应用SCPTu确定静止土压力系数的试验研究

Determination of coefficient of earth pressure at rest(K_0) using seismic piezocone tests

静止土压力系数(K0)的确定是地铁深基坑工程设计分析中的重要问题。采用三种原位测试手段:地震波孔压静力触探(SCPTu)、扁铲侧胀(DMT)和预钻式旁压试验(PMT),在苏州地铁1号线选择典型场地进行了试验,并采取高精度土样进行了室内试验,进而对各种K0确定方法进行了评价比较。试验结果表明,由于严重的钻进孔壁扰动等原因,PMT试验得到的K0值与室内实验值及设计值严重不符;基于DMT的K0确定方法,其精度取决于经验公式的来源,国外的经验公式大大高估了K0,而国内基于苏州试验样本的经验公式与室内试验值比较一致,但一定程度上低估了K0值;以设计使用值作为参考,基于SCPTu的Mayne(2001)方法和Mayne&Kulhawy(1982)方法预测的K0值是合理的,可用作初步设计值;K0值变化的影响因素、原位测试技术优缺点的比较等还说明现存经验方法需要根据场地特点进行校正及发展。

The determination of the coefficient of earth pressure at rest （K0 ） in soils is crucial for the design and analysis of subway excavation projects. In this work, a series of in-situ tests, including seismic piezocone tests （ SCPTu）, flat dilatometer tests （DMT） and pre-drilled pressuremeter tests （PMT） together with laboratory tests using high-quality soil samples, were conducted for the Suzhou Subway excavation projects. Furthermore, several K0-prediction methods were compared and evaluated. The results show that the PMT based prediction method has the poorest performance due to the significant wall disturbance during drilling, if the experimental values are taken as reference. The performance of the DMT methods may vary according to the used empirical formula. The existing formula may largely overpredict the K0 values of Suzhou soils. While the recent formula for Suzhou soils is in good agreement with the experimental values, though it may still underestimate the actual K0 values to some extent. The K0-values predicted from the Mayne （2001） method and the Mayne ＆ Kulhawy （1982） method are comparatively reliable, and they may be used for preliminary design values. The sources in variability of K0-values as well as the pros and cons of different in-situ methods were also discussed, indicating that further research is necessary for the calibration and improvement of existing empirical methods.