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In this study, the small-strain shear modulus of a calcareous sand was investigated by conducting bender element tests on both horizontal and vertical planes. The effects of sample preparation method, stress path and stress history on the developing of void ratio, the parameters in the modified Hardin Equation, and the stiffness anisotropy were examined. The test results show that the moist tamping samples have the least void ratio variation among the five samples. The void ratio recovery in effective horizontal stress [[sigma]'.sub.h] = 100 kPa tests is higher than that in the effective vertical stress [[sigma]'.sub.v] = 100 kPa tests. The samples prepared in the dry state have lower stiffness than those prepared in the moisture state, which is not influenced by the anisotropic stress state. The stiffness anisotropy induced by the sample preparation method is significant under anisotropic consolidation. In [[sigma]'.sub.h] = 100 kPa tests, the stiffness ratios at the end of the unloading stage are lower than the initial values at the loading stage, which is not found in the [[sigma]'.sub.v] = 100 kPa tests, meaning that the stress history and stress path could affect the stiffness anisotropy and eliminate the impact of fabric anisotropy. Key words: small-strain shear modulus, anisotropic consolidation, bender element, stiffness anisotropy, sample preparation method. Au cours de la presente recherche, on a etudie le module de cisaillement a petite deformation d'un sable calcaire en realisant des essais sur elements flexibles dans des plans horizontaux et verticaux. La methode de preparation des echantillons, la trajectoire et l'historique des contraintes ont ete examinees pour determiner le taux de vide, les parametres de l'equation de Hardin modifiee et l'anisotropie de la rigidite. Selon le rapport d'essai, les echantillons de bourrage humide presentent la plus faible variation du taux de vide parmi les cinq echantillons. Le rapport de vide recupere dans les essais a contrainte horizontale effective [[sigma]'.sub.h] = 100 kPa est plus eleve que dans les essais a contrainte verticale effective [[sigma]'.sub.v] = 100 kPa. De plus, les echantillons prepares a l'etat sec presentent une rigidite plus faible que ceux prepares a l'etat humide, independamment de l'etat de contrainte anisotrope. Sous une consolidation anisotrope, la methode de preparation des echantillons induit une anisotropie de la rigidite significative. Au cours des essais [[sigma]'.sub.h] = 100 kPa, les rapports de rigidite a la fin de la phase de dechargement sont inferieurs aux valeurs initiales de la phase de chargement, ce qui n'est pas le cas dans les essais a [[sigma]'.sub.v] = 100 kPa, indiquant que l'historique et la trajectoire des contraintes pourraient affecter l'anisotropie de la rigidite et eliminer l'impact de l'anisotropie du tissu. [Traduit par la Redaction] Mots-cles : module de cisaillement a faible deformation, consolidation anisotrope, element de flexion, anisotropie de la rigidite, methode de preparation des echantillons., Introduction Small-strain shear modulus G0 is an important mechanical parameter in geotechnical engineering, reflecting the deformation resistance of soil subjected to static and dynamic small-amplitude shear loadings. The factors affecting [...]

Cuttage is the main propagation method of tea plant cultivars in China. However, some tea softwood cuttings just form an expanded and loose callus at the base, without adventitious root (AR) formation during the propagation period. Meanwhile, exogenous auxin could promote the AR formation of tea plant cuttings, but the regulation mechanism has not yet explained clearly. We conducted this study to elucidate the regulatory mechanism of exogenous auxin-induced adventitious root (AR) formation of such cuttings. The transcriptional expression profile of non-rooting tea calluses in response to exogenous IBA and NAA was analyzed using ONT RNA Seq technology. In total, 56,178 differentially expressed genes (DEGs) were detected, and most of genes were significantly differentially expressed after 12 h of exogenous auxin treatment. Among these DEGs, we further identified 80 DEGs involved in the auxin induction pathway and AR formation. Specifically, 14 auxin respective genes (ARFs, GH3s, and AUX/IAAs), 3 auxin transporters (AUX22), 19 auxin synthesis- and homeostasis-related genes (cytochrome P450 (CYP450) and calmodulin-like protein (CML) genes), and 44 transcription factors (LOB domain-containing protein (LBDs), SCARECROW-LIKE (SCL), zinc finger protein, WRKY, MYB, and NAC) were identified from these DEGs. Moreover, we found most of these DEGs were highly up-regulated at some stage before AR formation, suggesting that they may play a potential role in the AR formation of tea plant cuttings. In summary, this study will provide a theoretical foundation to deepen our understanding of the molecular mechanism of AR formation in tea cuttings induced by auxin during propagation time. [ABSTRACT FROM AUTHOR]

