Criterion of Grouting Pressure in Regional Advance Grouting Treatment to Prevent Water Disaster from Karst Aquifers in Coal Seam Floors.

The deep mining of coal mines in North China faces the serious threat of water inrush from karst aquifers in the coal seam floors, and regional advance grouting technology (RAGT) is an effective means to prevent and control such disasters. However, it is difficult to choose the grouting pressure during the implementation of RAGT, and excessive grouting pressure will lead to the splitting of karst fracture and reduce the grouting effect. In this study, based on the Bernoulli equation, the relationship between the ground grouting pressure and critical grouting pressure during grouting is established. Based on the Hoek-Brown (H-B) strength criterion and a fracture mechanics analysis of hydraulic fracturing, a theoretical equation of the critical grouting pressure for fracture splitting during grouting is obtained. The determination methods of the main parameters, such as the length of the fracture, internal friction angle, and H-B constant of the intact rock and geological strength index, and their effects on the critical grouting pressure, are discussed. The results show that the joint influence of the H-B constant and geological strength index of the intact rock is the key factor influencing the critical grouting pressure. The theoretical research results are applied to the Xujiazhuang limestone grouting reinforcement project of the floor of coal seam 11 in the Zhaoguan coal mine. The critical grouting pressure of the aquifer is determined to be 14.54 MPa, which guides the smooth implementation of the project.

Fissure Grouting Mechanism Accounting for the Time-Dependent Viscosity of Silica Sol.

Subject to the complex hydrogeological environment where underground engineering is located, the grouting prevention and control of microfissure water ingress are increasingly strict. Silica sol grout has been increasingly used in field tests because of its fine particles and good injectability. Therefore, it is necessary to examine the time-dependent viscosity of silica sol grout and clarify its diffusion law in a rock fissure. In this study, the time dependence of the viscosity of silica sol grout was studied, and then the grout viscosity was subdivided into a slow growth period, accelerated growth period, and rapid curing period according to the growth rate. The effects of the concentration of colloidal silica suspension, the concentration of accelerant, and the mixing volume ratio of the two on the growth of the slurry viscosity were studied. A parameter λ was introduced to comprehensively characterize the influence of the three factors on the rheological properties of the slurry. The relationship between the gel induction time and λ and the accelerating growth stage of the slurry gel was obtained by data fitting. The time-dependent equation of the silica sol solution was established. The difference in the grouting diffusion law between silica sol grout and cement-sodium silicate grout (C-S grout) is compared and analyzed by a stepwise calculation method under two grouting modes (constant-pressure grouting and constant-rate grouting). The results show that under the condition of constant-pressure grouting, the silica sol grout migrates and diffuses continuously for a long time, while the C-S grout is close to the final diffusion form at 15-20 s, and the maximum diffusion distance is much smaller than that of silica sol grout. Under the condition of constant-rate grouting, the grouting pressure driving C-S grout increases sharply with time. Compared with C-S grout, silica sol grout has the obvious advantages of a longer effective diffusion time and lower energy consumption. The research results have certain theoretical significance and reference value for the engineering design of silica sol grouting.

Expression and stability of foreign epitopes introduced into 3A nonstructural protein of foot-and-mouth disease virus.

Foot-and-mouth disease virus (FMDV) is an aphthovirus that belongs to the Picornaviridae family and causes one of the most important animal diseases worldwide. The capacity of other picornaviruses to express foreign antigens has been extensively reported, however, little is known about FMDV. To explore the potential of FMDV as a viral vector, an 11-amino-acid (aa) HSV epitope and an 8 aa FLAG epitope were introduced into the C-terminal different regions of 3A protein of FMDV full-length infectious cDNA clone. Recombinant viruses expressing the HSV or FLAG epitope were successfully rescued after transfection of both modified constructs. Immunofluorescence assay, Western blot and sequence analysis showed that the recombinant viruses stably maintained the foreign epitopes even after 11 serial passages in BHK-21 cells. The 3A-tagged viruses shared similar plaque phenotypes and replication kinetics to those of the parental virus. In addition, mice experimentally infected with the epitope-tagged viruses could induce tag-specific antibodies. Our results demonstrate that FMDV can be used effectively as a viral vector for the delivery of foreign tags.

[Construction of a full-length infectious cDNA clone of inter-genotypic chimeric foot-and-mouth disease virus].

OBJECTIVE: A series of type O foot-and-mouth disease (FMD) outbreaks occurred in China seriously affect development of Chinese husbandry. Its causative agent-type O foot-and-mouth disease virus (FMDV) has been evolved three topotypes: Cathay, Middle East-South Asia and Southeast Asia, specifically, the viruses of Cathay topotype are highly adapted to pig, representing the biggest threat on Chinese pig industry. The available FMD vaccine in China provides insufficient protection against some arising viruses of Chathay topotype, which exert important obstacle to control porcinophilic FMD epidemics in China. To develop vaccine candidate with characteristics of good immunogenicity and broad spectrotype, a full-length infectious cDNA clone of inter-genotypic chimeric FMDV was constructed, which replaced part VP3 and VP1 gene of O/HN/93 strain with the corresponding to the variants of Cathay topotype (mainly replaced the B-C and G-H loop of structure protein VP1). METHODS: Linearized recombinant plasmid and plasmid expressing T7 RNA polymerase were cotransfected into BHK-21 cells to rescue the chimeric virus in vivo. RESULT: The transfected cells showed apparent cytopathic effects (CPE) after 36 h post-transfection. The rescued virus was checked by RT-PCR, indirect immunofluorescence, electron microscope. Results show that chimeric FMDV was successfully rescued in vivo. The study of sulk mice pathogenicity show chimeric FMDV has attenuated pathogenicity for suckling mice compared with its parental virus. CONCLUSION: The construction of inter-genotypic chimeric FMDV will lay the basis for developing novel vaccine against FMD.