【作者】 吴昊；

【导师】 岳丰田；

【作者基本信息】 中国矿业大学 ， 岩土工程， 2018， 硕士

【摘要】 人工冻结法凭借其安全和使用范围广等优点,在越来越多的地下工程建设中得到运用,但地下工程的开发遇到诸多工程难题,其中就包括浅层沼气地质灾害,例如杭州地区部分浅层就存在这一特殊地质状况。因此在该地区应用人工冻结法的时候就需要特别考虑地层赋存沼气造成大孔隙率软土现象对冻结效果的影响,本文研究课题就是在此背景下提出的,结合室内试验和数值模拟两种研究方法,研究杭州地区大孔隙率软土冻土物理力学特性。首先,对大孔隙率软土冻土试样制备方法进行研究,提出掺入泡沫颗粒制备大孔隙率软土冻土试样,并进行相关的热物理试验和无侧限单轴压缩对比试验,验证本文关于大孔隙率软土冻土制样方法的可行性,得到冻结温度随时间的变化符合冻土制样要求,以及大孔隙率软土冻土的导热系数与干密度关系。其次,进行室内试验,通过设计单因素试验方案和正交试验方案,进行大孔隙率软土冻土无侧限单轴压缩试验研究,分析含水量、温度和干密度等因素对大孔隙率软土冻土强度和弹性模量的影响,探究各因素与大孔隙率软土冻土强度和弹性模量的关系。通过回归分析,获得对应的拟合关系式,并且通过正交分析,得到含水量、温度和干密度三个因素对大孔隙率软土冻土强度和弹性模量的主次关系和显著性。再者,进行扫描电镜试验,获得大孔隙率软土冻土的微观图像,并通过IPP图像处理软件对SEM图像进行处理,获得相关细观参数,如孔隙率和最大最小颗粒半径比等,有利于PFC^2D的建模和加强对大孔隙率软土冻土的微观了解。最后,进行数值模拟,本文采用了PFC^2D颗粒流软件对含水量30%、温度-10℃、干密度1.37g/cm³的大孔隙率软土冻土试样进行无侧限单轴压缩试验的数值模拟。与室内试验结果进行对比,验证PFC^2D模拟大孔隙率软土冻土无侧限单轴压缩试验的可行性,并从微观角度对试样内部裂纹的发展、试样位移场和应力场进行研究分析,加强对大孔隙率软土冻土物理力学特性的理解。通过本文的相关研究分析,获得大孔隙率软土冻土物理力学特性,且了解到其发展规律与一般冻土基本符合,以及成功利用PFC^2D颗粒流软件对大孔隙率软土冻土无侧限单轴压缩试验进行模拟,从微观的角度加深对大孔隙率软土冻土物理力学特性的认识。更多还原

【Abstract】 The artificial freezing method has the advantages of safety and wide use,it is used in more and more underground engineering construction,however,there are many engineering problems in the development of underground engineering,it includes shallow biogas geological hazards,such as the existence of this special geological condition in some shallow layers in the Hangzhou area.Therefore,when the artificial freezing method is applied in the area,special consideration should be given to the effect of the formation of methane on the freezing effect caused by the formation of large porosity soft soil,the research topic in this paper is put forward in this context,two research methods combined with indoor test and numerical simulation,Study on physical and mechanical properties of frozen soil with large porosity soft soil in Hangzhou area.First,the preparation method of frozen soil with large porosity soft soil samples is studied,proposing preparation of frozen soil with large porosity soft soil samples by adding foam particles,and the related thermal physical test and unconfined uniaxial compression comparison test are carried out,verifying the feasibility of this paper on the method of making frozen soil with large porosity soft soil samples,and obtaining the change of freezing temperature with time accords with the requirement of frozen soil sample making,as well as the relationship between the thermal conductivity and the dry density of the frozen soil with large porosity soft soil.Secondly,the indoor test is carried out,through the design of single factor test scheme and orthogonal test scheme,carrying out the unconfined uniaxial compression test of frozen soil with large porosity soft soil.The influence of water content,temperature and dry density on the strength and elastic modulus of frozen soil with large porosity soft soil is analyzed,and the relationship between various factors and the strength or elastic modulus of frozen soil with large porosity soft soil is explored.Through regression analysis,the corresponding fitting relation is obtained.And through orthogonal analysis,the relationship and significance of three factors,including water content,temperature and dry density,to the strength and elastic modulus of frozen soil with large porosity soft soil are obtained.Furthermore,the microscopic images of the frozen soil with large porosity soft soil are obtained by scanning electron microscopy,and image processing software is used to process the SEM image by the IPP,obtaining the related mesoscopic parameters,such as porosity and maximum minimum particle radius ratio,etc.It is in favor of modeling of PFC^2D and strengthening microcosmic understanding of the frozen soil with large porosity soft soil.Finally,the numerical simulation is carried out.In this paper,the particle flow software by PFC^2D is used to simulate the unconfined uniaxial compression test of frozen soil with large porosity soft soil samples with water content 30%,temperature-10℃and dry density 1.37g/cm³.Compared with the indoor test results,it is proved that the PFC^2D simulation of unconfined uniaxial compression test of frozen soil with large porosity soft soil is feasible.From the microscopic point of view,the development of crack,the displacement field and stress field of sample are studied and analyzed,and the understanding of physical and mechanical characteristics of frozen soil with large porosity soft soil is strengthened.The physical and mechanical properties of frozen soil with large porosity soft soil are obtained through the relevant research and analysis in this paper.It is also understood that the law of development is basically consistent with the general frozen soil.The particle flow software by PFC^2D is successfully applied to simulate the uniaxial compression test of frozen soil with large porosity soft soil,and the understanding of physical and mechanical characteristics of frozen soil with large porosity soft soil is deepened from microscopic perspective.更多还原