人工冻土粘弹塑性蠕变本构理论及冻结壁力学特性研究

发布时间：2018-04-27 19:34

本文选题：人工冻土 + 双剪统一强度理论　；参考：《长安大学》2017年博士论文

【摘要】：随着地下矿产资源开采的不断加深,城市地下空间综合利用开发的不断扩大,人工冻结法在地下工程中得到越来越广泛的应用。冻结壁作为井筒开挖过程中的临时支护,经常会由于冻土的流变性而产生较大的变形,最终导致冻结管断裂、井壁破损,给井筒施工带来很多问题。因此,研究冻土的流变特性及冻结壁的力学特性对冻结工程及井筒开挖具有重要意义。本文采用理论研究和数值模拟相结合的方法研究人工冻土的蠕变特点及冻结壁的力学特性。采用元件模型的流变理论建立了人工冻土的粘弹塑性蠕变本构模型,基于双剪统一强度理论,考虑冻土的蠕变性、冻结壁的卸载作用及冻结壁的非均匀性研究了冻结壁的力学性能,利用有限元软件ANSYS分析了开挖过程中冻结壁的变形特性。本文的主要研究内容及结论如下:(1)考虑围压对冻土强度的影响,建立了人工冻土的统一强度准则;以西原模型为基础,采用非牛顿粘壶代替牛顿粘壶,非线性牛顿体代替线性牛顿体,双剪统一强度理论代替圣维南体,根据元件模型的流变理论建立了冻土的粘弹塑性蠕变本构方程。该本构方程考虑了冻土蠕变的非线性,可描述冻土蠕变的全过程,且所得结果可适用于不同类型的冻土材料。(2)考虑冻土的蠕变性及中间主应力的影响,建立了冻结壁的粘弹塑性应力场和位移场;采用有限元软件ANSYS对开挖过程中冻结壁进行数值模拟,比较考虑蠕变与不考虑蠕变时冻结壁的变形特点。研究结果表明,考虑冻土的蠕变性使冻结壁的变形随时间增大,冻结壁的蠕变变形不可忽略;冻结壁的粘弹性极限荷载随强度理论参数的增大而增大;冻结壁井帮的径向位移沿开挖段高呈抛物线分布,中部偏上位移最大;较不考虑蠕变时,冻结壁井帮的径向位移相对较大。(3)考虑冻结壁的卸载作用及中间主应力的影响,采用卸载状态下冻结壁-周围土体共同作用的冻结壁力学模型,推导得到冻结壁弹塑性应力场和位移场、弹塑性极限荷载及外载的统一解,分析了强度理论参数的影响规律。研究结果表明,考虑冻结壁的卸载作用,使冻结壁的外载较传统方法相对较小,冻结壁的应力场和位移场也相对较小;弹性极限外载和塑性极限外载均随强度理论参数的增大而增大。(4)考虑冻土材料的FGM(Functionally Graded Material)特性及中间主应力的影响,推导得到冻结壁的弹塑性应力场及弹塑性极限荷载的解析解,讨论了强度理论参数的影响规律。研究结果表明,考虑冻土的FGM特性,使冻结壁的应力分布更均匀;弹性极限荷载较均质冻结壁相对较大,塑性极限荷载相对较小;弹性极限外载和塑性极限外载均随强度理论参数的增大而增大。
[Abstract]:With the deepening exploitation of underground mineral resources and the expansion of comprehensive utilization of urban underground space, artificial freezing method has been more and more widely used in underground engineering. As the temporary support in the process of shaft excavation, the frozen wall often produces large deformation due to the rheology of frozen soil, which eventually leads to the breakage of freezing pipe and the breakage of shaft wall, which brings many problems to the shaft construction. Therefore, it is of great significance to study the rheological characteristics of frozen soil and mechanical properties of frozen wall for freezing engineering and wellbore excavation. In this paper, the creep characteristics of the artificial frozen soil and the mechanical properties of the frozen wall are studied by combining theoretical research with numerical simulation. The viscoelastic-plastic creep constitutive model of artificial frozen soil is established by using the rheological theory of element model. Based on the unified strength theory of double shear, the creep property of frozen soil is considered. The mechanical properties of the frozen wall are studied by unloading and non-uniformity of the frozen wall. The deformation characteristics of the frozen wall during excavation are analyzed by using the finite element software ANSYS. The main contents and conclusions of this paper are as follows: (1) considering the influence of confining pressure on the strength of frozen soil, the unified strength criterion of artificial frozen soil is established. The nonlinear Newtonian body replaces the linear Newtonian body and the double shear unified strength theory replaces the San Venan body. According to the rheological theory of the element model, the viscoelastic-plastic creep constitutive equation of frozen soil is established. The constitutive equation takes into account the nonlinearity of frozen soil creep, and can describe the whole process of frozen soil creep, and the obtained results can be applied to different types of frozen soil materials. The viscoelastic-plastic stress field and displacement field of the frozen wall are established, and the deformation characteristics of the frozen wall during excavation are compared by using the finite element software ANSYS. The results show that considering the creep property of frozen soil, the deformation of frozen wall increases with time, the creep deformation of frozen wall can not be ignored, and the ultimate viscoelastic load of frozen wall increases with the increase of theoretical strength parameters. The radial displacement of the frozen wall is parabolic along the height of the excavation section, and the upper displacement of the middle part is the largest; when the creep is not considered, the radial displacement of the frozen wall is relatively larger than that of the frozen wall, and the effect of the unloading action of the frozen wall and the effect of the intermediate principal stress are considered. By using the mechanical model of freezing wall under unloading condition, the unified solutions of elastic-plastic stress field, displacement field, elastic-plastic limit load and external load of frozen wall are derived, and the influence law of strength theoretical parameters is analyzed. The results show that considering the unloading effect of the frozen wall, the external load of the frozen wall is relatively smaller than that of the traditional method, and the stress and displacement fields of the frozen wall are also relatively small. The elastic limit external load and the plastic limit external load increase with the increase of the strength theoretical parameters. (4) considering the FGM(Functionally Graded material properties of the frozen soil and the influence of the intermediate principal stress, the analytical solutions of the elastic-plastic stress field and the elastic-plastic limit load of the frozen wall are derived. The influence of theoretical parameters on strength is discussed. The results show that considering the FGM characteristics of the frozen soil, the stress distribution of the frozen wall is more uniform, the elastic limit load is larger than that of the homogeneous freezing wall, and the plastic limit load is relatively small. Both the elastic limit and the plastic limit load increase with the increase of the theoretical strength parameters.
【学位授予单位】：长安大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TU445

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