Particle size characteristics of aeolian ripple crests and troughs

Ripples are prevalent in aeolian landscapes. Many researchers have focused on the shape and formation of sand ripples, but few have studied the differences in the particle size of sand on crests and in troughs along bed, especially the variations caused by changes in friction velocity and the wind‐blowing duration. A particle size of 158 μm (d ) was used to create aeolian ripples in a wind tunnel under four friction velocities (u *) with different wind duration times (t ). Samples were collected from the surfaces of ripple crests and troughs, respectively, at seven sites, and particle sizes were measured using a Malvern Mastersizer 2000. The main results were: (i) The particle size distributions of sand in troughs are unimodal with slight variations of particle size parameters, including mean particle size, standard deviation, skewness and kurtosis, etc., under different conditions, while these particle size parameters of sand on crests change with friction velocity and deflation time. Moreover, some of the particle distribution curves for the sand on crests do not follow typical unimodal curves. (ii) With increasing friction velocity or deflation duration, the sand on the crests shows a coarsening process relative to those on the bed surface. The particle size of sand on crests at a 1 m bed increases linearly with friction velocity (d  =  344·27 + 34·54 u *) at a given wind‐blowing duration. The particle sizes of sand on crests at 1 m, 2 m and 4 m beds increase with a power‐law relationship (d  = a + t ^b, where a and b are fitting parameters) with deflation time at a given friction velocity. (iii) The probability cumulative curves of sand showed a three‐section pattern in troughs and on most of the crests but a four‐section pattern at crest locations due to increased influence by friction velocity and deflation time. The proportions of the sediment moved by suspension, saltation and creep in the three‐section pattern were within the ranges of 0·2% to 2·0%, 97·0% to 98·9%, and 0·8% to 3·0%, respectively. For the four‐section pattern, suspension accounted for 0·3% and 3·0%, and the proportion of creep increased with friction velocity and deflation time, while saltation decreased accordingly. Although these results require additional validation, they help to advance current understanding of the grain‐size characteristics of aeolian ripples.     

Laboratory measurements of pivoting angles for applications to selective entrainment of gravel in a current

Important to grain entrainment by a flowing fluid is the pivoting angle of the grain about its contact point with an underlying grain. A series of experiments has been undertaken to determine how this angle depends on grain shape (rollability and angularity), on the ratio of the size of the pivoting grain to those beneath, and on factors such as imbrication. The experiments involved gravel-sized spheres (ball-bearings and marbles), natural pebbles selected for their approximately triaxial ellipsoid shapes, and angular crushed basalt pebbles. The pivoting angles for these grains were measured on an apparatus consisting of a board which can be progressively inclined, the angle of the board being equal to the pivoting angle at the instant of grain movement. The pivoting angles of spheres showed reasonable agreement with a theoretically derived equation, showing much better agreement than in previous studies which utilized sand-sized spheres. A series of measurements with spheres ranging from sand to gravel sizes reveals that the pivoting angles decrease with increasing particle size. Our results are therefore consistent with the earlier studies limited to sand-size spheres. The cause of this size dependence is unknown since moisture and electrostatic binding can be ruled out. Similar size dependencies are also found for the ellipsoidal pebbles and angular gravel. The experiments with ellipsoidal pebbles demonstrated a strong shape dependence for the pivoting angle, being a function of the ratio of the pebble's smallest to intermediate axial diameters. This ratio controls the grain's ability to roll and pivot; with small ratios of these diameters the pebbles tended to slide out of position, whereas with ratios closer to unity (circular cross-section) true pivoting took place and the angles were smaller. Experiments with flat pebbles placed in an imbricated arrangement yielded much larger angles than when the pebbles lay in a horizontal position, the pivoting angle being increased approximately by the imbrication angle. The angular crushed gravel also required high pivoting angles, apparently due to interlocking of the grains resulting from their angularity. Other factors being equal, the measurements of pivoting angles demonstrate that the order of increasing difficulty of entrainment is spheres, ellipsoidal grains, angular grains, and imbricated grains. The results obtained here make possible the quantitative evaluation of these shape effects on grain threshold, as well as evaluation of the selective entrainment of grains from a bed of mixed sizes.     

