降雨引发的兰州黄土滑坡时空规律分析和临界降雨量预测

降雨引发的兰州黄土滑坡时空规律分析和临界降雨量预测     

Early warning system for shallow landslides using rainfall threshold and slope stability analysis

A combined cluster and regression analysis were performed for the first time to identify rainfall threshold that triggers landslide events in Amboori, Kerala, India. Amboori is a tropical area that is highly vulnerable to landslides. The 2, 3, and 5-day antecedent rainfall data versus daily rainfall was clustered to identify a cluster of critical events that could potentially trigger landslides. Further, the cluster of critical events was utilized for regression analysis to develop the threshold equations. The 5-day antecedent (x-variable) vs. daily rainfall (y-variable) provided the best fit to the data with a threshold equation of y = 80.7–0.1981x. The intercept of the equation indicates that if the 5-day antecedent rainfall is zero, the minimum daily rainfall needed to trigger the landslide in the Amboori region would be 80.7 mm. The negative coefficient of the antecedent rainfall indicates that when the cumulative antecedent rainfall increases, the amount of daily rainfall required to trigger monsoon landslide decreases. The coefficient value indicates that the contribution of the 5-day antecedent rainfall is ∼20% to the landslide trigger threshold. The slope stability analysis carried out for the area, using Probabilistic Infinite Slope Analysis Model (PISA-m), was utilized to identify the areas vulnerable to landslide in the region. The locations in the area where past landslides have occurred demonstrate lower Factors of Safety (FS) in the slope stability analysis. Thus, rainfall threshold analysis together with the FS values from slope stability can be suitable for developing a simple, cost-effective, and comprehensive early-warning system for shallow landslides in Amboori and similar regions.     

降雨与滑坡灾害相关性分析及预警预报阀值之探讨

详细研究了深圳市降雨与滑坡的历史资料,对区域性滑坡与降雨量进行偏相关分析,与降雨强度进行相关分析以及与降雨时间进行了系统地统计分析。研究结果表明,（1）滑坡的活动1～4日的降雨量及一次降雨过程的降雨量偏相关系数较大,表明一次性降雨量达到或超过某一数值时区域性滑坡就可以出现;（2）暴雨尤其是大暴雨及特大暴雨与滑坡的关系非常密切,相关系数达0.8以上,大暴雨或特大暴雨具有直接触发滑坡的作用;（3）滑坡活动时间与季节性降雨相对应,季节雨量越多,滑坡亦越多;另外滑坡活动时间与暴雨、大暴雨相吻合或略滞后,滞后时间一般不超过4 d,暴雨的当天及次日发生滑坡的可能性最大。在此基础上,探讨了区域性滑坡发生的临界降雨量和降雨强度阀值。最后将滑坡灾害的地质模型与降雨模型耦合建立了滑坡灾害的空间预警预报区划指标和等级系统,为区域滑坡灾害发生的时间与空间预报预警提供了科学依据。     

Initiation conditions of shallow landslides in two man-made forests and back estimation of the possible rainfall threshold

Rainfall-induced shallow landslides and debris flows are one of the most common erosion process and primary channel initiation mechanisms in many steep landscapes. Their initiation conditions are physically controlled by the soil properties and topographically influenced by the competition between area- (A) and slope-dependent (S) sediment transport process. In this work, the A-S relationship of landslides in two forests was compared with respect to the physical properties of soil and plant roots. The results reveal that landslides in the Pinus tabuleaformis forest commonly have larger surface- and contributing area, deeper failure plane and gentler slope gradient than those in the Larix Kaemphferi forest. The saturated hydraulic conductivity in the Pinus tabuleaformis forest is higher and strongly correlates to plant root biomass. The effective cohesion and inner frictional angle of soil mass in the two forests are similar. Faster saturated hydraulic conductivity may lead to the higher upslope contributing area of landslides in the the Pinus tabuleaformis forest. A combination of finite-slope model and precipitation interception model reveals that landslides in the Pinus tabuleaformis forest require higher rainfall amount that those in the Larix Kaemphferi forest. Last but not least, this work provides a clue that strong root network and high saturated hydraulic conductivity may promote the A-S condition.

