A large-scale plane-strain permeameter was designed to investigate the hydraulic characteristics of gravelly clay base soil and a filter under various stresses and different water heads. The apparatus provides a specimen size about 80 cm long, 40 cm wide and 40 cm high. It is equipped with a horizontal and vertical loading system with capacities of 1000 kN in the horizontal direction and 2000 kN in the vertical direction and a water pressure system which can provide water head up to 300 m. The components of the planestrain permeameter are described in detail in this paper. The performance of the permeameter is demonstrated through a group of tests on specimens combining gravelly clay soil and a filter.