采用泡沫轻质土对高填明洞二次回填的结构受力特性研究

Study on Structural Mechanical Behavior of Secondary Backfill of High Filled Open Cut Tunnel with Foamed Lightweight Soil

以西部某地区铁路高填明洞二次回填实际工程为依托,采用泡沫轻质土作为回填材料,按等质量置换原则进行二次回填,通过数值模拟确定合理泡沫土回填范围和开挖置换深度,结果表明:利用轻质泡沫土对既有高填明洞顶部按照等质量置换原则在一定范围和开挖置换深度下进行二次回填,其结构位移、应力、安全系数均能满足要求。开挖回填轻质泡沫土范围越大,下挖置换深度越小,竖向位移值越小。泡沫土回填范围角度0°、30°且下挖置换深度较大时,拱顶和墙脚位移超过允许值,此时会影响隧道结构的安全性。各种情况组合计算下,泡沫土回填范围角度45°,下挖置换深度4 m时,衬砌仰拱拉应力达到最小值,墙脚和仰拱安全系数达到最大值。综合考虑结构受力安全性、合理性及工程经济性,确定泡沫土合理回填范围角度为45°,合理下挖置换深度为4 m,现场实际以此进行开挖回填,实测拱顶沉降、结构上浮、水平位移均未超过容许位移值,且由于土拱效应小于计算值。

In the case of the secondary backfilling project of a railway high-filled open-cut tunnel in western China,using foamedlightweight soil as backfill material,thesecondary backfilling wascarried outaccording to the principle of equal mass replacement.The numerical simulationwasconducted to determine the reasonable backfill rangeof foamedsoiland excavation replacement depth.The results show that,usingfoamed lightweight soil to refill the high-filledopen-cut tunnel according to the principle of equal mass replacement within a certain range and excavation replacement depth,the structural displacement,stress and safety coefficient can allmeet the requirements.The larger the range of backfilled foamedlightweight soil,the smaller the replacement depth of excavation and the smaller the vertical displacement value.When the angleof the backfill range of foam soil is 0°and 30°and the replacement depth of excavation is large,the displacement of arch roof and wall foot will exceed the allowable value,which will affect the safety of tunnel structure.Under the combined calculation of various conditions,the tensile stress of the lining invert reaches the minimum value and the safety coefficient of the wall and the invert reaches the maximum value at 45°angle ofthe backfill range of the foam soil and 4 m replacement depth of the excavation.Considering the safetyand rationality ofthe structural stressand engineering economy,the angle of the reasonable backfill range of the foam soil is determined to be 45°and the reasonable replacement depth of excavation to be 4 m.Based on this,actual excavation backfill was carried out.The measured settlement of arch roof,structure buoyancy and horizontal displacement have not exceeded the allowable displacement value.Because of soil arching effect,the measured value is less than the calculated value.