| With the large-scale construction of underground engineering in China,the control of adverse geological disasters in the process of underground engineering construction has become an important research subject.Broken rock mass is a commonly unfavorable geology in underground engineering.Due to its low bonding strength,poor self-stability and other characteristics,it is easy to induce engineering disasters such as collapse during construction,and has become one of the important geological disasters which affects the safety of underground engineering construction.Grouting is a common method to improve the mechanical properties of broken rock mass and ensure the stability of underground engineering excavation.Therefore,the strength of reinforced broken rock mass is an important parameter in geotechnical engineering design.However,because of the complexity of broken rock mass in nature,its reinforcement strength is affected by various factors,making it complicated to perform quantitative study on its strength.In this paper,we studies the effects of filling medium factors and grouting factors on the grouting reinforcement mode of broken rock mass through laboratory test,numerical simulation and theoretical analysis,and establishes a prediction method for grouting reinforcement mode of broken rock mass.Specifically,the influence mechanism of the properties of broken rock mass and grouting factors on the mechanical properties of the reinforcement under different lithological factors is clarified,the deformation and failure law of reinforced broken rock mass is revealed,and a prediction model for the strength of reinforced broken rock mass is established.Finally,a method aiming at broken rock mass grouting design is developed and used in engineering application.The main content and breakthrough of the present thesis are as follows:(1)The laboratory constant pressure automatic grouting test system is developed,and the laboratory test of the grouting reinforcement mode of broken rock mass is carried out.The influence of filling medium particle size gradation,density,slurry water cement ratio and grouting pressure on the grouting reinforcement mode of broken rock mass is studied.On this basis,with the test influencing factors as input variables,the slurry-soil mixing ratio as the quantitative evaluation index of grouting reinforcement mode,and based on the XGBoost machine learning algorithm,a prediction model for grouting reinforcement mode of broken rock mass is established.The absolute accuracy of prediction is as high as 98.73%,and the discrete state of prediction data is effectively controlled.(2)Taking reinforced broken rock mass without filling medium as the research object,the influence of volumetric block proportion of rock block,degree of fragmentation of rock block and properties of cement-based grout stone body on the mechanical properties of the reinforcement is studied under different lithological factors.The typical failure modes and overall failure characteristics of the reinforcement under different factors are obtained,and the influence mechanism of various factors on the strength of the reinforcement is revealed.On this basis,based on the discrete element numerical simulation method,the calculation model of reinforced broken rock mass is established.By reproducing the mechanical properties and failure characteristics of reinforced broken rock mass in the test process,the breakage law of rock block,the distribution and evolution of the contact force,the fracture development,and the distribution and evolution law of the stress during the compression process are acquired,which can be mutually verified and replenished with the experimental results.The deformation and failure mechanism of the reinforcement with different lithology affected by volumetric block proportion,degree of fragmentation and properties of cement-based grout stone body are revealed from the microscopic perspective.Through the numerical simulation of the influence of various factors on the full range of the strength of the reinforcement,the quantitative relationship between the factors and the strength of the reinforcement is established respectively.(3)Taking reinforced broken rock mass with filling medium as the research object,based on the research results of grouting reinforcement mechanism of broken rock mass without filling medium,according to different grouting reinforcement modes,controlling the properties of broken rock mass,considering the factors of filling medium,the influence of the filling medium content,the slurry-soil mixing ratio and the slurry-rock cementation degree on the mechanical properties of the reinforcement is studied,and the influence mechanism of various factors on the strength of the reinforcement is revealed.On this basis,the influence of the properties of broken rock mass and cement-based grout stone body on the research results is systematically analyzed.Based on the optimized test data,the quantitative relationship between the filling medium content,slurry-soil mixing ratio,slurry-rock cementation degree and reinforcement strength is established respectively.(4)Based on the equivalent inclusion theory,the reinforced broken rock mass is regarded as a three-phase composite material composed of broken rock mass,cement-based grout stone body and interface,and a three-phase mesoscopic model of reinforced broken rock mass is established.Based on the generalized self-consistent model theory,a method for calculating the effective elastic stiffness of the reinforced broken rock mass multiphase model is proposed.On this basis,considering the properties of broken rock mass,the properties of cement-based grout stone body,the interface effect and the stress concentration effect between blocks,the strength calculation model of reinforced broken rock mass is established,and the strength prediction of reinforced broken rock mass is realized.Compared with the experimental results,the rationality and accuracy of the calculation model are verified.(5)Based on the research results of the grouting reinforcement mechanism of broken rock mass,a grouting design method for broken rock mass is proposed.The research results have been successfully applied in the pre-grouting reinforcement project of fault fracture zone of Qingdao Metro Line 4 Renminhuitang Station,and the grouting effect is fairly good.Therefore,the current method proposed is of broad application prospects. |
