Effect of Contact Material on Tension Infiltrometer Measurements

A layer of contact material is often used to establish and maintain hydraulic contact between a tensioninfiltrometer membrane and the soil surface. The aims of this study were to determine the change in hydraulic properties oftwo types of contact materials after repeated use of the materials and to evaluate the effect of contact material on steadystateinfiltration rates. Reusing a natural sand contact material resulted in increasing values of satiated hydraulic conductivity,Kst (Kst = 246 to 311 mm h 1 ), due to a progressive loss of finetextured particles. However, Spheriglass No. 2227 glassspheres, previously proposed as a suitable contact material, maintained stable hydraulic properties after repeated use bothin the laboratory and in the field (Kst = 264 to 267 mm h 1 , water entry pressure head hw = 400 to 360 mm, air entry pressurehead ha = 640 to 650 mm). The steadystate tension infiltrometer infiltration rate, i0, at a pressure head h0 = 50 mm wasreduced by about 30% by removing the contact material from the smoothed and leveled surface of a sandy loam soil. It wasconcluded that Spheriglass No. 2227 glass spheres are adequate for both use and reuse as tension infiltrometer contactmaterial, and that contact material is required to maintain good hydraulic connection with the soil surface even when thesurface has been smoothed and leveled.