Research on the temperature field of a partially freezing sand barrier with groundwater seepage

To study the distribution characteristics and variation regularity of the temperature field during the process of seepage freezing,a simulated-freezing test with seepage of Xuzhou sand was completed by using a model test developed in-house equipment.By means of three group freezing tests with different seepage velocities,we discovered the phenomenon of the asymmetry of the temperature field under the influence of seepage.The temperature upstream was obviously higher than that downstream.The temperature gradient upstream was also steeper than that downstream.With a higher seepage velocity,the asymmetry of the temperature field is more pronounced.The asymmetry for the interface temperature profile is more strongly manifest than for the main surface temperature profile.The cryogenic barrier section is somewhat"heartshaped".With the increasing velocity of the seepage flow,the cooling rate of the soil decreases.It takes much time to reach the equilibrium state of the soil mass.In our study,seepage flow velocities of 0 m/d,7.5 m/d,and 15 m/d showed the soilcooling rate of 4.35°C/h,4.96°C/h,and 1.72°C/h,respectively.

Seepage field distribution and water inflow laws of tunnels in water-rich regions

Currently,the water inrush hazards during tunnel construction,the water leakage during tunnel operation,and the accompanying disturbances to the ecological environment have become the main problems that affect the structural safety of tunnels in water-rich regions.In this paper,a tunnel seepage model testing system was used to conduct experiments of the grouting circle and primary support with different permeability coefficients.The influences of the supporting structures on the water inflow laws and the distribution of the water pressure in the tunnel were analyzed.With the decrease in the permeability coefficient of the grouting circle or the primary support,the inflow rate of water into the tunnel showed a non-linear decreasing trend.In comparison,the water inflow reduction effect of grouting circle was much better than that of primary support.With the increase of the permeability coefficient of the grouting ring,the water pressure behind the primary lining increases gradually,while the water pressure behind the grouting ring decreases.Thus,the grouting of surrounding rock during the construction of water-rich tunnel can effectively weaken the hydraulic connection,reduce the influence range of seepage,and significantly reduce the decline of groundwater.Meanwhile,the seepage tests at different hydrostatic heads and hydrodynamic heads during tunnel operation period were also conducted.As the hydrostatic head decreased,the water pressure at each characteristic point decreased approximately linearly,and the water inflow rate also had a gradual downward trend.Under the action of hydrodynamic head,the water pressure had an obvious lagging effect,which was not conducive to the stability of the supporting structures,and it could be mitigated by actively regulating the drainage rate.Compared with the hydrostatic head,the hydrodynamic head could change the real-time rate of water inflow to the tunnel and broke the dynamic balance between the water pressure and water inflow rate,thereby affecting the stress state on the supporting structures.

Comparative Analysis of Tunnel Seepage Field under Different Waterproof and Drainage System Using Analytical Methods

Tunnel seepage is an important factor affecting the progress and safety of tunnel construction. In this paper, the mining method tunnel construction in the water-rich weathered granite stratum is taken as the research object. Through the analytical calculation method, the distribution law of tunnel seepage field under different waterproof and drainage types is studied, and the comparative analysis is carried out. According to the analytical solution, the influencing factors of grouting parameters are proposed. The sensitivity of the tunnel seepage field to the variation of grouting parameters is analyzed. A novel waterproof and drainage system, and construction technology suitable for subway tunnels with large buried depth below groundwater level were proposed.

Interval finite difference method for steady-state temperature field prediction with interval parameters

A new numerical technique named interval finite difference method is proposed for the steady-state temperature field prediction with uncertainties in both physical parameters and boundary conditions. Interval variables are used to quantitatively describe the uncertain parameters with limited information. Based on different Taylor and Neumann series, two kinds of parameter perturbation methods are presented to approximately yield the ranges of the uncertain temperature field. By comparing the results with traditional Monte Carlo simulation, a numerical example is given to demonstrate the feasibility and effectiveness of the proposed method for solving steady-state heat conduction problem with uncertain-but-bounded parameters.

