Effects of horizontal strain in estimating specific storage and compaction in confined and leaky aquifer systems

Mathematical and numerical distinctions are made between developments of governing equations involving groundwater flow and granular displacement where (1) only vertical strain and no change in total normal load are assumed, and (2) such limitations are eliminated. The former is referred to here as the Jacob-Terzaghi method; the latter is referred to as the Blot method. Numerical comparisons of drawdown, compaction, and strain are made for hypothetical confined and leaky aquifer systems for one- and three-dimensional strain problems. Simulation results indicate that incorporation of horizontal strain results in reduced drawdowns. Vertical compaction for a specified stress distribution is greatly reduced when horizontal strain is invoked. The distribution of strain components indicates that approximately two-thirds of the total volume strain originates from horizontal compaction in pumped aquifers. Incorporation of horizontal strain also affects the distribution of flux through the overlying confining layer as a function of distance from the pumping well and may ultimately affect the interpretation of aquifer-test data.