Research On The Rheological Properties Of The Modified Sandy Gravel

With the rapid increasing of China's economic,rail transportation and other tunnel constructions are expanding with amazing speed.EPB Shield is the widest application method in city tunnel constructions,EPB shield is characterized by using the soil to support surface of excavation,dynamically balanced the excavation layer.The pressure control of working chamber is the most important technology to ensure the construction successful.In the shield construction,the soil improvement technology turn soil into"plastic flow" material.The pressure of the chamber which is changing with the rate of excavating blances the pressure of layers.Study on the mechanism of chamber pressure control and screw conveyor has an important guiding significance for the development of Shield Technology,so we must determine the rheological properties of modified soil in the chamber.This paper selects Beijing typical sandy pebble soil as the research object,the soil has many characteristics such as high content of sand and gravel,bad plasticity and high permeability.Those characts would cause shield problems.According to the characteristics of sand gravel soil,a new rheometer that can simulate the pressure of the chamber was designed.Four groups of modified soil were selected by the slump test to be research in rheological experiments.The direct shear test was used to measure the influence of modifier on the soil.The main work and results are as follows:(1)Four groups of modified soil were tested in the rheological experiments with the new rheometer.The rheometer applys 0.05MPa?0.1 OMPa?0.15MPa?0.20MPa four levels of pressure on the soil.Rheological parameters of soils are measured in different conditions.(2)The experiments indentified the variation range of rheological parameters:the yield stress varies from 4720Pa to 11170Pa,the plastic viscosity varies from 274Pa·s to 1850Pa·s.The experiments also Summarize the variation of shear stress,apparent viscosity,yield stress and plastic viscosity.(3)The research calculated the rheology eqution of modified soil and modified the Bingham fluid equation with variable quantities including ?,?,?.Regression analysis is used to calculate the value of four quantities.