Preliminary Numerical Modeling of a Mechanically Stabilized Earth Wall under Flooding and Rapid Drawdown Conditions

Design guidelines to ensure stability and performance of mechanically stabilized earth (MSE) walls under flooding and rapid drawdown conditions are a priority for the Wisconsin Department of Transportation (WisDOT). Performance of a 4-m high MSE wall reinforced with metal strips was evaluated. Seepage and slope stability analysis were conducted on the model wall. Porewater pressure and free water surface obtained from transient and steady state seepage analyses were used as initial conditions for slope stability analysis. Results indicated that for a poorly graded (SP) sand backfill with a hydraulic conductivity of 7.4×10^-4 cm/s, a 2-m high flooding event in front of the MSE wall saturates the backfill and reaches the steady state condition in 6 hours. The limit-equilibrium factor of safety increased from 2.2 before flooding to 2.8 immediately after flooding and equilibrates back to 2.2 after 6 hours. On the other hand, rapid drawdown of a 2-m face flooding event drops the factor of safety from 2.2 to 1.7. Factor of safety increases back to 2.2 in about 6 hours after rapid drawdown. Flooding and rapid drawdown causes variation in the stability factor of safety of the MSE wall of around 25%. Construction of a 4-m high instrumented MSE wall to conduct complementary full-scale physical testing is ongoing. The wall will be subjected to flooding, precipitation, and rapid drawdown conditions. Porewater pressures, displacements, strains, and stresses within the backfill will be measured. The anticipated outcome of the simulation and testing program is a series of design graphs for use by WisDOT engineers.