软土地区盾构施工沉降界限

结合杭州地铁二号线实测沉降,采用“vi速度法”及“拟合直线法”分析不排水瞬时沉降与排水固结沉降的时间界限.分析发现,在地表无隆起的情况下,可以将地表变形分成3个阶段,其中瞬时沉降及固结沉降可以分别拟合为斜率不同的直线,前者斜率大于后者.在盾构脱开管片85～9 d后,地层进入排水固结阶段. 在同步注浆导致地表隆起的情况下,地层受到二次扰动,可以将地表变形分为5个阶段,在盾尾脱开管片105～12 d后,地层进入排水固结阶段．

Settlement boundary induced by shield tunnelling in soft ground

The time boundary between the immediate and consolidation settlements was analyzed by using the “vi settlement-rate method” and “linear-curve fitting method” based on the field-observed ground settlements in construction of the Hangzhou Metro Line-2. Results show that when no ground heave is observed, the ground movements can be classified into three stages, of which the immediate and consolidation settlements can be respectively fitted by lines of different slopes. Slope of the fitting-lines for the immediate settlements is generally stiffer than that for the consolidation settlements. Settlements due to consolidation start to be predominant about 85-9 days after passage of the shield tail. The ground heave is observed and the ground is severely disturbed during the process of heavy pressure backfilling grouting. In this condition, the ground movements can be separated into five stages, and consolidation settlements predominate about 105～12 days after passage of the shield tail．