下穿黄河盾构隧道“结构-壁后注浆-土体”结合部渗流研究

Study on Seepage at Junction of Lining Structure-Backfill Grouting-Soil of Shield Tunnel Undercrossing Yellow River

盾构隧道结构与土体间存在"衬砌结构-壁后注浆-土体"结合部,黄河下游"悬河"段河水水位高于两岸地表,修建于"悬河"下的盾构隧道"结构-壁后注浆-土体"结合部是否会形成渗流通道,使黄河水体涌入两岸从而影响两岸安全,是穿黄盾构隧道工程与其他穿越江河盾构隧道工程的最大不同之处,也是关系到工程建设是否可行的关键问题。对盾构隧道结构-壁后注浆-土体结合部进行理论简化和数值计算,并模拟了不同工况条件下沿结合部渗入两端的的渗流量,结果表明:壁后注浆对于减小结合部渗流具有重要作用,盾尾间隙厚度对渗流安全影响较小;随着壁后注浆体渗透系数减小,两端涌水量显著减少;盾尾间隙的减小对于降低两端渗流量作用不大。据此提出相应的工程建议:为防止"衬砌结构-壁后注浆-土体"结合部渗流通道形成,衬砌设计中增设注浆孔,施工时适当增大注浆量及注浆压力,防止无注浆空隙的产生,降低壁后注浆体渗透系数是首选措施;通过控制盾构掘进姿态、减少超挖,从而减小盾尾间隙厚度可作为辅助施工措施;施工过程中在隧道内进行壁后注浆开孔检漏试验并根据试验结果进行补充注浆可作为结合部渗流安全的检验、补充措施。

The junction of lining structure-backfill grouting-soil exists between the shield tunnel structure and strata.The water level at the perched river section in the lower reaches of the Yellow River is higher than the ground surfaces at both sides of river.The lining structure-backfill grouting-soil junction of shield tunnel constructed under the perched river whether or not to form the seepage channel to make the water of Yellow River gushing to the both sides and thus to influence the safety of the both sides is the greatest difference of the shield tunnel project crossing the Yellow River from the other shield tunnel projects crossing the rivers,and is also the key to the feasibility of engineering construction.The lining structure-backfill grouting-soil junction of shield tunnel is theoretically simplified and numerically calculated.The seepage flows into two ends along the junction are simulated under the different working conditions.The result shows that the backfill grouting has an important action to decrease the seepage of junction.The gap thickness at the tail of shield has a little influence on the seepage safety.With the decrement of backfill grouting seepage coefficient,the water inflow at two ends is obviously decreased.The decrement of gap at the tail of shield is hardly to reduce the seepage flow at two ends.Accordingly,the relevant engineering proposal is put forward.The grouting hole is added in the lining design in order to prevent the formation of seepage channel of the lining structure-backfill grouting-soil junction.The grouting amount and grouting pressure are properly increased during construction in order to prevent the cause of no-grouting space.The reduction of seepage coefficient of backfill grouting is the first measures.The control of shield tunneling posture and the decrement of over-excavation so as to decrease the gap thickness of shield tail can be taken as the auxiliary construction measures.The implementation of backfill grouting holing leakage test within the tunnel during construction and the additional grouting according to the test result can be taken as the inspection and additional measures for the seepage safety of the junction.