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1.
进一步验证和分析了作者早先提出的动床阻力关系,总结并提出了新的沙垄高度变化规律图,分析了它们与沙波阻力变化的关系,比较系统地揭示了不同水深、粒径条件下过渡区阻力变化规律.文中比较了作者及国内外其它五个重要的动床阻力关系,明确了这些公式的适用范围及限制条件.Einstein和钱宁的二个阻力关系只能用于过渡区,且后者只适用于粉细沙河床.李昌华的阻力关系可用于过渡区及低能态区.Engelund的阻力关系可用于一般沙质河床的低能态和高能态条件,但缺乏过渡区规律,对粉沙河床预报将系统偏小而对沙卵石河床则反之.Hayashi的阻力关系不适用于比降平缓的平原沙质河流.经验证和比较,作者的阻力公式适用于三个能态区各种水流强度及不同水深、粒径的情况,适用范围广泛,预报精度较高. 相似文献
2.
郑州至新郑机场城际铁路新郑机场站工程基坑开挖范围内地层条件复杂,砂性土与粘性土互为透镜体,开挖范围内主要为粉土、粉砂、粉质粘土,属黄土类地层,渗透性能差,若降水井施工质量差,抽不出水且容易带走细颗粒,开挖时又容易发生流砂。对此类复杂地层的降水设计应充分考虑地层条件、围护结构的特性,保证将水位降至开挖面以下,同时避免流砂、管涌、突涌的发生,确保基坑开挖安全。在采用三维数值模拟分析场区水文地质渗流情况的基础上,进行降水设计,并采取有效的降水井施工技术措施,实践证明取得了良好的降水效果。 相似文献
3.
The problem of predicting dependence of constant pressure batch dewatering of particulate suspensions on feed solids concentration is considered. Scaling transformations which demonstrate that evolution in the cake consolidation stage of dewatering is governed by an underlying self-similar behavior are proposed. The self-similar master curve, which can be obtained using only one set of experimental dewatering data obtained with a feed suspension having solids concentration above the gel point, is employed for estimating dependence of key dewatering process parameters on feed solids concentration. Using the parameter estimates in a Darcy's law based dewatering model, it is shown that the complete evolution of dewatering for a desired feed solids concentration can be predicted with reasonable accuracy. The approach is simpler to implement in comparison to available pressure filtration models, which require several suspension characterization experiments. 相似文献
4.
深基坑降水中不同的地质模型有限元应用研究 总被引：2，自引：0，他引：2
分析水-土耦合场相互作用时,将岩土视作弹塑性材料。在非线性本构关系下,考虑渗透作用,得出岩土体有限元方程,建立了基坑降水的三维水-土耦合的数学模型。对基坑降水中不同的地质模型潜水、承压水及有越流补给和实际工程条件井管、过滤管、止水帷幕分别进行了计算处理,并以武汉国际证券大厦降水工程为实例,对其降水过程进行了三维有限元计算。应用三维数值模拟方法,能很好地模拟基坑防渗帷幕、非均质和各向异性、承压-无压等一些解析法难以处理的实际工程条件和地质模型。 相似文献
5.
Joanna C. Curran 《Sedimentary Geology》2007,202(3):572-580
It is generally accepted that a gravel-bed river will aggrade if the supply of sediment to the river is increased. In a series of flume experiments using constant discharge and gravel feed rate, sand feed rates were increased to 6.1 times that of gravel. The slope of the bed decreased with increasing sand supply, indicating that the increased sediment load could be transported at the same rate due to a decrease in shear stresses. These results extend previous experiments to a wider range of boundary conditions. A recent surface transport model is used to predict the changes in bed composition and transport using the same sediment supply composition and feed rates as in the laboratory experiments. This model reasonably predicts a decrease in the reference shear stresses of the sand and gravel fractions as the sand supply is increased. An increase in sand supply can increase the mobility of gravel fractions in the stream bed, which can lead to bed degradation and preferential evacuation of these sediments from the river. 相似文献
6.
Michael Denis M. Guiraud M. Konat�� J.-F. Buoncristiani 《International Journal of Earth Sciences》2010,99(6):1399-1425
Subglacial deformation is crucial to reconstructing glacier dynamics. Sediments associated with the Late Ordovician ice sheet
in the Djado Basin, Niger, exhibit detailed structures of the subglacial shear zone. Three main types of subglacial shear
zones (SSZ) are discriminated. The lowermost SSZ, developed on sandstones, displays Riedel macrostructures and cataclastic
microstructures. These resulted from brittle deformation associated with strong glacier/bed coupling and low pore-water pressure.
