Abstract: For thorough research of the anti-seepage problem in terms of seepage flux and seepage stability due to the geosynthetic clay liner(GCL) defects, the seepage physical test method for the simulation of GCL with defects in dam anti-seepage hydraulic projects is established by means of developing the seepage experimental apparatus consisting of pressure control system and model test system. Factors which affect the joint impermeability of dam soil and GCL with defects are preliminarily discussed according to the seepage test of GCL with different defect conditions. The results show that the hole-defect’s size can be more sensitive to the impact of overall permeability of GCL with defects and soil than the defect rate. The main sensitive factors for defect’s healing capacity include hole-defect’s diameter and GCL specifications (material’s own performance). Therefore, two following points should be considered in the projects: (1) the hole-defect’s diameter should be less than 0.5 cm in the projects, the ones larger should be repaired; (2) make sure the GCL interface is smooth and flat in case that the local defect rate becomes more than 0.5%.

Key words: geosynthetic clay liner(GCL), defects, seepage properties