Tension Cracks in a Compacted Clay Embankment

Abstract

In a spirit of adventure, a boring was made and soil moisture contents measured along a tension crack near the crest of an earth embankment. Moisture contents increased linearly with depth and then sharply decreased at what is interpreted to be the bottom of the crack. Desiccation does not appear to have been a factor because of construction delays due to rains as the embankment still was under construction. It is hypothesized that the crack was created by quasi-elastic rebound of the recently compacted soil directed normal to the intersecting ground surfaces. A second increase in moisture content that appears to be linear with depth was discovered as the boring had been extended all of the way through to the bottom of the embankment. This change in moisture contents suggests a possible basal crack that can be attributed to differential settlement, and is assumed to connect to the upper crack as it was encountered in the same boring. Hydraulic connection may have been impaired by pinching action related to differential settlement but still could allow some water to go through. A comparison of the two mechanisms suggests that the upper crack probably formed first. A basal crack that remains open should be relevant for earth dams.