Gravel Mixtures Research Articles

Anthropogenic Land Changes and Sedimentation Response in the Tidal Straits of New York City

ABSTRACT Coch, N.K.; Lenna, M., and Deely, A., 2017. Anthropogenic land changes and sedimentation response in the tidal straits of New York City. The sand and gravel mixtures found in the northern part of New York Harbor (i.e. Upper Bay) have long been attributed to the transport of coarse-grained sediments into the harbor from the Atlantic. A recent sedimentological study of New York Harbor suggested that the origin of this facies may have been from the East and Harlem rivers. Today, there are no tributaries supplying sediment to the East River–Harlem River system. A review of oceanographic and historical data and a detailed bottom sediment mapping program has established the historical drainage changes in New York City and the effect on sediments supplied to the East River–Harlem River system. Before the 18th Century, the East River and the Harlem River were major suppliers of coarse sediments to New York Harbor. However, development and filling in of almost all of New York's tributaries have cut off th...

Numerical Estimation of Precision Equipment Vibration Isolation System

This work is devoted to the numerical estimation of the effectiveness of high-precision lithography scanner foundation and its vibration isolation system when it is installed in a reconstructed building. The manufacturer requires that the scanner's foundation has to be isolated from both the background vibrations and from the vibration sources that occurs inside the considered building. Based on manufacturer specifications of the foundation, its dynamic stiffness and power spectral density of the basement surface vibration accelerations in the frequency range 1 – 100Hz have to be within specified limits. In the course of this work, we performed field measurements of the vibration levels of the construction site, as well as at the bottom of the excavation. The results of the measurements revealed the presence of non-stationary random vibration sources at frequencies from 7 up to 150Hz. The problem of assigning the appropriate thicknesses of elastic and damping elements of the vibration isolation system is that at the time of designing the system, there was no information available about the levels of dynamic influence from the installed in the building vibrating equipment. To ensure utilization of the company's process technology, there was planned to install inside the building powerful ventilation systems, air conditioning, feeding and batching system of liquid nitrogen and other chemicals, etc. In order to meet the requirement of the foundation dynamic stiffness special reinforcing technology was applied, and to meet the vibration requirements – an increase in the mass of the concrete block due to under-foundation structure with gravel mixture filling was considered. To evaluate the effectiveness of the designed vibration isolation system, an analysis of vibration propagation from vibrating equipment through the supporting structures of the building and the ground layers to the scanner's foundation was performed using finite element package MSC Patran/Nastran. The results of non-stationary dynamic analysis of vibration propagation allowed us to estimate the amplitudes of foundation oscillations and to adjust the parameters of the vibration isolating materials both in the scanner's foundation, and at the sources of vibration.

Importance of advective mass transfer and sediment surface area for streambed microbial communities

Summary Variability of flow and shear stress cause local sorting and a patchy distribution of grain size in streambed sediments. Sediment microbial communities can be affected by the resulting heterogeneity because grain size determines (i) the sediment surface area available for microbial colonisation and (ii) the hydraulic conductivity and hence advective mass transfer of solutes and redox partners. However, the relative influence of the two factors on sediment microbial communities is not clear. We performed an experiment in 12 indoor flumes with three types of sediment: gravel (2–8 mm), a sand–gravel mixture (25 and 75% by mass) and sand (0.2–0.8 mm) in four flumes each. The sediments differed in both advective mass transfer (gravel > sand–gravel mixture = sand) and surface area (gravel < sand–gravel mixture < sand). We added a microbial inoculum to each flume. After 40 days of colonisation, we collected sediment samples to characterise the sediment microbial community by determining the abundance of bacteria and algae, respiration rates and potential enzyme activities. The consistent pattern found across all microbial variables showed that grain size clearly influences sediment microbial communities through advective mass transfer, although an influence of sediment surface area cannot be ruled out: (i) all variables were highest in gravel when expressed per surface area but differed little between sand and the sand–gravel mixture and (ii) all variables were similarly high in gravel and sand or the sand–gravel mixture on a volumetric basis, in spite of a greatly reduced surface area in gravel. Overall, our findings suggest that grain‐size distribution in streams should be taken into account in analyses of streambed microbial communities, especially if it has an effect on advective mass transfer.

