Abstract: Groundwater pipe drainage systems(GPDS)are often found in debris-containing clay slopes(DCS).Physical model simulation tests on seepage system in DCS were made to study the development and seepage behaviors of GPDS.From the test results,several conclusions were drawn as follows:(1)In the process of development of GPDS,the permeability of soil mass of DCS would decrease at the first stage,increase in the following stage,and be invariant at last;(2)In DCS,the deeper the soil mass was,the longer the time needed for the development of GPDS was;(3)The higher the clay particle content in DCS was,the longer the time needed for the development of GPDS was,and the worse the permeability of soil mass was;(4)It was more propitious to the development of GPDS for the soil mass with a higher debris and gravel content,bigger grain diameter;besides,the GPDS developed in this kind of soil mass often had larger permeability;(5)When GPDS developed in DCS,the permeability of soil mass would become dramatically larger,and the seepage force of groundwater and pore water pressure on sliding surface would reduce;(6)As GPDS in DCS was destroyed by external forces,such as construction loads,the groundwater level would rise obviously and this might induce the slope failure.Therefore,GPDS is a very important favorable factor for slope stability.