     

Evidential belief functions for data-driven geologically constrained mapping of gold potential,Baguio district,Philippines

A data-driven application of the theory of evidential belief to map mineral potential is demonstrated with a redefinition of procedures to estimate evidential belief functions. The redefined estimates of evidential belief functions take into account not only the spatial relationship of an evidence with the target mineral deposit but also consider the relationships among the subsets of spatial evidences within a set of evidential data layer. Proximity of geological features to mineral deposits is translated into spatial evidence and evidential belief functions are estimated for the proposition that mineral deposits exist in a test area. The integrated maps of degrees of belief for the proposition that mineral deposits exist in a test area is classified into a binary mineral potential map. For the Baguio district (Philippines), the binary gold potential map delineates (a) about 74% of the training data (i.e., locations of large-scale gold deposits) and (b) about 64% of the validation data (i.e., locations of small-scale gold deposits). The results demonstrate the usefulness of a geologically constrained mineral potential mapping using data-driven evidential belief functions to guide further surficial exploration work in the search for yet undiscovered gold deposits in the Baguio district. The results also indicate the usefulness of evidential belief functions for mapping uncertainties in the geologically constrained integrated predictive model of gold potential.     

台风-非台风降雨型滑坡的多时段临界雨量值预测模型

统计确定临界降雨量是滑坡早期预警常用的方法.东南沿海地区台风暴雨不同于一般降雨,常引发滑坡灾害,从而威胁沿海地区人民生命财产安全.为了建立台风和非台风降雨型滑坡临界降雨量预测模型,以浙江丽水市为例,基于2010-2020年台风暴雨、非台风降雨诱发滑坡与降雨量的统计,构建了丽水市滑坡发生概率和有效降雨量的关系,提出了多时...     

Data-driven predictive mapping of gold prospectivity,Baguio district,Philippines: Application of Random Forests algorithm

The Random Forests (RF) algorithm has recently become a fledgling method for data-driven predictive mapping of mineral prospectivity, and so it is instructive to further study its efficacy in this particular field. This study, carried out using Baguio gold district (Philippines), examines (a) the sensitivity of the RF algorithm to different sets of deposit and non-deposit locations as training data and (b) the performance of RF modeling compared to established methods for data-driven predictive mapping of mineral prospectivity. We found that RF modeling with different training sets of deposit/non-deposit locations is stable and reproducible, and it accurately captures the spatial relationships between the predictor variables and the training deposit/non-deposit locations. For data-driven predictive mapping of epithermal Au prospectivity in the Baguio district, we found that (a) the success-rates of RF modeling are superior to those of weights-of-evidence, evidential belief and logistic regression modeling and (b) the prediction-rate of RF modeling is superior to that of weights-of-evidence modeling but approximately equal to those of evidential belief and logistic regression modeling. Therefore, the RF algorithm is potentially much more useful than existing methods that are currently used for data-driven predictive mapping of mineral prospectivity. However, further testing of the method in other areas is needed to fully explore its usefulness in data-driven predictive mapping of mineral prospectivity.     

降雨对滑坡稳定性影响过程分析

通过对滑坡土条的受力分析进行改进,建立起能考虑滑带内存在任意孔隙水压分布情况下的稳定性计算公式。结合Lumb入渗理论和太沙基一维固结理论得到了滑坡在降雨期间的极限稳定性计算方法,该方法能够同时考虑降雨入渗导致土体重度和滑带内孔隙水压力变化。利用上述结果,提出了某些深层滑坡触发的一种机理,并可根据常用的土质参数比较容易得到滑坡在降雨期间稳定性演化过程。通过对某滑坡分析得到,降雨导致滑体重量增加而降低滑坡稳定性小于孔隙水压增加对稳定性的影响;超孔隙水压力的存在大幅提高了剩余下滑力值。     

Temporal Geochemical Evolution of Neogene Magmatism in the Baguio Gold–Copper Mining District (Northern Luzon, Philippines)

