Coral Sand Research Articles

Study on the particle breakage of coral sand in the ring shear experiment

Study on the particle breakage of coral sand in the ring shear experiment

Study on the pullout bearing characteristics of root piles in coral sand foundations under different water content states

Offshore wind energy will become one of the important sources of energy in the future, and root piles with good pullout bearing characteristics can be used for the foundation of offshore wind power generation facilities. Through the model test, the pullout bearing characteristics of root piles with different water content states in coral sand foundation are comparatively analyzed, and the pullout bearing deformation law and pile body force transmission characteristic law of root piles is revealed. The results show that when the coral sand foundation is saturated and the water level rises and falls, compared with the dry sand foundation, the pullout bearing capacity of the root pile decreases, and the ability to control the displacement is sharply weakened. The axial force curve at the root is in the shape of a step; after the foundation is affected by water, the maximum value of lateral friction resistance first appears at the bottom root, and the lateral friction resistance at the lower root is always greater than that at the upper root; the water level rise and fall leads to a decrease in the lateral friction resistance in the area of the pile without a root, and the lateral friction resistance in the area of the root is increased. Under saturated and water level rise and fall condition, the total bearing ratio of the root pile section increases, and the bearing ratio of the lower root pile section is always larger than that of the upper root. After loading, the soil in the upper part of the pile is compacted, and the soil in the lower part is loosened; the maximum value of soil pressure in the compacted area of the dry sand condition gradually moves downward, and the maximum value of soil pressure in the saturated and water level rise and fall condition is always located in the lowermost part of the compacted area; the pore water pressure in the saturated and water level rise and fall condition is basically equal with the hydrostatic pressure, and there is no obvious super pore water pressure generated. The research results provide scientific basis for the application of root piles in coral sand foundation.

Analisis Aspek Ekobiologi Ikan Kakatua (Scaridae) di Perairan Pulau Tikus Kota Bengkulu

The large potential of marine fisheries owned by the City of Bengkulu can be an economic source for the local community. The fish potential comes from pelagic fish and reef fish. One of the reef fish is the parrot fish (Scaridae). Parrot fish in Bengkulu City are obtained from Tikus Island which are sold on Malabero Beach. The purpose of this study was to analyze the ecobiological aspects of parrot fish (Scaridae) in Tikus Island waters, Bengkulu City. The results of this study are expected to provide information in the form of valid data regarding the ecobiological aspects of parrot fish (Scaridae) in Tikus Island waters, Bengkulu City. In this study, data collection to look at ecological or environmental aspects was carried out by direct observation in the field at 3 stations, while biological aspects, namely food habits (amount/type of food), were observed through a microscope in the laboratory. The results of water parameter measurements, namely the temperature at station 1 ranged from 28-29 0C, station 2 is 29 0C, station 3 is 29 0C. pH value at station 1 is 7.0-7.3, station 2 is 7.3-7.7, station 3 is 6.5-7.1. Salinity values at station 1 is 31 ppt, station 2 is 30 ppt and station 3 is 31 ppt. Dissolved oxygen (DO) at station 1 ranged from 5.6-6.3 mg/L, station 2 5.2-5.3 mg/L and station 3 5.6-6.1 mg/L. The water brightness at station 1 is 9.2 m, at station 2 is 6.6 m and at station 3 is 7.4 m. Current velocity at station 1 ranges from 0.09-0.11 m/s, station 2 are 0.08-0.14 m/s, and at station 3 ranges from 0.05-0.09 m/s. Water depth at station 1 is 9.2 m, station 2 is 7.3 and station 3 is 7.5 m. These results indicate that Tikus Island water have a good environment for survival and habitat of parrot fish (Scaridae) or other marine biota. Furthermore, the biological aspects studied are food habits. Based on the identification results, 4 groups of food types were found in the parrot fish stomach, namely phytoplankton, zooplankton, sand coral, and were not identified. The percentage of food groups found from phytoplankton, zooplankton, sand coral, and not identified were 53%, 3%, 15%, 29%, respectively.

