Research On The Safety Evaluation And Key Technologies For The Expressway Construction On Old Goaf Of Coal Mine

In recent years,China's economy is developing rapidly.Expressway as an inevitable product of economic development has has reached 130 thousand kilometers and ranked the first in the world as the end of 2016.With the encryption of the expressway network,it will be more common that the expressway to be constructed on the old goaf.How to ensure the vehicles safety will be the key problem for expressway construction on the old goaf.Therefore,field investigation,numerical simulation,similar material simulation and theoretical analysis are employed to study the safety evaluation and key technologies of expressway construction on the old goaf,the main research results are as follows:1)Overburden in old goaf is regarded as multi medium coupling mechanical structure.Generalized Kelvin,masonry beam and simply supported beam were employed to describe the movement and deformation of the caving zone,the fracture zone and the bending zone,respectively.The failure mechanism of the old goaf was revealed based on the above research.The old goaf activation types were divided into four types of Class I slow compression creep,Class II strength attenuation creep,Class I strength attenuation structure failure and Class II external interference structure failure.2)29 numerical models were established to study the influence mechanism of disturbance depth of embankment height,pavement stiffness,vehicle load and vehicle speed.The results showed that the disturbance depth is linear with the height of the embankment,and it is in logarithmic function with the stiffness of the road,the vehicle load and the vehicle speed.The influence degree of each influence factor on the disturbance depth was analyzed by the method of range normalization,and the order of importance was vehicle load,vehicle speed,road surface stiffness and embankment height.The formula for calculating the depth of vehicle load disturbance was obtained based on the multiple regression analysis and the superposition principle.Finally,the method for calculating old goaf safety depth was given.3)The influence mechanism of main factors on the old goaf stability was revealed using the numerical simulation method.The results showed that the rock mass structure,depth thickness ratio and the thickness of alluvium were positively related to the construction site stability.The geological structure,rock mechanical strength and repeated mining and other factors were negatively related to the construction site stability.The mining degree was nonlinear correlation with the construction site stability.With the increase of the mining degree,the stability was a process from high to low then high.The combined evaluation model for the expressway construction site stability on the old goaf was built.The grey relational analysis,analytic hierarchy process(AHP)and eigenvector method were used to calculate the weights of evaluation factors.The scatter diagram method was employed to analyze the membership function of quantitative factors,and the membership degree of each evaluation factor was determined using the membership function and the Delphi method.4)For overcoming the defects of the existing prediction models,a new combination prediction model was developed based on the distribution characteristics of the movement and deformation source in old goaf using the probability integral method and superposition principle.The effectiveness of the combination prediction model was analyzed with a specific example.The results showed that the new prediction model could reflect all the residual movement and deformation caused by the source,which could effectively solve the shortage of existing prediction models.In addition,the new model could take into account the time effect and make the prediction results more reasonable.5)The general working process for the safety evaluation of the expressway construction on the old goaf of coal mine was given.The work contents and working methods of each work stage were cleared.The applicable conditions of geophysical exploration and deformation monitoring technologies are analyzed.On the basis of above researches,the treatments for old goaf were put forward finally.Finally,the main contents of the research report are suggested.6)The safety of Wuyun expressway construction was studied using the research results.The results showed the Wuyun expressway construction site is basically stable with the activation types of Class I slow compression creep and Class II strength attenuation creep.The prediction results showed that the maximum residual subsidence was 184 mm,the maximum tilt was 1.2mm/m,the maximum curvature was 0.02mm/m2,the maximum horizontal movement was 76 mm,the maximum tensile deformation was 1.45mm/m,and the maximum compressive deformation was 0.76mm/m.However,the deformation occurred gradually,and there would be no sudden instability subsidence.In summary,the residual movement and deformation of the construction site would not threaten the vehicles safety.