红石河堰塞湖漫顶溃坝风险评估

四川省青川县红石河堰塞湖是2008年5月12日汶川大地震形成的34座大型堰塞湖之一,是由东河口滑坡堵塞红石河形成的。该堰塞体高度约50 m、宽度约250 m、顺河向长度约500 m、形成的最大库容约400万m3。本文作者对红石河堰塞体做了较详尽的现场试验,包括土的冲蚀试验、土的基本物性试验等。基于现场试验数据,对土的冲蚀性和漫顶溃坝风险做了详细的分析。结果显示,从土的抗冲蚀性角度考虑,只要有水溢出就会有土体被冲蚀,这说明红石河堰塞体的漫顶溃决可能性较高。本文还提出经验公式来预测红石河堰塞体漫顶的溃决时间,大约为4.5d,如果考虑到大石块对抗冲蚀稳定性的有利影响,这一数值会增大。此外,还研究了溃决深度随时间的变化规律。     

堰塞坝体材料渗透特性及其稳定性研究

堰塞坝是由于崩塌、滑坡、泥石流等形成的天然坝体,不同于人工土石坝,堰塞坝坝体结构松散,颗粒级配不均匀,在较高水头作用下坝体可能发生渗透破坏而导致溃坝,严重威胁下游人民群众的生命及财产安全。由于堰塞坝存在较大粒径颗粒,常规的渗透试验装置难以满足要求,本文研制了直径为60cm的大直径渗透试验仪,进行了不同堰塞坝级配材料的渗透破坏试验,并探讨了堰塞坝体材料渗透特性的主要影响因素。研究发现:（1）堰塞坝材料的渗透破坏形式取决于材料级配,粗颗粒含量较多时为管涌破坏,细颗粒含量较多或粒径缺失时为流土破坏;（2）堰塞坝渗透系数随干密度的增大而减小,主要取决于细料填充粗料孔隙的程度,单独使用不均匀系数或曲率系数不适用于评价渗透系数的变化;（3）基于试验数据提出了用于堰塞坝渗流破坏形式的判别公式,并推导出堰塞坝管涌破坏的临界水力坡降计算公式。     

余震作用下堰塞坝体破坏及溃决过程大型振动台试验研究

山区特大地震往往导致大量堰塞湖,例如2008年汶川地震形成了至少257个堰塞湖,并且主震后发生了大量余震,这些余震可能会影响堰塞坝体的安全状态。通过大型振动台模型试验,研究了余震及库水耦合作用下堰塞坝体的破坏及溃决机理和过程。共进行了两组不同材料的振动台模型试验,分别模拟含黏粒较多且颗粒较小（坝体Ⅰ）和基本不含黏粒且颗粒较大（坝体Ⅱ）的两种坝体。在不同水位条件下进行振动台试验。研究成果表明:（1）地震和库水耦合作用下堰塞坝体的主要溃决方式是漫顶溢流,主要溃决过程为地震力使松散的堰塞坝体发生沉陷,库水渗入使沉陷加剧,最终水位上升漫过坝顶发生溢流冲蚀破坏。（2）地震一般不会直接引起堰塞坝体的破坏。地震力对坝体稳定性的主要影响是使坝体发生沉陷变形。在地震和库水耦合作用下,坝体沉陷比单一因素作用下更为剧烈,因此地震作用会使漫顶溢流提前发生。（3）地震和库水耦合作用下坝体Ⅰ沉陷量大于坝体Ⅱ,说明现实中由大粒径岩土体组成的堰塞坝体具有更好的稳定性。     

