熔融石英砂动力特性动三轴试验

为探究振动荷载作用下熔融石英砂液化破坏过程中动变形和动强度变化规律, 促进透明土技术在岩土工程动力特性可视化模型试验中的推广和应用, 对构成透明砂土骨架结构的典型粒径(0.5~1.0 mm)熔融石英砂开展饱和试样动三轴试验; 研究了不同围压、加载频率和动应力比等试验条件下熔融石英砂试样的累积轴向应变、动孔压发展模式、动应力衰减、动弹性模量和阻尼比的变化规律, 并将试验结果与相同级配的标准砂进行了对比。分析结果表明: 熔融石英砂累积轴向应变随动应力比的增大呈现出由稳定型向破坏型转变的趋势, 加载频率为0.5~1.5 Hz时, 临界动应力比为0.150~0.175, 小于标准砂的0.200~0.225;升高围压、增大动应力比、降低加载频率会加快试样塑性应变累积, 缩短液化破坏时间; 熔融石英砂孔压发展模式随围压增大逐渐由Seed孔压模型向指数型过渡, 增大加载动应力会加剧液化破坏后孔压的振动幅度; 相同动应力比下, 熔融石英砂与标准砂的动应力与动应变呈现线性相关, 在围压大于200 kPa时, 二者动应力衰减幅度随围压的增大而逐渐减小; 熔融石英砂的动弹性模量和阻尼比表现为线性关系, 动弹性模量随动应变的增大呈现出双曲线型减小的趋势, 并随围压的增大而增大; 阻尼比随动应变的增加先增大后基本稳定在0.22, 发展曲线受围压影响较小。

Dynamic properties of fused silica sand based on dynamic triaxial test

To investigate the dynamic deformation and strength of fused silica sand in the process of liquefaction under vibration load, and promote the application of transparent soil technology in the dynamic characteristics visualization model test of geotechnical engineering, the dynamic triaxial tests on the saturated fused silica sand specimens with typical sizes(0.5-1.0 mm) forming the skeleton structure of transparent sand were carried out. The cumulative axial strain, development mode of dynamic pore pressure, attenuation of dynamic stress, and change rules of dynamic elastic modulus and damping ratio of fused silica sand specimens under the working conditions of different confining pressures, loading frequencies and dynamic stress ratios were studied, and the test results were compared with those of standard sand with the same gradation. Analysis result shows that the cumulative axial strain of fused silica sand changes from a stable type to a destructive type with the increase of dynamic stress ratio. The critical dynamic stress ratio is 0.150-0.175 as the loading frequency ranges from 0.5 Hz to 1.5 Hz, which is less than that of standard sand of 0.200-0.225. Increasing the confining pressure and dynamic stress ratio and decreasing the loading frequency will accelerate the accumulation of plastic strain of specimen and shorten the liquefaction failure time. With the increase of confining pressure, the development mode of pore pressure gradually changes from the Seed model to the exponential model. Increasing the dynamic stress will increase the vibration amplitude of pore pressure after the liquefaction failure. Under the same dynamic stress ratio, the dynamic stress changes of fused silica sand and standard sand are linearly correlated with the dynamic strain. When the confining pressure is greater than 200 kPa, the dynamic stress attenuation amplitude decreases with the increase of confining pressure. The relationship between dynamic elastic modulus and damping ratio is linear. The dynamic elastic modulus decreases hyperbolically with the increase of dynamic strain and increases as the confining pressure increases. The damping ratio increases first with the increase of dynamic strain and then basically stabilizes at 0.22, and its development curve is less affected by the confining pressure.