Rheological properties and filter-cake formation performances of slurry containing walnut shell in high-permeability sand stratum

In the high-permeability stratum, the slurry shield often encounters the problems of slurry leakage and poor air-tightness of filter cakes, leading to the instability of excavation face. Due to the high particle density and weak interfacial bonding, the traditional slurry containing sand has poor dispersion stability and poor filter-cake quality. In this study, a new type of shield slurry with walnut shell as the additive particle is proposed. In order to study the filter-cake formation and airtightness effects of the slurry in the high-permeability stratum, the whole process test system for the slurry permeation, filter-cake formation and air tightness is developed, and the tests on the rheology, slurry permeation and airtightness characteristics of the slurry containing walnut shell are performed. The mechanism of improving the filter-cake formation quality by the walnut shell is analyzed. The results show that the matching between the walnut shell and the bentonite slurry is better, which can obviously improve the colloidal ratio and dispersion stability of slurry, and ensure high gel strength and good fluidity. Compared with those of the slurry containing sand, the thickening effects of the walnut shell particles and the soft contact mode between particles make the slurry filter-cake formation in high-permeability stratum easier, and the density and high pressure resistance of the slurry filter cakes are also significantly improved.