Influences of soil water characteristic curve on rainfall-induced shallow landslides

The analysis of slope instability induced by rainfall was usually performed using the main drying curve as the measurement of the main wetting curve is a more time-consuming and costly task. In this study, the influences of the main drying and wetting curves on rainfall-induced shallow landslides are examined. Three designed scenarios and a real case scenario are used to conduct this examination. The prediction of shallow landslide occurrence is related to the main drying and wetting curves due to the strong relation between groundwater pressure head and hysteresis effect. The main wetting curve may have a less minimum landslide-triggering rainfall amount and a less rainfall duration threshold for landslide occurrence than the drying wetting curve. For safety’s sake, an underestimation of shallow landslide occurrence may be produced by the commonly used main drying curve. In addition, besides the shallow landslide occurrence, the failure depth and the time to failure are also influenced by the main drying and wetting curves. The hysteresis effect should be taken into account for assessing rainfall-induced shallow landslides.     

Vulnerability assessment of rainfall-induced debris flows in Taiwan

A GIS-based decision support system, which incorporates local topographic and rainfall effects on debris flow vulnerability is developed. Rainfall at a scale compatible with the digital elevation model resolution is obtained using a neural network with a wind-induced topographic effect and rainfall derived from satellite rain estimates and an adaptive inverse distance weight method (WTNN). The technique is tested using data collected during the passage of typhoon Tori-Ji on July 2001 over central Taiwan. Numerous debris flows triggered by the typhoon were used as control for the study. Our results show that the WTNN technique outperforms other interpolation techniques including adaptive inversed distance weight (AIDW), simple kriging (SK), co-kriging, and multiple linear regression using gauge, and topographic parameters. Multiple remotely-sensed, fuzzy-based debris-flow susceptibility parameters are used to describe the characteristics of watersheds. Non-linear, multi-variant regressions using the WTNN derived rainfall and topography factors are derived using self-organizing maps (SOM) for the debris flow vulnerability assessment. An index of vulnerability representing the degrees of hazard is implemented in a GIS-based decision support system by which a decision maker can assess debris flow vulnerability.     

降雨入渗对残积土填坡渗流变形数值模拟分析

许多研究已经证实了降雨引起的渗流能降低填土稳定性,特别是对于非饱和残积填土。降雨能使残积填土内形成渗流潜蚀破坏,并使地下水位和孔隙水压力发生变化,导致抗剪强度下降形成潜在破坏面,最终发生破坏。利用有限元数值分析,研究等降雨强度与降雨持续时间对于福建地区残积填土的影响,发现降雨强度变大或持续时间延长都能使残积填土内的地下水位上升,局部区域孔隙水压力增大,渗流速率也发生变化,从而影响残积填土的稳定性。另外,证实了存在降雨临界持续时间,一旦降雨持续时间超过了临界持续时间,地下水位线高度随降雨持续时间变长而降低,安全系数就转而变大。     

Centrifuge modelling of rainfall-induced slope failure in variably saturated soil

Acta Geotechnica - This paper presents the results of centrifuge tests on rainfall-induced instabilities in variably saturated slopes. The roles of rainfall intensity and initial conditions, such...     

Assessing water quality using water quality index and multivariate analysis

Groundwater is increasingly gaining significance as the main solution to the water supply problems in Ghana, especially in the rural areas. This study was conducted to determine which factors play significant roles in the hydrochemistry of groundwater from the southern Voltaian formation. Conventional graphical and multivariate statistical methods were used. The study reveals three main factors controlling the hydrochemistry. Silicate mineral weathering and reverse cation exchange are the most important processes affecting the hydrochemistry of groundwater at this part of the formation. Interpolation maps created from factor scores suggest that these processes are the most pervasive, recording high scores almost everywhere in the study area. Carbonate mineral weathering is the second most important process in the hydrochemistry. This study finds that carbonate mineral weathering in the area is probably facilitated by carbonic acid rather than sulfuric acid. Chemicals from agricultural activities constitute the third most important process influencing groundwater quality in the area. Eighty samples were used to calculate water quality indices, WQI, which were in turn used to classify groundwater from the study area. Over 98% of the samples fall within the “Excellent” and “Good” categories, suggesting that groundwater from the southern Voltaian formation is generally acceptable for drinking purposes.     

基于自然电位方法的土壤水分入渗过程监测

自然电位方法可以应用于水文地球物理领域获取土壤水分入渗特征.通过连续监测野外试验场的自然电位场,获取连续的自然电位平面图,直接获知了土壤水分在平面上的主要入渗区域,同时借助自然电位成像方法,揭示了土壤水分的两个主要通道,并探测出两个地下孔洞的位置,最终在地质雷达剖面图的辅助下证实了上述结论,为水文地球物理领域提供了新的技术手段和方法.     

Efficient approach in modeling the shear strength of unsaturated soil using soil water retention curve

Acta Geotechnica - Currently, there are debates on the relationship between the effective stress and shear strength of unsaturated soils. Thus, it is imperative to present an efficient method that...     

