岩脉对隧道围岩稳定性影响分析

岩脉是一类特殊的工程岩体,旧堡隧道施工中遇到了辉绿岩和花岗伟晶岩两类岩脉。其中辉绿岩脉在400m埋深处发生了热液蚀变,试验测得其膨胀力为25kPa,自由膨胀率为0.75%,软化系数小于0.12,遇水软化是蚀变带围岩发生大变形的重要原因;花岗伟晶岩脉与围岩呈破碎接触,破碎带岩体呈碎裂结构,属Ⅳ-Ⅴ类围岩,塌方时有发生。通过施工工程地质勘察,查明岩脉工程地质条件是解决相关问题的前提之一,提出以超前地质预报和施工监测作为施工工程地质勘察的两大技术手段。针对辉绿岩脉蚀变带大变形问题,采用了注浆堵水的措施防止围岩大面积淋水软化变形,效果良好。

Analysis on stability of tunnel surrounding rock affected by rock dikes

Rock dike is a special encountered in the construction of occurred hydrothermal alteration engineering rock mass, dikes of diabase and granitic pegmatite were Jiubu tunnel. The diabase dike, with an overburden of 400m, had Laboratory tests showed that its expanding force is 25kPa, the free expansion rate is 0. 75% , and the softening coefficient is less than 0. 12. Softening is the major reason causing large deformation at alteration zone. The rock mass at contact zone between granite pegmatite dike and its surrounding rock takes on cataclastic texture, belongs to IV-V surrounding rock, and cave-in frequently occurs. Ascertaining the engineering geological conditions of rock dikes during tunnel construction is the premise for solving relevant problems. Advance geological forecasting and monitoring are main tasks of engineering geological investigation in tunneling. At alteration zones of diabase dike, the large deformation could be controlled efficiently by grouting, to prevent large-scale water spray to soften rock mass.