Developing Smart Grouted Sand Columns for Real Time Monitoring of the Stability, Seepage, and Rapid Drawdown in Earth Dams
Kula, Halil Ibrahim
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The reservoir drawdown can negatively affect the upstream slope stability of earth dams due to removal of the balancing hydraulic forces acting on the dams during undrained condition in the soil. Therefore, monitoring upstream slope during rapid drawdown is an important task in terms of stability. Having lower wetting zone inside the earth dam using low permeability materials can provide a good design for earth dams and prevent possible failures which is related to seepage problems. In this study, acrylamide grouted sand was used to monitor upstream slope during rapid drawdown and control the seepage inside the earth dam. To better characterize the behavior, over 140 grouted sand specimens were prepared with different particle size of sands. Particle size, gradation, and compaction affected the compressive strength of grouted sands. The compressive strength of the grouted sands varied from 240 kPa to 775 kPa after 7 days of moist curing. Also, the curing time after 3 days did not affect the mechanical properties of the grouted sands. Nonlinear Vipulanandan p-q constitutive model was used to predict the mechanical behavior of acrylamide grouted sands. The permeability of grouted sand was 10-12 m/sec, and it was not affected by grain size distribution and particle size. Electrical resistivity was identified as the sensing and monitoring property for the acrylamide grouted sands. The acrylamide grouted sand with and without conductive filler were piezoresistive. Electrical resistivity change was identified as the sensing and monitoring property for the acrylamide grouted sands. 0.1% conductive filler (CF) was added to make the grouted sands very sensitive under water submerged and moist conditions. Adding CF increased piezoresistivity from 10% to 21%. Nonlinear Vipulanandan p-q constitutive model was used to predict the piezoresistive behavior of the grouted sands. Assigning acrylamide grouted sand to upstream face decreased phreatic line in the earth dam and seepage quantity and increased the stability of earth dam twice compare to clay core. In this study, the potential use of grouted sand in installation was numerically investigated using an earth dam 2-D model. Seepage and stability analysis were performed during rapid drawdown condition and change in shear stress were quantified. Shear stress change was used to check the piezoresistivity of acrylamide grouted sand columns used in the model embankment. Based on the changes in the electrical resistivity for real-time monitoring, location for the piezoresistive grouted sand columns were identified.