汶川强震区泥石流起动模型试验分析

强震使大量松散堆积物堆积于高山峡谷内,由于持续降雨的作用,导致泥石流在汶川灾区频繁发生。降雨强度和物源与泥石流的起动有着密切联系,分析雨强和物源与泥石流起动的相关关系,可得不同雨强下,不同物源区泥石流起动的特征。通过对典型泥石流沟（映秀镇烧火坪侧沟,牛莲花心沟）进行野外样品采集,将两条泥石流沟进行对比室内试验。控制起动坡度,降雨强度与颗粒级配得出不同坡度下泥石流起动的表面流形成流量,起动流量。同时,与非强震区（西昌市琅环乡）的泥石流简单对比,得到强震区泥石流起动的临界条件及雨强,为泥石流的预测和治理提供相应的理论依据。通过大量的试验结果,泥石流起动首先会形成表面流,然后形成冲沟,随着物源区雨强的增加,最终形成大面积松散堆积物失稳,整体起动。泥石流起动与汇水区面积成一定关系。     

强震区岷江沿岸泥石流物源体积估算模型与演变特征

2008年汶川大地震后,泥石流灾害表现活跃,至今经历了多个暴雨过程,那么如何才能较为准确地分析泥石流源区演变特征。首要是确定泥石流源区崩滑体体积。本文选择映秀镇附近,岷江沿岸的5条泥石流沟为研究对象,针对泥石流源区崩滑体体积难以确定的问题,野外调查研究区内167个崩滑体点,建立崩滑体体积与面积间的关系模型,并通过野外调查研究区内48个崩滑点进行验证。定量解译研究区3期航空影像的物源面积,利用崩滑体体积估算模型,进一步分析研究区泥石流物源的演变特征。     

台风暴雨矿渣型泥石流形成机制与动力特征——以兴宁乌石坑沟泥石流为例

受台风“尤特”登陆影响,台风暴雨直接激发兴宁乌石坑沟特大矿渣型泥石流灾害,物源巨大,潜在危害极大。笔者等通过现场调绘及室内试验,对本次泥石流的形成机制及动力特征进行研究,旨在为此类泥石流致灾机理及危害性评价提供借鉴。研究表明,其独特的流域地形特点为泥石流形成的基本因素,以沟道堆积物为主的丰富矿渣型物源是基础条件,高强度的台风暴雨是直接激发因素,与矿山开采、矿渣随意堆放等人为因素共同作用扩大了灾害规模。泥石流形成过程与动力特征为前期强降雨—崩滑碎屑流—矿渣型泥石流—台风暴雨—沟道堵塞雍高—溃决、规模放大。     

台风暴雨矿渣型泥石流形成机制与动力特征——以兴宁乌石坑沟泥石流为例

受台风“尤特”登陆影响,台风暴雨直接激发兴宁乌石坑沟特大矿渣型泥石流灾害,物源巨大,潜在危害极大。笔者等通过现场调绘及室内试验,对本次泥石流的形成机制及动力特征进行研究,旨在为此类泥石流致灾机理及危害性评价提供借鉴。研究表明,其独特的流域地形特点为泥石流形成的基本因素,以沟道堆积物为主的丰富矿渣型物源是基础条件,高强度的台风暴雨是直接激发因素,与矿山开采、矿渣随意堆放等人为因素共同作用扩大了灾害规模。泥石流形成过程与动力特征为前期强降雨—崩滑碎屑流—矿渣型泥石流—台风暴雨—沟道堵塞雍高—溃决、规模放大。     

贵州望谟县田坝沟泥石流灾害特征及防治建议

田坝沟是一条低频率泥石流沟,在2011年6月6日暴雨条件下暴发泥石流。文章着重分析其物源、地形和降雨条件,通过现场取样和断面截取,获得了流速、流量等参数,预测了田坝沟泥石流的未来活动趋势,并提出了相关的防治建议。     