Numerical simulation of seepage flow field in groundwater source heat pump system and its influence on temperature field

Energy utilization in the aquifers is a new technology closely related to development of heat pump technique. It is significant for the flow distribution to be predicted in the aquifer surrounding the Groundwater Source Heat Pump System （GSHPS）. The authors presented a new concept of ＂flow transfixion＂ by analyzing general features of aquifers, and then discussed interaction of the flow transfixion with the beat transfixion, which has practical significance to projects. A numerical model of groundwater flow was established based on the basic tenets of water-heat transferring in the aquifer. On this basis the flow field and the temperature field of GSHPS for a site in Shenyang City were numerically simulated. The basis of the flow transfixion was obtained; it was discussed for the influence of the flow transfixion on the heat transfixion. To a certain extent, the study offers some reference for the projects＇ design of GSHP in the studied area.

STUDY ON COUPLING MODEL OF (SEEPAGE-FIELD) AND STRESS-FIELD FOR ROLLED CONTROL CONCRETE DAM

Based on the construction interfaces in rolled control concrete dam(RCCD), the methods were proposed to calculate the influence thickness of construction interfaces and the corresponding physical mechanics parameters. The principle on establishing the coupling model of seepage_field and stress_field for RCCD was presented. A 3_D Finite Element Method(FEM) program was developed. Study shows that such parameters as the thickness of construction interfaces,the elastic ratio and the (Poisson's) ratio obtained by tests and theoretical analysis are more reasonable, the coupling model of seepage_field and stress_field for RCCD may indicate the coupling effect between the two fields scientifically, and the developed 3_D FEM program can reflect the effect of the construction interfaces more adequately. According to the study, many scientific opinions are given both to analyze the influence of the construction interfaces to the (dam's) characteristic, and to reveal the interaction between the stress_field and the seepage_field.

A study on impacts of groundwater seepage on artificial freezing process of gravel strata

Purpose–This paper aims to study the impacts of groundwater seepage on artificial freezing process of gravel strata,the temperature field characteristics of the strata,and the strata process,closure time and thickness evolution mechanism of the frozen wall.Design/methodology/approach–In this paper several laboratory model tests were conducted,considering different groundwater seepage rate.Findings–The results show that there is a significant coupling effect between the cold diffusion of artificial freezing pipes and groundwater seepage;when there is no seepage,temperature fields upstream and downstream of the gravel strata are symmetrically distributed,and the thickness of the frozen soil column/frozen wall is consistent during artificial freezing;groundwater seepage causes significant asymmetry in the temperature fields upstream and downstream of the gravel strata,and the greater the seepage rate,the more obvious the asymmetry;the frozen wall closure time increases linearly with the increase in the groundwater seepage rate,and specifically,the time length under seepage rate of 5.00 m d
1 is 3.2 times longer than that under no seepage;due to the erosion from groundwater seepage,the thickness of the upstream frozen wall decreases linearly with the seepage velocity,while that of the downstream frozen wall increases linearly,resulting in a saddle-shaped frozen wall.Originality/value–The research results are beneficial to the optimum design and risk control of artificial freezing process in gravel strata.

Three-dimensional stochastic seepage field for embankment engineering

Owing to the complexity of geo-engineering seepage problems influenced by different random factors, three-dimensional simulation and analysis of the stochastic seepage field plays an important role in engineering applications. A three-dimensional anisotropic heterogeneous steady random seepage model was developed on the basis of the finite element method. A statistical analysis of the distribution characteristics of soil parameters sampled from the main embankment of the Yangtze River in the Southern Jingzhou zone of China was conducted. The Kolomogorov-Smirnov test verified the statistical hypothesis that the permeability coefficient tensor has a Gaussian distribution. With the help of numerical analysis of the stochastic seepage field using the developed model, various statistical and random characteristics of the stochastic seepage field of the main embankment of the Yangtze River in the Southern Jingzhou zone of China were investigated. The model was also examined with statistical testing. Through the introduction of random variation of the upstream and downstream water levels into the model, the effects of the boundary randomness due to variation of the downstream and upstream water levels on the variation of simulated results presented with a vector series of the random seepage field were analyzed. Furthermore, the combined influence of the variation of the soil permeability coefficient and such seepage resistance measures as the cut-off wall and relief ditch on the hydraulic head distribution was analyzed and compared with the results obtained by determinate analysis. Meanwhile, sensitivities of the hydraulic gradient and downstream exit height to the variation of boundary water level were studied. The validity of the simulated results was verified by stochastic testing and measured data. The developed model provides more detail and a full stochastic algorithm to characterize and analyze three-dimensional stochastic seepage field problems.

