Study On Earth Pressure Balance Shield Cutterhead Adhesion Test And Soil Conditioning Mechanism In Clay Stratum

Since the 14th Five-Year Plan,China’s rail transit construction has entered a new stage of development,and the shield method has become the mainstream method of urban rail transit construction by virtue of its mechanized superiority.The urban construction environment is complex and changeable,and the construction risks and difficulties are increasing geometrically.In the process of urban metro construction in many clay stratum,it is easy to open the shield frequently due to problems such as mud cake and blockage of the cutterhead,delaying the construction period and causing imbalance of digging pressure due to poor slag discharge,which makes it difficult to ensure the construction efficiency and safety.In this paper,based on the two major problems of temperature and other factors affecting the adhesion of cutterhead during the construction of earth pressure balance shield in clay stratum and the unknown mechanism of clay conditioning,theoretical analysis,indoor test and numerical simulation were used to carry out the test of adhesion of cutterhead in earth pressure balance shield in clay stratum and the research on the mechanism of soil conditioning,which systematically explained the process of cutterhead adhesion formation during shield tunneling in clay stratum and the influence of various factors on the adhesion of cutterhead.A cutterhead rotation adhesion test system was developed to carry out cutterhead disc rotation adhesion tests on clay soil.The combination of soil conditioning agents performance under variable temperature conditions was evaluated,and the effect of the combination of soil conditioning agents conditioning was verified through indoor tests,and The soil conditioning technology based on consistency index is proposed.The rheological behavior of the clay conditioned soil is investigated to reveal the soil fluid migration law of the conditioned soil by earth pressure balance shield,and the specific studies are:(1)For shield cutterhead adhesion problem,based on the microscopic characteristic analysis of clay minerals and water film theory,the process of shield cutterhead adhesion formation during shield tunneling is revealed at the microscopic level;the cutterhead rotating adhesion test system is developed independently to realize the controlled cutterhead temperature,explore the change of cutterhead adhesion effect and rotating adhesion force under different cutterhead temperature,water content,clay type and clay content,obtain the change law of clay adhesion under the influence of different factors.and propose the equation of cutterhead adhesion change under the joint influence of temperature and consistency index.(2)Based on the selection of "foam+anti-clay " combination agent for clay stratum,the research on the performance of agent under different temperature conditions was carried out,and the half-life and foaming multiplier tests were conducted to reveal the performance change law of "foam+anti-clay" combination agent and analyze the change trend of foam performance under the influence of different temperatures,so as to obtain the concentration and ratio of improver with better improver performance and provide a basis for the determination of congditioning program in subsequent indoor tests for clay soil congditoning.(3)For the clay samples,the better performance agent concentration and ratio were obtained through the agent performance test,and the conditioning effect was evaluated through the slump test,direct shear test and cutterhead adhesion test to determine the conditioning effect of different combinations of agents programs on the clay samples,and to obtain the suitable conditioning program that can effectively reduce the occurrence of cutterhead adhesion problem in earth pressure shield structure and meet the requirements of efficient and safe construction of shield structure.(4)The quadruplex model of shield soil transportation system is established,the HerschelBulkley rheological model in computational fluid dynamics is used to describe the rheologicalmechanical behavior of conditioned clay soil,and the three-dimensional simulation of fluid field is carried out to obtain the migration law of conditioned clay under different conditioning degrees and the effect of changing the parameters of screw conveyor on the migration law of clay with different conditioning degrees.(5)Based on the synthesis of the previous research,a set of clay stratum suitability conditioning technology was summarized and applied to a shield interval of Changchun subway and a shield interval of Jinan subway,which effectively improved the construction efficiency and achieved better construction results.