A comparative analysis of interface erosion tests

Interface erosion is one of the main phenomena in dams, dikes and their foundations which may increase their failure risk. In laboratories, the jet erosion test (JET) and the hole erosion test (HET) are commonly used for the evaluation of the sensibility of interface erosion of fine soils. The results are interpreted by two distinct methods that are valid for one test only. A new energy analysis of the tests is developed, relating the total eroded mass to the dissipated fluid energy, and a new erosion resistance index is proposed. Seven naturally occurring fine-grained soils, covering a large range of erodibility, are compacted with the Proctor protocol, and they are tested with the two devices. It was shown that by using the commonly used methods, the values of the erosion coefficient are systematically higher with the JET than with the HET and the HET critical shear stress is about fifty times higher than the JET critical shear stress. Thus, the relative soil classifications yielded by the two erodimeters are not exactly the same. Based on energy analysis, values of erosion resistance index are roughly the same for each tested soil with the two apparatuses and a single classification of soil erodibility is obtained.     

Development of an empirical model for predicting peak breach flow of landslide dams considering material composition

The existing empirical models do not consider the influence of material composition of landslide deposits on the peak breach flow due to the uncertainty in the material composition and the randomness of its distribution. In this study, based on the statistical analyses and case comparison, the factors influencing the peak breach flow were comprehensively investigated. The highlight is the material composition-based classification of landslide deposits of 86 landslide cases with detailed grain-size distribution information. In order to consider the geometric morphology of landslide dams and the potential energy of dammed lakes, as well as the material composition of landslide deposits in an empirical model, a multiple regression method was applied on a database, which comprises of 44 documented landslide dam breach cases. A new empirical model for predicting the peak breach flow of landslide dams was developed. Furthermore, for the same 44 documented landslide dam failures, the predicted peak breach flow obtained by using the existing empirical models for embankment and landslide dams and that obtained by using the newly developed model were compared. The comparison of the root mean square error (E_rms) and the multiple coefficient of determination (R²) for each empirical model verifies the accuracy and rationality of the new empirical model. Furthermore, for fair validation, several landslide dam breach cases that occurred in recent years in China and have reliable measured data were also used in another comparison. The results show that the new empirical model can reasonably predict the peak breach flow, and exhibits the best performance among all the existing empirical models for embankment and landslide dam breaching.

     

中国喜马拉雅山地区滑坡堵江编目及空间特征分析

滑坡堵江数据获取与编目是其区域研究开展的基础。喜马拉雅山脉地处中国西南边陲,新构造运动强烈,滑坡堵江事件频发,在产生巨大经济损失的同时也造成了不良国际影响。鉴于该区区域滑坡堵江现场调查难以开展的问题,本文利用遥感技术、地理信息技术,结合野外验证获取了区内136处滑坡堵江事件的空间位置、基本属性和几何形态,建立了中国喜马拉雅山地区滑坡堵江编目。区内滑坡堵江集中分布在米林、札达、加查、错那、隆子、郎县等县,成因类型以滑坡、崩塌、泥石流为主。基于环境要素信息量计算得出该区滑坡堵江的易发程度随高程、坡度、地震加速度的增大先增大后减小,随地震点密度增大先减小后增大,随构造线密度增大逐渐增大,随与水系距离增大逐渐减小。不同坡向中,西向斜坡更容易诱发滑坡堵江,东南坡向最不容易诱发滑坡堵江。高位高山地貌类型、地层条件中的朗县构造混杂岩组和坚硬岩组,构造分区中的高喜马拉雅分区和雅鲁藏布江分区是滑坡堵江形成的有利条件。对比各环境要素不同类别的信息量取值认为影响该区滑坡堵江事件形成的主要背景因素是高程、地貌类型、地层岩组、构造分区和地震点密度。这些滑坡堵江事件几何参数的研究结果表明坝体长度-坝体面积与滑坡面积-坝体面积之间具有拟合程度较高的乘幂函数关系,而其他参数间的相关性并不突出。     

Numerical SPH analysis of debris flow run-out and related river damming scenarios for a local case study in SW China

