measurement is limited to the point or small zone where they are installed, forcing the assumption of a homogeneous sample response in accordance with the representative volume assumption. However, recent numerical and experimental studies have shown strain localization in the samples, even at early test stages (McBeck et al., 2019;Van der Baan & Chorney, 2019). This implies that when point measurement methods are used, the mechanical parameters obtained are dependent on the sensor location.

Importance of Water‐Clay Interactions for Fault Slip in Clay‐Rich Rocks

“…Distributed strain sensing (DSS) was performed using fiber optics (FO) strain sensors described for laboratory applications by Salazar Vásquez et al. (2022). Polyimide‐coated fibers with a cross‐sectional diameter of 155 μm and a LUNA ODiSI 6104 interrogator were used.…”

“…The strain coefficient of the polyimide fiber was calibrated to C ɛ = 0.15 × 10 6 GHz before the experiments (Salazar Vásquez et al., 2022). From the time‐strain (Δ ɛ ) data, the strain rate $$\dot{\varepsilon }$$ was determined based on a moving slope with a window length of 2.5 s (50 time steps).…”

Laboratory Investigation of Hydraulic Fracture Growth in Zimbabwe Gabbro

“… Note . The elastic properties have been measured via quasi‐static triaxial tests (Vásquez et al., 2022) at a confinement of 0 and 10 MPa (with similar values for both confinement), and the mode I fracture toughness from semicircular bending (SCB) test (Kuruppu et al., 2014). The connected pore volume was measured by gas pycnometer.…”

Laboratory acousto-mechanical study into moisture-induced changes of elastic properties in intact granite

“…Specimens were tightly wrapped in a rubber jacket and placed into a conventional triaxial machine, LabQuake, located in the Rock Physics and Mechanics Laboratory at ETH Zurich. 90 The system can achieve confining pressures up to 170 MPa and exhibits a minimum frame stiffness of 2500 kN/mm. P-and S-wave transmitter-receiver pairs, installed in the two loading platens, were assembled with specimens at two ends to generate P or S waves at a resonant frequency of approximately 1 MHz through the specimen in the axial direction.…”