5.12震源区牛眠沟暴雨滑坡泥石流预测模型

牛眠沟研究区位于2008-05-12汶川大地震线性震源的南端,受强烈地震力作用,区内山体遭受严重破坏,发生多处滑坡和泥石流灾害。根据已建立的暴雨滑坡、泥石流预测概念模型,暴雨滑坡、泥石流预测可视为判断滑坡形成的地质环境和确定触发滑坡的降雨特征。查明研究区地质环境及灾害特征,确定了产生滑坡、泥石流的必要地质环境因子,以数字滑坡技术获取这些因子数据,代入模型,即可评价研究区各处、各沟谷发生滑坡、泥石流的危险程度;与相似地质环境及气候条件进行类比,确定研究区触发滑坡、泥石流的降雨特征及降雨量阈值后,最终建立暴雨滑坡、泥石流预测模型。据此模型进行研究区暴雨滑坡、泥石流预测,实地验证表明滑坡、泥石流发生位置的准确率>90%。     

基于遗传规划的泥石流多因子融合预测方法

泥石流是一种多发的地质灾害,常对人民生命财产安全带来极大的威胁,其暴发不仅与降雨有关,还与众多地质环境因子相关。本文以流域面积、松散物质比率、沟床平均坡度为地质因子,以最大小时雨强（T）和总降雨量（R）的乘积作为降雨指数,在获取的泥石流地质因子和降雨指数因子综合样本库的基础上,采用遗传规划法建立了泥石流临界降雨指数智能预测模型,克服了以往以雨量为单一指标的预警模型的弊端,模型验证结果显示,泥石流预测精度高、适应性强。     

甘肃武都马槽沟泥石流松散物源分析

马槽沟是甘肃陇南山区一条典型的暴雨泥石流沟,该区地质环境条件复杂。受"5.12汶川"地震影响,沟内岩土体结构松散,沟岸崩滑体发育,泥石流物源丰富,按成因有构造破碎基岩、风化破碎泥岩、结构松散黄土及重力侵蚀堆积物。上述松散物质对泥石流的补给主要表现为降雨坡面冲刷、滑坡崩塌和流体冲刷,其中又以滑坡、崩塌为主。     

台风暴雨型泥石流单沟危险度研究

台风暴雨型泥石流分布广泛并常造成重大灾害,有必要对其危险度进行研究。选取温州山区的14处典型台风暴雨型泥石流为研究对象,构建了基于组合因子的单沟泥石流危险度评价模型。选取泥石流规模（M）、泥石流频率（F）、冲沟纵比降（J）、形成区完整系数（C）、台风降雨综合值（E）和地质综合因子（G）来表征泥石流危险程度,并基于信息熵理论获得各组合因子权重值。针对研究区均为低频泥石流的特点,引入麦尔登比率（R值）以间接确定基于不同R值范围的泥石流爆发频率（F）。将评价模型应用于所选的典型沟谷,得到各沟谷泥石流危险度,评价结果符合研究区泥石流沟谷为中、小型低频泥石流的实际情况,并且评价为危险度高的沟谷具备区域上最易形成泥石流的地质地貌条件。     

物源条件对震后泥石流发展影响的初步分析

强震过后一定时期内,泥石流的活跃性增强,即数量增多、规模增大、频率增加。而随着松散物质储量的减少,泥石流的活跃性会随之衰减。为了具体考察物源条件对震后泥石流活动的影响,使用震后泥石流逐年平均输沙量作为刻画泥石流活跃性的指标,在云南蒋家沟和西藏古乡沟泥石流数据的基础上,定量地分析了震后泥石流活跃性的变化过程。分析表明存在降雨控制型和物源控制型两种泥石流流域。前者的泥石流在震后很长一段时间内都不衰减,其发生主要取决于降雨条件。后者最大规模的泥石流发生于地震过后的短时间内,尔后泥石流活动随时间显著减弱。泥石流规模和频率的关系与暴雨不一致。当物源控制型流域的无量纲化活跃性指标值降为0.12左右时,可以认为泥石流进入了稳定或者衰弱期,不会再有大规模的泥石流事件发生。数据拟合结果表明,整个泥石流活跃性的衰减过程可以用幂函数来描述。其衰减指数与剩余物质储量和总物质储量之比存在密切的关系。这为定量预测震后泥石流发展趋势提供了一个初步的模型。     

Analysis of the relationship of landslide occurrence with rainfall: a case study of Wudu County,China

