Shear Strength and Pore Pressure Response of Coal Ash Under Undrained Shearing at Isotropic and K0 Consolidation

Coal ash is utilized as structural fill material in highway and railway construction. Shear strength tests are commonly conducted on specimens consolidated under isotopic conditions (IC); however, stress conditions in the field are anisotropic (horizontal and vertical stresses are not equal). The current study focuses on evaluation of shear strength and pore pressure response of coal ash consolidated under K0 conditions simulating field conditions more accurately. Two series of CU triaxial testing were conducted on coal ash under IC and K0 conditions at different mean effective stresses (at the end of consolidation) ranging from p′ 0 = 50, 100, 150, 200, and 300 kPa. Peak stresses for K050 and K0100 tests were observed to be less as compared to IC50 and IC100, respectively. For IC specimens, pore pressure was obtained to be less dilative with increasing pꞌ0; however, the behavior was in contrast for the K0 specimens. For the higher range of mean effective stresses (pꞌ0 = 100, 200, and 300 kPa), peak deviatoric stress showed a large increase for both IC and K0 specimens with increasing pꞌ0. For the same pꞌ0, the K0 specimen exhibited lower peak stress as compared to IC specimen although a smaller difference for higher pꞌ0 was observed. The contractive pore pressure response was observed to increase with increasing pꞌ0 for IC specimens. However, K0 specimens exhibited a significant increase in dilative pore pressure response with increasing pꞌ0.