Carbonate Sand Research Articles

KOMBINASI TRAY AERATOR DAN FILTRASI UNTUK MENURUNKAN KADAR BESI (FE) DAN MANGAN (MN) PADA AIR SUMUR

The problem that is often found in water well is the high content of iron (Fe) and manganese (Mn). This study aims to decrase the content of Fe and Mn in water well with aeration and filtration systems. Aeration used is a multilevel tray aerator by using a tray within 50 cm, while the filtration media used are activated carbon and zeolite sand with a height of 70 cm each. The results showed that the aeration process with tray aerator was able to reduce Fe levels up to 98.34% and Mn reached 97.40%. In the filtration process with activated carbon can reduce Fe levels by 98.48% and Mn by 98.25%. In the filtration process with zeolite sand media can reduce Fe levels by 98.43% and Mn by 97.44%.

Cyclic behavior of interface shear between carbonate sand and steel

The shear properties of carbonate sand and structure interface are of significance for the engineering construction. The parallel paper (Rui et al. in Acta Geotech, 2020) focuses on the monotonic behavior of the interface between carbonate sand and steel. In this paper, by a series of shear tests on the interface between carbonate sand and steel, the evolutions of interface strength during cyclic interface shear were investigated. Further, the influences of cyclic amplitude, particle size, surface roughness and normal stress on the sand–steel interface shear behavior were discussed. Using a kind of transparent ring, the particle movements near the interface were observed to explain the mechanism during cyclic interface shear. The experimental results show that the shear zone appears near the interface, and is mainly composed of crushed fine particles and original particles. With lower steel roughness condition, the volume contraction is dominant in cyclic interface shear, while the dilation and contraction occur alternatively for higher roughness, which leads to higher interface shear strength. Compared with monotonic shear, the thickness of shear zone after cyclic shear is relatively small. Cyclic interface shear can lead to more fine particles, but less is embedded into the interface. It is found that under cyclic shearing, the interaction between particles and steel is enhanced, which is the main factor for promoting the interface strength, so interface strength in cyclic shear is higher than that in monotonic shear.

Improved drag coefficient and settling velocity for carbonate sands

Sediment transport calculations are used globally in the numerical models that coastal managers, scientists and engineers use to assess and forecast coastal change. Most of the existing sediment transport equations were defined based on experimental results using siliciclastic sands. Yet these equations are applied to all types of sand, including carbonate sands that have different characteristics and therefore, settling behaviour. A rigorous management of the transport of carbonate sand is essential for the present and future management of sedimentary features in coral reefs such as sandy beaches or reef islands. Here we present a new approach to estimating the drag coefficient of carbonate sands that considers both friction and pressure. Based on our new method, the calculated drag coefficients explain the great variability in settling velocities of carbonate sand observed in nature (from 0.025 m/s to 0.364 m/s in our database). Using our formula, we demonstrate that even small differences in the settling velocity obtained with the new drag coefficient can lead to substantial changes in sediment transport and call for an update of numerical models.

Monotonic behavior of interface shear between carbonate sands and steel

The characteristic of interface shear between carbonate sands and steel is important for the design of onshore/offshore foundations in coral reef deposit. By using an interface ring shear apparatus, the influences of particle size, normal stress, steel roughness and shear displacement on the interface shear strength were studied in this paper. During the tests, the particle movement localized in the deformation band was observed and the degree of particle breakage was evaluated. The test results showed that under the effect of large displacement interface shear (≥ 1 m), a significant particle breakage occurred in the thin zone near the interface, and the roughness of steel interface decreased accordingly. The relative smooth steel surface shows small interface friction angle without dilation phenomenon during shearing, while higher roughness leads to higher interface strength due to stress dilation. It was also found that there was a kind of particle size discontinuity in the shear zone. Particle breakage is main reason for the increase in interface friction angle in large displacement shear. A new dimensionless parameter was proposed to consider the influences of particle breakage and interface roughness on the mobilization of interface strength between sands and steel. It is recommended that the influence of fine particles embedded into steel interface should be considered in large displacement shear for carbonate sands.