Numerical Simulation of the Influence of Tunnel Construction by Mining Method on the Seepage Field in Weathered Granite Stratum

In actual space, considering the heterogeneity and anisotropy of rock and soil, the difference of hydrogeological conditions and the influence of tunnel excavation, tunnel seepage problem is a very complex three-dimensional seepage problem, which is very difficult to solve. The equivalent continuum model is one of the most commonly simplified models used in solving tunnel seepage problems. In this paper, the finite element software ABAQUS and the research results are used to establish a seepage numerical calculation model, study the influence of mining method construction on the seepage field in weathered granite, and clarify the influence of each stage of mining method construction on the groundwater environment. On this basis, the sensitivity of the seepage field to various factors such as natural environment, engineering geology and hydrogeology, tunnel construction and so on is analyzed, which provides a basis to establish the evaluation system of groundwater environment negative effect in weathered granite stratum by mining method tunnel construction.

Seepage simulation of high concrete-faced rockfill dams based on generalized equivalent continuum model

This research focused on the three-dimensional(3 D) seepage field simulation of a high concrete-faced rockfill dam(CFRD) under complex hydraulic conditions. A generalized equivalent continuum model of fractured rock mass was used for equivalent continuous seepage field analysis based on the improved node virtual flow method. Using a high CFRD as an example, the generalized equivalent continuum range was determined, and a finite element model was established based on the terrain and geological conditions, as well as structural face characteristics of the dam area. The equivalent seepage coefficients of different material zones or positions in the dam foundation were calculated with the Snow model or inverse analysis. Then, the 3 D seepage field in the dam area was calculated under the normal water storage conditions, and the corresponding water head distribution, seepage flow, seepage gradient, and seepage characteristics in the dam area were analyzed. The results show that the generalized equivalent continuum model can effectively simulate overall seepage patterns of the CFRD under complex hydraulic conditions and provide a reference for seepage analysis of similar CFRDs.

Seepage and stress analysis of anti-seepage structures constructed with different concrete materials in an RCC gravity dam

This study used the finite element method （FEM） to analyze the stress field and seepage field of a roller-compacted concrete （RCC） dam, with an upstream impervious layer constructed with different types of concrete materials, including three-graded RCC, two-graded RCC, conven- tional vibrated concrete （CVC）, and grout-enriched vibrated RCC （GEVR）, corresponding to the design schemes S 1 through $4. It also evaluated the anti-seepage performance of the imperious layer in the four design schemes under the normal water level and flood-check level. Stress field analysis of a retaining section and discharge section shows that the maximum tensile stress occurs near the dam heel, the maximum compressive stress occurs near the dam toe, and the stress distributions in the four schemes can satisfy the stress control criteria. Seepage field analysis shows that the uplift pressure heads in schemes S3 and S4 descend rapidly in the anti-seepage region, and that the calculated results of daily seepage flow under the steady seepage condition in these two schemes are about 30%-50% lower than those in the other two schemes, demonstrating that CVC and GEVR show better anti-seepage performance. The results provide essential parameters such as the uplift pressure head and seelga^e flow for physical model tests and anti-seepage structure selection in RCC dams.

Gas seepage equation of deep mined coal seams and its application

In order to obtain a gas seepage law of deep mined coal seams, according to the properties of coalbed methane seepage in in-situ stress and geothermal temperature fields, the gas seepage equation of deep mined coal seams with the Klinkenberg effect was obtained by confirming the coatbed methane permeability in in-situ stress and geothermal temperature fields. Aimed at the condition in which the coal seams have or do not have an outcrop and outlet on the ground, the application of the gas seepage equation of deep mined coal seams in in-situ stress and geothermal temperature fields on the gas pressure calculation of deep mined coal seams was investigated. The comparison between calculated and measured results indicates that the calculation method of gas pressure, based on the gas seepage equation of deep mined coal seams in in-situ stress and geothermal temperature fields can accu- rately be identical with the measured values and theoretically perfect the calculation method of gas pressure of deep mined coal seams.

FEM Simulation on Artificial Freezing of Seepage Ground

The coupling mechanism in freezing process of seepage ground was studied and a simplified coupling math model was proposed. The nonlinear and coupling problems of PDEs were well solved using the exponential function, error function and normal distribution function, and a series of FEM equations of coupled fields of temperature and seepage were deduced and put forward. With the example of shaft ground freezing, the formation of freezing wall in seepage ground was simulated.

