大直径盾构浅覆土下穿铁路桥涵的影响分析及施工控制

The Effect and Construction Control of Large Diameter Shield Tunneling Under Railway Culvert

为揭示大直径盾构浅覆土下穿施工对铁路桥涵的影响,结合杭州环北地下快速路大直径泥水平衡盾构隧道工程实践,采用数值分析的方法对盾构穿越引起的运营铁路桥涵力学行为进行预测,并结合工程实测分析了盾构施工参数的变化规律、控制方法和桥涵变形的实施效果.数值分析结果表明:未进行桥涵区域的土体加固时,若直接穿越铁路桥涵施工,桥涵的最大沉降可以达到21.6 mm,且在桥涵中隔墙的顶部和底部出现应力集中,最大拉应力可达1.60 MPa;进行土体加固后,穿越铁路桥涵施工时桥涵的最大沉降为9.3 mm,部分区域的最大拉应力为1.46 MPa.工程实践中,常规情况下切口压力较静止土压力大15 kPa,为确保盾构穿越铁路桥涵结构的安全,切口压力调大至25 kPa.考虑上覆水土荷载降低约13%,盾构总推力降低约10%,转矩降低约10%,盾尾注浆量处于150%～200%之间可确保穿越铁路桥涵盾构施工安全.现场实测表明:当盾构机将要穿越桥涵时,桥涵结构产生3～4 mm的预隆起;待盾构穿越后,又产生约4 mm的沉降;盾构机通过3 d后,差异沉降降低并较快趋于稳定,最终稳定在0.01%左右.

In order to reveal the effect of large diameter shield tunneling under railway culvert,the mechanical behavior of the operating railway bridge and culvert caused by shield crossing were predicted by numerical method,based on the practice of large diameter slurry balance shield for boring North Huancheng Road underground expressway tunnel in Hangzhou.Then the implementation effects such as shield construction parameters,controlling technology and bridge deformation were verified by field testing.The numerical analysis shows that the maximum settlement will reach 21.6mm at the bottom of the bridge and culvert,while the maximum tensile stress will reach 1.60MPa at the top and bottom of the middle wall of the bridge during the shield tunneling machine passing without the underneath soil strengthened.On the contrary,the maximum settlement and tensile stress will reduce to 9.3mm and 1.46MPa respectively when the underneath soil is reinforced.In the actual practice,the pressure at the cutting face is 15kPa larger than the static earth pressure.However,to ensure the operating bridge and culvert structure in the state of security during shield machine passing,the cutting face pressure increases to 25kPa larger than the static earth pressure,the total thrust and torque reduces by 10%approximately respectively considering the upper load decrease 13%.Furthermore,the tail grouting volume is parameterized between 150%and 200%.The field testing shows that the deformation of bridge and culvert will upheaval 3-4mm before the shield crossing,then translate into settlement about 4mm after the shield crossing.After 3 days since crossing completed,the differential settlement will decrease and tend to be stable gradually,and the final stability value is about 0.01%.