北京地区砂卵石地层新建地铁隧道小角度下穿施工时既有地铁隧道的变形规律及控制措施

Deformation Law and Control Measures for Existing Metro Tunnel during Newly-built Metro Tunnel Small-angle Under-passing Construction through Sandy Gravel Stratum in Beijing

目的:砂卵石地层中新建隧道对附近既有隧道的变形影响较大。为了控制既有隧道变形,需研究既有隧道的变形规律,并提出有效的控制措施。方法:依托北京地区砂卵石地层中某地铁区间隧道小角度、近距离下穿既有地铁区间隧道项目,采用数值模拟和现场实测相结合的方法,研究了砂卵石地层新建隧道小角度、近距离斜穿既有隧道引起的结构变形规律,验证数值模型的准确性。通过数值模型分析新建隧道与既有隧道的叠交夹角对既有隧道结构沉降的影响。通过数值模型,对深孔注浆、管棚、注浆抬升及水平旋喷桩等变形控制措施的控制效果进行对比。结果及结论:在隧道下穿施工时,隧道下穿施工对正上方既有隧道结构的竖向变形影响较大;距离下穿区越远,结构受影响越小;叠交夹角越小,既有隧道沉降槽底部越宽,竖向位移值也越大;注浆抬升措施的变形控制效果最优,建议类似项目采用注浆抬升措施来加固地层。

Objective:The impact of newly-built tunnel in sandy gravel stratum on adjacent existing tunnel is significant.To control existing tunnel deformation,it is necessary to study the deformation law and propose effective control measures.Method:Based on a metro interval tunnel project under-passing the existing one at small angle and close distance in sandy gravel stratum of Beijing,a combination of numerical simulation and field measurements is used to study the law of structural deformation caused by the above construction.The accuracy of the numerical model is verified.Through numerical models,the influence of the intersection angle between newly-built and existing tunnels on existing tunnel structure settlement is analyzed.The deformation control measures,including deep-hole grouting,pipe shed,grouting uplift,and horizontal jet grouting piles,are compared through the numerical models.Result&Conclusion:During tunnel under-passing construction,the impact of it on the vertical deformation of the existing tunnel structure directly above is significant.The impact decreases with the increasing distance away from the under-passing section.A smaller intersection angle results in wider settlement trough at existing tunnel bottom and larger vertical displacement values.The grouting uplift measure has the best deformation control performance,which is suggested for similar projects in stratum reinforcement.