基于地统计学分析的渗透系数空间变异性应用研究

在对研究区域含水层实测渗透系数值分析的基础上,充分考虑了区域含水层水文地质参数各向异性的特点,采用地统计学分析方法对渗透系数进行空间变异性分析,对该区域含水层渗透系数的空间变异性特征有了一定的认识。结果表明,含水层渗透系数空间变异性主要受到含水层自身结构的影响,对数渗透系数在空间上具有明显的几何各向异性特点,区域渗透系数整体表现为由东北至西南逐渐减小的趋势,这与整个区域含水层的结构和分布特征相符。研究结果为合肥市轨道交通工程抗浮设防水位的模拟研究提供了有参考价值的水文地质参数空间分布规律。     

各向异性潜水层坑道稳定渗流的一个解析解

针对层状分布土体中的坑道渗流 ,建立一个均质、各向异性稳定渗流的数学模型 ;采用座标变换法 ,推出等效潜水层中圆形断面水平坑道二维稳定渗流场的流量、水头及流函数公式 ;定义ξ为渗透系数各向异性率 ,以表达含水层在各渗透主轴方向上渗透性的差别。无量纲化算例证明了该解析解的正确性和实用性。     

径向双层各向异性的承压层井流模型及渗流分析

考虑了抽水井表皮层的非均质、各向异性和上覆弱透水层的越流作用,建立径向双层各向异性非稳定承压井流模型。对竖向空间变量采用有限差分法将三维渗流偏微分方程初边值问题转化为矩阵偏微分方程初边值问题。应用拉普拉斯变换和矩阵理论求得径向扰动层(表皮层)和非扰动层各自水头降的半解析解。应用所求解对表皮层径向渗透系数沿抽水井线性变化和随机变化两种情形进行实例计算和分析,结果表明,负表皮效应使承压含水层的水头降增幅变大,导致水头降曲线在径向交界处出现上折;而正表皮效应使承压含水层的水头降增幅变小,导致水头降曲线在径向交界处出现下折;某一层位处的承压含水层水头降,既受同水平层的表皮层渗透系数影响,又受到相邻上下层的表皮层渗透系数的影响。     

高速铁路隧道围岩参数空间变异性的力学响应分析

 针对大断面高速铁路隧道围岩的参数变异性及空间相关性等问题,在随机场理论的基本框架下,将非侵入式随机分析、地层结构模型、有限差分法和蒙特卡洛模拟有机结合,提出考虑围岩参数空间变异性的非侵入式随机有限差分分析模型。运用该模型对隧道开挖后围岩的力学响应进行分析,得到围岩参数空间变异性的2个基本要素：参数变异性和空间相关性,其特征参数的取值变化会直接影响到围岩变形特性、塑性区发展模式以及地表沉降形态。同时与确定性模型的计算结果进行比较,提炼出隧道开挖后围岩参数空间变异性的4种典型工程效应：(1) 围岩结构性低强度荷载占优效应;(2) 围岩结构空间相关各向异性效应;(3) 功能函数敏感性差异及非线性效应;(4) 功能函数转变分布类型效应。研究成果为拓展基于空间变异性的高速铁路隧道工程稳健性设计奠定了一定的基础。     

堆积碎石土斜坡浅表入渗的空间分布与变异性研究

为探究强降雨下堆积体斜坡入渗参数的空间分布与空间变异性,通过筛分试验及双环入渗试验分别对堆积体斜坡试验点不同粒径区间碎石质量分数、碎石土渗透系数、饱和渗透系数、不同深度碎石土含水率进行测量,对数据进行普通Kriging插值统计分析,运用交叉检验选定合理理论模型与参数,获得其空间分布与变异性特征。研究结果表明:测试区碎石土入渗符合Kostiakov模型;不同粒径区间碎石质量分数采用高斯半变异函数理论模型空间插值精度最高,碎石土渗透系数和不同深度碎石土含水率采用球状半变异函数理论模型空间插值精度最高;粒径大于10 mm碎石主要分布于坡顶与坡腰区域且使该区域碎石土渗透系数的空间变异性相对较大,细小碎石(粒径2~10 mm)则聚积在坡脚位置,碎石土渗透系数速率沿坡面由上至下呈逐渐减少的空间分布趋势;浅土层(0~15 cm)坡腰含水率比坡顶、坡脚要高,而深土层(15~25 cm)坡脚含水率比坡顶、坡腰要高,且随深度增加缓慢上升。研究结果可作为碎石土滑坡降雨致滑的理论参考依据。     

