Experimental Study On Slurry Penetration Mechanism Of Large Diameter Slurry Shield Excavation Face

Large-diameter mud shield construction technology has been widely used in the construction of traffic tunnels that cross rivers and straits.Due to the complex stratum conditions during the tunnel construction process,how to keep the excavation surface stable is an urgent problem to be solved.When the shield is excavated,the slurry is injected into the soil,and the slurry forms a micro-permeable mud film on the surface of the excavation surface under the action of grouting pressure,thereby maintaining the stability of the excavation surface of the mud shield.In order to explore the adaptability between mud and stratum soil with different mechanical properties,this paper uses a self-made mud penetration device to conduct mud penetration simulation tests in different strata,and at the same time observe the microscopic structure of the mud film of the soil body with the help of scanning electron microscope,and combine fractal The theory explores the interaction between the microscopic structure of the mud film and the characteristics of the mud and formation,and has achieved the following research results:(1)Orthogonal test plan was used to investigate the factors of mud composition affecting mud viscosity and API filtration loss,and to organize the test results and analyze the influence of relevant factors on mud viscosity and API filtration loss.(2)Observe the particle accumulation pattern of the mud penetration test and analyze the mud filtration loss and the formation time of the mud film.Summarize the three types of particle filling and three variation modes of the filtration loss of mud infiltration in the formation.Analyze the influence law of mud mixing ratio on mud filtration.Mud specific gravity is the main influencing factor of Mud penetration.With the increase of the specific gravity of mud,the loss of mud filtration showed a trend of increasing first and then decreasing.(3)Measure and analyze the ultra-static pore water pressure in the stratum,and calculate the effective stress conversion rate of the mud,combined with the earth pressure in the stratum,to study and analyze the distribution law of formation water and earth pressure when the mud penetrates into the stratum.The mud quickly penetrates into the formation under pressure,and a large amount of water penetrates into the formation,causing the water pressure of the ultra-quiet pores in the formation to increase rapidly.As mud particles fill the formation pores,the permeability of the formation surface decreases,preventing further penetration of the mud the pore water pressure quickly decreases and stabilizes.(4)Observe the microstructure of the mud film with the help of scanning electron microscope to study the mutual influence of the microstructure of the mud film on the adaptability of mud and formation the two-dimensional porosity of the resulting interface infiltrated in each layer.Combining pore fractal and fractal dimensions,it can be seen that mud filtration loss is related to micro-microstructure.The greater the porosity,the larger the pore fractal dimension and the greater the filtration loss.