Regulation effect of the grille spacing of a funnel-type grating water–sediment separation structure on the debris flow performance

The size of pores or the grille spacing of water–sediment separation structures directly affects their regulation effect on the debris flow performance.A suitable pore size or grille spacing can effectively improve the water–sediment separation ability of the structure.The new funnel-type grating water–sediment separation structure(FGWSS)combines vertical and horizontal structures and provides a satisfactory water–sediment separation effect.However,the regulation effect of the grille spacing of the structure on the debris flow performance has not been studied.The regulation effect of the structure grille spacing on the debris flow performance is studied through a flume test,and the optimal structure grille spacing is obtained.An empirical equation of the relationship between the relative grille spacing of the structure and the sediment separation rate is established.Finally,the influence of the water–sediment separation structure on the regulation effect of debris flows is examined from two aspects:external factors(properties of debris flows)and internal factors(structural factors).The experimental results show that the gradation characteristics of solid particles in debris flows constitute a key factor affecting the regulation effect of the structure on the debris flow performance.The optimum grille spacing of the FGWSS matches the particle size corresponding to the material distribution curves d85~d90 of the debris flow.The total separation rate of debris flow particles is related to the grille spacing of the structure and the content of coarse and fine particles in the debris flow.

Morphodynamics and sediment connectivity index in an unmanaged,debris-flow prone catchment:a through time perspective

Torrential processes are among the main actors responsible for sediment production and mobility in mountain catchments.For this reason,the understanding of preferential pathways for sediment routing has become a priority in hazard assessment and mitigation.In this context,the sediment Connectivity Index(IC)enables to analyse the existing linkage between sediment sources and the selected target(channel network or catchment outlet).The IC is a grid-based index that allows fast computation of sediment connectivity based on landscape information derived from a single Digital Terrain Model(DTM).The index computation is based on the log-ratio between an upslope and a downslope component,including information about drainage area,slope,terrain roughness,and distance to the analysis target(e.g.outlet).The output is a map that highlights the degree of structural connectivity of sediment pathways over analysed catchments.Until now,these maps are however rarely used to help defining debris-flow hazard maps,notably due to a lack of guidelines to interpret the IC spatial distribution.This paper proposes an exploitation procedure along profiles to extract more information from the analysis of mapped IC values.The methodology relies on the analysis of the IC and its component variables along the main channel profile,integrated with information about sediment budgeting derived from Difference of DEMs(DoD).The study of connectivity was applied in the unmanaged sub-catchment(without torrent control works)of the Rio Soial(Autonomous Province of Trento–NE Italy)to understanding the geomorphic evolution of the area after five debris flows(in ten years)and the related changes of sediment connectivity.Using a recent DTM as validation,we demonstrated how an IC analysis over the older DTM can help predicting geomorphic changes and associated hazards.The results show an IC aptitude to capture geomorphic trajectories,anticipate debris flow deposits in a specific channel location,and depict preferential routing pathways.

Coupled Model of Two-phase Debris Flow,Sediment Transport and Morphological Evolution

The volume fraction of the solid and liquid phase of debris flows, which evolves simultaneously across terrains, largely determines the dynamic property of debris flows. The entrainment process significantly influences the amplitude of the volume fraction. In this paper, we present a depth-averaged two-phase debris-flow model describing the simultaneous evolution of the phase velocity and depth, the solid and fluid volume fractions and the bed morphological evolution. The model employs the Mohr–Coulomb plasticity for the solid stress, and the fluid stress is modeled as a Newtonian viscous stress. The interfacial momentum transfer includes viscous drag and buoyancy. A new extended entrainment rate formula that satisfies the boundary momentum jump condition （Iverson and Ouyang, 2015） is presented. In this formula, the basal traction stress is a function of the solid volume fraction and can take advantage of both the Coulomb and velocity-dependent friction models. A finite volume method using Roe’s Riemann approximation is suggested to solve the equations. Three computational cases are conducted and compared with experiments or previous results. The results show that the current computational model and framework are robust and suitable for capturing the characteristics of debris flows.

