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 eases 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.

Impact of Fine Sediment on TSS and Turbidity in Retention Structure

A study of the impact of fine sediment on various water quality parameters in retention structure such as sediment basin was conducted on stagnant and flowing condition. 7 water quality parameters (pH, TSS, turbidity, DO, BOD, COD, ammonium nitrogen) were measured and classified according to the Interim National Water Quality Standard (INWQS) for Malaysia. Results show higher fine sediment concentration causes higher TSS and turbidity. Besides, results show TSS and turbidity were influenced by soil type for the same amount of fine sediment. Soil Siri Rasau 1 showed highest TSS and turbidity value followed by soil Siri Bungor and soil alluvium. A good positive correlation of TSS versus turbidity and has been investigated in this study. Multiple nonlinear regression analysis revealed that parameter TSS is dependent on time, total soil mass, fine soil mass and flow rate.

Flocculation process of fine-grained sediments by the combined effect of salinity and humus in the Changjiang Estuary

For the great amount of organic compounds and the variation of salinity in the Changjiang Estuary, the study on the flocculation process of fine-grained sediments by the combined effect of salinity and humus in the high-turbid system is of critical significance for the understanding of the mechanism of the formation of the turbidity maximum （TM） . For the great amount of organic compounds and the variation of salinity in the Changjiang Estuary, the study on the flocculation process of fine-grained sediments by the combined effect of salinity and humus in the high-turbid system is of critical significance for the understanding of the mechanism of the formation of the turbidity maximum （TM） . The effects of salinity and humus on the fine-grained sediments have been analyzed through the synthetic study of the aspects of flocculation/coagulation power （ F）, diameter （D） and zeta potential （Z）. And the microcosmic configuration of the flocs has been analyzed by using a scan electron microscope and Fourier Transform Infrared Spectrometry. The results show that： （ 1 ） with the increase of salinity, F and D become greater and Z becomes smaller, and with the increase of the concentration of humus, F becomes smaller, but D and Z become greater; （2） the microcosmic configuration of the flocculation shows that humus packs on the fine sediments in the form of salt, and the flocculation model of C - P - OM （C stands for clay; P cations; OM organic materials） can successfully demonstrate the mechanism of the formation of the finegrained sediments in the high-turbid area of the Changjiang Estuary.

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.

CHARACTERIZATION OF FINE-GRAINED TURBIDITE DEPOSITS FROM THE SOUTH CHINA SEA SEDIMENT CORES

Two depositional processes controlled the muddy sediments in the South China Sea Basin. Bathyal sediments depositional rate was 7.66 cm/la in the northern continental slope of the Basin where turbidity current was almost nonexistent. In the northern margin of the Basin, abyssal sediment depositional rate was 5.05cm/ka and turbidity current occurrence averaged 0.22 per 1000 years. Turbidite was found in the middle of the Basin. Over half of the muddy sediments in the deep sea basin were deposited by turbidity currents, and had typically graded bedding, and contents of organic matter, calcareous material and micropaleontologic species inconsistent with the environment.

Laminae characteristics of gas-bearing shale fine-grained sediment of the Silurian Longmaxi Formation of Well Wuxi 2 in Sichuan Basin,SW China

Based on various test data, the composition, texture, structure and lamina types of gas-bearing shale were determined based on Well Wuxi 2 of the Silurian Longmaxi Formation in the Sichuan Basin. Four types of lamina, namely organic-rich lamina, organic-bearing lamina, clay lamina and silty lamina, are developed in the Longmaxi Formation of Well Wuxi 2, and they form 2 kinds of lamina set and 5 kinds of beds. Because of increasing supply of terrigenous clasts and enhancing hydrodynamics and associated oxygen levels, the contents of TOC and brittle mineral reduce and content of clay mineral increases gradually as the depth becomes shallow. Organic-rich lamina, organic-rich + organic-bearing lamina set and organic-rich bed dominate the small layers 1-3 of Member 1 of the Longmaxi Formation, suggesting anoxic and weak hydraulic depositional setting. Organic-rich lamina, along with organic-bearing lamina and silty lamina, appear in small layer 4, suggesting increased oxygenated and hydraulic level. Small layers 1-3 are the best interval and drilling target of shale gas exploration and development.

