小净距隧道洞口段地表下沉分段曲线拟合研究

Study on Piecewise Curve Fitting of Surface Settlement at Neighborhood Tunnel in the Portal Section

针对基于最小二乘法的曲线拟合方法无法考虑小净距隧道先、后洞相互影响的施工特点,根据隧道先、后洞不同步开挖对洞口段地表下沉规律的影响,提出一种新的预测地表下沉的分段曲线拟合方法,并对隧道施工现场洞口段地表下沉量测数据进行分段曲线拟合分析.结果表明:采用分段曲线拟合法能较好反映地表下沉随先行洞与后行洞掌子面向前掘进的变形规律并可预测最终下沉量,避免了多项式函数无法预测最终下沉量以及指数与对数函数拟合精度偏低等问题;隧道先、后洞由不同步施工开挖引起的地表下沉量沉降槽曲线并不对称,最大地表下沉量偏向后行洞.

The construction characteristics of mutual influence in the first tunnel and the second tunnel are not considered in curve fitting method based on the least squares. A new piecewise curve fitting method is proposed to predict surface settlement according to the influence of unsynchronized excavation of the first and second tunnels. The piecewise curve fitting is used to analyze on-site monitoring measurement data of surface settlement at tunnel portal section. The results show that using the piecewise curve fitting method can better reflect the deformation law of surface settlement along with the excavation of the first tunnel and the second tunnel, and can forecast the final settlement. At the same time, the problems, such as the failure of polynomial function fitting to predict the final settlement and the low accuracy of exponential and logarithmic function fitting are avoided. The curve of surface settlement caused by unsynchronized excavation in two tunnels is asymmetry, and the maximum surface settlement happens to the second tunnel.