Effect of Moisture on Attraction Force in Beach Sand

Beach sands located above the sea water level exist in an unsaturated, rather than a fully saturated or dry state. Within the unsaturated zone, a steep excavated surface can be sustained for some unknown but finite time, and some slopes may remain stable for extended time periods due to capillary forces. These observations clearly indicate small but nonzero values for attraction strength (tensile strength and cohesion) in unsaturated beach sands, especially apparent but not confined to settings where there are low stress levels. Thus, experiments were carried out to quantify the magnitude of attraction strength in moist sands (D _r ?=?30%) and to examine the variation of these values as a function of moisture content and presence of a small amount of fines. Tensile strength, which is significantly different from zero, increases with increasing moisture content and fines. However, the influences of fines on the tensile strength are substantially dependent on the water content. Apparent cohesion strength is also identified in moist sands. A simple relationship between tensile strength and apparent cohesion is proposed using the obtained data. This study would help to further understand the phenomenon of stability of beach sands.     

Geotechnical Characteristics of Volcanic Beach Sands with Varying Iron Contents

One of the distinguishing features of volcanic beach sand compared to typical silica sand can be found in its relatively high iron content; however, studies on the effect of iron content on the engineering properties of volcanic beach sand have been very limited until now. Consequently, this experimental investigation quantifies the effect of iron content on the engineering properties of Ulleung volcanic beach sands, including small strain stiffness, compressibility, friction angle, and cone tip resistance. Various geotechnical experiments were performed, and test results demonstrate that the small strain stiffness increases with an increase in iron content because of the increased interparticle contact stiffness. In addition, the elastic deformation of soil particles decreases with an increase in iron content because of the greater elastic modulus of iron compared to that of silica. In contrast, the effects of iron content on the intermediate strain constrained modulus and on the large strain friction angle are insignificant, and these properties are mainly determined by state variables. The relationship between the stress-normalized cone tip resistance and the state parameter of tested Ulleung sand is very similar to that on silica sands, reflecting that the effect of iron contents on the cone tip resistance is minimal.     

A numerical investigation of influence of low-plasticity fines in sand on lateral response of piles

Abstract

Experimental evidence suggests that sands containing non-plastic or low-plasticity fines may show either decreasing or increasing shear strength with increasing fines content in certain situations. Accordingly, the presence of low-plasticity fines can significantly affect the ultimate lateral soil resistance; thus low-plasticity fines can affect the lateral response of piles. In this study, a quantitative method is proposed for determining the effect of low-plasticity fines in sand on the lateral response of piles in sand by combining a strain wedge model and a unified critical state compatible (UCSC) framework. An equivalent granular state parameter is employed in the UCSC framework to define the soil state uniquely in the strain wedge. The proposed quantitative method is incorporated in a finite element program. A series of numerical analyses are performed on a laterally loaded pile embedded in various relative densities of the base (clean) sand, to which various quantities of low-plasticity fines are added. The effect of low-plasticity fines on the lateral response is investigated. Furthermore, the effect of the low-plasticity fines on the response of the strain wedge is discussed.     

Sedimentology and morphodynamics of a macrotidal beach, Pendine Sands, SW Wales

The foreshore of Pendine Sands forms the seaward part of an extensive, sandy coastal barrier in a shallow Carmarthen Bay, SW Wales. The sedimentological features of the macrotidal foreshore reflect a tide-induced modification of nearshore wave characteristics. As the tide ebbs, the breaker height may decrease, the surf zone widens and becomes increasingly dissipative, and swash/backwash velocities diminish. A concomitant change from plunging to spilling breakers and increasingly symmetrical swash zone flows are associated with a decreasing beach gradient.

A zero net transport model demonstrates that the beach profile is self-stabilising in the short-term, and periodic levelling has shown that the beach is in long-term equilibrium with prevailing conditions, though this does not preclude a significant dynamic response to changing tides and waves.

