ABSTRACT:

Compensation grouting is an effective way to reduce surface settlement induced by construction activities in urban areas. However, the long-term behaviour of the compensated area is still not known very well. Grout injection in clayey soils was performed in the laboratory to measure both short and long-term deformation of the clay around the grout and to investigate the fundamental behaviour of the compensation grouting process, which includes hydraulic fracture and cavity expansion mechanisms. The experimental results indicate the growth of a fracture plane in soil in a very fast manner both in normally and overconsolidated clays. Finite element analyses of compensation grouting have been performed to assess its ability to model the complex behaviour of compensation grouting observed in the laboratory. The finite element analyses clearly show that the long-term behaviour of compensation grouting is greatly dependent on the overconsolidation ratio of the clay. The finite element analysis agreed reasonably well with the long-term behaviour of the grouted clay in the experiments

INTRODUCTION

In recent years, compensation grouting has been applied successfully in many major tunneling projects to limit ground settlement (e.g. Mair, 1994). For example, during tunnel construction projects in Lisbon and for the underground construction of the Jubilee Line Extension Project in London, extensive compensation grouting systems were applied to protect the surface structure around the area influenced by tunneling construction activities (Harris et al, 1996; Schweiger and Falk, 1998). Compensation grouting can involve two different modes;

  • compaction grouting and

  • fracture grouting.

The possible factors that affect the occurrence of different modes of behavious are: type of grout, soil type, stress history of the soil, stress state, boundary conditions and rate of injection. Because of the complex behaviour of grouting in soils, a conceptual modelling of compensation grouting in clayey soils is necessary.

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