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1.
Measurements of sand transport by wind on a natural beach   总被引：6，自引：0，他引：6  
Bagnold's (1954) and Kawamura's (1951) formulae may be used for the calculation of the sand movement on a natural beach, provided the shear stress velocity U* > 0·D4 m/s. Great discrepancies have been found between calculated and measured sand transport rates for U* < 0·D4 m/s, mainly because of the capillary forces acting on a wet beach. The measured critical shear velocity U*c at the beginning of sand movement on a clean dry beach agrees very well with that predicted by Bagnold's formula. On a dry beach where the sand grains are stuck together, U*c was found to be about 10% higher. On a wet beach U*c appeared to depend on the moisture content of the surface layer. Grain size is a determining parameter in the U*c-moisture content relation. When the angle a between the wind direction at sea and the dune face is between 15° and 85° the streamlines of the wind will bend in the vicinity of the dune face. In consequence this may influence the direction of sediment movement.  相似文献   

2.
Interactions between catchment variables and sediment transport processes in rivers are complex, and sediment transport behaviour during high‐flow events is not well documented. This paper presents an investigation into sediment transport processes in a short‐duration, high‐discharge event in the Burdekin River, a large sand‐ and gravel‐bed river in the monsoon‐ and cyclone‐influenced, semi‐arid tropics of north Queensland. The Burdekin's discharge is highly variable and strongly seasonal, with a recorded maximum of 40 400 m3 s?1. Sediment was sampled systematically across an 800 m wide, 12 m deep and straight reach using Helley‐Smith bedload and US P‐61 suspended sediment samplers over 16 days of a 29‐day discharge event in February and March 2000 (peak 11 155 m3 s?1). About 3·7 × 106 tonnes of suspended sediment and 3 × 105 tonnes of bedload are estimated to have been transported past the sample site during the flow event. The sediment load was predominantly supply limited. Wash load included clay, silt and very fine sand. The concentration of suspended bed material (including very coarse sand) varied with bedload transport rate, discharge and height above the bed. Bedload transport rate and changes in channel shape were greatest several days after peak discharge. Comparison between these data and sparse published data from other events on this river shows that the control on sediment load varies between supply limited and hydraulically limited transport, and that antecedent weather is an important control on suspended sediment concentration. Neither the empirical relationships widely used to estimate suspended sediment concentrations and bedload (e.g. Ackers & White, 1973) nor observations of sediment transport characteristics in ephemeral streams (e.g. Reid & Frostick, 1987) are directly applicable to this river.  相似文献   

3.
The relation between the crystallography of artificially abraded quartz sand grains and aeolian surface textures has been studied using an X-ray precession camera and the scanning electron microscope (SEM). Crushed Brazilian quartz was sieved to between 250 and 350 μm, eroded in a paddle wheel device which simulated aeolian action at 8 m s?1 for 3 h, and photographed with the SEM. A typical grain was selected and over 1100 photographs were combined to create a 3 × 3 m photomosaic; because of the large size, it was possible to observe and measure the angular and linear relations between the various features. After the c axis direction in the grain was determined by precession X-ray analysis, the most important aeolian features were related to the crystallography of quartz. The upturned plates or cleavage plates probably represent traces parallel to r(10ī1) and z(01ī1) cleavages in quartz. Blocky areas appear to be an expression of a cleavage parallel to m(10ī0). In addition, plate spacing on thirty-five experimental, modern, and ancient quartz sand grains is fairly constant. Assuming that abrasion in most sedimentary environments acts in the same manner with respect to quartz crystallography, much of the fine silt and clay in sediments and sedimentary rocks may be the result of cleavage following abrasion parallel to the r and z cleavage planes, while the less common blocky particles are probably the result of cleavage parallel to the m planes.  相似文献   