On the Application of the Lattice Boltzmann Method to Predict Soil Meso Seepage Characteristics

In this study,a two-dimensional approach is elaborated to study with the lattice Boltzmann method(LBM)the seepage of water in the pores of a soil.Firstly,the D2Q9 model is selected to account for the discrete velocity distribution of water flow.In particular,impermeability is considered as macroscopic boundary condition for the left and right domain sides,while the upper and lower boundaries are assumed to behave as pressure boundaries controlled by different densities.The micro-boundary conditions are implemented through the standard rebound strategy and a non-equilibrium extrapolation scheme.Matlab is used for the development of the related algorithm.Finally,the influence of porosity,permeability,osmotic pressure and other factors is assessed with regard to seepage characteristics and the ensuing results are compared with Darcy’s law.The computations show that,for fixed initial conditions,the pore structure has a certain influence on the local velocity of seepage,but the overall state is stable,and the average velocity of each layer is the same.The larger the pore passage is,the faster the flow velocity is,and vice versa.For low permeability,the numerical results are consistent with the Darcy's law.The greater the pressure difference between the inlet and outlet of seepage,the greater the seepage rate.The relationship between them is linear(yet in good agreement with Darcy’s law).

成层土中基坑二维稳态渗流场解析解研究

成层土中基坑渗流场与均质土层中渗流场有较大差别,最有可能发生突涌事故的位置也不同,因此准确确定成层土中基坑二维稳态渗流场是基础工程建设中的重要课题。针对成层土中基坑稳态渗流问题,将基坑周围土体按成层条件划分为多个区域,采用叠加原理和分离变量法给出各区域水头分布的级数形式解,根据各区域间连续条件和傅里叶级数正交性求得成层土中基坑二维稳态渗流场水头分布的显式解析解。将解析解计算得到的水头分布、挡墙水压力与有限元软件计算结果进行验证,并将解析解退化为单层土形式与半解析解进行对比,结果吻合较好,验证了解析解的正确性和有效性。将解析解与考虑水土相互作用的水压计算方法和等效渗透系数方法进行对比,基于解析解进一步给出计算基坑内出逸比降、挡墙水压力和抗突涌安全系数的计算公式,并结合工程案例分别采用解析方法和等效渗透系数方法对成层土中基坑的抗突涌性能进行分析对比。研究结果表明:解析解在求解成层土中基坑渗流场时更贴合实际情况;考虑不同土层间渗透系数差异时,水头在渗透性较差的土层中变化更快;上层土体渗透系数较小时,在土层分界面处发生突涌的风险比挡墙底部更大;等效渗透系数方法在求解某些成层土基坑渗流场时误差较大。

无单元Galerkin法的电流场与渗流场耦合正演

联合求解渗流场与电流场是确定土石坝渗流精确分布及评价渗流严重程度的重要途径.为解决水文-地球物理方法中存在的渗-电拟合度差及分辨率损失严重等问题,针对电性参数对水文状态变量的敏感性,本文开发一种基于无单元Galerkin法(Element-Free Galerkin Method,EFGM)的渗流场与电流场耦合正演算法.一方面,通过引入岩石物理关系经验公式及水文状态变量构建耦合模型;另一方面,通过滑动最小二乘法构造形函数,利用罚函数计算边界条件,以解决耦合模型的构建过程中对网格单元过度依赖问题来提高渗-电拟合精度.数值模拟的渗-电关联响应及耦合正演中,分析了土石坝内电流场及渗流路径,探索了各分量对土石坝不同附属结构体的异常响应特征.关联响应结果显示,饱和区内渗-电关联响应吻合较好.但由于非饱和渗流的特殊性,非饱和区介质岩石的物理特性会随着饱和度、孔隙度等因素的变化而发生改变,从而导致土石坝内非饱和区物性参数的分布与饱和区不同,从而造成非饱和区内渗-电场关联响应存在差异.在非饱和区域,耦合电位及电流密度分布与渗流分布吻合度高.渗-电耦合结果对实施模型约束的水文-地球物理耦合反演具有重要理论和实际意义.