Vertical Migration of Fine-Grained Sediments from Interior to Surface of Seabed Driven by Seepage Flows–‘Sub-Bottom Sediment Pump Action'

A scientific hypothesis is proposed and preliminarily verified in this paper: under the driving of seepage flows, there might be a vertical migration of fine-grained soil particles from interior to surface of seabed, which is defined as ‘sub-bottom sediment pump action' in this paper. Field experiments were performed twice on the intertidal flat of the Yellow River delta to study this process via both trapping the pumped materials and recording the pore pressures in the substrate. Experimental results are quite interesting as we did observe yellow slurry which is mainly composed of fine-grained soil particles appearing on the seabed surface; seepage gradients were also detected in the intertidal flat, under the action of tides and small wind waves. Preliminary conclusions are that ‘sediment pump' occurs when seepage force exceeds a certain threshold: firstly, it is big enough to disconnect the soil particles from the soil skeleton; secondly, the degree of seabed fluidization or bioturbation is big enough to provide preferred paths for the detached materials to migrate upwards. Then they would be firstly pumped from interior to the surface of seabed and then easily re-suspended into overlying water column. Influential factors of ‘sediment pump' are determined as hydrodynamics(wave energy), degree of consolidation, index of bioturbation(permeability) and content of fine-grained materials(sedimentary age). This new perspective of ‘sediment pump' may provide some implications for the mechanism interpretation of several unclear geological phenomena in the Yellow River delta area.

陆相坳陷湖盆细粒沉积岩岩相类型及成因——以松辽盆地晚白垩世青山口组为例

页岩油是目前非常规油气研究的热点与难点。细粒沉积岩岩相类型及成因分析是页岩油“源储”特征研究及“甜点”预测的有效途径。松辽盆地青山口组细粒沉积广泛发育,是页岩油富集的有效层段。本文通过岩性、矿物成分、有机质丰度与沉积构造4个参数,将松辽盆地青山口组细粒沉积岩划分为6种岩相:高有机质泥纹层黏土质页岩(A)、中高有机质含细粉砂纹层长英质页岩(B)、中低有机质含粗粉砂纹层长英质页岩(C)、低有机质层状粉砂岩(D)、低有机质层状介形虫灰岩(E)和低有机质层状白云岩(F)。进一步从水动力学与有机质富集方面探讨了不同岩相类型的成因,并建立了相应的沉积模式。具体为:在风暴浪基面之下的静水、咸水环境、高湖泊生产力背景中,浮游藻类与黏土絮状物均匀悬浮沉降,形成贫富有机质黏土质纹层,沉积A岩相;在正常浪基面之下的相对静水(浪基面附近局部动荡)、半咸水环境、高湖泊生产力背景中,三角洲径流与洪流带来的细粉砂颗粒继续向湖盆中央搬运,经均匀悬浮沉降形成长英质纹层,间歇期悬浮沉降形成黏土质纹层,形成B岩相;正常浪基面之下,洪水携带粉砂级颗粒,顺着水下分流河道搬运至外前缘,以稳定性浊流的形式进入前三角洲,随流速逐渐降低,分异形成粗粉砂—细粉砂纹层,间歇期悬浮沉降形成黏土质纹层,形成C岩相;正常浪基面之下,三角洲前缘早期沉积物在阵发性浊流的作用下,滑塌至较深水区,形成D和E岩相;于正常浪基面与风暴浪基面之间,在相对干燥的气候背景下的咸水环境中,形成F岩相。