Undrained dynamic behavior of geogrid-reinforced coral sand

In this research, the reactions of geogrid reinforcement on the dynamic performance of medium-dense coral sand with various cyclic stress ratios were investigated using stress-controlled undrained dynamic triaxial tests. The results indicate that the insertion of geogrid decreases the dynamic deformations, and pore pressure build-up rate, and impeded the liquefaction of coral sand. The liquefaction resistance of coral sand increases with the increase in the number of reinforcement layers. The liquefaction resistance of coral sand reinforced with three-layer and two-layer geogrid increases by 333% and 6% compared to unreinforced ones. The geogrid reinforcement layers can effectively resist the complete stiffness degradation of coral sand under cyclic loading. The coral sand stiffness decays at an accelerated rate as the cyclic stress ratio increases, whereas increasing the number of reinforcement layers reduces the coral sand stiffness degradation rate, especially for three-layer geogrid reinforced coral sand at low cyclic stress ratios. Generally, the geogrid as a reinforcement material to coral sand is considered a better alternative to enhance the engineering properties of coral sand and offers significant prospects in coastal and marine engineering construction with coral sand.

Study on Effect of Particle Size Distribution on Water-Retention Capacity of Coral Sand from Macro and Micro Perspective

The reclamation coral sand (CS) layer is the survival environment for island reef vegetation in the South China Sea. The root system within the CS bed draws water necessary for vegetation growth, implying that the water-retention capacity of CS plays a pivotal role in determining vegetation viability. Particle size distribution (PSD) significantly influences the water-retention capacity of geomaterials. This study examines the impact of PSD on the water-retention capacity of CS from both macro (soil–water characteristic curve, SWCC) and micro (pore water distribution) perspectives using the pressure plate test and nuclear magnetic resonance technique, and an F&X model was used to analyze the SWCC of CS. The findings indicated that the F&X model aptly describes the SWCC of CS with different PSDs. Both the air entry value and residual water content rise with an increased content of fine grains (d < 0.25 mm), suggesting that the presence of fine grains augments the water-retention capacity of CS. It is considered that a size range of d = 0.075–0.25 mm predominantly impacts the water-retention capacity of CS. The PSD primarily influences the water-retention capacity by affecting the pore size distribution of CS. The volume of small pores swells with the surge of fine-grain content, while the maximum pore size contracts with increasing fine-grain content. Limited pore connectivity in CS means macropores can retain water even under high suction, bolstering the water-retention capacity of CS. These findings offer theoretical guidance for selecting gradation parameters for the planting layer on island reefs.

Effect of gradation and relative density on shear strength of coral sand

ABSTRACT Due to the wide particle size distribution of coral sand, There are significant differences in mechanical behaviour of coral sand with different particle size distribution. It is of great significance to propose a quantitative analysis method for mechanical properties considering the effect of gradation. In this study, 27 groups of coral sand specimens with particle size ranging from 5 mm to 0.125 mm were prepared. The consolidated undrained (CU) triaxial shear tests were carried out and the influence of gradation and relative density on the shear characteristic were discussed. The grading and relative density of coral sand are controlled by the median particle size (d50) and relative density (Dr), The results show that the peak deviator stress decreased, and the effective internal friction angle first increased and then decreased with the increase of d 50. Both the peak deviator stress and effective internal friction angle of coral sand increase with the relative density. A parabolic relationship was founded between the effect internal friction and d 50 as D r was constant. The effective friction angle peaked when d 50 was 2 mm. Finally, a calculation method of shear strength parameter considering the gradation and relative density of coral sand was proposed.