4.
再论花岗岩按照Sr-Yb的分类:标志   总被引：41，自引：14，他引：27  
张旗  金惟俊  李承东  王元龙 《岩石学报》2010,26(4):985-1015
2006年作者曾经按照Sr=400×10~(-6)和Yb=2×10~(-6)作为标志将花岗岩分为埃达克岩、喜马拉雅型花岗岩、浙闽型花岗岩和广西型花岗岩,在浙闽型中又分出南岭型(Sr100×10~(-6)和Yb2×10~(-6)),于是花岗岩被分为5类。Sr=400×10~(-6)和Yb=2×10~(-6)是根据阿留申群岛中的Adak岛的资料得出来的。本文统计了全球花岗岩6000多个数据(其中,埃达克型花岗岩为2810个,喜马拉雅型花岗岩636个,浙闽型花岗岩1183个,南岭型花岗岩1518个,广西型花岗岩142个,总共6289个),统计的结果,各类花岗岩的地球化学特征大致如下:(1)埃达克型花岗岩富Al_2O_3和Sr,贫Y和Yb,具较高和变化的铕异常,绝大多数样品的Sr300×10~(-6),Yb2.5×10~(-6)(当Sr=400×10~(-6)～600×10~(-6)时Yb值最大,Sr超过600×10~(-6),Yb降低至2×10~(-6)),Al_2O_3在14%～18%之间,Eu/Eu~*大多在0.6～1.2范围;(2)喜马拉雅型花岗岩贫Sr和Yb,具中等的Al_2O_3和变化的Eu/Eu~*,Sr300×10~(-6)和Yb2×10~(-6)(少数Sr300×10~(-6)),Al_2O_3为13%～17%,Eu/Eu~*为0.2～1.0;(3)浙闽型花岗岩贫Sr富Yb,Sr在40×10~(-6)～400×10~(-6)之间,Yb1.5×10~(-6),Al_2O_3和Eu/Eu~*的变化类似喜马拉雅型花岗岩,Al_2O_3为12%～17%,Eu/Eu~*为0.4～1.0;(4)南岭型花岗岩以很低的Sr、Al_2O_3和Eu/Eu~*以及很高的Yb而不同于上述各类花岗岩,通常Yb1.5×10~(-6),Sr100×10~(-6)(Yb变化大,绝大多数2×10~(-6);当Yb在2×10~(-6)～8×10~(-6)时,部分样品Sr可100×10~(-6),但很少200×10~(-6));Al_2O_314%,集中在11%～13%之间,Eu/Eu~*0.7,大多0.4;Yb越大,Sr越低,负铕异常越明显。文中讨论了花岗岩Sr-Yb分类的意义,指出本分类适用于产于大陆和海洋的绝大多数中酸性岩浆岩(可能不适用于一部分特别富铁和钾的花岗岩,如具有高Sr和Yb特征的广西型花岗岩)。不同类型的花岗岩主要反映了源区压力的不同,而源区成分、温度、部分熔融程度、水和挥发分的加入以及岩浆混合等的影响可能是次要的。文中指出,该分类的依据、其实质,是熔体与残留相平衡的理论。与浙闽型花岗岩平衡的残留相是斜长石,与喜马拉雅型花岗岩平衡的是斜长石+石榴石,与埃达克型花岗岩平衡的是石榴石,与南岭型花岗岩平衡的是富钙的斜长石。文中指出,加强实验岩石学研究,将年代学和地球化学研究密切结合起来是深化花岗岩研究的关键。  相似文献   