Where they developed on a clay-rich bed, the overlying SSZ display S–C to S–C′ fabrics, sheath folds, and dewatering structures.
These features indicate high ductile shear strain and water overpressure. On fine-grained sand beds, the SSZ exhibit homogenized
sand units with sand stringers, interpreted as fluidized sliding beds. The succession of subglacial deformation processes
depends on fluid-pressure behavior in relation to subglacial sediment permeability. Fluid overpressure allows subglacial sediment
shear strength and ice/bed coupling to be lowered, leading to ice streaming. 相似文献
7.
8.
Yosry A. Attia 《International Journal of Mineral Processing》1983,10(3):173-181
One of the main usages of ball clays is in the pottery industry. However, in order to transport the clay suspensions from the mine site, some distance away from the consumer, dewatering of the clay suspension must be performed. The main restriction is that any dewatering treatment must not interfere in obtaining deflocculated, free flowing suspensions required by the pottery manufacturer.Investigations in the flocculation/deflocculation of these clay suspensions, resulted in finding a technique capable of achieving both requirements. The technique employs flocculation by an anionic flocculant in the presence of 10 mM of magnesium sulfate, thus achieving the dewatering step. When the magnesium sulfate was removed from the flocculated suspensions by simply washing the filter cake, good deflocculation of the clay suspension was achieved at alkaline pH. The role of MgSO4 in the flocculant adsorption/flocculation, and subsequently in the flocculant desorption/deflocculation, was discussed. 相似文献
9.
Interpreting flash flood palaeoflow parameters from antidunes and gravel lenses: An example from Montserrat,West Indies 
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下载免费PDF全文 The wavelength of stationary water‐surface waves and their associated antidune bedforms are related to the mean velocity and depth of formative flow. In past published sand‐bed flume experiments, it was found that lens structures were preserved during antidune growth and change, and the dimension of the lenses was empirically related to antidune wavelength, and thus could be used to estimate flow velocity and depth. This study is the first to compare observations of formative flow conditions and resulting sedimentary structures in a natural setting, testing the previously published relationship at a field‐scale. Trains of stationary and upstream migrating water‐surface waves were prevalent during the flash flood in October 2012 in the Belham Valley, Montserrat, West Indies. Wave positions and wavelengths were assessed at 900 sec intervals through the daylight hours of the event within a monitored reach. The wave data indicate flow depths up to 1·3 m and velocity up to 3·6 m sec?1. Sedimentary structures formed by antidune growth and change were preserved in the event deposit. These structures include lenses of clast‐supported gravel and massive sand, with varying internal architecture. The lenses and associated low‐angle strata are comparable to sand‐bed structures formed from stationary and upstream migrating waves in flume experiments, confirming the diagnostic value of these structures. Using mean lens length in the event deposit underestimated peak flow conditions during the flood and implied that the lenses were preserved during waning flow. 相似文献
10.
D.R. Nagaraj L. McAllister P. Somasundaran 《International Journal of Mineral Processing》1977,4(2):111-129
The dewatering of stable phosphatic clay suspensions resulting from the processing of phosphate rock is a problem of much practical and theoretical significance. In order to investigàte this aspect, the sedimentation behavior of suspensions of major components of phosphatic slimes, or morphologically similar meterials, both separately and in appropriate combinations, was studied. Systems which behaved very similarly to phosphatic slimes were termed “model systems”. Study of these model systems revealed that the minerals montmorillonite and attapulgite, with their special properties — morphology, swelling, ion exchange capacity, surface charge, and viscosity — were responsible for the behavior of phosphatic slimes.Mechanisms by which coarse particles and micro air bubbles enhance the dewatering of the phosphatic slimes are reviewed. In both cases, creation of paths for water seepage as a result of their movement is considered to be mainly responsible for the enhanced subsidence of the slurry. 相似文献
11.
