Study On 3-D Analysis Theory Of Excavation Considering Unloading Impacts

Excavation is actually an unloading process to inner soils of pits. Conventional analysis of retaining structures can not reflect the spatial effects of excavation on account of neglecting unloading impacts. A number of projects implicate the fact that the measured deformation of retaining walls is usually larger than theoretical one, which relates to ignoring the unloading deformation as this paper figured. In addition, almost all of current analysis methods for retaining structures have used "m" method to determine the coefficient of lateral subgrade reaction, during where needs much experience for users. This paper takes a study on 3-D analysis of excavation considering unloading impacts, which will be presented as followed.1. The calculated expressions of unloading stress and unloading deformation are educed with the application of minus superimposed stress to simulate excavation unloading, and the distribution of stress, deformation and modulus of deformation are discussed. It shows that rectangle pits can be substituted by strip pits by meeting some condition, and the lateral deformation of inner soils are commonly contractive. The deformation modulus is larger than compression modulus and will increase as the depth of subgrade adding. The secant modulus of soil is smaller than axial modulus for strip pits.2. The coefficient of lateral subgrade reaction considering unloading impacts is got on the basis of former research results. Thus, the coefficient can be attained from the experiment data rather than the experience of users.3. The deformation of retaining structures can be divided into two stages: one is unloading effecting stage; another is lateral earth and water pressure effecting stage. A 3-D analysis program considering unloading stress path and lateral unloading deformation has been designed finally.4. Three representative examples are computed respectively using the program and conventional methods. The unloading impacts to retaining structures are discussed. The regard of excavation unloading causes the deformation increasing for 15% upward and a small effect on the internal force of retaining structures. It shows that the larger pits have larger deformation of retaining walls and larger impacts to environment around.