Experimental Analysis of the Changes in Coral Sand Beach Profiles under Regular Wave Conditions

This study utilized 50 laboratory experiments to document the evolution of coral beaches under varying regular wave conditions, including five distinct wave periods and ten wave heights. Both the type of equilibrium beach and the shape of sand bars were used to represent beach evolution. The evolution of coral sand beaches was then compared to quartz sand beaches. The experimental results show that the predicted (modeled) equilibrium profile of a quartz sand beach was not applicable to coral sand beaches. Compared to sand bars on quartz sand beaches, the distance from bar crests to the beach berm in coral sand beaches was greater, whereas the erosional depth of sand troughs was deeper. However, the grain size distribution of sand associated with the coral sand beach under wave action was consistent with Celikoglu’s law. Both an equilibrium beach profile classification model and a sand bar shape prediction model for coral sand beaches were developed based on the experimental data.

Study on the interaction between particle shape and particle breakage of coral sand by discrete element method

A series of biaxial tests with different initial particle shapes, confining pressures, bond strengths and depositional angles were conducted on coral sand by using a 2D discrete element method simulation. The interactions between particle shape and particle breakage were investigated, and their combined effects on the mechanical behavior of coral sand were analyzed. The test results showed that particle breakage considerably weakens the effect of particle shape and inherent anisotropy on shear strength. The difference between the internal friction angles of unbreakable and breakable agglomerates Δφ decreases with increasing aspect ratio AR, sphericity S, and depositional angle θ. There exists a unique relationship between the relative breakage BrDe and the input energy E for the same agglomerates, which is independent of axial strain and confining pressure. However, this relationship is significantly influenced by the agglomerate shape and depositional angle, and irregular and low depositional angle specimens are more easily broken. In addition, the evolution of the aspect ratio AR and sphericity S of agglomerates was controlled by particle breakage, regardless of the axial strain, confining pressure, bond strength and depositional angle, and these trends were determined by the initial particle shape.

Bacterial carbonic anhydrase-induced carbonates mitigate soil erosion in biological soil crusts

Soil erosion is a significant environmental issue worldwide, particularly in island regions where land resources are exceedingly scarce. Biological soil crusts play a crucial role in mitigating soil erosion, yet the precise effect and mechanism of biological soil crusts against erosion remain ambiguous. In this study, biological soil crusts at various developmental stages from a tropical coral island in the South China Sea were chosen to investigate the role of carbonic anhydrase in mitigating erosion. A cohesive strength meter, real-time quantitative PCR, and 16S rRNA gene high-throughput sequencing were employed to assess variations in soil antiscouribility as well as bacterial abundance and composition during the formation and development of biological soil crusts. Scanning electron microscopy was utilized to detect carbonates induced by bacterial carbonic anhydrase and elucidate their role in the solidification of sand particles. The findings indicate that the formation and development of biological soil crusts significantly enhance anti-scouribility. Comparison to those of bare coral sand, the shear stress increased from 0.35 to 1.11 N/m2 in the dark biocrusts. Moreover, significantly elevated carbonic anhydrase activity was observed in biological soil crusts, demonstrating a positive correlation with antiscouribility. In addition, there was a significant increase in bacterial abundance within the biological soil crusts. The enrichment of Cyanobacteriales and Chloroflexales potentially contributed to the increased carbonic anhydrase activity and antiscouribility. Furthermore, three cyanobacterial strains with carbonic anhydrase activity were isolated from biological soil crusts and subsequently confirmed to enhance sand solidification through microbial carbonate precipitation. This study presents initial evidence for the role of microbial carbonic anhydrase in enhancing the antiscouribility of biological soil crusts during their formation and development. These findings offer novel insights into the functional and mechanistic dimensions underlying the mitigation of soil erosion facilitated by biological soil crusts, which are valuable for implementing sustainable biorestoration and environmental management technologies to prevent soil erosion.

