A sink hole and caves caused by earth balance shield and digital twin observational method to control face stability

Abstract

A sink hole was found at ground surface in a residential area in Tokyo in October 2020. The site was above a construction line of earth pressure balance shield tunnel with16.1 m in diameter and the crown at the depth of GL-47m. Further study revealed the dense sand layer above the tunnel has been loosened along the tunnel for about 200m length from the tunnel face. 3DFEM simulation based upon the site conditions showed a possibility of the loosing stability of the face when the ground is dense sand with little fine component. A digital twin observational method is proposed to discuss the face stability and to keep digging safe.