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 this 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.
Design control and monitoring of a jet grouted excavation bottom plug
MODONI, Giuseppe;
2012-01-01
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 this 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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