沉积物粒度特征及其对环境的指示意义——以濠河为例

为了研究河流沉积物粒度对区域气候变化的指示作用,对濠河中游、下游、濠河入淮河口3个典型河床沉积物剖面及石英尾砂的粒度进行了测量。结果显示:3个沉积物剖面按粒度的变化特征均可分成四层,第一层沉积物以细粉砂为主,第二、三、四层以粗粉砂为主,其中第二、三、四层沉积物的粒度频率分布曲线与石英尾砂非常相似,说明大量石英尾砂排入濠河后,沉积物粒度特征由石英尾砂控制。在近30年中,濠河沉积物的粒度随河水动力的变化而出现波动,这种波动与降雨量的年际变化、洪水的发生等自然因素有关,沉积物平均粒径的峰值与降雨量大或洪水发生的年份存在对应关系。濠河沉积物的粒度特征具有濠河流域气候干湿变化的指示意义:粒径粗指示降雨量较多的湿润气候,粒径细指示降雨量较少的干旱气候。     

Aerodynamic grain‐size distribution of blown sand

Aeolian sand entrainment, saltation and deposition are important and closely related near surface processes. Determining how grains are sorted by wind requires a detailed understanding of how aerodynamic sand transport processes vary within the saltating layer with height above the bed. Grain‐size distribution of sand throughout the saltation layer and, in particular, how the associated flux of different grain size changes with variation in wind velocity, remain unclear. In the present study, a blowdown wind tunnel with a 50 cm thick boundary layer was used to investigate saltating sand grains by analyzing the weight percentage and transport flux of different grain‐size fractions and the mean grain size at different wind velocities. It was found that mean grain size decreases with height above the sand bed before undergoing a reversal. The height of the reversal point ranges from 4 to 40 cm, and increases with wind velocity following a non‐linear relationship. The content of the finer fractions (very fine and fine sand) initially increases above the sand bed and then decreases slightly with height, whereas that of the coarser fractions (medium and coarse sand) exhibits the opposite trend. The content of coarser grains and the mean grain size of sand in the saltation layer increase with wind velocity, indicating erosional selectivity with respect to grains in multi‐sized sand beds; but this size selectivity decreases with increasing wind velocity. The vertical mass flux structure of fine sand and very fine sand does not obey a general exponential decay pattern under strong wind conditions; and the coarser the sand grain, the greater the decrease rate of their transport mass with height. The results of these experiments suggest that the grain‐size distribution of a saltating sand cloud is governed by both wind velocity and height within the near‐surface boundary layer.     

Estimating the settling velocity of bioclastic sediment using common grain‐size analysis techniques

Most techniques for estimating settling velocities of natural particles have been developed for siliciclastic sediments. Therefore, to understand how these techniques apply to bioclastic environments, measured settling velocities of bioclastic sedimentary deposits sampled from a nearshore fringing reef in Western Australia were compared with settling velocities calculated using results from several common grain‐size analysis techniques (sieve, laser diffraction and image analysis) and established models. The effects of sediment density and shape were also examined using a range of density values and three different models of settling velocity. Sediment density was found to have a significant effect on calculated settling velocity, causing a range in normalized root‐mean‐square error of up to 28%, depending upon settling velocity model and grain‐size method. Accounting for particle shape reduced errors in predicted settling velocity by 3% to 6% and removed any velocity‐dependent bias, which is particularly important for the fastest settling fractions. When shape was accounted for and measured density was used, normalized root‐mean‐square errors were 4%, 10% and 18% for laser diffraction, sieve and image analysis, respectively. The results of this study show that established models of settling velocity that account for particle shape can be used to estimate settling velocity of irregularly shaped, sand‐sized bioclastic sediments from sieve, laser diffraction, or image analysis‐derived measures of grain size with a limited amount of error. Collectively, these findings will allow for grain‐size data measured with different methods to be accurately converted to settling velocity for comparison. This will facilitate greater understanding of the hydraulic properties of bioclastic sediment which can help to increase our general knowledge of sediment dynamics in these environments.     