Influence of Fine Sediment on the Fluidity of Debris Flows

Debris flows include a great diversity of grain sizes with inherent features such as inverse grading,particle size segregation,and liquefaction of fine sediment.The liquefaction of fine sediment affects the fluidity of debris flows,although the behavior and influence of fine sediment in debris flows have not been examined sufficiently.This study used flume tests to detect the effect of fine sediment on the fluidity of laboratory debris flows consisting of particles with various diameters.From the experiments,the greatest sediment concentration and flow depth were observed in the debris flows mixed with fine sediment indicating increased flow resistance.The experimental friction coefficient was then compared with the theoretical friction coefficient derived by substituting the experimental values into the constitutive equations for debris flow.The theoretical friction coefficient was obtained from two models with different fine-sediment treatments:assuming that all of the fine sediments were solid particles or that the particles consisted of a fluid phase involving pore water liquefaction.From the comparison of the friction coefficients,a fully liquefaction state was detected for the fine particle mixture.When the mixing ratio and particle size of the fine sediment were different,some other cases were considered to be in a partially liquefied transition state.These results imply that the liquefaction of fine sediment in debris flows was induced not only by the geometric conditions such as particle sizes,but also by the flow conditions.

Coseismic landslide sediment increased by the“9.5”Luding earthquake,Sichuan,China

The"9.5"Luding earthquake(Ms 6.8),which occurred on September 5,2022,has triggered thousands of landslides,and caused coseismic landslide sediment in the mountain basin to increase significantly.After the Luding earthquake,landslide sediment may continue to divert to channels,and increase the activity of debris flows.Importantly,the formation of debris flows can pose a major threat to infrastructure,lives and property.To better understand the landslide sediment that increased by the"9.5"Luding earthquake and its impact on the activity of debris flows,we mapped the coseismic landslide database using satellite images.A total of9142 landslides with an area of 49.51 km^(2),covering4.81%of the whole basin,were triggered by the Luding earthquake.The coseismic landslides induced by this earthquake are dominated by shallow landslides and are densely distributed in the combined zone of the Xianshuihe fault and the Daduhe fault.Approximately 333.31×10^(6)m^(3)(error:111.43×10^(6)m^(3)/-70.73×10^(6)m^(3))of coseismic landslide sediments were induced by the earthquake in the epicenter,and the landslide materials were concentrated downstream of the basins.In addition.more than 13986.45×10^(4)m^(3)(error:4675.67×10^(4)m^(3)/-2967.92×10^(4)m^(3))of landslide sediment may supply for debris flow occurrence.Simultaneously,the small basins that are distributed near Moxi,Detuo and the junction of the Xianshuihe fault and Daduhe fault are more susceptible to debris flows when rainstorms hit these regions.Therefore,prevention and mitigation measures,early warning,and land use planning should be adopted in advance in these regions.However,from the perspectives of landslide scale and the degree of landslide-channel coupling,the activity or active intensity of debris flows in the Luding earthquake area may be lower than that in the epicenter area of the 2008 Wenchuan earthquake.

THE CATASTROPHE FORECAST OF THE ANNUAL SIDEMENT TRANSPORT BY DEBRIS FLOW IN JIANGJIA GULLY,YUNNAN PROVINCE, CHINA

On the basis of the observational data on the annual sediment transport by debris flow in recent 8 years, appling the catastrophe forecast method of Grey System Theory, this study has established the catastrophe model of the annual sediment transport by debris flow in Jiangjia Gully. It has forecasted the next potential catastrophic year in which the annual sediment transport will be over the catastrophic. threshold 2 million m3. Furthermore, it has introduced the 'equal dimension-new information model', which makes the forecast be done continuously.