Landslides are a significant hazard in many parts of the world and represent an important geohazard in China. Rainfall is the primary triggering agent for landslides and often used for prediction slope failures. However, the relationship between rainfall and landslide occurrences is very complex. Great efforts have been made on the study of regional rainfall-induced landslide forecasting models in recent years; still, there is no commonly accepted method for rainfall-induced landslide prediction. In this paper, the quantitative antecedent soil water status (ASWS) model is applied to investigate the influence of daily and antecedent rainfall on the triggering of landslides and debris flows. The study area is Wudu County in Gansu Province, an area which exhibits frequent landslide occurrences. The results demonstrate a significant influence of high intensity rainfall events on landslide triggering. Still, antecedent rainfall conditions are very important and once a threshold of approximately 20 mm is exceeded, landslides and debris flows can occur even without additional rainfall. The study presented could also facilitate the implementation of a regional forecasting scheme once additional validation has been carried out.     

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.     

Objective definition of rainfall intensity–duration thresholds for the initiation of post-fire debris flows in southern California

Rainfall intensity–duration (ID) thresholds are commonly used to predict the temporal occurrence of debris flows and shallow landslides. Typically, thresholds are subjectively defined as the upper limit of peak rainstorm intensities that do not produce debris flows and landslides, or as the lower limit of peak rainstorm intensities that initiate debris flows and landslides. In addition, peak rainstorm intensities are often used to define thresholds, as data regarding the precise timing of debris flows and associated rainfall intensities are usually not available, and rainfall characteristics are often estimated from distant gauging locations. Here, we attempt to improve the performance of existing threshold-based predictions of post-fire debris-flow occurrence by utilizing data on the precise timing of debris flows relative to rainfall intensity, and develop an objective method to define the threshold intensities. We objectively defined the thresholds by maximizing the number of correct predictions of debris flow occurrence while minimizing the rate of both Type I (false positive) and Type II (false negative) errors. We identified that (1) there were statistically significant differences between peak storm and triggering intensities, (2) the objectively defined threshold model presents a better balance between predictive success, false alarms and failed alarms than previous subjectively defined thresholds, (3) thresholds based on measurements of rainfall intensity over shorter duration (≤60 min) are better predictors of post-fire debris-flow initiation than longer duration thresholds, and (4) the objectively defined thresholds were exceeded prior to the recorded time of debris flow at frequencies similar to or better than subjective thresholds. Our findings highlight the need to better constrain the timing and processes of initiation of landslides and debris flows for future threshold studies. In addition, the methods used to define rainfall thresholds in this study represent a computationally simple means of deriving critical values for other studies of nonlinear phenomena characterized by thresholds.     

Comparing the performance of TRIGRS and TiVaSS in spatial and temporal prediction of rainfall-induced shallow landslides

This study compares the performance of transient rainfall infiltration and grid-based regional slope stability (TRIGRS) model and time-variant slope stability (TiVaSS) model in the prediction of rainfall-induced shallow landslides. TRIGRS employs one-dimensional (1-D) subsurface flow to simulate the infiltration rate, whereas a three-dimensional (3-D) model is utilized in TiVaSS. The former has been widely used in landslide modeling, while the latter was developed only recently. Both programs are used for the spatiotemporal prediction of shallow landslides caused by rainfall. This study uses the July 2011 landslide event that occurred in Mt. Umyeon, Seoul, Korea, for validation. The performance of the two programs is evaluated by comparison with data of the actual landslides in both location and timing by using a landslide ratio for each factor of safety class (\({\text{LR}}_{\text{class}}\) index), which was developed for addressing point-like landslide locations. Moreover, the influence of surface flow on landslide initiation is assessed. The results show that the shallow landslides predicted by the two models are highly consistent with those of the observed sliding sites, although the performance of TiVaSS is slightly better. Overland flow affects the buildup of the pressure head and reduces the slope stability, although this influence was not significant in this case. A slight increase in the predicted unstable area from 19.30 to 19.93% was recorded when the overland flow was considered. It is concluded that both models are suitable for application in the study area. However, although it is a well-established model requiring less input data and shorter run times, TRIGRS produces less accurate results.     

