| Water and sand inrush in fractured rock mass frequently causes heavy losses and even disasters during engineering construction and mining process in underground area.Grouting technology is one of the key measures to prevent and control water and sand disasters.Underground rock masses are often coupled with multiple fields such as temperature,stress and seepage.Therefore,based on the existing grouting theory and practice,investigation on the characteristics of grouting in the fractured rock mass with flowing water under the coupled interaction of seepage,stress and temperature fields is necessary for determining the underground grouting efficiency.Comprehensive indoor tests and theoretical analysis were used based on a case study of the Zhuxianzhuang Coalmine.Visualized fracture network for grouting test system have been established.Experiments and theories on diffusion mechanism of grouting in fracture network under multi-field coupling were conducted,and effects of hydrodynamic conditions,temperature environment and fracture network morphology on the grouting efficiency were also analyzed.Main results are as follows:(1)An engineering geological and hydrogeological model of grouting construction in the Zhuxianzhuang Coalmine was established.The engineering geology and hydrogeological conditions were analyzed and discussed in detail.The main sources of water inrush disasters were analyzed.There are hydraulic connections between the fifth and fourth aquifers,the Tai-limestone and O-limestone aquifers,which causes disadvantageous drainage.Therefore,the fifth aquifer is the main object of grout curtain project.The hydrogeological engineering geological model of the accident mining area has been generalized to provide basic data for the implementation of the grouting project.(2)The influence of confining pressure and temperature on the permeability of fractured rock mass was studied.Based on the geological environment of grouting strata in Zhuxianzhuang Coalmine,different confining pressure(3 MPa,5 MPa and 7 MPa)and temperature(0?,20?,28?,35? and 50?)were selected,and permeability tests were performed on the in-situ rock samples using the GDS high pressure environmental triaxial tester.The results show that,under a same confining pressure condition,the stable flow rate in each temperature section of original breccia sample increases with the increase of temperature.The maximum value occurs at 35 ?.The steady seepage at each temperature section of fractured samples is increasing with temperature.At the same temperature conditions,the permeate flux of original and fractured samples decreases with increasing confining pressure.(3)The characteristics of seepage field,stress field and temperature field of the fractured rock mass were analyzed.The mathematic model for the diffusion of viscous and time-varying slurry in the grouting process of fractured rock mass under thermo-hydro-mechanical coupling was deduced.According to the basic features of these fields,the entire underground engineering is regarded as a whole system,and a network model based on the coupling interaction was established to analyze the interaction process and interaction products.The coupling equations of the seepage field,stress field and temperature field of grouting in fractured rock mass with flowing water were established.(4)A hydrodynamic grouting test system under multi-field coupling with single fracture,two-dimensional fracture intersecting fracture network and three-dimensional orthogonal fracture networks was developed.The characteristics of chemical grout and cement grout at different temperatures were analyzed.The test system mainly includes the fixed head water device,the double liquid grouting pumping device,the rough fractured rock mass simulation device,data acquisition system,image acquisition system,the weighing device and the constant temperature and humidity environment control device.The results of chemical grout and cement grout analysis show that with the increase of oxalic acid concentration and the ambient temperature,the initial setting time of chemical grout gradually becomes shorter.The initial setting time of cement grout increases with the increase of water-cement ratio.However,as the temperature increases,the initial setting time of the same water-cement ratio becomes smaller and then increases.When the ratio is higher,the time is more sensitive to temperature.(5)The hydrodynamic conditions,environment temperature,properties of different grout on sealing efficiency and diffusion of grouting in a single fracture with flowing water were analyzed.The criteria for evaluation of sealing effect were optimized,and the relative water sealing rate and relative sealing efficiency were proposed.It can be seen from the efficiency,that the higher the temperature is,the better the efficiency is.With the increase of flow rate,the advantages of high temperature conditions are gradually reduced.With the same flow rate,the curves of different temperature levels show a similar change.(6)The hydrodynamic conditions,environment temperature,properties of different grout on sealing efficiency and diffusion of grouting in fracture network with flowing water were analyzed.The test temperatures were 10?,20?,35? and 50?.Injecting the same volume of grout with the same temperature,the efficiency of grouting at 20? and 50? is good when it comes to two-dimensional fracture network.For a three-dimensional fracture network,under the condition of low velocity,grouting efficiency of each temperature level presents good.However,with the flow rate increasing from 0.45 cm/s to 0.77 cm/s,the relative grouting efficiency is good when temperature is 10? and 20?.According to the diffusion form of the grouting tests,the diffusion pattern is divided by horizontal/vertical directions into pressure diffusion/diffusion along the crack direction,gravity and downstream diffusion/near circle diffusion,and downstream diffusion/downstream near-circle diffusion.The effects of seepage pressure,grouting pressure and temperature of these three kinds of fracture networks(single fracture,two-dimensional fracture intersecting fracture network and three-dimensional orthogonal fracture networks)are the same.There is a positive correlation between fracture seepage pressure and grouting pressure,and a negative correlation between the temperature variation curve and the seepage pressure curve show.(7)The macroscopic and microcosmic effect test of the grouting project in the Zhuxianzhuang Coalmine was analyzed.The results show that the grouting project successfully cut the replenishment of the aquifer and verified that the diffusion distance was consistent with the theoretical and experimental values.Through on-site pumping test,it was proved that the grouting project can effectively cut off the hydraulic connection between the fifth aquifer and the Ordovician aquifer.The diffusion distance was verified with the theoretical calculation value.With mercury intrusion porosimetry and electron microscopy scanning experiments,it shows the hydration gels formed on the fracture surface,which reduced the porosity of fractured rock mass.The permeability coefficient of the fractured rock mass was also decreased,which indicates the interception effect of the grouting project. |
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