Study On The Loads Equivalence And Transferring Behavior Of The EPB Shield Machines Penetrating In The Heterogeneous Geological Conditions

Earth pressure balance (EPB) shield machines are the important heavy apparatuses which were used in the national fundamental construction, research exploitation and national defense construction such as the metro, civic structures, railway, mine and military affairs. Since they have little influence on the environment and the penetrating efficiency is high, the TBMs are extending used in the underground engineering. It is a coupling mechanical system which is consisted by the redundant driving thrust system and revolving system. The cutting load on the cutterhead is dependent on the thrusting force and driving torques. When the TBMs penetrate in the complex geological conditions, the offset load and mutational load usually appear on the cutterhead which are in range from 500 to 125000kNm. Although the complex geological conditions are taken account in the early design, the accidents such as excessive wear and rapid stop usually occur since the irrational controlling parameters are given. Therefore, the study on the description method of the load when the TBMs penetrate in the heterogeneous geological conditions should be conducted. It is important for the determination of the penetrating control parameters and the compliance control.According to the complex geological conditions, the mathematical description method for the heterogeneous geological conditions containing the hard rock and soft ground was given. Based on the cutting mechanisms of the single disc cutter and scrape cutter, the equivalent models of the thrust forces, moments and torques on the cutterhead were established in which the mechanical behavior of the rock and soil and the layout of the cutters were taken account. Then, the typical cutterhead of Herrenk- necht was employed to study the fluctuating behavior of the forces, moments and torques when it penetrates in the heterogeneous geological conditions. The result is approximately in agreement with the engineering cases. Based on this result, the coupling behavior of the thrusting force and torque was discussed and the mathematical model was given. Finally, the redundant driving mechanical system of the Shenzhong No.11 shield machine was established to investigate the load transferring behavior. The finite element method was used to analyze the deformation of the main bear to obtain the non-uniformed distribution of the loads. The load transfer behavior for the reluctant driving revolving system under the offset load was simulated. The main content and conclusion are given as:1. The equivalent model of the load on the cutterhead of the shield machines penetrating in the heterogeneous geological conditions. The layouts of the heterogeneous geological conditions were analyzed and the section cycle model for the geological conditions containing hard rock and soft soil was given. In terms of the cutting mechanism of the disc cutter and the scrape drag, the equivalent model of the thrust load, moment and torque applied on the cutterhead when it advances in the heterogeneous geological conditions.2. The equivalence loads behavior analysis penetrating in the heterogeneous geological conditions. Based on the equivalent load models, the thrust force, moment and torque applied on the cutterhead of Herrenknecht shield machine were obtain when it advances in the heterogeneous geological conditions where the fraction of the hard rock and soft soil is different. The fluctuating behaviors of the load penetrating in the various fractions of the hard rock and soft soil were discussed. The results show that the obvious vibration appears when the fraction of the rock and soil is 30%～33%,65%～68%. In this case, the rapid stop easily occurs. This result is approximately in agreement with the Shanggongshan tunnel. The since and cosine functions can be used to describe the correlation between the moments and the revolving angles.3. The coupling correlation of the thrust force and torque penetrating in the heterogeneous geological conditions. In terms of the mathematical models for the total thrust force and torque, the coupling relationship of the thrust force and torque was obtained. At the same time, the thrust force and torque under the various geological conditions were simulated. The curves of the thrust force versus torque were presented. The parameters in the function of the thrust force and torque were determined.4. The load transferring behavior of the redundant driving system under the offset load. Considering the non-uniformed elastic deformation of the bear, the distribution behavior of the mating stiffness of the redundant driving bear pairs was obtained. The load transferring behavior of the redundant driving system was discussed when it penetrates in the worst geological conditions. The results show that the difference of the mating stiffness will induce the non-uniformed damage evolution in the shaft which will cause fracture of some shaft. It can explain the cause of the accident that happened in the Wuhan tunnel.