Landslide and debris flow initiated characteristics after typhoon Morakot in Taiwan

Typhoon Morakot brought extreme rainfall and initiated numerous landslides and debris flows in southern Taiwan in August of 2009. The purpose of this study is to identify the extreme rainfall-induced landslide frequency-area distribution in the Laonong River Basin in southern Taiwan and debris flow-initiated conditions under rainfall. Results of the analysis show that debris flows were initiated under high cumulative rainfall and long rainfall duration or high rainfall intensity. The relationship of mean rainfall intensity and duration threshold could reflect debris flow initiation characteristics under high rainfall intensity in short rainfall duration conditions. The relationship of cumulative rainfall and duration threshold could reflect debris flow initiation characteristics under high cumulative rainfall in long rainfall duration. Defining rainfall events by estimating rainfall parameters with different methodologies could reveal variations among intermittent rainfall events for the benefit of issuing debris flow warnings. The exponent of landslide frequency-area distribution induced by Typhoon Morakot is lower than that induced by the Chi-Chi earthquake. The lower exponent of landslide frequency-area distribution can be attributed to the transportation and deposition areas of debris flow that are included in the landslide area. Climate change induced high rainfall intensity and long duration of precipitation, for example, Typhoon Morakot brought increased frequency of debris flow and created difficulty in issuing warnings from rainfall monitoring.     

Rainfall-induced landslides in Hulu Kelang area, Malaysia

Hulu Kelang is known as one of the most landslide-prone areas in Malaysia. The area has been constantly hit by landslide hazards since 1990s. This paper provides an insight into the mechanism of rainfall-induced landslide in the Hulu Kelang area. Rainfall patterns prior to the occurrences of five selected case studies were first analyzed. The results showed that daily rainfall information is insufficient for predicting landslides in the area. Rainfalls of longer durations, i.e., 3–30 days prior to the landslides should be incorporated into the prediction model. Numerical simulations on a selected case study demonstrated that both matric suction and factor of safety decreased steadily over time until they reached the lowest values on the day of landslide occurrence. Redistribution of infiltrated rainwater in the soil mass could be a reason for the slow response of failure mechanism to rainfall. Based on 21 rainfall-induced landslides that had occurred in the area, three rainfall thresholds were developed as attempts to predict the occurrence of rainfall-induced landslide. The rainfall intensity–duration threshold developed based on the local rainfall conditions provided a reasonably good prediction to the landslide occurrence. The cumulative 3- versus 30-day antecedent precipitation index threshold chart was capable of giving the most reliable prediction with the limiting threshold line for major landslide yielded a reliability of 97.6 %.     

降雨型滑坡时间概率的逻辑回归拟合及连续概率滑坡危险性建模

提高降雨型滑坡危险性预警精度和空间辨识度具有重要意义.以江西宁都县1980—2001年156个降雨型滑坡为例,首先基于传统的EE-D（early effective rainfall-rainfall duration）阈值法计算不同降雨诱发滑坡的时间概率级别;然后以各级别临界降雨阈值曲线对应的时间概率为因变量,并以对应的前期有效降雨量（early effective rainfall,EE）和降雨历时（D）为自变量,采用逻辑回归拟合出上述因变量与自变量之间的非线性关系,得到降雨诱发滑坡的连续概率值;之后对比C5.0决策树和多层感知器的滑坡易发性预测性能;最后利用降雨诱发滑坡的连续概率值与易发性图相耦合以实现连续概率滑坡危险性预警.结果显示:（1）宁都降雨型滑坡连续概率值的逻辑回归方程为1/P=1+e4.062+0.747 4×D-0.079 44×EE,其拟合优度为0.983;（2）2002—2003年的20处用于连续概率阈值测试的降雨型滑坡大都落在连续概率值大于0.7的区域,只有4处落在小于0.7的区域;（3）C5.0决策树预测滑坡易发性的精度显著高于多层感知器;（4）近5年的4次降雨型滑坡的连续概率危险性值都在0.8以上,且高和极高预警区的面积较传统滑坡危险性分区更小.可见连续概率滑坡危险性预警法相较于传统危险性分区法具有更高的预警精度和空间辨识度,且通过叠加滑坡易发性图及其临界降雨阈值可开展实时滑坡危险性预警制图.      

