MJS工法在砂卵石地层盾构近距离下穿运营地铁隧道的应用

依托在建长沙轨道交通4号线盾构区间，对砂卵石复杂地层下穿既有2号线运营区间预加固保护措施进行研究，并对多种预加固方案综合比选，最终采用MJS(全方位高压旋喷加固)工法对既有2号线进行预加固保护。工程实践表明，MJS工法水平加固过程中，既有2号线变形可控，最大变形约7 mm，加固体强度可达5～8 MPa，确保了4号线盾构穿越过程中既有区间的运营安全。这是国内首次在该类地层采用MJS工法对小净距既有运营线路进行水平预加固，可为今后类似工程提供参考和借鉴。

The Application of MJS Method in Under-Traversing the Operating Metro Line Nearly at Sand Gravel Layer

For urban rail traffic, under-traversing the operating metro line always poses a serious risk, and is also an important research direction. In this article, a study and comparison of multiple reinforcement schemes for the shield tunnel of metro line 4 under-traversing the tunnel of operating metro line 2 in ChangSha city at the sand gravel layer is presented. The metro jet system or MJS method was adapted for the pre-reinforcement of the existing line 2. Practical application shows that the largest deformation of existing tunnel reached approximately 7 mm and the strength of the reinforced ground reached approximately 5~8 MPa, which controlled the deformation within the construction allowance and ensured the operational safety of the existing tunnel during the construction process. The MJS method is the first used for the pre-reinforcement of the operating metro line with a small clear spacing tunnel at this suite in China. This article will provide some experience in the field and ideas for similar projects.