ISSN 1000-3665 CN 11-2202/P

    北京不同区域明挖基坑地表沉降变形特征研究

    Characteristics of surface settlement and deformation of open cut foundation pit in different areas of Beijing

    • 摘要: 基于近年北京地区不同区域大量明挖基坑工程地表沉降实测数据,利用理论计算与回归分析方法,对预测地表沉降的典型曲线“四点折线法”及其模型参数(斜率K及截距b)进行了反演分析,获得了不同区域地质条件下明挖基坑地表沉降预测经验参数;通过对沉降数据及经验参数的统计分析,总结了地表沉降区域变化规律,明确了参数的取值范围,并利用实测数据验证了经验参数的预测精度。结果显示:北京西部区域最大沉降点距离围护结构的水平距离相对中、东部偏大,约为基坑深度的30%,中、东部区域相对较小,均约为基坑深度的26%;地表沉降曲线形态随着区域地质条件不同而不同,四点折线图第一段直线AB的斜率K的绝对值由西向东依次增大,表明东部粉细砂地层比西部砂卵石地层沉降坡度更加明显,第二段直线BC的斜率K的绝对值东部区域比西部区域反而较小,这表明东部区域的沉降影响范围较大;参数bAB绝对值均值由西向东依次增大,表明东部粉质黏土、细沙层相对西部砂卵石地层的桩侧土体沉降值更大,约为最大沉降值的31%,中部区域为21%,西部区域仅为16%。该研究成果将为本地区明挖基坑工程地表变形预测和安全风险控制提供重要的参考依据。

       

      Abstract: Based on a large number of measured data of surface settlement of open cut foundation pit engineering in different areas of Beijing in recent years, the typical curve "Four Point Broken Line Method" and its model parameters (slope K and intercept b) for predicting surface settlement are inversely analyzed by using theoretical calculation and regression analysis methods, and the empirical parameters for predicting surface settlement of open cut foundation pit under different regional geological conditions are obtained. Based on the statistical analyses of data and empirical parameters, the regional variation law of surface subsidence is summarized, and the range of parameters is defined. The prediction accuracy of empirical parameters is verified by using the measured data. The results show that the horizontal distance between the maximum settlement point and the retaining structure in the west of Beijing is larger than those in the middle and east of Beijing, which is about 30% of the depth of the foundation pit, while those in the middle and east of Beijing is relatively small, which are about 26% of the depth of the foundation pit. The surface settlement curve shape varies with the regional geological conditions, and the absolute value of the slope K of the first line AB of the four point broken line graph increases from west to east, showing the settlement slope of the east silty fine sand is more obvious than that of the west sandy cobble, and the absolute value of the slope K of the second straight line BC in the east is smaller than that in the west, indicating that the settlement influence range of the east is larger, the absolute value of the parameter bAB increases from west to east, indicating that the settlement value of the pile side soil of the silty clay and fine sand in the east is larger than that of the sandy pebble in the west. It is about 31% of the maximum settlement, 21% in the central region and only 16% in the western region. The research results will provide an important reference for surface deformation prediction and safety risk control of open cut foundation pit engineering in this region.

       

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