The Deformation Characteristics And Numerical Simulation Of Compound Soil Nailed Structure Of Deep Excavations In Soft Clay

Composite soil nailed structure is of wide-spread application in soft soil in recent years. However, the research on the behavior and the stabilizing mechanism of the structure lags behind application in the engineering practice. In this paper, based on a case study on the typical composite soil nailing project in Hangzhou soft clay, finite element numerical analysis was carried out to study the deformation characteristics of composite soil nailed wall. The main research contents were as following:(1) Undisturbed soil specimens were tested in lab with triaxial apparatus in order to see soft clay's mechanical properties. Moreover, parameters for different constitutive models were presented, such as Mohr-Coulomb model, Duncan-Chang model and modified Cam-clay model, which can offer reference to the finite element numerical analysis.(2) Case study of a typical composite soil nailed wall in Hangzhou soft clay was carried out. The horizontal displacement and surface settlement were analyzed based on the observation and measurement. (3) By using finite element numerical simulation to analyze the deformation behavior of deep foundation of composite soil nailed wall, the adaptability of different constitutive models were clarified.The main conclusions of research were as follows:(1) From case study it could be seen that the excavation sequence, retaining forms and surroundings are all have effects on ground deformation.(2) Compared with two other constitutive models, the modified Cam-clay model was much better in reflecting the soft clay behaviour in soil nailed excavation.(3) By finite element analysis, it was shown that the soil nail's length, the excavation depth, extra excavation are all affect the deformation development. For the sake of horizontal displacement control, it is more effective to lengthen the upper layer soil nailing than to lengthen the lower layer ones. If excavation was near to the surrounding buildings, it's better to widen the vertical retaining components. With composite vertical components, soil nailed wall has a better flexibility to extra excavation.