A new technique for measuring the bed surface texture during flow and application to a degradational sand‐gravel laboratory experiment

AbstractWe present a new image analysis technique for measuring the grain size distribution (texture) of the bed surface during flow in a laboratory experiment. A camera and a floating device are connected to a carriage used to take images of the bed surface over the entire flume length. The image analysis technique, which is based on color segmentation, provides detailed data on spatial and temporal changes of the areal fraction content of each grain size at the bed surface. The technique was applied in a laboratory experiment conducted to examine a degradational reach composed of a well sorted two‐fraction mixture of sand and gravel. The initial bed consisted of an upstream reach that was characterized by an imposed stepwise fining pattern (the bimodal reach) and a downstream sand reach. A lack of sediment supply and partial transport conditions led to the formation of a static armor in the bimodal reach, which resulted in a more abrupt spatial transition in the bed surface mean grain size. The associated spatial transition in slope led to a backwater effect over the bimodal reach, a streamwise reduction in sand mobility, and so a static armor that was governed by a downstream fining pattern. Although a morphodynamic equilibrium state under steady flow is generally characterized by normal flow, here the partial transport regime prevented the bed from adjusting toward normal flow conditions and the morphodynamic steady state was governed by a backwater. We applied a numerical morphodynamic sand‐gravel model to reproduce the laboratory experiment. The numerical model captured the hydrodynamic and morphodynamic adjustment and the static armor well, yet the armoring occurred too slowly. Although the final configuration of the experiment shows features of a gravel‐sand transition (i.e., a sudden transition in slope and mean grain size), we are hesitant to claim similarities between our results and the physical mechanisms governing a gravel‐sand transition in the field.

Concrete creep mechanism explained

Concrete is ubiquitous as a building material, but it suffers from “creep,” long-term deformations caused by its own weight, that damage its integrity and make it susceptible to cracking and crumbling. Now, scientists have evidence this creeping phenomenon stems from nanoscale dissolving of concrete’s primary phase, calcium silicate hydrate (CSH) grains, under high stress (J. Chem. Phys. 2016, DOI: 10.1063/1.4955429). The discovery, by a team led by Gaurav Sant, Mathieu Bauchy, and Isabella Pignatelli at UCLA, could allow further study to devise concrete compositions that are more resistant to creep. Concrete—various mixtures of sand or gravel with a binder and water—has been used as a building material for thousands of years, and today, next to water, it’s the most widely used material in the world. Scientists have proposed models for concrete creep mechanisms, but none have been able to explain all of the physical manifestations of creep. In the new

Experimental study of the mechanical behavior of clay–aggregate mixtures

Clay–aggregate mixtures are widely distributed in nature and are often used in engineering applications. To improve the understanding of the effects of coarse particles on the mechanical behavior of clay–aggregate mixtures, a series of oedometer and triaxial tests were conducted on clay–steel bead and clay–fine gravel mixtures. Based on computed tomography scans, both the number and total volume of the inter-particle voids were observed to increase with the coarse aggregate content. Because of the combined effects of the inter-particle voids and clay–aggregate skeleton, the compression index of the mixture first increased and then decreased with the coarse aggregate content. During the undrained loading, the specimen with higher compressibility tended to generate a larger pore-water pressure and exhibit a smaller shear strength. The effective friction angle was observed to increase with the coarse aggregate content. For the clay specimens mixed with 33.3% 1-mm beads, 2-mm beads, and fine gravels, the increases in the effective friction angles were 4.4°, 3.4°, and 6.2°, respectively.

Influence of the percentage of sand on the behavior of gap-graded cohesionless soils

Abstract In this work, the effect of the fine content on the undrained mechanical behavior of a granular material is studied. Consolidated undrained triaxial tests were carried out on sand and gravel mixtures. The intact sample contains 30% of sand. In order to simulate suffusion in the sample, degradation consisted in reducing the fines amount to 20, 10 and 5%. The undrained peak strength and the dilative phase amplitude decrease when the fine content decreases, with the highest values for the intact sample and the lowest values for the sample with 5% fines. On the other hand, the contractive phase progressively increases with the fine content. The degraded samples present a higher internal friction angles than the intact one.

