非开挖铺管阻力新计算模型及减阻措施

在非开挖工程中,计算出当前工艺条件下的铺管阻力、选择正确的铺管方法是整个工程成败的关键。通过数学解析方法,重点考虑回拖过程中管道弯曲段弯曲阻力的影响,建立了铺管阻力新计算模型。实践证明,该模型计算值与实测值仅相差6%,比较符合实际,提出的减阻措施对现场施工也有一定的指导意义。     

Depositional processes,bedform development and hybrid bed formation in rapidly decelerated cohesive (mud–sand) sediment flows

Flows with high suspended sediment concentrations are common in many sedimentary environments, and their flow properties may show a transitional behaviour between fully turbulent and quasi‐laminar plug flows. The characteristics of these transitional flows are known to be a function of both clay concentration and type, as well as the applied fluid stress, but so far the interaction of these transitional flows with a loose sediment bed has received little attention. Information on this type of interaction is essential for the recognition and prediction of sedimentary structures formed by cohesive transitional flows in, for example, fluvial, estuarine and deep‐marine deposits. This paper investigates the behaviour of rapidly decelerated to steady flows that contain a mixture of sand, silt and clay, and explores the effect of different clay (kaolin) concentrations on the dynamics of flow over a mobile bed, and the bedforms and stratification produced. Experiments were conducted in a recirculating slurry flume capable of transporting high clay concentrations. Ultrasonic Doppler velocity profiling was used to measure the flow velocity within these concentrated suspension flows. The development of current ripples under decelerated flows of differing kaolin concentration was documented and evolution of their height, wavelength and migration rate quantified. This work confirms past work over smooth, fixed beds which showed that, as clay concentration rises, a distinct sequence of flow types is generated: turbulent flow, turbulence‐enhanced transitional flow, lower transitional plug flow, upper transitional plug flow and a quasi‐laminar plug flow. Each of these flow types produces an initial flat bed upon rapid flow deceleration, followed by reworking of these deposits through the development of current ripples during the subsequent steady flow in turbulent flow, turbulence‐enhanced transitional flow and lower transitional plug flow. The initial flat beds are structureless, but have diagnostic textural properties, caused by differential settling of sand, silt and cohesive mud, which forms characteristic bipartite beds that initially consist of sand overlain by silt or clay. As clay concentration in the formative flow increases, ripples first increase in mean height and wavelength under turbulence‐enhanced transitional flow and lower transitional plug‐flow regimes, which is attributed to the additional turbulence generated under these flows that subsequently causes greater lee side erosion. As clay concentration increases further from a lower transitional plug flow, ripples cease to exist under the upper transitional plug flow and quasi‐laminar plug flow conditions investigated herein. This disappearance of ripples appears due to both turbulence suppression at higher clay concentrations, as well as the increasing shear strength of the bed sediment that becomes more difficult to erode as clay concentration increases. The stratification within the ripples formed after rapid deceleration of the transitional flows reflects the availability of sediment from the bipartite bed. The exact nature of the ripple cross‐stratification in these flows is a direct function of the duration of the formative flow and the texture of the initial flat bed, and ripples do not form in cohesive flows with a Reynolds number smaller than ca 12 000. Examples are given of how the unique properties of the current ripples and plane beds, developing below decelerated transitional flows, could aid in the interpretation of depositional processes in modern and ancient sediments. This interpretation includes a new model for hybrid beds that explains their formation in terms of a combination of vertical grain‐size segregation and longitudinal flow transformation.     

Summary and Prospects of Numerical Simulation Research of the Atmospheric Boundary Layer

As an important bridge between the underlying surface and the free atmosphere, the atmospheric boundary layer is not only closely related to the development of various weather processes, but also plays a key role in local and regional weather and climate changes. In view of the complexity of the atmospheric boundary layer, the numerical simulation of the atmospheric boundary layer has always been a hotspot and difficulty in the numerical simulation research of the atmosphere. In this paper, the three numerical model development stages of the atmospheric boundary layer in recent decades were summarized and the important advances in arid and semi-arid areas, Tibet Plateau, urban complex underlying surface, and special typhoon boundary layer were reviewed. At present, there are still five scientific problems to be solved urgently, including cloud and boundary layer interaction, boundary layer parameterization, model resolution, boundary layer data assimilation and boundary layer development mechanism. Moreover, it was pointed out that in this field we need to strengthen the understanding of different types of atmospheric boundary layer processes, boundary layer bottom and top interface exchange, boundary layer development mechanism in special regions, improve boundary layer parameterization scheme and give full play to the advantages of LES in boundary layer simulation.     

