A Computer Program for Nonlinear Seismic Response Analysis of Horizontally Layered Soil Deposits, Earthfill Dams, and Solid Waste Landfills
Short Description of D-MOD2000
D-MOD2000 is a one-dimensional nonlinear effective-stress site response analysis computer program, i.e., a computer program that allows for the time-dependent generation of porewater pressure and accounts for its effects on soil stiffness and strength over the duration of an earthquake. The nonlinear response of the soil is represented by a backbone curve with inelastic response governed by unloading-reloading rules postulated by Masing and Pyke. Porewater pressure generation is controlled by semi-empirical models developed by Dobry and Vucetic (for sand) and Matasovic and Vucetic (for clay), with a computed porewater pressure used to degrade the backbone curve in a way that represents the softening and weakening of soils expected at lower effective confining pressures.
Genesis of D-MOD2000
The computer program D-MOD2000 is an interactive, WindowsTM-based version of D-MOD_2 developed by GeoMotions, LLC. D-MOD_2 is an enhanced version of D-MOD (Matasovic, 1993) which combined the dynamic response model of DRAIN-2D1 as implemented in the computer program DESRA-22 with the nonlinear stress-strain model developed by Matasovic and Vucetic (1993), and the Dobry et al. (1985) porewater pressure generation model for sand with modifications made by Vucetic and Dobry (1988) to simulate quasi two-directional pore water pressure response3, and a porewater pressure generation/cyclic degradation model for clay developed by Matasovic and Vucetic (1995a).
In D-MOD_2, modifications have been made with respect to stress-strain constitutive model employed (reference strain has been introduced to facilitate evaluation of the nonlinear stress-strain model material parameters4) and dynamic equation of motion solver (Wilson’s θ algorithm used in earlier versions of the program was replaced by the Newmark β algorithm). D-MOD_2 further allowed for modeling of soil profile with up to 200 soil layers and 200 material parameter sets (as opposed to 15 layers/materials in D-MOD) and for up to 2,000 nodes for calculation of pore water pressure dissipation (100 in early versions of the program). D-MOD_2 was further modified to allow for use of the extended Rayleigh damping formulation (matching of target damping ratio at up to four frequencies), and for direct calculation of average acceleration of sliding mass within the profile (for use in Newmark-type seismic deformation analysis).
Other notable improvements with respect to the previous version of the program include adjustments for dissipation of negative (suction) pore water pressure (negative pore water pressures occur in overconsolidated clays subjected to cyclic straining and, when in composite soil profile, may reduce positive porewater pressures in liquefiable layers), an extension of the nonlinear stress-strain model to simulate seismically-induced “slip” along the composite landfill liner interfaces, and introduction of an option for “quasi” 2-D site response analysis of earthfill dams, levees and slopes. The latest version of the program (V9.3.1) incorporates routines for the processing and error checking of output data, and for displaying that output in a format familiar to geotechnical engineers.
1 Computer program DRAIN-2D (Kannan and Powell, 1975) is a classical program for calculation of in-elastic (bi-linear) structural response in time domain.
2 The computer programs DESRA/DESRA-2 were written in 1977-78 by Michael K. W. Lee and W. D. Liam Finn at the University of British Columbia (UBC) Department of Civil Engineering.
3 The modified Dobry et al. (1985) porewater pressure model was first implemented in DESRA-2 by Vucetic (1986). The version of DESRA-2 with the implemented Dobry et al. (1985) model is called DESRAMOD.
4 In the previous versions of the program, material parameters were evaluated by fitting the initial loading stress-strain curve, while in the current version, the parameters are evaluated by fitting modulus reduction and damping curves, hence a need to introduce reference strain into the model.
For more information about the different features included in D-MOD2000, please browse through the User's Manual.
A step-by-step example showing how the program can be used to conduct a nonlinear and effective-stress site response analysis is provided in the Quick Tutorial.
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