地基应力解除法纠偏机理的离心模型试验研究

In-flight centrifuge modeling of vertical relief boring technique

地基应力解除法是对建筑物倾斜进行纠偏的一种方法 ,在国内、外得到广泛的应用。该方法已由原先打设斜孔从地下浅层掏土 ,发展到现今钻设大孔径竖孔向深部掏土。很显然 ,在建筑物基础边沿垂直向下掏土比倾斜向从建筑物基础正下方掏土容易得多。然而 ,与斜孔应力解除法相比 ,竖孔应力解除法的有效性尚缺乏很好的试验研究 ,其纠偏的设计分析也基本上是完全根据经验的。首先报道了在香港科技大学新近开发的土工离心机上 ,利用四轴机器人式操纵臂 ,为研究竖孔应力解除法的纠偏有效性而完成的一组不停机条件下的竖孔开挖模拟试验 ;其次 ,利用Mindlin解导出了单个竖孔应力解除纠偏效果的弹性理论积分解 ,对竖孔的开挖顺序、间距、深度以及开孔位置等因素影响的规律进行分析研究 ;最后 ,将离心模型试验结果与弹性理论分析计算结果进行了比较 ,并讨论了两者的差异。离心模型试验结果和弹性理论分析证明 ,竖孔应力解除法能非常有效地减小建筑物的倾斜 ;此外 ,简单弹性分析表明 ,对于某一深度的竖向应力解除孔 ,它距离建筑物越近 。

Similar to soil extraction through inclined boreholes, the use of relief boring techniques with soil extraction through vertical boreholes is popular in China to reduce tilting and to stabilize the buildings founded on soft grounds.It is obvious that vertical soil extraction is generally simpler than inclined extraction underneath the foundation of a building.However,the effectiveness of vertical boring,as compared with inclined drilling, may be somewhat doubtful and is often questioned by some engineers and the design analysis of remedial action to reduce building tilts is essentially empirical.In this paper,the effectiveness of vertical soil extraction is investigated in the state of the art geotechnical centrifuge at the Hong Kong University of Science and Technology (HKUST) using a newly developed 4 axis robotic manipulator to carry out in flight vertical boring.Results of a centrifuge test are compared with a newly derived theoretical elastic solution based on the Mindlin's equations.The discrepancies between the centrifuge model test and the theoretical elastic solutions are discussed. Both the results of the centrifuge test and theoretical solutions reveal that vertical relief boring technique can be very effective to reduce building tilts.Moreover,a simple elastic analysis using the derived theoretical solutions shows that for a given depth of boring, the closer the borehole from a building,the more significant the reduction of building tilts.