Sedimentologic and stratigraphic properties of Early Cretaceous Neo-Tethys shelf margin of Arabia: The Qamchuqa Formation of the Zagros Folded zone – Kurdistan Region of Iraq

The Qamchuqa Formation is well-exposed in the High Folded Zone (HFZ) of northeast Iraq. The formation is highly dolomitized and contains thick reservoir units in the subsurface region south of the HFZ. Deposition of the formation took place at the shelf margin of Early Cretaceous Neo-Tethys Ocean. It merges south- and southeastward to the shallow marine shelf of Arabia and to deep basin accumulations farther north. In the study area, the formation is divided into three members: lower member (250m thick) of interbedded bioclastic calcimudstone/wackestone (MW), bioclastic packstone (BP), bioclastic floatstone (BF) and medium-to coarse-crystalline dolorudstone/dolograinstone (CD). These strata accumulated in low to medium energy, subtidal, fore-shoal setting. The middle member consists of thick succession (325m) of massively bedded CD lithofacies interpreted as high energy shoal facies which represents Barremian-Aptian main shelf-margin succession. The upper member (155m thick) consists of three lithofacies of MW, CD and fine crystalline dolomudstone (FD), in ascending order. It is interpreted as lagoon (MW) through subtidal carbonate sand shoal (CD) to supratidal (penecontemporaneous) dolomudstone (FD). The lower two members represent a long-term Barremian to Aptian shallowing-upward megacycle capped by late Aptian unconformity incurred by relative sea level drop. This temporal gap is coeval with an erosional vacuity recognized throughout the Arabian Peninsula. Sea level rise in early Albian heralded deposition of the upper member which also represents a shallowing-upward cycle surmounted by regionally extensive subaerial unconformity recognized in the Arabian Peninsula. Correlation and stratigraphic position of the formation under regional context has been discussed.

Rock magnetics of carbonate systems–investigating palaeodune archives on Fuerteventura (Canary Islands)

ABSTRACTThe mineral magnetic properties of Pleistocene aeolian dune sands from the island of Fuerteventura (Canary Islands, Spain) were studied in order to reconstruct the palaeoenvironmental evolution of Pleistocene climates during their formation. The palaeodunes on Fuerteventura mainly consist of carbonate sands admixed with dust and material of volcanic origin. Due to the low magnetic background caused by the diamagnetic character of carbonate sands, these archives offer a lot of potential for environmental magnetic studies to detect the imprint of dust, volcanic material and paedogenesis. Four sections of alternating palaeosurface–aeolianite sequences in palaeodune fields have been analysed by means of extensive rock magnetic measurements. These Quaternary archives consist of deposits originating from different sources. I. material blown from the shallow shelf, II. material of volcanic origin, and III. long‐range transported dust. The rock magnetic findings enable a more detailed interpretation of the palaeosurfaces within the sequences. We are able to differentiate semiquantitatively between the different source materials on one hand and to distinguish on the other hand those from soil‐forming processes. Soil formation is only weakly developed in the dust imprints in the palaeosol aeolianite sequences, linked to sparse vegetation cover during the Pleistocene on Fuerteventura.

Effects of Load Duration and Stress Level on Deformation and Particle Breakage of Carbonate Sands

Abstract Time-dependent deformation of crushable soils attributable to particle breakage could dominate the postconstruction stability of high rockfill dams and pile foundations. The evolutionary t...

