| In recent years,it is a common method to use raise boring machine method(RBM)to drill the mucking shaft to form the slag discharge channel and solve the slag discharge problem in the construction of tunnel ventilation shaft.However,due to its special structure and many construction influencing factors,the mucking shaft often suffers from blockage accidents,which seriously affects the efficiency of shaft construction.Therefore,it is of great significance to carry out research on prevention and dredging measures for mucking shaft blockage.Based on the construction project of deep and large ventilation shaft in Jinhua mountain tunnel,this paper puts forward the anti-blocking technical measures of mucking shaft based on the optimization of shaft blasting parameters through the analysis of the blocking mechanism of mucking shaft and the on-site verification,and verified in combination with the engineering practice.The main work and conclusions are as follows:Firstly,the paper introduces the shaft construction of Jinhua mountain tunnel,Combined with the actual situation of the field,The blockage area of tunnel ventilation shaft is divided into slag feed area,slag slip area,slag discharge area,Based on the formation principle of hang-ups phenomenon in mine chute and the characteristics of mucking shaft,By using the static balance method,the mechanism of the plugging of the mucking shaft is analyzed.The results show that the plugging body of the mucking shaft is formed by the combination of the occlusal arch and the viscous arch.The main reason for the plugging of the mucking shaft is that the rock mass put into the mucking shaft after blasting is too large,and the vibration damage caused by blasting vibration shock on the mucking shaft wall.Secondly,in order to prevent the vibration damage of the mucking shaft wall caused by blasting,in analyzing the principle of blasting vibration,vibration monitoring of shaft blasting excavation is carried out.Attenuation law of shaft blasting vibration is obtained by using Sadowski regression formula with elevation factor.Furthermore,the influence range of blasting vibration on mucking shaft wall under different design blasting parameters of surrounding rock is obtained.The analysis results show that the influence range of blasting vibration of Grade V,Grade IV and Grade III surrounding rock is 10.53 m,9.38 m and 14.11 m respectively.The blasting vibration has a great influence on the mucking shaft wall.Aiming at the problem that the blasting block is too large,using analytic hierarchy process,quantifying the blasting parameters on site,it is determined that the explosive consumption,the maximum charge per hole,the hole depth,the number of holes,the hole distance,the rock compressive strength and the minimum resistance line are the main blasting parameters that affect the maximum fragmentation after blasting.BP neural network algorithm based on double hidden layers is use to train that actual blasting parameters and block size data collected in the field,and the blasting maximum block size control model is obtained.The average absolute error between the predicted value and the actual value of the shaft blasting maximum block size control model is only 2.6%.The accuracy of the model can meet the actual needs of engineering.Finally,aiming at the problem of blocking and dredging of mucking shaft well,on the basis of the shaft construction of Jinhua mountain tunnel and according to the blocking zoning,the main dredging methods of mucking shaft wall is summarized at present.Verify the maximum block control method proposed in this paper,the results show that it is necessary to adjust measures to local conditions and select reasonable measures to dredge the blockage.There is a small error between the prediction result of the maximum block size model proposed in this paper and the actual block size after blasting,so the method can effectively control the maximum block size of rock after blasting and can be used to guide the construction of rock tunnel ventilation shaft. |
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