In-flight centrifuge modeling of vertical relief boring technique

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.