Measurement and prediction on thermal conductivity of fused quartz

Thermal conductivity of soil is a basic physical property related to heat conduction, and also is one of parameters widely applied in geotechnical engineering. The effect of gradation on the thermal conductivity of fused quartz was analyzed by thermal needle tests. The different particle size with the same uniformity coefficient (Cu = 3.2) and different uniformity coefficient for the same particle size (0.10~1.00 mm) were considered in this study. It shows that the thermal conductivity of fused quartz decreases with the decreasing of the mean particle size and with the increasing of the porosity. Simple modified methods to estimate the value of thermal conductivity are proposed, and had been demonstrated successfully by conducting fused quartz, carbonate sand and Ottawa sand.

The study of dynamic properties of carbonate sand through a laboratory database

Carbonate soils are located in temperate and tropical regions of the earth. This kind of soil has special mechanical properties compared with siliceous sand due to special sedimentary environment. In this paper, resonant column device is used to investigate the shear modulus and damping ratio of carbonate sand in the South China Sea at small and moderate shear strain amplitudes. At the same time, the dynamic properties of siliceous sands with the same gradation are also studied for the comparison. The influence of isotropic effective confining pressure and relative density on the dynamic characteristics of the sands is studied. The shear modulus of tested carbonate and siliceous sands increases with the increase of effective confining pressure and relative density. The influence of relative density on the shear modulus and maximum shear modulus of carbonate sand is more obvious than that of siliceous sand under identical test conditions. The damping ratio of both two sands decreases significantly with the increase of effective confining pressure, but the influence of relative density on the damping ratio is not obvious. A comparison between the dynamic characteristics of the carbonate and siliceous sand shows that carbonate sand has higher shear modulus, higher damping ratio, and faster shear stiffness degradation. Based on this study and other existing dynamic and cyclic tests data of different carbonate soils, a database of normalized shear modulus and damping ratio for carbonate soils was created, and a modified hyperbolic model was proposed for calculating the normalized shear modulus and damping ratio of carbonate soils with different calcium carbonate contents.

Issues with integrating carbonate sand texture data generated by different analytical approaches: A comparison of standard sieve and laser-diffraction methods

Palaeoenvironmental reconstructive work relies on sediment-texture information as a proxy for particle-transport dynamics. As the integration of data from multiple sources is often sought for studies at the regional scale, a body of work exists that addresses compatibility levels of different analytical approaches. Past insights are derived predominantly from siliciclastic deposits. This study instead addresses standard sieve and laser-diffraction methods of texture analysis on a suite of carbonate beach sands from San Salvador Island, Bahamas. While the near-equant grain shapes of siliciclastic sands generate comparable results between methods, our findings show that laser diffraction tends to overestimate the coarser fractions in carbonate sands, given indiscriminate measurement of elongate particle axes. Peloidal grains that have width-to-length ratios on the order of 0.5 can pass through much smaller mesh sizes when sieved than diffraction would suggest. The resulting deviation in analytical outputs significantly influences measures of skewness, sorting, and other derivative metrics, which vary by up to several Wentworth classes between procedures. Meaningful integration of texture data obtained by different methods is ill-advised when dealing with carbonate beach sands. Similar problems are documented for muddy deposits, wherein platy clay minerals favor size-overestimation by laser diffraction and a size underestimation by settling tube technique. An improved understanding of methodological biases resulting from application of different particle-size methods is needed to help facilitate data-reconciliation efforts. This study provides a glimpse of issues facing the integration of carbonate sand-texture information, troublesome given prevalence of irregular grain shapes.

Particle breakage of uniformly graded carbonate sands in dry/wet condition subjected to compression/shear tests

