针对砂卵石地层盾构下穿铁路路基工程，通过FLAC 3D数值模拟，结合现场监测数据分析，对路基的变形规律进行研究，基于钢花管地层注浆实践，证明地层注浆加固对控制路基沉降的有效性。主要结论如下： 1）列车运行速度越大、盾构埋深越小，路基沉降越大，但列车速度对路基沉降的影响远小于埋深。2）成都砂卵石地层地铁双线盾构常规净距（约7 m）下穿铁路路基时，路基沉降与埋深、列车速度的近似关系为S=－26.54+0.85z－0.01v；
由于盾构先后2次施工扰动，路基出现2次位移突降，位移沉降曲线呈台阶状，且二次扰动的地层反应灵敏度快于首次,施工过程应警惕二次扰动造成的位移超标。3）钢花管地层注浆作为一种可操作性强的地层加固方式，在成都砂卵石地区具有良好的加固效果，工程采用“跳孔、分段、多次、中低压”的钢花管注浆方式，路基沉降由11 mm以上降低到7 mm，保障了施工的顺利进行。
A case study is conducted on a doubletrack
metro shield tunnel crossing underneath railway subgrade in sandypebble strata. The deformation law of the subgrade is studied using
FLAC 3D numerical simulation based on field monitoring data analysis. The
applicable results of ground grouting by steeltube
prove the effectiveness of grouting reinforcement in controlling the subgrade
settlement. The main conclusions are drawn as follows: (1) The greater the
train speed and the smaller the shield burial depth, the greater the subgrade
settlement, whereas the influence of train speed on subgrade settlement is far
less than that of burial depth. (2) The approximate relationship among the
subgrade settlement, the burial depth, and the train speed is S=-26.54+0.85z-0.01v when the doubletrack metro shield undrcrosses the railway subgrade in sandypebble strata in Chengdu with a conventional clear distance of
approximately 7 m. Due to the twice disturbance of the shield tunneling, the
subgrade has experienced twice sudden drops in displacement, the displacement
and settlement curve shows a step shape, and the sensitivity of strata response
caused by the second disturbance is faster than that of the first one, as a
result, attention should be paid to the displacement caused by the second
disturbance. (3) The steel tubegrouting, as a highly
operable method for ground reinforcement, has a good reinforcement effect in
sandycobble strata in Chengdu. The settlement of
subgrade after grouting reinforcement is reduced from over 11 mm to 7 mm, which
ensures the smooth and successful shield tunneling.
