粗粒土三轴试验橡皮膜嵌入量测量方法研究

Measuring method for membrane penetration capacity of coarse-grained soil in triaxial tests

粗粒土试验的橡皮膜嵌入效应使得试样体积变形测量结果失真,从而影响其强度变形指标测量精度。为此,在同一试验仪器上开展了多组不同直径试样粗粒土的等向固结三轴试验,分析了橡皮膜的嵌入量的变化规律和影响因素,在此基础上提出了一个计算粗粒土橡皮膜嵌入量的经验公式。研究表明,橡皮膜的嵌入量随围压的增大而增大,与其围压大体呈幂函数关系。相同围压下,随着试样直径的增加,橡皮膜的嵌入量占总体变的比例减小;试样直径相同时,围压变化对橡皮膜嵌入量占总体变比例的影响明显小于试样直径变化的影响,且随着试样直径的增大,影响逐渐降低。因此,粗粒土的强度变形试验应尽可能采用较大直径的试样进行,以降低橡皮膜嵌入量对其试验结果的影响。由于粗粒土的母岩性质和级配变化较大,既有橡皮膜嵌入量计算公式将明显低估堆石料试样的橡皮膜嵌入量,建议采用本文提出的方法对粗粒土试样橡皮膜嵌入量进行估算。

The membrane penetration effects displayed in the coarse-grained soil tests will distort the measurement of volume deformation of samples,thereby affecting the measuring accuracy of strength and deformation index.To this end,by using the same test apparatus,multiple series of isotropic consolidation triaxial tests on the samples of coarse-grained soil with different diameters are implemented.The changing rules of membrane penetration capacity and the related impact factors are analyzed,and an empirical formula is proposed to calculate the membrane penetration capacity of coarse-grained soil.It is shown that the membrane penetration capacity increases with the increase of the confining pressure,and the relationship roughly follows a power function.Under the same confining pressure,with the increase of the sample diameter,the capacity of membrane penetration decreases.The influences of the confining pressure on the membrane penetration capacity are significantly smaller than those of sample size which gradually decreases as the sample diameter increases.Therefore,the strength and deformation tests on coarse-grained soil should be carried out by preparing larger-diameter samples,so that the influences of the membrane penetration effects can be greatly reduced.Due to the great changes in the nature and gradation of coarse-grained parent rock,the existing formulas for the membrane penetration capacity will significantly underestimate the membrane penetration effects of rock-fill samples.It is recommended to use the proposed method to estimate the membrane penetration capacity of coarse-grained soil.