Study On Shield Tunneling Parameters Of Zhengzhou Typical Engineering Geological Unit

Accidents such as collapse,ground water leakage,large ground settlement,and damage of existing pipelines are common types of accidents in TBM(Tunnel Boring Machine)excavation.Based on engineering conditions,the determination of scientific TBM control parameters is the key to avoiding the above accidents.TBM parameters are closely related to geological features.Although several subway tunnels have been constructed and operated in Zhengzhou,the summary of the geological features along the tunnels and the corresponding TBM parameters have not been fully studied;TBM parameter empirical formula has yet to be verified,and the relevant empirical coefficients have yet to be determined based on practical engineerings.It is of engineering signifcants to set up the typical geological zones in Zhengzhou,and to study the reasonable values of TBM parameters on this basis.Through state-of-art research,geological data along the Zhengzhou subway tunnels are collected extensively.Then,verified by typical cases,Zhengzhou city shallow soil(within 35m depth)is divided into 3 geological units.The geotechnical units each possesses similar geotechnical characteristics.The rationality of geological unit division is verified,and the corresponding geotechnical mechanical characteristics of each units is further summarized.Through the methods of on-site investigation and statistical analysis,the total thrust,the torque of the cutter head,the plenum pressure,and the synchronous grouting amount of each ring were selected as the control parameters.Using tunneling speed and surface subsidence as evaluation indexes of construction quality,the scopes of tunneling parameters of corresponding to typical geological units in Zhengzhou are obtained,and the correlation database between geological characteristics and TBM parameters is established,which can provide reference for actual TBM construction.The rationality of the above results is verified by the empirical formula commonly used in the construction,and the range of the empirical coefficient suitable for the geotechnical characteristics of Zhengzhou area is determined by substituting the measured data into the empirical formula.Finally,6 parameters representing the operating conditions were selected as input values.These 6 parameters are:tunnel axis depth(m),groundwater depth(m),soil natural gravity(k N/m~3),soil viscosity Cohesion(k Pa),internal friction angle(°),TBM cutter head opening ratio(%);select 4 control parameters as output values,which are total shield thrust(t)and cutter torque(k Nm),plenum pressure(bar),grouting volume per ring(m~3/road);a BP network structure is established with two hidden layers,the number of nodes in both hidden layers is 25.Then the relation between the operating conditions and the control parameters of TBM is studied.700 samples were used to consist the training sets;137 samples were used as the test sets,the operating conditions were input,and the predicted values of TBM control parameters were obtained.Further more,the error between the predicted value and the actual value is given to verify the prediction effect of BP neural network.Finally,the purpose of using operating conditions to predict the tunneling control parameters is realized.The main conclusions are as follows:(1)The friction coefficient of sand is large,the self-stability is poor,and the tunnel shrinks fast after the cutter head passes through,resulting in the increase of the total thrust and torque.However,in viscous soil,the hole will not shrink significantly after the cutter head passes through,and the friction resistance of the shield sidewall is small,so the total thrust and torque are small,and the amount of synchronous grouting is large.Finally,this conclusion is further verified by comparing the measured value of total thrust of TBM under different soil types.(2)The calculation model commonly used in practical is not applicable to all embeded depths.When the embeded depth is greater than 30m,the calculated values of thrust,torque and plenum pressure are too conservative and far greater than the measured values.(3)The thrust required for the unit excavation unit P_j of Zhengzhou I unit(northeast)is recommended to be 412-1200k N,The P_j of Zhengzhou II unit is recommended to be 366-702k N,The P_j of Zhengzhou III unit is recommended to be342-528k N,which is obviously less than the general value of the other unit.The torque coefficient?of Zhengzhou I unit(northeast)is recommended to be 8.16-14.41k N/m~2,which is relatively stable and significantly smaller than the field experience value,only reaching about 50%of the general experience value;the grouting rate?of Zhengzhou I unit(northeast)is recommended to be 116-186%,the grouting rate?of Zhengzhou II unit(southeast)is recommended to be 150-183%,and the grouting rate?of zone III of Zhengzhou(west)is recommended to be 168-195%.The amount of grouting per ring is mainly related to the gap outside the shield segment,while the size of the grouting rate is related to the type of soil.The grouting rate is smaller under the conditions of silty sand and silty soil layers than under the conditions of silty clay soil layers.(4)Using a BP neural network with 2 hidden layers and 25 nodes per layer,the key parameters of TBM can be predicted according to the characteristics of the external environment,with an error no more than 10%.