Baguio, in the Central Cordillera of Northern Luzon, is a district that displays porphyry copper and epithermal gold mineralization, associated with Early Miocene–Pliocene–Quaternary calc‐alkaline and adakitic intrusions. Systematic sampling, K‐Ar dating, major and trace elements, and Sr, Nd, Pb isotopic analyses of fresh magmatic rocks indicate three magmatic pulses: an Early Miocene phase (21.2–18.7 Ma), a Middle–Late Miocene phase (15.3–8 Ma) and finally a Pliocene–Quaternary event (3–1 Ma). The first phase emplaced evolved calc‐alkaline magmas, essentially within the Agno Batholith complex, and is thought to be related to the westward‐dipping subduction of the West Philippine Basin. After a quiescence period during which the Kennon limestone was deposited, magmatic activity resumed at 15.3 Ma, in connection with the start of the subduction of the South China Sea along the Manila Trench. It emplaced first petrogenetically related and relatively unradiogenic low‐K calc‐alkaline lavas and intermediate adakites. Temporal geochemical patterns observed from 15.3 to 1 Ma include progressive enrichment in K and other large ion lithophile elements, increase in radiogenic Sr and Pb and corresponding decrease in radiogenic Nd. These features are thought to reflect the progressive addition to the Luzon arc mantle wedge of incompatible elements largely inherited from South China Sea sediments. The origin of the long quiescence period, from 8 to 3 Ma, remains problematic. It might represent a local consequence of the docking of the Zambales ophiolitic terrane to Northern Luzon. Then, magmatic activity resumed at 3 Ma, emplacing chemically diversified rocks ranging from low K to high K and including a large proportion of adakites, especially during the Quaternary (dacitic plugs). The authors tentatively relate this diversity to the development of a slab tear linked with the subduction of the fossil South China Sea ridge beneath the Baguio area.     

降雨诱发缓倾顺层滑坡机制离散元模拟

降雨在节理岩体的离散元模拟中有一定的局限性。文章提出一种等效渗流法模拟降雨条件下地下水向坡脚的渗流过程。以西南地区某顺层岩质滑坡为例,采用施加固定水头的方法,实现地下水在滑体内部的渗流过程,从而诱发滑坡形成。研究结果表明:(1)雨水入渗从坡顶向坡脚渗流,导致滑体内部空隙水压力升高;(2)斜坡受地下水渗流影响,坡脚首先发生变形并逐渐向上部呈阶梯状扩展。随渗流时间的延长,坡脚产生滑移,斜坡中上部和后缘出现拉裂,沿软弱夹层发生整体向河流方向滑动堆积形成堰塞湖;(3)滑坡形成的地质力学模式为"滑移-拉裂",滑体前缘运动至河流对岸形成前缘鼓丘,模拟结果与现场实际特征吻合。该方法可实现降雨条件下节理岩质斜坡中地下水渗流对滑坡形成的影响模拟。     

Influence of saturation on rainfall generated landslides in shale along Murree-Kohala road,Pakistan

On August 10, 2010 a series of landslides of more than 90,000 m³ occurred along the Muree-Kohala road in the northern area of Pakistan. A study was undertaken to evaluate the likely impacts of percent saturation and bulk density on mobilized shear strength along the basal rupture surface of the landslide. A series of unconfined compression test and unconsolidated undrained triaxial tests were performed on remolded samples of different densities with varied percentages of saturation. The results of these tests suggest that soil cohesion and friction decreases with increasing saturation. The tests also showed that the shear strength parameters tend to increase with increasing dry density; however, all the samples exhibited a noticeable loss of shear strength with increasing degree of saturation, independent of soil density.Limit equilibrium slope stability analyses were performed along the most probable failure planes, based on shear strength parameters corresponding to degrees of saturation, which varied between 30% to about 100%. This resulted in drop of factor of safety from FS = 1.64 down to 0.51 as the degree of saturation approaches unity.These results suggest that the causative factor in triggering the landslide along Murree-Kohala was the partial saturation of the zone that developed the basal rupture plane. As rain infiltrated the slope, the bulk unit weight of the soil increased, while the shear strength along the developing plane of rupture decreased sufficiently to concentrate shear strain when the material became more than 60% saturation (FS < 1.0).     

Updating EWS rainfall thresholds for the triggering of landslides

In this paper, the updating of rainfall thresholds for landslide early warning systems (EWSs) is presented. Rainfall thresholds are widely used in regional-scale landslide EWSs, but the efficiency of those systems can decrease during the time, so a periodically updating should be required to keep their functionality. The updating of 12 of the 25 thresholds used in the EWS of Tuscany region (central Italy) is presented, and a comparison between performances of new and previous thresholds has been made to highlight the need of their periodical update. The updating has been carried out by collecting ca. 1200 new landslide reports (from 2010 to March 2013) and their respective rainfall data, collected by 332 rain gauges. The comparison has been made by the use of several statistical indexes and showed a marked increasing in the performances of the new thresholds with respect to previous ones.     

