The effectiveness of grouting to reduce surface settlements during undergro
und construction in clayey ground was investigated by a field trial and lab
oratory tests. The field trial was carried out during shield tunnelling wor
k conducted in alluvial clay deposits in Koto-ku, Tokyo. Grout was injected
at some distance away from the tunnel, and both surface and subsurface set
tlements above the tunnel were monitored. Although the initial heave was ac
hieved immediately after the grout injection, the ground continued to settl
e 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 tha
t the amount and extent of excess pore pressures generated during injection
govern the longterm grout efficiency. Finite element analysis of the field
trial was also performed to simulate the long-term ground deformation afte
r grout injection.