5.
Measurements are described of the geometry of ripples formed on beds of sand exposed to a steady current at right angles to an oscillatory flow. Four different sands were studied. The oscillation was produced by an oscillating tray set into the bed of a steady-flow flume. It was observed that straight-crested ripples formed by oscillatory flow would usually develop a ‘serpentine’ form when the superimposed steady current exceeded a certain limit. For amplitudes of the tray velocity U∞ less than about 0.38 m s-1 this limit corresponded to U∞/ū*c>31, where ū*c is the shear velocity measured just upstream of the oscillating tray. It is suggested that the serpentine form is caused by the interaction of vortices carried back and forth between adjacent ripples. On this assumption, the wavelength of the serpentine form would be proportional to the product of period of oscillation and near-bed steady current velocity. The present measurements appear to support this hypothesis although there is also evidence that the wavelength is influenced by preferred spacing patterns between vortices. The measurements also show the ratio of the amplitude of the serpentine form to its wavelength to be approximately constant. Empirical relationships are derived relating ripple geometry to flow and sediment properties. It is observed that the influence of Reynolds number and sediment properties on the geometry is very weak. It is suggested that this is typical of ripples formed with relatively low sediment transport rates. It is also found that, under the present experimental conditions, the ripple spacing in the direction of oscillation is almost independent of the magnitude of the steady current and in close agreement with the wavelengths previously measured in an oscillating water tunnel. This suggests that the additional inertia effects associated with oscillating tray rigs were not sufficient to affect bed geometry under the present test conditions.  相似文献   

6.
This research describes the goals, design and implementation of a quasi natural gradient, laboratory scale, sand tank (aquifer) model experiment. The model was used to study the transport of an inorganic tracer (Chloride) in groundwater, within a tropical aquifer (porous medium) material. Three-dimensional sand tank (1.8 m × 0.3 m × 0.8 m) experiments were conducted to investigate contaminant transport and natural attenuation within the sand tank. In all, 360 samples were collected during 24 sampling sessions, for the three days of the tracer experiments in the Sand Tank. The Owena sand is a poorly graded sand with 88.1 % sand and 11.9 % gravel. Geotechnical properties including; coefficient of uniformity Cu = 2.53, coefficient of gradation Cz = 0.181, hydraulic conductivity K = 5.76 × 10?4 m/s, bulk density p = 1.9 Mg/m3, effective porosity ne = 0.215 and median grain diameter D50 = 0.55 mm, were determined. Other relevant hydraulic and solute transport parameters, such as dispersion coefficients and dispersivities were also established for the tropical soil.  相似文献   

7.
Flexible-wall hydraulic conductivity tests were carried out on bottom ash, fly ash and compacted specimens of sand with additions of 0, 3, 6, 9 and 18% of bentonite. In order to study the effect of bentonite inclusion and particle morphology on the hydraulic conductivity of the admixtures, an investigation was undertaken based on thin section micrographs. It was found that, for both bottom and fly ash admixtures, bentonite addition reduced only one order of magnitude the hydraulic conductivity, from 1.78 × 10−6 m/s to 1.39 × 10−7 m/s. On the other hand, the sand hydraulic conductivity was reduced five orders of magnitude, from 3.17 × 10−5 m/s to 5.15 × 10−10 m/s. Among several factors that can be responsible for the difficulty in reducing hydraulic conductivity, such as ash grain size distribution and elevated cation concentration (leached from the ash) in pore water, it can also be recalled the high particle voids observed in the ash by means of microscopic analysis. The same is not true with the sand, which has solid particles, without inner voids.  相似文献   

8.
The load bearing capacity of soils in Otukpa area of Benue state, Nigeria was evaluated by characterizing the geotechnical, geophysical and structural properties of the soil. The evaluation was necessary because aside the area holding good prospect for future increase in human population, sparsely distributed low-weight buildings in the area have cracks and other signs of failure. Remote sensing/GIS, geophysical and geotechnical approaches were integrated to achieve the objective. 2-D tomography and processed remotely sensed data confirmed the presence of areas of strength especially to the north. Stratigraphy of the northern portion consist of four layers; loose top soil (0-0.26m), compact clayey sand (0.26m-3.33m), dry clayey sand (3.33m-74.21m) and saturated clayey sands (74.21m-201.58m) While the stratigraphy in the south is slightly different; compact topsoil (0-1.2m), loose sand (1.2m-10.81m), compact sand (10.82m-19.71m) and compact clay sand (19.71m-56.03m). The plastic limit range from 11-17% with average specific gravity of 2.64g/cm3. Permeability ranges from 7.8×10-6m/sec to 3.36×10-4m/sec while volume compressibility under 250kN ranges from 7.27×10-5m2/kN to 1.3×10-4m2/kN and the rate of consolidation under 250kN is within 12.43 m2/year to 1.33m2/year. MDD peaks at 1.85g/cm3 at an OMC of 12.11% and is lowest at 1.67g/cm3 at an OMC of 11.99%. UCS ranges from 31-45kN/m2 while shear strength is between 258.81kN/m2 to 338 kN/m2. Due to the variability of engineering properties of soils, the southern part of the area is preferred for locating the buildings. Generally, careful foundation design in the area is necessary.  相似文献   