波流边界层水沙运动数值模拟——II.泥沙运动模拟

为解析波流边界层内泥沙运动,建立了基于水动力-泥沙-床面互馈过程的波流边界层1DV泥沙数学模型,可用于模拟不同床面形态下粉沙-沙的含沙量过程。床面形态模块提供床面形态类型和相应参数;给出了平底和沙波床面粗糙高度和泥沙扩散系数的确定方法;采用了适宜粉沙及沙的制约沉速、底部参考浓度和起动剪切应力等公式;引入含沙量层化效应和制约沉降反映水动力与泥沙之间的相互影响。水槽试验资料验证表明,建立的模型较好地模拟了不同床面不同波流组合条件下的含沙量剖面。在此基础上,讨论了不同床面含沙量剖面模拟方法的差异,指出床面形态是决定含沙量变化的重要因素之一,仅通过改变床面粗糙高度不足以反映漩涡沙波床面的含沙量剖面特征。该模型可为研究波流边界层内泥沙运动和物质输运提供工具。     

青藏高原不同高寒生态系统类型下多年冻土活动层水热过程差异研究

基于青藏高原北麓河地区高寒草原、高寒沼泽草甸和高寒草甸生态系统下多年冻土活动层水热过程的监测数据,对活动层水热过程特征开展了相关研究。研究结果显示,在活动层厚度、冻融时间、持续时间以及活动层土壤水分含水量分布方面,不同的高寒生态系统下活动层的上述属性特征差异明显。高寒草原下多年冻土活动层厚度最大,土体开始融化的时间最早,每年持续融化的日数也最长;高寒草甸最小,高寒沼泽草甸居中。高寒草原下活动层土壤含水率从上到下逐渐增加,水分基本集中在活动层的中下部分;高寒沼泽草甸下活动层土壤水分的分布情况相对比较均衡;高寒草甸下活动层土壤含水率分布呈现从上到下逐步减少的模式,越靠近地表土壤含水率越大。对监测数据的进一步分析发现,不同的高寒生态系统下,近地表地温与气温温差累计值、近地表土壤有机质含量、n因子特征以及近地表地温标准差统计特征都具有明显的区别。研究分析表明,多年冻土活动层水热过程特征与高寒生态系统类型具有明显的关联性,高寒生态系统会影响近地表能量通量,从而使地-气热量交换产生差异,这一差异又将改变活动层土壤温度、水分分布特征及其动力学过程。     

Sediment suspension dynamics and a new criterion for the maintenance of turbulent suspensions

The vertical component of the turbulent flow acceleration term, , is used to determine the net positive vertical force that may support a suspended sediment load. A dimensionless criterion, Λ, is proposed for the maintenance of suspension, defined as the ratio of the maximum vertical turbulent stress to immersed weight of the suspended load above a unit bed area. In order that a suspension be maintained: where v ′ is instantaneous vertical turbulent velocity, σ and ρ are solid and fluid densities, respectively and m is the suspended load dry mass. The Λ criterion is dynamic, being a ratio of stresses and is analogous in this respect to Shields dimensionless stress criterion, θ, for the initiation of bedload motion. The new criterion is successful in predicting the maintenance of steady-state suspended sediment transport in open channel shear flow and deposition from non-uniform particulate density flows of wall jet type.     

基于涡轮-转阀驱动的小直径水力振荡减阻器设计研究

小直径水平钻井在钻探中应用广泛,可以有效提高效率,降低成本。但钻柱与井壁之间存在较大的摩阻,导致出现托压现象,影响钻压传递,进而严重影响钻进效率。本文研究了一种基于涡轮-转阀驱动的小直径水力振荡减阻技术,通过振荡器的轴向振动,降低钻柱在钻井过程中所受阻力,提高钻进效率。文章从振动减阻器的研究现状、结构设计和实验结果等方面做了系统分析,得到实验结论:当泵排量相同时,振动频率越小,振幅越大,此时转速对压降影响较小。在转速保持不变的情况下,泵排量越大,振幅越大,且压降明显增加。这一研究成果可为该技术的发展提供一定参考。     

