冻融循环冻土的冲击动态力学性能

以典型冻土为研究对象,通过不同冻融循环次数的冻融循环实验、不同温度的冻结实验以及不同应变率的冲击动态实验,综合研究了冻融循环冻土的冲击动态力学性能。结果表明,冻土存在冻融循环效应,随着冻融循环次数的增加,冻土的峰值应力有一定程度的降低,但在达到临界冻融循环次数后,峰值应力将维持稳定;同时,冻土表现出明显的应变率效应和温度效应,其峰值应力随应变率的增加或温度的降低而增加。通过定义冻融损伤因子,推导满足Weibull分布的冲击损伤,提出了一个基于Z-W-T方程的损伤黏弹性本构模型。该模型可较好地描述冻融循环后冻土的冲击动态力学行为,为研究季节性冻土区冻土的冲击动态破坏提供参考。     

A perturbation solution for non-Newtonian fluid two-phase flow through Porous media

In this paper, the mathematical problem of weak non-Newtonian fluid two-phase flow through porous media, including the effect of capillary pressure, is solved by singular perturbation method in combination with regular perturbation method. The asymptotic analytical solutions of the fractional flow function and the wetting phase saturation are obtained. The results are verified by numerical calculations and by classical solutions for corresponding Newtonian case. The influences of the non-Newtonian exponent and capillary pressure are discussed.     

Experimental Study of the Impact and Penetration of A Cone in Frozen Sand

A reverse experiment technique is used along with the technology of measuring rods to study the impact and penetration of a steel conical body in frozen sandy soil. This paper presents the dependences of maximum values of the force of resistance of cones with base diameters of 10.0, 12.0, and 19.8 mm to penetration into sand on the impact velocity in the range of values 100–400 m/s. The numerical solution of the problem in an axisymmetric formulation with the use of the “Dinamika-2” software package is used to show the effect of waves reflected from the walls of the container on the contact force. A comparative analysis of the forces of resistance to penetration of the shocker into compacted dry, water-saturated, and frozen sandy soils is carried out.     

冻土单轴动态加载下的力学性能

研究冻土的动态力学性能对于地下工程人工冻结法施工等具有重要意义。本文应用分离式霍普金森压杆(SHPB),研究了冻土单轴动态加载下的力学性能,涉及-3、-8、-13、-17、-23和-28℃共6个负温的冻土,应变率范围350～1200s-1。获得了相应条件下的冻土应力应变关系。冻土的单轴动态应力应变曲线具有脆性特征。发现冻土具有温度和应变率效应,其强度随温度降低和应变率增大而增大,最终应变随应变率增大而增大。冻土温度越低,应变率敏感性越强;加载应变率越高,冻土的温度效应越显著。文中提出的粘弹性损伤型本构模型能够较好的描述6个温度冻土的应力应变关系。     

考虑围压效应的冻结砂土动态本构模型研究

为描述主动围压作用下冻结砂土的动态力学特性,通过在朱-王-唐模型的非线性体上串联塑性体,建立了能够考虑围压效应的冻结砂土动态损伤本构模型;分析了损伤参数对应力-应变曲线特征、屈服点、峰值应力和峰值应变的影响规律,基于冻结砂土动力学试验数据确定了模型参数;通过将模型和试验数据进行对比,并对不同试验条件下模型的预测误差进行分析,验证了模型的适用性和准确性。结果表明,损伤参数对应力-应变曲线弹性阶段和屈服点无明显影响,而对塑性阶段和破坏阶段的影响较为显著,本构模型预测的应力-应变曲线与试验结果具有较好的一致性。模型能够预测围压引起冻结砂土塑性阶段占比大和屈服点明显的特征,且能够描述围压对冻结砂土动态强度的增强效应;不同负温和主动围压条件下,模型对峰值应力和屈服强度的预测效果优于峰值应变和屈服应变。     

A Dynamic Micromechanical Constitutive Model for Frozen Soil under Impact Loading

By taking the frozen soil as a particle-reinforced composite material which consists of clay soil(i.e., the matrix) and ice particles, a micromechanical constitutive model is established to describe the dynamic compressive deformation of frozen soil. The proposed model is constructed by referring to the debonding damage theory of composite materials, and addresses the effects of strain rate and temperature on the dynamic compressive deformation of frozen soil. The proposed model is verified through comparison of the predictions with the corresponding dynamic experimental data of frozen soil obtained from the split Hopkinson pressure bar(SHPB) tests at different high strain rates and temperatures. It is shown that the predictions agree well with the experimental results.     

