USE OF POLYMERS TO STRENGTHEN WEAK ERODIBLE ROCKS AFFECTING THE STABILITY OF HIGHWAY CUT SLOPES

Mudrocks (mudstones, claystones, and shales) are common clastic sedimentary rocks covering about a third of the Earth’s crust. Cut slopes along highways consisting of mudrocks interlayered with strong rock units such as limestone and sandstone are prone to differential weathering and therefore release undercutting-induced rock falls. Undercutting-induced rockfalls cause damage to roadways and hazard to motorists. The three main types of current stabilization techniques used for such cut slopes include the use of rock bolts on stronger rocks, draping slope faces with a wire mesh, and shotcreting. The objective of this research is to investigate polymers’ ability to coat weak rocks and slow down the weathering processes to reduce the risk of rockfall occurrence. The chosen polymer is polyurethane which is a water based Acrolon urethane. Sodium Dodecyl Sulfate (SDS) solution was used for creating a foam in the polyurethane coating to serve as openings for water passage. Multiple polyurethane/SDS mixing times and concentrations were tested to develop adequate foaming that would make the polyurethane coating permeable. The Hampshire (Devonian red beds) from West Virginia and Conemaugh (Pennsylvanian) from Ohio were used as study samples to test the effectiveness of the polyurethane coating. Rock durability tests such as absorption, slake durability index (SDI), and jar slake were performed on the samples. The results for the Hampshire showed an average of 90.8% SDI for uncoated samples whereas the polyurethane coated samples resulted in an average of 99.1%. The Conemaugh, which is much weaker, resulted in an average SDI of 11.9 % for the uncoated samples and 23.3 % for coated samples. The jar slake test on the Conemaugh showed a significant improvement from a value of 2 (Breaks readily and/or forms many chips) for uncoated samples to 5 (Breaks slowly and/or develops few fractures) for coated samples. These results are encouraging but there needs to be more testing on more mudrocks as well as investigating methods of application on slopes.