Study On The Diffusion Law Of Nano Slurry Based On Three-Dimensional Characterization Of Coal-Measure Mudstone Pores And Fractures

Argillaceous soft rock is common in geotechnical engineering such as mines,water conservancy,tunnels,subways,etc.It has the characteristics of easy swelling,mudding and disintegration,which seriously threatens the safety and stability of the project.Focusing on the difficulties of excavation and support of argillaceous soft rock roadway,this paper started from the basic parameters test of the mineral composition,fine microscopic morphology,pore structure of mudstone from 8₁ coal seam floor of Guobei coal mine in Huaibei mining Area,and grouting characteristics of nano-slurry silica sol.Then the reasons for softening and difficult anti-seepage of argillaceous soft rock were analyzed,and the basic properties of nano-slurry silica sol and cement-based materials were compared.Next,the mudstone samples were scanned by three-dimensional X-ray microscopy imaging system with high resolution.The real three-dimensional pore and fracture of mudstone was reconstructed and digital core physics experiments were carried out.After that,the real three-dimensional pore and fracture structure of mudstone was introduced into COMSOL Multiphysics finite element simulation software.The diffusion law of silica sol slurry grouting mudstone was simulated and analyzed,and verified by artificial core grouting experiments.Finally,a zoning multi-granularity grouting anti-seepage reinforcement method for argillaceous soft rock roadway was proposed.The design of anti-seepage reinforcement and grouting effect monitoring scheme was carried out for specific mudstone roadway.The main conclusions are as follows:?1?The main minerals of the Huaibei 8₁ coal floor mudstone were quartz and clay mineral kaolinite and illite.The porosity of the mudstone sample is 2.2%,and the surface micro-fractures of mudstone were developed.The existence of micro-scale fracture was the crux of the argillaceous soft rock roadway which was difficult to anti-seepage and reinforcement.The theoretical minimum injectable width of silica sol in mudstone was 188.01 nm,which meant silica sol could theoretically inject 47.68%of mudstone pores and fractures,and the injection performance is much higher than cement-based materials.?2?The threshold value of the mudstone CT image was determined by the moment-preserving method and the sample was segmented to extract the pores and fractures.Most of the mudstone samples had long and fine fractures,sporadic pores,and obvious spatial heterogeneity.The local pore connectivity and permeability were quite different.?3?The first choice for slurry fluid flow was the path with large pore radius,short path and short distance from outlet.Under different grouting speeds,the flow radius of grouting was basically the same,and it stopped flowing in the two small pipe-like fractures.However,with the increase of grouting speed,the grouting hydraulic pressure at the entrance increased continuously.When the grouting speed was higher than 0.05 mm/s,the grouting hydraulic pressure rose in a straight line,which would bring serious burden to the grouting equipment in the engineering site.The grouting diffusion process of artificial cores shows that there would be filter effect at the injection end and slurry retention effect in the injection process.Because of the existence of filter effect and silica sol were blocked at the injection end.The higher the grouting pressure was,the easier the filter effect would be formed.It was feasible to grout silica sol into low permeability rock with low pressure and slow permeability.According to the research results,a grouting anti-seepage reinforcement method for argillaceous soft rock roadway was proposed.The core of the method was to spray concrete on the surface of the roadway after excavation,re-spraying silica sol,shallow hole grouting cement slurry,and deep hole low pressure injection of silica sol.Therefore,two anti-seepage layers would be formed on the surface of the roadway and the deep surrounding rock part of the roadway and a shallow cement slurry reinforcement layer would be formed.The two anti-seepage layer and reinforcement layer could theoretically solve the large deformation support problem of softening rheology of argillaceous soft rock roadway to a certain extent.There are 55 diagrams,6 tables and 97 references in the paper.