合水地区长6_(3)深水重力流沉积特征研究

合水地区是鄂尔多斯盆地近年来原油勘探的重点区块,在系统分析沉积构造、岩石学特征、结构粒度特征等沉积相识别标志的基础上,结合区域沉积背景,开展了合水地区长6_(3)重力流沉积类型及展布特征研究。结果表明,合水地区长6_(3)油层亚组为湖泊-重力流沉积体系,发育半深湖-深湖沉积亚相,可进一步划分为浊流沉积、砂质碎屑流、滑塌沉积三种重力流沉积类型;其中砂质碎屑流及浊流为主要控砂微相,主要分布在研究区的中部、南部区域,为区内有利储集相带。

A hyperspectral detection model for permeability coefficient of debris flow fine-grained sediments, Southwestern China

Fine-grained sediments are Quaternary sediments with grain sizes of not more than 2 mm.They startfirst when meeting water,their stability is related to the initial water volume triggering debrisflow,and thus plays an important role in debrisflow hazards early warning.The permeability coefficient is the inter-controlled factor offine-grained sediment stability.However,there is no hyperspectral model for detecting thefine-grained sediment permeability coefficient in large areas,which seriously affects the progress of debrisflow hazards early warning.Therefore,it is of great significance to establish a hyperspectral detection model for the permeability coefficient offine-grained sediments.Taking Beichuan County,Southwestern China as the case,a permeability coefficient hyperspectral detection model was established.The results show that eight bands are sensitive to the permeability coefficient with correlation coefficient(R)of 0.6343.T-test on the model shows that P-a values for sensitive bands are all less than 0.05,indicating the established model has a good prediction ability with a precision of 85.83%.These sensitive bands also indicate the spectral characteristics of the permeability coefficient.Therefore,it provides a scientific basis forfine-grained sediment stability detection in large areas and lays a theoretical foundation for debrisflow hazards’early warning.

Determination of optimal grid opening width for herringbone water-sediment separation structures based on sediment separation efficiency

The herringbone water-sediment separation structure(HWSSS) was developed to prevent debris flows. This paper mainly focuses on evaluating the sediment separation efficiency of HWSSS in debris flow prevention and determining the grid opening width D, a crucial structure parameter for HWSSS design. Theoretical analysis on the total sediment separation rate Pt reveals that the efficiency of sediment separation is much related with sediment grain size distribution(GSD) and grid opening width. The lower limit of Pt is deduced from the perspective of safety consideration by transforming debris flow into sediment-laden flow. Hydraulic model tests were carried out. Based on the regression analysis of the experimental data, the quantitative relationships between Pt and D and GSD characteristic values were finally established. A procedure for determining optimal grid opening width is proposed based on these analyses. These results are of significance in evaluating sediment separation effect by HWSSS in debris flow prevention and contribute to a more explicit methodology for design of HWSSS.

The Effect of Grain Size on the Viscosity and Yield Stress of Fine-Grained Sediments

In debris flow modelling,the viscosity and yield stress of fine-grained sediments should be determined in order to better characterize sediment flow.In particular,it is important to understand the effect of grain size on the rheology of fine-grained sediments associated with yielding.When looking at the relationship between shear stress and shear rate before yielding,a high-viscosity zone(called pseudoNewtonian viscosity) towards the apparent yield stress exists.After yielding,plastic viscosity(called Bingham viscosity) governs the flow.To examine the effect of grain size on the rheological characteristics of fine-grained sediments,clay-rich materials(from the Adriatic Sea,Italy; Cambridge Fjord,Canada; and the Mediterranean Sea,Spain),silt-rich debris flow materials(from La Valette,France) and silt-rich materials(iron tailings from Canada) were compared.Rheological characteristics were examined using a modified Bingham model.The materials examined,including the Canadian inorganic and sensitive clays,exhibit typical shear thinning behavior and strong thixotropy.In the relationships between the liquidity index and rheological values(viscosity and apparent yield stress),the effect of grain size on viscosity and yield stress is significant at a given liquidity index.The viscosity and yield stress of debris flow materials are higher than those of low-activity clays at the same liquid state.However the viscosity and yield stress of the tailings,which are mainly composed of silt-sized particles,are slightly lower than those of low-activity clays.

