【作者】 李康；

【导师】 李伟华； 蔡国庆；

【作者基本信息】 北京交通大学 ， 土木水利（专业学位）， 2022， 硕士

【摘要】 冻土在我国分布广泛,由此引发的基础设施建设及运营中的安全问题也日益突出。尤其是在季节性冻土区,受复杂气候条件影响,土体总是处于冻融循环交替作用下,因此土体持水、变形及强度特性会发生强烈变化,从而引发诸如路基冻胀融沉、翻浆冒泥、基坑冻害等工程问题。因此,开展冻融循环作用下季节性冻土的持水、变形及强度特性的试验研究,具有重要意义。作为川藏铁路的重要组成,拉林段总体位于我国西藏自治区东南部,其中山南站所在区域属于典型大陆性季风气候,基坑土体冻融效应显著。本文依托川藏铁路拉林段山南站站房基坑工程,采用室内试验和数值模拟手段,开展了冻融循环作用下山南砂土的持水、变形和强度特性试验研究,并对基坑冻胀机理开展了有限元数值模拟研究。具体研究内容和成果如下:(1)基于轴平移技术和滤纸法,开展了山南砂土持水特性的试验研究。基于轴平移技术和滤纸法,对不同干密度条件下山南砂土的土-水特征曲线进行了试验测定,得到了全吸力范围内的土-水特征曲线,并对轴平移法与滤纸法的结果进行了对比分析,揭示了受干密度影响的山南砂土持水特性演化规律。(2)基于固结仪和三联温控非饱和土三轴仪,开展了山南砂土变形特性的试验研究。基于固结仪,研究了考虑初始含水率、压实度及冻融循环次数影响的山南砂土一维压缩特性;基于课题组研制的三联温控非饱和土三轴仪,研究了考虑初始干密度、饱和度及冻融循环次数影响的山南砂土三维体变特性。(3)基于直剪仪和三联温控非饱和土三轴仪,开展了山南砂土强度特性的试验研究。基于直剪仪,研究了冻融循环影响下的山南砂土强度指标演化特征;基于课题组研制的三联温控非饱和土三轴仪,研究了考虑初始干密度、饱和度及冻融循环次数影响的山南砂土强度指标演化特征。(4)基于多场耦合数值模拟软件COMSOL,开展了典型站房基坑工程热-水-力耦合效应数值模拟研究。基于多场耦合模拟软件COMSOL以及山南砂土的试验研究成果,建立了山南站基坑有限元模型,开展了基坑温度场、水分场和应力场的数值计算,揭示了由于气温周期更替诱发的基坑变形规律。更多还原

【Abstract】 Frozen soil is widely distributed in China,which causes the security problems in infrastructure construction and operation.Especially in the seasonal frozen soil region,the soil is always under the alternating action of freezing-thawing cycles under the influence of complex climate conditions,so the water retention,deformation and strength characteristics of the soil will change strongly,which leads to engineering problems such as roadbed frost heaving and thawing settlement,mud turning and caking,and foundation pit freezing damage.Therefore,it is of great significance to carry out experimental research on water retention,deformation and strength characteristics of seasonal frozen soil under freezing-thawing cycles.As an important component of Sichuan-Tibet Railway,the Lalin section is generally located in the southeast of Tibet Autonomous Region of China.The area where Shannan Station is located has a typical continental monsoon climate,and the soil in the foundation pit has a significant freezing-thawing effect.In this paper,based on the foundation pit of shannan station of Lalin section of Sichuan-Tibet Railway,laboratory tests and numerical simulation methods were used to carry out the experimental research on the characteristics of water retention,deformation and strength of sand soil in Shannan under freezing-thawing cycles,and the finite element numerical simulation study on the mechanism of pit frost heave was carried out.The specific research contents and results are as follows:(1)Based on axial translation technology and filter paper method,the experimental study on water holding characteristics of sand in Shannan was carried out.Based on axistranslation technique and the method of filter paper,shannan sandy soil under the condition of different dry density of soil and water characteristic curve,the test is carried out by the range of suction of soil water characteristic curve,and the results of axial translation method and filter paper method has carried on the comparison and analysis,reveals the shannan sandy soil moisture characteristics affected by dry density evolution.(2)Based on the consolidation instrument and the triple temperature control unsaturated soil triaxial instrument,the experimental study on the deformation characteristics of sand in Shannan was carried out.Based on the consolidation instrument,one-dimensional compression characteristics of sand in Shannan were studied considering the influence of initial water content,compaction degree and number of freeze-thaw cycles.Based on the triple temperature-controlled unsaturated soil triaxial apparatus developed by the research group,the three-dimensional volume change characteristics of sand in Shannan were studied considering the effect of initial dry density,saturation and the number of freeze-thaw cycles.(3)Based on direct shear apparatus and triaxial apparatus of unsaturated soil controlled by triple temperature,experimental research on strength characteristics of sand in Shannan was conducted.Based on direct shear apparatus,the evolution characteristics of sand strength indexes under the influence of freezing-thawing cycle in Shannan were studied.Based on the triple temperature-controlled unsaturated soil triaxial instrument developed by the research group,the evolution characteristics of sand strength indexes in Shannan were studied considering the influence of initial dry density,saturation and the number of freeze-thaw cycles.(4)Based on multi-field coupling numerical simulation software COMSOL,the numerical simulation study on thermal-hydro-mechanical coupling effect of typical station foundation pit engineering was carried out.Based on the multi-field coupling simulation software COMSOL and the experimental research results of shannan sand,the finite element model of foundation pit of Shannan station was established,and the numerical calculation of temperature field,moisture field and stress field of foundation pit was carried out,revealing the deformation law of foundation pit induced by temperature cycle replacement.更多还原