Mud Materials Selection In Slurry Shield And Ratio Optimization Analysis Used For Sandy Cobble Ground

Excavated surface instable failure is one of the major defects of slurry shield construction. Because of the high permeability coefficient and the poor self-stability of stratum, when tunneling in the sandy cobble ground, the frequency of excavated surface instable failure will be increased greatly. It is one of the two main functions of the slurry in ensuring the stability of excavated surface during slurry shield construction process, and the realization of this function depends on the types and characteristics of the slurry used and the reasonableness of its composition. For this purpose, a systematic and further study about the excavated surface stability mechanism of the slurry shield in sandy cobble ground is conducted in this dissertation, by analyzing and researching in the slurry type, the slurry material properties, the slurry proportion optimization, the adaptability between slurry and stratum, and the influence of slurry properties on the stability of the excavated face, adopting theoretical analysis, laboratory test and other research methods. Research results are as follows:(1) Providing preliminary type classification for the slurry of slurry shield in sandy cobble ground, combining theoretical analysis and laboratory tests. Tested suspended capacity for clay polymer slurry, bentonite polymer slurry and mixed solid phase polymer slurry, and determined that the applicable type of mud for slurry shield in sandy cobble ground is mixed solid phase polymer slurry, according to the test results and the analysis about engineering characteristics of sandy cobble ground.(2) On the basis of mud material characteristics tests, determined that the basic proportion interval of the slurry solid phase material (clay and bentonite) of the slurry shield in sandy cobble ground is4:5-3:2.(3) Analyzed the influence of pulping additives on the properties of the slurry, and ascertained the influence of six kinds of pulping additives the main characteristics of slurry under different content conditions. Eight kinds of improved slurry additives are summarized by the means of improving commodity slurry additives. Combining theoretical analysis with projects, reference value of slurry property index for sandy cobble stratums confirmed.Based on the reference value of slurry property parameters, twelve groups of slurry ratio for sandy cobble ground in slurry shield are picked.(4) Conducted mud infiltration experiments for slurry with different characteristics, and investigated the influence of three main characteristics (slurry viscosity, slurry specific gravity and slurry filtration rate) of slurry on the permeability.(5) Proposed the evaluation index for the adaptability of slurry and stratum, combined with the engineering practice. Conducted laboratory test, and made comparative analysis of adaptability for stratum between the slurry specified by slurry shield construction sites in Beijing and the slurry optimized by test. Analyzed economic benefit of different slurry, and elected six sets of slurry with good adaptability and meeting the requirements of economic and practical.(6) On the basis of the analysis results of slurry proportion optimization, proposed value of slurry index of characteristic references has been suggested for slurry shield in sandy cobble ground.