Experimental study on large wood filtration performance by herringbone water-sediment separation structure

A herringbone water-sediment separation structure(hereinafter referred to as "herringbone structure") has been shown to be effective in separating coarse inorganic debris; however, less is known regarding the large wood(LW) filtration effect in this structure. This paper presents preliminary research on the wood filtration effect of the herringbone structure based on physical model tests.The results show that the herringbone structure exhibited effective performance in large wood size segregation, with a 100% component filtration rate for LW that diameter(D) larger than ribbed beam opening width(a). The total filtration rate also exceeded 80% when the Fraud number(Fr) is larger than 2.64 and increased with the increase of Fr. After exceeding Frmax, total filtration rate would be decreased due to overflow. Beside flow condition,structure parameters influence significantly on LW filtration rate. We attempt to explain the filtration process via particle contact trajectory and particle movement trajectory. The inclined angle of ribbed beam(γ) contributed the most variation to the filtration rate via influencing the coincidence with particle contact trajectory and particle movement trajectory. The high sensitivity coefficient of ribbed beam(θ) under relatively low Fr conditions implies remarkable influences on LW filtration effects by causing clogging problem. The ribbed beam opening width(a) together with LW diameter(D) influenced the size segregation performance.

南堡凹陷东北部东二段重力流砂岩储层发育规律

随着勘探程度的提高,深水重力流成因的浊积岩储层已成为我国东部断陷湖盆油气勘探开发的重要目标之一。因为沉积分异不足和成岩破坏,重力流砂岩的储层质量通常整体较差,优质储层的预测成为制约其有效油气勘探的关键地质因素。利用岩心、测井资料及储层物性、岩石薄片分析结果,研究了南堡凹陷东北部东营组二段重力流砂岩的岩相特征、成因类型、储层特征,以探索优质储层的控制因素和发育规律。研究表明,区内重力流沉积可细分为8种岩相,解释为滑动滑塌、砂质碎屑流、泥质碎屑流、浊流4类成因。储层物性参数统计分析证实,本区重力流砂岩储层非均质性强,储层质量受控于砂岩成因、砂-泥结构及其影响的溶蚀强度。从成因看,砂质碎屑流和浊流对重力流砂岩优质储层的发育贡献最大。砂质碎屑流成因的块状砂岩厚度较大、泥岩夹层较少、钙质胶结物的溶蚀程度高,储层质量最好;而浊流成因的砂岩厚度较薄,与泥岩呈互层或夹层产出,成岩环境封闭、钙质胶结物溶蚀程度低,储层质量较差。本研究为湖盆深水重力流砂岩油气的高效勘探开发提供了一种基于成因和结构的储层预测思路。

花红树沟泥石流灾害特征及堰塞区工程地质问题分析

汶川地震后泥石流长期频发,局部形成堰塞湖灾害,极大危害了当地人民生命财产及工程建设安全。本文以地震强烈影响区花红树沟泥石流为研究对象,通过遥感解译、现场调查、钻探、原位测试及室内试验等勘察方法,综合分析了泥石流孕灾环境及发育特征。在动力学计算的基础上对新发泥石流堵河危害进行了评价,并对其形成的堰塞沉积场地工程地质问题进行了分析。研究表明:花红树沟为中等易发、中型规模黏性泥石流冲沟,沟内动储量物源约16×10^(4) m^(3),最大淤积高度约2.82 m,最大堵河范围约10 m;该泥石流堰塞场地范围较大,主要工程地质问题为砂土液化。研究结果可为确保该区域居民安全及工程建设提供科学参考依据。

