Design control and monitoring of a jet grouted excavation bottom plug

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Design control and monitoring of a jet grouted excavation bottom plug

 طراحی و کنترل های عملیات جت گروتینگ در ایستگاه های زیرزمینی
N. Eramo & G. Modoni
University of Cassino, Cassino, Italy
M. Arroyo Alvarez de Toledo
Universidad Politécnica de Catalunya, Barcelona, Spain
ABSTRACT: Jet grouting is adopted in different geotechnical conditions to ensure provisional earth
retaining and waterproofing functions in excavations. Despite careful theoretical models available to
predict the mechanical response of these structures, design is often carried out without adequate control,
i.e. by assuming ideal effectiveness of ground improvement. On the contrary, adverse effects have been
documented by past experiences which can be traced back to erroneous prediction of treatments effects,
inaccurate control of the execution or to unexpected responses of the surrounding environment. All these
uncertainties, which are critical when working in urban areas, can be minimized by detailed preliminary
field trials, accurate treatment execution control and a prompt monitoring of the surrounding area. The
present paper illustrates these issues with a description of the design and execution of a massive jet grouting
bottom plug forming the base of a large excavation for a tube station. The results of preliminary field
trials are summarized to directly compare the effectiveness of different injection systems and introduced
in statistical design analyses of the jet grouted structure. A detailed investigation of the surface movements
induced by injections is also reported. To this aim, the evolution of displacements recorded around
trial columns and on the area surrounding the excavation is mapped to evaluate the effects of the different
adopted injection techniques.

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