9.
Several hydraulic techniques were used to estimate the flow depth (0.3 m) associated with the deposition of a tabular set (micro-delta) of cross-stratified sand in the Brampton esker. The competency of the flow, deduced from both the grain size and structural characteristics of the set, gave a value of approximately 0.65 m/sec for the palaeo-velocity of the flow. Estimates of palaeo-depth and velocity facilitated calculation of the Froude and Reynolds numbers, about 0.38 and 1.24 · 105, respectively. Extrapolation of other parameters included bed shear stress τ0 (4.50 N/m2), shear velocity U* (0.067 m/sec), dimensionless Chezy coefficient C/√g (9.7), slope of the energy gradient S(0.00153), Darcy-Weisbach friction factor f(0.085), Manning roughness coefficient n(0.027) and discharge of bed-material load (19 metric tons/day/m). The figures cited are reasonable estimates only. The occurrence of regressive ripples in the bottomset of the micro-delta aided in the hydraulic interpretation. These flow characteristics are only representative of the final stages of deposition at one location on the flank of the esker. The core of the esker was probably deposited under different hydraulic conditions.  相似文献   

10.
边千韬  林传勇 《地质科学》1996,31(2):170-175
在可可西里北缘发现的糜棱岩化带,经显微构造研究确定为韧性剪切带。此带发育流劈理及拉伸线理。糜棱岩化花岗岩和糜棱岩化石英脉中的石英发育亚晶粒构造、位错构造和动态重结晶,长石主要发育机械双晶。石英c轴组构属韧性剪切带中的典型形式,石英变形以位错蠕变机制和位错滑移机制共存为特征,石英的动态重结晶作用是由亚晶粒旋转机制形成。长石的变形主要是通过机械双晶实现的。此韧性剪切带形成时的温度约400℃,差异应力约30MPa,应变速率约1.9×10-13s-1.  相似文献   

11.
Nanoscale zero-valent iron flakes for groundwater treatment   总被引：1，自引：0，他引：1  
Even today the remediation of organic contaminant source zones poses significant technical and economic challenges. Nanoscale zero-valent iron (NZVI) injections have proved to be a promising approach especially for source zone treatment. We present the development and the characterization of a new kind of NZVI with several advantages on the basis of laboratory experiments, model simulations and a field test. The developed NZVI particles are manufactured by milling, consist of 85 % Fe(0) and exhibit a flake-like shape with a thickness of <100 nm. The mass normalized perchloroethylene (PCE) dechlorination rate constant was 4.1 × 10?3 L/g h compared to 4.0 × 10?4 L/g h for a commercially available reference product. A transport distance of at least 190 cm in quartz sand with a grain size of 0.2–0.8 mm and Fe(0) concentrations between 6 and 160 g/kg (sand) were achieved without significant indications of clogging. The particles showed only a low acute toxicity and had no longterm inhibitory effects on dechlorinating microorganisms. During a field test 280 kg of the iron flakes was injected to a depth of 10–12 m into quaternary sand layers with hydraulic conductivities ranging between 10?4 and 10?5 m/s. Fe(0) concentrations of 1 g/kg (sand) or more [up to 100 g/kg (sand)] were achieved in 80 % of the targeted area. The iron flakes have so far remained reactive for more than 1 year and caused a PCE concentration decrease from 20.000–30.000 to 100–200 µg/L. Integration of particle transport processes into the OpenGeoSys model code proved suitable for site-specific 3D prediction and optimization of iron flake injections.  相似文献   