The flow regimes of wave-generated currents decline as the tide ebbs, and normal beach processes do not usually affect the lower foreshore. Accordingly, there is an overall seaward-fining of the primary framework component of the sands. In more detail, this framework component displays a slight seaward-coarsening across an upper foreshore dominated by high water swash and surf; a rapid seaward-fining across the mid-foreshore in response to the ebb-attenuating swash zone flow velocities; and a slight seaward-fining across the lower foreshore under the action of nearshore shoaling waves. Bedforms vary from a swash/backwash emplaced flat bed across the upper foreshore to the small ripples of nearshore asymmetric oscillatory flows across the lower foreshore.

The surface sediment veneer is not representative of the subsurface sediments which form in response partly to fairweather conditions, partly to storms. The upper foreshore is characterised by swash/backwash emplaced plane bedding in fine sands frequently disrupted by bubble cavities. The mid-foreshore is composed of coarser-grained shelly traction clogs arranged as landward- and seaward-dipping large-scale cross bedding and/or plane bedding; these are probably storm breaker/surf deposits. The lower foreshore, though partially and sometimes totally bioturbated, shows landward-dipping small-scale cross bedding in very fine sands sorted by nearshore shoaling waves.

Tide- and storm-induced modification of the nearshore flow regimes therefore produces a distinctive shore-normal array of sedimentary facies. Each facies is characterised by diagnostic textural and structural signatures. A prograding sequence of such macrotidal deposits would be similar to, but more extensive than, a comparable microtidal sequence.     

Mechanisms Controlling the Undrained Strength Behavior of Remolded Ariake Marine Clays

The soft clay of Ariake Bay, in western Kyushu, Japan covers several hundred square kilometers. Ariake clay consists of the principal clay minerals namely smectite, illite, kaolinite and vermiculite, and other minerals in lesser quantity. The percentage of the principal clay mineral can vary significantly. The percent clay size fraction and the salt concentration can also vary significantly. In view of the importance of undrained shear strength in geotechnical engineering practice, its behavior has been studied with respect to variation in salt concentration. Basically two mechanisms control the undrained strength in clays, namely (a) cohesion or undrained strength is due to the net interparticle attractive forces, or (b) cohesion is due to the viscous nature of the double layer water. Concept (a) operates primarily for kaolinitic soil, and concept (b) dominates primarily for montmorillonitic soils. In Ariake clay, different clay minerals with different exchangeable cations and varying ion concentration in the pore water and varying nonclay size fraction are present. In view of this while both concepts (a) and (b) can coexist and operate simultaneously, one of the mechanisms dominates. For Isahaya clay, concept (a), factors responsible for an increase in level of flocculation and attractive forces result in higher undrained strength. Increase in salt concentration increases the remolded undrained strength at any moisture content. For Kubota and Kawazoe clays, concept (b) factors responsible for an expansion of diffuse double layer thickness, resulting in higher viscous resistance, increase the undrained shear strength, that is, as concentration decreases, the undrained strength increases at any moisture content. The liquid limit of Isahaya clay increases with increase in ion concentration and a marginal decrease is seen for both Kubota and Kawazoe clays, and their behavior has been explained satisfactorily.     

烟台套子湾海滩泥沙运动方向研究

采用筛析法分析了套子湾中滩面上66个表层样品的粒度。结果表明:套子湾海滩沉积物为中、细砂,为典型海滩砂。标准偏差较小,分选较好至好;频率曲线呈近正态分布,稍呈负偏;峰度中等至较窄。平均粒径和标准偏差由夹河口向东西两侧海滩变小,由于突堤的阻挡,海滩沿岸沉积物在突堤东侧产生堆积,西侧侵蚀。粒度特征和海滩地貌变化显示:套子湾海滩沉积物是由夹河口向东西两侧发生沿岸运移。为烟台开发区海水浴场的海滩养护以及芝罘岛连岛沙坝海岸的合理利用提供科学依据。     

应用探地雷达方法对海南岛博鳌海岸沙坝的研究

了解海岸沙坝的内部结构对于动态地恢复海岸沙坝与海平面变化的相互关系具有重要的意义，探地雷达（GPR）为海岸沙坝的研究提供了一种快速、经济和高分辨率的地球物理方法；探地雷达利用高频电磁波在介电特性不均匀的沉积体中产生反射获得图像，通过解译可确定地下沉积体的性质和结构；在海南岛东部博鳌玉带滩海岸沙坝的近口门处、决口堤处和南岗村东侧玉带滩海岸沙坝顶部进行了探地雷达反射剖面的测量；研究结果表明自然堆积的沙体反射波连续，受风暴浪改造的沙体同相轴错断，反射波杂乱不连续，无法进行对比；运用探地雷达相分析方法并结合钻孔资料，认为5－6m以上的平行反射波形可能代表中细砂沉积，以下的丘状或杂乱反射波形可能代表中粗砂沉积，并显示砂砾或细小卵砾等粗颗粒含量的增加。     