静压沉桩挤土机理探讨及有限元分析

针对预制桩在静压沉桩过程中出现的挤土现象,从土体小主应力方向加载的角度考虑,视浅层土体的隆起为小主应力方向(水平向)加载引起大主应力(垂直向应力)增加所致.在已有的柱形小孔扩张理论基础上,通过引入考虑位移的土压力计算方法提出了桩周土体隆起分界面表达式.利用该表达式分析浅层土体的隆起量,并利用Randolph提出的深层土体径向位移解析公式给出深层土体的变形量.最后运用有限元数值模拟计算与本文的数值解答进行对比分析,结果相近.     

三向受力条件下淡水冰破坏准则研究

为了更清楚地认识含冰冻结壁力学特性、解决复杂冰岩耦合问题以及给冰工程设计和数值仿真分析提供参数,有必要对冰在三向受力条件下的力学特性进行深入研究.以内蒙古自治区东胜煤田石拉乌素矿立井井筒建设为背景,参考现场水文地质资料在室内制作相似冰样,利用TDW-200低温冻土试验机,进行了4组温度和7组围压的人工淡水柱状冰三轴压缩强度试验,加载速率为0.5 mm/min,加载方向垂直于冰的晶轴方向.结果表明:在恒定温度条件下,柱状冰随围压增大塑性增强,而恒定围压条件下,柱状冰随温度降低脆性增强;在试验温度范围内,淡水柱状冰和多晶冰强度均随围压、温度升高而增大,但同条件下柱状冰强度高于多晶冰;采用D-A模型、Teardrop模型解释了高压下偏应力与围压之间的非线性关系,从不同角度对拟合得到的破坏准则综合考虑,认为D-A准则更适合用于描述淡水冰的破坏特征.研究结果可为后期同条件冰-岩耦合、数值模拟研究提供参考.     

MODEL TEST AND NUMERICAL SIMULATION OF BEARING CAPACITY OF ARTIFICIAL FROZEN CLAY1)

在天然冻土地区进行工程建设需研究冻土地基承载力。在人工冻结黏土蠕变试验的基础上建立广义开尔文模型,通过改造人工冻土大型冻结试验平台,进行人工冻结黏土地基承载力试验,发现载荷-沉降曲线可以分为3个阶段,基础呈局部剪切破坏。在ANSYS中将考虑相变的温度场转化为温度载荷施加在三维实体模型上,并将广义开尔文模型应用于软件中,采用增量加载方式分级加载。对比数值模拟与模型试验结果,发现地基载荷-沉降曲线规律一致,极限承载力大小基本相等,基础破坏模式相同。结果表明ANSYS软件可以分析复杂边界、初始条件下冻土材料的性质, 且能得到不同载荷下冻土材料的应力、位移、塑性区发展状况。     

CONSOLIDATION THEORY OF UNSATURATED SOIL BASED ON THE THEORY OF MIXTURE(Ⅱ)

The present paper uses the mathematics model for consolidation of unsaturatedsoil developed in ref.[1]to solve boundary value problems.The analytical solutionsfor one-dimensional consolidation problem are gained by making use of Laplacetransform and finite Fourier transform.The displacement and the pore water pressureas well as the pore gas pressure are found from governing equations simultaneously.The theoretical formulae of coefficient and degree of consolidation are also given inthe paper.With the help of the method of Galerkin Weighted Residuals,the finiteelement equations for two-dimensional consolidation problem are derived.A FORTRANprogram named CSU8 using8-node isoparameter element is designed.A plane strainconsolidation problem is solved using the program,and some distinguishing features onconsolidation of unsaturated soil and certain peculiarities on numerical analysis arerevealed.These achievements make it convenient to apply the theory proposed by theauthor in engineering practice.     

含损伤的冻土本构模型及耦合问题数值分析

从复合材料的细观力学机理出发,建立了含损伤的冻土弹性本构模型. 对于在不同冰体积 含量和不同温度下的冻结砂土,由该损伤本构模型计算的结果与实测的应力-应变曲线比较 吻合. 利用自主开发的程序,分别对渠道冻结和冻土路基的水分场、温度场、应力场3场耦 合进行数值模拟,得到了比较准确、详尽的符合实际的温度场与应力场、位移场、应变场耦 合的计算结果,与前人的计算及实测结果相符合,规律一致. 表明该程序能够计算冻土材料 的相关物理量,并能很好地描述这些相关物理量之间的关系.     

Flux calculation at the interface between two rock types for two-phase flow in porous media

When simulating two-phase flow in porous media, one has to consider the case where there is a discontinuity in the medium. There relative permeabilities and capillary pressure functions may change and we address the problem of calculating the convective part of the numerical flux at the interface between the two rock types. Several solutions are compared.     

