Based on manifold element method system balance numerical form, concepts of direct and indirect analysis and excavation imbalance force computation method are put forward. In excavation modification indirect analysis method, the excavation of system release the force between the released excavation proportion and residual system proportion lose balance and form the corresponding displacement, the excavation effect analysis point to the force between the released excavation proportion and residual system proportion. In excavation modification direct analysis method, displacement of every step in excavation is the interaction result of all actual internal and exterior forces on the residual system proportion of the very excavation step, effects of released excavation proportion to the system are ignored and the computation of excavation geotechnical engineering numerical modification only aim at the residual system proportion. Compared with the indirect analysis method, the direct analysis method has more obvious meaning and the corresponding computation is more reliable and convenient.
Excavation with load release problems are very popular in geotechnical engineering (Zheng et al. 1995), the corresponding modification is an important research subject in geotechnical engineering numerical methods. Finite element method is the special circumstance of manifold element method, many achievements are obtained on both theory and application in geotechnical engineering excavation problems (Zhu et al. 2002; He et al. 2002; Xiao 2000).
In finite element method, the excavation effect analysis point to the force between the released excavation proportion and residual system proportion. Based on this theory, many computation methods about excavation with load release were researched and discussed (Wang et al. 1998; Gao et al. 1999; Zhang 1999; Wang et al. 2001; Pan 1995; Britto et al. 1987; Clough et al. 1966; Mana et al. 1981; Shi 1997). But the actualities are that both right and wrong computation methods are used currently.
Manifold method has more merits than finite element method (Shi 1997). These merits also behaved in the excavation modification correspondingly (Zhu et al. 2006). The estimation for the excavation effect to the system is researched and the direct indirect analysis methods of numerical excavation modification are put forward in this paper. The numerical realization measures of two methods are strictly proved in t he system balance numerical forms of manifold element method.
According to the generality of manifold element method, the excavation direct analysis method can be used in the other numerical methods such as finite element method and so forth. This method provides excavation numerical modification with a more direct and concise thought. The complication of release load computation and the corresponding error maybe occurred can be avoided.
Before excavation, analysis system enforced by internal and exterior loads is in balance. Expect for the failure circumstance of system that loses balance, excavation changes the shape of analysis system, the imbalance of internal and exterior loads on residual proportion cause the corresponding deformation and the residual proportion system final form a new balance of all loads.