12.
Creep and saltation are the primary modes of surface transport involved in the fluid‐like movement of aeolian sands. Although numerous studies have focused on saltation, few studies have focused on creep, primarily because of the experimental difficulty and the limited amount of theoretical information available on this process. Grain size and its distribution characteristics are key controls on the modes of sand movement and their transport masses. Based on a series of wind tunnel experiments, this paper presents new data regarding the saltation flux, obtained using a flat sampler, and on the creeping mass, obtained using a specifically designed bed trap, associated with four friction velocities (0·41, 0·47, 0·55 and 0·61 m sec?1). These data yielded information regarding creeping and saltating sand grains and their particle size characteristics at various heights, which led to the following conclusions: (i) the creeping masses increased as a power function (q = ?1·02 + 14·19u*3) of friction wind velocities, with a correlation (R2) of 0·95; (ii) the flux of aeolian sand flow decreases exponentially with increasing height (q = a exp(–z/b)) and increases as a power function (q = ?26·30 + 428·40 u*3) of the friction wind velocity; (iii) the particle size of creeping sand grains is ca 1·15 times of the mean diameter of salting sand grains at a height of 0 to 2 cm, which is 1·14 times of the mean diameter of sand grains in a bed; and (iv) the mean diameter of saltating sand grains decreases rapidly with increasing height whereas, while at a given height, the mean diameter of saltating sand grains is positively correlated with the friction wind velocity. Although these results require additional experimental validation, they provide new information for modelling of aeolian sand transport processes.  相似文献   

13.
The behavior of pile groups in sand under different loading rates is investigated. A total of 60 tests were conducted in the laboratory using model steel piles embedded in a medium dense sand. The model piles have an outside diameter of 25 mm and embedment length of 500 mm. Five different configurations of pile groups (2 × 1, 3 × 1, 2 × 2, 2 × 3, 3 × 3) with center to center spacing between the piles of 3d, 6d and 9d (d is the pile diameter) were tested. The piles were subjected to axial compressive loads under four different loading rates: 1.0, 0.5, 0.1 and 0.05 mm/min. Test results indicated that the axial compressive capacity of pile group increases with the loading rate such that the pile capacity versus logarithm of loading rate data plot approximately along a straight line. The slope of this line increases as the number of piles in a group increases and it decreases by increasing the spacing between piles in a group.  相似文献   

14.
The continental shelf of the State of Rio Grande do Norte, Brazil, is an open shelf area located 5°S and 35°W. It is influenced by strong oceanic and wind-driven currents, fair weather, 1·5-m-high waves and a mesotidal regime. This work focuses on the character and the controls on the development of suites of carbonate and siliciclastic bedforms, based on Landsat TM image analysis and extensive ground-truth (diving) investigations. Large-scale bedforms consist of: (i) bioclastic (mainly coralline algae and Halimeda) sand ribbons (5–10 km long, 50–600 m wide) parallel to the shoreline; and (ii) very large transverse siliciclastic dunes (3·4 km long on average, 840 m spacing and 3–8 m high), with troughs that grade rapidly into carbonate sands and gravels. Wave ripples are superposed on all large-scale bedforms, and indicate an onshore shelf sediment transport normal to the main sediment transport direction. The occurrence of these large-scale bedforms is primarily determined by the north-westerly flowing residual oceanic and tidal currents, resulting mainly in coast-parallel transport. Models of shelf bedform formation predict sand ribbons to occur in higher energy settings rather than in large dunes. However, in the study area, sand ribbons occur in an area of coarse, low-density and easily transportable bioclastic sands and gravels compared with the very large transverse dunes in an offshore area that is composed of denser medium-grained siliciclastic sands. It suggests that the availability of different sediment types is likely to exert an influence on the nature of the bedforms generated. The offshore sand supply is time limited and originates from sea floor erosion of sandstones of former sea-level lowstands. The trough areas of both sand ribbons and very large transverse dunes comprise coarse calcareous algal gravels that support benthic communities of variable maturity. Diverse mature communities result in sediment stabilization through branching algal growth and binding that is thought to modify the morphology of dunes and sand ribbons. The occurrence and the nature of the bedforms is controlled by their hydrodynamic setting, by grain composition that reflects the geological history of the area and by the carbonate-producing benthic marine communities that inhabit the trough areas.  相似文献   

