珊瑚礁岛钙质砂细颗粒渗透运移规律研究

Experimental study of filtration&fine particles migration of calcareous sand in coral reef island

钙质砂因其独特的生物成因、形成环境和沉积过程,颗粒形态不规则易破碎,结构松散黏聚力弱,与常见的陆源砂存在较大差异。黏聚力弱的细粒成分可能会因渗透作用而挣脱束缚,发生迁移和再积聚,从而引起孔隙和渗透性的变化。为此,开展不同初始条件下的渗透试验和渗出液沉淀物激光粒度分析,研究钙质砂渗透过程中渗透系数的变化规律和细颗粒运移特征。试验结果显示细颗粒容易在渗流条件下流失,导致土体结构和渗透性的局部变化。级配、密实度、渗流水力梯度均对渗透过程中细粒流失产生重要影响,表现为土体粗粒含量越高,密实程度越低,渗流水力梯度越大;细颗粒越易流失且流失颗粒粒径越大,渗透系数变化幅度越大。钙质砂渗透过程中细粒流失的主要粒径范围受级配影响显著,颗粒级配中粗颗粒含量越少,则流失的颗粒粒径越小,反之亦然。

Due to its unique biogenesis,forming environment and deposition process,calcareous sand is featured with irregularity,brittleness,weak structure and low cohesion,and is considered substantially different from the common terrestrial sand deposits.Fine particles bonded with weak cohesion may be resolved by osmotic action and then migrate and reaccumulate,thus causing changes in porosity and permeability.This study has carried out filtration experiment and laser particle size analysis of exudate sediment under different initial conditions to analyze the principles of evolution,involving permeability coefficient and the characteristics of fine particle transporting during the filtration process in calcareous sand.The results show that the loss of fine particles tends to occur under the seepage condition,and that results in the local changes of soil structure and permeability.The factors including the grading,compactness and percolation hydraulic gradient play important roles in fine grain loss in the process of filtration.The results show that the higher soil coarse grain content is,the lower degree of compactness is,and the larger percolation hydraulic gradient is,which lead to the loss of fine particles easily and additionally,enlarging the size of losing particles as well as range of permeability variation.The main particle size range of fine grain loss during calcareous sand filtration is significantly affected by grading.The smaller the content of coarse grain in grading results in smaller particle size of grain loss,and vice versa.