A probabilistic approach for computing water retention of particulate systems from statistics of grain size and tessellated pore network     

Richard Wan  Mehdi Pouragha  Mahdad Eghbalian  Jérôme Duriez  Tai Wong 《国际地质力学数值与分析法杂志》2019,43(5):956-973

The paper offers an analytical determination of the hydraulic properties of an unsaturated soil with reference to its retention curve, which describes the relationship between the volumetric water content and capillarity through matric suction. The analysis combines a particulate approach focused on the physics at the pore scale, including microstructural aspects, with a probabilistic approach where the void space and grain size are considered as random variables. In the end, the soil water characteristic curve of an unsaturated granular medium along a drying path can be derived analytically based on the sole information of particle size distribution. The analysis hinges on the tessellation of a wet granular system into an assemblage of tetrahedral unit cells revealing a pore network upon which capillary physics are computed with respect to pore throat invasion by a non-wetting fluid with evolving pendular capillary bridges. The crux of the paper is to pass from particle size probability distribution to a matching void space distribution to eventually reveal key information such as void cell and solid volume statistics. Making reasonable statistically based assumptions to render calculations tractable, the water retention curve can be readily constructed. Model predictions compare quite favourably with experimental data available for actual soils, especially in the high saturation range. Having a sound scientific basis, the model can be made amenable to address a variety of soils with a wider range of particle sizes.  相似文献   

Soil pipe flow tracer experiments: 1. Connectivity and transport characteristics          下载免费PDF全文

G. V. Wilson  J. R. Rigby  M. Ursic  S. M. Dabney 《水文研究》2016,30(8):1265-1279

Much debate has occurred in catchment hydrology regarding the connectivity of flow paths from upslope areas to catchment outlets. This study was conducted in two catchments, one with three upper branches, in a loess soil with a fragipan that fosters lateral flow and exhibits an extensive distribution of soil pipe collapse features. The study aimed to determine the connectivity of multiple soil pipe networks as well as determine pipe flow velocities during storm events. Fluorescein dye was injected directly into soil pipes at the upper most pipe collapse feature of four different hillslopes. Breakthrough curves (BTC) were determined by sampling multiple pipe collapse features downslope. The BTCs were used to determine the ‘average’ (centre of mass) and ‘maximum’ (first arrival) flow velocities. This study confirmed that these catchments contain individual continuous soil pipe networks that extend over 190 m and connect the upper most hillslopes areas with the catchment outlet. While the flow paths are continuous, the individual pipe networks consist of alternating reaches of subsurface flow through soil pipes and reaches of surface flow through gullies formed by pipe collapses. In addition, flow can be occurring both through the subsurface soil pipes simultaneous with surface flow generated by artesian flow from the soil pipes. The pipe flow velocities were as high as 0.3 m/s, which was in the range of streamflow velocities. These pipe flow velocities were also in the range of velocities observed in pinhole erosion tests suggesting that these large, mature soil pipes are still actively eroding. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

磁浮交通试验线压力管道直线度的测量方法研究及应用     

韩冰  刘成龙  杨雪峰 《测绘通报》2019,(6):126-130,135

目前，国内外对于磁浮交通真空压力管道直线度测量问题的研究较少。本文结合西南交通大学在建的真空磁浮高速列车试验装置，提出了一种真空压力管道直线度测量方法。该方法在管道内建立高精度三维控制网，依据三维控制网测量采用圆曲线拟合方法确定各节管道的圆心坐标，并采用直线拟合方法分析整个管道的直线度。最后依据上述方法编制程序对实测数据进行了处理分析，验证了方法的可行性和正确性，可为今后真空磁浮压力管道的建设提供技术参考。  相似文献   

New graphical methods for estimating aquifer hydraulic parameters using pumping tests with exponentially decreasing rates     

Chao Zhuang  Zhifang Zhou  Hongbin Zhan  Jinguo Wang  Yabing Li  Zhi Dou 《水文研究》2019,33(17):2314-2322

Actual pumping tests may involve continuously decreasing rates over a certain period of time, and the hydraulic conductivity (K) and specific storage (S_s) of the tested confined aquifer cannot be interpreted from the classical constant‐rate test model. In this study, we revisit the aquifer drawdown characteristics of a pumping test with an exponentially decreasing rate using the dimensionless analytical solution for such a variable‐rate model. The drawdown may decrease with time for a short period of time at intermediate pumping times for such pumping tests. A larger ratio of initial to final pumping rate and a smaller radial distance of the observation well will enhance the decreasing feature. A larger decay constant results in an earlier decrease, but it weakens the extent of such a decrease. Based on the proposed dimensionless transformation, we have proposed two graphical methods for estimating K and S_s of the tested aquifer. The first is a new type curve method that does not employ the well function as commonly done in standard type curve analysis. Another is a new analytic method that takes advantage of the decreasing features of aquifer drawdown during the intermediate pumping stage. We have demonstrated the applicability and robustness of the two new graphical methods for aquifer characterization through a synthetic pumping test.  相似文献   

