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Rock mass pressure has always been a research hotspot in the field of tunnel engineering, especially in the super large-span tunnel, which is characterized by flat section, large excavation span, and complex stress field. Based on the Letuan Tunnel (a bi-directional tunnel with eight traffic lanes) of Binlai expressway expansion project in Shandong Province, China, this paper focused on the calculation method of rock mass pressure and the evolution law of load release in the construction process of the super large-span tunnel excavated by upper-bench central diaphragm (CD) method. Based on field measured data of Letuan Tunnel, the deformation behavior of primary lining and the distribution state of rock mass pressure during the tunnel construction were analyzed. According to the bearing mode of supporting structure, the mechanical models of different construction stages were established. Then, the rock mass pressures in different construction stages were back-calculated using mechanical models and compared with the measured values, and the evolution law of load release during the tunnel construction was discussed. The study results show that the tunnel deformation and rock mass pressure were significantly affected by the construction process and support form, and the excavation span was the key factor affecting the stability of rock mass. For the shallow-buried super large-span tunnel constructed by upper-bench CD method, the primary support of upper bench was under eccentric pressure. The comparison between the back-calculated value and the field measured value indicated that they were similar, and the average relative error was 17.23%. According to the concept of load release coefficient proposed in this paper, the load release coefficient after the pilot tunnel ahead (Part I) excavation reached 63%, and the load release coefficient after the pilot tunnel behind excavation (Part II) was 37%, which means that the rock mass pressure of Part I is increased about 59% due to the excavation of Part II.

Strong ratoon ability is the key factor in improving sugarcane productivity and reducing production costs. Soil microorganisms are sensitive to environmental changes and play an important role in regulating soil ecological functions. However, the impacts of sugarcane varieties with different ratooning abilities on soil microorganisms are poorly understood. Therefore, two common cultivated varieties with different ratooning abilities (Yuetang 94-128 with strong ratooning ability and Yuetang 03-373 with low ratooning ability) were selected to study the effects of sugarcane varieties on sugarcane yield and microbial community structure from 2017 to 2019 in South China. The Illumina MiSeq platform was applied in the present study to detect the diversity and community structure of rhizosphere soil bacteria and fungi in the different sugarcane varieties in 2019. The results showed that sugarcane cane yield and sugar yield were higher in Yuetang 94-128 during the three years, whereas the sugar content was lower in Yuetang 94-128 than in Yuetang 03-373 during this time. Different years influenced cane yield and sugar yield, while the sucrose content remained stable during the different years. The pH, organic matter (SOM) and total nitrogen (TN) contents were significantly lower in Yuetang 03-373 than in Yuetang 94-128, whereas the other indices had no significant difference between the different varieties. The α-diversity of sugarcane rhizosphere soil bacteria and fungi was not significantly different between the different varieties. Compared with Yuetang 03-373, the increase in bacterial taxa associated with the soil carbon and nitrogen cycles may be one of the reasons for the strong ratooning of Yuetang 94-128. The difference in rare fungal taxa between the two sugarcane varieties may lead to different ecological functions in the soil. Redundancy analysis (RDA) and Mantel test showed that the soil physical and chemical properties did not significantly influence the microbial community structure, which could indicate that sugarcane variety was the primary variable responsible for microbial community structure. This study provided important information on the rhizosphere soil microbial community structure of different sugarcane varieties with different ratooning abilities and provided a theoretical basis for improving the ratooning ability of sugarcane varieties from the perspective of improving soil microbial community.

Large deformation has always been a focus and difficult issue in the construction of deep-buried tunnels in squeezing rock. Previous studies mainly focused on the large deformation of medium and small span railway/highway tunnels in soft ground. However, there are limited researches on the large deformation control methods for large-span (three-lane) highway tunnels constructed in unfavorable geological environment. Based on the Lianchengshan Tunnel of the Baoji-Hanzhong expressway in Shaanxi Province, China, this paper studied the deformation behaviors and mechanical mechanisms of a large-span tunnel excavated in chlorite schist formation with single primary lining method and double primary lining method by in-situ test and numerical simulation. The achieved results indicate that the double primary lining method is much more effective than that of the single primary lining method in restraining the deformation of surrounding rock, and the maximum vertical displacement and horizontal convergence are reduced by 67% and 66%, respectively. The support method of double HK200b-type steel sets combined with large-diameter foot reinforcement bolt (FRB) and deep invert could effectively control the large deformation of the case tunnel, which effectively avoided the supporting structure failure, repeated clearance invasion and multiple reshaping work caused by the single primary lining method and conformed to the energy-saving construction concept of “no clearance interfering, no support reshaping” of tunnels in squeezing ground. Simulation analysis of surrounding rock deformation, supporting structure stress and plastic zone distribution was performed to evaluate the support effect of the two deformation-controlled methods. Finally, the deformation and stress characteristic curves of rock-support of the two deformation-controlled methods were established, which revealed the supporting mechanism of double primary linings for large-span tunnels in chlorite schist. The research results can provide a theoretical basis and practical reference for the large-deformation control of similar large-span tunnels in squeezing rock.