Real-time estimation of hazard for landslides triggered by rainfall

 Landslide movements triggered by rainfall can be foreseen in real-time by modelling the relationship between rainfall amount and landslide occurrence. This paper deals with the problem of the reliability of the FLaIR (Forecasting of Landslides Induced by Rainfalls) model when applied to forecasting landslide movements in the usual condition of poor historical information availability. In this case, the identification of the admissibility field for the model parameters, instead of a point estimation, leads to an improvement of the forecasting reliability. Moreover, this approach makes the model capable of taking into account information embodied in periods of heavy rain but without movement. The concepts of informative content and foreseeability of landslide movements are introduced and their duality is analyzed. The effectiveness of the estimation procedure described has been tested by application on two landslides located in southern Italy. Received: 15 October 1996 · Accepted: 25 June 1997     

四川雅安市雨城区降雨诱发滑坡研究

降雨是滑坡灾害的重要诱发因素之一。通过详细的地质灾害调查及地质灾害与降雨相关关系的研究,得出降雨对雅安雨城区地质灾害诱发作用的规律并进一步定量评价了诱发因素级别。研究发现,降雨量对滑坡的诱发因素可划分为4级,1d降雨量分级临界值分别为20mm、50mm和100mm,3d降雨量分级临界值分别为100mm、150mm和240mm。这一研究成果为雅安雨城区地质灾害预警预报提供了基础。     

四川雅安市雨城区降雨诱发滑坡临界值初步研究

四川省雅安市雨城区位于四川盆地西部,素有"雨城"之称。地质灾害以滑坡为主,且有群发性、浅层、规模小、降雨诱发的特点。作者分析了雨城区大量历史滑坡和降雨量数据,结合雨城区滑坡发育特点,选择3日(72h)内发生2个以上滑坡的点作为统计分析样本,进行不同阶段降雨量耦合关系分析,应用滑坡前3日累计降雨量与3日前15日累计降雨量,建立了滑坡发生与降雨量的统计关系:在雨城区,当前期无降雨、3日累计降雨量达到70mm时,将有滑坡发生;15日累计降雨量达到339mm时,也将可能出现滑坡。     

Spatially distributed rainfall thresholds for the initiation of shallow landslides

The evaluation of the combined influence of rainfall patterns (in terms of mean intensity and duration) and the geomorphological and mechanical characteristics of hillslopes on their stability conditions is a major goal in the assessment of the shallow landslide triggering processes. Geographic Information Systems (GIS) represent an important tool to develop models that combine hydrological and geomechanical analyses for the evaluation of slope stability, as they allow to combine information concerning rainfall characteristics with topographic and mechanical properties of the slopes over wide areas. In this paper, a GIS-based code is developed to determine physically based intensity/duration rainfall thresholds at the local scale. Given the rainfall duration and the local geometric, hydrological and mechanical characteristics of the slopes, the code evaluates the spatial distribution of the minimum rainfall intensity that triggers shallow landslides and debris flows over a given area. The key feature of the code is the capability of evaluating the time t _p required to reach the peak pore pressure head on the failure surface and computing the corresponding critical intensity/duration thresholds based on post-event peak pore pressures. The reliability of the model is tested using a set of one-dimensional analyses, comparing the physically based thresholds obtained for three different slopes with some empirical rainfall thresholds. In a log–log scale, the thresholds provided by the model decrease linearly with increased rainfall duration and they are bracketed by the empirical thresholds considered. Finally, an example of application to a study area of the Umbria region in central Italy is presented, describing the capability of the model of providing site-specific thresholds for different rainfall scenarios.     

降雨型滑坡危险性区划方法

降雨诱发的滑坡等地质灾害分布广、危害大,开展地质灾害危险性区划是减轻地质灾害损失的有效途径之一。以湖南省为例,根据地质灾害调查成果,选取3 412处滑坡,分析了区域降雨型滑坡的发育特点和分布规律,建立了危险性区划指标体系,利用不确定性推理中的确定性系数法,对滑坡与工程地质岩组、坡度、坡向、植被和年均降水量5个评价因子进行了相关性分析,建立了Logistic多元回归模型;采用不规则网格单元划分方法,形成了湖南省滑坡灾害危险性区划图。