中国典型陆相盆地细粒沉积环境和岩相特征

细粒沉积环境和岩相时-空分布规律是控制页岩油富集高产的主要因素。在前人细粒沉积环境和岩相研究的基础上,分析研究了松辽、渤海湾、鄂尔多斯和准噶尔等中国典型陆相盆地的细粒沉积环境及主要特征。研究认为:①淡水-微咸水湖盆发育粉砂质纹层、黏土质纹层、有机质纹层的黏土岩、粉砂岩以及二者之间过渡岩性,咸水湖和盐湖多发育具方解石(白云石)纹层及黏土级灰泥纹层的细粒碳酸盐岩和细粒混积岩。②陆相湖盆不同演化阶段发育不同细粒岩相组合。裂陷期细粒沉积岩以富碳酸盐矿物的岩相组合发育为特征,拗陷期形成的富有机质页岩层系则以长英质+黏土质沉积岩相组合为主。③湖盆泥页岩沉积机制主要为悬浮沉降、风成输入、浊流、异重流和泥质碎屑流。④中国陆相页岩油类型多样且资源丰富,松辽、鄂尔多斯、准噶尔、渤海湾等中生代—新生代陆相盆地是中国页岩油勘探开发的重要领域。⑤未来细粒沉积环境和岩相研究重点发展方向:开展天文旋回研究,建立系统有效的沉积古环境判识参数及标准;建立陆相湖盆页岩型、夹层型和混合型细粒沉积岩岩相分类和沉积模式,有效地预测细粒沉积岩岩相时空分布;开展细粒沉积成因过程物理和数值模拟,研究细粒沉积物物理、化学和生物沉积耦合过程和形成发育机理;关注数据集成与深度挖掘、人工智能大数据与计算机辅助技术,研究细粒沉积物分布规律。

渤海湾盆地沾化凹陷古近系沙三下亚段旋回地层学分析及地层划分

湖相细粒沉积多具有连续性,能记录和保存显著的天文旋回信号,是进行天文旋回分析的理想地层。通过对渤海湾盆地沾化凹陷重点井沙三下亚段自然伽马数据进行MTM频谱分析和FFT进化谐波分析,建立了“浮动”天文年代标尺,并在单井上进行了天文旋回地层划分及连井地层对比,为全区搭建了地层格架。研究结果表明:(1)渤海湾盆地沾化凹陷沙三下亚段记录了显著的天文旋回信号,匹配出最优沉积速率为9.0×103cm/Ma;由长偏心率、短偏心率、斜率和岁差周期产生的旋回地层厚度分别为42.3 m,9.0 m,2.4~4.7 m和1.3~1.9 m;(2)沙三下亚段比较稳定的记录了6个长偏心率旋回、25个短偏心率旋回,可将短偏心率曲线作为地层划分依据来进行高精度地层对比。(3)运用天文旋回理论进行岩相发育规律、岩相空间配置关系的预测,可为湖盆沉积中心页岩油气地质“甜点”的精细勘探提供依据。

长江口—东海内陆架悬浮重矿物组成与颗粒特征

沉积物重矿物矿物组成和颗粒大小对揭示沉积物源和水动力分选过程具有重要指示意义。然而,受研究手段的制约,对于长江细粒沉积的重矿物组成和物源、水动力分选之间关系的探究还尚属空白。本研究利用自动定量矿物分析系统(TIMA)对长江口—东海内陆架不同水层悬浮物的重矿物组成和颗粒大小进行了研究,同时,结合电子探针分析对细粒级重矿物自动识别结果进行了验证。研究表明,长江口悬浮物中特征重矿物组合为角闪石—绿帘石—铁质金属矿物,与长江下游沉积物特征重矿物组合一致。长江口悬浮物与长江下游沉积物的重矿物组成具有极好的相关性,指示其来源与长江有关。而长江口外悬浮物中赤/磁铁矿相对富集,可能是强潮作用导致的中等密度重矿物再搬运和扩散的结果。值得关注的是,在舟山群岛附近站位悬浮物样品中发现了铬铁矿的异常富集,推测与海区人类生产活动有关。长江口悬浮重矿物颗粒绝大部分为粗粉砂—极细砂,富集在悬浮物中的较粗粒级(Φ<D_(0.5))中,主要由径流携带搬运。不同水层悬浮物中不同类型重矿物的粒径无明显差异,受沉降差异的影响小。