A note on the generation of periodic granular microstructures based on grain size distributions

This short communication discusses an algorithm suited for the generation of periodic microstructures of granular media. Its particular features are a user‐defined grain size distribution, a representative volume element which is intrinsically periodic ab initio and a user‐defined termination criterion, controlled by an increase of volume fraction. For low densities our particle packings resemble fluids or gases, while we aim to reach for rather dense particle packings, similar to granular solids. The generated microstructures can thus be readily incorporated into large multiscale simulations, e.g. on the integration point level of a finite element analysis of a particular sand or concrete. The individual grain size distribution of the granular medium is incorporated through the introduction of different growth rates governing the final particle size distribution. We briefly sketch the generation of the representative volume element within a serial event‐driven scheme and demonstrate how periodic boundary conditions are ensured throughout the representative volume element generation process. The potential of the suggested algorithm will be illustrated through the generation of two different periodic multi‐disperse microstructures. They are based on different given grain size distributions, one for a quartz sand with a low non‐uniformity index and one for concrete aggregates classified as A32 by the German standard norm DIN 1045 to have a rather large variation in grain size. Copyright © 2007 John Wiley & Sons, Ltd.     

A comparison of grain‐size analysis methods for sand‐dominated fluvial sediments

Grain‐size distribution is a fundamental tool for interpreting sedimentary units within depositional systems. The techniques assessed in this study are commonly used to determine grain‐size distributions for sand‐dominated sediments. However, the degree of consistency and differences in interpretation when using a combination of grain‐size methods have not yet been assessed systematically for sand‐dominated fluvial sediments. Results obtained from laser diffraction, X‐ray attenuation and scanning electron microscopy grain‐size analysis techniques were compared with those obtained from the traditional sieve/hydrometer method. Scanning electron microscopy was shown to provide an inaccurate quantitative analysis of grain‐size distributions because of difficulties in obtaining representative samples for examination. The X‐ray attenuation method is unsuitable for sand‐dominated sediments because of its upper size range of only 300 μm. The consistently strong correlation between the laser diffraction results and the sieve/hydrometer results shows that these methods are comparable for sand‐dominated fluvial sediments. Provided that sample preparation is consistent, the latter two methods can be used together within a study of such sediments while maintaining a high degree of accuracy. These results indicate that data for sand‐dominated fluvial sediments gained from the long‐established sieve/hydrometer method can be compared with confidence to those obtained by modern studies using laser diffraction techniques.     

基于数字图像处理技术的砂土颗粒级配分析研究

砂土颗粒级配是影响砂土工程性质的重要参数之一,传统的颗分试验方法由于试验原理不同而具有不同的适用范 围。为更加方便、准确地获取砂土颗粒级配,提出了一种基于数字图像处理技术来获取SEM照片中的砂颗粒粒径参数及级 配特征的新方法。将准备好的砂土样品打磨成薄片放在扫描电镜下拍照,然后利用Photoshop软件对照片进行拼接,并采用 自主研发的SMAS数字图像分析系统对拼接好的照片进行定量分析处理,获取样品的微观结构参数,将获得的“土颗粒等 效直径”和“土颗粒面积”分别等效为实际土颗粒粒径和土颗粒质量,进而换算得到砂土的颗粒级配曲线;然后将通过数 字图像技术获得的砂土颗粒级配曲线与通过传统筛分法和激光粒度分析法得到的颗粒级配曲线进行对比,验证了提出的数 字图像处理方法的有效性和可靠性,同时分析了两种方法之间存在的差异及其原因,并对数字图像处理方法和传统颗分方 法各自的优缺点进行了讨论。     

基于数字图像处理技术的砂土颗粒级配分析研究

砂土颗粒级配是影响砂土工程性质的重要参数之一，传统的颗分试验方法由于试验原理不同而具有不同的适用范 围。为更加方便、准确地获取砂土颗粒级配，提出了一种基于数字图像处理技术来获取SEM照片中的砂颗粒粒径参数及级 配特征的新方法。将准备好的砂土样品打磨成薄片放在扫描电镜下拍照，然后利用Photoshop软件对照片进行拼接，并采用 自主研发的SMAS数字图像分析系统对拼接好的照片进行定量分析处理，获取样品的微观结构参数，将获得的“土颗粒等 效直径”和“土颗粒面积”分别等效为实际土颗粒粒径和土颗粒质量，进而换算得到砂土的颗粒级配曲线；然后将通过数 字图像技术获得的砂土颗粒级配曲线与通过传统筛分法和激光粒度分析法得到的颗粒级配曲线进行对比，验证了提出的数 字图像处理方法的有效性和可靠性，同时分析了两种方法之间存在的差异及其原因，并对数字图像处理方法和传统颗分方 法各自的优缺点进行了讨论。     