A smoothed particle hydrodynamics (SPH) numerical modeling method implemented for the forward simulation of propagation and deposition of flow-type landslides was combined with different empirical geomorphological index approaches for the assessment of the formation of landslide dams and their possible evolution for a local case study in southwestern China. The SPH model was calibrated with a previously occurred landslide that formed a stable dam impounding the main river, and it enabled the simulation of final landslide volumes, and the spatial distribution of the resulting landslide deposits. At four different sites on the endangered slope, landslides of three different volumes were simulated, respectively. All landslides deposited in the main river, bearing the potential for either stable impoundment of the river and upstream flooding scenarios, or sudden breach of incompletely formed or unstable landslide dams and possible outburst floods downstream. With the empirical indices, none of the cases could be identified as stable formed landslide dam when considering thresholds reported in the literature, showing up the limitations of these indices for particular case studies of small or intermediate landslide volumes and the necessity to adapt thresholds accordingly for particular regions or sites. Using the occurred benchmark landslide as a reference, two cases could be identified where a complete blockage occurs that is more stable than the reference case. The other cases where a complete blockage was simulated can be considered as potential dam-breach scenarios.     

松散土坡结构特征与滑坡堰塞体堆积特征之间的关系试验研究

通过模型实验,探讨了松散土坡3种不同结构特征条件下(均匀坡体(坡体物料均匀混合)、平行坡体(土层成层且层面与滑面平行)和斜交坡体(土层成层且层面与滑面斜交))形成滑坡堰塞体的动力过程和堆积特征,通过分区域取样及三维扫描技术研究了堰塞体的物质分布规律与形态特征。研究结果表明：堰塞体堆积特征与坡体特征存在紧密联系,堰塞体纵向(沿主沟道方向)和横向(沿滑坡运动方向)上的物质分布与坡体纵向和横向的物质分布特征基本对应;在垂向(表层到底部)上,由于不同坡体条件下滑坡的动力过程和机理不同,从而导致堰塞体堆积特征存在一定区别。均匀坡体和平行坡体呈整体启动模式,运动过程中物料间存在垂向渗透和交换作用,导致堰塞体物质在垂向上呈明显的上粗下细反粒序分布特征,堰塞体横剖面多呈平坦型和倾斜型。斜交坡体呈分层启动模式,运动堆积过程中保持原有层序,粗、细颗粒先后启动条件下颗粒间存在推挤、爬升和水平渗透作用,使得堰塞体更加密实且垂向上也呈现反粒序分布特征,横剖面多呈起伏型。本研究为滑坡堰塞体稳定性快速评估和复原滑坡初始状态提供依据。     

The Bhuj, India, earthquake: lessons learned for earthquake safety of dams on alluvium

The Bhuj, India, earthquake of 26 January 2001, M_s 7.9, caused dams built on alluvium to sustain damage ranging from cosmetic to severe. Major damage was caused almost entirely by soil liquefaction in the alluvium. The critical factor was the level of earthquake ground motion.

The Bhuj earthquake showed that peak horizontal accelerations (PHAs)≤0.2 g were generally safe. PHAs>0.2 g were hazardous, when unconsolidated granular foundation soils were water saturated. N values of <20 are indicative of susceptibility to soil liquefaction. The Bhuj experience showed that alluvial foundation soils, subject to a PHA>0.2 g, must be evaluated over the full area beneath a new dam and all soils deemed susceptible to liquefaction must be either removed or treated. For remediating an old dam, reliable options are removal and replacement of liquefiable alluvium beneath upstream and downstream portions of the dam, combined with building berms designed to provide stability for the dam should there be a strength loss in soils beneath the dam.     

