砂性土细颗粒起动临界水力坡降计算方法

地下水渗流作用下内部不稳定砂性土将发生潜蚀现象，潜蚀作用引起的土体渗透破坏会对土工建筑物或地基造成不良影响。考虑土体有效应力和细颗粒应力折减，建立渗流场中细颗粒受力模型，根据极限受力平衡状态得到潜蚀过程中砂性土细颗粒起动临界水力坡降计算公式，并通过DEM-CFD耦合方法以及现有试验数据进行验证。结果表明：砂性土中细颗粒以滚动方式起动，起动临界水力坡降受渗流水流、土体特性以及颗粒自身特性共同影响；砂性土表层细颗粒起动临界水力坡降受埋深影响较大，埋深1 cm的细颗粒最高、最低起动临界水力坡降相差10.169%，埋深10 cm时差异减少至1.061%。该计算方法与数值模拟和渗流试验结果的最大标准误差分别为6.038%、11.211%，可以较为准确地预测砂性土细颗粒起动临界水力坡降。

Analytical solution of startup critical hydraulic gradient of fine particles migration in sandy soil

Suffusion will occur in the internally unstable sandy soil because of the groundwater seepage. Soil failure caused by the suffusion has adverse effects on the building structures or foundations. In this paper, a model that can calculate the force acted on fine particles in seepage field was established by considering the effective stress of soil and the stress reduction of fine particles. According to the equilibrium state of ultimate stress, the formula for calculating the startup critical hydraulic gradient of fine particles migration in sandy soil during the suffusion process was obtained. A DEM-CFD coupled method and the existing experimental data were used to validate the proposed model. The results showed that the fine particles in the sandy soil started in rolling mode in the beginning, and the startup critical hydraulic gradient is found to be affected by the seepage flow, soil characteristics, and the properties of the particles. The startup critical hydraulic gradient of fine particles on the surface of sandy soil was found greatly affected by the buried depth. The difference between the highest and lowest startup critical hydraulic gradient of the fine particles buried in 1 cm depth was 10.169%, and the difference was reduced to 1.061% when the buried depth was 10 cm. The maximum standard error of the calculation method was 6.038% while compared to the numerical simulation results, the maximum standard error compared to the seepage test results was 11.211%. Therefore, the proposed model can accurately predict the startup critical hydraulic gradient of sandy soil fine particles.