The behaviour of a granular material is primarily affected by its particle size distribution (PSD), which is not necessarily a soil constant as assumed in traditional soil mechanics. The PSD may change over time due to mechanical as well as environmental actions. In this study, a series of ring shear tests and one-dimensional compression tests were completed on carbonate sand, in both dry and saturated conditions. Samples were prepared with different initial uniform gradings, to investigate: (1) the influence of the saturation state and initial grading on mechanical and deformational behaviour of carbonate sands and (2) the evolution of the PSD as a result of breakage. The ring shear tests show that the residual friction angle remains almost constant, but dilatancy reduces with increasing saturation degree. In the one-dimensional compression test, the yield stress decreases with increasing saturation degree, but the compressibility (as defined by Cc) remains almost constant, irrespective of the saturation state. Moreover, saturated samples suffer more breakage than dry samples during ring shear tests, while there is no obvious effect of saturation state on particle breakage in one-dimensional compression. A recently proposed PSD model with only two parameters (λp and κp) is employed to model the evolution of PSD, as it can more broadly capture the whole PSD throughout the breakage process than existing breakage indices. Test results demonstrate that parameter λp is linearly related to Einav’s breakage index $$ B_{\text{r}}^{*} $$ and is dependent on initial grading, but independent of test mode. Parameter κp is in power relationship with $$ B_{\text{r}}^{*} $$ and is independent of initial grading or test mode. The evolution of parameters λp and κp is related to the input work for both ring shear and compression tests, with λp being hyperbolically related to input work and κp in power relationship with input work. Using such an evolution law provides an alternative approach to capture the effects of particle breakage in constitutive models.

The influence of particle shape and mineralogy on the particle strength, breakage and compressibility

It is widely accepted that both particle shape and mineralogy could have a great effect on the particle strength. However, due to the complexity of nature grains, it is difficult to distinguish the influence of particle shape from mineralogy. This paper shows measurements of the particle shape and mineralogy of carbonate sand, completely decomposed granite, Leighton Buzzard sand and pumice sand. The particle shape of carbonate sand and completely decomposed granite is similar, but the mineral of carbonate sand is carbon dioxide while the mineral of completely decomposed granite is mica and feldspar. It is found that the single particle strength of completely decomposed granite is higher than that of carbonate sand, and the particle breakage caused by one-dimensional compressing tests of completely decomposed granite is higher than that of carbonate sand. The mineralogy of both completely decomposed granite and Leighton Buzzard sand are quartz, but completely decomposed granite is more heterogeneous, result in the single particle strength of completely decomposed granite is much lower than that of Leighton Buzzard sand. It is also found the particle breakage from the one-dimensional compression test for completely decomposed is larger than Leighton Buzzard sand. It should be noted that carbonate sand is stronger than completely decomposed granite after quantitatively analysis the particle shape, particle breakage and compressibility behavior although carbonate sand has extremely irregular shape such as a branch shape, and also several pores. On the other hand, although Leighton Buzzard sand, completely decomposed granite and also pumice sand to some extent have composition of silica, the crystal of those three is completely different, result in the strength or compressibility are quite different. It seems that particle shape is not a major factor to affect strength or compressibility, but the mineralogy could be a major factor.

Checklist, assemblage composition, and biogeographic assessment of Recentbenthic foraminifera (Protista, Rhizaria) from São Vincente, Cape Verdes.

We describe for the first time subtropical intertidal foraminiferal assemblages from beach sands on São Vincente, Cape Verdes. Sixty-five benthic foraminiferal species were recognised, representing 47 genera, 31 families, and 8 superfamilies. Endemic species were not recognised. The new checklist largely extends an earlier record of nine benthic foraminiferal species from fossil carbonate sands on the island. Bolivina striatula, Rosalina vilardeboana and Millettiana milletti dominated the living (rose Bengal stained) fauna, while Elphidium crispum, Amphistegina gibbosa, Quinqueloculina seminulum, Ammonia tepida, Triloculina rotunda and Glabratella patelliformis dominated the dead assemblages. The living fauna lacks species typical for coarse-grained substrates. Instead, there were species that had a planktonic stage in their life cycle. The living fauna therefore received a substantial contribution of floating species and propagules that may have endured a long transport by surface ocean currents. The dead assemblages largely differed from the living fauna and contained redeposited tests deriving from a rhodolith-mollusc carbonate facies at <20 m water depth. A comparison of the Recent foraminiferal inventory with other areas identified the Caribbean and Mediterranean as the most likely source regions. They have also been constrained as origin points for littoral to subtidal macroorganisms on other Cape Verdean islands. Micro-and macrofaunal evidences assigned the Cape Verde Current and North Equatorial Current as the main trajectories for faunal immigrations. The contribution from the NW African coast was rather low, a pattern that cannot be explained by the currently available information.