Application of near-surface seismic refraction tomography and multichannel analysis of surface waves for geotechnical site characterizations: A case study

In this case study two geophysical methods based on seismic waves were employed to evaluate the geotechnical properties of the soil deposits at a site for a planned wind farm. Regional geological information shows that the study area is mainly covered by recent alluvium, which is classified as a mixture of fine sand and gravel. Twenty five seismic refraction surveys were carried out in the study area. The acquired shot gathers were processed, from which primary wave (P-wave) and shear wave (S-wave) velocities were derived. The P-wave velocities were obtained by using the Seismic Refraction Tomography method (SRT) while the S-wave velocities were extracted by utilizing the Multichannel Analysis of Surface Waves (MASW) technique, which is established based on the dispersion characteristics of Rayleigh waves. Seismic hazard at the site was evaluated according to the Iranian code using the measured S-wave velocities, and the friction angles of the soil deposits were approximated using an empirical method and by making use of Jaky's formula for earth pressure at rest, which yielded similar values. The deformation properties of the foundation soil were also estimated based on the correlations between seismic wave velocities and elastic properties of soil as well as Janbu's formula for soil modulus. The findings of this study may serve as references for economic and non-destructive geotechnical site characterizations using seismic-wave methods.

Triaxial shear behaviour of sand-gravel mixtures reinforced with cement and fibre

Results of consolidated-drained and consolidated-undrained triaxial tests conducted on fibre-reinforced cement-treated sand–gravel mixtures are described in present study. The base soils were sand–gravel mixtures containing 30 and 50% gravel content. Cement content was 3% (dry wt.) of sand–gravel mixture and polypropylene fibres 0.012 m in length and 23 μm thick were added at 0.0, 0.5 and 1% (dry wt.) of soil–cement composite. Stress–strain curves besides volume and pore pressure changes, energy absorption and deformability characteristics of the reinforced mixture were evaluated. Mechanical behaviour of the composite was compared with the results of previous studies on fibre-reinforced cement-treated sand in both drained and undrained conditions. According to the results, impact of fibre reinforcement on shear strength of cemented sand–gravel mixture decreased with the increase in gravel content in drained condition. However, for undrained state, the strength was more influenced by the fibres in higher gravel contents. Moreover, increase in gravel content increased the potential of energy absorption and brittleness of the reinforced mixture. Using a single failure envelope for both drained and undrained tests, it was concluded that cohesion intercept was more affected by inclusion of fibres in mixture with lower gravel content.

Quick Triaxial Consolidated Drained Test on Gravelly Soil

Abstract Gravelly soil, a mixture of clay and gravel, has been widely used as a core material of high earth core rock fill dams. The triaxial consolidated drained (CD) test for gravelly soil is time-consuming, especially for larger scale test samples because of its low permeability caused by the high content of clay. This study presents a quick triaxial consolidated drained (QCD) test, which can greatly accelerate the CD test on gravelly soil. In the QCD test, the traditional cylindrical specimen was modified to a sand-core cylindrical specimen containing a hollow cylindrical specimen, and the sand column filled in the central hollow. As a result, the sand column in the center of the specimen greatly accelerates the water drainage of the specimen, and both the consolidation stage and the shear stage of the test can be finished quickly. Based on gravelly soil, the comparative tests, including CD tests and QCD tests, are performed. It is concluded that the QCD tests can be conducted more rapidly than CD tests, and the test results of QCD tests, for both stress–strain curves and the parameters of the Duncan–Chang model, are basically identical with that of the CD tests. The QCD test can greatly shorten the studying time on gravelly soil, i.e., the core material of earth core rock fill dams, thus speeding up the future design of dams.

