Effects of Coal Gangue Content on Water Movement and Solute Transport in a China Loess Plateau Soil

The mining industry has grown strongly in China in recent decades, resulting in large amounts of coal gangues, which cause water and soil pollution, soil erosion, and various other environmental problems. They are often used in reclamation projects in attempts to restore land damaged by mining, hence they are frequently present (in widely varying proportions) in the topsoil in areas around mines. Their presence can strongly affect key soil variables, including its bulk density, structure, water retention, water movement, and solute transport rates. In the study presented here, the effects of gangue contents on infiltration, saturated hydraulic conductivity, and solute transport parameters of a Chinese Loess plateau soil were examined. The results show that infiltration rates and saturated hydraulic conductivity decreased with increasing gangue content. The Peck–Watson equation modeled these relationships well, but Bouwer–Rice equations provided poorer matches with the acquired data. Cumulative infiltration over time was described well by both the Philip equation and Kostiakov equation. Both the simplified convection–dispersion equation and a two‐region model described the solute transport processes well. In addition, the dispersion increased, while both the Peclet number and mobile water fraction decreased, with increases in gangue contents.     

Incompressible or nearly incompressible soil dynamic behaviour—a new staggered algorithm to circumvent restrictions of mixed formulation

The restriction of the Babuska–Brezzi stability criteria for the mixed formulation requires non-uniform interpolation of displacement and pore-pressure variables, which complicates the coding in the finite element analysis. This will certainly preclude the use of many otherwise useful elements. A possible solution to overcome this problem introduced earlier by the authors requires a semi-explicit form. However, the effectiveness of the semi-explicit procedure is dependent on the time step length used, which presents difficulties for transient analysis. In this paper, an unconditionally stable staggered implicit-implicit algorithm is developed, which is generalised from the semi-explicit form. For non-uniform mesh configurations, the results indicate a significant improvement compared with those obtained by using the semi-explicit procedure.     

Establishing the role of pedogenesis in changing soil hydraulic properties

Chronosequences provide suitable sources for the study of changes in soil hydraulic behaviour as a result of long-term pedogenesis. For a podsol chronosequence in the Scottish Highlands, data are presented to indicate the changes that have occurred over 13000 years in the saturated hydraulic conductivity (K_sat) in each horizon. As the soil profile has evolved into a differentiated sequence of three horizons, the resulting hydrological changes can be both measured and quantified by relating K_sat to textural properties and bulk density. The results are significant for interpretation of changing runoff processes and slope stability.     

Fluctuation responses of saturated porous media subjected to cyclic thermal loading

Normalized, coupled governing equations for one-dimensional thermal consolidation problems are established. The non-dimensional coefficients of thermal consolidation and thermal diffusivity are defined accordingly. An analytical solution is deduced by using the Laplace transform and the Gauss–Legendre method of Laplace transform inversion. The responses of saturated porous media subjected to cyclic thermal loading are studied. The evolution of temperature, pore pressure and displacement from instantaneous state to quasi-steady state, with elapsed time, are analysed. The characteristics of cyclic fluctuation and the attenuation of the field variables with increased depth are also analysed. The influences of the permeability of media on thermal responses are discussed.     

Spatial and temporal analysis of groundwater recharge with application to sampling design

A numerical experiment of flow in variably saturated porous media was performed in order to evaluate the spatial and temporal distribution of the groundwater recharge at the phreatic surface for a shallow aquifer as a function of the input rainfall process and soil heterogeneity. The study focused on the groundwater recharge which resulted from the percolation of the excess rainfall for a 90-days period of an actual precipitation record. Groundwater recharge was defined as the water flux across the moving phreatic surface. The observed spatial non-uniformity of the groundwater recharge was caused by soil heterogeneity and is particularly pronounced during the stage of recharge peak (substantial percolation stage). During that stage the recharge is associated with preferential flow paths defined as soil zones of locally higher hydraulic conductivity. For the periods of low percolation intensity the groundwater recharge was exhibiting more uniform spatial characteristics. The temporal distribution of the recharge was found to be a function of the frequency and intensity of the rainfall events. Application of sampling design demonstrates the joint influence of the spatial and temporal recharge variability on the cost-effective monitoring of groundwater potentiometric surfaces.     