Numerical simulation of landslide dam breaching due to overtopping

The breach of landslide dam often causes significant disaster in the inundated area; the prediction of breach hydrograph is in high demand for the dam breach risk evaluation. In this study, according to the model tests and Tangjiashan landslide dam breach case, the surface erosion accompanied by intermittent mass failure is known as the key breaching mechanism for landslide dam due to overtopping failure. The downstream slope angle would gradually decrease during the dam-breaching process, whereas a planar wedge failure occurs when the breach slopes at the dam crest and downstream breach channel fail. Based on the breach mechanism, a numerical model for landslide dam breach due to overtopping is developed to simulate the coupling process of water and soil. The model focuses on the breach morphology evolution during the breaching for the sake of the improvement of breach hydrograph prediction. Furthermore, the model can handle one- and two-sided breach, as well as incomplete and base erosion at the vertical direction. The case study of Tangjiashan landslide dam-breaching feedback analysis testifies the rationality of the present model with the relative errors less than 10% for peak discharge, final breach widths, and time to peak. The sensitivity analysis indicates that the final breach depth and soil erodibility affect the breach flow prediction of the landslide dam significantly, whereas the one- or two-sided breach mode is less sensitive.     

Logistic regression model for predicting the failure probability of a landslide dam

Landslides may obstruct river flow and result in landslide dams; they occur in many regions of the world. The formation and disappearance of natural lakes involve a complex earth–surface process. According to the lessons learned from many historical cases, landslide dams usually break down rapidly soon after the formation of the lake. Regarding hazard mitigation, prompt evaluation of the stability of the landslide dam is crucial. Based on a Japanese dataset, this study utilized the logistic regression method and the jack-knife technique to identify the important geomorphic variables, including peak flow (or catchment area), dam height, width and length in sequence, affecting the stability of landslide dams. The resulting high overall prediction power demonstrates the robustness of the proposed logistic regression models. Accordingly, the failure probability of a landslide dam can also be evaluated based on this approach. Ten landslide dams (formed after the 1999 Chi-Chi Earthquake, the 2008 Wenchuan Earthquake and 2009 Typhoon Morakot) with complete dam geometry records were adopted as examples of evaluating the failure probability. The stable Tsao-Ling landslide dam, which was induced by the Chi-Chi earthquake, has a failure probability of 27.68% using a model incorporating the catchment area and dam geometry. On the contrary, the Tangjiashan landslide dam, which was artificially breached soon after its formation during the Wenchuan earthquake, has a failure probability as high as 99.54%. Typhoon Morakot induced the Siaolin landslide dam, which was breached within one hour after its formation and has a failure probability of 71.09%. Notably, the failure probability of the earthquake induced cases is reduced if the catchment area in the prediction model is replaced by the peak flow of the dammed stream for these cases. In contrast, the predicted failure probability of the heavy rainfall-induced case increases if the high flow rate of the dammed stream is incorporated into the prediction model. Consequently, it is suggested that the prediction model using the peak flow as causative factor should be used to evaluate the stability of a landslide dam if the peak flow is available. Together with an estimation of the impact of an outburst flood from a landslide-dammed lake, the failure probability of the landslide dam predicted by the proposed logistic regression model could be useful for evaluating the related risk.     

正反粒序结构条件下滑坡堰塞坝破坏模式研究

滑坡堰塞坝是大型滑坡堆积体堵塞河道形成的土石坝。正、反粒序结构作为大型远程滑坡所特有的2种具有显著差异的地质结构特征,2种情况下坝体的破坏模式差异及稳定性影响因素亟需试验研究。文章通过室内水槽物理模型实验,对比不同粒径、不同结构的滑坡堰塞坝坝体的破坏过程差异,探究了正、反粒序结构条件下堰塞坝的稳定性差异、破坏模式及影响因素。研究结果表明：（1）堰塞坝破坏模式的变化取决于浸润线在下游坡面的出露位置,相比上游水位有一定的延迟性;（2）正、反粒序堰塞坝的破坏模式取决于坡体渗流与下游坡面临界起动坡降的关系;（3）细砂层的位置分布,不同埋深细砂层的起动临界坡降差异和细砂与中粗砂的孔隙率差异是造成正、反粒序坝体破坏差异的主要原因。该研究成果可为大型滑坡堰塞坝的防灾减灾提供理论指导。     

