Study on rheological property and filter-cake formation performance 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-cake, which lead to the instability of excavation face. Due to the high particle density and weak interfacial bonding, the traditional sand-containing slurry has poor dispersion stability and poor filter-cake quality. In this paper, a new type of shield slurry with walnut shell as the additive particle is proposed. In order to study the filter-cake formation and air tightness effect of the slurry in the high permeability formation, the whole process test system of slurry permeation, filter-cake formation and air tightness is independently developed, and the rheology, slurry permeation and air tightness characteristics of the slurry containing walnut shell are tested. The mechanism of improving filter-cake forming quality of walnut shell was analyzed. The results show that the matching between walnut shell and 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 sand-containing slurry, the thickening effect of walnut shell particles and the soft contact mode between particles make the slurry filter-cake formation easier, and the slurry filter-cake density and high pressure resistance are also significantly improved.