A practical numerical method for large strain liquefaction analysis of saturated soils

Accurate prediction of the liquefaction of saturated soils is based on strong coupling between the pore fluid phase and soil skeleton. A practical numerical method for large strain dynamic analysis of saturated soils is presented. The u–p formulation is used for the governing equations that describe the coupled problem in terms of soil skeleton displacement and excess pore pressure. A mixed finite element and finite difference scheme related to large strain analysis of saturated soils based on the updated Lagrangian method is given. The equilibrium equation of fluid-saturated soils is spatially discretized by the finite element method, whereas terms associated with excess pore pressure in the continuity equation are spatially discretized by the finite difference method. An effective cyclic elasto-plastic constitutive model is adopted to simulate the non-linear behavior of saturated soils under dynamic loading. Several numerical examples that include a saturated soil column and caisson-type quay wall are presented to verify the accuracy of the method and its usefulness and applicability to solutions of large strain liquefaction analysis of saturated soils in practical problems.     

饱和湿大气Brunt-V3/4is3/4l3/4频率及修正的相当位温

实际大气中受扰动的饱和气块发生凝结后 ,凝结水会部分脱离气块。以前研究饱和湿大气的Brunt V is l 频率 (N2 m)没有考虑凝结水的部分脱离 ,相当位温 (θe)也忽略了饱和气块的混合比的作用。文中针对这些不足 ,在假设饱和空气中只存在气液转换条件下 ,推导出液态水部分脱离气块的、更符合实际情况的N2 m 表达式和修正的饱和湿大气θe 表达式。新的N2 m 表达式增加了部分脱离气块的液态水的作用项 ,新的θe 表达式中包含有饱和气块的混合比 ,并对有关的表达式分别作了讨论和比较     

两相饱和介质半无限空间位错位移场

弹性位错理论是研究地震震源正演和反演的重要工具之一. 单相介质位错理论求得的地面变形场是稳定的、不变的，而实际地震后的地面变形场是变化的. 本文利用集中力作用下无限空间中两相饱和介质Green函数的柱函数表达式，通过弹性运动方程积分解的Helmholtz方程的Hansen矢量变换，再叠加自由表面影响场的方法求得两相饱和介质半无限空间位错位移场. 本文结果结合Nur的DD模式，在进水排水的假说下能解释地震后地面变形场的变化.     

具有饱和土沉积层的充水河谷对平面波的散射

把波函数展开方法用于地震波散射问题的研究中,首次在频域内给出了具有饱和土沉积层的圆弧形充水河谷对平面P波和SV散射问题的解析解答. 其中半空间场地用单相介质弹性动力理论模拟,河谷中的饱和土沉积层用饱和多孔介质的Biot动力学理论模拟,河谷中的水用无黏性流体(理想流体)介质模拟. 文中还给出算例,计算了不同高宽比的河谷谷底的位移幅值,分析表明河谷地形的存在使得半空间介质表面的位移幅值随着观察点位置的变化变化较大.     

甘肃引洮供水工程饱和黄土隧洞施工方法选择的工程地质研究

甘肃引洮供水一期工程总干渠13#、14#、15#隧洞围岩为al-lQ2饱和黄土,地下水位高于洞顶437m,饱和度一般在98%100%,水稳性很差。因此,该段隧洞施工方法的选择十分重要,从工程地质角度研究其工程特性,采用D rucker-Prager弹塑性模型、关联流动法则,模拟了传统钻爆法开挖时隧洞稳定性,计算表明,若采用钻爆法,由于围岩的岩性软弱,隧洞开挖后,在隧洞周围较大范围内存在应力降低区,隧洞位移十分迅速而且位移量非常大,洞顶下降发生塌方并引起地面沉降。从盾构法施工对地质条件的适应性分析,其施工风险相对较小,施工过程中可利用护盾很快封闭围岩,因此该段隧洞宜采用盾构法施工。