单环入渗试验与数值反演法结合推求土壤水力参数

单环入渗试验广泛应用于野外测定土壤水力参数。文章在三维非饱和带水分模拟程序VSF基础上,加入了单环入渗水流计算模块,并将改进的VSF与参数优化程序LEVMAR相耦合,构建了适用于单环入渗试验的土壤水力特征参数反演程序VSF-LEVMAR。利用大型室内土槽单环定水头入渗及变水头入渗试验资料,反求水平及垂向饱和入渗系数等土壤水力参数。应用结果表明:该方法既可以利用单环定水头入渗试验单独推求吸湿过程中的土壤水力参数,也可以结合单环定水头入渗与变水头入渗试验同时推求吸湿及脱湿过程中的土壤水力参数。     

裂隙水流运动的入渗试验及数值模拟研究

裂隙对喀斯特水流起着重要控制作用。选取具有垂向与水平向交叉裂隙的岩石剖面,做单环注水入渗试验,基于Navier-Stokes(N-S)方程组建立入渗水流数值模型,运用试错法,以实测单环水位变化为目标推求裂隙水力隙宽,计算入渗水量在不同裂隙中的比例;利用立方定律,估计出裂隙饱和渗透系数,基于地下水流连续性方程构建裂隙水流数值模型;比较两种数值模型计算结果。模拟结果表明:N-S方法推求的裂隙等效水力宽度远小于实测裂隙宽度;裂隙水流大部分沿垂向裂隙下渗,但也有部分水流沿横向裂隙渗流;立方定律与N-S方法数值模拟结果差异不大,前者估计的裂隙下渗率稍小于后者,相对而言,N-S方法能更精确地描述裂隙水流运动过程。     

石羊河流域平原区土壤入渗特性空间变异的研究

在野外原位入渗试验的基础上,建立了简化Philip入渗模型及其土壤转换函数,借助ARCVIEW软件生成了石羊河流域平原区土壤入渗特性参数的空间分布图,并分析了入渗特性的空间变异特征。研究表明,简化Philip入渗模型是点面转化中比较理想的模型,模型参数α的土壤转换函数可以简便地估算土壤入渗特性,两者的结合是研究大尺度土壤入渗空间变异的一种有效方法。     

基于Green-Ampt模型的饱和-非饱和黄土入渗改进模型及其参数研究

黄土中水分入渗理论分析对预测土体附加变形及强度弱化十分重要,但现有针对均质地基的Green-Ampt入渗分析模型运用于黄土区还有较多不足。基于黄土入渗饱和-非饱和分层假定,考虑入渗过程中土体实际渗透系数随深度的变化,对Green-Ampt模型进行修正,并用实例进行了验证;通过测量累积入渗量和含水率的时变规律,并结合Philip模型与Green-Ampt模型的相关关系及实际渗透系数随时间的变化关系获取模型参数。结果表明,相比于WGAM和Kostiakov模型,修正模型在黄土区的应用效果更好。在修正模型基础上,分析了饱和渗透系数、饱和含水率、初始含水率以及基质吸力对水分入渗深度的影响规律,并对参数的敏感指数进行了分析与对比。发现土体初始和饱和含水率变化对模型计算结果产生较大影响。该模型的建立对黄土地区水分入渗规律相关研究有一定的积极作用。     

新疆三工河流域厚层包气带区地下水垂向补给量的厘定

通过对荒漠区荒地、绿洲区耕地及摞荒地厚层包气带剖面土壤水的含水率、易溶盐离子及稳定同位素(δD、δ18O)的测定和分析,对厚层包气带区土壤水的补给来源及地下水的垂向补给量进行了厘定。结果表明:荒漠区荒地、绿洲区耕地与摞荒地土壤含水率、易溶盐中氯离子与土壤水氢氧同位素在垂向上均呈现旋回变化,每个旋回经历了一次新水入渗补给的过程。绿洲区土壤水与荒漠区土壤补给水中的δD值为-124.10‰~-94.44‰,土壤补给水来源于冬季大气降水或降雪的入渗补给。绿洲内耕地区、摞荒地区及荒漠区地下水垂向入渗补给量分别为1.29~5.53 mm/a、0.52~1.85 mm/a及0.03~0.08 mm/a。     

