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Abstract The deterioration and deformation of brittle rock generally appear in railway tunnels with the operation of large buried deep tunnel. To investigate the macro-micro fracture and acoustic emission evolution characteristics of brittle rock, this paper conducted the uniaxial compression, scanning electron microscope (SEM), and acoustic emission (AE) signal monitoring under different loading rates. The results showed that the loading rate has an obvious enhancement effect on mechanical parameters. The increased loading rate extends the elastic deformation and improves the bearing strength, elastic modulus and deformation modulus. The fracture patterns include shear fracture, composite fracture, and tension fracture. The oblique shear fracture is transformed into composite fracture and tension fracture with the loading rate increasing. The microscopic fracture shows that increasing loading rate inhibits the evolution of oblique shear fractures and promotes the expansion of tensile fractures. The roughness level of tensile fractures is significantly lower than that of oblique shear fracture and composite fracture. The AE parameters and deformation behavior are characterized by simultaneous evolution. The AE amplitude changes from low-level and low-density distribution to high-level and high-density distribution as the loading rate increases. The AE activity intensity of tensile fracture is significantly greater than that of oblique shear fracture and composite fracture. The warning timeliness of cumulative AE events and cumulative AE energy is generally earlier than the AE b-value under the same loading rate, and the early warning timeliness of cumulative AE events is similar to that of cumulative AE energy.

A rate-dependent constitutive model for saturated frozen soil is vital in frozen soil mechanics, especially when simultaneously describing the nonlinearity, dilatancy and strain-softening characteristics. The distribution of the non-uniform strain rate of saturated frozen soil at the meso-scale due to the local ice-cementation breakage is described by a newly binary-medium-based homogenization equation. Based on the field-equation-based approach of the meso-mechanics theory, the interaction expression of the strain rate at macro- and meso-scale is derived, which can give the strain rate concentration tensor at different crushed degrees. With the thermodynamics and empirical assumption, a breakage ratio in the rate-dependent form is determined. This overcomes the limitations of the existing binary-medium-based models that are difficult to simulate rate-dependent mechanical response. Based on these assumptions, a newly binary-medium-based rate-dependent model is proposed considering both the ice bond breakage and material composition characteristics of saturated frozen soil. The proposed constitutive model has been validated by the test results on frozen soils with different temperatures and strain rates.

As the most common geological disaster problem in mines, slope geological disasters have become a focus of research, along with the difficulty of mine safety and ecological environment protection together with the ecological restoration of open-pit mines. At present, a large number of slope-retaining wall structures lack research on safety monitoring, real-time acquisition, and intelligent early warning. Therefore, this paper combines cement-modified loess with gravity retaining wall structures and puts forward a new type of greening gravity retaining wall structure. From the perspective of “the Internet of Things + construction”, a video monitoring system is established to monitor the retaining wall structure in real time. Finally, based on video image processing technology, the deformation of the retaining wall surface is identified and the inclination angle of the wall surface is calculated, so as to improve the real-time and intelligent monitoring of the new greening gravity retaining wall. The results show that the new greening gravity retaining wall based on video monitoring proposed in this paper has the characteristics of a gravity retaining wall and ecological retaining wall, which are conducive to improving the real-time and intelligent monitoring of the new greening gravity retaining wall. Cement-modified loess is used as the planting matrix, and the cement mixing ratio should not exceed 10%. Considering the requirements of economy and shear strength, the cement mixing ratio should be selected from 5% to 12%.

At present, there are some key issues in the traditional preimmersion method for reducing the collapsibility of the loess ground, such as the difficulty in determining the total water consumption and the long immersion time. In response to these issues, a new method, the borehole preimmersion method, is presented, and a specific theoretical design model is proposed for application in projects. The method is specifically discussed from a new perspective, and the diffusion mechanism and evolution law of water in the ground are presented in detail through theoretical analysis and numerical calculation, respectively. The water diffusion is a mushroom-type form for a single water injection hole immersed in water. A calculation model derived for a single water injection hole or a group of water injection holes based on the research results is used to calculate the volumes of soaked loess and the total water consumption. Through an in situ immersion test, the treatment effect of this method is evaluated to verify the rationality of the method and the theoretical calculation model proposed in this study, which provides a new method and theoretical framework for effectively reducing the collapsibility of the loess ground.

