Evaluation of the Vertical Moisture Barrier Installed on IH 45 Near Palmer, Texas (7-3930-1)

To minimize problems with expansive clays, TxDOT decided to install vertical moisture barriers on a major widening project on IH 45 near Palmer, Texas. This 14 mile project required barriers on each side of the pavement in both directions. To evaluate the effectiveness of the barrier, the variation in moisture content with depth was measured at four locations, with measurements both inside and outside of the barrier.|The monitoring was performed with a Troxler AP-200 Sentry gauge. This report describes the gauge, the installation procedures and the measured moisture contents.|The barrier seems to be performing as designed at three of the four monitor locations. At these three locations, during wet and dry periods the moisture contents inside the barrier were relatively constant, whereas outside the barrier substantial variations were monitored. At the fourth location very little difference could be detected between the moisture fluctuations inside or outside of the barrier.|Concerns were expressed concerning the installation procedure, which requires the cutting of a 250 mm trench, which is backfilled with gravel. This trench appears to trap water, which may have a detrimental impact on long-term barrier performance. Future research work should be directed at "trench-less" barrier installation techniques.