滞后补给权函数与包气带的关系

降雨入渗补给潜水存在滞后效应.利用HYDRUS程序建立垂直一维非饱和渗流数值模型,模拟了补给过程对脉冲式地面入渗的响应.根据不同潜水面埋深补给强度的变化过程计算补给权重,获得了滞后补给权函数曲线.模拟结果表明权函数曲线具有单峰形式,随潜水面埋深增加,峰值减小,其出现的时间推迟.相对粗颗粒土壤,缅颗粒土壤产生的权函数峰值较小,出现时间更晚.前人提出的滞后补给权函数经验公式能够近似地刻画单峰曲线形态,在包气带介质颗粒较粗、潜水面埋深较小时比较适用,但是对细颗粒土壤和潜水面埋深较大的情况则存在一定的偏差.土壤类型和含水量的垂向分布,都可以通过对包气带渗透性的控制而影响滞后补给过程.可为研究地下水模型处理动态降雨入渗补给及包气带溶质淋滤过程提供参考.     

含碎石土壤水分入渗试验研究

采用一维积水垂直入渗法测定含碎石土壤的入渗过程,分析碎石含量和碎石组成对土壤水分运动影响。对试验数据采用Kostiakov入渗公式拟合,得出反映入渗速率的拟合参数比值与土石比成幂函数关系;采用简略的Philip垂直入渗方程幂级数解拟合湿润峰随时间的变化,拟合精度高,并发现拟合参数与土石比仍成幂函数关系。采用简单相关分析碎石粒径对入渗过程影响,得出粒径2~3 mm碎石与入渗过程成显著的负相关关系,而>25 mm碎石有利于入渗。研究结果可为含碎石土壤的水循环提供重要的基础。     

层状非均质多孔介质中LNAPLs污染物运移与分布的锋面扩展模型

通过建立二维物理模型,研究非饱和层状非均质多孔介质中轻非水相液体LNAPLs(Light Non-a-queous Phase Liquids)的入渗机制与变化特征,建立LNAPLs运移与分布的锋面扩展模型,探讨入渗阶段油流锋面扩展速率的变化规律。结果发现:模型中砂土的渗透系数、孔隙度及油的相对渗透系数对LNAPLs运移的锋面扩展速率影响较大,而油的饱和度与压头变化对其影响较小。当LNAPLs由中砂进入细砂与细砂倾斜透镜体时,砂的渗透系数、孔隙度及油的相对渗透系数减小,这种介质结构面的突变改变了LNAPLs锋面扩展速率,其在中砂中锋面扩展速率快而在细砂与细砂倾斜透镜体中锋面扩展速率慢。此外,当LNAPLs进入干湿界面后,由于毛细作用的增强与含水量的加大,其横向比垂向运移的平均锋面扩展速率大。     

基于原位双环、试坑浸水试验和数值模拟反演的Q3黄土饱和渗透系数对比研究

为准确获取原状Q3黄土的竖向和水平饱和渗透系数,进行了原位、室内试验测试以及数值模拟反演,并应用大型试坑浸水试验检验了所获饱和渗透系数的可靠性。进行了不同内径尺寸的原位双环入渗试验,获取了竖向饱和渗透系数,并应用室内试验测试了竖向和水平饱和渗透系数以及持水曲线;应用COMSOL软件对双环入渗试验进行数值模拟,检验了所测饱和渗透系数的可靠性,利用正交试验获得了最优的竖向和水平饱和渗透系数取值,并利用反演结果对试坑进行数值模拟,将其水分入渗情况与实测值对比。研究结果表明：在现场进行双环入渗试验时选取较大内径的双环获得的竖向饱和渗透系数更为合理。针对双环入渗试验,数值模拟反演所得最优饱和渗透系数在竖向上接近于原位试验所得竖向饱和渗透系数、水平向上接近室内所测水平向饱和渗透系数,竖向饱和渗透系数比水平向饱和渗透系数更加显著地影响水分入渗过程。通过对大型试坑水分入渗情况的验证,检验了反演所得最优饱和渗透系数的可靠性。     