Cultivation of Seaweed Kappaphycus alvarezii with Various Substrates Different on Laboratory Scale

Kappaphycus alvarezii is an important red algae and can be used as one of the primary raw materials in fisheries. It is widely cultivated because of its relatively cheap production technology, and post-harvest handling is simple and easy. This algae has excellent economic value for carrageenan producers. Carrageenan is used as a food ingredient, cosmetics, and medicine. The success of cultivating K. alvarezii seaweed can be achieved if a suitable environment for its growth supports it. One of the environmental aspects that influence the growth of K. alvarezii seaweed is the bottom substrate of the waters. This research aims to analyze the best substrate for cultivating green K.alvarezii seaweed on a laboratory scale. This research used an experimental method with a Completely Randomized Design (CRD) consisting of 4 treatments and three repetitions, resulting in 12 experimental units. The treatments tested were different substrates: a coral substrate, a sand substrate, a volcanic rock substrate, and a coral sand substrate. The results of this study showed that the average survival rate in various substrate treatments ranged from 7.16% to 39%, final weight ranged from 1.43 g to 7.8 g, specific loss rate ranged from -3.157%/day to -5.124%/day, carrageenan yield ranged from 6.8% to 18.4%, and thallus tissue showed that all treatments still showed the presence of cortex and medullary tissue with varying shapes and structures

Laboratory testing on cracking characteristics and improvement mechanism of coral mud

In recent years, the development and construction of island reefs have been flourishing. Due to the remoteness of island reefs from the mainland, the scarcity of building materials, and the high transportation costs, it is imperative to use local marine resources, and the potential value and status of coral mud on island reefs, which is formed by the remains of corals and other biological entities, is becoming increasingly prominent. Utilization and optimization of natural resources on island reefs have become a brand-new research direction and challenge. This article mainly focuses on the development of a new type of green engineering material, coral mud, for use in building surface layers. Thickness effects, PVA fiber (vinylon staple fiber) modification, and HPMC (Hydroxypropyl Methyl Cellulose) adhesive modification are taken into consideration. Through laboratory tests and image processing technology, fractal theory, and electron microscopy experiments, the macro-meso-microscopic multi-scale cracking rules of the coral mud surface layer and the optimization modification rules of PVA fibers and HPMC adhesives are revealed. The results demonstrate that the performance of the coral mud surface layer is superior to that of the kaolin surface layer, and the 10 mm thickness performs better than the 5 mm and 20 mm thicknesses. As the thickness of the coral mud surface layer increases, the contact between coral mud particles becomes denser, the scale of surface micro-cracks decreases, and the number of micro-pores decreases. PVA fibers can effectively inhibit the further development of macro and micro cracks and play a good bridging role. There is a bonding and adhesion relationship between coral mud and PVA fibers, and they have a good synergistic effect in inhibiting macro and mesoscopic cracks. With the increase in HPMC adhesive content, the number of micro-cracks and the scale of micro-cracks decrease accordingly, and the structure and performance of the coral mud surface layer are further improved. Overall, PVA fibers are more effective than HPMC adhesives in inhibiting the cracking of the coral mud surface layer. This provides valuable guidance for the development and application of coral mud in wall surface materials.

The Physical and Mechanical Properties of Coral Sand

Coral sand interacts with a variety of particles and species in tropical marine habitats due to its special characteristics. particular emphasizes the benefits of using contemporary mathematical technologies to examine the characteristics and behavior of coral sand for engineering applications. Coral sand's composition and creation processes influence its distinctive qualities. Coral sand is mostly made up of the skeletal remains of tiny coral polyps and has a white or off-white appearance due to its high calcium carbonate content. Particularly in the area of geotechnical engineering, the interaction of coral sand particles is of great importance. Particle form, size distribution, and interparticle forces are a few examples of the variables that affect how coral sand behaves as a granular material. Investigations on its geotechnical characteristics, such as its shear strength, permeability, and compressibility, are the main focus of current research. To learn more about the engineering behavior of coral sand, researchers are examining field monitoring approaches and laboratory testing procedures. Additionally, research aims to comprehend how biological activity, cementation, and particle form affect coral sand's mechanical characteristics. In the coral sand study, the benefit of contemporary computation technologies is remarkable. Advanced computer methods, in combination with numerical modeling and simulation approaches, provide precise forecasting of coral sand behavior under various loading and climatic conditions. Engineers may use these technologies to examine foundation design issues, determine the stability of coastal buildings, and create methods for controlling coastal erosion. The study of coral sand and its characteristics has important ramifications for geotechnical engineering. The capacity to assess and construct engineering structures in coral sand settings is improved by the application of contemporary computation technologies.