鄂尔多斯盆地南部彬长区块延长组长6-长7段深水重力流沉积特征分析

鄂尔多斯盆地南部彬长区块的延长组长6-长7段发育厚层无沉积构造的块状砂岩,具有良好的油气显示和开发效益,然而关于该套砂岩的形成机制尚不清晰。确定长6-长7段砂岩的沉积相及沉积模式,对于该套低渗砂岩储层“甜点”形成机制的理解,“甜点”分布模式的预测,以及后续勘探开发都具有重要的指导意义。对彬长区块36口取心井的长6-长7段1024 m长的岩心进行了沉积学特征描述,结合粒度分析资料及地质制图分析,确定了该套厚层砂岩的沉积相及沉积模式。结果表明:鄂尔多斯盆地南部彬长区块的延长组长6-长7段砂岩共发育15种岩相和3种主要沉积微相类型,即:砂质碎屑流、浊积岩和震积滑塌岩微相,以及它们在空间上的3类组合关系。其深水重力流沉积模式可以概括为扇根(坡折带斜坡上半部分)的震积滑塌相-砂质碎屑流亚相(沉积组合)、扇中(斜坡中下部位-坡脚)的砂质碎屑流-浊积岩沉积亚相(沉积组合)和扇端(坡脚-盆底)浊积砂等亚相(沉积组合)。通过对彬长区块延长组长6-长7段发育的致密砂岩沉积特征的分析与讨论,确定了该厚层块状砂岩的主要沉积相及沉积微相的特征及分布,为致密砂岩储层的高效开发及“甜点”预测提供了科学依据与良好借鉴。

末次冰期内威德尔海的冰筏碎屑增多事件与底流增强事件的耦合性

晚第四纪的气候变化控制了南极地区的冰架进退。冰架崩塌形成的冰山在其破碎、漂流、融化过程中把冰筏碎屑(IRD)搬运到海洋中。同时,大量的冰川融水促进了海洋垂直剖面结构和动力的改变,从而影响冰筏碎屑的沉积过程。此前对于揭示极地海域冰筏碎屑与底流活动变化之间关系的研究尚不充分。因此,本文分析了南极威德尔海西北部柱状沉积物的沉积记录,在对比沉积物粒度数据特征、分析沉积物端元模型的基础上,发现4次明显的沉积物粒度变化事件和底流增强事件同时发生。这种同步性说明冰架系统与海洋环境之间存在内在的调节机制。两次较强的冲刷事件证明岩心形成过程中存在着两次沉积间断,同时也合理地解释了古地磁数据和AMS^(14)C数据存在的显著年龄差异。此外,鉴于D4-9岩心样品蛋白石、有机碳等指标均指示了极低的输出生产力情况,且与冰期的生产力水平相当,推断该岩心主要形成于末次冰期期间。综上分析,D4-9岩心所记录的事件反映出南极地区千年尺度的气温变化诱发了冰架的后退,导致了明显的冰筏碎屑事件和底流增强事件,解释了威德尔海区冰架-海洋过程的内在耦合关系。

Fast clogging problem of open check dams and a new type suggestion:curved footed type open check dam

Driftwood is one of the important physical components in mountainous rivers which causes severe hazards due to the clogging of bridges,culverts,and narrow sections during floods.Therefore,the understanding of driftwood dynamics and mitigation measures are crucial for managing wood in rivers.Open check dams are the most commonly used engineering measure for preventing driftwood from reaching downstream areas.Nevertheless,these open check dams frequently lose their sediment transport function when they are blocked by sediment and driftwood,especially during major flood events.This paper proposes a new type of open check dam for preventing from clogging.Thus,flume experiments were conducted to examine the influence of different types of open check dams on the characteristics of driftwood deposition.For the model with wood length(LWD)=16.5 cm,wood diameter(D)=15 mm,and wood number(N)=172,the highest trapping efficiency was observed with 90.1%and 87.2%retention rates for the classical debris flow breaker and curved footed open check dams,respectively.Laboratory tests showed that through this proposed design,woody debris blockage in a very short time was prevented from the accumulation of woods beside the dam.In addition to this,most of the sediment passed through the check dam and most of the driftwood got trapped.It can be briefly stated that the geometrical design of the structure plays an important role and can be chosen carefully to optimize trapping efficiency.By designing this type of open check dams in mountain river basins,it may provide a better understanding of the driftwood accumulation and basis for the optimal design of these structures.Further development of the solution proposed in this work can pave the way for designing different types of open check dams for effective flood management.

