Study On The Rheological Properties Of Foam Sand Shield Improvement

In the process of shield construction, there are many complex geoglogical environmrnt problems, such as sand stratum. The poor rheological property would led to many technical problems, and many projects judge the rheological property of sand soil by slump and experience, that is unscientific. In order to insure construction successfully, the sand soil must be improved, which can make the soil mass in the chamber or the excavation face keep a suitable “plastic flow state”.This paper selects the sand soil of a subway in Beijing as object, and uses two kinds of foams to improve the sand soil with poor rheological property. Select modified sand with good slump by slump test to test it’s rheological properties and test the resistance torque values under the circumstances of different revolving speed and different confining pressure; evaluate the effect of the foam on the exchange of the internal friction angle and cohesive force of the modified sand soil by direct shear test; based on the Bingham fluid model, establish fluid equations of the modified sand soil. The mail work and results are as follows:(1) Eight groups modified soil are tested in the rheological experiments, test the reheological parameters of modified soil under the circumstances of different confining pressure including 0.05MPa、0.10MPa、0.15MPa、0.20 MPa four levels pressure. The experiments also Summarize the variation of shear stress, apparent viscosity, yield stress and plastic viscosity.(2) Analyzed the variation range of the yield stress and Plastic viscosity: for the fist modified sand soil, the yield stress varies from 825.85 Pa to 5492.3Pa, the plastic viscosity varies from 295.27Pa?s to 1493.7Pa?s; for the second modified sand soil, the yield stress varies from 930.84 Pa to 5890.41 Pa, the plastic viscosity varies from 332.79Pa?s to 1780.21Pa?s.(3) Based on the Bingham fluid model, introduce the pressure coefficient k and analyze data to establish fluid equations. Modified the Bingham fluid equation, for the fist modified sand soil, the yield stress coefficient varies from 1539.3Pa to 2514.8Pa, the plastic viscosity coefficient varies from 838.6Pa?s to 1354.1Pa?s; for the second modified sand soil, the yield stress coefficient varies from 1711.9Pa to 2726.1Pa, the plastic viscosity coefficient varies from 1048.6Pa?s to 1852.3Pa?s.