Computation of the grain-size distribution of the suspended load above a sand bed must take into consideration: (1) sorting processes from the bed to the bed layer and (2) sorting between the bed layer and suspension. Grain-size distributions of the bed layers above sand beds of three different types have been computed in this work, both by the Einstein and the Gessler methods. Using these as references, suspended load distributions have been obtained in each case by the Rouse suspension equation. A new formula has also been developed in partial modification of Hunt's method for direct computation of bed load and suspended load from a bed's grain-size distribution and flow parameters. Comparison of the computed data with actual observations in laboratory flumes show that no one method is particularly superior to the others, but the present method is advantageous because it affords direct computation of the suspended load from a bed's grain-size distribution, without going through an intermediate stage (bed load). The possible sources of error in each of the methods have been discussed. 相似文献
12.
复合加筋排水褥垫加固路基有限元计算 总被引：1，自引：0，他引：1
复合加筋排水褥垫是针对沿海缺砂地区开发的,具有水平排水与加筋作用的一项新型专利技术,可取代软基加固中的排水砂垫层。采用二维平面应变Biot固结有限元模型对复合加筋排水褥垫软土路堤进行了数值模拟,结果表明复合加筋排水褥垫可以满足水平排水要求,另外与传统的水平排水砂垫层相比,该技术可降低地基附加正应力和超孔隙水压力,有效抑制路基侧向变形的发展,减小路基沉降与不均匀沉降,提高路基稳定性,加筋效果显著。 相似文献
13.
HOWARD D. JOHNSON 《Sedimentology》1977,24(3):389-411
Water escape structures are abundant in the Grønnes Formation, a tectonically undeformed, late Precambrian shallow marine sandstone deposit in North Norway. Trough cross-bedded sandstones of the current-dominated shallow marine environment were frequently liquefied, presumably due to recurring seismic shocks. Subsequent dewatering resulted in deformation of the cross-bedding and the formation of convolute lamination. A three-fold upward vertical sequence developed where liquefaction occurred below the sediment-water interface: convoluted bed → passively deformed bed → undeformed bed. The passively deformed bed resulted from differential subsidence of a relatively plastic bed above a liquefied bed. It is characterized by anticlinal ridges and sand volcanoes at the sites of vertical sediment extrusion, and synclinal troughs at the sites of lateral sediment movement. Liquefaction may have been induced by either tectonic (earthquake shocks) or non-tectonic (storm-induced microseisms) trigger mechanisms, or a combination of both. The restriction of such a high frequency of water escape structures to deposits immediately above a gentle regional unconformity lends support for a tectonic trigger mechanism. 相似文献
14.
The effect of wind speed and bed slope on sand transport 总被引：7，自引：0，他引：7
This paper reports on a wind tunnel study of the effects of bed slope and wind speed on aeolian mass transport. The use of a sloping wind tunnel has enabled estimation of the friction angle α to be about 40° for saltating particles in the range 170–540 μm. A formula relating dimensionless mass transport to friction speed and bed slope is proposed, and mass transport data for five uniform sand samples and one non-uniform sand sample are shown to fit the equation well. In particular, the relationship reveals an overshoot in mass transport slightly above threshold collisions, a feature also evident when previous experimental data is re-examined. As the number of mid-air collisions between the saltating particles increases greatly with wind speed, the overshoot may occur as a result of increasing energy losses resulting from the collisions. Finally, it is demonstrated that data for saltating snow shows a similar overshoot in the dimensionless transport rate. 相似文献
15.
工程上通常用降水的方法来保证基坑开挖的顺利进行,但是基坑降水会改变基坑周围土的工程性质,所以基坑周围的建筑物必然会受到很大影响,如出现不均匀沉降、建筑物开裂等。济南西客站站房基坑施工降水对其附近的京沪高速铁路路基的沉降产生了很大影响。本文针对此问题,基于在宽大站场条件下基坑降水对其周围的桩板复合地基沉降影响的理论尚未成熟,对基坑降水对复合地基沉降的影响进行了研究。本文选取济南西客站断面DIK419+250作为研究对象,现场采用沉降板进行路基表面的沉降变化监测,采用分层沉降仪进行路基深层土层的沉降变化监测,采用剖面沉降管进行路基横断面的沉降变化监测,并将各监测结果整理得出站房基坑降水对高铁路基表面沉降的影响、对路基深度方向土层沉降的影响、对路基横断面方向沉降的影响; 又根据现场的工况采用有限元软件进行数值模拟计算分析; 最终将数值模拟计算结果与现场监测所得结果进行对比,总结了基坑降水对复合地基沉降的影响。通过对比分析结果得出以下结论:(1)复合地基的加固会使路基沉降受基坑降水的影响减小; (2)复合地基的变桩长区域受基坑降水影响较大; (3)基坑降水对路基加固区沉降的影响大于对下卧层沉降的影响。 相似文献
16.
