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Fine-grained soils containing diatom microfossils of biological origin are found worldwide. However, although these soils are acknowledged to have unique physical and mechanical properties, the exact role of diatoms in determining their compression and hydraulic behaviours remains unclear, especially when high effective stress is involved, and the underlying micromechanism is yet to be revealed. This study investigated the compression and permeability of diatomaceous soils prepared by mixing pure diatom and kaolin powders through one-dimensional constant rate of strain compression tests with a maximum vertical stress of 10 MPa. The microstructure of the soils studied was observed by atomic force microscopy, scanning electron microscopy and mercury intrusion porosimetry, and the microstructural evolution during compression was traced. The results indicate that the special hollow structure of diatom particles with internal pores contributes significantly to the high void ratio, compressibility and permeability of diatomaceous soils, and increasing the diatom content improves the pore distribution non-uniformity of the diatom–kaolin mixtures. In addition, the diatom particles have high brittleness and breakage potential, leading to microstructural rearrangement during compression, especially pore-structure adjustment. Lower compressive stress deforms the inter- and intra-aggregate pores, but higher vertical stress damages the diatoms' hollow structure, which changes the compression and hydraulic parameters in a different manner from the case of conventional clay. This paper enriches the knowledge concerning the multilevel behaviour of fine-grained soils containing diatom microfossils and provides a fundamental dataset. [ABSTRACT FROM AUTHOR]

The mechanical characteristics of the soil–structure interface have a crucial impact on the bearing capacity of offshore foundations. The thixotropy-induced strength recovery of remolded soils has a significant effect on the increase in the stability of the foundation. To explore the effects of thixotropy on the recovery characteristics of the soil–structure interfacial shear strength, a self-designed interfacial mechanical characteristic apparatus is designed in this study to perform a series of soil–structure interface tests on clays from the South China Sea and offshore Dalian, respectively. The relationship between the recovery of undrained shear strength and the change of interfacial shear strength is analyzed by the index of shear-resistant coarseness. And the effect mechanism of thixotropy on interfacial shear strength is discussed from the microscopic view. The test results indicated that the rate of increase of the soil–structure interfacial shear strength is higher than that of the undrained shear strength. The particle size index of the soil was found to significantly influence the strength recovery characteristics of the soil–structure interface. A higher clay content will accelerate the development of the interfacial shear strength. This article provides a deep insight into the thixotropic effect on the mechanical properties of the marine soil–structure interface. [ABSTRACT FROM AUTHOR]

Rosmarinic acid (RA) is a natural phenolic compound extracted from the Labiatae family and is a natural antioxidant. In this study, walnut oil added with RA was treated with different ultraviolet radiations, and stabilization effects in terms of the same conditions (0.2 mg/g) were compared with synthetic antioxidant (BHT). In order to compare the effectiveness of three UV treatments, different lab tests were conducted, namely, the acid value, peroxide value, iodine value, anisidine value, DPPH free radical scavenging rate, and malondialdehyde content. The enhanced UV-A, UV-B, and UV-C radiation intensities have increased the oxidation stability of RA-added walnut oil, of which UV-B has the greatest influence on the oxidative stability of walnut oil. When both RA and BHT were added at 0.2 mg/g, the antioxidant effect of RA is superior to the general antioxidant BHT. [ABSTRACT FROM AUTHOR]

The HT ht value versus time of clays is shown in Fig. When the HT ht value is equal to 100%, it means the strength of soil has recovered its original intact shear strength. The regained strength of YS-1 clay is also considerable, and the value of HT ht is greater than 40% after 2 months. By contrast, the HT ht of YS-2 and ES-2 clays in the corresponding deep layer is much lower (see Table 1 in the original paper). [Extracted from the article]

This paper presents an experimental investigation on the ultra-soft marine soil recovered from the seabed in deep-water areas in South China Sea (SCS). An improved T-bar penetrometer is made and employed in laboratory to measure the undrained shear strength of the soils and its degradation with the penetration cycles. A further investigation on the microstructure of the marine soils during the cyclic penetration has been conducted. The findings indicate that there is a kind of "crust zone" existing in the upper layer of seabed sediment. The reasons of this "crust zone" are further interpreted. By comparing the intact and remoulded samples, it is found that the former exhibits a higher strength degradation degree than that of the latter. This discrepancy in shear strength degradation between the two kinds of samples can be attributed to the microstructure changes. During the cyclic penetration process, the natural flocculated structure of intact soil samples collapses with the breakage of particle aggregates, and a further destruction of large-sized inter-particle pores occurs. As far as the remoulded soil samples, their microstructures experience a continuing fracturing course starting with a dense packing of soil particles and followed by a progressive development of the loose packing state. [ABSTRACT FROM AUTHOR]