On the Formation of Discontinuities of Wave Fronts in a Saturated Granular Body

The paper deals with propagation of plane wave fronts in a solid with a non-linear relation between stress and deformation. The objective is to calculate the distance that a wave front covers before it loses continuity. The formulae derived for a general quasi-linear system of two equations are applied to the propagation of plane compression waves in dry and partially saturated granular bodies. In the case of a saturated body with gas bubbles, the influence of gas and capillary pressure on the stiffness of the body is taken into account. Numerical calculations relevant to soil mechanics are presented. For the numerical calculations a constitutive equation of the hypoplasticity theory for granular materials has been used. Received November 1, 1997     

Experimental and numerical analysis of two-phase infiltration in a partially saturated soil

The purpose of this study is to analyze the effects of the soil air flow on the process of water infiltration in a 93.5 cm deep vertical column for varied boundary conditions at the surface - positive time constant head; time constant fluxes smaller and greater than saturated soil hydraulic conductivity.Several experiments conducted on a sandy soil column with and without a possible air flow through the wall are presented. Continuous and simultaneous measurements of water content and air and water pressure heads at different depths allow the analysis of the air and water movements within the soil and the determination of the capillary pressure and relative permeability for each phase as functions of the volumetric water content.A numerical solution of the equations describing the simultaneous flow of air and water is compared with the experimental data and with the traditional one-phase flow modeling. The results show that the air movement may significantly affect water flow variables such as infiltration rates, water content profiles, and ponding times.Furthermore, some basic assumptions used in two-phase flow modeling, such as the hydrodynamic stability of the wetting fronts and the pertinence of the relative permeability concept, are discussed in the light of the experimental data.     

On the pressure correction of capillary melt rheology data

In this paper, the importance of a pressure correction of viscosity data obtained in capillary melt rheology is demonstrated. A linear polycarbonate has been chosen as a highly pressure-sensitive material for which data obtained by rotational rheometry does not overlap with capillary data. This apparent problem with the Cox–Merz relation is attributed to the existence of a mean pressure inside the capillary which is significantly different from atmospheric conditions. Different methods to determine the pressure coefficient of polycarbonate have been evaluated based on experiments performed with a capillary rheometer equipped with a pressure chamber. It is demonstrated that the pressure coefficient obtained at constant shear stress and the pressure coefficient obtained by the superposition method represent accurate pressure coefficient values. Two approaches are proposed to correct the original capillary data. In the direct methodology, the pressure coefficient is used to rescale the mean pressure inside the capillary to atmospheric conditions. The indirect approach consists of first constructing a mastercurve at a certain reference pressure using capillary data obtained with a pressure chamber. The resulting mastercurve can then be rescaled to atmospheric conditions. It is shown that both methods lead to viscosity curves on which both rotational and capillary data overlap, hence confirming the Cox–Merz relationship for polycarbonate. The indirect method is proven to be advantageous since it opens the possibility to significantly extend the shear rate window in which viscosities can be measured.     

非牛顿流体两相渗流问题的摄动解

本文用奇异摄动法结合正则摄动法求解了考虑毛管力因素时多孔介质中弱非牛顿流体的两相驱替问题,得到了分流函数和湿相饱和度的渐近解析解。所得结果同数值解和经典的牛顿流体两相渗流结果进行了比较,并着重讨论了非牛顿因素的影响。     

Distinctive features of countercurrent capillary imbibition

Capillary imbibition of a wetting fluid in a porous medium is studied. A method of constructing the exact solution of the corresponding problem is developed. An iteration procedure is developed for the case of countercurrent capillary imbibition. The salient features of the flow generated by capillary forces are revealed on the basis of numerical results.     

侧移土体被动桩成拱效应及主动侧土压力计算

采用三维数值模型模拟土体水平位移条件下被动桩的成拱效应。分析结果表明,被动桩的成拱效应和桩间距关系最为密切,桩间距较小时,侧移土体在桩周附近呈现出明显的土拱效应,应力等值线密集,相互连通成一整体,并向两端突出,桩间距增大时土拱效应减弱;随着作用于土体侧向荷载的增大,土拱效应增强,桩周应力区增大。在数值分析的基础上,以T.Itos土压力为依据,考虑土体的实际分层,探讨了考虑土拱效应的土压力计算方法,给出了被动桩计算模式,最后将简化方法与数值分析的桩侧土压力进行了对比。     

立井冻土爆破冻结管振动力学响应研究

以赵固二矿西风井冻结爆破掘进施工为背景,对爆破作用下冻结管的振动力学响应进行了研究.依据爆炸应力波理论,分析了考虑P波垂直入射时冻结管的力学响应机制.采用ANSYS/LS-DYNA有限元分析软件模拟了冻结管受爆炸作用下的振动响应规律:振动波入射冻结管同一截面各测点振动速度相差不大,背爆侧振动速度最大,与P波入射成45°...