FLAC3D (Fast Lagrangian Analysis of Continua in 3 Dimensions) is numerical modeling software for geotechnical analyses of soil, rock, groundwater, constructs, and ground support. Such analyses include engineering design, factor of safety prediction, research and testing, and back-analysis of failure. Continuum analysis can be applied to engineering design of civil, mining, and geotechnical excavations (e.g., slopes, tunnels, caverns, stopes, etc.) and constructs (dams, foundations, footings, walls, etc.) in soil, intact rock, and rock masses (i.e., heavily jointed rock). Using interfaces, FLAC3D can also simulate discontinuities such as faults, joints, bedding planes, and engineered boundaries along constructs.* FLAC3D utilizes an explicit finite volume formulation that captures the complex behaviors of models that consist of several stages, show large displacements and strains, exhibit non-linear material behavior, or are unstable (including cases of yield/failure over large areas, or total collapse).