富水砂卵石地层盆形冻结止水技术研究

为解决全断面砂卵石地层地下工程的地下水控制问题,提出盆形冻结止水技术。首先,采用三轴力学试验研究冻结砂卵石的压缩力学特性和蠕变力学特性;然后,采用大尺度物理模型试验和数值模拟方法研究盆形冻结的温度场扩展规律,并根据研究结果进一步提出盆形冻结积极冻结期的群孔布置技术和维护冻结期的精细化控制技术。结果表明:1)低围压(小于3 MPa)条件下,三轴抗压强度与围压呈正线性相关,然后围压继续增大时,强度基本不变;基于损伤理论建立冻结砂卵石全过程蠕变模型。2)荷载对冻胀率及融沉系数影响最大,细粒土质量分数次之,原状饱和砂卵石是不冻胀材料,并由此建立饱和砂卵石冻胀率及融沉系数三维预测模型。3)基于大型物理模型试验及数值模拟结果,盆形冻结可以在地下水渗流条件下形成完整的盆形结构,起到有效止水的效果。4)盆底冻结管在冻结过程中表现出与单管冻结迥异的“群孔效应”,根据试验结果提出包含冻结管间距、土体导热系数、渗流速度3因素的积极冻结期冻结管合理间距的确定与布置技术。5)为节约维护冻结期的能源,提出隔排切割冻结管、仅保留盆壁冻结管2种维护形式以对冻结区域进行精细化控制,经过分析,2种方式均可以有效满足盆形结构维护期的冷量供给,保持完整的盆形形态。

渗流作用下深部高温巷道围岩温度场分布规律

为探究渗流作用下深部高温巷道围岩温度场分布规律,以新城金矿为工程背景,运用Fluent软件模拟不同渗流因素下围岩温度场分布规律。结果显示:深部巷道围岩在渗流作用下温度场分布特征发生改变,等温线沿渗流方向分布;随着围岩孔隙率增大,温度场受扰动范围及调热圈半径不断增大,围岩径向温度和壁面温度随之降低;渗流水速度对围岩温度场分布特征影响较大,当渗流水速度≥2×10^(-8)m/s时,等温线沿渗流方向分布,渗流水速度<2×10^(-8)m/s时,等温线呈对称分布;随着渗流水速度增加,围岩温度场受扰动范围、调热圈半径、壁面温度升高,围岩径向温度随之降低;水流温度对围岩温度场分布特征、调热圈半径、温度场受扰动范围影响较小,围岩径向温度、壁面温度随水温升高而升高。

隧道拱顶渗漏稳态渗流场的解析研究

针对隧道运营中发生拱顶渗漏且无泥沙涌入的稳态渗流情况,结合保角变换法和分离变量法推导出隧道拱顶渗漏稳态渗流场的显式解析解.应用PLAXIS有限元软件建立数值模型,从渗流场分布、衬砌水压力两方面验证所得解的正确性,通过与现有解析解、数值解、试验结果的渗流量对比来验证所得解的准确性.进行参数分析,探究隧道埋深、渗漏宽度对衬砌水压力和渗流量的影响规律.结果表明,衬砌水压力在以渗漏位置为中心±60°范围内明显降低;随着隧道埋深的增大,衬砌最大水压力减小,渗流量先减小后增大,且渗流量最小值对应的隧道埋深随着地表水头的增大而增大;随着渗漏宽度的增大,衬砌最大水压力减小,渗流量增大,当渗漏宽度大于0.05 m时,渗漏宽度变化对水压力和渗流量的影响较小;在渗漏宽度较小时进行渗漏控制的效果明显.

地形因子对尾矿坝渗流场的影响规律分析

尾矿坝渗流安全稳定性受地形条件影响显著,合理的尾矿库选址是坝体后期安全稳定运行的基础。基于数值模拟方法,通过改变岸坡坡度、山谷宽度和沟谷纵坡比等因素,探究了单个地形因子对坝体渗流场的影响规律。研究发现,山谷两侧坡度对于尾矿坝坝体浸润线的影响最大,底宽的影响次之,沟谷纵坡比的影响最小。同时,结合具体工程实测DEM数据与地层勘察资料,构建了尾矿库三维渗流数值模型。提取地形因子对坝体渗流场进行数值分析,发现山谷地形是影响地下水流动状态的主要因素,建议选择沟谷纵坡比较小、地势较平坦的地形作为尾矿库的选址要求。在此基础上,基于多元线性回归模型建立了地形因子与浸润线高程的关系公式。研究成果可为保障尾矿坝的安全稳定设计提供理论基础。