Experimental Study On Rock-breaking Characteristics Of Disc Cutter In Limestone Formation

Due to the great difference between the surrounding soil layer and the strength of limestone or limestone filling materials and limestone caves,the limestone strata has presented a lot of construction challenges to the shield excavation construction.The problem of the stress of the disc cutter in the limestone composite strata is the key reason of the problem of shield tunneling construction in limestone composite strata.In this paper,the study is conducted in terms of the cutter rock breaking problem of full-section limestone model and soft and hard composite stratigraphic model with different stratigraphic angles.The results can provide reference for the construction of shield tunneling in limestone strata,and also provide experimental reference for the research of disc cutter.The main studies completed are as follows:(1)Collect and analyze the construction data of the shield structure of the limestone strata in Guangzhou,and summarize the engineering properties and common construction problems of the limestone strata;According to the results of the determination of rock mechanical properties of limestone specimens,combined with the definition standards of soft and hard uneven strata,using the theory and technology of rock similarity simulation,a soft and hard composite stratigraphic model with concrete grit as soft rock and limestone as hard rock is proposed.Based on actual engineering construction data and reference experiment experience,the parameters of linear cutting experiment are designed.(2)In the process of disc cutter cutting at the interface of soft and hard composite strata,there is a certain relationship between normal force and rolling force: When the disc cutter transitions from the soft rock stage to the hard rock stage,there will be substantial growth in the normal to broken rock force and rolling rock force.However,when the disc cutter leaves the soft and hard rock interface and is steadily cut at the hard rock stage,the normal breaking rock force remains high,while the rolling force will drop to a certain stable value.If the normal rock breaking force of the disc cutter fluctuates frequently,the rolling force will also remain basically the same as its fluctuation.(3)During the process of disc cutter cutting at the soft and hard rock interface,there will be an impact zone in the range of 10 cm before and after the interface.The fluctuation of normal and rolling rock force mainly occurs in this area where the normal rock breaking force will drop first and then rise sharply.In addition to removing the size effects at both ends,the rocks in the 10 cm range before and after the hard and soft rock interface are the most severely broken,and the most fragmented pieces inside and on both sides of the groove are also in this range.(4)The mutation of broken rock force will increase accordingly with the increase of invasion depth,and when it reaches the invasion depth of rock complete destruction,the difference of rock breaking force in soft and hard rock stages reaches the maximum,that is,the impact load of the disc cutter is also the largest.In this experiment,when the model of soft and hard composite strata is completely destroyed,the peak of rock breaking force has reached more than 180 k N,and the peak of normal rock breaking force at the hard rock stage has exceeded the peak of normal rock breaking force at the soft rock stage.2.2 times,And its difference is about 2 times the difference between soft and hard rock strength.