Study On Mud Characteristics And Transportation Performance Of Slurry Balance Shield

With the expansion of Metro lines,hydraulic tunnels and deep underground tunnels in China,shield tunneling method has been widely used.Slurry balance shield is widely used in complex geological conditions and underwater tunnel construction across rivers because of its wide adaptability.Slurry shield construction is mainly divided into two systems:main and auxiliary system.The main system includes excavation equipment,excavation surface stabilization system and support system.The auxiliary system includes slurry circulation system and slurry treatment system.More and more engineering require efficiency,fast speed and long-distance excavation,and the effective operation of slurry circulation system is the basic guarantee of these requirements.Aiming at the problems of pipeline abrasion and pipe blockage in slurry circulation system in engineering,this paper studies the slurry characteristics and transportation performance by means of literature research,data collection,theoretical analysis and laboratory tests,based on the field circulation system.The main work and research results are as follows:1)On the basis of summarizing the three characteristics of slurry and the key parameters of slurry,the force,transport speed and movement pattern of slurry particles during slurry transportation are studied.It is found that the force of slurry particles is mainly related to slurry density and viscosity,particle size and density,slurry flow rate,pipe diameter and pipe form,etc.The minimum velocity of slurry in slurry discharge pipe shuold be adjusted dynamically.The muck particles can be divided into bed load,suspended load and suspended load according to their movement form.The bed load is usually coarse particles with larger particle size,and it has the largest pipeline wear.2)Taking the large-size pebbles taken from the field as the research object,using the self-designed settling speed research test device,the movement law of pebbles in water and slurry is similar by the method of free settling.There is no big difference between the two situations.The increase of density and viscosity has no great influence on the pebble movement speed,and the situation of forced the pebbles when they move in the water and slurry is similar.3)On the basis of the above experiments and referring to the slurry circulation system in practical engineering,the slurry circulation system is designed and built independently in the laboratory.With water as the carrier fluid,the critical velocity law of large-sized pebbles in different pipeline positions in the circulation system,as well as the typical movement pattern and velocity of different pipeline forms under different flow velocities are obtained.4)On the basis of summarizing the test results and existing research,the factors affecting the slurry transport performance are put forward as follows:slurry flow rate,slurry parameters,solid particle size in slurry,pipeline layout and pipeline inner diameter.It is considered that the evaluation indexes of slurry transport performance are slurry flow rate to critical flow rate ratio,slurry density,slurry viscosity,average particle size of stratum soil d₅₀,pipeline layout complexity coefficient and ratio of inner diameter of pipeline to maximum particle size of stratum.On the basis of fuzzy theory,the slurry transportation performance is evaluated by "percentage score" method.