Landslides associated with the colluvial soils overlying the Natal Group in the greater Durban region of Natal, South Africa

In the last 25 years, many of the landslides that have occurred in the greater Durban region have been associated with the colluvial soils overlying the Natal Group, most of which occurred during the very heavy rains of September 1987. Subsequently, a very heavy rainfall event in February 1999 also gave rise to landslides. In fact, prior to 1987 these colluvial soils were considered relatively stable. A critical precipitation coefficient has been developed which included the cumulative precipitation up to a landslide event. In addition, an attempt has been made to establish a threshold value for triggering of landslides for the colluvial soils from a study of pluviometric data. The results indicate that when a rainfall event exceeds 12% of the mean annual rainfall, small-scale landslides are likely to occur. When a rainfall event is greater than 16% of the mean annual rainfall, a moderate number of landslides take place. Major landslides are associated with rainfall events with intensities in excess of 20% of the mean annual precipitation. An example of a landslide which occurred on the Natal Group due to construction operations is provided, as well as an account of those which took place during September 1987. In the latter case, most of the slides took the form of mudflows and were responsible for some of the worst damage which has occurred in the Durban region. The colluvial soils involved were relatively thin and therefore became quickly saturated by the heavy rainfall. In some places the situation was further aggravated by liquefaction of the soils. Received: 15 June 1999 · Accepted: 30 August 1999     

Modeling landslide recurrence in Seattle, Washington, USA

To manage the hazard associated with shallow landslides, decision makers need an understanding of where and when landslides may occur. A variety of approaches have been used to estimate the hazard from shallow, rainfall-triggered landslides, such as empirical rainfall threshold methods or probabilistic methods based on historical records. The wide availability of Geographic Information Systems (GIS) and digital topographic data has led to the development of analytic methods for landslide hazard estimation that couple steady-state hydrological models with slope stability calculations. Because these methods typically neglect the transient effects of infiltration on slope stability, results cannot be linked with historical or forecasted rainfall sequences. Estimates of the frequency of conditions likely to cause landslides are critical for quantitative risk and hazard assessments. We present results to demonstrate how a transient infiltration model coupled with an infinite slope stability calculation may be used to assess shallow landslide frequency in the City of Seattle, Washington, USA. A module called CRF (Critical RainFall) for estimating deterministic rainfall thresholds has been integrated in the TRIGRS (Transient Rainfall Infiltration and Grid-based Slope-Stability) model that combines a transient, one-dimensional analytic solution for pore-pressure response to rainfall infiltration with an infinite slope stability calculation. Input data for the extended model include topographic slope, colluvial thickness, initial water-table depth, material properties, and rainfall durations. This approach is combined with a statistical treatment of rainfall using a GEV (General Extreme Value) probabilistic distribution to produce maps showing the shallow landslide recurrence induced, on a spatially distributed basis, as a function of rainfall duration and hillslope characteristics.     

Comparative analysis of contributing parameters for rainfall-triggered landslides in the Lesser Himalaya of Nepal

In the Himalaya, people live in widely spread settlements and suffer more from landslides than from any other type of natural disaster. The intense summer monsoons are the main factor in triggering landslides. However, the relations between landslides and slope hydrology have not been a focal topic in Himalayan landslide research. This paper deals with the contributing parameters for the rainfall-triggered landslides which occurred during an extreme monsoon rainfall event on 23 July 2002, in the south-western hills of Kathmandu valley, in the Lesser Himalaya, Nepal. Parameters such as bedrock geology, geomorphology, geotechnical properties of soil, and clay mineralogy are described in this paper. Landslide modeling was performed in SEEP/W and SLOPE/W to understand the relationship of pore water pressure variations in soil layers and to determine the spatial variation of landslide occurrence. Soil characteristics, low angle of internal friction of fines in soil, medium range of soil permeability, presence of clay minerals in soil, bedrock hydrogeology, and human intervention were found to be the main contributing parameters for slope failures in the region.     