水平单裂隙介质井流分数阶模型及其解

为了计算裂隙介质井流问题的渗透系数张量,基于水平单裂隙介质含水层渗流有各向异性的特性,利用分数阶微分方程理论建立了水平单裂隙介质径向各向异性非稳定完整井流问题的时间分数阶(1/2阶)数学模型。通过特殊函数、分数阶导数和函数的Laplace变换和Fourier的定义及性质求出水平单裂隙介质径向各向异性非稳定完整井流模型的解析解。最后通过降深曲线的切线斜率和降深公式的特性得出了确定渗透系数张量的解析公式,结果表明,该公式不仅使计算更简便,而且使得计算值更精确。     

考虑井周堵塞效应的定水头非完整回灌井流模型

针对传统定水头井流模型无法反映井周含水层堵塞对含水层渗流响应影响的问题,在假设井周含水层渗透系数在堵塞作用下随时间呈指数形式衰减的基础上,建立了考虑堵塞效应的定水头非完整回灌井流模型。通过对模型进行变量代换、Laplace变换和有限余弦Fourier变换及其逆变换,推导了定解问题在Laplace空间的解,并采用Stehfest数值逆变换方法得到了实时空间内的半解析解。参数分析结果表明,较小的渐近渗透系数K_r,∞会减小回灌过程中回灌流量和水头抬升,并降低含水层的拟稳态渗流响应,而较大的渗透系数衰减指数λ仅降低了渗透系数衰减过程中水头抬升和回灌流量,并不影响含水层达到拟稳态时的渗流状态;因K_r,∞和λ不同引起的水头差沿径向距离先增大后减小,在井周堵塞区与主含水层交界面达到最大值;回灌堵塞使得水头抬升分布在井周堵塞区与主含水层交界面上存在明显的折点,并造成含水层水头在抬升过程中存在显著的下降阶段,上述特征可为回灌堵塞评估与预测提供参考。     

岩体强度参数空间变异性分析

应用地质统计学的理论和方法,以变差函数为工具,对现场实测的岩体强度参数进行了分析,拟合出相应的最优化理论变差函数,并求出了岩体性质参数的相关距离和相关函数,说明了岩体性质的空间变异性特征。     

非平稳随机场下饱和渗透系数空间变异性的无限长边坡稳定概率分析

土体饱和渗透系数表现为天然的空间强变异性,其均值通常沿土层深度方向呈递减趋势,但目前鲜有文献考虑这一特性。为此,以FLAC为平台,利用fish语言基于局部平均法建立了表征土体饱和渗透系数均值随深度递减的一维非平稳随机场模型,采用FLAC两相流模块模拟雨水的入渗过程,以蒙特卡罗法为框架,结合考虑正孔隙水压力的广义有效应力无限边坡稳定模型,探讨了饱和渗透系数空间变异性在不同降雨时刻下对边坡最危险滑裂面分布规律以及相应的边坡破坏概率的影响。结果表明：忽略饱和渗透系数的空间变异性的确定分析方法将不能真实反映边坡的安全性;随着降雨持时的增加,边坡最危险滑裂面发生在坡底基岩处的概率逐渐降低;随着饱和渗透系数竖向相关距离的增加,边坡最危险滑裂面发生在坡底的概率逐渐增加,而相应的边坡破坏概率却随竖向相关距离的增加而逐渐降低。     

裂隙岩体地区导热-对流型温度场垂向渗透系数的计算及分布特征研究

阐述应用温度场方法研究裂隙岩体地区地下水渗流场参数的优点和存在垂向流作用下的导热–对流型温度场的地温特征。基于含水层导热–对流型温度场的地温曲线和渗流连续性方程,考虑受垂向流影响的温度场,建立地温与深度之间的函数关系,并建立不动点迭代方程,编制程序计算垂向渗透系数。针对渗透系数计算结果的统计特征分别构造满足正态分布、对数正态分布和均匀分布的3组新样本,构造减速膨胀曲线,对比分析渗透系数的概率分布特征。结果表明,同正态分布和均匀分布相比,裂隙岩体地区的垂向渗透系数更接近对数正态分布。利用温度场方法和统计学方法研究裂隙岩体地区地下水渗流场参数,如渗透系数,具有避免过多主、客观因素干扰,计算过程清晰,结果明确的特点。     

Evaluation of a pressure pulse in a fractured‐rock aquifer to reduce uncertainty of hydraulic conductivity measurements,Rio Grande Rift,New Mexico,United States