Benthic Habitat Classification Using Sentinel-2a Image With And Without Water Column Correction In Pengudang Village, Bintan Regency

Research on the mapping of benthic habitats in the waters of Pengudang Village, Bintan Regency, uses Sentinel-2A imagery. This mapping process has the potential to display the results of classification of benthic habitats in shallow waters. The purpose of this study was to assess the Maximum Likelihood Classification (MLH) algorithm model for mapping benthic habitat cover through Sentinel-2A satellite imagery using the lyzenga water column correction and without water column correction and to calculate the accuracy of the MLH classification results for benthic habitats in waters Pengudang Village. This classification uses a pixel-based image classification which is grouped into a cover class for each pixel. This classification groups into 4 benthic habitat classes, namely dead coral sand (KMP), sea grass (LM), live coral sand (PKH) and sand (PS). The results showed that the application of the lyzenga correction using the MLH algorithm in mapping benthic habitats resulted in a significant accuracy rate (80,00%), while the application without lyzenga correction using the MLH algorithm resulted in an accuracy rate (76,00%). These findings support the use of the lyzenga correction method which can increase the level of accuracy by (4,00%) with the MLH algorithm as a guide in better mapping of benthic habitat cover in Pengudang Village.

Development of Strength‐Maturity Relationship for Coral Sand Concrete Incorporating Bamboo Leaf Ash

Development of Strength‐Maturity Relationship for Coral Sand Concrete Incorporating Bamboo Leaf Ash

Seepage deformation characteristic of gap-graded coral sand in the South China Sea

Foundation settlement and collapse disasters resulting from seepage deformation in hydraulic-filled islands and reefs have been observed in the South China Sea, but the underlying failure mechanism and characteristic remain unclear. This study aims to investigate the influence of compactness and fine particle content on the seepage deformation of gap-graded coral sand and revel the characteristics and mechanism of seepage deformation of gap-graded coral sand through laboratory seepage deformation tests. The results indicate that the seepage deformation failure mode of gap-graded coral sand is influenced by the content of fine particles which undergo an evolution process from continuous piping to discontinuous piping to boiling. Particle loss is affected by the constraints between coarse particles, and the ability of different particle contact forms to restrict the loss of fine particles is different. Moreover, irregular particle morphology increases intergranular constraints, enhancing the coral sand's resistance to seepage deformation compared to standard quartz sand. Based on these findings, the instability coefficient was used to consider the influence of particle morphology and inter-particle contact on the seepage deformation. A hydraulic criterion for the internal stability of coral sand was established, demonstrating its versatility. Furthermore, the applicability of existing geometric criteria in evaluating coral sand was analyzed. The existing methods were found to be inaccurate in evaluating the internal stability of coral sand specimens with a fine particle content below 20 %.

Investigating the influence of root layer quantity on the pullout bearing characteristics of root piles in coral sand foundations

Root piles with good load-bearing characteristics can be used as foundations for offshore wind power facilities. By conducting model tests on root piles with varying numbers of root layers in coral sand foundations and studying the theoretical pullout ultimate bearing capacity, the influence of the number of root layers on the pullout bearing characteristics of root piles is analyzed. Subsequently, a formula for calculating the pullout ultimate bearing capacity of root piles is derived, drawing on the Vesic foundation bearing capacity theory and the Rankine soil pressure theory. The results indicate that increasing the number of root layers enhances the ultimate bearing capacity of root piles, enabling them to better withstand pullout forces and control displacement. The axial force curve of the roots exhibits a step-like pattern. Additionally, the maximum lateral mechanical resistance of the root piles in 3 and 5 layers gradually shifts downwards with increased loading. While the total bearing capacity of the root section increases, the rate of increase diminishes over time. Model test data validates the proposed theoretical formula for calculating bearing capacity, affirming its reliability. These research findings furnish a theoretical groundwork for the practical application of root piles in engineering.