包气带增厚区土壤水力参数及其对入渗补给的影响

为探讨包气带深部增厚区土壤水力参数变化对入渗补给过程的影响,采用压力膜仪对河北正定深部包气带(8.0~21.0 m)10个原状土样进行水分特征曲线测试,利用RETC软件中Mualem-van Genuchten导水率模型对其拟合,获取含水率与非饱和导水率的关系曲线,并根据达西法对其进行分析讨论.结果表明:场地包气带深埋区的非饱和导水率为25~240 mm/a.当某一埋深历史水位下降速度越快,该埋深处相同含水率情况下土壤非饱和导水率越大,说明对应土层的入渗补给强度越大;因包气带厚度增大使原来位于饱水带的层状非均质土层转变为包气带,潜水位波动下降过程中深部包气带土层因排水压密作用,使得土壤水力特性发生变化,进而影响垂向入渗补给过程.      

Evaluation of methods for determination of hydraulic properties in an aquifer–aquitard system hydrologically connected to a river

Field and laboratory methods have been used to determine the hydraulic properties in a multiple-layer aquifer–aquitard system that is hydrologically connected to a river. First, hypothetical pumping tests in aquifer–aquitard systems were performed to evaluate the feasibility of MODFLOW-PEST in determining these parameters. Sensitivity analyses showed that: the horizontal hydraulic conductivity in the aquifer has the highest composite sensitivity; the vertical hydraulic conductivity has higher composite sensitivity than the horizontal hydraulic conductivity in the aquitard; and a partial penetration pumping well in an aquifer layer can improve the quality of the estimated parameters. This inverse approach was then used to analyze a pumping-recovery test conducted near the Platte River in southeastern Nebraska, USA. The hydraulic conductivities and specific yield were calculated for the aquitard and aquifer. The direct-push technique was used to generate sediment columns; permeameter tests on these columns produced the vertical hydraulic conductivities that are compatible with those obtained from the pumping-recovery test. Thus, the combination of the direct-push technique with permeameter tests provides a new method for estimation of vertical hydraulic conductivity. The hydraulic conductivity, determined from grain-size analysis, is smaller than the horizontal one but larger than the vertical one determined by the pumping-recovery test.     

Determination of the anisotropy of an upper streambed layer in east-central Nebraska, USA

Information on the anisotropy of streambed hydraulic conductivity (K) is a necessity for analyses of water exchange and solute transport in the hyporheic zone. An approach is proposed for the determination of K, developed from existing in-situ permeameter test methods. The approach is based on determination of vertical and horizontal hydraulic conductivity of streambed sediments on-site and eliminates the effects of vertical flow in the hyporheic zone and stream-stage fluctuation, which normally influence in situ permeameter tests. The approach was applied to seven study sites on four tributaries of the Platte River in east-central Nebraska, USA. On-site permeameter tests conducted on about 172 streambed cores for the determination of vertical hydraulic conductivity (K _v) and horizontal hydraulic conductivity (K _h) at the study sites indicate that the study sites have relatively small anisotropic ratios, ranging from 0.74 to 2.40. The ratios of K _h to K _v from individual locations within a study site show greater variation than the anisotropic ratios from the mean or median K at each of the study sites.     

In Situ Pore Water Pressure Dissipation Testing of Marine Clay under Reclamation Fills

In situ dissipation tests provide a means of evaluating the in situ coefficient of horizontal consolidation and horizontal hydraulic conductivity of soft clays. Dissipation tests by means of piezocone (CPTU), dilatometer (DMT), self-boring pressuremeter (SBPT) and BAT permeameter (BAT) were utilized in the characterization of the coefficient of horizontal consolidation and horizontal hydraulic conductivity of Singapore marine clay at Changi in a land reclamation project. Dissipation tests were carried out prior to reclamation as well as after ground improvement with vertical drains to compare the changes in the coefficient of horizontal consolidation and horizontal hydraulic conductivity prior to and after ground improvement. Tests were carried out in a vertical drain area as well as in an adjacent untreated control area after 23 months of surcharge loading, for comparison purposes. The purpose of this research is to determine the horizontal consolidation parameters of Singapore marine clay prior to reclamation as well as after 23 months of surcharge loading with and without vertical drains by means of in situ dissipation tests.     

