Numerical simulation of the deposition and consolidation history of Lake Agassiz clay at three representative field sites in Manitoba and North Dakota.

摘要

This purpose of this research was to test the hypothesis that artesian conditions in the bedrock underlying the Lake Agassiz basin inhibited compaction and caused variations in water contents in the clay deposits. FLAC, a numerical model used to test the hypothesis, simulated the deposition and consolidation history of the clay at three representative field sites. These sites, Manvel, Montcalm and Drayton, are located in Manitoba and North Dakota.; Assumptions implicit in the model conceptualization include: (1) the presence of artesian bedrock conditions during the deposition, (2) uniform deposition rate during high lake levels and (3) minimal head loss across glacial drift deposits between the bedrock and the clay. The numerical modeling results supported the hypothesis because water contents calculated by the model compared well to the field measured values at all three sites. The numerical model results indicate that the hydraulic head in the bedrock has to be much higher than the clay thickness to inhibit consolidation. Sensitivity analyses on input parameters and boundary conditions show that the model results are most sensitive to changes in initial water content, stress-strain relationship and hydraulic conductivity and less sensitive to bulk modulus, shear modulus, cohesion, tension and friction angle.; These model results confirms that (1) the numerical model accurately simulates the deposition and consolidation history, (2) the artesian bedrock porewater pressures inhibited consolidation and caused the water contents to be relatively high at Manvel and (3) the lower artesian bedrock conditions caused water content to be lower at Montcalm and Drayton.; Considering that the bedrock porewater pressures measured in the field only varied between 420 kPa and 450 kPa, clay thickness may be good indicator of the degree of consolidation within the clay plain.