Developement of sand-mixed slurry and study of the permeation film-forming characteristics for coarse-grained soil layers

Abstract:

As a commonly used vertical protection method， the cut-off wall is highly favored in the hydropower construction industry. However， during the trenching construction of cut-off walls in coarse-grained soil strata， because of strong permeahility， serious leakage of wall-fixing slurry often occurs， leading to difficulties in film-forming and frequent trench wall collapse accidents. Therefore， to improve the stability of trench walls caused by slurry permeation， the base fluid was optimized by selecting suitable clay， pH modifiers， and rheological modifiers. Subsequently， a self-designed slurry permeation experiment apparatus was used to select coarse sand as the coarse-grained material， forming a wall-fixing slurry system for cut-off walls in coarse-grained strata. The effects of coarse sand particle size and dosage on the slurry''s permeation and film-forming characteristics were also analyzed. The study concluded that the slurry system for trenching in coarse-grained strata consists of clean water+4% clay+4% sodium bentonite+0.2% 3.4-modulus sodium silicate+0.18% sodium carboxymethyl cellulose+2.5% 0.154 mm sand particles. The film-forming speed and quality of sand-added slurry in coarse-grained strata primarily depend on the particle size and dosage of coarse sand. As the particle size and dosage of coarse sand increase， the film-forming speed of the slurry accelerates， whereas the film-forming quality decreases with the increasing sand dosage. The permeation and film-forming mechanism of sand-added slurry involves three synergistic effects： the preliminary improvement of the coarse-grained stratum by sand particles， the stable clogging of the permeation zone within the stratum， and the filtration and film-forming of mud cake on the stratum surface. These combined actions reduce slurry leakage and maintain the stability of the excavation face in coarse-grained strata. The research findings provide guidance for optimizing the formulation of engineering wall-fixing slurry in coarse-grained strata and offer valuable references for similar engineering projects.