Settling velocity of sediments at high concentrations

New data on the settling velocity of artificial sediments and natural sands at high concentrations are presented. The data are compared with a widely used semiempirical Richardson and Zaki equation (Trans. Inst. Chem. Eng. 32 (1954) 35), which gives an accurate measure of the reduction in velocity as a function of concentration and an experimentally determined empirical power n. Here, a simple method of determining n is presented using standard equations for the clear water settling velocity and the seepage flow within fixed sediment beds. The resulting values for n are compared against values derived from new and existing laboratory data for beach and filter sands. For sands, the appropriate values of n are found to differ significantly from those suggested by Richardson and Zaki for spheres, and are typically larger, corresponding to a greater reduction in settling velocity at high concentrations. For fine and medium sands at concentrations of order 0.4, the hindered settling velocity reduces to about 70% of that expected using values of n derived for spheres. At concentrations of order 0.15, the hindered settling velocity reduces to less than half of the settling velocity in clear water. These reduced settling velocities have important implications for sediment transport modelling close to, and within, sheet flow layers and in the swash zone.     

潮汐作用下的海滩风沙运动若干特征研究——以福建平潭岛远垱澳海滩为例

海岸风沙是海岸带陆-海-气相互作用的突出产物。本文通过福建平潭岛远垱澳海滩风沙全环境要素观测,从海滩风沙垂向分布、滩面风沙起动和搬运等方面,探讨并总结自然海滩潮汐动态作用下的风沙运动过程。主要研究结论为:（1）海滩湿沙表面风沙流绝大部分（98.9%）在离滩面30 cm高度层内运动,不同粒径组沙粒的垂向分布形式不同;（2）潮汐旋回中的海滩起沙风速显著高于同等粒径内陆沙漠地区,其变化过程主要为滩面平均表层湿度与风区长度相互"博弈"的结果;（3）海滩风沙输送量主要受风速、滩面平均表层湿度与风区长度耦合作用,涨落潮不同阶段输沙量变化的主导影响因素不同;（4）"干沙起动+湿沙表面传输"为典型的海滩风沙搬运模式之一,滩面风沙运程较短,总体呈"接力"式特征向海岸前缘沙丘搬运。     

Comparison Between Shear Behaviors of Overconsolidated Nakdong River Sandy Silt and Silty Sand

From this research, overconsolidated undrained and drained behaviors of specimens with high sand content were highly dilatant. According to the comparison results of laboratory tests, the deviator stresses of silty sand were greater than sandy silt due to high sand content under increasing OCRs, and both silty sand and sandy silt were presented strain softening tendency after failure under undrained loading. The pore water pressure increased with increasing fines content under increasing OCRs. Silty sand exhibited more dilatancy and increasing shear strength than sandy silt because pore water pressures of silty sand were lower than sandy silt under higher OCRs. In overconsolidated drained tests, silty sand is higher strength than sandy silt because silty sand has a lower volumetric strain and higher deviator stress than sandy silt under increasing OCRs. As the degree of overconsolidation increased, similar behaviors of silty sand and sandy silt observed that volumetric strain decreased to negative values due to dilatancy effect and low-cohesion under current effective confining pressures.     

On helical vortex motions of moist air

Two results that are fundamentally different from what takes place in a dry atmosphere have been obtained for adiabatic motions of unsaturated moist air: (1) the steady helical motion of moist air with collinear velocity and vorticity vectors everywhere is dynamically impossible; (2) the spontaneous amplification (generation) of helicity in a moist air due to baroclinicity is dynamically and thermodynamically feasible. In the absence of helicity flux through the boundary of the domain occupied by air flows, the difference between the values of integral helicity H at time instant t delaying at a small time interval from the initial instant t ₀ (at which the instantaneous state of air motion is isomorphic either to a steady Beltrami flow or to an irrotational flow) and the initial value of H increases proportionally to (t ? t ₀)⁴. The nonzero value of the proportionality factor is ensured by the difference in values of the Poisson ratio for dry air and water vapor, respectively.     

