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Apparent cohesion leads to eventual failure

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These photos show a wall failure next to a corner. This failure occurred in an area where successive triangular sectors of geogrid layers were not installed. Failure is to be expected because reinforced walls without reinforcement should fail.

Curiously, this failure occurred about one year after the end of construction. Clearly, failure was delayed because of substantial apparent cohesion. Some change in moisture content was sufficient to trigger failure. Looking at it differently, assume that construction was properly done and the wall was instrumented. What loads would have been measured in the not-missing sectors of geogrids? Small load values, probably induced by compaction; certainly not values needed for stability as assumed in design. Normal condition in this case corresponds to an apparent cohesion producing misleadingly small force values in the geogrid. Can one assure that the water content level will remain constant during the life span of the wall? What if an earthquake has occurred? Geotechnical practice ignores apparent cohesion for good reasons. Measuring reinforcement force in the field while apparent cohesion of unknown magnitude exists leads to potentially significant underestimation of the force needed for stability during the structure’s life span.

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