Experimental study on influence of dry density and temperature on uniaxial compression characteristics of frozen sand
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摘要: 以南昌轨道交通2号线东延工程的砂土为对象,通过单轴压缩试验,系统分析了相对密度和冻结温度对冻结砂土的破坏模式、应力−应变关系、抗压强度和弹性模量的影响。研究发现,冻结砂土在单轴压缩下的破坏模式主要表现为塑性剪切破坏和塑性劈裂破坏,且应力−应变曲线呈现出应变软化行为。相对密度的增加和冻结温度的降低均导致试样破坏的脆性特征更加明显。冻结砂土单轴抗压强度和弹性模量均呈现出随相对密度增加和冻结温度降低而显著增长的规律。随着相对密度的提高,砂土对温度波动的敏感度增加。通过回归分析,建立了单轴抗压强度和弹性模量与相对密度及温度之间的关系方程。基于试验数据,建立了一个数学模型来描述冻结砂土的应力−应变曲线,并通过与试验数据的比较验证了模型的有效性。Abstract: Sandy soil specimens obtained from the East Extension Project of Nanchang Metro Line 2 underwent uniaxial compression testing to systematically investigate the effects of relative density and freezing temperature on failure modes, stress-strain relationships, uniaxial compressive strength, and elastic modulus of frozen sand. The investigation revealed that frozen sand under uniaxial compression predominantly exhibits failure modes characterized by plastic shear failure and plastic splitting failure, with stress-strain curves displaying notable strain-softening behavior. An increase in compaction degree coupled with a decrease in freezing temperature markedly enhances the brittle characteristics observed in specimen failure. The uniaxial compressive strength and elastic modulus of frozen sand exhibit a significant increase in response to higher compaction degrees and lower freezing temperatures. As compaction degree rises, the sensitivity of sand to temperature fluctuations correspondingly intensifies. Through regression analysis, a relationship equation was formulated between uniaxial compressive strength and elastic modulus as functions of compaction degree and temperature. Based on the experimental data, a mathematical model was developed to characterize the stress-strain behavior of frozen sand, with its validity substantiated through comparison with experimental results.
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Key words:
- metro tunnel /
- frozen sand /
- uniaxial compression /
- mechanical properties /
- stress-strain relationship
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表 1 隧道围岩基本分类和岩土施工工程分级
层号 土层名称 主要工程地质特征 开挖后土岩稳定状态 围岩分级 岩土施工工程分级 ①1 杂填土 主要为素填土和耕土,局部为杂填土,全场分布,
均位于地表浅部,疏密不均易崩塌 Ⅵ Ⅰ—Ⅱ(砼路面为Ⅳ级) ③1 粉质黏土 可塑,局部软塑,中等压缩性 自稳性差,易塌 Ⅵ Ⅱ级普通土 ③2 中砂 稍密—中密,级配不良,局部含黏性土 自稳性差,易塌 Ⅵ Ⅰ级松土 ③3 砾砂 中密,级配不良 自稳性差,易塌 Ⅵ Ⅰ级松土 ③4 圆砾 中密,级配不良 易出现地表下沉(陷)或塌至地表 Ⅴ Ⅲ级硬土 表 2 砂土的基本物理性质
粒度成分/% 最小干密度/(g∙cm−3) 最大干密度/(g∙cm−3) 2~5 mm 1~2 mm 0.5~ 1mm 0.25~0.5 mm 0.075~0.25 mm <0.075 mm 19.54 9.38 23.26 35.27 11.99 0.56 1.56 1.82 表 3 冻结砂土单轴压缩试验方案(w=20%)
组别 相对密度/% 干密度/(g∙cm−3) 饱和度/% 温度/℃ 1 30 1.63 86 −5,−10,−15,−20 2 50 1.68 93 −5,−10,−15,−20 3 70 1.73 100 −5,−10,−15,−20 表 4 弹性模量与温度拟合曲线参数
相对密度/% a b 拟合系数 30 215.76 0.944 0.9866 50 268.19 0.944 0.9973 70 345.59 0.944 0.9990 表 5 应力应变曲线模型参数
相对密度/% 温度/℃ m n l(10−3) 30 −5 0.034 1.906 3.227 −10 0.004 1.912 2.766 −15 0.022 1.722 1.913 −20 0.021 1.203 1.474 50 −5 0.061 1.352 2.761 −10 0.005 1.950 2.167 −15 0.037 1.052 1.546 −20 0.015 1.570 1.179 70 −5 0.090 0.789 2.223 −10 0.042 1.023 1.601 −15 0.012 1.630 1.223 −20 0.041 0.688 0.913 -
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