FORECASTING MODEL OF GRAIN SIZE GRADING CURVES OF COARSE-GRAINED MATERIALS BASED ON DISCARDING RATIO
CHANG Shuai1，2，XU Riqing1，2
(1. Research Center of Coastal and Urban Geotechnical Engineering，Zhejiang University，Hangzhou，Zhejiang 310058，China； 2. Key Laboratory of Soft Soils and Geoenvironmental Engineering，Ministry of Education，Zhejiang University， Hangzhou，Zhejiang 310058，China)
Abstract：To construct a forecasting model of grading curve of coarse-grained materials considering breakage，particle breakage is divided into three stages. And the new concept of discarding ratio Rk is introduced in the model-building process. By investigating the relationship of discarding ratio with confining pressure，dry density and particle size with the breakage test results of quartz sandstone，gneiss，mixture of sandstone and slate，breccias and sandy conglomerate，it is indicated that on the simplified hypothesis of geometric progressional distribution，there is a linear relationship，which has a slope turning point between Rk and σ3，for different granular materials when particle size and confining pressure vary in the ranges of 10–60 mm and 0.0–1.6 MPa，respectively. By exploring the particle breakage of well-rounded sandy conglomerate，it is found that 3-Rk relationship becomes linear globally while particle size is less than 10 mm and confining pressure ranges from 0.0 to 1.2 MPa. Considering the combined effect of confining pressure，strength of mother rock and original particle size，it is concluded that the variation of discarding ratio is unanimous for the breakage of gneiss，mixture of sandstone and slate，weak weathering quartz sandstone with the same grain group once particle size changes from 10 to 60 mm. Thus a prediction formula for estimating discarding ratio is presented，and the ranges of its parameters are given preliminarily，which makes possible the forecast of soil grain size grading curve of coarse-grained materials based on the concept of Rk.
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2014, Vol. 33 