不同粒径级砂土渗透特性试验研究

渗透性是砂土的重要工程性质之一,影响砂土渗透性的因素有很多,比如土体密实程度、土颗粒自身特性、流体性质等,其中孔隙率与颗粒粒径是两个重要影响因素。而以往基于混合粒径的天然砂土的研究很难分别对这两个因素进行独立的研究。基于此,首先开展了单一粒径级砂土的常水头渗透试验,分别研究了同一粒径级砂土渗透系数随孔隙率的变化和同一孔隙率下不同粒径级砂土渗透系数随均值粒径的变化规律。试验结果显示,渗透系数随着孔隙率的增加而线性增加、随均值粒径二次方的增加而线性增加,其中均值粒径的影响较大,其变化能导致渗透系数量级上的差异。在此基础上,开展了多粒径混合砂土的渗透试验,讨论了曲率系数、不均匀系数等级配参数对渗透性的影响,从而将单一粒径级的研究成果推广到天然砂土,最终拟合出渗透系数与相关影响因素的经验公式,以便工程实践参考使用。     

钙质砂的休止角研究与工程应用

砂土的天然休止角对土堆设计、基坑设计和边坡稳定性研判有重要的指导意义。砂土的天然休止角受土颗粒的摩擦特性、颗粒形状、粒径和含水状态等诸多因素的影响。开展了钙质砂的天然休止角试验,研究了多种因素对钙质砂天然休止角的影响规律。结果表明：钙质砂3种常见颗粒形状中,片状休止角最大,枝棒状次之,块状最小;钙质砂天然休止角随着粒径的增大而增大;当平均粒径相同时,天然休止角随着不均匀系数的增大而增大,随着曲率系数的增大而减少;通过与标准石英砂的对比试验发现,石英砂的天然休止角小于钙质砂天然休止角。对现场钙质砂边坡测量后表明,钙质砂地基经过振冲挤密后基坑开挖最大坡角略大于室内测得的天然休止角。研究结果对钙质砂土堆和基坑设计等工程实践有一定指导意义。     

Generation of a realistic 3D sand assembly using X‐ray micro‐computed tomography and spherical harmonic‐based principal component analysis

Three‐dimensional particle morphology is a significant problem in the discrete element modeling of granular sand. The major technical challenge is generating a realistic 3D sand assembly that is composed of a large number of random‐shaped particles containing essential morphological features of natural sands. Based on X‐ray micro‐computed tomography data collected from a series of image processing techniques, we used the spherical harmonics (SH) analysis to represent and reconstruct the multi‐scale features of real 3D particle morphologies. The SH analysis was extended to some highly complex particles with sharp corners and surface cavities. We then proposed a statistical approach for the generation of realistic particle assembly of a given type of sand based on the principle component analysis (PCA). The PCA aims to identify the major pattern of the coefficient matrix, which is made up of the SH coefficients of all the particles involved in the analysis. This approach takes into account the particle size effect on the variation of particle morphology, which is observed from the available results of micro‐computed tomography and QICPIC analyses of sand particle morphology. Using the aforementioned approach, two virtual sand samples were generated, whose statistics of morphological parameters were compared with those measured from real sand particles. The comparison shows that the proposed approach is capable of generating a realistic sand assembly that retains the major morphological features of the mother sand. Copyright © 2016 John Wiley & Sons, Ltd.     

平均粒径对砂土剪切特性的影响及细观机理

针对平均粒径对砂土剪切特性的影响作用,结合室内试验和离散元模拟方法对不同平均粒径砂土进行了细观研究。基于3种不同平均粒径砂土的直剪试验结果,通过建立反映砂土剪切试验特征的PFC（particle flow code）颗粒流模型,详细研究了不同粒径砂土在剪切过程中土样体积变化、力链网络、孔隙率和配位数等细观结构参数的变化特征和规律,并从细观角度分析了颗粒粒径对土样宏观剪切特性的影响机制。结果表明：具有不同平均粒径砂土的细观结构参数在剪切过程中存在显著差异,并且其细观参数差异主要集中体现在剪切带处;剪切力学特性的影响主要体现在抗剪强度和剪胀效应方面,砂土平均粒径越大,抗剪强度越高,剪胀效应越明显;具有不同平均粒径的砂土在剪切过程中土颗粒运动规律及剪切带形态变化特征存在一定的差异,平均粒径越大,剪切带内上跨式颗粒占比越大,剪切带厚度越大。     

The link between grain‐size components and depositional processes in a modern clastic lake