河口细颗粒泥沙与微塑料异质聚集的环境效应理论研究进展

近年来微塑料污染给全球生态环境带来的危害与威胁已不容忽视,由于水环境与水动力条件改变,大量微塑料随水流迁移至河口会与细颗粒泥沙相遇碰撞而发生异质聚集,显著改变各自输移行为,进而影响颗粒物的归趋,并对环境中其他要素产生影响。为进一步梳理并明晰泥沙与微塑料异质聚集的驱动因素、聚集输移特征与机理及其环境效应,本文结合近年国内外研究动态,探讨并总结河口细颗粒泥沙与微塑料异质聚集的驱动因素及其环境效应,充实了泥沙及其聚集物的环境效应理论,拓展延伸理论研究维度,从宏观、介观、微观层面提出了异质聚集环境效应的评估指标体系。本研究有助于丰富与深化环境泥沙及其环境效应的理论体系,可为强化河口水环境治理技术、提升水污染防控水平和能力提供理论支撑。

塔河下游高含沙浑水絮凝沉降试验研究

细粒悬移质高含沙浑水对微灌系统的淤堵一直困扰着区域节水灌溉的推行和农业节水能力的提升。以典型的塔里木河高含沙浑水为例,选用5种不同浓度的絮凝剂,以泥沙沉降比、淤积泥沙的体积、上清液浊度、处理成本等参数为指标,应用层次分析法及熵权法耦合得到各参数综合权重,优选去除细粒泥沙的最佳组次。试验结果表明,考虑絮凝沉降效果、絮凝剂成本、泥沙浑浊液的浊度和絮凝物的体积等因素,阴离子聚丙烯酰胺PAM(-)沉降效果最好;泥沙浓度为12%,PAM(-)的添加量为0.01 g/L为试验组次最优。试验结果可为塔河中下游灌区高含沙浑水絮凝沉沙提供参考。

神狐海域高饱和度天然气水合物储层特征及其分布

2017年,中国地质调查局在南海北部神狐海域进行了水合物试验开采,累计产气30.9×10^(4)m^(3),平均日产超5000 m^(3),甲烷含量最高达99.5%,实现了水合物勘察领域的历史性跨越。在水合物试验开采前,精细剖析研究区的测井数据和地震资料,并通过对研究区的区域地质背景和钻井岩芯样品的分析研究,含水合物地层的沉积、断裂、气体成分、碳同位素等特征以及水合物饱和度数据分析,总结研究区高饱和度水合物的储层特征及分布规律。结果表明:①研究区中—高饱和度水合物主要分布在迁移峡谷群的峡谷脊部,而低饱和度水合物站位则主要分布在峡谷群的谷底位置;②海底峡谷水道是陆源物质向深海运移的重要通道,研究区浊积水道和天然堤发育,与水合物富集成藏密切相关;③研究区高饱和度水合物层对应的电阻率和声波速度值显著升高,而中子孔隙度、密度和自然伽马值则有所降低;④高饱和度水合物在地震反射剖面上具有似海底反射(BSR)、穹状反射和模糊杂乱反射特征,BSR之下气烟囱和断裂通道发育,碳氢气体容易运移到温度和压力稳定区域形成高饱和度水合物储集层;⑤研究区水合物聚集和赋存的地层沉积骨架主要为细粒沉积,水合物以均匀颗粒和扩散的形式分布于沉积物中;⑥研究区水合物气源主要为混合成因气,热成因气通过断裂、裂隙、气烟囱构造向浅层运移,降解并与原位生物气混合为水合物形成共同提供气源。

改良斜管沉砂和旋流除砂在汉江中下游原水预处理中的应用

汉江承担着重要的水资源供应任务,其下游含有较多粒径在200μm以下的微细砂,给水厂处理系统带来了一系列问题。以汉江中下游原水迁改工程为例,介绍了“改良斜管沉砂+旋流除砂”工艺在工程中的应用情况,并通过旋流除砂工艺对废水进行除砂回用,形成了一套较好的微细砂沉降去除及废水回收利用工艺,既满足了标准要求,又实现每天节约水量约1.7‰,为含微细砂预处理设计提供经验。