An approach to mass movements in the Jiuzhaigou catchment

This paper presents a preliminary study of the main types, features, genesis, and countermeasures of mass movements in the Jiuzhaigou catchment, which is one of the most scenic regions in China. The main features are debris flows, rock-segment flows, landslides, and avalanches. Rough relief, fractured rocks, drifts, steep slopes, intensive rainstorms, and earthquakes produced their geneses. Countermeasures should include the integration of engineering and biological projects.     

The formation and evolution of a coastal alluvial fan in eastern Taiwan caused by rainfall-induced landslides

The formation and evolution of a coastal fan in eastern Taiwan associated with a sequence of rainfall-induced landslides during the 2009–2013 period are explored in this study. The evolution of these landslides is mainly attributed to the head-cutting process initiated by Typhoon Parma in October 2009. During the attack of Typhoon Megi in October, 2010, a subaerial coastal fan with a surface slope of 8.9° was formed after the mobilization of the rainfall-induced landslides. The geomorphic features both in the steep gully and on the coastal fan were categorized as the sequence of granular debris flows and sheet floods. Severe fan toe erosion occurred thereafter due to the wind-wave forcing. Even if the variations of both the cumulative rainfalls and the drainage areas are one or two orders of magnitude among devastating fan-forming landslides worldwide, the mean annual precipitation and the basin ruggedness index (Melton ratio) are effective indicators to normalize the rainfall threshold and to characterize the fan surface slope, respectively. Severe catastrophic landslides generally occur when the normalized cumulative rainfalls with respect to mean annual precipitation are greater than 0.1. The fan slope generally increases with the increasing Melton ratio for the catchment. Uchiogi’s empirical model is applicable for predicting the rainfall-induced area ratio of newly generated landslides. In this case study, the relationship of the fan area to the total landslide area follows a linear regressive curve when the ratio of landslide area with respect to the drainage area exceeds 0.0056.     

Impact of mass movements in the Kocaeli Province,Turkey

Recent mass movements in the Kocaeli Province, Turkey in 2010 caused damage to people, property and infrastructure, especially in Izmit and its vicinity. The causes and impact of these mass movements are outlined, so as to increase awareness of their dangerous aspects. Some of these mass movement events took place in urban areas, bringing attention to the need for better and more effective land use practices. The impact of these movements indicates the benefit there would be from geology and engineering geology in the planning of any property development and land use.     

Predicting river water quality index using data mining techniques

This paper demonstrates the application of data mining techniques to predict river water quality index. The usefulness of these techniques lies in the automated extraction of novel knowledge from the data to improve decision-making. The popular classification techniques, namely k-nearest neighbor, decision trees, Naive Bayes, artificial neural networks, rule-based and support vector machines were used to develop the predictive environment to classify water quality into understandable terms based on the Overall Index of Pollution. Experimentation was conducted on two types of data sets: synthetic and real. A repeated k-fold cross-validation procedure was followed to design the learning and testing frameworks of the predictive environment. Based on the validation results, it was found that the error rate in defining the true water quality class was 20 and 28%, 11 and 24%, 1 and 38% and 10 and 20% for the k-nearest neighbor, Naive Bayes, artificial neural network and rule-based classifiers for synthetic and real data sets, respectively. The decision tree and support vector machines classifiers were found to be the best predictive models with 0% error rates during automated extraction of the water quality class. This study reveals that data mining techniques have the potential to quickly predict water quality class, provided data given are a true representation of the domain knowledge.     

土壤及水中As价态分析方法研究

建立了用原子荧光光谱仪测定水体中的砷及土壤中有效砷的价态分析方法。采用控制酸度的方法实现水中砷的价态分析。选用AB—DTPA为浸提剂提取土壤中的有效砷,经巯基棉吸附,分离五价砷和三价砷,实现有效砷的价态分析。方法快速简便,经济实用,可用于环境研究中的大批量样品分析。     

利用土壤温度估算土壤有效热导系数和水流通量

土壤有效热导系数和水流通量是研究大气-土壤系统水分转化的重要变量。采用动态回归模型（DHR）获取土壤温度的振幅和相位变化,联合土壤水热耦合方程的解析解估算土壤有效热导系数和土壤水流通量,并将该方法应用于毛乌素沙地的土壤水流通量估算中。结果显示,实例研究估算获得的有效热导系数在10-7m2/s数量级变化,且随振幅比的增加呈指数增加,随相位差的增加呈指数衰减。当土壤含水率小于0.08时,有效热导系数呈线性增加;当土壤含水率大于0.08时,接近恒定值（定量0.08）,土壤水流通量随土壤含水率的变化无明显的线性关系。     

