Soil consolidation associated with grouting during shield tunnelling in soft clayey ground

The effectiveness of grouting to reduce surface settlements during underground construction in clayey ground was investigated by a field trial and laboratory tests. The field trial was carried out during shield tunnelling work conducted in alluvial clay deposits in Koto-ku, Tokyo. Grout was injected at some distance away from the tunnel, and both surface and subsurface settlements above the tunnel were monitored. Although the initial heave was achieved immediately after the grout injection, the ground continued to settle with time, owing to soil consolidation and grout shrinkage. A laboratory investigation was conducted to investigate the parameters that control the long-term behaviour of grouting in clay. It was found that better long-term grout efficiency can be achieved in overconsolidated clay than in normally consolidated clay, and the efficiency increased with increasing injection volume. Finite element analysis of the laboratory experiments confirmed that the amount and extent of excess pore pressures generated during injection govern the long-term grout efficiency. Finite element analysis of the field trial was also performed to simulate the long-term ground deformation after grout injection.Original Abstract: Nous etudions l'efficacite de la cimentation pour reduire le tassement de surface pendant les constructions souterraines dans des sols argileux au moyen d'essais sur le terrain et d'essais en laboratoire. Les essais sur le terrain ont ete faits pendant des travaux de percage de tunnels protecteurs effectues dans les depots d'argile alluviale de Koto-ku a Tokyo. Le ciment a ete injecte a une certaine distance du tunnel et les tassements de surface et de sous-surface au-dessus du tunnel ont ete observes. Bien que le gonflement initial se soit produit immediatement apres l'injection de ciment, le sol a continue a se tasser peu a peu en raison de sa consolidation et de la contraction du ciment. Une investigation en laboratoire a ete menee pour trouver les parametres qui commandent le comportement a long terme de la cimentation dans l'argile. On a trouve que l'efficacite a long terme du ciment est meilleure dans une argile surconsolidee que dans une argile a consolidation normale et que l'efficacite augmentait en meme temps avec le volume injecte. L'analyse d'elements finis pratiquee sur les essais en laboratoire a confirme que l'importance et l'etendue des pressions interstitielles excessives produites pendant l'injection gouvernent l'efficacite