15.
八达岭花岗岩的年龄、地球化学特征及其地质意义   总被引：4，自引：2，他引：2  
八达岭花岗岩基是由不同时代、不同类型的花岗岩侵入体组成的,对八达岭花岗岩中的黄花城花岗斑岩、分水岭北西花岗岩和铁炉子二长花岗岩的岩石学、岩相学、地球化学特征及锆石U-Pb年代学研究的结果表明,铁炉子二长花岗岩具有高Sr (312×10-6)、低Yb(0.98×10-6)和高Sr/Yb值(318),属于埃达克型花岗岩,其侵位年龄137Ma;黄花城花岗斑岩具低Sr (193×10-6)、低Yb (1.43×10-6)的特征,属喜马拉雅型花岗岩,其侵位年龄为133Ma;分水岭花岗岩Sr含量很低(10.2×10-6)、低Yb (0.98×10-6)、贫铝(Al2O3=13.66％),且REE图上具明显的负铕异常(Eu/Eu*=0.32),属于南岭型花岗岩,侵位年龄为128.5Ma.研究表明,137Ma的埃达克型花岗岩代表了中国东部高原存续的时间,133Ma的喜马拉雅型花岗岩指示高原可能开始垮塌了,而128Ma的南岭型花岗岩表明高原已经垮塌了.因此,八达岭花岗岩不同类型花岗岩的时代及其Sr、Yb特征可能反映了中国东部高原北部经历了从形成到垮塌的全过程.  相似文献   

16.
Three sets of Landsat? satellite images for the years 1993, 1998, and 2003 show that the sand dunes at the southwestern Desert of Egypt are generally moving towards southeast direction with a mean annual creeping speed over ground attaining 15 m/year. The manual-stickled field measurements show that the net annual extension of the longitudinal dunes in the coastal area is between 4 and 5 m/year, while the inland longitudinal dunes showed a net movement ranging between 5 and 6 m/year. Seasonal variations of drift potential and sand movement refer to a strongly high energy wind desert environment in the spring season, high energy wind desert environment in the summer season, and relatively high to intermediate in the autumn and winter seasons, respectively. The total annual estimated volume of transported sand which falls down into Lake Nasser basin attains 16,225,808 m3 as calculated by Bagnold's equation and quantities of sand collected from the sand traps. Comparing this value with the total volume of Lake Nasser Basin, which attains 120?×?109 m3, we can conclude that the sand sheets or sand accumulations may represent serious natural hazards to Lake Nasser in some locations. However, the sand drifting towards the lake may be obstructed by high contour topography hindrance, and the mean grain size of the sand sheets is bigger than 0.25 mm, which needs high wind velocity more than 4 m/s. In addition, the direction of the prevailing wind is N-NNW to S-SSE, and this direction sometimes is parallel to Lake Nasser in some places according to the meandering of the lake. The total lengths of hazardous areas along the western bank of Lake Nasser, which receive the most amounts of the drifted sands, attain 43.6 km only.  相似文献   

