A Study On Preparation Of Environment Friendly Slurry And Its Adaptation During Slurry Shield Tunnelling In High Permeability Stratum

ABSTRACT:There are many technical problems when slurry shield passing through high permeability stratum, in which reducing slurry filtration, maintaining stability of the excavation face is the key to the slurry shield construction. In slurry shield, the working face is supported by the pressed slurry. So it is very important to build up a filter-cake to protect the working face, especially in high permeability stratum where the slurry is easy to permeate the ground without allowing to form the required support pressure. The widely use of slurry shield method makes a lot of excavated mud soil which is difficult to deal with. At present, most of the slurry is composed of clay, bentonite, water and CMC(carboxymethyl cellulose), which makes it difficult to degrade and polluted the environment. On that account, based on the principle of orthogonal experiment, the feasibility of using pre-gelatinized starch to replace the traditional additives is studied in this paper. A series of slurry penetration tests were carried out in3set of high permeability stratums which permeability coefficient more than5x10"3m/s with home-made apparatus for the research of the influence of slurry property on filter-cake quality at the working face of slurry shield. The main research work and achievements are as follows:(1) In order to examine the influence of slurry viscosity and API filtration, L9(34) orthogonal test is designed. The experiment result indicates:pre-gelatinized starch significantly reduced API filtration and increased the viscosity, and the influence of pre-gelatinized starch is significant. This indicates that the pre-gelatinized starch can replace other additives to increase the viscosity and reduce filtration in slurry shield.(2) Three type of slurry particles filled in ground and three kinds of varitation of filtration with time are proposed, three type of slurry penetration curve and three type of slurry particles filled types in the formation have a certain relationship. The type of infiltration is certain matched with the type of slurry particles filled in ground, in other words, slurry infiltration process determines the type of slurry particles filled in ground.(3) In the same stratum conditions, slurry penetration distance and slurry formation during the formation of filter cake along with the change of slurry four components have the same change trend, meanwhile variation between the two is showed a positive correlation. Particle size of solid particles which was added in slurry and the specific gravity of slurry are the main influence factors slurry penetration distance and slurry formation during the formation of filter cake in highly permeable sandy gravel stratum.(4) According to the change law of excess pore water pressure in the stratum in front of excavation face, the effective stress conversion rate of slurry pressure are obtained, and then the formation time of filter cake is analyzed. Combined with the actual construction of slurry shield cutter speed, driving efficiency, it can be found that the type of filter cake can meet the requirements of the stability of excavation face.