It is widely recognized that lake sediment grain‐size distributions tend to be polymodal and consist of two or more grain‐size components. However, for specific cases, the genesis of each component usually is poorly understood. In this study, the grain‐size components of the surface sediments of Hulun Lake, Inner Mongolia, were partitioned using the log‐normal distribution function method and the relationship between the identity of each grain‐size component and the hydraulic condition of the lake was investigated in order to relate the constituent components to specific depositional processes in the lake. The data indicate that the modern clastic sediments of Hulun Lake contain six distinct unimodal grain‐size distributions representing six grain‐size components. Each of the components retains its identity including modal size, manner of transportation and environment of deposition, although the relative percentage varies with the hydraulic conditions throughout the lake. These components are specified from fine to coarse modes as long‐term suspension clay, offshore‐suspension fine silt and medium to coarse silt, and nearshore‐suspension fine sand, saltation medium sand and traction coarse sand. The percentage contribution of several grain‐size components interpreted as being indicative of nearshore environments is shown to be correlated negatively with water depth across the modern lake bed; this suggests that the proportion of these components in core data might be useful as a proxy for water depth. This possibility was tested using a sediment core from Hulun Lake where high percentages of the nearshore grain‐size components were found to be correlated with low regional precipitation reconstructed from the pollen profile of the same core. The coincidence of two independent proxies does not only demonstrate the validity of log‐normal distribution function in partitioning polymodal sediments but reveals the potential of lake sediment grain‐size components for the research of lake‐level fluctuations during the geological past.     

土体强度与变形尺度特性的理论与试验分析

土体是一种颗粒介质,其强度与变形特性具有显著的颗粒尺度效应。采用胞元土体模型和三轴抗剪试验分析了土体强度和变形的尺度效应特性。根据土体中不同尺度颗粒间相互作用表现出的聚集和摩擦效应,提出了“基体-增强颗粒”土体胞元模型,胞元体由基体和增强颗粒组成,其中基体由微小土颗粒集成,而增强颗粒为砂粒,宏观土体则简化为由许多胞元体构成的介质。引入广义球应变和广义等效应变,基于应变能导出了考虑颗粒尺度效应的应力-应变关系以及屈服应力计算公式;同时,针对增强颗粒不同粒径和体分比的土体进行一系列三轴不排水抗剪试验,给出了应力-应变和屈服应力尺度效应的测试结果。试验和理论计算结果均表明,土体强度和变形的尺度效应随增强颗粒的体分比增加以及粒径的减小而增强,由此反映出土体强度和变形显著的尺度效应;土体强度和变形尺度效应的理论预测结果与试验具有较好的一致性。     

The Morwell interseam “sands”

Interseam “sands” of Morwell form part of a sequence of brown‐coal seams, sediments and volcanic rocks which, together, make up the Tertiary Latrobe Valley Coal Measures. A detailed investigation and computer analysis of the “sands” show that they are fluviatile deposits which accumulated within the tectonically stable Latrobe Valley Depression.

On an inclusive‐graphic comparative scale, particle‐size analyses show that the sediments tend to be poorly sorted, positively skewed and mesocurtic with a mean size within the coarse‐sand range. Modal frequency peaks occur between –0.5 and –1 and between 1 and 2 phi. Presented evidence suggests that the coarser fraction represents a rolled grain population with fine‐medium sand reflecting parallel deposition from graded suspension.     

Deposits of depletive high-density turbidity currents: a flume analogue of bed geometry, structure and texture

