不同颗粒粒径的松散沉积物抗剪强度试验研究

Experimental Study on Shear Strength of Loose Sediments with Different Particle Sizes

浙江省嵊县组玄武岩中的河湖相沉积夹层,因胶结弱、强度相对较低,对山体边坡稳定存在威胁。该松散沉积层充填颗粒呈现下粗上细的沉积结构特征,颗粒粒径组成对整体抗剪强度特征有一定的影响。为此,基于缩尺方法设计并配制了3组最大颗粒粒径d_(max)分别为60,40,20 mm的重塑样,采用大型直剪设备对不同颗粒粒径组成的松散沉积物进行直剪试验,并结合分形理论,采用分形维数D_(F)作为粒度分布评价指标,分析了松散沉积物抗剪强度特征与d_(max)、D_(F)的相关性。结果表明:在直剪过程中,松散沉积物的剪应力-水平位移曲线无明显峰值,应力-应变关系呈应变硬化型;在控制含石量不变的条件下,对粗颗粒部分进行缩尺后发现,分形维数D_(F)随着最大颗粒粒径d_(max)的增大而增大;松散沉积物抗剪强度参数随颗粒组成特征变化明显,在同一干密度制样标准下,d_(max)、D_(F)越大,黏聚力c增大,而内摩擦角φ显著减小。研究结果对含松散沉积夹层边坡工程建设与稳定性分析具有一定借鉴意义。

The fluvial-lacustrine sedimentary interlayer in Shengxian formation basalt in Zhejiang Province is a threat to slope stability due to weak cementation and relatively low strength.The filling particles of the loose sediments have the characteristics of dual structure,and the particle size distribution has a certain influence on the overall mechanical strength characteristics.Therefore,the influence of particle size on shear strength is studied by large-scale direct shearing test.Based on scale theory,three groups of remodeled samples with maximum particle size d_(max)of 60 mm,40 mm and 20 mm were designed and prepared for direct shear test.Fractal dimension D_(F)was used as the evaluation index of grain size distribution,and the correlation between shear strength characteristics of loose sediments and d_(max),D_(F)was analyzed.The results show that there is no obvious peak value in the shear stress-horizontal displacement curve of loose sediments during direct shear test,and the stress-strain relationship is strain hardening.Under the condition that the rock content remains unchanged and only the bulk stone is scaled,the fractal dimension D_(F)of loose sediments is positively correlated with the maximum particle size d_(max),and the larger the d_(max)is,the higher the D_(F)value of the sample is.Shear strength parameters of loose sediments vary significantly with the characteristics of particle composition.Under the same dry density sample preparation standard,cohesion c increases with the increase of d_(max)and D_(F),while friction angleφdecreases with it.The results can provide reference for engineering construction and stability analysis of slopes with loose sediment interlayers.