Study On The Dynamic Interaction Mechanism Of "Machine-Soil" In Shield Tunneling

The outline of the national medium and long-term science and technology development plan points out the need to focus on the development of difficult transportation infrastructure such as cross-sea passages and large tunnels.Crossing the river and sea tunnel is of great significance to the development of a country or region.Therefore,the safety of tunnel construction,the function of the tunnel,and the ability to respond to disasters are major issues that must be addressed.In this context,the design and construction requirements for the construction of shield tunnels will be higher.At present,there are problems such as unknown shield-soil interaction and difficult control of shield attitude in shield tunnel construction,and these problems will become more prominent under high water pressure conditions.In view of this,this paper started from the research on the mechanism of shield-soil interaction,and then studied the theory of shield attitude control,and used a self-developed multifunctional slurry shield model test platform that could achieve 2.0MPa water pressure.The effects of shield-soil interaction and shield attitude under high water pressure were studied.(1)Independently developed a multifunctional slurry shield model test platform capable of achieving 2.0MPa high water pressure.The size of the soil box of the test platform model was 5.9m × 3.3m × 4.5m,the outer diameter of the shield model machine was 0.62 m,and it had multiple functions,such as research on the stability of the excavated face of the shield,the tool wear under complex conditions,and shield-soil interaction problems related to shield attitude.The successful development of the test platform provided the basic test conditions for this paper and the future need to do shield-related test research under high water pressure.(2)In order to link the engineering background of the Qiongzhou Strait with the shield model test platform,and to conduct an early test for the slurry shield tunneling model test under high water pressure,experimental Research on proportion of similar materials had been studied.Based on the orthogonal test method,the changes of physical and mechanical parameters of similar materials with different proportions were analyzed by using barite powder/standard sand,binder concentration,silicon ratio and gypsum content as the four control factors.Finally,a similar material ratio that can be simulated under the conditions of sandy soil layers in the deep sea environment was developed: barite powder/standard sand(0.4),binder concentration(4.5%),silicon ratio(3:1),gypsum content(3%).(3)The research on the mechanism of shield cutter-soil interaction is mainly carried out from two aspects: the cutting effect of the cutter on the soil and the compression effect of the cutter disk on the soil.Aiming at the problems existing in the Mckeys-Ali model and combining the characteristics of shield tunneling,the Mckeys-Ali model was improved.Based on the improved Mckeys-Ali model,the force state of the cutter during the shield tunneling process was analyzed and derived,and the calculation method of the cutter force was obtained.On the other hand,based on the basic solution of the Kelvin problem,the problem of the squeezing action of the cutter disk during shield tunneling was answered and solved.Based on the above theoretical calculation results,the selfdeveloped test platform was used to verify the thrust force and cutter head torque of the shield.The test results show that the theoretical calculated values of the thrust force and cutter disk torque of the shield formed based on the shield cutter-soil interaction model established in this paper were close to the test monitoring values;(4)In order to find out the mechanism of shield shell-soil interaction during shield tunneling and guide the control and adjustment of shield attitude,the theoretical calculation method of earth pressure acting on the shield shell and the prediction model of shield attitude angle were studied.First,based on the reaction curve of the foundation,an equivalent spring approximation model was used to establish the interaction model of the shield and the soil,and the theoretical calculation method of the surrounding earth pressure acting on the shield shell was obtained.Then,the improved loose earth pressure calculation method was cited,and the calculation method of the initial earth pressure of the shield was obtained.The initial boundary problem of the calculation of the attitude angle was solved,and the method was obtained by combining the calculation method of the action load of the soil on the shield.Finally,in combination with the Jinan subway R2 shield tunnel project,the calculation method of the formed shield attitude angle was applied in three aspects,namely the inverse calculation of the shield-soil interaction force,the prediction of the pitch angle and the yawing angle.(5)The shield tunnel project faces higher water pressure,which puts forward higher requirements for the shield machine's own sealing and waterproofing problem.Combined with this engineering problem,the dynamic sealing test of shield tail grease under high water pressure was independently developed.Using this device,three representative greases were selected for sealing tests under different conditions.Shield tail grease was tested for water resistance under different water pressures,metal mesh types(similar to the effect of a shield tail brush),and dynamic boundaries.The test results show that: under the same water pressure,different greases showed different water pressure resistance performance under different metal mesh conditions;the presence of dynamic boundaries increases the risk of seal failure;as the temperature increases,the viscosity of the material of the grease will obviously decrease,which will cause the water pressure sealing performance of the grease to decrease;compared with fresh water environment,the seawater environment weakened the water pressure-resistant sealing performance of the grease,and the leakage of grease would be faster.Finally,the experimental results were verified by numerical simulation methods.(6)Combined with the engineering background of Qiongzhou Strait,based on the similar sand ratio obtained based on the similar principle,the slurry shield shield tunneling models under high water pressure conditions were carried out in soilless and similar sand environments,respectively.The test results show that the calculation method of the shield thrust force and cutter disc torque established in this paper fitted well under high water pressure conditions;high water pressure had little effect on cutter disc torque,and had a significant effect on the thrust force of the shield;the difficulty of adjusting the shield attitude under high water pressure conditions had increased.