嵌岩隔离桩对基坑邻近隧道的保护效果分析

Shielding Effect of Rock Socketed Isolation Piles on A Tunnel Adjacent to the Pit

采用嵌入中风化砂岩的隔离桩对邻近地铁隧道进行保护时,桩底被强度较高的中风化砂岩固定与约束其保护效果较好,但在设计与有限元分析中若等效计算模型不合理,会计算得到隔离桩效果较差的结论。基于有限元方法,探讨了数值计算中嵌入中风化砂岩隔离桩的合理等效方法。对比计算表明,数值计算中不对嵌岩段进行位移固定,得到的计算结果与实际不符,低估了隔离桩的作用,建议对进入中风化岩石的桩端位移设定为固定边界条件。隔离桩距隧道的水平净距不小于3.0m,桩顶不高于隧道拱顶位置线标高、不低于隧道中心位置线标高,嵌岩段不小于4.0m,其隔离效果好、性价比高。

When using isolation piles embedded in moderately weathered sandstone to shield adjacent subway tun-nels,the pile bottom is fixed and constrained by high-strength moderately weathered sandstone,which has a good shield effect.However,if the equivalent calculation model is not reasonable in design and finite ele-ment analysis,it can be concluded that the isolation pile effect is poor.Based on the finite element meth-od,a reasonable equivalent method for embedding moderately weathered sandstone isolation piles in nu-merical calculations was explored.Comparative calculations show that the displacement of the embedded rock segment is not fixed in numerical calculations,resulting in calculation results that are inconsistent with reality and underestimating the role of isolation piles.It is recommended to set the displacement of the pile end entering moderately weathered rock as a fixed boundary condition.The horizontal net distance between the isolation pile and the tunnel shall not be less than 3.0m,and the pile top shall not be higher than the elevation of the tunnel arch position line or lower than the elevation of the tunnel center position line.The embedded rock section shall not be less than 4.0m,and its isolation effect is good and cost-effec-tive.