Subjected to dynamic loading and humid environment condition,the mudstone will swell and lose its strength due to the argillization just in a few hours,which hinders normal coal mining.In order to reinforce swelled mudstone instead of removing it from tunnel,a local thermal power plant byproduct,fly ash(class C fly ash,ASTM C618) and lime were proposed as(additives) to stabilize it.A series of experimental tests and microstructure observation were conducted to determine geotechnical properties of stabilized mudstone and possibility of(using) as base material of roadway floor.The unconfined compressive strength(UCS) tests show that the mixture of lime-fly ash and swelled mudstone has the strength(UCS) of about(1.78 MPa) and elastic modulus of about 210 to 400 MPa after 28 d curing ages.The analytical results show that it is possible for the treated soil to be used as base material.And,the treatment provides a time-saving way to stabilize the swelled mudstone in excavated roadway floor of coal mine.