GGSD Program Details for LASS II-III

LASS II-III

Category	Dynamics (behaviour and earthquake)
Platform	CDC mainframe
Status	Public domain
Description	LASS-II (Liquefaction Analysis of Saturated Soil Deposits) analyses seismic response and liquefaction of horizontally layered saturated solids. The saturated soil below the water table is modeled as a coupled two - phase medium with solid granular skeleton and pore water as the constituent materials. Coupling between these two phases is taken into account. The pore water is allowed to flow with respect to granular solid and this process is assumed to be governed by Darcy flow law with the coefficient of permeability as the material constant. Above the water table, soil is modeled as one phase solid. A nonlinear material model is used in the program which includes yielding, failure, volume change characteristics, cyclic effects and criteria for initial and final liquefaction. Two different material models are used for the behavior of soil before and after initial liquefaction. All the material parameters needed for the material model used in this program can be determined from routine laboratory tests. Cyclic tests are not required for this model. Damping is not included as an independent parameter in the model. Two effective damping mechanisms are inherently included: hysteretic and dissipative damping. LASS-III analyses seismic response and liquefaction of horizontally layered ground subjected to multidirectional shaking. The saturated sand below the water table is modeled as a coupled two phase medium. The two phases are the porous deformable granular solid and the pore water. A nonlinear material model is used to represent the behavior of sand under cyclic biaxial shear stress. A vertical column of the horizontally layered ground is divided into a number of layer elements. At each nodal plane separating two adjacent layer elements there are four displacement degrees of freedom: three components of displacement of granular solid and the vertical displacement of pore water. The stress state for the solid portion consists of two horizontal shear stresses and effective pressure. Effective pressures at each element are monitored for initial liquefaction and complete liquefaction. When the liquefaction criterion is satisfied the element properties are modified accordingly. After completion of earthquake the program provides an option for analysing dissipation of pore pressures. Outputs from the program include: time histories of accelerations; velocities and displacements; time histories of shear stresses; effective pressures and pore pressures; maxima of the preceding quantities; liquefaction time history and response spectra.
Cost	Free on WWW
Data formats supported	None stated
Supplier in United States of America	NISEE - University of California, Berkeley