A numerical study of the impacts of sediment composition on debris flows

Debris flows in their natural environments are made up of different sediment sizes,even though they are often considered to be uniform in numerical studies.This prompted the present study to investigate the behaviors of debris flows with nonuniform sediment composition.A model is developed to investigate nonuniform debris flows and the characteristic behavior of their compositions.The model’s framework of mass and momentum equations and mass exchange with the bed are solved using the shock-capturing finite volume method.The model is first tested with a uniform sediment laboratory experiment,where there is a good agreement.The model is then tested against two flume experiments with different bed water content and porosity.The model performed well in both cases,however,the slight underprediction in the second case can be associated with the complexity of debris flows which may not be fully captured by physical equations.The model is further used to investigate different compositions of debris flows including mixed grain sizes,mean size,fine and coarse sediment size,and no erosion/deposition.The modeling of the mixed grain sizes produced a more accurate result,and this justifies the consideration of nonuniform sediment sizes in the numerical studies of debris flows.To enhance the understanding of frontal coarsening and rear fining in experimental debris flow,the model is also used to investigate cases with different sediment compositions,and the model was able to reproduce the frontal coarsening and rear fining observed in experiments.

泥石流沉积物力学特性研究进展

泥石流爆发后,其沉积物常淤埋城镇建构筑物与交通设施,造成交通中断与人民生命财产损失。进行泥石流爆发后的应急抢险救灾通行及泥石流沉积物未完全固结前城镇与桥梁道路的建设,需更加深入了解泥石流沉积物力学特性。通过查阅相关文献与研究成果,对近年来泥石流沉积物力学特性方面的研究内容进行比较系统的阐述与总结,指出当前研究中存在的问题与不足,并提出泥石流沉积物固结与承载计算方面需进一步研究与解决的关键科学问题。

陆相湖盆深水砂质碎屑流成因机制与分布特征——以鄂尔多斯盆地为例

国外深水沉积发展了50年,从浊流定义的普遍应用,到今天对鲍马序列、约克扇等经典模式持否定态度,深水沉积研究经历了一个推陈出新的过程。目前国外流行的砂质碎屑流理论是经典浊流理论的部分否定与新发展。本研究阐述国外砂质碎屑流的概念、实验、鉴别特征、沉积模式等最新认识,以运用砂质碎屑流理论解释鄂尔多斯盆地湖盆中部厚砂岩的成因机制为例,揭示我国陆相湖盆中心坡折带砂体分布特征与形成机制,为开拓陆相勘探领域提供理论支撑。

青藏高原东北边缘泥石流发生与沉积史初探

文章对青藏高原东北边缘的古泥石流发生历史进行了分析 .研究表明 :古泥石流主要发生于 3 0～ 3 5Ma,2 4～ 2 5Ma ,1 9～ 1 6Ma ,1 0～ 1 1Ma ,0 7～ 0 9Ma ,0 6Ma,0 33Ma ,0 1～ 0 14Ma以及全新世 .泥石流是气候变化和构造运动的共同产物 ,随着晚上新世以来青藏高原及周围山地在一系列构造运动影响下逐步隆升 ,导致地形反差加大 ,气候冷暖变化频繁 ,泥石流爆发的频率加大 .人类活动只能加剧泥石流的爆发 ,却不能从根本上阻止它的发生 .随着全球变暖 ,有可能出现一些灾害性的气候变化 ,这必然会导致中国西部泥石流的发生频率和规模有所加大 .