In the geogenetic overburden excavation of underground space projects (such as comprehensive pipe corridors or subways), the foundation stress is in an unloading state. The effect(s) from the unloading on the coefficient of subsidence in the loess area should be considered. In this study, to explore the effect of unloading on the collapsibility of loess, the collapsible loess in the Guanzhong area was considered as the research object. An expression for the unloading collapse coefficient was established based on the unloading stress ratio, unloading collapse ratio, and other parameters. The influence of the unloading on the loess collapse coefficient was studied using an indoor collapsibility test, and the function form and parameters for the expression were determined. As combined with the field test, the accuracy of the expression for the unloading coefficient was verified based on the test value for the specific collapsibility, calculated value for the specific collapsibility, and calculated value for the unloading collapsibility.

The prediction of foundation settlement is an important topic in loess filling engineering. Based on a filled foundation in Yan’an, China, this study explores the consolidation characteristics of compacted loess with different compaction energy and consolidation pressure through consolidation tests, analyzes the strain-time curve and refines the curve within 2 h, separates the primary and secondary consolidations, and obtains the critical time point between the primary and secondary consolidations. Deformation rate St′ and cumulative deformation St were introduced to analyze the St′ − St curve at the secondary consolidation stage; the secondary consolidation coefficient was employed to describe the secondary consolidation characteristics of compacted loess. According to the secondary consolidation characteristics, a prediction model of loess settlement considering different compaction energy and fill thickness was proposed, and the applicability of the model was further analyzed. The model will facilitate in guiding the design and construction of loess filling engineering.

The moisture and the temperature variation of shallow loess during the freeze-thaw process have tremendous influences on the freeze-thaw disease and agricultural development. The present paper, based on the field test of the temperature and water content of the shallow loess in the seasonal frozen region, probes into the variation of the temperature and moisture fields of shallow loess in the freeze-thaw period. Field test shows that the daily variation of surface temperature reaches the maximum with the peak temperature appearing around 14:00, and the time when the peak temperature appears gradually postpones as the depth increases. Moreover, the daily variation of soil temperature decreases with the increase of temperature, and the variation can be ignored given the depth of more than 30 cm. In addition, there is an obvious variation of moisture content in shallow soil under the action of freeze-thaw cycles. In this regard, the coupled calculation model is proposed in this paper to simulate the dynamic variation of temperature and moisture in shallow soil in Bin County located in Western China under natural conditions, compare the calculation value with the measurement value, and further verify the rationality of the numerical calculation method and parameter selection. Furthermore, the variation law of the maximum frozen depth with the air temperature is obtained through the simulation of extreme cold climate conditions.

Vertebrates achieve adaptive immunity of all sorts against pathogens through the diversification of antibodies. However the mechanism of invertebrates' innate immune defense against various pathogens remains largely unknown. Our study used shrimp and white spot syndrome virus (WSSV) to show that PjCaspase, a caspase gene of shrimp that is crucial in apoptosis, possessed gene sequence diversity. At present, the role of gene sequence diversity in immunity has not been characterized. To address this issue, we compared the PjCaspase gene sequence diversities from WSSV-free and WSSV-resistant shrimp. The sequence analysis indicated that the PjCaspase gene from the WSSV-resistant shrimp contained a special fragment, designated as fragment 3 (221-229 aa). Down-regulation or overexpression of the PjCaspase gene containing fragment 3 led to significant inhibition or enhancement of virus-induced apoptosis, but had no effect on bacterium challenge. We found evidence that the silencing or overexpression of this gene led to a 7-fold increase or 11-fold decrease of WSSV copies, respectively. Our results suggested that the PjCaspase gene containing fragment 3 provided the molecular basis for the antiviral defense of shrimp. This study represented the first report of the role of gene sequence diversity in the immunity of an invertebrate against virus infection. Invertebrates may employ this gene sequence diversity as a system to avoid pathogen interference with their immune response.