根据城市地下工程特点，结合武汉市在富水砂层中修建的地下过街道实例，分析了地面降水所采取的降水方案，同时，也对本工程深井降水对地表、周围建筑物沉降做了全面的观察分析，观察结果分析表明，该方案能充分满足工程需要。 相似文献
17.
J.R.L. Allen 《Sedimentary Geology》1980,26(4):281-328
Sand waves are large flow-transverse bedforms coupled to oscillatory boundary-layer currents of tidal origin. Like the much smaller ripple-marks generated by short-period wind waves, sand waves are observed to grow more asymmetrical with increase in the time—velocity asymmetry of the governing currents, that is, with increase in the steady component of flow (mass-transport strictly related to wave-motion) relative to the periodic component. Wind-wave ripple-marks owe their origin directly to a mass-transport component dependent on bed-curvature, which arises naturally wherever a sufficiently powerful oscillatory flow is imposed on a deformable grain boundary. This curvature-related current, flowing from troughts to crests on the bed, drifts grains mobilized by the periodic component into transverse bands. Sand waves may also owe their origin and growth to an unstable interaction within tide-generated oscillatory boundary layers between the mobile bed and a curvature-related mass-transport.Sand-wave internal structure apparently depends on the strength and degree of asymmetry of the governing currents. Relatively symmetrical forms associated with currents of low asymmetry are expected to contain comparatively small, intricately related herring-bone or climbing cross-bedding sets. Relatively asymmetrical currents shape sand waves with one side so steep that large-scale flow separation is inevitable. The predominant structure is then expected to be long avalanche bedding broken into sets by mud drapes and bioturbated zones representing periods of gentle flow, and/or by erosional discontinuities recording tidal reversals. The expected structures have parallels in the stratigraphic record and amongst modern sand waves. 相似文献
18.
A high-resolution side-scan sonar survey of the lake bed off the Keweenaw Peninsula, Lake Superior, demonstrates that bottom currents are affecting lake bed morphology at depths up to 240 m. Numerous lineations which run parallel to the shore appear to be sand ribbons. A field of sedimentary furrows which occurs in one area demonstrates the long-term directional stability of the near-bottom flow. Large (100–300 m in diameter, 2–5 m deep), unusual ring-like or arcuate depressions are common throughout the western half of Lake Superior. These rings themselves do not appear to have been formed by bottom currents, but may have developed as water was released by the rapid compaction of glacial sediments which underlie the lake bed. Off the Keweenaw Peninsula the forms of the rings have been modified by bottom currents. The bottom currents which have modified the lake bed are probably generated when storms cross the lake at times when it is poorly stratified. 相似文献
19.
风积沙轻骨料混凝土冻融损伤及寿命预测研究 总被引：8，自引：0，他引：8
基于浮石轻骨料混凝土为基础, 将不同质量的风积沙作为细骨料替代部分河砂, 研究风积沙轻骨料混凝土冻融损伤机理及服役寿命. 通过室内快速冻融循环试验, 定量分析风积沙轻骨料混凝土的抗冻耐久性能. 在整个冻融循环期内, 相对动弹性模量的变化规律可分为直线下降阶段、 直线+曲线下降阶段、 曲线下降阶段. 以此为基础, 建立轻骨料混凝土直线和曲线双段式相对动弹性模量衰减方程, 依据5组混凝土的抗冻试验结果对方程进行了验证, 并预测其在西部地区的服役寿命. 结果表明: 直线和曲线双段式的相对动弹性模量衰减方程能够准确的反应混凝土冻融损伤劣化规律. 风积沙最优替代率为20%, 可以满足25 a的使用寿命. 损伤模型可为沙漠地区混凝土使用提供一定的理论依据. 相似文献
20.
首钢京唐钢铁联合有限责任公司是一个在曹妃甸岛上吹填砂造地形成的场地上新建的大型现代化精品钢铁基地。分析了该建筑场地的地质环境情况和常用的基坑支护、降水方法,对该建筑场地上的建（构）筑物的基坑支护、降水设计及方案选择提出建议。 相似文献