Effects of Mudstone Particle Content on Shear Strength of a Crushed Sandstone–Mudstone Particle Mixture

The present study focuses on the shear strength, deformation, and particle crushing of sand which is mixed by crushed sandstone and mudstone particles. Two triaxial tests—one for unsaturated specimens and the other for saturated specimens—were performed, along with sieve analysis tests. Results obtained from the triaxial tests indicate that, with the increment of the mudstone particle content by weight, the angle of internal friction decreases, the cohesion increases and then decreases, and both the initial angle of shearing resistance at the atmospheric pressure and decremental angle increase and then decrease. Compared to the unsaturated specimens, the deviator stress or normalized deviator stress of the saturated specimens at the same axial stress may decrease due to the wetting action. Thus, the shear strength of the tested materials may be reduced by the wetting action. Results of sieve analysis tests indicate that the mixing of some mudstone particles into the sandstone particle mixture may reduce the amount of particle crushing, but the wetting action may increase the amount. The amount of the crushed particle may arrive at a minimum of 40% of mudstone particle content by weight.     

Cementation of sand due to salt precipitation in drying process

Salt in soil can cause cementation effect and increase the shear strength and stiffness of soil during the drying process. In this paper, an experimental study is presented to explore the strength, stiffness, and particle level structure of a salt-cemented sand at the dry state. Unconfined compression tests were carried out on sands with various amounts of precipitated dry salt. Scanning electron microscopic and elemental analysis were also conducted. The study shows that the strength and stiffness of sand can increase significantly with salt content. The strength versus salt content curve displays a convex shape, instead of a concave shape as found in cemented or biocemented sands. This implies that the effect of dry salt on soil strength is strong at low levels of salt content. The microscopic and elemental analysis evidences that salt tends to precipitate at particle contacts and form bridges between particles at relatively low salt content. The results presented in the paper may explain why even small amount of salt can lead to an overestimation of soil strength.     

The sandy beach macrofauna of Gulf of Gabès (Tunisia)

This study describes the macrofauna of the three beaches situated in central Gulf of Gabès (Tunisia): Ouderef, Gabès and Zarrat. The Gulf of Gabès has the largest tides in the Mediterranean and the beaches showed a wide intertidal zone. The beaches were sampled once during the spring low tides of June 2005. A transect was extended at each beach, from above the drift line to below the swash line at five sampled levels; at each level six 0.05 m² replicates were taken to a depth of 30 cm and sieved through a 1-mm mesh, and the organisms collected and preserved. The three beaches showed a different physical environment. Sediment type was medium sand at the steeper Ouderef beach, fine sands at Gàbes beach, and very fine sands at the flatter Zarrat beach. The total number of species collected was 31: 12 crustaceans, 10 polychaetes, four molluscs and five insects. The supralittoral and mediolittoral zones were very different. The supralittoral zone was dominated by Talitrus saltator and insects. The most abundant mediolittoral species were the amphipod crustacean Bathyporeia guilliamsoniana at Ouderef beach (23069 ind.m⁻¹), the surf clam Donax trunculus at Gabès beach (60711 ind.m⁻¹) and the spionid polychaete Scolelepis mesnili at Zarrat beach (18345.6 ind.m⁻¹).     