西安市白鹿塬滑坡发生时间预测研究

笔者通过对白鹿塬区降水与滑坡发生时间之间的规律进行总结，认为本区滑坡发生与降水的丰年有着密切的关系，并应用卡尔曼滤波分析法对白鹿塬区滑坡发生时间进行了全区性预测，提出白鹿塬滑坡发生具有10年左右的中周期，20年左右的长周期，应及早作好防治工作。     

灰色关联度法和距离判别分析法在溪洛渡库区潜在滑坡判识中的应用

以溪洛渡库区深入研究的14个典型滑坡为研究对象,在初步建立潜在滑坡判识指标的基础上,运用灰色关联度理论优选确定了影响库区潜在滑坡孕育的8个关键主控因素:坡面平均坡度、滑体内冲沟切割程度、洼地封闭状况(或排水条件)、滑面平均倾角、滑面形态、下滑段长度与总滑面长度之比、滑体结构及近期活动迹象,并依据距离判别分析的理论和方法,建立了溪洛渡库区潜在滑坡的距离判识模型。该判识模型对库区5个待判滑坡样本和9个滑坡学习样本的判识准确率均达到了100%。     

岷江上游河流阶地发育特征及与古滑坡关系初步分析

河流阶地形成演化及其对滑坡的控制是近年来古滑坡研究的热点问题。笔者在对岷江上游河流阶地和古滑坡实地调查测试的基础上,对岷江上游河流阶地的级序、拔河高度、成因类型等进行了分析,绘制了阶地高程位相图和年龄位相图,并结合阶地和古滑坡年代,讨论了阶地与古滑坡的发育关系等。主要取得了以下认识：1）岷江上游的河流阶地具有分段性,成因主要为气候多期次波动与构造活动共同作用,古滑坡及堰塞湖是影响高山峡谷区河流阶地发育的重要因素;2）叠溪-茂县段在20~30 ka B. P.发生了多处大型古滑坡,其中20 ka B. P.的古滑坡可能主要是气候波动引发,30 ka B. P.发生的古滑坡可能主要受控于构造活动（地震）;3）岷江上游大量分布的古滑坡堆积体与阶地发育的叠置关系有待进一步理清,开展该地区的河流阶地级序研究要充分考虑古滑坡和堰塞湖的影响

     

Head-based isogeometric analysis of transient flow in unsaturated soils

An isogeometric analysis (IGA) is introduced to obtain a head-based solution to Richards equation for unsaturated flow in porous media. IGA uses Non-Uniform Rational B-Spline (NURBS) as shape functions, which provide a higher level of inter-element continuity in comparison with Lagrange shape functions. The semi-discrete nonlinear algebraic equations are solved using a combination of implicit backward-Euler time-integration and Newton-Raphson scheme. The time-step size is adaptively controlled based on the rate of changes in the pore pressure. The results from the proposed formulation are compared and verified against an analytical solution for one-dimensional transient unsaturated flow in a homogenous soil column. The proposed method is then applied to four more complex problems including two-dimensional unsaturated flow in a two-layered soil and a semi-circular furrow. The test cases in two-layered soil system involve sharp variations in the pressure gradient at the intersection of the two media, where the pore water pressure abruptly changes. It is shown that the proposed head-based IGA is able to properly simulate changes in pore pressure at the soils interface using fewer degrees of freedom and higher orders of approximation in comparison with the conventional finite element method.     

成层土中考虑桩土相对滑移的单桩沉降分析

基于Mindlin位移解,对成层土中的单桩及桩周土作离散化处理,建立了桩土之间有相对滑移和土体存在极限阻力的单桩分析模型,其中桩体沉降采用有限差分法求解,而桩周成层土体的沉降则利用考虑了各单元土体相互影响的ML法计算。两部分之间通过位移协调建立联系,并采用迭代法求解,建立的模型具有较严密的理论基础,且能反映真实的土体分层特性,算例结果亦表明有较高的计算精度。     

漳州市城市土壤重金属含量特征及控制因素

讨论了 108个取自漳州市城区公园、生活区及环城菜地等不同功能区的表层 (0～ 20 cm)土壤样品中重金属含量及分布特点,根据土壤中重金属元素与主元素间的相关分析、聚类分析,探讨了影响土壤中重金属分布和来源的因素.结果表明,漳州市城市土壤 Hg、 Cd、 Pb、 Cu、 Zn、 As、 Cr和 Ni的平均含量分别为 0.471 mg/kg、 0.353 mg/kg、 75.9 mg/kg、 32.6 mg/kg、 106.7 mg/kg、 6.86 mg/kg、 29.7 mg/kg和 12.8 mg/kg,其中相对于区域土壤背景值与国家土壤环境质量标准,污染较突出的元素是 Hg和 Cd.深受人为污染活动影响的城区土壤和菜地土壤重金属平均含量也尤为突出,城区土壤 Hg平均含量最高,菜地土壤 Cd平均含量最高.元素的相关性分析和聚类分析结果表明 Hg相对于其他元素表现较独立, S对 Hg有一定的捕获能力;As、 Cr和 Ni是受控于成土母质的元素组合;Cd和 Pb是受人为污染影响较强的元素, Cu来源于地质成因的比例较大;Zn受控于土壤中锰氧化物粘粒.     