Ostracoda as bioindicators of anthropogenic impact in salt lakes, saltpans, and a lagoon: A case study from the Gulf of Saros coast (NE Aegean Sea), Turkey

The study area consists of wetlands and semi-wetlands (saltpan and salt lakes) that are separated from the Gulf of Saros in the northeastern Aegean Sea by a littoral cordon. Twenty-four samples were collected from the Enez Salt Lake; Dalyan, Enez Gala, Kuvalak, Isik, and Tasalti Lakes; Vakif and Erikli Saltpans; and Karagol Lagoon. The overall distribution of the sediment sizes reveals that they consist predominantly of mud and sand and a mixture of mud, sand, and gravel. The average proportion of gravel size particles is 8.36%. Feldspar and mica are abundant in sand and gravel-sized materials. Ecological conditions of these coastal areas were assessed on the basis of ostracod assemblages that can be considered as useful bioindicators and depend on water depth, temperature, and salinity. In this context, the effects of physical and chemical properties of the environment, geochemistry of the sediment, and anthropogenic impact on the meiofauna, in particular ostracoda, was here evaluated. Cyprideis torosa Jones, a cosmopolitan species of ostracoda, was found in salt lakes. Other species of ostracoda were shown to be affected by environmental conditions. The toxicity of some heavy metals in the saltpans, salt lakes, and hypersaline lagoons was evaluated. Lake Dalyan and Erikli Saltpan display high toxicity for Cu and Cd levels. The distribution of hydrocarbon pollution of terrestrial origin was determined.

Coevolution of bed surface patchiness and channel morphology: 2. Numerical experiments

In gravel bed rivers, bed topography and the bed surface grain size distribution evolve simultaneously, but it is not clear how feedbacks between topography and grain sorting affect channel morphology. In this, the second of a pair of papers examining interactions between bed topography and bed surface sorting in gravel bed rivers, we use a two‐dimensional morphodynamic model to perform numerical experiments designed to explore the coevolution of both free and forced bars and bed surface patches. Model runs were carried out on a computational grid simulating a 200 m long, 2.75 m wide, straight, rectangular channel, with an initially flat bed at a slope of 0.0137. Over five numerical experiments, we varied (a) whether an obstruction was present, (b) whether the sediment was a gravel mixture or a single size, and (c) whether the bed surface grain size feeds back on the hydraulic roughness field. Experiments with channel obstructions developed a train of alternate bars that became stationary and were connected to the obstruction. Freely migrating alternate bars formed in the experiments without channel obstructions. Simulations incorporating roughness feedbacks between the bed surface and flow field produced flatter, broader, and longer bars than simulations using constant roughness or uniform sediment. Our findings suggest that patches are not simply a by‐product of bed topography, but they interact with the evolving bed and influence morphologic evolution.

Coevolution of bed surface patchiness and channel morphology: 1. Mechanisms of forced patch formation

AbstractRiverbeds frequently display a spatial structure where the sediment mixture composing the channel bed has been sorted into discrete patches of similar grain size. Even though patches are a fundamental feature in gravel bed rivers, we have little understanding of how patches form, evolve, and interact. Here we present a two‐dimensional morphodynamic model that is used to examine in greater detail the mechanisms responsible for the development of forced bed surface patches and the coevolution of bed morphology and bed surface patchiness. The model computes the depth‐averaged channel hydrodynamics, mixed‐grain‐size sediment transport, and bed evolution by coupling the river morphodynamic model Flow and Sediment Transport with Morphological Evolution of Channels (FaSTMECH) with a transport relation for gravel mixtures and the mixed‐grain‐size Exner equation using the active layer assumption. To test the model, we use it to simulate a flume experiment in which the bed developed a sequence of alternate bars and temporally and spatially persistent forced patches with a general pattern of coarse bar tops and fine pools. Cross‐stream sediment flux causes sediment to be exported off of bars and imported into pools at a rate that balances downstream gradients in the streamwise sediment transport rate, allowing quasi‐steady bar‐pool topography to persist. The relative importance of lateral gravitational forces on the cross‐stream component of sediment transport is a primary control on the amplitude of the bars. Because boundary shear stress declines as flow shoals over the bars, the lateral sediment transport is increasingly size selective and leads to the development of coarse bar tops and fine pools.

