Fig. 4.27 Apparatus for unsaturated Hydraulic conductivity Tests: (a) Side View (b) Top View (after, Meerdink et al. 1996)

It consists of suction and moisture content measurement ports along the column length, and inlet and outlet ports on either of the boundaries. The ports along the length of column are used to monitor changes in the moisture content and suction by respective probes, such as TDR, and suction measurement techniques, such as tensiometers, thermocouple psychrometers, etc. The boundary ports are used for controlling the flow of water. Initially, air-dried uniform soil is compacted in columns and is instrumented for measuring the moisture content and suction along the spatial length of the column as shown in Fig. 4.27. The boundary port is connected to water reservoir for actuating the flow of water into the column. The initial moisture content of the air-dry specimen, at time t₀ , is very small and the suction head is designated with h₀.The water is steadily injected through the left boundary using a flow pump and is made sure that the water distribution at the soil-water interface is uniform. The right boundary is exposed to the atmosphere pressure. Care must be taken to avoid any evaporation losses from this boundary during the testing process. The water diffuses in the soil specimen and yields transient moisture content profiles in the soil. The conceptual distribution of water content and suction along the column length are shown in Fig 4.28 for different time instants.