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Deep underground engineering is in a true three-dimensional stress state, and the adjustment of the three-dimensional stress state caused by engineering excavation will induce the fracture or even instability of the surrounding rock. However, three-dimensional mechanical model research suitable for the stability analysis of deep surrounding rock is very scarce. Therefore, a series of tests under different true triaxial stresses on two rocks (rhyodacite and marble) were conducted, and the characteristic strength (crack stable propagation initiation stress, crack unstable propagation initiation stress and peak strength) and deformation characteristics were further analyzed. After that, using the Lemaitre strain equivalence hypothesis and rock statistical damage theory, a new statistical damage constitutive model at true triaxial stress states was proposed, which introduced the three-dimensional strength criterion Modified Wiebols Cook to characterize the three-dimensional strength of the rock microelement. Therefore, the intermediate principal stress can be reasonably considered. The damage threshold, initial compaction effect and residual strength of the rock microelement at different true triaxial stress conditions were also considered. Then the relationships between the proposed model parameters and σ 2 and σ 3 were analyzed. Furthermore, sensitivity analysis of the influence of parameters m and F 0 in proposed model on the shape of rock stress–strain curve and peak strength was also investigated. The comparison between the results predicted by proposed model and the experimental data shows that the new model established in this study can well simulate the prepeak and postpeak deformation characteristics of rock and the intermediate principal stress effect under true triaxial stress conditions. [ABSTRACT FROM AUTHOR]

Deep underground engineering excavation will induce complex change in the true three-dimensional stress state of the surrounding rock, causing rock damage and then leading to a change in mechanical properties. In this research, the true triaxial compression tests are conducted to study the influence of σ 2 and σ 3 on the mechanical properties of marble, such as the characteristic strength (crack initiation stress σ ci, damage stress σ cd, peak strength σ p, and residual strength σ r), post-peak deformation, ductility and brittleness. The peak strength σ p, crack initiation stress σ ci and damage stress σ cd of rock increase with the increase in σ 2, while the variation of residual strength σ r with σ 2 is different from that of peak strength. As σ 2 increases or σ 3 decreases, the pre-peak plasticity of the rock decreases, the post-peak curve shape of the rock changes significantly, and the overall shape of the post-peak curve transforms from Class I to Class II. The Mogi-Coulomb strength criterion with intermediate principal stress effect was used to characterize the rock microelement strength, and then the new statistical damage constitutive model considering the initial compaction effect and damage threshold was proposed, and the model validation was carried out based on the experimental results and the effects of the proposed model parameters m and F 0 on the rock strength and post-peak curve morphology were further explored. [ABSTRACT FROM AUTHOR]

A rapid, sensitive and visual loop‐mediated isothermal amplification (LAMP) method for detecting Acidovorax citrulli in cucurbit seed was developed in this study. The LAMP primers were designed to recognize the non‐ribosomal peptide synthetase (NRPS) gene (locus tag: Aave_4658) from A. citrulli. The LAMP assay was conducted at 64°C in 1 hr with calcein as an indicator. The sensitivity and specificity of the LAMP assay were further compared with those of a conventional polymerase chain reaction (PCR). The LAMP assay is highly specific to A. citrulli, and no cross‐reaction was observed with other bacterial pathogen. The sensitivity of the LAMP assay was 100‐fold higher than that of conventional PCR with a detection limit of 1 pg of genomic DNA. Using the LAMP assay, 7 of 12 cantaloupe seedlots collected from Xinjiang province were determined to be positive for A. citrulli. In contrast, only 2 of 12 seedlots showed positive for the pathogen with conventional PCR. Moreover, A. citrulli was detected in 100% of artificially infested seedlots with 0.01% infestation or greater. Our results demonstrated that the LAMP assay was simple, visual and sensitive for detecting A. citrulli, especially in seed health testing. Hence, this method has great potential application in routine detecting seed‐borne pathogens and reducing the risk of epidemics. [ABSTRACT FROM AUTHOR]