Numerical Analysis of Dry Excavation Using a Tie Back Wall Under Static and Dynamic Load
Deep excavations are common in urban areas, nearby existing constructions. The support systems have the main function of preserve the stability and control soil displacements close to the excavation. Settlement control of nearby structures is an essential aspect during design and construction. Settlements prediction is usually made by empirical methods and in some cases also by numerical modeling. The paper presents a numerical modeling of a dry excavation by Plaxis program. The program allows the prediction of stress and deformation behavior of different geotechnical constructions using the Finite Element Method. The excavation has been modeled in five stages, in order to reproduce the construction phases. The numerical modeling was capable to reproduce satisfactorily the horizontal profile of the displacements of the diaphragm wall. In relation to settlements, the shape of the settlement profile was quite similar
Construction, Monitoring, and Analysis: Guiyang Metro Line 1, China
: The Huo-Sha Tunnel of Guiyang Metro Line 1 in China, which runs from the Guiyang Railway Station to the Shachong Road Station, passes through the railway station platform closely. The minimum distance between the vault and the pile foundation is only 2.19 m. The geology is complex, and the settlement control requirements for the oblique sections, platforms, station buildings, pile foundations, and existing buildings are remarkably strict. Comprehensive measures of “super pipe shed support, surrounding rock reinforcement, inverted arch grouting, and lining strengthening are strictly adopted” to prevent the influence of construction on the operation of station buildings and in-service railways, high-speed railways, and other buildings. It also analyzes the changing laws of the existing building subsidence, subgrade settlement, station longitudinal displacement variation, and the development trends of lining safety, stability, eccentricity, compression types, and internal force of the lining. The following results are presented. The Huo-Sha Tunnel is gradually excavated. The roadbed settlement of the Guiyang Railway Station platform gradually increases but does not exceed the existing railway deformation control standards for the subsurface excavation section. The longitudinal distribution of the existing railway settlement is approximately a normal curve after the construction of the secondary lining. This result is consistent with the law of the surface settlement trough proposed by Peck, and the range is between −50 m and 50 m. The stress of the lining is mainly concentrated at the arch waist and the vault, the compression types include large and small eccentric, the axial force value gradually increases symmetrically from the vault to the arch footing, the maximum axial force appears at the arch footing, and all control indicators meet the corresponding control standards. The subgrade settlement of the skew section meets the deformation control standards of the existing railway of the subsurface excavation sections after the stabilization of the secondary lining deformation.
Behaviour of a propped embedded retaining wall in stiff clay at Bell Common Tunnel
Extensive instrumentation has been installed at Bell Common Tunnel to monitor the performance of a propped embedded retaining wall and the behaviour of the stiff clay in which it has been constructed. Earth and porewater pressures, ground and wall movements, and roof loading have been monitored during the construction period. The deformations and stresses measured at each stage of construction are presented and the performance of the wall is discussed. Un systeme important d'instrumentations a ete installe au tunnel de Bell Common pour controler le comportement d'un mur de soutenement encastre et celui de l'argile raide dans laquelle il a ete construit. Pendant la periode de construction on a controle les pressions du sol et de l'eau interstitielle, les mouvements du sol et du mur et le chargement du mur. L'article presente les deformations et les contraintes mesurees a chaque etape de la construction et analyse le comportement du mur.