Finite element software on large deformation analysis for soft rock engineering at great depth, briefly called Large Deformation Engineering Analyses Software (LDEAS), is developed. The software has five features as follows:
It includes a nonlinear theory of mechanics based on S-R decomposition theorem proposed by Chen as well as the classical large deformation theory for comparison,
The three design method for non-linear mechanical problem proposed by He (1993) is fulfilled,
the codes is programmed using FEPG (Finite Element Program Generator) provided by FEGEN company which only partial equations need be written,
it include generally used constitutive models and element types for geomaterials and supports, and therefore is fit for slope, foundation and underground engineering, and
Coupled thermal-mechanical-seepage analyses will be available.
At present, the interface and programs for two-dimensional problem have finished. Four numerical examples confirmed the accuracy of the software.
Phenomena of large deformation occur frequently in geotechnical engineering. For example, with the excavation of a softrock tunnel at great depth, large deformation of rock mass around tunnel such as roof caving, floor bulging and side bulging will occur. For softrock engineering at great depth, non-linear problems in physical, geometrical and contact boundary are complicated. Since the analytic solutions to non-linear differential equations of soil-rock mechanics are extremely difficulty to obtain, it is rather important to investigate numerical methods and software such as FEM, FDM and DEM. It is well recognized that the effectiveness of computational methods for solving rock and soil mechanics depends largely on the exactness of theoretical foundation on which the computational programs are based. Besides a reliable constitutive model for geomaterials, an accurate mechanical theory for large deformation is necessary to make a reasonable analysis for soil and rock engineering. The linear small deformation theory of mechanics is only fit for small displacement field where the principle of superposition holds. For large displacement field, there are two theories of mechanics, i.e., classical large deformation theory (see Truesdell and Noll, 1965; Biot, 1965; Guo, 1980), in which Green strain tensor is used as strain definition while rotation tensor is defined by Finger-Truesdell's polar decomposition theorem separately, and large deformation theory proposed by Chen, which is based on S-R decomposition theorem (see Chen, 1979; Chen, 2000) using a co-moving coordinate system method. Although Green strain is applicable for large displacement and therefore is generally used, deficiencies of Green strain tensor are:
it defined through the quadratic form of ratio of the length of line elements after deformation to that before deformation, which is not congruent with common engineering definition of stain as linear form, and
there is no definition of finite mean rotation angle in compatible with finite strain.
In order to overcome above deficiencies, Chen proposed the S-R decomposition theorem, which deformation gradient is decomposed to one unique addition of a positive definite strain tenor and an orthogonal rotation tensor. By using a co-moving coordinate system method, a nonlinear theory of mechanics for large deformation is developed.