大型粉煤灰坝模型抗震试验研究

以某电厂填顶高程170,180,230 m灰坝的模型为研究对象,基于基本动力特性试验,进行了在有干滩和无干滩两种工况下模拟Ⅵ度与Ⅶ度地震烈度的响应试验和破坏试验研究,同时对用3种不同灰渣拌合料加高的180 m高程灰坝模型进行了抗震性能做出评价。研究结论对灰坝抗震理论的研究和减震防灾具有一定的指导意义。     

The 12 May Wenchuan earthquake-induced landslide lakes: distribution and preliminary risk evaluation

The Wenchuan earthquake, measured at M _s 8.0 according to the China Earthquake Administration, occurred at 14:28 on 12 May 2008 in the Sichuan Province of China. It brought overwhelming destruction to eight provinces and cities. Landslides and rock avalanches triggered by the earthquake produced 257 landslide lakes which were distributed along the fault rupture zone and river channels. The authors traveled to the disaster zone immediately after the earthquake to examine some of the features of the debris dams and performed a quick evaluation of the potential for outburst of earthquake-induced landslide lakes for the purpose of disaster relief. The preliminary analysis indicated that the landslide lakes could be classified as those exhibiting extremely high risk, medium risk, and low risk according to field observations and remote sensing, to determine material composition, dam structure, dam height, maximum water storage capacity, and size of the population potentially affected area. The failure risk of 21 debris dams were evaluated as follows: one dam with an extremely high danger risk, seven dams with a high danger, five dams with a medium danger, and eight dams of low danger. More concern was given to the Tangjiashan Lake and different scenarios for the potential sudden failure of its dam were assessed. The risk evaluation result was accepted in full, by the earthquake disaster relief office. A successful emergency dam treatment for risk reduction was planned, based on our assessments, and these measures were quickly carried out. According to this research, the earthquake destabilized the surrounding mountains, resulting in a prolonged geohazard for the area. Landslides and debris flows will continue to develop for at least 5 to 10 years after the Wenchuan earthquake and will produce additional dammed lakes. Recommendations and plans for earthquake–landslide lake mitigation were proposed, based on past successful practices.     

Breaching parameters of landslide dams

Landslide dams pose enormous risks to the public because of the potentially catastrophic floods generated by breaching of such dams. The need to better understand the threats of landslide dams raises questions about the proper estimation of breaching parameters (breach size, breaching duration, and peak outflow rate) of landslide dams and the feasibility of applying models for estimating the breaching parameters of man-made earthen dams to landslide dams. This paper aims to answer these two questions. In this study, a database of 1,239 landslide dams, including 257 cases formed during the 12 May 2008 Wenchuan earthquake, has been compiled. Based on records of 52 landslide dam cases with breaching information in the database, empirical models for estimating the breaching parameters of landslide dams are developed. A comparison study between landslide dams and man-made earth and rockfill dams is conducted, which shows that the models for man-made earth and rockfill dams are not suitable for estimating the breaching parameters of landslide dams. Two case studies are presented to show the application of the set of empirical models developed in this paper.     

