13. VERTICAL MOVEMENT UNDER TEST LOAD AND BUILDINGS.
A study of levels taken on the tank and on the four indicator pegs (see Section 8) with one of the office post footing as datum, showed from the results available for twenty-five days slight cyclical variations in level.- Assuming that any relative vertical movement decreased with depth, and that any movement under a load was less than that on an unloaded area, i.e., movements entirely due to changes in moisture content, then the levels taken indicated with the loaded area as datum that: (a) on fine days, during the rains, there is a small relative rise of the soil surface of from 1/16 inch to 1/8 inch between 7.30 a.m. and 4.30 p.m., but no difference on a cloudy day; (b) after a period of rain the daily variation is at the minimum value of 1/16 inch, and throughout the day the surface is about 1/16 inch higher than on a fine day after a period of fine days. This difference on the second day increased to 1/8 inch, presumably as the excess moisture became absorbed lower down, giving rise to additional expansion. After a period of rain there seems to be a tendency for the surface to go on rising for four or five days until the excess moisture is absorbed in full. (see Table I.)