南京地铁软流塑地层盾构下穿既有隧道处理加固技术

Treatment and Reinforcement Technology of Shielding under Soft Flow Plastic Stratum through Existing Tunnel

新建地铁极近距离下穿既有运行地铁的设计和施工是其重点和难点,土质条件和地下水赋存等条件是其控制性因素。以南京地铁5号线三山街站-朝天宫站盾构区间隧道出三山街站下穿既有地铁1号线为研究背景,研究软流塑地层新建地铁下穿既有运行地铁的设计和施工要点。分别选取3种地层加固方案确保盾构机顺利穿越隧道:方案1(管棚+水泥土搅拌桩+袖阀管注浆联合加固)、方案2(微扰动注浆加固)、方案3[水平旋喷桩全方位高压喷射(metro jet system,MJS)加固],通过对方案加固效果进行对比分析,最终选定方案1。随后在选定方案的基础上研究了土舱压力和注浆压力对既有隧道位移的影响。结果表明:土舱压力在0.19 MPa以内变动时对隧道控制效果最显著,在实际施工过程中,注浆压力不宜过大,以防水泥浆液劈裂土体造成土体破坏,应实时进行监测。

The design and construction of a new subway underneath an in-operation subway at a very close distance are the key and difficult points,and the soil conditions and the occurrence of groundwater are the controlling factors.Nanjing Metro Line 5 Sanshanjie Station-Chaotiangong Station shield-bored tunnel exiting Sanshanjie Station under the existing Metro Line 1 was taken as the case,the design and construction key points of the new asthenoplastic stratum subway are studied.Three stratum reinforcement schemes were selected to ensure that the shield machine could pass through the tunnel smoothly:scheme 1(pipe shed+cement soil mixing pile+sleeve valve tube grouting joint reinforcement),scheme 2(perturbation grouting reinforcement),and scheme 3(horizontal rotation spray pile metro jet system reinforcement).Through the comparative analysis of the reinforcement effect of the schemes,scheme 1 was finally selected,to which the influence of soil tank pressure and grouting pressure on the displacement of the existing tunnel was studied.The results show that the tunnel control effect is the most significant when the soil tank pressure changes within 0.19 MPa.In the actual construction process,the grouting pressure should not be too high in order to prevent the soil from being damaged by cement grout splitting the soil.It should be monitored in real time.