Physical Properties,Over-Consolidation And Constitutive Modeling Of Shanghai Deep Clays

With the continuous development of underground space,the depth of underground structure construction has been increasing,and the study of deep soils has become more and more important.In this paper,a series of physical and chemical tests,high-pressure consolidation tests,triaxial undrained shear tests,and constitutive simulation analysis of deep soils in Shanghai were carried out to obtain the physical properties of Shanghai deep clay.The main conclusions were as follows:1)By comparing the physical and chemical properties of deep and shallow soils in Shanghai and the results of electron microscopy(SEM),the differences in mechanical properties between deep and shallow soils in Shanghai were analyzed.In terms of plasticity index,Shanghai deep soil and shallow soil are both low liquid limit clay,shallow soil is closer to low liquid limit silt.In terms of activity,the activity value of deep soil in Shanghai is generally larger than that of shallow soil.In terms of microstructure analysis,Shanghai deep soil particles are loosely distributed in the horizontal and vertical directions,and the spatial relationship between the particles is strong.2)The over-consolidation characteristics of the 8th and 10 th layer clays of Shanghai were analyzed by high-pressure consolidation test and three-axis undrained shear test(CU)on the 8th and 10 th layer clays of Shanghai.In terms of over-consolidation,the over-consolidation ratio(OCR)of Shanghai eighth-layer clay is about 3,which is over-consolidated soil.Shanghai 10 th layer clay has an over-consolidation ratio(OCR)of 1.05,which is a normal consolidated soil.The stress history of the two clay layers is consistent with the characteristics exhibited in the triaxial undrained shear test.In the cause of over-consolidation,the overconsolidation of Shanghai eighth-layer clay is the result of a combination of stress history caused by water level decline and age effect.3)The constitutive simulation of the indoor test of the 8th and 10 th layers of clay in Shanghai was carried out by using the modified unified constitutive model.The obtained consolidation compression curve,stressstrain curve and experimental values were in good agreement.The revised unified constitutive model can be applied to Shanghai deep clay.