汶川八级地震地质灾害研究

汶川地震触发了15000多处滑坡、崩塌、泥石流,估计直接造成2万人死亡。地质灾害隐患点达10000余多处,以崩塌体增加最为显著,反映出地震对山区高陡斜坡的影响差异性非常大,在山顶上的放大作用非常显著。通过综合分析堰塞湖库容、滑坡坝高以及坝体物质组成和结构,对地震形成的33处坝高大于10m的滑坡堰塞湖进行了评估,划分出极高、高、中和低4种溃决危险。汶川地震滑坡滑床往往不具连续平整的滑面,尖点撞击是极震区滑坡的一大共性,可以分为勺型滑床、凸型滑床和阶型滑床等类型。据实地调查,滑坡附近震毁建筑物垂向震动非常明显,具有地震抛掷撞击崩裂高速滑流三阶段特征。在高速滑流中,发生3种效应:(1)高速气垫效应,滑坡体由较大块石和土构成,具有一定厚度,飞行行程可达1~3km;(2)碎屑流效应,撞击粉碎的土石呈流动状态,特别是含水丰富时,形成长程流滑;(3)铲刮效应,巨大撞击力导致下部岩体崩裂,形成新滑坡、崩塌,但是,其厚度不大,滑床起伏不平。本文以北川城西滑坡和青川东河口滑坡为例,分析了地震滑坡高速远程滑动及成灾机理。北川县城城西滑坡导致1600人被埋死亡,数百间房屋被毁,是汶川地震触发的最严重的滑坡灾难,举世罕见。青川东河口滑坡碎屑流是汶川地震触发的较为典型的高速远程复合型滑坡,滑程约2400m,高速碎屑流冲抵清江河左岸,形成滑坡坝,致使7个村庄被埋,约400人死亡。     

Stability of landslide dams and development of knickpoints

The Wenchuan earthquake triggered many landslides and numerous avalanches and created 100 odd quake lakes. The quake lakes may be removed or preserved. The removal strategy was applied to several large landslide dams, which were dangerous because massive amounts of water pooled up in the quake lakes. The dams could eventually fail under the action of dam outburst flooding, potentially endangering the lives of people in the downstream reaches. This paper studied the stability of landslide dams and the development of knickpoints by field investigations and experiments, and analyzing satellite images. The study concluded that if landslide dams were preserved, they would develop into knickpoints and act as a primary control of riverbed incision and, thus, reduce the potential of new landslide. The stability of landslide dams depends mainly on the development of the step-pool system and stream power of the flood flow. If a landslide dam consists of many boulders, a step-pool system may develop on the spillway channel of the dam, which would maximize the resistance, consume most of the flow energy and consequently protect the dam from incision. The development degree of the step-pool system is represented by a parameter S _p, which was measured with a specially designed instrument. A preservation ratio of landslide dams is defined as the ratio of preserved height after flood scouring to the original height of the dam. For streams with peak flood discharge lower than 30 m³/s, the preservation ratio is linearly proportional to S _p. For rivers with a peak flood discharge higher than 30 m³/s (30–30,000 m³/s), the minimum S _p value for stable channel increases with log p, in which p is the unit stream power. For a landslide dam with a poorly developed step-pool system, S _p is smaller than the minimum value and the outburst flood incises the spillway channel and causes failure of the dam. For preserved landslide dams, sediment deposits in the quake lakes. A landslide dam may develop into a knickpoint if it is stabilized by long-term action of the flow. Large knickpoints can totally change the fluvial processes and river morphology. Uplift of the Qinghai–Tibetan Plateau has caused extensive channel bed incision along almost all rivers. For many rivers, the incision has been partly controlled by knickpoints. Upstream reaches of a knickpoint have a new and unchanging base level. This brings about a transition from degradation to aggradation and from vertical bed evolution to horizontal fluvial process. Multiple and unstable channels are prominent in the reaches, upstream of the knickpoints. If hundreds of landslide dams occurred simultaneously on a reach of a mountain river, the potential energy of bank failure and the slope erosion would be greatly reduced and sediment yield from the watershed may be reduced to nearly zero. The quake lakes may be preserved long term and become beautiful landscapes. Streams with long-term unfilled quake lakes have good aquatic ecology.     

