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AbstractThis study conducts a series of large-scale pullout tests to explore the pullout behavior of the biaxial geogrid-calcareous sand interface. It investigates the effects of normal stress, relative density, and embedded length on the interface pullout behavior of geogrid reinforcement in calcareous sand. In addition, this research examines changes in interface shear strength and the interface friction coefficient. The interface interaction mechanism of geogrid reinforcement in calcareous sand and the evolution of pullout force-clamp displacement curves are determined. The results indicated that the pullout force-clamp displacement curve primarily exhibits softening and hardening behaviors. The passive resistance of the geogrid mesh significantly influences the softening behavior, while shear friction predominantly affects the hardening behavior. The interface friction coefficient ranged from 0.28 to 0.88 for embedded lengths of 300 − 460 mm. The effects of relative density and embedded length on interface cohesion are more pronounced than those on the interface friction angle. When the embedded length increased from 300 to 460 mm, the rise in interface cohesion ranged from 42.0% to 47.7%, whereas the increase in internal friction angle ranged from 9.5% to 14.5%.

Damaged structures on coral islands have been spalling and cracking due to the dual corrosion of tides and waves. To ensure easy access to aggregate materials, magnesium potassium phosphate cement (MKPC) and coral sand (CS) are mixed to repair damaged structures on coral islands. However, CS is significantly different from land-sourced sand in mineral composition, particle morphology, and strength. This has a substantial impact on the hydration characteristics and macroscopic properties of MKPC mortar. Therefore, in this study we investigated the compressive strength, interfacial mechanical properties, and corrosion resistance of MKPC CS mortar. Changes in the morphology, microstructure, and relative contents of hydration products were revealed by scanning electron microscope-energy dispersive spectrometer (SEM-EDS) and X-ray diffraction (XRD). The results indicated that the compressive strength increased linearly with the interfacial micro-hardness, and then stabilized after long-term immersion in pure water and Na2SO4solution, showing excellent corrosion resistance. Compared with MKPC river sand (RS) mortar, the hydration products of CS mortar were an intermediate product 6KPO2·8H2O with a relative content of 3.9% at 1 h and 4.1% at 12 h. The hydration product MgKPO4·6H2O increased rapidly after 7-d curing, with an increased growth rate of 1100%. Our results showed that CS promoted the nucleation and formation of hydration products of MKPC, resulting in better crystallinity, tighter overlapping, and a denser interfacial transition zone. The results of this study provide technical support for applying MKPC mortar as a rapid repair material for damaged structures on coral islands.

AbstractThe identification of oleaginous yeast species capable of simultaneously utilizing xylose and glucose as substrates to generate value-added biological products is an area of key economic interest. We have previously demonstrated that the Cutaneotrichosporon dermatisNICC30027 yeast strain is capable of simultaneously assimilating both xylose and glucose, resulting in considerable lipid accumulation. However, as no high-quality genome sequencing data or associated annotations for this strain are available at present, it remains challenging to study the metabolic mechanisms underlying this phenotype. Herein, we report a 39,305,439 bp draft genome assembly for C. dermatisNICC30027 comprised of 37 scaffolds, with 60.15% GC content. Within this genome, we identified 524 tRNAs, 142 sRNAs, 53 miRNAs, 28 snRNAs, and eight rRNA clusters. Moreover, repeat sequences totaling 1,032,129 bp in length were identified (2.63% of the genome), as were 14,238 unigenes that were 1,789.35 bp in length on average (64.82% of the genome). The NCBI non-redundant protein sequences (NR) database was employed to successfully annotate 11,795 of these unigenes, while 3,621 and 11,902 were annotated with the Swiss-Prot and TrEMBL databases, respectively. Unigenes were additionally subjected to pathway enrichment analyses using the Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), Cluster of Orthologous Groups of proteins (COG), Clusters of orthologous groups for eukaryotic complete genomes (KOG), and Non-supervised Orthologous Groups (eggNOG) databases. Together, these results provide a foundation for future studies aimed at clarifying the mechanistic basis for the ability of C. dermatisNICC30027 to simultaneously utilize glucose and xylose to synthesize lipids.

