基于大型真三轴试验的粗粒料强度特性研究

基于长江科学院自主研制的大型微摩阻土工真三轴仪,对某土石坝粗粒料开展不同中主应力系数(等b)条件下的真三轴试验,探讨三向应力条件下粗粒料强度变化特征。研究表明:(1)中主应力对粗粒料强度影响显著,强度随b值增加而增加,特别是b值在0~0.25区间内,相较于常规三轴试验其强度指标显著增长;(2)经与几种经典强度准则对比,拉德–邓肯强度准则能相对较好地反映粗粒料在三向应力状态下强度演化趋势;(3)通过一组平面应变试验认为,不同围压下当偏应力接近峰值时,b值基本稳定在0.17~0.19,实际工程在试验条件有限的情况下,平面应变试验成果可用于粗略估算粗粒料在复杂三向应力状态下的强度。研究成果可为合理确定粗粒料复杂应力状态下强度参数及精细化研究粗粒料强度准则提供参考。

Large-scale true triaxial tests on strength characteristics of coarse-grained soils

In order to obtain the strength evolution of coarse-grained soils under three-dimensional stress conditions, a series of true triaxial tests under different intermediate principal stress ratios (also called b value) are conducted for a kind of sandstone coarse-grained soil using the large-scale low friction true triaxial apparatus developed by Changjiang River Scientific Research Institute. The results show that: (1) The effect of the intermediate principal stress (σ₂) on strength index is significant. With the increase of b value, the strength of coarse-grained soils increases, especially when the b value increases from 0 to 0.25, compared with that of the conventional triaxial tests, the strength shows a significant growth. (2) Comparison of several classical strength criteria for soils indicates that the Lade-Duncan strength criterion is more suitable in revealing the strength evolution of the research samples. (3) A group of plane strain tests are also carried out. Under the confining stress conditions, when the deviatoric stress approaches the peak value, the values of b are stable at the range of 0.17 to 0.19, so, for practical projects, if the test condition is limited, the plane strain tests can be used to make a rough estimation for the strength index of coarse-grained soils under complex three-dimensional stress conditions. The conclusions will offer the references for determining the strength index and making a refine research on strength criteria of coarse-grained soils under complex stress conditions.