石膏岩中粘土矿物提取的一种新方法及在古气候重建中的应用

目前通用的前处理方法难以从石膏岩中有效提取足量粘土矿物进行测试分析,针对这一技术问题,本研究改进了原有的粘土矿物分析前处理方法,采用新的试剂乙二胺四乙酸二钠（以下简称EDTA）溶解石膏岩,释放其中所含的粘土矿物,有效提高石膏岩中粘土矿物的提取能力。本文以位于青藏高原东北缘西宁盆地塔山剖面（36.5°N,101.8°E） 始新世祁家川组、洪沟组和马哈拉沟组的9个石膏岩样品为研究对象,通过详细对比试验确定了EDTA的溶解条件,明确了采用EDTA提取石膏岩中粘土矿物的实验流程和方法,并探讨了溶解过程对粘土矿物的影响。实验结果表明,EDTA对石膏岩的最佳溶解条件为：温度=100℃、pH=10~12、浓度=0.32mol/L,改进后的前处理方法提取粘土矿物质量是原来的1~25倍,且不破坏粘土矿物的晶型结构。使用EDTA溶解法提取9个样品中的粘土矿物经X射线衍射分析结果表明,西宁盆地始新世石膏岩样品中粘土矿物含量以伊利石为主（62%~90%）,含少量绿泥石（3%~17%）,蒙脱石（含伊蒙混层矿物）含量变化较大（0~35 %）。粘土矿物组合特征反应该区域始新世以干旱气候为主,盆地内石膏岩地层形成时期的气候环境可能存在一定程度的干湿波动现象。     

潮滩剖面形态与泥沙分选研究进展

潮滩剖面形态与多组分泥沙分选是海岸动力学与河口、海岸地貌学的重要研究内容,对保持生物多样性、研究沉积历史和沿海工程评估等具有重要的实际意义。从现场观测、理论解析和数值模拟等方面,归纳了在潮滩剖面形态特征与多组分泥沙分选方面研究的主要进展。回顾了潮滩剖面形态分别在潮流和波浪主导下的经典理论解析解,剖析了包括潮流、波浪泥沙来源及特性等主要影响因子以及植被、海平面上升、围垦工程等其他影响因子对潮滩剖面形态水平向、垂向泥沙分选过程的作用机理,同时提出了考虑水动力、生物作用、人类活动等多因子耦合作用下潮滩演变研究以及定量化预测方向的若干亟待解决的科学问题。     

氨氮在黏土防渗层中渗透和运移规律试验研究

对太湖疏浚污染底泥中含有的一种主要污染物--氨氮在底泥堆场黏土防渗层中的渗透和运移规律进行了试验研究。在室内通过渗透模拟试验和动态土柱试验,测定了不同固结压力作用下黏土的渗透系数和弥散系数,通过静态吸附试验测定了黏土对氨氮的吸附系数。试验结果表明,底泥堆场下部的黏土防渗层对底泥中的氨氮具有较强的吸附和阻隔能力。     

云南压实黏土层对油类污染物的防渗性能实验研究

目前在压实黏土层(CCL)应用于油类污染物的防渗工程设计中,以水在CCL中的渗透系数低于10-7 cm/s为依据,该依据可能存在偏颇。文中以0#柴油和93#汽油作为典型油类污染物,在云南CCL中进行油相水相交替渗流实验。结果表明：(1)不同渗透压力下,水在云南CCL中的渗透系数为(0.41~2.52)×10-8 cm/s,云南黏土压实后可作为天然防渗衬层。(2)0#柴油和93#汽油穿透饱水的云南CCL时,存在临界水力梯度,分别为0.05和0.02 MPa;一旦突破临界水力梯度,CCL的渗透性急剧增大,0#柴油和93#汽油在CCL中的渗透系数较水在CCL中的高出1~3个数量级。(3)水相驱替0#柴油和93#汽油的过程中,CCL的渗透系数为10-7～10-6 cm/s;被油浸透过的CCL不能继续作为防渗衬层使用。(4)针对油类污染物的CCL防渗工程设计,以水在CCL中的渗透系数低于1.0×10-7 cm/s为标准是不适用的,需要提高CCL防渗的设计等级。     

