水平渗流作用下无黏性土接触冲刷细颗粒起动机理分析

FINE SOIL PARTICLE ENTRAINMENT INDUCED BY CONTACT EROSION BETWEEN COHESIONLESS SOIL LAYERS UNDER HORIZONTAL SEEPAGE CONDITION

为了在细观层面上研究水平渗流作用下无黏性土接触冲刷的临界水力条件,构建了粗-细粒土层接触面上细粒土的两种冲刷起动模型。根据细粒土滑动和滚动两种失稳模式进行受力分析,并采用层流假设对流动切应力进行分析。提出了上部为粗粒土、下部为细粒土的无黏性土接触冲刷水平临界水力梯度的理论计算公式,依据试验中接触面可动细粒土起动位置的特征对公式进行了简化,并通过试验数据将本文公式与已有经验公式进行了对比,验证了其适用性。研究结果表明:水平临界水力梯度受粗-细粒土的粒径比和可动细粒土粒径的影响较大,受粗粒土孔隙率影响较小。该值与粒径比和粗粒土孔隙率成负相关,与可动细粒土粒径成正相关。当粗-细粒土粒径比不大于10时,接触冲刷不发生;当粒径比大于10且小于50时,临界水力梯度取决于粒径比和可动细粒土粒径的影响;当粒径比大于50时,临界水力梯度受可动细粒土粒径的影响较大。该文提出的公式中,可动细粒土的粒径值d_(i)由接触面上细粒土粒径分布特征决定,在计算时建议其取值不大于细粒土特征粒径d_(50);当细粒土粒径分布特征未知时,可取细粒土的特征粒径d_(15)。

To investigate the critical hydraulic cond_(i)tion of contact erosion between cohesionless soil layers under horizontal seepage flow,two instability modes of removable soil particles are established at the meso-level.A force analysis based on the slid_(i)ng and rolling process is employed for a single removable fine-grained soil particle at the interface between the coarse-and fine-grained layers,while the laminar flow hypothesis is used to analyze the flow shear stress.A theoretical formula for the critical hydraulic grad_(i)ent with overlying coarsegrained soil and underlying fine-grained soil is proposed.This formula is then simplified by considering the characteristics of the location where the fine particles initiate in the experimental observation.It is verified by comparing the calculation with existing empirical formulas accord_(i)ng to the experimental data.The results show that the particle size ratio of the coarse-and fine-grained soil and the particle size of the removable fine-grained soil are the two primary factors of the critical hydraulic grad_(i)ent.The influence of porosity of the coarse-grained soil is not apparent.The critical hydraulic grad_(i)ent is negatively correlated with the particle size ratio and porosity of the coarse-grained soil,while it is positively correlated with the size of the removable fine-grained soil particle.When the particle size ratio is no greater than 10,contact erosion does not occur.When the particle size ratio is greater than 10 but is no greater than 50,the critical hydraulic grad_(i)ent is mainly affected by the particle size ratio and the size of the removable fine-grained soil particle.When the particle size ratio is greater than 50,the main factor becomes the size of the removable fine-grained soil particle.The theoretical formula considers the d_(i)stribution of the fine-grained soil particles that determines the value of d_(i),which is recommended not to exceed d_(50).When the d_(i)stribution characteristics are not available,d_(15) is recommended as the value of the removable fine-grained soil particle size.