盾构隧道开挖引起地层位移计算理论的对比与修正

Assessment and modification of traditional methods for ground displacements induced by shield tunneling

隧道开挖引起的地层位移历来是学术界和工程界所关注的热点问题。首先,阐述了盾构隧道开挖引起地层位移的传统计算理论,对国外5条经典盾构隧道实例进行了计算和对比,分析结果表明:Peck经验公式、Yoshikoshi法和Celestino法拟合精度均较高;Loganathan和Poulos法计算得到的最大沉降值略小于实测值;Sagaseta法与Verruijt和Booker法的计算结果几乎相同,最大沉降量均明显偏低;Park浅埋法计算结果与实测值较为吻合。其次,基于多条盾构隧道的地表沉降实测数据,得到了地表沉降槽宽度系数is的修正拟合公式,该公式表明:is与隧道的开挖半径R、埋深h和土质条件(土体内摩擦角φ)有关,且与R+h tan(45°-φ/2)呈线性关系;此外,对多组盾构隧道深层土体沉降实测数据进行统计分析,获取了深层土体沉降槽宽度系数iz的修正拟合公式,该公式表明:iz与地表沉降槽宽度系数is之比iz/is,同该土层深度hz与隧道上覆土层厚度T之比hz/T之间呈对数函数关系。实例对比分析结果表明:地表和深层土体沉降槽宽度系数修正拟合公式均能较好地预测地层变形。

The issue of soil displacements caused by shield excavation is the hot topic in academic and engineering fields. Firstly, the traditional computation theories of soil vertical displacements are introduced. The ground surface settlements of 5 classical shield tunnels are calculated and analyzed. The analysis results show that: the fitting precision of Peck equation, Yoshikoshi method and Celestino method is higher, and the maximum settlements calculated by Loganathan & Poulos method are a little less than the measured data. The calculated results by Sagaseta method are mostly the same with those by Verruijt & Booker, while the maximum settlement is obviously small. The calculated results of Park method for shallow tunnel match well with the measured data. Secondly, based on cases of measured data of surface settlements, the modified fitting formula of width coefficient is of soil surface settlement trough is obtained. The formula is related to the tunnel radius R, axis depth h and soil conditions(internal friction angle φ of soil). The value of is is linear with R+h tan(45°-φ/2). In addition, according to the statistical analyses of some cases of measured data of subsurface settlements, the modified fitting formula for width coefficient iz of subsurface settlement trough is acquired. The formula for relationship between iz/is and hz/T is the logarithmic function(hzis ground depth and T is thickness of overlying soil). The case analyses show the modified fitting formulae for the width coefficient of ground surface and subsurface trough agree with the measured data.