Drift of Flush-Mounted Pressure Cell Readings

Readings from earth pressure cells that were flushmounted in an instrumented retaining wall exhibited progressive change with time (drift) after backfill placement. The test procedures and conditions precluded the possibility that temperature effects could account for the drift. A series of experiments showed that the drift was caused by moisture migration from the backfill to the concrete retaining wall. It appears that the moisture causes a slight expansion of the concrete around the cells, resulting in distortion of the cells and decrease of the fluid pressure inside the cells. A surface treatment reduced the magnitude of the drift. A pressure cell design is proposed to mitigate this source of drift in new installations.