基于随机森林算法的盾构改良渣土渗透系数预测及工程应用

为解决土压平衡盾构在富水粗粒土地层掘进时，由于盾构渣土渗透性较高而引起螺旋输送机出口处易出现喷涌等风险问题，基于随机森林算法，选取渣土改良参数包括含水率、泡沫注入比、膨润土泥浆注入比以及掘进地层参数土体有效粒径、水力梯度作为模型输入参数，提出一套适用于盾构渣土渗透系数预测的模型。研究结果表明：该模型预测精度较高，渣土渗透系数预测值与实测值均位于同一数量级，且均方误差仅为2.4×10-9 cm/s，拟合决定系数可达0.981 9。依托滇中引水龙泉倒虹吸盾构隧洞工程进行应用，对下穿盘龙江喷涌风险源进行判定，并基于该预测模型给出推荐改良参数。在采用推荐改良参数后，盾构下穿过程中渣土渗透系数满足要求，土舱压力稳定，且对上部桥梁结构影响较小，保障了盾构安全、高效掘进。

Prediction and Engineering Application of PermeabilityCoefficients inImprovedMuck of Shield Based on Random Forest Algorithm

When earthpressure balance shields tunneling in water rich coarse grained grounds, muck spewing often occurs due to the highpermeability of the muck. As a result, a model for predicting the permeabilitycoefficient of shield muck is proposed based on the random forest algorithm.First, conditioning parameters, such as the water content, foam injectionratio, bentonite slurry injection ratio, the effective particle size of soil,and the hydraulic gradient are collected as input paraters of the model. Theresults reveal that while the predicted and the measured values are in the sameorder of magnitude, the root mean square error is 2.4×10-9 cm/s, and the fitting determinationcoefficient reaches 0.981 9, indicating good prediction accuracy of the model.Then, the model was applied to the Longquan shield tunnel project in CentralYunnan, China, to determine the risk of water spewing during the shieldundercrossing the Panlong river. Consequently, recommended conditioningparameters were provided, which accounted for the recorded achievements likethe relatively low permeability coefficient of improvedmuck, stable chamber pressure, small influence on the upper bridge structure,and safe/efficient shield tunneling.