土壤团聚体与地面碰撞时的临界破碎速度与粒径分布

Threshold velocity and fragment size distribution for the rupture of soil aggregates colliding with land surface

风蚀导致的土地退化是全球性问题,跃移颗粒对地表冲击是关键的土壤风蚀过程。目前,土壤团聚体在跃移运动中的破碎过程和机制尚未完全被揭示。通过室内模拟实验,探讨干燥致密的土壤团聚体在与地面碰撞时的临界破碎速度与粒径分布规律。结果表明:(1)低速冲击下,土壤团聚体与地面碰撞过程中主要以损伤状态为主,碰撞产生的裂纹沿经线平面形成贯穿裂纹;较高速度下,碰撞接触区出现锥形体导致团聚体破碎。(2)粒径、密度、抗压强度和杨氏模量共同决定临界碰撞速度。由量纲理论和实验数据给出了具体的函数关系与经验常数。(3)碰撞过程中,壤土粉尘释放量随速度变化显著,黏土、砂土、砂质黏土、壤质黏土的粉尘释放量大部分小于团聚体质量的1%。(4)碰撞后的碎片分布规律可由双参数Weibull累积分布函数描述。由于存在内部缺陷,土壤团聚体碎片分散性不同于玻璃、陶瓷等常规脆性材料。

Land degradation due to wind erosion is a global problem,and the impact of saltation particles on the ground surface is the key soil wind erosion process.At present,the fragmentation process and mechanism of soil agglomerates in saltation movement have not been fully revealed.This paper explores the critical fragmentation velocity and fragment size distribution of dry dense soil agglomerates in collision with the ground through indoor simulation experiments,and obtains the following preliminary conclusions:(1)Under low-velocity impact,the collision process between soil agglomerates and the ground is mainly in the damage state,and the cracks generated by the collision form penetration cracks along the meridional plane;under higher velocity,cones appear in the collision contact area leading to agglomerate fragmentation.(2)The particle size,density,compressive strength,and Young's modulus jointly determine the threshold velocity.Specific functional relationships and empirical constants are given by the dimensional analysis and experimental data.(3)During the collision,the dust release of loam varies significantly with the velocity,and the dust release of clay,sandy soil,sandy clay,and loamy clay is mostly less than 1%of the aggregate mass.(4)The number and size of fragments after the collision can be described by the two-parameter Weibull distribution function.The collision of soil agglomerate fragments differs from that of conventional brittle materials such as glass and ceramics due to the presence of internal defects.