During the tunnel construction in soft ground, the insufficient bearing capacity of tunnel foundation usually causes a series of settlement problems. Tunnel feet-lock pipe (TFP) has been widely used to take the vertical load acting at the foundation of a tunnel foot. However, the detailed bearing performance of TFP is still not clear, and there is a lack of quantitative research. In this paper, a simple analytical approach is adopted to evaluate the performance of the TFP, and the main parameters affecting the supporting performance of the TFP are analyzed. The results show that the ϕ42–ϕ140 TFP with the angle of 10° can take 3.8%–40.4% of vertical load. TFP has an effective length of 1.7 m–2.8 m, which is related to the relative stiffness between the TFP and the stratum. With the increase of the installation angle, the TFP shares more vertical load. This trend is more obvious when the angle of the TFP is greater than 20°. If the proportion coefficient of the subgrade reaction coefficient is doubled, the vertical load shared by the TFP can be increased by 34%–38%. For every 10 cm increase in overbreak behind the steel rib, the vertical load shared by TFP is reduced by 16%.

A functional pesticide–fertilizer combination is in high demand due to the many potential advantages, including the dual reduction in pesticide and fertilizer inputs, increased crop yield, safe to use, and environmental friendly. To investigate the impact of a pesticide–fertilizer on the soil environment of sugarcane, the effects of clothianidin and/or organic fertilizer treatments on the diversity, structure, and function of the rhizosphere bacterial community were studied using 16S rRNA gene sequencing in 2019 at Guangzhou Sugarcane Research Institute. The bacterial community treated with the pesticide–fertilizer displayed a higher diversity compared with the control treatments (added with pesticide or fertilizer only). The dynamic changes of the bacterial community structure revealed that the pesticide–fertilizer treatment showed a significant variation in the second week. Functional analysis demonstrated that four bacterial genera, including Dyella, Mucilaginibacter, Massilia, and Telmatospirillum, could play an important role in degrading clothianidin and improving soil health. The relative abundance of nitrogen cycle genes showed that the nitrification-related gene pmoA-amoA and denitrification-related genes nirK and norB were increased significantly in the pesticide–fertilizer treatment compared with that of the control treatments. This preliminary study provides a good basis to understand the effect of a pesticide–fertilizer integration on the soil rhizosphere microbiome which would be helpful for the evaluation of its application in the field.

The issue of large deformation mechanism in soft rock tunnels has puzzled tunnel scholars for decades. Previous studies have not evolved a clear and common understanding. Therefore, detailed on-site measurement, full investigation and statistical analysis have been conducted on the instability and failure of Muzhailing Tunnel since its construction, whose length is beyond 15 km. The study aims at systematically analyzing the failure mechanisms and modes of Muzhailing Tunnel in monoclinic and soft-hard interbedded rock strata. Study results show that the angle between strata strike and tunnel axis greatly determines the magnitude of deformation, the dip direction significantly controls the bias direction and maximum deformation direction, and the dip angle deeply affects the deformation form. The failure modes of surrounding rock mainly include four types: spalling and overturning failure, bending failure, shear slip failure and buckling failure. Large deformation characteristics are summarized from six aspects: failure form, groundwater, sensitivity to influencing factors, deformation degree, deformation speed and deformation duration. The instability modes of primary lining include in-plane (transverse) instability and out-plane (longitudinal) instability. Finally, the causes of large deformation are analyzed from geological, structural, engineering and human factors.

The rhizosphere microbial community is important for plant health and is shaped by numerous environmental factors. This study aimed to unravel the effects of a pesticide/fertilizer mixture on the soil rhizosphere microbiome of field-grown sugarcane. A field trial on sugarcane was conducted in Zhanjian City, Guangdong Province, China, and soil samples from the rhizosphere were collected after clothianidin pesticide and/or organic fertilizer treatments. The effects of pesticide and/or organic fertilizer treatments on the composition, diversity, and predictive function of the rhizosphere microbial communities were examined using 16S rRNA gene and ITS1 amplicon sequencing. Compared with the controls (no pesticide or fertilizer used), the microbial community that resulted from treatment with the pesticide/fertilizer mixture (SPF) had a higher relative bacterial diversity and fungal richness, and contributed more beneficial functions to sugarcane, including xenobiotics biodegradation and metabolism of amino acids. The bacterial and fungal compositions at various taxonomic levels were not significantly different in SPF and SP (pesticide only) treatments compared to treatments without the pesticide, suggesting that the clothianidin addition did not cause a detrimental impact on the soil microbiome. Moreover, five bacterial genera, including Dyella, Sphingomonas, Catenulispora, Mucilaginibacter, and Tumebacillus, were significantly more abundant in the SPF and SP treatments, which could be associated with the pesticide addition. With the addition of organic fertilizers in SPF, the abundances of some soil-beneficial bacteria Bacillus, Paenibacillus, and Brevibacillus were highly increased. Our study provides insights into the interactions between the rhizosphere soil microbiome and pesticide-fertilizer integration, which may help improve the application of pesticide-fertilizer to sugarcane fields. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s13205-021-02770-3.