砂-粘-粉互层地层明挖隧道沉降特征分析及预测

Analysis and Prediction of Open-Cut Tunnel Settlement in Sand,Clay and Silt Interbedded Stratum

为研究华北冲积平原边缘处砂-粘-粉互层地层中明挖暗埋隧道工后沉降特点及地下水位对隧道沉降影响,依据京雄铁路机场2号隧道施工期及运营期18个月的沉降监测数据,结合地质条件和地下水位资料,对该隧道沉降特征及差异性原因进行综合分析,并利用Asaoka、双曲线和三点法对最终沉降量进行预测。结果表明,地下水位较高的砂-粉-粘互层地层沉降曲线可以分为类双曲线型、U型和振荡型三类。隧道沉降量及沉降特征与主要压缩层中粘性土含量呈正相关,主要压缩层中粘性土含量超过64%时,沉降曲线表现为类双曲线型。地下水位高度与回填深度是影响隧道沉降的重要因素,地下水浮力是隧道抬升的主动力。数据累计时间越长,曲线拟合法预测精度越高,恒载后数据积累9个月时Asaoka法和三点法预测最终沉降量误差均小于10%。

In order to study the post-construction subsidence characteristics of open-cut and buried tunnels in the sand-stick-powder interbedded strata at the edge of the North China alluvial plain and the influence of the groundwater level on the tunnel subsidence,according to the 18 months settlement monitoring data during the construction and operation of the Jingxiong Railway Airport Tunnel 2,by combining with the geological conditions and groundwater level data,the subsidence characteristics and differences of the tunnel were comprehensively analyzed and the Asaoka,hyperbolic and three-point methods were used to predict the final settlement values.The results show that the settlement curves of sand-silt-clay interbedded strata with higher groundwater levels can be divided into three types:hyperbolic-like,U-shaped and oscillatory,and that the settlement values and settlement characteristics of the tunnel are positively correlated with the content of cohesive soil in the main compression layer.When the content of cohesive soil in the main compression layer exceeds 64%,the settlement curve is quasi hyperbolic.Groundwater level height and backfill depth are important factors affecting tunnel settlement,and groundwater buoyancy is the main force of tunnel lifting.The longer data accumulation time,the higher prediction accuracy of curve fitting method.After the 9 months of data accumulation after dead load,the error of final settlement predicted by Asaoka method and three-point method is less than 10%.