Revised runoff curve number for runoff prediction in the Loess Plateau of China     

Wenhai Shi  Ni Wang  Miaomiao Wang  Donghao Li 《水文研究》2021,35(10):e14390

The soil conservation service (now Natural Resources Conservation Service) Curve Number (SCS-CN), one of the most commonly used methods for surface runoff prediction. The runoff calculated by this method was very sensitive to CN values. In this study, CN values were calculated by both arithmetic mean (CN_C) and least square fit method (CN_F) using observed rainfall-runoff data from 43 sites in the Loess Plateau region, which are considerably different from the CN₂ values obtained from the USDA-SCS handbook table (CN_T). The results showed that using CN_C instead of CN_T for each watershed produce little improvement, while replacing CN_T with CN_F improves the performance of the original SCS-CN method, but still performs poorly in most study sites. This is mainly due to the SCS-CN method using a constant CN value and discounting of the temporal variation in rainfall-runoff process. Therefore, three factors—soil moisture, rainfall depth and intensity—affecting the surface runoff variability are considered to reflect the variation of CN in each watershed, and a new CN value was developed. The reliability of the proposed method was tested with data from 38 watersheds, and then applied to the remaining five typical watersheds using the optimized parameters. The results indicated that the proposed method, which boosted the model efficiencies to 81.83% and 74.23% during calibration and validation cases, respectively, performed better than the original SCS-CN and the Shi and Wang (2020b) method, a modified SCS-CN method based on tabulated CN value. Thus, the proposed method incorporating the influence of the temporal variability of soil moisture, rainfall depth, and intensity factors suggests an accurate runoff prediction for general applications under different hydrological and climatic conditions on the Loess Plateau region.  相似文献   

Predicting the dependency of a degree of saturation on void ratio and suction using effective stress principle for unsaturated soils     

David Mašín 《国际地质力学数值与分析法杂志》2010,34(1):73-90

The paper presents an approach to predicting variation of a degree of saturation in unsaturated soils with void ratio and suction. The approach is based on the effective stress principle for unsaturated soils and several underlying assumptions. It focuses on the main drying and wetting processes and does not incorporate the effects of hydraulic hysteresis. It leads to the dependency of water retention curve (WRC) on void ratio, which does not require any material parameters apart from the parameters specifying WRC for the reference void ratio. Its validity is demonstrated by comparing predictions with the experimental data on four different soils taken over from the literature. Good correlation between the measured and predicted behaviour indirectly supports applicability of the effective stress principle for unsaturated soils. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

基于Logistic和Gompertz曲线模型拟合的建筑物沉降分析     

冉雍 《测绘与空间地理信息》2016,(2):192-195

重大工程建设一般会有定期的沉降和变形监测,本研究利用具有规律变化的Logistic和Gompertz曲线模型进行拟合,并以某大型发电厂为研究对象,利用近15年的监测数据,建立预测模型并进行精度评估。研究结果表明,若监测数据具有一定程度的稳定性,并对计算时监测数据进行合理取舍,对采取的全区、分区平均值或单一点高度值的检测数据,运用Logistic和Gompertz曲线模型来预测大型建筑物的沉降情况是可行的。  相似文献   

采用弯曲进行道路化简冲突避免的方法   总被引：1，自引：1，他引：0  

何海威  钱海忠  王骁  胡慧明  陈竞男 《测绘学报》2016,45(3):354-361

针对道路化简后可能导致要素间空间关系前后不一致的问题,提出了一种采用弯曲进行道路化简冲突避免的方法。首先,以弯曲为单元分析道路化简前后弯曲的形态变化规律,对化简过程产生的要素间空间冲突类型进行了归纳和总结;其次,基于道路弯曲与要素之间的空间关系,提出了相应的冲突判别规则;最后,利用弯曲化简的可控性和弯曲组的间接化简策略实现对化简冲突的避免。试验表明,该方法能有效地识别和避免道路化简产生的空间冲突,确保化简前后道路与其他要素空间关系的一致性。  相似文献   

一种迭代法的圆曲线拟合方法     

陈明晶  方源敏  马波  陈杰 《测绘科学》2016,41(5):133-136

针对在实际测量工作中量测圆心坐标及半径时存在的问题,该文基于迭代法的思想,推导了一种圆曲线拟合的方法,并用实例数据进行了检验。结果显示,该方法在离散点均匀采集或非均匀采集的情况下均具有良好的拟合效果,与目前在圆曲线拟合方法中普遍采用的最小二乘法相比,具有同样高的拟合精度,验证了该拟合方法的正确性与可行性。  相似文献   

一种曲线拟合圆心坐标算法及精度分析     

田镇  杨志强  石震  党永超  马骥 《测绘科学》2016,41(11):31-34,55

针对在工程应用中,经常需要根据某些圆形物体上的离散点求取其圆心坐标,而采用何种算法简单易行,其精度又与哪些因素有关的相关研究较少的问题,该文提出一种利用曲线拟合求取圆心坐标的简洁算法,并编程实现。然后采用模拟仿真结合统计分析的方法评估了该算法在不同条件下的拟合精度,得出测点误差越大,拟合精度越低;测点个数越多,分布越均匀,拟合精度越高;圆半径对拟合精度影响甚小等结论。在某工程项目中使用该算法得到的结果精度较高,验证了其有效可行,且与采用其他方法得到的坐标值较为接近,说明了该算法的可靠性高。  相似文献