Assessment of Sentinel‐2A multispectral image for benthic habitat composition mapping

Sentinel-2A accuracy for benthic habitat composition mapping was tested and compared to ALOS AVNIR-2. Aerial image acquired using custom-made unmanned aerial vehicle was used to train and validate the model. The mapping was conducted regardless of the benthic class and at individual benthic class. Benthic habitat class spatial distribution was obtained using the combination of image segmentation and classification tree analysis. The aerial image was interpreted based on the percentage of the constructed and non-constructed classes. The constructed class includes coral reefs, dead coral, seagrass, and macroalgae, while non-constructed class covers carbonate sand, rock, and rubble. Sentinel-2A produced higher accuracy (92%) than ALOS AVNIR-2 (78%) for benthic habitat spatial distribution mapping. However, in the empirical modelling of benthic habitat composition, ALOS AVNIR-2 (SE 23-24%) produced slightly better accuracy than Sentinel-2A (SE 23-27%). Several factors affected the low accuracy, which include the sub-pixel mixing of benthic habitat and constructed class, the delay between dates of acquisition, and radiometric quality of the images. Since the fundamental relationship between reflectance value and the percentage of the constructed class has been justified and consistent, given more experiments it has the potential to predict benthic habitat composition with higher accuracy in the future.

Deformational Assessment of Shallow Footings Founded on Carbonate Sand

Carbonate (calcareous) sandy soils are well known to be prone to crushability and to have higher compressibility compared to siliceous sands. This study assess the deformational behavior of carbonate (calcareous) sand under shallow footings by carrying out back analyses load tests of twelve full-scale footings founded on improved carbonate (calcareous) sand fill and uniformly loaded up to the allowable bearing pressure. The footings are reinforced concrete isolated pads ranging from 1.5×1.5 m up to 3×3 m in size. These full-scale loading tests are combined with extensive in-situ static cone penetration tests carried out under the location of each footing to test the foundation soil. The recoded measurements of these full-scale load tests are utilized to measure the immediate settlements of the sand fill under variable stresses and to extrapolate long-term (creep) settlement as wells. Based on the analyzed results, comprehensive back analyses were carried out to validate several commonly-used settlement prediction formulae, including Schmertmann’s method (Schmertmann et al., 1978) and Meyerhof (1965 and 1974) for utilization validation with carbonate (calcareous) coarse-grained materials.

Particle Breakage and Deformation Behavior of Carbonate Sand under Drained and Undrained Triaxial Compression

AbstractThe results of a series of drained and undrained triaxial compression tests terminated at various axial strains were reported to show the gradual accumulation process of particle breakage o...

Fractal breakage of porous carbonate sand particles: Microstructures and mechanisms

In situ, three-dimensional (3D) characterizations of particle breakage in porous carbonate sands are presented, for the first time, with synchrotron-based micro computed tomography. Evolution of grain-scale characteristics are identified and quantified via elaborate image processing and topology analyses. The sequential 3D images reveal distinctly different fracture mechanisms for carbonate sands from silica sands. The angular shape of carbonate sand particles facilitates bending fracture, and particles with a lower sphericity and a higher porosity are more prone to break. 3D crack networks extracted from fractured particles imply considerable cleavage along initial pores. The fractal dimension of crack networks increases with external loading due to crack branching via cleavage. The resultant fragment size distribution also appears fractal and the fractal feature is valid down to the breakage limit of calcium carbonate. Crack propagation along the initial pores reduces the energy barrier for particle breakage and thus fracture strength of particles.