Fractured‐rock aquifers are inherently difficult for determining flow dynamics because of variability in fracture orientation and extension. A confined, fractured‐rock aquifer in a semi‐arid mountainous area of the Rio Grande Rift Zone was analysed for its response to recharge events that produced a pressure pulse within its potentiometric surface. The pulse was evaluated at the well scale and subaquifer level to evaluate flowpaths, travel times and dispersion and compare the bulk‐scale aquifer response to possible velocities from slug test hydraulic conductivity measurements. Travel time and dispersion from the pulse proved comparable to probable travel times based on hydraulic conductivity measurements. Evaluation of the pressure pulse and the hydraulic conductivity measurements allowed for a holistic interpretation of the fractured‐rock aquifer through analysis of two distinct data sets that provided corroborative evidence of flow dynamics and fracture connectivity. This holistic approach reduced uncertainty regarding the individual hydraulic conductivity values.     

非拘限含水层之水力传导系数模糊特性

地下水流于非拘限含水层流动时,因含水层之非均质性,使得垂直平均之饱和水力传导系数随地下水水位高低而变化。本研究就屏东平原之水文变量及边界条件等已知资料,利用MODFLOW模式计算屏东平原之地下水水位与水力传导系数之相关性。并运用模糊理论之模糊集与归属函数,分析水力传导系数在指数函数变换下,其所具有之模糊归属函数分布特性。由分析可知,屏东平原各地下水位观测站井之水力传导系数随地下水位变化具模糊关系。因此,在进行现地地下水流数值模拟时,水力传导系数不能只假设为单一值。     

A GIS-based DRASTIC model for assessing aquifer vulnerability in Kakamigahara Heights, Gifu Prefecture, central Japan

Vulnerability assessment to delineate areas that are more susceptible to contamination from anthropogenic sources has become an important element for sensible resource management and land use planning. This contribution aims at estimating aquifer vulnerability by applying the DRASTIC model as well as utilizing sensitivity analyses to evaluate the relative importance of the model parameters for aquifer vulnerability in Kakamigahara Heights, Gifu Prefecture central Japan. An additional objective is to demonstrate the combined use of the DRASTIC and geographical information system (GIS) as an effective method for groundwater pollution risk assessment. The DRASTIC model uses seven environmental parameters (Depth to water, net Recharge, Aquifer media, Soil media, Topography, Impact of vadose zone, and hydraulic Conductivity) to characterize the hydrogeological setting and evaluate aquifer vulnerability. The western part of the Kakamigahara aquifer was dominated by "High" vulnerability classes while the eastern part was characterized by "Moderate" vulnerability classes. The elevated north-eastern part of the study area displayed "Low" aquifer vulnerability. The integrated vulnerability map shows the high risk imposed on the eastern part of the Kakamigahara aquifer due to the high pollution potential of intensive vegetable cultivation. The more vulnerable western part of the aquifer is, however, under a lower contamination risk. In Kakamigahara Heights, land use seems to be a better predictor of groundwater contamination by nitrate. Net recharge parameter inflicted the largest impact on the intrinsic vulnerability of the aquifer followed by soil media, topography, vadose zone media, and hydraulic conductivity. Sensitivity analyses indicated that the removal of net recharge, soil media and topography causes large variation in vulnerability index. Moreover, net recharge and hydraulic conductivity were found to be more effective in assessing aquifer vulnerability than assumed by the DRASTIC model. The GIS technique has provided efficient environment for analyses and high capabilities of handling large spatial data.     

应用水力层析法刻画含水层非均质性

为了研究含水层多孔介质参数非均质性,利用一系列连续的交叉孔水力试验获取含水层对于外界干扰的反应信息,应用序贯连续线性估计方法（Sequential Successive Linear Estimator）对多系列水头信息进行随机参数估计,即水力层析法。应用该方法对随机产生参数的一维含水层进行了渗透系数K和储水率Ss的估算,并对估计值和真实值进行了对比,其中使用单井数据计算就可使K值的平均相对误差控制在2.67％,证明了该方法的有效性。在对某地浸采铀厂区长、宽为150m×150m的含水层进行了实例研究,使用29口井孔进行层析试验,对于该二维水平分布含水层的非均质特征进行了刻画,其中K值为0.5-1.4m／d,Ss为0.00005／m—0.0002／m。该数据在后期的地下水污染溶质运移模拟中取得了很好的应用。作为研究地下水参数的新方法,水力层析法能够对三维分布的含水层特征进行高精度刻画,这种层析的概念和反演方法可广泛应用于环境和地球科学领域的研究。     

Optimization of dewatering schemes for a deep foundation pit near the Yangtze River,China