17.
The Conway Trough is a 40 km × 10 km, 1000 m deep, rectangular, tectonically controlled sedimentary basin situated on an active plate boundary. The basin lies at the junction of the Alpine transform and Hikurangi subduction sectors of the Indo-Australian/Pacific plate boundary. It is incised into Cainozoic sedimentary rocks and contains a thick fill of late Neogene sediment. Study of the continental shelf near the Conway Trough indicates: (1) that transport mechanisms operate in a net north-easterly direction, and (2) that the neritic sediment drift system is confined to within a few kilometres of the shoreface, with the result that (3) large areas of the shelf south of the trough comprise bare bedrock, or relict late Pleistocene sediment. Despite reaching to within 3 km of shore, the Conway Trough receives little modern bedload sediment, as indicated by a paucity of sand fill. However, the trough has intercepted some Holocene bedload, since the main channel contains redeposited graded gravel and sand with a C-14 age of 4670 yr. Satellite imagery and piston cores reveal that abundant mud is provided to the trough, much of it from river sources up to 200 km to the south. Some of this sediment is inferred to move by turbid layer transport through Conway Trough and out via Kaikoura Canyon into nearby Hikurangi Trough. Nonetheless, sedimentation rates in the Conway Trough may be as high as 1-7 m (1000 yr) 1. The Conway Trough forms a modern example of a transform basin, varying Neogene examples of which are found widely in north-eastern South Island. Sedimentation models are constructed to compare transform and transduction basins, particularly with respect to the effects of Pleistocene sea-level changes.  相似文献   

18.
A large‐scale survey for offshore aggregates is carried out on the northern shelf of the East China Sea. Results show that most of them are directly exposed in the Yangtze Shoal and the linear sand ridges system at water depths 25–55 m and 60–120 m, respectively. The components of these deposits belong to fine aggregates in terms of the fineness modulus. The potential resources are as high as 147.8 × 1012 kg for the Yangtze Shoal yet only 36.68 × 1012 kg for the sand ridges area, respectively. A preliminary feasibility analysis suggests that the Yangtze Shoal is suitable for dredging under the present conditions of technology and economy.  相似文献   

19.
An experimental investigation was conducted in order to evaluate the influence of distance from the injection point and of parameters pertinent to the cement, the suspension and the sand on the effectiveness of microfine cement grouts. Three different cement types, each at three different gradations having nominal maximum grain sizes of 100, 20 and 10 μm, were used. Grouting effectiveness was evaluated by injecting suspensions with water to cement (W/C) ratios of 1, 2 and 3, by weight, into five uniform sand fractions with different grain sizes and eight composite sands with different gradations, using a specially constructed apparatus. Unconfined compression and permeability tests were conducted on the resulting grouted sand specimens, after curing for 28 and 90 days. Microfine cement grouted sands obtained unconfined compression strength values of up to 14.9 MPa and permeability coefficients as low as 1.3 × 10?6 cm/s or by up to 5 orders of magnitude lower than those of clean sands. The W/C ratio and the bleed capacity of suspensions as well as the effective grain size and the permeability coefficient of sands are very important parameters, since they affect substantially the grouted sand properties and are correlated satisfactorily with them. The strength and permeability of grouted sands can increase, decrease or remain constant with distance from the injection point depending on the easiness of suspension penetration into the sands. The improvement of grouted sand properties with increasing distance from the injection point is consistent with the observed increase of the cement content of grouted sands.  相似文献   

20.
In order to investigate directly the structure and properties of grain boundaries in silicate materials undergoing pressure solution, in situ measurements of these properties are required. We report electrical impedance spectroscopy measurements, performed, under hydrothermal conditions, on individual glass–glass and glass-quartz contacts undergoing pressure solution. Resulting estimates of the average grain boundary diffusivity product ( Z = Dd\textav C* Z = D\delta_{\text{av}} C^{*} ) for silica transport and of the average grain boundary fluid film thickness ( d\textav \delta_{\text{av}} ) fall in the ranges 6.3 ± 1.4 × 10−18 m3 s−1 and 350 ± 210 nm, respectively. However, the average values for Z and d\textav \delta_{\text{av}} obtained were likely influenced by cracking and irregular dissolution of the dissolving contact surfaces, rather than representing uniformly wetted grain boundary properties. Post-mortem SEM observations indicate that the contact surfaces were internally rough. Taken together, our data support the notion that during pressure solution of quartz, grain boundary diffusion is rapid, and interface processes (dissolution and precipitation) are more likely to be rate-limiting than diffusion.  相似文献   

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