Abstract:The characteristics of two kinds of silty clays in shallow-buried large-span soil-layered tunnel,which are soft-plastic and hard-plastic soils,are studied using centrifugal model test;and the main deformation characteristics are discussed through the unconfined compression strength,rebound and arching capabilities. The effect on construction stability is also analyzed. By contrast of unsupported tunnel excavation with different soil covers,the great difference between soil and rock tunnels in arching is found,and the hard-plastic soil has arching ability while the soft-soil does not have. It is shown from the deformation characteristics that there isn¢t relaxed earth pressure in shallow clay but deformation pressure,then the load on the tunnel can be determined according to the deformation. Besides,the influence of soft-plastic interlayer with different locations to excavation deformation and construction stability is studied. It is found that the soft-plastic interlayer has a large effect on the excavation stability,especially for the interlayer at the crown. The layered horizontal and vertical deformations of soil with different covers are measured. Thus,whether the shear band exits or not,the deformation characteristics inside the shear band are analyzed.