水泥-膨润土泥浆配比对防渗墙渗透性能的影响

作为一种垂直防渗墙体材料,水泥-膨润土泥浆已在欧美等一些国家被广泛应用于垃圾填埋场的垂直防渗系统中,而国内对此类墙体材料的研究和应用较少。通过对不同配合比的水泥-膨润土泥浆固结体进行渗透试验,研究了原材料对泥浆固结体渗透性能的影响以及渗透性随龄期变化的情况。试验结果表明,水泥和膨润土对固结体渗透系数的影响相互依赖,只有在水泥用量达到一定程度后,增加膨润土用量才能有效地降低固结体的渗透性能;随着龄期的增加,水泥-膨润土泥浆固结体的渗透系数明显降低。     

Identification of a hydrodynamic threshold in karst rocks from the Biscayne Aquifer, south Florida, USA

A hydrodynamic threshold between Darcian and non-Darcian flow conditions was found to occur in cubes of Key Largo Limestone from Florida, USA (one cube measuring 0.2 m on each side, the other 0.3 m) at an effective porosity of 33% and a hydraulic conductivity of 10 m/day. Below these values, flow was laminar and could be described as Darcian. Above these values, hydraulic conductivity increased greatly and flow was non-laminar. Reynolds numbers (Re) for these experiments ranged from <0.1 to 7. Non-laminar flow conditions observed in the hydraulic conductivity tests were observed at Re close to 1. Hydraulic conductivity was measured on all three axes in a permeameter designed specifically for samples of these sizes. Positive identification of vertical and horizontal axes as well as 100% recovery for each sample was achieved. Total porosity was determined by a drying and weighing method, while effective porosity was determined by a submersion method. Bulk density, total porosity and effective porosity of the Key Largo Limestone cubes averaged 1.5 g/cm³, 40 and 30%, respectively. Two regions of anisotropy were observed, one close to the ground surface, where vertical flow dominated, and the other associated with a dense-laminar layer, below which horizontal flow dominated.     

High-resolution saturated hydraulic conductivity logging of borehole cores using air permeability measurements

Saturated hydraulic conductivity (K _s) is one of the most important parameters determining groundwater flow and contaminant transport in both unsaturated and saturated porous media. The hand-held air permeameter technique was investigated for high-resolution hydraulic conductivity determination on borehole cores using a spatial resolution of ～0.05 m. The suitability of such air permeameter measurements on friable to poorly indurated sediments was tested to improve the spatial prediction of classical laboratory-based K _s measurements obtained at a much lower spatial resolution (～2 m). In total, 368 K _s measurements were made on ～350 m of borehole cores originating from the Campine basin, northern Belgium, while ～5,230 air permeability measurements were performed on the same cores, resulting in a K _s range of seven orders of magnitude. Cross-validation demonstrated that, using air permeameter data as the secondary variable for laboratory based K _s measurements, the performance increased from R ²?=?0.35 for ordinary kriging (laboratory K _s only) to R ²?=?0.61 for co-kriging. The separate treatment of horizontal and vertical hydraulic conductivity revealed considerable anisotropy in certain lithostratigraphical units, while others were clearly isotropic at the sample scale. Air permeameter measurements on borehole cores provide a cost-effective way to improve spatial predictions of traditional laboratory based K _s.     

A new method for mapping variability in vertical seepage flux in streambeds

A two-step approach was used to measure the flux across the water-sediment interface in river channels. A hollow tube was pressed into the streambed and an in situ sediment column of the streambed was created inside the tube. The hydraulic gradient between the two ends of the sediment column was measured. The vertical hydraulic conductivity of the sediment column was determined using a falling-head permeameter test in the river. Given the availability of the hydraulic gradient and vertical hydraulic conductivity of the streambed, Darcy’s law was used to calculate the specific discharge. This approach was applied to the Elkhorn River and one tributary in northeastern Nebraska, USA. The results suggest that the magnitude of the vertical flux varied greatly within a short distance. Furthermore, the flux can change direction from downward to upward between two locations only several meters apart. This spatial pattern of variation probably represents the inflow and outflow within the hyporheic zone, not the regional ambient flow systems. In this study, a thermal infrared camera was also used to detect the discharge locations of groundwater in the streambed. After the hydraulic gradient and the vertical hydraulic conductivity were estimated from the groundwater spring, the discharge rate was calculated.     