The Interstitial Environment of Sandy Beaches

Abstract. The interstitial system of sandy beaches is lacunar and has its dimensions defined by the sand granulometry. It can be described by features such as pore size, porosity, permeability, and water content. The most important process occurring in this system, water filtration, is driven by inputs of freshwater from groundwater discharge, and inputs of seawater by tides, wave run-up, and subtidal wave pumping. Reflective beaches have seawater input effected mainly by waves; they filter large water volumes with short residence times. Dissipative beaches display the opposite patterns, slowly filtering small volumes input by tides. Flow patterns and their effects on interstitial climate are described. The water table of the beach moves in response to groundwater discharge, tides, and waves and influences erosion/accretion processes on the beach face: a high water table promotes erosion. A series of moisture zones can be recognised from the dry surface sand at upper tide levels, to permanently saturated sand below the low tide water table, namely: a stratum of dry sand, a stratum of retention, a stratum of resurgence, and stratum of saturation. Interstitial chemistry is briefly described in terms of salinity changes, organic loads, oxygen content, and nutrient cycling. It is concluded that the interstitial environment of sandy beaches spans a continuum between physically and chemically controlled extremes: the former condition occurs on coarse sand reflective beaches, which experience low organic inputs and high filtration rates of large water volumes — resulting in powerful hydrodynamic forces; the latter occurs on dissipative beaches of fine sand, which are subject to high organic inputs and low filtration volumes — resulting in stagnation and steep vertical chemical gradients. Many intermediate situations occur and these are more favourable to interstitial life than either of the extremes.     

河北省沙质海岸侵蚀灾害和防治对策

河北省沙质海岸是渤海海岸侵蚀灾害最严重的区段之一,海岸侵蚀主要表现于海滩沙粗化,滩肩迅速变窄,滩坡变陡,基岩裸露的比率增多.岸线蚀退率达1.5～3.5m/a,严重制约了海滩旅游事业.整治海难,刻不容缓.采取岸外潜坝和丁坝群等人工建筑物和大量补沙相结合的海滩养护方法应是当前最迫切、最科学和最实际的方法,只有南段沙丘和沙坝-泻湖岸段可采用植树种草的生物学方法护岸.     

Carbonate Sediment Deposits on the Reef Front Around Oahu, Hawaii

Large sediment deposits on the reef front around Oahu are a possible resource for replenishing eroded beaches. High-resolution subbottom profiles clearly depict the deposits in three study areas: Kailua Bay off the windward coast, Makua to Kahe Point off the leeward coast, and Camp Erdman to Waimea off the north coast. Most of the sediment is in water depths between 20 and 100 m, resting on submerged shelves created during lowstands of sea level. The mapped deposits have a volume of about 4 × 10⁸ m³ in water depths less than 100 m, being thickest off the mouth of channels carved into the modern insular shelf, from which most of the sediment issues. Vibracore samples contain various amounts of sediment of similar size to the sand on Oahu beaches, with the most compatible prospects located off Makaha, Haleiwa, and Camp Erdman, and the least compatible ones located in Kailua Bay. Laboratory tests show a positive correlation of abrasion with Halimeda content: samples from Kailua Bay suffered high amounts of attrition, but others were comparable to tested beach samples. The common gray color of the offshore sediment, aesthetically undesirable for sand on popular tourist beaches, was diminished in the laboratory by soaking in heated hydrogen peroxide.     

Ore Sands in Curonian Spit Sediments (Baltic Sea)

Oceanology - For the first time, the results of a study of ore sands formed during storm waves and winds on the sea beach of Curonian Spit and in the quieter wind environment on the beach of the...     

Behavior of Loose Silty Sand of Chlef River: Effect of Low Plastic Fine Contents and Other Parameters

This article presents a laboratory study of static behavior of silty-sand soils. The objective of this laboratory investigation is to study the effect of initial confining pressures and fines content on the undrained shear strength (known as liquefaction resistance) response, pore pressure, and hydraulic conductivity of sand–silt mixtures. The triaxial tests were conducted on reconstituted saturated silty-sand samples at initial relative density D_r = 15% with fines content ranging from 0 to 50%. All the samples were subjected to a range of initial confining pressures (50, 100, and 200 kPa). The obtained results indicate that the presence of low plastic fines in sand–silt mixture leads to a more compressible soil fabric, and consequently to a significant loss in the soil resistance to liquefaction. The evaluation of the data indicates that the undrained shear strength can be correlated to fines content (F_c), inter-granular void ratio (e_g), and excess of pore pressure (Δu). The undrained shear strength decreases with the decrease of saturated hydraulic conductivity and the increase of fines content for all confining pressures under consideration. There is a relatively high degree of correlation between the peak shear strength (q_peak) and the logarithm of the saturated hydraulic conductivity (k_sat) for all confining pressures.