Experimental study of the shear strength of carbonate gravel

Current studies on carbonate soils are mostly directed at carbonate sands rather than widely distributed carbonate gravels. In this study, a series of large-scale direct shear tests were conducted to evaluate the parameters that affect the mechanical behaviours of carbonate gravels, including the particle size, gradation, relative density and normal stress. Simultaneously, several tests on quartz gravels with similar gradations were conducted for a comparison. The experimental results showed that a large cohesion, which is defined as the interlocking cohesion in this paper, appears in carbonate gravels and it increases as the average particle size and relative density increase. The strength envelope of the carbonate gravel with an average particle size greater than or equal to 3.9 mm could be expressed as a broken-line with two straight lines in the stress range of 0–1600 kPa, but for quartz gravel, the broken-line mode appears when the average particle size reaches 7.7 mm. This result could be related to the breakage of the particles. Therefore, a certain number of gravel particles with different sizes and different shapes were coloured to trace the breakage mode of the particles. At the same time, it could be found that the strength of the carbonate gravel is not always greater than that of the quartz gravel with a similar gradation.

Compression behaviour of hydrate bearing carbonate sand - fines mixtures

High gas hydrate content has been found in fine-grained sediments containing substantial amount of foraminifera in the South China sea. One of the possible hydrate accumulation habits is filling the intra- particle voids in the foraminifera. To understand the effects of this hydrate accumulation habit on the compression behaviour of the fine-grained sediment, two series of isotropic compression tests were conducted. Due to high intra-particle porosity, carbonate sand (CS) was mixed with the fines to mimic the hydrate formation in the intra-particle voids in the laboratory prepared soil specimens. The compression test results revealed that the mixtures of fines with as high as 40% CS content can exhibit the transitional behaviour such that non-convergent compression lines are observed at the high stress level. It is evident that breakage of CS grains is negligible in these mixtures. Hence, the initial fabrics are not erased under the high stress level resulting in non-convergent compression lines. The compression curves of the hydrate bearing CS-fines mixtures can be classified into three different stress regimes. There is no significant difference in the compressibility of the soil mixtures with and without hydrate in the low stress regime. As the stress increases further reaching the medium stress regime, the hydrate reduces the compressibility of the soil mixtures with increasing hydrate saturation. Upon reaching the high stress regime, the bond breakage at the inter-particle contacts becomes significant leading to the convergence of compression curves between the hydrate bearing and host soil mixtures. It is also found that a new effective hydrate saturation, representing the amount of hydrate in the inter-particle voids, is better correlated to the compressibility of the hydrate bearing soil mixtures.

Identification of reworked foraminifera in temperate carbonate sediments – A pilot study from the Coorong Coastal Plain, southern Australia

The extent of aspartic acid and valine racemization (total hydrolysable amino acids) in single tests of the benthic foraminifer Lamellodiscorbis dimidiatus is examined as a potential method for identifying remanié fossils within temperate, bioclastic carbonate sediments. The foraminifer Lamellodiscorbis dimidiatus is a physically robust species capable of withstanding reworking from weathered calcarenites, and has the potential to experience multiple sedimentary cycles of deposition and erosion with subsequent inclusion in younger sedimentary units. The extent of racemization measured in single tests of Lamellodiscorbis sp., reveals that the skeletal carbonate sand sampled from the modern foreshore at Long Beach, Guichen Bay, southern Australia, contains foraminifera ranging in age, from modern individuals, to specimens of late Holocene and Late Pleistocene age. The age of individual foraminifer, however, cannot easily be distinguished based on their taphonomic appearances. The AAR data for Lamellodiscorbis sp., imply that a significant proportion of the skeletal carbonate constituents within the calcarenites of the Coorong Coastal Plain represent reworked bioclasts. The reworked sedimentary constituents within younger sediments, has resulted from the erosion of older calcarenites during glacial cycles.