One of the main concerns of a pavement engineer is the change in moisture content of subgrade soil and the resulting impact on the structural performance of the pavement. Under saturation, the resilient modulus of the base, sub-base, and subgrade layers decreases, and the pavement begins to show premature failures. To avoid this major cause of pavement deterioration, a permeable drainage layer is usually recommended. The recommended horizontal permeability of drainage layers is typically 150–300 m/day. However, the horizontal permeability of the granular subbase material conforming to the guidelines of the Ministry of Road Transporation and Highways (MoRTH) was found to be less than 20 m/day. In the current study, a geocomposite containing a geonet core and a nonwoven geotextile filter and separator on both sides was used to improve the drainage properties of a granular subbase layer. The horizontal permeability of the composite drainage layer was measured using a newly developed large-scale permeameter apparatus capable of also applying a static load up to 50 kN on the pavement. It was noticed that the horizontal permeability of the granular subbase layer increased by about 10 times. The horizontal permeability of the geocomposite is reduced by 20% when a single axle wheel contact pressure of 560 kPa was applied on the base surface. The resilient modulus of the GSB layer was improved by 2.5 times and the pore water pressure was reduced by about 75% with the inclusion of GC layer. Overall, the horizontal permeability of the granular subbase layer with geocomposite has crossed the 300 m/day requirements.