波流边界层水沙运动数值模拟——Ⅲ.底部高含沙层模拟

为了解析底部高含沙层特征,研究了物理影响机制和时均含沙量剖面。采用波流边界层1DV泥沙数学模型,结合试验资料,通过设置不同的计算工况进行了影响因素敏感性分析;在此基础上,提出波浪相关的时均泥沙扩散系数分布,考虑主要影响机制,推导了基于边界层物理过程的波浪作用下时均含沙量剖面表达式。结果表明,底部高含沙层与波浪边界层密切相关,是受水动力和床面形态综合影响的结果。仅建立高含沙层与水动力或床面形态的单一关系是有局限性的。含沙量层化效应和制约沉速对底部高含沙层具有重要影响。提出的平底床面含沙量剖面表达式为幂函数-Rouse-指数分布,漩涡沙波床面为指数-幂函数-Rouse分布。预期可应用于二维和三维泥沙数值模拟。     

波浪作用下黄河口粉土液化与“铁板砂”形成机制的模拟试验研究

通过室内水槽试验,观测波浪作用下土体产生的振荡现象,分析土体内孔隙水压力的变化及波浪作用后土体强度变化特征,研究了波浪荷载作用下黄河口粉土粒径粗化和“铁板砂”的形成过程。试验及讨论结果表明：在波浪作用下上层粉土体大部分时间处于液化状态;由液化土形成的振荡土层与下部土层之间形成“W”型的滑动面,振荡土层的厚度随着波浪作用时间的增加而变小;细粒物质从振荡土层中的骨架中脱离进入水体中,并在土体表层形成一层以黏粒为主的絮凝状沉积物,其厚度随波浪作用时间的增加而增加,在土体停止振荡前达到最大值;土体液化是“铁板砂”形成的必要条件,而波浪引起的液化土体振荡则使“铁板砂”的形成成为可能。     

长江三角洲北翼第一硬土层理化特征及其地质成因

在长江河口两翼广泛分布第一硬土层（FHSL）,研究其形成机制及工程地质特性对工程建设具有很好的指导意义。根据调查资料（钻孔935个,累计进尺42128 m）和试验资料,首次精确确认了长江河口北翼第一硬土层分布界线,研究了第一硬土层的形成年代、粒度特征、地球化学特征、工程地质特性等。研究表明：第一硬土层形成年龄为20 ~ 11 ka B.P.（多个光释光和14C测年资料） ;硬土层含水率随深度的增加有增大的趋势,表明气候自下向上逐渐变凉和变干;第一硬土层的颗粒级配、粒度分布频率曲线、C-M沉积图等特征显示,第一硬土层主要由粉砂、极细砂和粘土粒级组成,样品的粒度频率曲线主要呈单峰分布,反映出物质沉积前所受搬运营力性质单一,土体颗粒沉积以均匀悬浮占绝对优势,沉积环境是一种相对稳定的低能环境。第一硬土层的发育受气候控制,大致可以分为3个阶段：第1阶段(20 ~ 15 ka B.P.)为沉积与成土交替作用时期,且以沉积作用为主,硬土层剖面厚度主要受该阶段控制,至末次盛冰期结束;第2阶段(15 ~ 11 ka B.P.)为暴露成土期,这时洪水不能形成越岸沉积,加积作用基本停止,硬土层厚度不再明显增加,已形成的第一硬土区域受到频繁变迁的分合河网的侵蚀切割,形成多条不规则古河道和台地,硬土层逐渐脱水成陆,经历了风化成壤的过程;第3阶段(11 ka B.P. 至今)为淹埋期,随着全新世的到来,气候变暖,海平面不断上升,硬土层被其上覆的海相沉积层掩埋,成岩作用开始直到现今。土体易溶盐含量较高,为典型氯盐渍土类型,自下而上具有从低变高的趋势,为海相层覆盖硬土层以后成岩过程造成的。     

A field study of turbulence and sediment dynamics over subaqueous dunes with flow separation

This study examines flow, turbulence and sand suspension over large dunes in Canoe Pass, a distributary channel of the Fraser River delta, Canada. Dune morphology is characterized by a symmetrical shape and steep leeside slopes over 30°. Velocity was measured with an electromagnetic current meter and suspended sand concentration with four optical backscatter (OBS) probes. The general patterns of time-averaged velocity and sand suspension are consistent with previous studies, including an increase in mean velocity and decrease in turbulence intensity and sand concentration with height above the bed, reversed flow with high turbulence intensity and high sand concentrations in the leeside flow separation zone and an increase in near-bed velocity and sand concentration along the stoss side of the dune. Frequency spectra of near-bed velocity and OBS records from leeside separation zones are composed of two distinct frequencies, providing field confirmation of scale relations based on flume experiments. The low-frequency spectral signal probably results from wake flapping and the high-frequency signal from vortex shedding. The wake-flapping frequency predominates outside the separation zone and is linked to turbulent structures that suspend sand. Predictions from a depth-scale Strouhal Law show good agreement with measured wake-flapping frequencies. Cross-correlations of OBS records reveal that turbulent sand suspension structures advect downstream at 23–25° above the horizontal. These advection angles are similar to coherent flow structures measured in flumes and to sand suspension structures visualized over large dunes in the field.     

