粗粒土缩尺级配的渗透系数规律试验

Experimental Study on Permeability Coefficient Test Method of Coarse-grained Soil with Scaled Gradation

粗粒土广泛应用于土石坝和软弱地基处理工程,渗透特性对工程设计的安全性具有重要影响。受室内仪器尺寸限制,只能对原级配粗粒土进行缩尺处理才能试验。然而,原级配粗粒土缩尺会改变土颗粒之间的孔隙大小及孔隙通道之间的连通性,导致缩尺后粗粒土室内渗透试验结果与原级配土的渗透系数存在一定差异,这种差异对准确了解原级配土的渗透特性十分重要。因此,如何通过缩尺试样试验结果准确预测原级配土的渗透系数,成为评价工程现场粗粒土渗透特性的关键。本文基于连续级配方程,将颗粒最大粒径d_(max)和级配面积S作为变量,设计16组不同级配试样,利用自制大型常水头渗透仪对各组试样进行室内渗透试验,定量研究缩尺级配的渗透系数变化规律,并找出不同级配土之间渗透系数换算的方法。结果表明:当级配面积S一定时,渗透系数k随d_(max)增大而增大,级配面积越小该规律越明显;当最大粒径d_(max)一定时,渗透系数k随级配面积S增大而减小;d_(max)和S对k的影响规律可分别用特定函数形式定量描述。根据d_(max)和S与k的关系式建立粗粒土不同级配之间的渗透系数换算模型,通过文献计算出该模型对各类粗粒土不同级配下渗透系数预测值与实测值的误差均在6%内,并利用缩尺级配试验结果反推出原级配渗透系数值且误差仅为2.5%,验证了该渗透系数计算模型对粗粒土的适用性。

Coarse-grained soil is extensively utilized in soil and rock dam engineering as well as in projects addressing weak foundations.The permeability characteristics of coarse-grained soil are critical to the safety of engineering designs.Due to indoor instrument size limitations,only a scaled-down version of the original coarse-grained soil can be tested.However,reducing the original grain size alters the pore size between soil particles and the connectivity of pore channels,leading to variations in the permeability coefficient between the scaled-down and original grainsized soils.This variation is crucial for accurately determining the permeability characteristics of the original grain-sized soil.Therefore,accurately predicting the permeability coefficient of the original grain-sized soil through tests on scaled-down samples has become essential in evaluating the permeability characteristics of coarse-grained soil at engineering sites.Utilizing the continuous grading equation,16 different grading samples are designed,using the maximum particle diameter d_(max)and grading area S as variables.The permeability of each sample is quantitatively analyzed using a self-made large constant head permeameter,and the variations in the permeability coefficient of scaled-down grading are examined along with a method for converting the permeability coefficient between coarse-grained soils with varying gradations.The results indicated that when the grading area S remains constant,the permeability coefficient k increases with the increase in the maximum particle diameter d_(max).This trend is more pronounced when the grading area is smaller.Conversely,when the maximum particle diameter d_(max)remains constant,the permeability coefficient k decreases with the increase in the grading area S.The impacts of d_(max)and S on k can be quantitatively described using specific functions.A permeability coefficient conversion model between different gradations of coarse-grained soil is established based on the relationship among d_(max),S,and k.According to the literature,the prediction errors of the permeability coefficient values for different grades of coarse-grained soil obtained using this model are within 6%of the measured values.Additionally,the original permeability coefficient values are successfully estimated using the scaled-down sample test results,with an error of only 2.5%,verifying the applicability of this permeability coefficient calculation model to coarse-grained soil.