Mechanism Of Grouting Reinforcement For Completely Weathered Granite With Rich Water And Its Application

With the rapid development of transportation infrastructure construction in China,the control of disaster due to bad geological condition during the construction of the tunnel has become an important research topic,especially with the focus of construction shifting to the mid-west and south-west mountainous area.These areas are located in strong weathering zone of granite and the conditions of surrounding rock is poor,which increase the difficulty of safety construction of tunnel.The granite are widely distributed in the east of Yunnan-Guizhou plateau in our country,including Qinling-Dabie mountain as well as vast area at southeast of China,especially concentrated in Fujian,Guangxi,Guangdong,Hunan and Jiangxi Province.These regions present distinctive features of "strong weathering,highsand content,poor cementation and high-risk disintegration encountering water" for hot and wet climate where it can easily lead to geological disasters such as water inrush and mud gush during the process of tunneling.Grouting is widely used in the treatment of water inrush and mud gush in completely weathered granite strata as an effective controlling method.However,due to the influence of physico-mechanical properties and hydraulic characteristics,it presents different diffusion model and reinforcement mechanism duringgrouting which increases the difficulty for study.The grouting theory is far left behind engineering practice,and it is badly in need of further study.In this paper,the completely weathered granite was specially proposed as the study object.The special physico-mechanical properties and hydraulic characteristics were systematically studied by laboratory test,and the characteristics of completely weathered granite were determined afresh.The diffusion and reinforcement mode of slurry in completely weathered granite strata was discussed,and the mechanism how grouting conditions affect grouting effects was quantitatively depicted,which revealed the grouting reinforcement mechanism of completely weathered granite.Based on large 3-D grouting model test system,the evolution law of multi-physical field under the influence of different grouting stage was studied,and the spatial distribution law of slurry extension form and grouting reinforcement effect was investigated.Finally drainage and guidance grouting technology for inrush of water and mud in completely weathered granite strata was put forward,with its utility and efficiency verified by developing of a series of field test in the grouting treatment engineering of water inrush and mud gush in Junchang tunnel in Guangxi Province.(1)Through the geological data analysis of completely weathered granite,and based on the systematic study of physico-mechanical properties and hydraulic characteristics,the feature attribute of completely weathered granite in Guangxi province grouting diffusion and reinforcement pattern of completely weathered granite was obtained,and the influence of physical parameters on mechanical property and hydraulic characteristics was investigated.(2.)The clay mineral contents of completely weathered granite had an effect on the permeability and water stability of medium,and then had an effect on the diffusion and reinforcement pattern of slurry.With the increase of clay mineral contents,the grouting diffusion and reinforcement pattern of completely weathered granite was divided into 4 categories:permeation diffusion mode,strong permeation-weak fracturing mode,strong fracturing-weak permeation mode and fracturing diffusion pattern.(3)Based on the grouting simulation test of completely weathered granite,the reinforcement effect made by single-fluid grouting to the strength characteristics,impermeability and water stability of weak medium was quantitatively studied.Besides,the influence mechanism of diffusion and reinforcement pattern and strength characteristics of grouting reinforced soil respectively adopted by single and double-fluid grouting was comparatively analysed.(4)The influence of spatial attenuation characteristic of slurry pressure on spatial distribution shape of slurry vein was considered,and based on Flamant answer to the stratum displacement caused by the concentrated force acting on the boundary of half-plane body,the control equation of slurry vein width was established,which revealed the time and spatial distribution of channel aperture during the corresponding process of grout penetration.(5)Grouting reinforcement mechanism of progressive segmented grouting in completely weathered granite was studied.Based on the model test of progressive segmented grouting in completely weathered granite,the evolution law of multi-physical field under the influence of different grouting segments was obtained in real time,and the response characteristics of grouting pressure,grouting rate and mass of drainage was investigated.The expansion and thickness variation law of slurry vein in different grouting segments was revealed,and the reinforcement effect of soil medium before and after progressive segmented grouting was quantitatively depicted.(6)The development status of main run-off channel of groundwater in water-rich strata of completely weathered granite had a great effect on the slurry diffusion form.The extension characteristics of slurry vein and reinforcement effect were studied based on changing the drainage conditions of grouting simulation test.It was found that the quantity and location of the drainage holes was an important factor affecting slurry vein extension,and grouting reinforced soil corresponding to different extension forms of slurry vein presented different reinforcement effect.(7)Drainage and guidance grouting technology based on integrated geological exploration was put forward.Based on the geologic characteristic of completely weathered granite,the hydrogeological information obtained by integrated geological exploration was regarded as precursor,and the curtain grouting was selected as the main grouting treatment measure.Through the drainage and decompression of drainage holes,the slurry was guided to spread and reinforce,which improved the extensibility and increased the branches of the slurry veins,and the reinforcement effect of surrounding rock was strengthened.Finally,the systematic grouting treatment for inrush of water and mud in completely weathered granite strata was formed.The research results were applied in the grouting treatment engineering of water inrush and mud gush in Junchang tunnel,Censhui express way,Guangxi province,which ensured the tunnel through safely.