Cracks in the anti-seepage layer of earth-rock dams can lead to landslides or seepage damage, and during earthquakes, cracking is one of the most common seismic damages. Determining whether a dam cracks during an earthquake, estimating the depth of the crack, and assessing its impact on the dam’s stability are critical challenges in earthquake-resistant design. To address these issues, understanding the tensile properties of soil is essential. However, for accurate results, the testing methods must reflect the actual stress conditions the soil experiences. Several techniques have been developed to measure soil tensile properties, and this paper provides an overview of these methods and their key findings.
Currently, various tensile tests are used both domestically and internationally. The direct tensile test involves clamping the sample ends with fixtures or bonding them with cement to apply axial tension. Most tests are conducted under unconfined conditions, while some use triaxial devices to apply lateral pressure. However, stress concentration at the clamped areas often leads to fractures at those points, making it difficult to accurately assess the material’s true tensile behavior.
Indirect tensile tests avoid directly applying tension to the sample. Instead, they rely on theoretical models to estimate tensile strength. Common types include the soil beam bending test, where a rectangular beam is supported at both ends and loaded from above, causing tensile stress at the bottom. Another method is the Brazilian test, which applies diametrical pressure to split a cylindrical sample, commonly used for brittle materials like concrete. The axial fracturing test, also known as the unconfined stamping test, applies axial loads to split the sample, while the air pressure split test uses internal pressure to induce tangential fracture.
Published research has shown that soil tensile strength increases with water content and plasticity index up to optimal moisture levels, after which it declines. Tensile strain at failure also increases with higher moisture content. Different testing methods yield varying results, with the beam bending test generally giving the highest tensile strength and the fracturing or air pressure methods the lowest. Loading rate significantly affects the measured values, and repeated loading can reduce tensile strength, indicating progressive damage.
The Griffith criterion explains some cracking mechanisms but isn’t universally applicable. Experimental data from these studies are vital for understanding soil behavior, especially for seismic risk assessment. However, two key factors should be considered: first, most tests are conducted without confining pressure, whereas earth-rock dams experience significant vertical loading, requiring tests under different stress states. Second, dynamic earthquake loading differs from static conditions, with cyclic stresses influencing soil behavior. Therefore, dynamic triaxial tests with reverse loading are necessary to simulate real-world conditions.
To conduct such tests, specialized equipment is required. A triaxial device capable of applying both tension and compression is essential, along with a dynamic version that can simulate periodic loading. Acoustic emission sensors can detect micro-cracks by monitoring sound waves generated during deformation. Special molds are also needed to prevent premature failure at sample interfaces.
Triaxial tensile tests under static and cyclic loading help determine how soil behaves under different stress conditions. Acoustic emission analysis further aids in tracking internal damage progression, offering insights into when and how cracks form. These methods collectively enhance our ability to predict and mitigate seismic risks in earth-rock dams.
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