Experimental Investigation On Mechanism Of Grouting Reinforcement Based On Fault Zoning

Experimental investigation on the mechanism of grouting reinforcement in the fault zone is a positive significance to reduce fault water inrush accidents and guarantee the safety of engineering construction since fault zone often constituting an important underground water sources.In this paper,in view of the complex geological conditions of the fault zones encountered in a roadway excavation,engineering geological models of fault zone grouting based on fault zoning were simplified and established.The scale model test and theoretical analysis were used to investigate the grouting propagation mechanism and the grouting efficiency based on different material compositions of the fault zone and different grouting methods.The experiment and theoretical analysis were combined to obtain the relationship between the grouting pressure and the stress change of the injected medium,and the grouting reinforcement effect of each zone and the zone interface.Based on the theory of grouting in the fault zone,combined with the experimental phenomenon and engineering practice,the grouting efficiency evaluation of each zone and the method of improving the grouting effect was proposed according to the research results.The main results of this paper are as follows:(1)Two-dimensional and three-dimensional engineering geological models of fault zone were established based on the zonation of the fault zone.Based on the zonation characteristic of the fault F2 zone of the Renlou Coal Mine and combined with the practice of grouting engineering in the fault zone,the engineering geological model of fault zone based on the zonation of fault was established,which was used as the basis of the physical grouting simulation test.(2)The two-dimensional fault zone grouting simulation tests were carried out focusing on the influence of different factors on grouting efficiency,such as the ratio of coarse to fine particles by mass(refers to the ratio of particle sizes of 5-20 mm to particle sizes smaller than 2mm by mass)and the degree of cementation in the fault induced fracture zone,the ratio of sand to clay particles by mass(refers to the ratio of sand particle sizes smaller than 2mm to clay particles by mass)in the fracture zone,the grouting pressure and the position of the grouting hole.The investigation was aimed to obtain the grouting propagation and grouting reinforcement mode of each zone and the entire fault considering fault horizontal zoning.The results show that changes of the injected media conditions and grouting parameters would change the grouting propagation mode: penetrating grouting appearing in the induced fracture zone,compaction-fracturing grouting in fracture zone,dominant fracturing grouting from the induced fracture zone to fracture zone,fracturing grouting appearing in the induced fracture zone if the grouting pressure was satisfied,passive penetrating or fracturing grouting from the fracture zone to the induced fracture zone.Different methods of grouting and different material compositions of the fault zone,different combinations of the above-mentioned grouting modes might occur in the whole grouting process.The grouting propagation mode affected by the grouting conditions and the injected medium condition have analyzed when grouting in fault zone according to test results.(3)The results of two-dimensional simulation tests of fault zone grouting show that there was a big difference in the mechanism of grouting reinforcement in different zones of the fault.The reinforcement effect of each zone was generated under certain conditions mainly containing: cementation and filling in the induced fracture zone,compaction and consolidation,micro-pulp veins and slurry-supporting in the fracture zone.There exists anisotropy of grouting in the zoning interface forming multi-layer thin fracturing vein from the induced fracture zone to the fracture zone and point connections from the fracture zone to the induced fracture zone to form an anchoragelike effect.Due to the influence of the medium condition and the grouting mode,the grouting efficiency would change with the propagation stage.(4)The three-dimensional fault zone grouting model tests based on fault zoning were carried out.The pre-grouting and roadway excavation process of the fault zone considering fault horizontal zoning and the grouting propagation in fault with vertical zonation were simulated.Results show that the diffusion and grouting effects of in the fault zone appeared the zonation and relatively dominant seepage flow feature.Because of the dominant seepage flow in the induced fracture zone,in the place where the induced crack zone was poorly injectable,the fracture zone was more likely to form slurry veins.In the vertical direction of the fault,there exited a preferential diffusion tendency in the region where the ratio of coarse to fine particles was lager.The simulation of roadway excavation showed that,after the multiple boreholes grouting,the induced fracture zone was well reinforced and stable,and the fracture zone was not well reinforced as the collapsed substance appeared after excavation.After that,a supplementary grouting was applied in the fracture zone and formed reinforcement grouting vein skeletons.This zoning grouting of different zones method avoided the appearance of poorly grouting area and improved the global stability of the fault zone.(5)The results of two-dimensional and three-dimensional simulation tests of grouting in the fault zone indicate that the pore-filling rate and the dry density growth rate of the induced fracture zone was proportional to the ratio of coarse to fine particles of the induced fracture zone,proportional to grouting pressure,inversely proportional to cementation degree and distance from grouting hole,and was not obviously affected by the ratio of sand to clay particles of the fracture zone.The grout take in the fracture zone was proportional to the grouting pressure and the ratio of sand to clay particles of the fracture zone.In addition,it was affected by the induced fracture zone,which was proportional to the cementation degree and inversely proportional to the ratio of coarse to fine particles.The porosity was inversely proportional to the ratio of coarse to fine particles.The larger the proportion,the better the grouting efficiency was.(6)Combined with the testing results of this paper and the previous studies,the method of zoning evaluation was proposed for the zoning grouting effect in fault zone grouting.The complex compression modulus method was used for the fracture zone,the pore-filling rate inverse calculation method for the induced fracture zone.And the strength of the stabilized mass in different lithological fracture zones was estimated.The research results of this paper had guiding significance for optimizing the design of fault zone grouting.The optimized methods of grouting according to fault zone features were recommended combined with engineering grouting,for example,zoning grouting and staged grouting to reduce the fracture rate step by step in the induced fracture zone,the grouting control technique and zonating grouting method can be adopted for different zones to strengthen the global stability of the zoning interface.