波流边界层水沙运动数值模拟——I:水动力模拟

波流边界层水动力模拟对研究波流相互作用和泥沙运动具有重要的理论意义和实践价值。开发了波流边界层1DV垂向一维水动力数值模型,可用于模拟漩涡沙波床面和平底床面水动力特征。模型的构建基于边界层控制方程,平底床面采用k-ε模型,沙波床面采用双层模型,提出了漩涡层和紊动扩散层交界面紊动动能和紊动耗散率表达式。试验资料验证表明,模型较好地模拟了波浪-水流-床面共同作用下的边界层水动力特征,包括波周期内不同相位流速分布、紊动动能、剪切应力等以及波致时均流速分布和波流相互作用下的时均流速分布等。根据所建模型,讨论了不同床面和波流组合条件下的水动力特征。该模型可为研究波流边界层内水动力特征提供工具。     

岩溶地下工程施工抽水诱发黏土层地面塌陷机理及临界条件探讨

岩溶地下工程施工抽水容易诱发地面塌陷工程事故,目前关于此问题的研究,主要针对砂性土层,较少涉及黏土层,但大量的抽水致塌事例发生在黏土层。本文分析施工抽水对界面上黏土性质、地下水动力条件的影响,并划分出Ⅰ、Ⅱ、Ⅲ三个影响区。依据“土-水”耦合作用,在Ⅰ、Ⅱ区建立非饱和黏土地面塌陷崩解作用模式及其判据,在Ⅲ区建立饱和黏土地面塌陷潜蚀作用模式及其判据。为了应用于施工抽水实践,推导出潜水非完整孔和承压水非完整孔抽水诱发地面塌陷的临界抽水流量表达式,并计算出南宁地铁工程场地地面塌陷的临界抽水量为17.97 m3?d-1。在场地内进行的现场抽水验证性试验的结果表明此临界抽水量具有一定的工程应用性及参考借鉴意义。      

GIS morphometric indicators for the analysis of sediment dynamics in mountain basins

Watershed management and headwater reconstruction programs require a reliable knowledge of sediment dynamics. Geographical Information Systems (GIS) provide the framework for the implementation of different complex techniques for the assessment of shallow landsliding and erosion processes in mountain basins. This paper presents some morphometric indicators aimed at erosion and sediment delivery analysis. The proposed indicators can be easily derived from medium to fine resolution Digital Elevation Models (DEM). Applications conducted in Eastern Italian Alps have shown the adequateness of the proposed approach to address erosion and sediment-related problems. The analysis considered the classification of sediment source areas with regard to their activity, the comparison between drainage basins having different morphological characteristics and the topographic control on sediment transport capacity, with a particular attention to the identification of channel reaches characterised by a low sediment transport capacity.     

Analysis of influencing factors of clay particle diffusion in electric double layer北大核心CSCD

双电层结构对研究黏土力学特性、冻土水分迁移等具有重要意义。为了探究不同影响因素对黏土颗粒扩散双电层电势分布的影响,借鉴Gouy-Chapman-Stern双电层理论,基于Nernst-Planck方程和Poisson-Boltzmann方程,利用数值软件COMSOL定量分析了温度、浓度、颗粒尺寸、颗粒形状以及溶液相对介电常数对扩散双电层电势分布的影响规律。研究表明：温度对电势分布的影响不明显,但随着温度以及Stern层厚度增加,黏土颗粒表面电势和Stern电势均增加;而随着溶液浓度以及相对介电常数减小,表面电势值增加;在矿物成分、表面电荷密度以及颗粒形状确定的情况下,尺寸对于扩散双电层电势分布的影响不显著;但颗粒的不规则形状对电势分布的影响较为明显,当颗粒形状存在夹角时,夹角处的表面电势远大于其他位置,且夹角越小,夹角处表面电势值越大。