Computing method of filter cake formation time in sandy stratum

Bentonite slurry is widely used in the construction of slurry shield tunneling. The formation of filter cake is the decisive factor for the stability control of tunnel face. High rotate speed of cutter can easily lead to the missing of filter cake, resulting the collapse on tunnel face. The computing method of filter cake was proposed. A multilayer slurry infiltration test device was developed to measure the change of solid particle content after penetration in soil with different particle size. The calculating formula of filtration coefficient was established with slurry mass concentration and the ratio of soil to slurry particle size as variables. Then, a formula for calculating the formation time of filter cake of solid particles was proposed combined with the criterion of filter cake formation. The rationality was verified according to the experimental research. The influences of slurry pressure, slurry mass concentration, soil porosity, particle size ratio and cutter rotate speed on forming time were investigated. The results show that the permeability coefficient is closely related to the rheological characteristics of slurry and the pore characteristics of soil. The adsorption capacity of soil skeleton to slurry particles in coarsely grained formation is low. Increasing the bentonite content in slurry or adding fine sand or clay particles to reduce the particle size ratio is more conducive to the rapid formation of filter cake. In actual engineering, the setting of cutter rotate speed should consider the formation particle size and rheological property of slurry. For the formation with high particle size ratio and strong permeability, the cutter speed can be appropriately reduced to ensure the effectiveness of mud film. © 2024 Central South University. All rights reserved.