PREDICTION OF CONSOLIDATION TIMES FOR SHEAR STRENGTH TESTING OF GEOSYNTHETIC CLAY LINERS USING CS2 MODEL

Open Access
Author:
Wang, Chu
Graduate Program:
Civil Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
October 26, 2016
Committee Members:
  • Patrick Joseph Fox, Thesis Advisor
  • Tong Qiu, Committee Member
  • Ming Xiao, Committee Member
Keywords:
  • Geosynthetic clay liner
  • consolidation
  • shear strength testing
Abstract:
The objectives of this study were to investigate the consolidation behavior and predict consolidation times for shear strength testing of geosynthetic clay liners (GCLs). These objectives were achieved by performing a series of numerical simulations using the numerical model CS2 (Fox and Berles 1997; Fox and Pu 2012). GCL consolidation was assessed for three values of initial overburden stress (10 kPa, 100 kPa and 1000 kPa), six load increment ratios (LIRs) (0.25, 0.5, 0.75, 1.0, 1.25, 1.5), double-drained (DD) and single-drained (SD) conditions, and two values of specific gravity (1.0 and 2.21). Constitutive relationships for GCL compressibility and hydraulic conductivity were taken from experimental data published by Kang and Shackelford (2010). Values of consolidation times t_50, t_70, t_90, t_95, and t_98 are presented for various conditions and plotted versus LIR. Consolidation times for both DD and SD conditions decrease as LIR increases for a given initial overburden stress, and these times decrease as initial overburden stress increases at a given LIR. The longest predicted time required for 98% GCL consolidation and SD conditions is 32.5 h, which corresponds to low initial stress and low LIR. Thus, for a direct shear test, the recommended consolidation time for a GCL prior to the start of shearing is 48 h for single-drainage. The longest predicted time required for 98% GCL consolidation and DD conditions is 8.1 h, which also corresponds to low initial stress and low LIR. Thus, the recommended consolidation time for a GCL prior to the start of shearing is 24 h or overnight for double-drainage. This study found that the ratios of consolidation times for DD to SD conditions are approximately equal to 4.0 in all cases, which is consistent with classical consolidation theory. Numerical solutions obtained for G_s = 1 are nearly identical to corresponding solutions obtained for G_s = 2.21. This indicates the effect of self-weight of GCL solids is negligible, which is consistent with GCLs being very thin materials.