基于非均质系数的裂隙岩体表征单元体研究

表征单元体（REV）是岩体力学中的一个基础性概念,其存在性是确定岩体等效参数和应用连续介质方法进行研究的前提条件。为综合反映裂隙大小、产状和密度对岩体REV的影响,本文提出采用岩体非均质系数HI来确定岩体的REV。首先,详细介绍了非均质系数的概念和含义。利用General Block软件建立了中等间距-中等延展性（MS1-MP1）裂隙的网络模型,并完成20次随机实现。从各模型中选取10个不同尺寸的岩体模型计算非均质系数,结果表明：非均质系数具有明显的尺寸效应,当岩体尺寸不小于8 m时,非均质系数的平均值和标准差分别为0.5和0.14,综合确定该岩体的REV为8 m。采用HI对三峡地下电站厂房围岩的研究表明,该岩体的REV为60 m,可作为非连续介质方法适用性的判断标准。HI是从岩体结构角度提出的新指标,适用于确定岩体的REV和统计范围,对岩体的统计分析和等效参数研究具有重要意义。     

水汽场中气液态水质量比的确定方法

包气带中裂隙岩体含水量无法用仪器或者实验的方法获取,也无法用理论方法计算,而这部分水对生态复绿和文物保护等的影响不容忽视。为了解决这一问题,确定岩体内气液态水的质量比（α）是关键。在岩体、气态水和液态水组成的开放系统中,当系统内相对湿度达到100%,系统达到局域平衡态。根据热动力学平衡理论,此时系统内气液态水的密度和质量都相等,即液态水和气态水的质量之比为一常数。因此,为了求取α值,文章设计了室内试验,通过对有效试验数据的分析,获取计算α经验公式。试验研究表明:质量比α跟温度t呈指数函数关系;当气态水达到饱和时,液态水的质量远大于气态水的质量。此研究不仅为定量评价包气带中岩体内水汽含量提供一种计算方法,同时对探讨包气带中岩体内气液态水转化规律具有十分重要的参考价值。     

Arsenic immobilization in water and soil using acid mine drainage sludge

Adsorption onto Fe-containing minerals is a well-known remediation method for As-contaminated water and soil. In this study, the use of acid mine drainage sludge (AMDS) to adsorb As was investigated. AMDS is composed of amorphous particles and so has a large surface area (251.2 m² g⁻¹). Here, adsorption of both arsenite and arsenate was found to be almost 100%, under various initial AMDS dosages, with the arsenate adsorption rate being faster. The optimum pH for As adsorption onto AMDS was pH 7.0 and the maximum adsorption capacities for arsenite and arsenate were 58.5 mg g⁻¹ and 19.7 mg g⁻¹ AMDS, respectively. In addition, experiments revealed that AMDS dosages decreased As release from contaminated soil. Therefore, the AMDS used in this study was confirmed to be a suitable candidate for immobilizing both arsenite and arsenate in contaminated soils.     

基于Cobb-Douglas生产函数的新疆各地区典型作物生产水足迹驱动因素研究

水资源紧缺是限制我国西北干旱区农业发展的主要瓶颈,正确评估地区农业用水效率及其影响机制,可为提高农业用水效率提供理论依据。以新疆为研究区,基于1988-2015年的长系列数据,分别计算出历年北疆、南疆、东疆典型作物（小麦、棉花）生产水足迹,并采用Cobb-Douglas生产函数定量分析气象因素（年降雨量、年日照时数、年均温度、年均风速、年均湿度）和技术因素（农机总动力、有效灌溉率、化肥施用折纯量）对作物生产水足迹的影响贡献率。结果表明： 1988年至2015年,东疆小麦、棉花生产水足迹显著高于北疆和南疆,在气候变化和技术进步的综合影响下,各地区典型作物生产水足迹逐年降低,其中技术进步对新疆典型作物单产水足迹影响显著高于气候因素,是驱动新疆各地区典型作物生产水足迹变化的主要控制因素。地区尺度上,北疆、南疆、东疆气候变化和农业技术发展均呈现显著的地区差异,总体来看,北疆气候条件最适宜作物生长,东疆气候最为恶劣,北疆、南疆农业技术发展速率整体上高于东疆。     

Simulation of the availability index of soil copper content using general regression neural network

Excessive soil copper (Cu) availability leads to plant growth retardation and leaf chlorosis, and the contamination of Cu in the food chain would be detrimental to human and animal health. The most important path for Cu accumulation in plants is uptake from soils. It is therefore important to understand the availability of soil Cu and its controlling factors to modify Cu availability and prevent excessive Cu from entering the food chain. The present study proposed a general regression neural network (GRNN) to simulate the availability index of soil Cu (available heavy mental concentrations/total heavy metal concentrations), based on the influencing factors of total Cu concentration, pH, organic matter (OM), available phosphorus (AP), and readily available potassium (RAK). Results showed that total Cu concentration, combined with OM and AP, achieved the lowest RMSE value (0.0524) for the modeled value of the availability index of soil Cu. The simulated results by GRNN and the ground truth values had better agreement (R ² = 0.7760) than that by a linear model (R ² = 0.6464) for 23 test samples. Moreover, GRNN obtained lower averaged relative errors than linear model. This demonstrated that GRNN could be used to simulate the availability index of soil heavy metals and gained better results than linear model.