Dam-break risk analysis of the Attabad landslide dam in Pakistan and emergency countermeasures

The Attabad landslide dam caused significant property losses and many human casualties in Pakistan, and also greatly affected the operation of the China-Pakistan Karakoram Highway (KKH). This paper discusses the risk of dam breach and hazards to the KKH project construction site following a dam breach. The paper examines the following three topics. (1) The geomorphologic dimensionless blockage index (DBI) and the analogy method were used to analyze the stability of the Attabad landslide dam. The long-term behaviors of landslide dams downstream of the Attabad landslide dam indicate that the risk of a dam breach exists, but the probability of a total dam failure is low. (2) The peak discharge of a potential breach of the Attabad landslide dam was calculated for scenarios in which 1/4, 1/3, 1/2, and total failure of the dam was breached. The potential breach discharge decreases with the downstream distance. (3) The potential impacts of the landslide dam breach on the KKH project construction site were analyzed. Based on the composition of the landslide dam, the probability of a 1/3 dam breach is high. To ensure the safety of downstream areas, disaster preparedness plans that correspond to the 1/2 dam breach scenario should be developed. Based on experience in addressing the landslide dam that was caused by the Wenchuan Earthquake, artificial controlled drainage measures are suggested and provide a technical reference for addressing the Attabad landslide dam and achieving recovery and normal operation of KKH.     

最近20年地震中场地液化现象的回顾与土体液化可能性的评价准则

回顾了1994年美国Northridge地震、1995年日本阪神地震、1999年土耳其Kocaeli地震、1999年台湾集集地震、2008年中国汶川地震、2010年智利Maule地震、2010～2011新西兰Darfield地震及余震、2011年东日本地震中大量的、不同类型的液化实例调查与研究,发现这些地震的液化具有以下特点：（1）罕见的特大地震（Mw9.0）使远离震中300～400 km的新近人工填土发生严重的大规模液化;（2）特大地震（Ms8.0、Mw8.8）使远离震中的低烈度Ⅴ～Ⅵ度地区发生严重液化;（3）海岸、河岸附近地区的新近沉积冲积、湖积土,填筑时间不到50年的含细粒、砂砾人工填土,容易发生严重液化;（4）天然的砂砾土层液化发生严重液化;（5）发生了深达20 m的土层液化现象;（6）松散土层液化后可以恢复到震前状态并再次发生液化;（7）高细粒（粒径≤75 ?m）含量≥50%或高黏粒（粒径≤5 ?m）含量≥25%的低-中塑性土严重液化,对介于类砂土与类黏土之间的过渡性态土,有时地表未见液化现象;（8）液化土层的深度较深或厚度较小时,容易出现地面裂缝而无喷砂现象;有较厚的上覆非液化土层时,场地液化不一定伴随地表破坏。液化实例证明,第四系晚更新世Q3地层可以发生严重液化;黏粒含量不是评价细粒土液化可能性的一个可靠指标;低液限、高含水率的细粒土易发生液化,采用塑性指数PI、含水率wc与液限LL之比作为细粒土液化可能性评价的指标是适宜的。综合Boulanger和Idriss、Bray和Sincio、Seed和Cetin等的液化实例调查与室内试验研究成果,建议细粒土液化可能性的评价准则如下：PI ＜12且wc/LL＞0.85的土为易液化土,12＜PI≤20和/wc/LL≥0.80的土为可液化土;PI ＞20或wc/LL＜0.80的土为不液化土。     

泥石流堆积物中细颗粒含量与渗透系数关系试验研究

泥石流拦砂坝通常建造在沟床堆积物上。泥石流堆积物的渗透性是影响坝底扬压力的关键因素。目前关于土体渗透性的研究主要集中于无黏性粗粒土,对泥石流堆积物这种宽级配土体渗透性的研究比较缺乏。选择北川县泥石流沟床堆积物作为试验材料,通过渗透试验,确定了影响宽级配土渗透性的细颗粒上限粒径;在此基础上,通过试验研究了细颗粒含量与渗透系数的关系。结果表明,泥石流堆积物中粗颗粒仅起骨架作用,细颗粒才是决定其渗透性能的关键;显著影响宽级配土渗透性的细颗粒上限粒径为0.1 mm;细颗粒（<0.1 mm）含量与渗透系数呈负指数关系,并且当细颗粒含量超过20%以后,泥石流堆积土的渗透性趋于稳定。