CULTIVATION OF SEAWEED Caulerpa racemosa USING DIFFERENT SUBSTRATES ON A LABORATORY SCALE

Caulepa racemosa is a type of sea grape from the group of green algae (Chlorophyceae) that can be found in Indonesian waters. Coastal communities use this species as a source of daily food. Besides being a food ingredient, C. racemosa can be used for medical purposes because it contains antioxidants. The distribution of C. racemosa and its density in waters depends on the type of substrate and season. The substrate in the cultivation container is an essential factor in cultivating C. racemosa. Various substrates have different characteristics and influence the growth of C. racemosa. This research aims to analyze the best substrate for the survival of seaweed on a laboratory scale. This research used an experimental method using a Completely Randomized Design (CRD) consisting of 4 treatments, namely different substrates of sand, coral, volcanic rock, and coral sand. The results of this research are that different types of substrates have a real influence on the survival rate of C. racemosa cultivated on a laboratory scale. Sand substrate gave the best results: a survival rate of 112.83%, a final weight of 22.56 g, and the highest antioxidant content on volcanic rock substrate of 83.19%. This research concludes that differences in substrate directly influence the survival rate and final weight of C.racemosa. The substrate that provided the best survival rate of 112.83% was sand substrate

High ductility cementitious composites incorporating seawater and coral sand (SCS-HDCC) for offshore engineering: Microstructure, mechanical performance and sustainability

In support of sustainable development strategies, engineering construction on remote islands is conductive to promoting the development of marine resources and mitigating increasingly severe resource conflicts. However, marine engineering, facing extreme weather and natural disasters, necessitates concrete with high ductility, durability and crack control capacity. This study evaluates the feasibility of using seawater and coral sand instead of fresh water and river sand to prepare the high ductility cementitious composites (SCS-HDCC). The results indicate that increased coral sand substitution introduces defects and expands the aggregate-matrix interfacial zone due to its rough surface, high specific area, and low strength. Coral sand's internal curing enhances compactness and reduces harmful pores. The dual action of seawater and coral sand, SCS-HDCC matrix is more tenacious, and the damage and blockage during the fiber pull-out process becomes obvious, and the slip hardening coefficient of fiber-matrix interfacial zone increases. SCS-HDCC achieves satisfactory ductility (up to 1.18 %) with initial cracking strength of 4.18 MPa, ultimate tensile strength of 5.66 MPa, and crack width of 71.2 ± 6.74 μm, average crack spacing of 6.02 mm. The SCS-HDCCs prepared in this study offers economic and environmental benefits by reducing economic costs and carbon emissions through transporting raw materials from the continent. The research results have guiding significance for the construction of islands and reefs by SCS-HDCC.

Cl- dissolution and mechanical properties of PVA, CSA modified coral sand

Due to high Cl- content and porosity in coral, coral-aggregate concretes usually present poor durability and mechanical properties. In this paper, two types of materials, polyvinyl alcohol (PVA) and Calcium Sulphoaluminate (CSA) clinker, were used to modify properties of coral sand and consequently inhibit leaching of Cl- from coral and improve mechanical properties of yield mortar. Results showed that the smaller the particle size, the greater Cl- dissolution rate of crushed coral sand. PVA and CSA materials could effectively inhibit the Cl- dissolution, and the most obvious decrease could reach 6% and 23%, respectively, in comparison of 35% prior to the modifications. However, mechanical properties of these two modified coral sand mortars were unsatisfactory under standard curing, which the CSA-modified specimens generate thaumasite resulting in a strength decrease and could be improved by a slight increase in curing temperature to 35 ℃.

Centrifuge model tests on bearing behavior of lateral-loaded single pile in coral sand

Centrifuge model tests on bearing behavior of lateral-loaded single pile in coral sand