荷载频率与粉粒含量对砂性土液化势影响试验研究

Experimental Study on Effects of Cyclic Loading Frequency and Silt Content on Liquefaction Potential of Sandy Soil

摘要:

荷载频率与粉粒含量对砂性土液化势及液化特性的影响，都有较多研究，但认识并不充分。基于福建标准砂筛选 1 种 0.5 mm 以下砂土，配以银川黄河粉砂筛选粉粒，采用 KTL 动三轴试验系统，分别进行等相对密度 30%、 70%，粉粒含量 0%、20%、40%、60% 试样，循环荷载频率分别为 0.1 Hz 和 1 Hz 下的均等固结动三轴液化试验。结果表明：加载 0.1 Hz 相对于 1 Hz，稳定变形阶段持续时间长、循环次数多，初始液化以后孔压波动幅度变得更大，表现出强剪胀性。但是，加载 0.1 Hz 液化强度低于 1 Hz 下，且 0.1 Hz 下轴向双幅应变会急剧增大，不应将这种液化模式归于“循环活动性”。加载 0.1 Hz 时，土颗粒间移动、摩擦更充分，拉压方向都能发挥出全段土样的强度，滞回圈拉压方向相对对称且饱满。而加载 1 Hz时，由于试样顶端软化出现应力集中，从变形增长阶段开始，动应力出现衰减，滞回圈表现出明显的拉压不对称，深度液化阶段，拉方向失去刚度和承载能力。总体来说，加载 0.1 Hz 相对于 1 Hz， 孔压发展更慢、最终孔压更低，应变发展先慢后快，抗液化强度更低。无论荷载频率和相对密度大小，随着粉粒含量增大，孔压上升和应变发展都越快，抗液化强度呈下降趋势。

Abstract:

The effects of cyclic loading frequency and silt content on the liquefaction potential and characteristics of sandy soil have been extensively studied, but the understanding remains insufficient. Based on Fujian standard sand, a type of sandy soil with particle size below 0.5 mm was selected, which was then mixed with silt particles sieved from the Yellow River silt in Yinchuan. Using the KTL dynamic triaxial test system, consolidated undrained cyclic triaxial liquefaction tests were conducted on soil samples with relative densities of 30% and 70% and silt contents of 0%, 20%, 40%, and 60% under cyclic loading frequencies of 0.1 Hz and 1 Hz, respectively. The results showed that compared to the 1 Hz load, under 0.1 Hz load, the stable deformation phase had a longer duration and a higher number of cycles. The amplitude of pore pressure fluctuation became larger after initial liquefaction, showing significant dilatancy. However, the liquefaction strength under 0.1 Hz was lower than that under 1 Hz, and the axial double amplitude strain increased sharply under 0.1 Hz loading. This liquefaction mode should not be classified as "cyclic mobility". Under 0.1 Hz load, the movement and friction between soil particles were more sufficient, the strength of the whole soil sample could be mobilized in both tensile and compressive directions, and the stress-strain hysteresis loop was relatively symmetrical and well-developed. In contrast, under 1 Hz load, stress concentration occurred due to softening at the top of the sample. From the deformation growth stage, the dynamic stress attenuated, and the stressstrain hysteresis loop showed obvious tensile-compressive asymmetry. During the deep liquefaction stage, the sample lost its stiffness and bearing capacity in the tensile direction. In general, compared to the 1 Hz load, under 0.1 Hz load, the pore pressure develops more slowly and reaches a lower final value, the strain initially develops slowly and then accelerates, and the liquefaction resistance is lower. Regardless of cyclic loading frequency and relative density, as the silt content increases, pore pressure rise and strain development become faster, and the liquefaction resistance shows a decreasing trend.