上软下硬地层大直径土压平衡盾构下穿民房建筑群沉降控制

On Settlement Control in Large-diameter EPB Shield Tunnelling under CivilHousing Complex in Upper-soft and Lower-hard Strata

依托广州地铁18号线盾构施工,针对其地层分布复杂、软硬差异大及穿越密集民房建筑群等特点,通过注浆加固、现场动态监测、优化掘进参数等一系列主动措施,解决实际工程中掘进参数合理取值与地表建筑沉降变形控制两大难题。研究结果表明:(1)在该类软硬地层中掘进时,刀盘在通过不同岩层断面分界线时扭矩、推力等参数波动较大,总推力与扭矩有良好的相关性,各掘进参数宜控制为:推力30000~35000 kN、扭矩4500~6000 kN·m、推进速度35~45 mm/min;(2)提出的多段式封孔洞内超前注浆工艺可使刀盘前18 m范围内的地表上抬3~5 mm,最大上抬值能达9.02 mm,同时能缓解土体在盾构下穿时及后续固结稳定的沉降趋势;(3)因刀具磨损、掘进参数波动大、螺旋机卡死等引起的临时停机会造成地表建筑日沉降速率超过3 mm/d,在预设停机点位置前采取洞内超前注浆和克泥效工法能有效缓解沉降趋势,在带压开舱期间日沉降速率控制在2 mm/d以下;(4)左右隧道轴线附近的地表建筑沉降基本可分为“微小隆起—沉降较大—逐渐稳定”三个阶段,测点最大沉降值最终稳定在-21.38 mm、-22.49 mm,均小于控制值。

The shield tunnelling of Guangzhou Metro Line 18 is faced to such characteristics as complex ground dis⁃tribution,large strength differences between soft and hard rocks,and dense residential building complex located above the tunnel.In view of this,it is intended to address two major problems in actual construction,i.e.settling the reasonable tunnelling parameters and controlling the settlement deformation of buildings on the ground surface through a series of active measures,such as grouting reinforcement,on-site dynamic monitoring,and optimization of tunnelling parameters.The results show that:(1)in this type of soft and hard rock interbedded strata,tunnelling pa⁃rameters(such as torque and thrust)would fluctuate greatly when the cutterhead passes through the geological boundary of different strata,and the total thrust would be in a fine correlation with the torque,where it is appropriate to control the tunnelling parameters at certain values,i.e.the thrust at 30000~35000 kN,the torque at 4500~6000 kN·m,and the advancing speed at 35~45 mm/min;(2)the proposed technological process of multi-section sealing and advanced grouting in the tunnel can lift the ground surface by 3~5 mm within the scope of 18 m in front of the cutterhead,with maximum lifting value of 9.02 mm,while it can also mitigate the settlement tendency of the soil mass induced by shield driving and subsequent consolidation and stabilization;(3)temporary shield stoppage caused by tool wear,large fluctuation in tunnelling parameters,and the jamming of the screw conveyor can cause the daily settlement rate of the buildings on the surface to exceed 3 mm/d.The adoption of advanced grouting in tunnel and the clay shock method ahead of the preset machine stop point can effectively alleviate the settlement tendency and control the daily settlement rate below 2 mm/d during the hyperbaric intervention of the earth chamber;(4)the settlement of the surface buildings near the left and right tunnel axes can be basically divided into three phases of slight heave—large settlement—gradual stabilization,with maximum settlement of-21.38 mm and-22.49 mm re⁃spectivly,being less than the control values.