An experimental,analytical and numerical study on the thermal efficiency of energy piles in unsaturated soils

Energy piles are bi-functional foundation elements used as structural support as well as ground heat exchangers for shallow geothermal energy systems. Because they are relatively short, energy piles may be partially embedded in unsaturated soils. Saturation conditions influence the thermal properties of the ground and therefore the heat exchange rate, which in turn affects the efficiency of energy piles. This paper combines analytical, experimental and numerical investigations to evaluate the heat exchange rate of energy piles partially or fully embedded in unsaturated soils. The proposed analytical solution is based on the cylindrical heat source theory that treats the soil as a semi-infinite, homogeneous, and isotropic medium. The solution from this theory is multiplied by a function developed analytically in this paper and the outcome is the heat exchange rate for energy piles in unsaturated soils. The proposed function depends on soil saturation, soil and pile thermal properties, and pile geometry. The analytical solution was compared against a finite element solution; which was in turn validated against results from laboratory experiments. Very satisfactory agreements between the analytical, numerical and experimental outputs were observed. The proposed method can be used for a quick and simple evaluation of the efficiency of energy piles in unsaturated conditions. The proposed analytical solution can also be a useful tool for the verification of numerical codes developed for the design of energy piles in unsaturated soils.     

云南省泗南江水电站库区滑坡危险性分析

水电站地质灾害危险性分析一直以来都是水利工程建设中的研究重点,尤其是滑坡地质灾害,是云南分布较为普遍的不良地质现象。文章通过对泗南江水电站库区的地理地貌概况、地质构造、地层岩性、水文地质等资料进行综合研究,总结并分析库区滑坡的分布规律、规模、危害、活动特征、主要诱发因素等以及库区蓄水后滑坡对工程安全的影响,并对其进行危险性现状分析和预测分析。最后按危险性高Ⅰ、危险性中等Ⅱ、危险性低Ⅲ的标准对滑坡做危险性分区。针对滑坡危险性的高低,提出相应的防灾减灾建议,对泗南江水电站的建设具有一定的指导意义。     

甘肃永靖黑方台地区黄土滑坡土的力学性质

与地下水位以下的饱和黄土力学性质相比,包气带黄土力学性质具有不同的表征参数和测试方法,其对黄土斜坡渗流场和稳定性的影响不容忽视.以甘肃黑方台地区黄土为例,分别采用张力计和轴平移技术量测了黄土的部分区段土-水特征曲线,依据Gardner、Van Genuchten和Fredlund and Xing 3种经验公式对轴平移测试数据进行拟合,获取了完整的土-水特征曲线.基于GDS多功能三轴仪,通过控制基质吸力的三轴剪切试验,获取了考虑基质吸力的黄土强度参数.结果显示:张力计和轴平移技术量测的部分区段土-水特征曲线具有相近的曲线形态,但张力计曲线位于轴平移技术曲线的上方;当基质吸力由100kPa减小至20kPa时,黄土内摩擦角减小约1°,粘聚力下降近22kPa;拟合所得的黑方台地区黄土的基质吸力摩擦角为15.6°.试验为进行黑方台黄土斜坡的非饱和渗流和稳定性分析提供了参数.     

甘肃天水红旗山黄土滑坡群成因及稳定性分析

天水市位于西秦岭北缘断裂带,区内活动断裂发育,历史上强震频发,诱发了大量黄土滑坡。基于对天水市北山地震滑坡群的野外调查,研究了地震滑坡变形破坏特征;以红旗山滑坡群为典型案例,结合室内测试结果,剖析了红旗山滑坡的变形破坏机制;利用FLAC3D模拟分析了现今红旗山滑坡的稳定性。研究结果表明:天水北山滑坡群由地震作用诱发;红旗山滑坡包含两个主滑动带,历史上经历了3期以上变形活动,演化过程复杂,属地震-降雨耦合型滑坡。现今红旗山滑坡体在天然状态下相对稳定,如遇强震作用将造成坡体内部塑性区贯通,斜坡顶部岩土体将发生滑移。这一研究成果可为潜在强震区地震滑坡的变形机理及防灾减灾提供依据。     

