宽级配砾性土橡皮膜嵌入量计算新方法

橡皮膜嵌入影响分析是决定砾性土试验结果可靠性的关键问题,其影响因素、规律和计算方法存在很大争议,为目前影响砾性土力学性能理论研究发展和工程应用的瓶颈。通过双尺寸法,利用大型三轴仪,对11种级配的砾性土开展不同橡皮膜厚度的嵌入体积量测分析,获取单位面积橡皮膜嵌入体积与土骨架回弹体应变2个关键指标,分析主要因素影响规律,建立宽级配砾性土试样橡皮膜嵌入量新的计算模型和公式,并进行多方比较验证。研究及试验结果表明:双尺寸法在大尺寸三轴试验中对砾性土具有适用性和可靠性;单特征粒径如d₅₀或d₂₀都无法完整描述级配条件对橡皮膜嵌入体积的影响;橡皮膜厚度影响随土颗粒大小而变化,当d₂₀>2.5倍膜厚时影响可忽略不计;均等固结状态下卸载回弹中砾性土并非一直呈现各向同性,基于各向同性假定的嵌入量计算模型对宽级配砾性土不适用;宽级配砾性土橡皮膜嵌入体积计算可用d₁₀,d₂₀与d₅₀三因素新模型表示,新模型和计算公式形式简单,且较现有模型公式在精度和适用性上均明显占优。

A new calculation method for membrane penetration in wide-graded gravelly soils

The influence of membrane penetration is the key to determine the reliability of test results of gravel soils. Influencing factors and laws,and calculation methods of membrane penetration are still very controversial,which is the bottleneck of current theoretical research and engineering application of gravelly soils. By using the two-scale method and the large-scale triaxial apparatus,the penetration volumes of 11 kinds of graded gravelly soils were measured and analyzed with different membrane thicknesses,and two key indexes,the penetration volume of membrane per unit area and the elastic volumetric strain of soil skeleton,were obtained. Influencing laws of main factors were analyzed,and a new calculation method for the penetration volume of membrane in wide-graded gravel soil samples was established and verified in many aspects. The results show that the two-scale method is applicable and reliable for large-scale triaxial test of gravelly soils,and that the influence of grading condition on the membrane penetration cannot be fully described by single characteristic particle size such as d50 and d20. The influence of the membrane thickness varies with the size of soil particles and can be ignored when d20 is greater than 2.5 times the membrane thickness. It is also revealed that,under isotropic consolidation condition,the gravel soil in unloading stage is not always isotropic and hence,the calculation models of the penetration volume based on isotropy assumption are not suitable for wide-graded gravelly soils. The membrane penetration volume in wide-graded gravel soils can be calculated by the developed model with three factors of d10,d20 and d50. The new model and calculation formula are simple in form and obviously superior to the existing model formulas in accuracy and applicability.