Surfactants and personal care products removal in pilot scale horizontal and vertical flow constructed wetlands while treating greywater

Studies were conducted on pilot scale horizontal (HFCW) and vertical subsurface flow constructed wetland (VFCW) systems for the treatment of greywater. The fate of emerging contaminants in these systems was evaluated. Sodium dodecyl sulphate (SDS), propylene glycol (PG) and trimethyl amine (TMA) were selected as the target emerging contaminants. Pilot plants were designed to treat 2.5m3/day of greywater generated in a student’s hostel, with a hydraulic retention time (HRT) ranging from 8.9days to 14.9days. The greywater passed through a pre-treatment (settling tank) unit before entering the horizontal and vertical flow constructed wetlands (10.1m×2.55m×1.2m). The substrate material in wet land systems was a mixture of sand, brick bats and gravel, and systems were planted with reed plant (Phragmites australis). Performance of systems was evaluated for the removal of organics, nutrients, bacterial contamination and emerging contaminants. Accumulations of emerging contaminants in soil and plant tissues were also studied. Performance was monitored over a year to study the effect of operating conditions such as hydraulic retention time, external organic load, and the seasons. It was found that the vertical flow system was marginally more efficient in treating the pollutants when compared to horizontal flow system. Removal efficiencies of SDS, PG and TMA in VFCW for different operating conditions were around 89%, 95% and 98%, respectively. In the case of HFCW, removal efficiencies were 85%, 90% and 95% for SDS, PG and TMA, respectively. The treated water from both the systems was meeting the USEPA standard limits for reuse.

Influence of cohesion on scour around submerged dike founded in clay–sand–gravel mixtures

This study presents the influence of cohesion on scour depth around submerged spur dike founded in the mixtures of cohesive sediment consisting of clay–gravel and clay–sand–gravel. Studies related to scour around submerged dike founded in such type of cohesive sediment mixtures are not reported in the literature to best of our knowledge. All experiments were conducted with singular submerged spur dike under clear water flow conditions. The process of scour around submerged spur dike founded in clay–gravel/clay–sand–gravel mixtures was found significantly different from that of cohesionless sediments. The process, geometry and scour depth around submerged spur dike in cohesive sediments were significantly affected by clay percentage and unconfined compressive strength of cohesive sediment mixtures. Relationships are proposed for the assessment of scour depth at nose and, at the wake of submerged spur dike in cohesive sediments mixtures. The proposed relationships give satisfactory agreement between observed and calculated values.

A simplified approach to computing flow and bedload along gravel dune-like bedforms

River dunes are important bedforms. Problems associated with the development and evolution of dune bedforms include increased flood risks, channel erosion, and damage to fish habitats. The purpose of this paper is to investigate the near-bed flow structure and bedload transport along gavel dune-like bedforms. The velocity field is computed using a relatively simple multi-layer hydrodynamic model, with a parameterization of flow separation in the leeside of dunes. The computation is of high efficiency and avoids uncertainties caused by flow separation. Fractional transport rates for a sediment mixture of sands and gravel are calculated using surface-based techniques. The computed flow velocities and bed shear stresses are in good comparison with acoustic Doppler velocimeter measurements. Bedload transport is shown to increase non-linearly with distance toward the dune crest and reach the maximum at the crest. This implies that dune-length averaged bed shear stress is not suitable for bedload calculations. At low discharges, the bed shear stress is the limiting factor, resulting in insignificant bedload. At high discharges when the bed shear stress exceeds a threshold, the effect of sediment-grain hiding and sediment-size availability are important for bedload calculations. The discharge–transport relationship is highly non-linear. This paper has demonstrated selective transport and potential dune surface coarsening. The simplified modelling approach has a good potential for application to field conditions.

Granite Waste from Diamond Wire Sawing Addition into Concrete for Civil Construction

The ornamental stone industry in Brazil is a major world producer of marble and granite with a significant amount being destined to foreign countries export. A considerable amount of waste is generated at the several stages of stone processing specially the sawing with the so called diamond wire technique. In the present work a granite waste from a diamond wire sawing was added into conventional mixture of cement, gravel and sand to fabricate concrete used in civil construction. The waste was chemically and mineralogically characterized by X-ray and its pozzolanic activity was evaluated. Concretes with 0, 10 and 20 wt% of waste were tested for the water absorption and mechanical strength as well as environmental behavior. The results indicated that up to 20 wt% addition, the granite waste does not change the concrete performance and attends its environmental requirements.