冀东平原土壤重金属元素的来源分析

通过对比冀东平原表层和深层土壤样品中8种重金属含量,并利用因子分析提取了7个主因子,结合因子得分图进行重金属来源分析。结果显示Cr的来源具有分异性,一部分源于土壤本底,另一部分来源于矿业污染造成的元素叠加;Hg的来源主要为农业生产,部分地区Hg是由冶金、交通等污染排放所致;唐海县附近Cd主要为河流上游元素搬运成因。局部地区Pb高度富集是由于采矿污染造成。As、Cu、Zn、Ni等元素主要来源于当地自然地质背景。     

甘肃永靖黑方台地区滑坡形成的黄土时效特性

甘肃黑方台地区是中国滑坡预测预报研究和实践的热点地区,开展黄土时效特性试验是进行滑坡预测预报的基础.以黑方台原状黄土为研究对象,开展了2个含水量、4个围压、八级偏应力水平下的黄土三轴固结排水蠕变试验,研究了黑方台黄土的粘-弹-塑性变形破坏规律.蠕变试验结果表明,相同含水量和围压下,偏应力越大时,黄土的蠕变变形量越大;围压和偏应力水平一定时,含水量越高,蠕变越容易,蠕变量越大;黄土具有显著的非线性粘-弹-塑性变形特征.分析认为黑方台黄土普遍表现出稳定型和渐变型的变形特征,进行该地区滑坡预测预报是有科学基础的.以试验数据为基础,采用幂函数和对数函数分别拟合得到黄土的蠕变模型.建议采用对数型经验方程进行黑方台黄土斜坡长期稳定性分析和滑坡预测预报.     

河南南襄盆地泌阳凹陷东南部古近系核桃园组物源分析*

在层序地层格架的基础上,结合区域地质概况和前人研究成果,充分运用重矿物的组合特征、岩心观察描述的岩性序列特征、岩性及电性的横向变化特征、地震反射特征,结合砂岩厚度、砂地比的平面展布规律,对南襄盆地泌阳凹陷东南部古近系渐新统核桃园组的物源方向进行了研究。结果表明,泌阳凹陷东南部主要发育5个物源,其中主要物源有1个,为泌150—泌285井区的平氏物源,该物源对研究目的层各个层序的西南部沉积砂体均有控制;次要物源有4个,即泌102—泌239井区的杨桥物源、正南方向的泌151—泌251井区的魏庄物源、东南方向泌129井区的栗园物源、以及东北方向的泌319井区的栗园东北物源,这些次要物源仅对部分层序的沉积砂体有控制作用。     

Stability analysis of a slip-debris flow in the Ogbajala Hills of Benue State, Nigeria

A slip-debris flow occurred in the Ogbajala Hills of Benue State on 3 September, 1987 after three days of consecutive rainfall. Field measurements of the landslide showed that the slip originated on the upper one-third of the hill at a depth of 1.37 m and extended uniformly to about 50 m downslope before turning into a flow.Stability analysis of the slip using infinite slope analysis yielded a slip surface depth of 1.4 m with a perched water table that rose seven-tenths (0.7) into the thickness of the slipped soil before failure. These analysis results agree closely with field measurements and give an insight into the water table conditions that led to the failure.     

Facies analysis of tertiary alluvial fan deposits in the Jundiaí region, São Paulo, southeastern Brazil

This article presents an analysis of facies of sedimentary sequences that occur as discontinuous bodies in the Jundiaí region, west of the main Tertiary continental basins of the southeastern Brazil continental rift. Nine identified sedimentary facies, grouped into four associations, suggest the existence of an ancient alluvial fan system whose source area was the Japi mountain range (Serra do Japi). The deposits are considered Tertiary in age and chronocorrelated with those identified in the Atibaia region and at other sites up to 100 km east and northeast of Jundiaí. The depositional model adopted to explain the filling of the basin proposes that the alluvial fans, which directly derive from the source area, terminated in a braided channel longitudinal to the basin axis that flowed to northwest, in a similar configuration to that of the present day. This basin may have extended to the Atibaia region or formed a set of small basins laterally contiguous to the faults associated with the rift. Such occurrences show that the formation of rift basins was broader than the area presently occupied by the main deposits.     

浅析新疆焉耆盆地土壤次生盐渍化治理途径

新疆焉耆盆地农田土壤次生盐渍化程度严重，分布面积大，灌溉用地表水量多，排碱渠密布，排碱渠大量高矿化度水排人博斯腾湖，使湖水水质受到影响，其生态环境极其脆弱。本文试图从土壤次生盐渍化的形成机制、成因分析，采用开采地下水、竖井排灌，置换地表水，结合调整农业产业结构等综合治理方法，从根本上解决盆地土壤次生盐渍化问题，以减少高矿化度水向博斯腾湖的排放，使盆地生态环境向良性方向发展。