Laboratory Measurement of Discharge Capacity Under Incremental Confining Pressure of Geosynthetic Drains

Prefabricated Vertical Drains (PVD) and Prefabricated Horizontal Drains (PHD) are commonly used in soft soil improvement projects to accelerate the consolidation process. The effectiveness of PVD and PHD are mostly controlled by its discharge capacity. This paper discusses the impact of incremental confining pressure on geosynthetic drains’ discharge capacity. ASTM D4716, a method to measure the in-plane flow rate and transmissivity of geosynthetics, was adopted to determine the discharge capacity of the drains. Three types of PVD with harmonica core shape and three types of PHD with cuspated core shape were tested under five variations of hydraulic gradient and incremental confining pressure in the range of 50 to 200 kPa. The result indicated that the discharge capacities of drains on particular hydraulic gradients (i = 0.2 to 1.0) decreased as the confining pressure increased. Furthermore, a compressive strength test was conducted to examine the effect of vertical pressure on the drains. It is found that when the vertical pressure reached 200 kPa, there was no drainage area available in PHD, whereas PVD could restrain over than 1000 kPa of vertical pressure.