Catastrophic failure in engineering structures of island reefs would occur when the tertiary creep initiates in coral reef limestone with a transition from short- to long-term load. Due to the complexity of biological structures, the underlying micro-behaviors involving time-dependent deformation are poorly understood. For this, an abnormal phenomenon was observed where the axial and lateral creep deformations were mutually independent by a series of triaxial tests under constant stress and strain rate conditions. The significantly large lateral creep deformation implies that the creep process cannot be described in continuum mechanics regime. Herein, it is hypothesized that sliding mechanism of crystal cleavages dominates the lateral creep deformation in coral reef limestone. Then, approaches of polarizing microscope (PM) and scanning electronic microscope (SEM) are utilized to validate the hypothesis. It shows that the sliding behavior of crystal cleavages combats with conventional creep micro-mechanisms at certain condition. The former is sensitive to time and strain rate, and is merely activated in the creep regime.

Soil-rock mixtures (S-RMs) are widely distributed in the nature. The mesoscopic deformation and failure mechanisms as well as the macro-mechanical behaviors of the S-RMs depend largely upon the rate of deformation, water content and particle sizes. In this research, a series of large-scale direct shear tests with different water contents and different grain-size distributions were conducted to study the influence of the aforementioned factors on the mechanical properties of the S-RMs. Due to the effect of the rock blocks’ breakage in the S-RMs, the relationship between the shear strength and the vertical stress of S-RM follows a power law instead of a linear one. It is found that there exists a threshold value for the vertical stress during the shearing process, below which the soil strength is mainly determined by the inter-locking of particles and the re-arrangement of meso-structure, and otherwise large-sized rock blocks are gradually broken into smaller fragments, resulting in a decrease in the soil strength. The shear rate can also significantly influence the degree of particle breakage and the meso-structural rearrangement of the S-RMs, namely, under low shear rate, the particles of the samples are fully broken resulting in enhanced macro-strength. As a result, the lower the shear rate, the higher the macroscopic strength. So under unsaturated conditions, the water content will affect the strength of the S-RMs by reducing the strength of rock blocks. As the water content increases, the soil strength decreases gradually, and assumes a moderate value when the water content reaches 8%. At the same water content, the soil strength increases with the sizes of large rock blocks. For the occlusion, breakage and structure re-arrangement of the oversized rock blocks inside S-RM, which have a huge influence on the mechanical characteristics of the samples.

Different sedimentary zones in coral reefs lead to significant anisotropy in the pore structure of coral reef limestone (CRL), making it difficult to study mechanical behaviors. With X-ray computed tomography (CT), 112 CRL samples were utilized for training the support vector machine (SVM)-, random forest (RF)-, and back propagation neural network (BPNN)-based models, respectively. Simultaneously, the machine learning model was embedded into genetic algorithm (GA) for parameter optimization to effectively predict uniaxial compressive strength (UCS) of CRL. Results indicate that the BPNN model with five hidden layers presents the best training effect in the data set of CRL. The SVM-based model shows a tendency to overfitting in the training set and poor generalization ability in the testing set. The RF-based model is suitable for training CRL samples with large data. Analysis of Pearson correlation coefficient matrix and the percentage increment method of performance metrics shows that the dry density, pore structure, and porosity of CRL are strongly correlated to UCS. However, the P-wave velocity is almost uncorrelated to the UCS, which is significantly distinct from the law for homogenous geomaterials. In addition, the pore tensor proposed in this paper can effectively reflect the pore structure of coral framework limestone (CFL) and coral boulder limestone (CBL), realizing the quantitative characterization of the heterogeneity and anisotropy of pore. The pore tensor provides a feasible idea to establish the relationship between pore structure and mechanical behavior of CRL.

A study on the interface monotonic shear behavior of calcareous sands reinforced with geogrid was reported. Large-scale monotonic direct shear tests were carried out on calcareous sand samples with and without geogrid. The interface shear behavior was investigated by considering the effects of normal stresses ranging from 25 to 100 kPa and relative densities ranging from 50 to 90%. The results demonstrate that the shear strength of geogrid-reinforced calcareous sand (GRCS) and unreinforced calcareous sand accords with the Mohr–Coulomb strength theory. The shear stress–shear displacement curve presents significant strain-softening behavior, and has experienced elasto-plastic stage, softening stage, residual stage. When the relative density is 50%, 70%, and 90%, the interface peak cohesion of GRCS is increased by 1.6 times, 1.9 times, and 1.4 times compared with the unreinforced calcareous sand, and the interface peak internal friction angle is increased by 1.2 times, 1.1 times, and 1.0 times, respectively. Furthermore, under different normal stresses and relative densities, the interface friction coefficient and the reinforcement effect coefficient are both greater than 1.0, indicating that the geogrid reinforcement can improve the shear strength of calcareous sand.