基于SVM的富水岩溶区双线盾构隧道下穿既有线临界安全距离研究

Study on Critical Safety Distance for Double-Line Shield Tunnels Beneath Existing Lines in Water-Rich Karst Area Using SVM

双线盾构隧道在极复杂的岩溶地质中下穿既有线施工时,会对地层造成较大扰动,从而增加既有地表沉降过大或坍塌的风险,严重威胁既有线的运营安全。同时,隧道穿越富水岩溶区域时,需要保持一定距离以避免与溶洞相交,确保双线盾构隧道围岩的稳定性。利用FlAC^(3D)软件建立不同工况组合下双线盾构隧道与左侧溶洞的临界安全距离数值模型,分析不同地下水位对既有线沉降和围岩塑性区范围的影响,并采用正交试验和多元线性回归方法建立双线盾构隧道在不同围岩等级、地下水埋深、开挖隧道埋深和溶洞孔径组合下与溶洞的临界安全距离计算公式。此外,还基于SVM模型对正交试验结果进行机器学习,得到可以预测岩溶地区双线盾构隧道临界安全距离的智能预测系统,实现双线盾构隧道下穿既有线临界安全距离的非线性智能预测。结果表明:当地下水位位于既有线以上时,其水位越高,既有线的沉降量越大、围岩塑性区范围越大,地下水对盾构隧道与溶洞的临界安全距离有很大影响,应用SVM模型和多元线性回归方法确定双线盾构隧道与溶洞之间的临界安全距离是行之有效的。

The construction of double-line shield tunnels beneath existing lines in extremely complex karst geology can cause significant disturbance to the strata,thereby increasing the risk of excessive settlement or collapse of ground surface,which poses a serious threat to the operational safety of existing lines.In addition,when the tunnel passes through water-rich karst areas,a safe distance must be maintained to avoid intersecting with karst caves,ensuring the stability of surrounding rock around the double-line shield tunnels.Using FlAC^(3D) software,the paper established a numerical model of the critical safety distance between double-line shield tunnels and the left-side karst caves under different working conditions,and analyzed the impact of varying groundwater levels on the settlement of existing lines and the extent of plastic zone in the surrounding rock.An orthogonal experiment and multiple linear regression methods were used to establish formulas for the critical safety distance under different combinations of surrounding rock grade,groundwater burial depth,excavated tunnel burial depth,and karst cave diameter.Furthermore,based on the SVM model,machine learning was applied to the results of the orthogonal experiments to develop an intelligent prediction system for the critical safety distance of double-line shield tunnels in karst areas,achieving nonlinear intelligent prediction of the critical safety distance under existing lines.The results showed that when the groundwater level was above the existing lines,higher water levels resulted in greater settlement of the existing lines and a larger plastic zone in the surrounding rock.Groundwater significantly influenced the critical safety distance between shield tunnels and karst caves.The application of the SVM model and multiple linear regression methods to determine the critical safety distance between double-line shield tunnels and karst caves is effective.