Investigation of explosive compaction (EC) for liquefaction mitigation using CPT records

Explosive compaction (EC) or Blast densification (BD) has been realized as an efficient technique for soil improvement and mitigation of the liquefaction potential in loose saturated sands. Due to providing continuous and precise records, Piezocone (CPTu) is the most applicable in situ test in geotechnical practice for evaluation of liquefaction potential. In this research a data bank including eight case histories in different locations has been compiled for investigation of EC effects on mitigation of loose sands instability. The sites geomaterials are in the category of fine to medium sand, silty sand and mixture of sand and gravel with relative density between 30 and 60 % and thickness of 5–40 m. Four CPT-based criteria have been used including cyclic stress ratio approach, cone tip resistance (qc) variations before and after modification, Qtn and qc1N, and soil behavior classification charts. Analyses have shown that due to EC the state of soil changes from loose to dense, the contractive behavior of sands changes to dilative, and the liquefaction potential diminishes. Also, by using soil behavior classification charts pre and post explosion, it can be observed that improved soils are not in the liquefiable zone, anymore. This improvement has a significant effect on layers where located in deeper zones, whereas in surface layers in some cases, liquefaction phenomenon has been observed. Moreover, by blasting in two stages between first and phases for boreholes, liquefaction potential decreases significantly.

Turbulence statistics of flow through degraded channel bed of sand–gravel mixture

This paper describes the results of an experimental study on the turbulence characteristics of flow through bed profile of a laboratory channel that was degraded by detachment of its bed material consisting of sand–gravel mixture. The measurements of velocity and turbulence characteristics over the degraded bed profile were made at three locations along the degraded bed profile using an ADV. The maximum value of turbulence intensity and the Reynolds shear stress were found to occur at the level of bed surface existing before the detachment and these values decreased towards the flow surface. The magnitude of turbulence intensities and Reynolds shear stress are observed to reduce, as one moves towards the downstream along the degraded bed profile which signifies that vortex structure weakened by bed profile degradation. Quadrant analysis was performed which demonstrated the importance of ejection and sweep phases in sediment detachment and transport. Highest occurrence probabilities are found for sweep and ejection event. The other two events i.e. outward and inward interactions are found to have very small occurrence on the probabilities. Variation of occurrence probability with hole size (H) is also discussed.

Sorting of a sand–gravel mixture in a Gilbert‐type delta

AbstractThis paper presents the results of a Gilbert‐type delta progradation experiment within an impoundment created by a dam. The delta was composed of a poorly sorted sand–gravel mixture in a bedload‐dominated environment. The main goal of the paper is to analyse the sorting process of material within the deposit as the delta progrades towards the dam. Bed profile evolution has been documented and the entire delta has been extensively sampled in order to study sorting processes. Longitudinal and vertical sorting mechanisms are illustrated. What is novel in this investigation is the complete record, within an entire deltaic deposit, of the vertical distribution of streamwise sorting in the absence of suspended load. The data presented herein provide a detailed description of sorting processes in a Gilbert‐type delta. The experimental set‐up, the water flow and the sediment feed rate chosen determine the evolution of the delta: it initially progrades with little topset aggradation and degrades afterwards. Experimental results fit well with a previously presented empirical sorting model, despite the fact that the experimental conditions used here were well outside the range of those used to derive that model. The relative coarsening of the upper layers of the delta is found to be related to the slow speed at which the delta progrades, the formation of a mobile armour layer and the erosion of the topset towards the end of the run. Furthermore, a strong correlation between the coarsening of the bottom layer of the delta and its front height has been documented and explained: as the delta gets higher, as there is more space to sort sediment, it is more likely that coarse particles failing near the top of the foreset reach the bottom of the foreset. These findings provide new and useful data documenting sediment sorting in granular, bedload‐dominated deltas.