CASE STUDY OF SETTLEMENT DURING DOUBLE-O-TUBE TUNNELING IN SENSITIVE SOFT GROUND

摘要

DOT (Double-O-tube) tunneling method has been adopted in constructing various tunnels in soft ground both in Japan and China.Early practice of such method in China has been reported in Shanghai metro network construction during Line 8 and 6,in which the ground surface settlements were controlled within several cm.However,in a recent line construction,the practice of DOT tunneling was not so satisfying.The ground is sensitive alluvial clays of 20 ～ 30m thick,which is not competent for shield tunneling.Among three tunnels which were conducted by DOT shield machine,settlement of the ground surface has gone beyond allowable level,and even 80 cm of settlement were measured in the worst case.In this paper,the ground conditions and the construction process are checked carefully first.Special attentions are paid to earth pressure at the cutter face and the injecting parameters of backfill grouting.An in-situ monitoring,including the surface settlement and subsurface settlement was conducted to obtain the change of ground deformation during shield driving.Based on the monitoring and corresponding field investigation,the masons related to the unexpected large settlements are discussed.From this case study,it is found out that the backfill grouting during the construction play a very important role in controlling the ground surface,and unsuitable grouting is accounted for the large surface settlement.