Experimental Investigation on Flexural Behaviors in Framed Structure of PST Method
Existing underground pipe jacking methods use a reinforcing rod in a steel tube to obtain structural stiffness. However, some problems such as inconvenience of works and expensive materials resulted from limited working space and reinforcing works are existed. To resolve these problems, a new pipe jacking method, namely PST (Prestressed Segment Tunnel) method, was developed which used joint to connect the steel segment and form erection structure. For evaluating the flexural capacity of the PST method structure, a experimental test was conducted. The parameters considered in the test were span-to-depth ratio of segment, diameter of steel tube at the corner, prestressing force, and welding of joint. The flexural behaviours with the effect of load capacity in serviceability state according to different parameters were examined.. The frame with long segments could increase flexural stiffness and the specimen with large diameter of concave corner showed excellent resistance ability to the negative moment. In addition, welding of joints increased the flexural capacity. Keywords—PST method, Pipe jacking method, Flexural behavior, Prestressed concrete.
Analysis of Ultimate Bearing Capacity and Parameters of Steel Support Cutting Pipe Roofing Structure
A new pipe-roof construction method, the steel support cutting pipe method (SSCP), was proposed to improve the construction security and accuracy of pipe jacking as well as underground space usage. The pipe-roof method is one of the underground excavation methods which push multiple steel pipes into the soil, then connect the steel pipes horizontally to form a whole. The proposed structure’s failure mode and force characteristics were determined through theoretical analysis, and then its ultimate bearing capacity and influencing parameters were analyzed through laboratory experiments and numerical simulation. The research results show that the structure’s bearing capacity depends on the steel pipe’s buckling load; the structure’s failure mode is a result of the steel pipe’s buckling. The ultimate bearing capacity of the pipe-roof structure first increases and then decreases with the increase of the steel pipe chord height ratio. The ultimate bearing capacity reaches the maximum when the ratio is 0.33. In addition, the structure’s ultimate bearing capacity is positively related to the steel pipe wall thickness and the pipe section’s length. This can be obtained from the relationship curve showing that the steel pipe wall thickness should be selected according to the engineering requirements and that the pipe section’s length is preferably 2.3 times the diameter of the steel pipe in the construction design.
Contrôle de la déformation du massif renforce par boulonnage au front de taille d'un tunnel : étude d'un cas réel en site urbain : exploitation des mesures et modélisation par une méthode d'homogénéisation
Dans le cadre de l'etude d'un ouvrage reel, le memoire aborde la problematique des travaux souterrains en milieu urbain sous deux points de vue complementaires, celui des mouvements de terrain induits par le creusement et celui des dispositions constructives pour la phase de creusement-soutenement en terrain difficile. En 1ere partie, l'aspect phenomenologique des deplacements induits fait l'objet d'un inventaire critique des methodes de mesures existantes. Les etapes du developpement d'un systeme adapte a la mesure de la deformation du massif a l’avant du front de taille sont alors presentees. On etablit ensuite les principes de 1' analyse « stationnaire » des deplacements autour du front de taille a partir des mesures realisees aux frontieres du massif, a savoir la surface sus-jacente et les parois du tunnel. L'application de ces principes a un volume important de donnees conduit a un bilan quantitatif des facteurs a l'origine des mouvements de terrains. En 2eme partie, la disposition constructive etudiee est la technique de boulonnage au front de taille. Cette technique est replacee dans le cadre plus general des methodes de preconfinement en tunnel et de renforcement des terrains en place. La modelisation mecanique du massif renforce est abordee par une methode d'homogeneisation dont on rappelle les principes, les acquis recents et les imperfections. On montre alors qu'une description simple des interactions entre le terrain et le renforcement par le «transfert de charge limite » conduit a une correction realiste du modele. Le modele est ensuite applique au massif renforce par boulonnage au front de taille, par le biais d'un probleme equivalent, geometriquement tres simplifie. Une etude parametrique sommaire met en lumiere certains aspects du fonctionnement du renforcement et ses limites pratiques.