Experimental Apparatus And Tests On Sandy-Gravel Soils’ Rheological Property

Sandy gravel layer is the main area of earth-pressure-balanced shield construction, whose rheological property is critical in the construction. Soils in the pressure chamber is difficult to form the "plastic flow state" for low-content clay gravel layers and weathered rock layers, causing difficulties in shield. In this case, soils need to be modified to change the state of excavation earth. The paper is about the effect of rheological property for modified soils acted by different mixing blades.Based on the purpose of tests in the paper, firstly appropriate experimental apparatus are developed, then laboratory tests are taken as main methods to evaluate the improvement effects for soils produced by different kinds of mixing blades through collapsed slump tests, friction coefficient tests, and direct shear tests, analyzing the optimum mixing blade, and finally the rheology equation for modified soils is obtained. The main conclusions are as follows:(1) A sandy gravel rheometer for tests herein is developed, which is able to replace various mixing blades.(2) The mixing effect of cross-plate blades is the best according to the comprehensive analysis of test data.(3) Through calculation and analysis for soils modified by the cross-plane mix ing blade, the relation equations of g, h, yield stress, and plastic viscosity are derived, and the approximate range of yield stress and plastic viscosity of sandy gravel at the p lastic flow state is obtained.(4) The data from rheometer in the paper is valid, which is resulted from comparing rheometer calibration with ICAR rheometer for business use. Also, the rheometer herein is capable to modify soil particles whose sizes are smaller than 6cm, but ICAR rheometer is only effective for particle sizes smaller than 2cm.At the basis of properties of sandy gravel, the apparatus for measuring the rheological characteristics of modified sandy-gravel soils is developed and calibrated, obtaining the rheological parameters of sandy-gravel soils under different-content modifiers. The modified sandy-gravel soil is considered to be Bingham fluid through analysis, whose rheological property can be represented by yield stress as well as plastic viscosity, obtaining the range for rheological parameters of sandy-gravel soil which is at "plastic flow state".