利用直接推进技术测定渗透系数的最新进展

高精度测定渗透系数（K）的重要性不言自明,但是现阶段野外试验手段能够提供的关于K的信息不能满足高度非均质地层中污染物迁移预测模拟的需求。直接推进注入记录器(Direct Push Injection Logger, DPIL)和直接推进渗透仪(Direct Push Permeameter, DPP)是新发展的水文地质参数测量仪器,能够使K值的测定达到前所未有的分辨率和成本效益水平。工具向地下推进过程中,通过对注水量、注水压力和其它的水文地球物理参数的同步监测,直接推进技术(Direct Push, DP)能快捷准确地获得地层渗透系数的垂向分布。DP技术几乎适用于所有野外松散地层,并且对场地的干扰很小。因此,它克服了许多基于既有井的传统含水层测试方法的局限性。最近在美国MADE试验场的一个案例研究表明,使用DPIL/DPP可以获得空间分辨率达15cm的K值垂向分布。未来,高精度直接推进技术还可以与新一代的地球物理技术,例如高精度探地雷达相结合,以实现不同位置DP测定K值的互联以及整个试验场K值三维分布的确定。     

Heterogeneity of hydraulic conductivity and Darcian flux in the submerged streambed and adjacent exposed stream bank of the Beiluo River,northwest China

Recognizing the heterogeneity of hydraulic conductivity and hyporheic flow is critical for understanding contaminant transfer and biogeochemical and hydrological processes involving streams and aquifers. In this study, the heterogeneity of hydraulic conductivity and Darcian flux in a submerged streambed and its adjacent exposed stream banks were investigated in the Beiluo River, northwest China. In the submerged streambed, Darcian flux was estimated by measurement of vertical hydraulic conductivity (K _v) and vertical head gradient (VHG) using in-situ permeameter tests. On exposed stream banks, both horizontal hydraulic conductivity (K _h) and K _v were measured by on-site permeameter tests. In the submerged streambed, K _v values gradually decreased with depth and the higher values were concentrated in the center and close to the erosional bank. Compared to the exposed stream banks, the K _v values were higher in the streambed. From stream stage to the topmost layer of tested sediment, through increasing elevation, the K _h values increased on the erosional bank, while they decreased on the depositional bank. The values of VHG along the thalweg illustrate that downwelling flux occurred in the deepest area while upwelling flux appeared in the other areas, which might result from the change of streambed elevation. The higher value of the Darcian flux in the submerged streambed existed near the erosional bank.     

溶液和温度作用下膨润土防水毯的渗透性能

以颗粒状和粉末状膨润土防水毯(GCLs)为对象,运用GDS (global digital systems)全自动渗透仪开展渗透试验,研究CaCl_2溶液作用下GCLs渗透性能的温度效应,初步探讨其机理。试验表明:当水化液为0.05mol/L的CaCl_2溶液时,两种GCLs渗透系数随温度升高呈现增大趋势;当水化液为去离子水时,颗粒状GCL渗透系数随温度升高而减小,粉末状GCL渗透系数随温度升高而增大。去离子水情况下,膨润土吸附结合水量随温度升高而减小;CaCl_2溶液作用下,吸附结合水量较去离子水情况大幅降低。当CaCl_2溶液浓度一定时,膨润土膨胀指数随温度升高而略有增大;当温度一定时,膨润土膨胀指数随CaCl_2溶液浓度升高而显著减小。以去离子水进行试验时:颗粒状和粉末状GCLs渗透系数随温度的变化主要影响因素为凝胶态蒙脱石数量,其次为流体黏滞系数和吸附结合水量;颗粒状GCLs膨润土孔隙结构越不均匀,凝胶态蒙脱石数量的影响就越显著,导致渗透系数随温度升高而减小、固有渗透率随温度升高显著降低。以CaCl_2溶液进行试验时,两种GCLs渗透系数随温度变化的主要受流体黏滞系数和吸附结合水量的影响,而受凝胶态蒙脱石数量的影响较小。孔隙溶液性质、温度和膨润土类型均对GCLs的防渗性能具有重要影响。