A deep foundation pit constructed for an underground transportation hub was excavated near the Yangtze River. Among the strata, there are two confined aquifers, between which lies an aquiclude that is partially missing. To guarantee the safety of pit excavation, the piezometric head of the upper confined aquifer, where the pit bottom is located, should be 1 m below the pit bottom, while that of the lower confined aquifer should be dewatered down to a safe water level to avoid uplift problem. The Yangtze River levee is notably close to the pit, and its deformation caused by dewatering should be controlled. A pumping test was performed to obtain the hydraulic conductivity of the upper confined aquifer. The average value of the hydraulic conductivity obtained from analytical calculation is 20.45 m/d, which is larger than the values from numerical simulation(horizontal hydraulic conductivity K_H = 16 m/d and vertical hydraulic conductivity K_V = S m/d). The difference between K_H and K_V indicates the anisotropy of the aquifer. Two dewatering schemes were designed for the construction and simulated by the numerical models for comparison purposes. The results show that though the first scheme could meet the dewatering requirements, the largest accumulated settlement and differential settlement would be94.64 mm and 3.3‰, respectively, greatly exceeding the limited values. Meanwhile, the second scheme,in which the bottoms of the waterproof curtains in ramp B and the river side of ramp A are installed at a deeper elevation of-28 m above sea level, and 27 recharge wells are set along the levee, can control the deformation of the levee significantly.     

抽水试验法推求南方岩溶地区双重介质水文地质参数

岩溶地区裂隙水文地质参数是地下水运动研究的基础。本文将岩溶裂隙介质概化为等效多孔介质和双重介质,通过南方岩溶地区陈旗流域洼地的抽水试验和探地雷达勘测,推求了渗透系数和贮水系数等水文地质参数,讨论了两种介质水流运动模型得到的水文地质参数差异,并结合该地区水文地质条件,分析了岩溶含水层在不同渗流方向上渗透性的差异。研究表明,采用抽水试验方法,等效多孔介质和双重介质模型推求的渗透系数及贮水系数能反映以裂隙为主导的水力特性;设定不同方位观测井推求的水文地质参数反映岩石裂隙发育方向;双重介质模型较好地定量辨识出多孔介质(溶孔、微裂隙)和溶隙(裂隙)介质的储存能力和渗透性。     

Saturated anisotropic hydraulic conductivity of a compacted lateritic soil

This study focuses on the saturated anisotropic hydraulic conductivity of a compacted lateritic clayey sandy soil. The effects of the molding water content and the confining stress on the anisotropic hydraulic conductivity are investigated. The hydraulic conductivity is measured with a flexible-wall permeameter. Samples are dynamically compacted into the three compaction states of a standard Proctor compaction curve: the dry branch, optimum water content and wet branch. Depending on the molding water content and confining stress, the hydraulic conductivity may increase or decrease. In addition, the results indicate that, when the samples are compacted to the optimum water content, lower hydraulic conductivity is obtained, except at a confining stress equal to 50 kPa. The increase of the confining stress decreases the hydraulic conductivity for each of the evaluated compaction states. In the wet branch, horizontal hydraulic conductivity is about 8 times higher than the vertical value. The anisotropic hydraulic conductivities of the dry and wet branches decrease when the confining stress increases, and the opposite is observed in the optimum water content state.     

含水层和上覆弱透水层水文地质参数的计算方法

本文建立非线性回归方法与地下水三维数值模型———MODFLOW相结合的优化模型 ,利用含水层抽水试验资料确定含水层水平渗透系数Kr 和储存率Ss,以及上覆弱透水层垂直渗透系数Ka 和给水度Sy。通过 2个示例分析模型计算过程 ,结果表明 ,该模型不仅能有效地确定这些水文地质参数 ,而且可以给出计算参数的误差范围和参数之间的相关程度     

Grundwasserbilanzmodell Benker Sandstein in Mittelfranken/Bayern

The balance model “Benker Sandstein” is a 2-layered regional-scale groundwater model comprimising both important aquifers für water supply in Mid Franconia, the Sandsteinkeuper and the Benker Sandstein. The investigation is aiming at evaluating the groundwater balance and therefore recharge for the Benker Sandstein to estimate resources for future water supply in the lower aquifer. As input data for the model, the flux for both aquifers has been estimated from water balance calculations. Spatial distribution of hydraulic conductivity has been based on hydrogeological aspects. Areally distributed recharge from infiltrating water and the withdrawals of groundwater have been realized. Model calibraton has been evaluated by variation of hydraulic conductivity with groundwater leel and runoff data along the major streams taken into consideration. The groundwater budget for the Benker Sandsteins has been calculated. The hydrogeological model for the southwestern part of the investigation area has been improved.