气化细渣强化微细粒高岭石沉降研究

探索了不同pH溶液环境和不同絮凝剂用量时煤气化细渣(CGFS)对高岭石沉降的影响规律。研究发现,CGFS在多种溶液环境中均可以强化微细粒高岭石的沉降。在酸性条件中,CGFS表面荷正电,与表面荷负电的微细粒高岭石更易凝聚。当pH为7时,上清液浊度由56754 NTU降至27918 NTU;同时CGFS可以强化阴离子型聚丙烯酰胺对高岭石的絮凝沉降效果,上清液浊度可由8217 NTU降低至2020 NTU。

100μm砂粒在精细除砂一体化设备中的沉降模拟

对粒径100μm砂粒的精细除砂一体化设备进行计算流体力学模拟,考察了设备的流体力学特性和100μm颗粒的沉降规律。砂粒去除率的模拟值与理论计算值一致,证明模拟方法和结果的可靠性。模拟中100μm砂粒主要沉积在螺旋脱泥机尾部和出泥口,以及最下层斜板表面。气水比为0.1时,紧凑集成的沉降结构可以使细砂的去除率始终维持在96%以上,具有较好的除砂效果,其性能远优于国内同类产品;且能够消除出泥口开闭所带来的流体扰动,去除率波动更小、更稳定,可以避免小于200μm的颗粒物“穿透”预处理,干扰后续生化单元的稳定运行。

广西龙川地区水系沉积物地球化学特征与找矿潜力分析

为了研究广西龙川地区的水系沉积物地球化学特征和找矿潜力,在该地区开展1∶5万水系沉积物地球化学测量,通过对2111个样品分析结果进行统计分析,综合研究元素地球化学特征参数、元素平均含量地球化学分布特征及元素异常特征,圈定了11处水系沉积物综合异常。依据水系沉积物综合异常圈定及解释推断,结合本区矿产分布情况、成矿地质背景及区域成矿规律等,划分出了4个微细粒型金矿找矿远景区。并对找矿远景区找矿潜力进行分析,初步建立了研究区内微细粒型金矿地质-化探综合找矿方法。

Analysis on Suspended Sediment Deposition Rate for Muddy Coast of Reclaimed Land

A new expression for calculating suspended fine-sediment deposition rate is developed based on theoretic analysis and experiments. The resulting equation is applied to simulation of fine sediment deposition in the reclaimed land in the Hangzhou Bay, China. The hydrodynamic environment in this area is solved by use of a long wave model, which gives the 2D-velocity field and considers bathymetric changes due to fine sediment deposition. The expression is proved convenient to use in engineering practice, and the predicted deposition rate agrees with the annual data available from field measurements from the first year to the third year after the construction of the long groin as a reclaiming method.

四川盆地及其周缘下寒武统筇竹寺组细粒沉积特征与影响因素

四川盆地及其周缘下寒武统筇竹寺组页岩气资源丰富,已成为盆地重要的页岩气开发层段之一。受控于复杂的沉积格局,该区筇竹寺组粉砂质页岩纵向储层的岩相多样,非均质性强,制约了页岩气勘探和开发,因此亟需对其沉积特征、沉积相带和沉积模式开展研究。基于前期构造、层序地层研究认识,通过对矿物岩石、钻测井、地球化学和古生物等主要资料开展精细分析,明确四川盆地及其周缘早寒武世为海洋—古陆联合影响、水体深度中等、还原作用普遍发生的沉积背景,认为筇竹寺组主要沉积于滨岸相和陆棚相,并以陆棚相为主体,包括浅水陆棚亚相和深水陆棚亚相。通过对波浪和潮汐联合作用、海水蒸发作用、悬浮作用、上升洋流以及沉积古地貌等细粒沉积影响因素开展分析,结合沉积物空间分布特征,建立了四川盆地及其周缘筇竹寺组细粒岩沉积模式,即沉积初期差异沉降作用显著,层序厚度变化大,不同地区沉积特征及影响因素差异较大;沉积中期差异沉降作用不断减弱,层序厚度差异持续减小;沉积末期稳定沉降,进入“广盆”阶段,层序厚度趋于一致。