PULLDOWN FORCES FOR COLLECTING LARGE SOIL MONOLITHS

The force for pulling down large, steel monolith tanks was measured fo r a fine sandy loam, a silt loam, and clay loam soil with varying soil water contents in two of the soils. Pressure gages on hydraulic jacki ng equipment were used to measure force as a function of depth through out the 2.4-m installation depth of the soil monolith tanks. Monolith tank areas were 0.75 x 1.00 m or 3.00 x 3.00 m, and the tank wall thic kness was 9.5 mm. Except for the effects of natural hard pans or plow pans, pulldown force was linearly related to depth. When pulldown forc e was converted to wall friction, the average wall friction after wett ing for each of the three soils was about 20 kPa. For most agricultura l soils without rocks or cemented layers, the monolith tank wall frict ion from prewetted soil should also be less than 20 kPa. Wall friction variability decreased with depth so that a safety factor of 1.25 woul d be satisfactory in designing monolith collection equipment.