Flume experiments were performed to study the flow properties and depositional characteristics of high‐density turbidity currents that were depletive and quasi‐steady to waning for periods of several tens of seconds. Such currents may serve as an analogue for rapidly expanding flows at the mouth of submarine channels. The turbidity currents carried up to 35 vol.% of fine‐grained natural sand, very fine sand‐sized glass beads or coarse silt‐sized glass beads. Data analysis focused on: (1) depositional processes related to flow expansion; (2) geometry of sediment bodies generated by the depletive flows; (3) vertical and horizontal sequences of sedimentary structures within the sediment bodies; and (4) spatial trends in grain‐size distribution within the deposits. The experimental turbidity currents formed distinct fan‐shaped sediment bodies within a wide basin. Most fans consisted of a proximal channel‐levee system connected in the downstream direction to a lobe. This basic geometry was independent of flow density, flow velocity, flow volume and sediment type, in spite of the fact that the turbidity currents of relatively high density were different from those of relatively low density in that they exhibited two‐layer flow, with a low‐density turbulent layer moving on top of a dense layer with visibly suppressed large‐scale turbulence. Yet, the geometry of individual morphological elements appeared to relate closely to initial flow conditions and grain size of suspended sediment. Notably, the fans changed from circular to elongate, and lobe and levee thickness increased with increasing grain size and flow velocity. Erosion was confined to the proximal part of the leveed channel. Erosive capacity increased with increasing flow velocity, but appeared to be constant for turbidity currents of different grain size and similar density. Structureless sediment filled the channel during the waning stages of the turbidity currents laden with fine sand. The adjacent levee sands were laminated. The massive character of the channel fills is attributed to rapid settling of suspension load and associated suppression of tractional transport. Sediment bypassing prevailed in fan channels composed of very fine sand and coarse silt, because channel floors remained fully exposed until the end of the experiments. Lobe deposits, formed by the fine sand‐laden, high‐density turbidity currents, contained massive sand in the central part grading to plane parallel‐laminated sand towards the fringes. The depletive flows produced a radial decrease in mean grain size in the lobe deposits of all fans. Vertical trends in grain size comprised inverse‐to‐normal grading in the levees and in the thickest part of the lobes, and normal grading in the channel and fringes of the fine sandy fans. The inverse grading is attributed to a process involving headward‐directed transport of relatively fine‐grained and low‐concentrated fluid at the level of the velocity maximum of the turbidity current. The normal grading is inferred to denote the waning stage of turbidity‐current transport.     

The spatial and temporal distribution of grain‐size breaks in turbidites

Grain‐size breaks are surfaces where abrupt changes in grain size occur vertically within deposits. Grain‐size breaks are common features in turbidites around the world, including ancient and modern systems. Despite their widespread occurrence, grain‐size breaks have been regarded as exceptional, and not included within idealized models of turbidity current deposition. This study uses ca 100 shallow sediment cores, from the Moroccan Turbidite System, to map out five turbidite beds for distances in excess of 2000 km. The vertical and spatial distributions of grain‐size breaks within these beds are examined. Five different types of grain‐size break are found: Type I – in proximal areas between coarse sand and finer grained structureless sand; Type II – in proximal areas between inversely graded sand overlain by finer sand; Type III – in proximal areas between sand overlain by ripple cross‐laminated finer sand; Type IV – throughout the system between clean sand and mud; and Type V – in distal areas between mud‐rich (debrite) sand and mud. This article interprets Types I and V as being generated by sharp vertical concentration boundaries, controlled by sediment and clay concentrations within the flows, whilst Types II and III are interpreted as products of spatial/temporal fluctuations in flow capacity. Type IV are interpreted as the product of fluid mud layers, which hinder the settling of non‐cohesive grains and bypasses them down slope. Decelerating suspensions with sufficient clay will always form cohesive layers near to bed, promoting the generation of Type IV grain‐size breaks. This may explain why Type IV grain‐size breaks are widespread in all five turbidites examined and are commonplace within turbidite sequences studied elsewhere. Therefore, Type IV grain‐size breaks should be understood as the norm, not the exception, and regarded as a typical feature within turbidite beds.     

颗粒级配与形状对钙质砂渗透性的影响

钙质砂是富存于热带海洋环境（包括中国南海海域）中的一种特殊岩土介质,具有不同于陆源砂的水理性质。采用传统常水头渗流试验,首先探究了不同不均匀系数和曲率系数条件下级配对钙质砂渗透性的影响。针对钙质砂的颗粒形状特性,采用扫描电镜（SEM）与图像处理技术,引入球度 和圆度X的比值 从三维空间角度上对颗粒形状进行了定量描述。并在粒径区间、相对密实度相同的条件下,通过与福建标准砂、玻璃珠进行对比试验来考察钙质砂渗透特性,从而进一步探究颗粒形状对钙质砂渗透性的影响。试验结果表明,钙质砂渗透性随着颗粒粒径不均匀系数和曲率系数的增大而增大,符合级配对一般砂土渗透性的影响规律;钙质砂颗粒形状具有较强的结构性和不均匀性,同等密实度下钙质砂的渗透性小于陆源的石英砂。本研究获得的钙质砂渗透规律对今后南海岛礁填筑和海上平台基础工程设计具有一定的指导意义。