Response of the ground and adjacent buildings due to tunnelling in completely weathered granitic soil

• Field monitoring of tunnelling in weathered granitic residual soil is presented.
• Groundwater control is the prerequisite for controlling large ground movements.
• Being piled and reinforced reduce differential settlements and retard cracking.
• Rigid RC buildings tend to tilt and embed into the soil.
• Flexible masonry structures deform according to Greenfield and distort to crack.

The excavation induced ground movements and their impact on adjacent buildings is one of the major concerns for tunnelling in urban areas. This paper presents a case study on the response of the ground and a group of buildings to the construction of a sprayed concrete lining (SCL) subway twin tunnel through completely weathered granitic residual soil in Shenzhen, China. Ground and nearby structures displacements were monitored through extensive field instrumentation. The observed maximum surface settlements exceeded 400 mm, which caused considerable damage to certain buildings. Potential risks of large ground deformation for tunnelling in similar ground condition, with structures nearby, are highlighted. Encouraging effectiveness of the permeable grouting on this ground condition was demonstrated by the distinct Greenfield behaviour at the two monitoring sections. Different responses between Greenfield ground and adjacent structures show an evident soil structure interaction. Piled reinforced concrete frame buildings were found to behave rigidly in response to the tunnelling induced ground movement and to be without visible crack in contrast to masonry wall structures.