Microbially induced calcite precipitation is an environment-friendly method for improving stiffness, strength, and dilatancy of loose or weak soils. Although many experimental studies have been performed on biocemented sands, few efforts have been devoted to establishing constitutive models for such materials. A critical-state-based bounding-surface model for biocemented sands was proposed in this research. An exponential equation of the plastic deviatoric strain was used to describe the degradation in a biocemented bond. The established model was applied to predict the drained triaxial test results of biocemented calcareous sands at different confining pressures and biocementation levels. We found that the current proposed biocemented model can well predict the softening and dilation of biocemented calcareous sands. [ABSTRACT FROM AUTHOR]

Microbially induced calcium carbonate precipitation (MICP) is a novel cementation technique. The improved responses of biotreated soils are mainly attributed to interparticle MICP bonds and have been extensively studied by element-scale tests. However, the particle-scale mechanism of MICP bonds has not been fully understood, especially when considering the discrepancy in particle morphology. In this paper, we carried out a series of particle-scale tensile tests on biotreated quartz sands and glass beads and found that tensile strength of the MICP bonds increased with an increase in cementation level or a decrease in regularity of particle shape. We also interpreted the statistical distribution of the tensile strength and tensile failure modes. The results of this study could provide a solid base for theoretic modeling of biotreated soils. [ABSTRACT FROM AUTHOR]

Biotreatment has the potential to be used in restoration and conservation of stone-cultural relics, but less research has been focused on the anisotropic strength of rock with biotreated cracks. In this study, a series of Brazilian splitting tests (BSTs) was conducted on the intact disc sandstone specimens to generate mimicking natural cracks. A specifically designed biocementing system was then adopted to form effective biocementation between the two halves of the specimen, as indicated by microimages. The sandstone specimens with a biotreated crack were then subjected to BSTs at different loading angles. The apparent tensile strength (ATS) of the biotreated specimen can reach and even exceed that of the intact specimen, with low anisotropy. Furthermore, four failure modes are identified based on optical photos. The aforementioned findings reveal that the biotreatment is a remarkable method for repairing cracks of stone-cultural relics. [ABSTRACT FROM AUTHOR]

Microbially induced calcium carbonate precipitation (MICP) has attracted much attention as a promising green technique for soil improvement. Despite the significance of precipitation pattern in mind, constitutive relations or numerical models considering the finite‐strain mechanical effects of the various precipitation patterns are rarely developed. In this paper, we propose a novel 3D DEM modeling scheme by using coarse particles to represent sand grains and fines as cementing agents, to reproduce the various precipitation patterns in MICP‐treated sand. Based on the topological relations with adjacent particles and the contribution to the mechanical improvement, the cementing fines are classified into effective, partially effective, surface coating, and pore filling ones. The microstructural characteristics and their evolution upon external loading are investigated quantitatively after a careful calibration and validation. The microstructural variation in experiments can be well reproduced, pinpointing this variation as a possible cause for the fluctuation in experimental data. Massive coating fines are produced accompanying the microstructural degradation, which is initiated by the breakage of effective bonds. The breakage of partially effective bonds may become dominating later in the medium to strong cemented specimens. One weakly cemented specimen shows diffuse failure with simultaneous bond‐breakage and friction. In contrast, the medium to strong cemented specimens show localized failure with the dominating mechanism transiting from bond‐breakage to friction producing notable pore filling fines. We propose a relation between unconfined compressive strength and the equivalent effective volume fraction of cementing agents normalized by the pretreatment porosity, which reveals the coupling effects of the initial configuration and the precipitation pattern on the mechanical improvement. [ABSTRACT FROM AUTHOR]

Particle breakage is a major factor that determines the strength and deformation of coral sand. Consolidated drained triaxial compression tests under different confining pressures have been conducted on coral sands as a basis for 3D discrete element simulations, focusing on the particle breakage characteristics. Considering angular breakage and overall breakage in the numerical model, particle breakage is simulated with a fragment replacement method, and the particle size and the equivalent stress are combined as the criterion to judge the occurrence of particle crushing. The validation of the numerical model is proved by reproducing comparable stress-strain relations, evolutions of grain size distribution and relative breakage rate. The overall behavior of the specimen transit from strain softening to strain hardening with the increase in confining pressure from 100 kPa to 400 kPa. Meanwhile, the number of angular breakages increases at a decreasing rate, while the number of overall breakages increase at an increasing rate. This phenomenon implies that overall breakage overwhelms angular breakage and becomes the dominating particle breakage mechanism gradually with increasing confining pressure. Microscopic analyses reveal that higher confining pressure increases the overall contact force, the portion of strong contact force and the coordination number. [ABSTRACT FROM AUTHOR]