The neocene mudstone,which is widely distributed in eastern Gansu,is water-sensitivity.Many geological disasters in this stratum may occur when groundwater is enriched.To understand the impact of groundwater on the engi-neering properties of the mudstone,the water-softening(immersion)tests and confining expansion tests were carried out.Meanwhile,a novel expansive model of loaded mudstone was proposed considering the water-softening and volume expan-sion.The results show that:the water softening coefficients Kc of mudstone is 0.221.The water softening behaviour of the mudstone is mainly affected by water saturation.Once the sample is staturated,the continuous immersion has almost no impact on the mechanical properties of the mudstone.The confined expansive rate(without load)is 0.325,and the expan-sive stress of the undisturbed mudstone is 450 kPa.The swelling pressure and water content have the characteristics of piecewise linearity.By the normalization of the water content and the introduce of water-relative damage variable,the no vol expansive model is avaliable to describe the loaded expansion of mudstone,whose predicted deformation is match to tests.Therefore,the novel model can be used to the deformation prediction of tunnel surround rocks.
neocene red bedswelling rockwater-softeningdamage variableconstitutive model
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