汶川地震强震区地震诱发滑坡与后期降雨诱发滑坡控制因子耦合分析

本文以汶川地震强震区北川县典型研究区为例,利用高分辨率航片、SPOT5卫星图像对北川县典型研究区进行了512地震之后和924降雨之后诱发的滑坡解译,解译结果显示:512地震诱发滑坡1999个,924强降雨诱发滑坡828个,924强降雨导致原有地震滑坡面积扩大的滑坡150个。研究表明:地震和强降雨都是诱发滑坡的动力成因,924强降雨诱发的滑坡面积是512地震诱发滑坡面积的1/4倍,强降雨诱发滑坡的数量增加了41.4%; 强降雨不仅诱发新的滑坡,而且促使原来地震滑坡复活,并扩大其面积,强降雨导致地震诱发的滑坡面积扩大了原面积的68.7%。同时,在遥感解译数据基础之上,开展地震诱发滑坡与降雨诱发滑坡规模对比和控制因子耦合分析及地震与降雨耦合灾害链模式研究,为进一步分析研究地震灾区滑坡的产生、发展趋势、危险性和风险评价等预测预报提供科学依据,也为汶川震区恢复重建中的减灾防灾提供决策参考。     

A Simplified Numerical Approach for the Prediction of Rainfall-Induced Retrogressive Landslides

Retrogressive landslides are common geological phenomena in mountainous areas and on onshore and offshore slopes. The impact of retrogressive landslides is different from that of other landslide types due to the phenomenon of retrogression. The hazards caused by retrogressive landslides may be increased because retrogressive landslides usually affect housing, facilities, and infrastructure located far from the original slopes. Additionally, substantial geomorphic evidence shows that the abundant supply of loose sediment in the source area of a debris flow is usually provided by retrogressive landslides that are triggered by the undercutting of water. Moreover, according to historic case studies, some large landslides are the evolution result of retrogressive landslides. Hence the ability to understand and predict the evolution of retrogressive landslides is crucial for the purpose of hazard mitigation. This paper discusses the phenomenon of a retrogressive landslide by using a model experiment and suggests a reasonably simplified numerical approach for the prediction of rainfall-induced retrogressive landslides. The simplified numerical approach, which combines the finite element method for seepage analysis, the shear strength reduction finite element method, and the analysis criterion for the retrogression and accumulation effect, is presented and used to predict the characteristics of a retrogressive landslide. The results show that this numerical approach is capable of reasonably predicting the characteristics of retrogressive landslides under rainfall infiltration, particularly the magnitude of each landslide, the position of the slip surface, and the development processes of the retrogressive landslide. Therefore, this approach is expected to be a practical method for the mitigation of damage caused by rainfall-induced retrogressive landslides.     

岩溶山区崩滑灾害变形破坏地质模式分类

岩溶山区特殊的地质结构导致崩塌、滑坡等地质灾害时常发生,带来了严重的人员伤亡和经济社会损失。研究岩溶山区崩滑灾害特征,建立相应的变形破坏地质模式,对于岩溶山区崩滑灾害风险防控与治理工程具有重要理论意义与指导价值。文章以典型地质灾害形成演化过程为例,在系统地分析研究区典型崩滑灾害地质背景、影响因素、动力学与运动学特征的基础上,提出了岩溶山区崩滑灾害变形破坏地质模式,得出以下主要结论:（1）影响崩滑成灾基本因素（崩滑灾害体势能、岩溶结构面、岩组结构、斜坡地貌和斜坡结构）、影响因素（水文地质条件、工程活动、地震、降雨）和变形运动特征（运动形式和变形机制）三个方面,据此建立了岩溶山区崩滑灾害地质分类指标体系。（2）结合研究区特征对模型体系里面的每个要素进行系统分析,崩滑灾害的发生是各个要素相互组合、相互作用的结果。（3）总结了研究区内5种典型崩滑地质模式:高势能反倾降雨型高速远程滑坡—碎屑流模型、高势能斜倾视向采矿型高速远程崩滑灾害模型、超高势能横向陡倾地震型高速远程滑坡、高势能采矿型高速崩塌—碎屑流模型、低势能差异风化崩塌模型。为后续开展物理模拟、数值模拟、稳定性计算和变形破坏预测等工作奠定基础。下一步将更加深入全面地建立研究区的崩滑灾害模式,并进行崩滑灾害的危险性分级工作。