EXPERIMENTAL STUDY ON UNLOADING EFFECT OF DRILL AND BLAST EXCAVATION IN HIGH AXIAL GEOSTRESS

摘要

During deep underground rock masses excavation, an unloading effect is shown due to transient release of high natural geostress. As drill and blast method remains the common method for rock masses excavation, 3D geomechanical model experiments are carried out to investigate the excavation unloading effect in high axial geostress. To decouple transient release of high axial geostress and blasting load, three excavation methods, digging, extraction and blasting, are involved. Test results indicate that both radial and circumferential strains develop with the advance of model tunnel and a dramatic variation presents when model tunnel excavated over strain measuring points plane. For extraction excavation, there is a dynamic unloading process for transient release of high axial geostress. After complete excavation, a nonmonotonic unloading radial strain distribution with peaks and troughs is presented for both extraction and blasting excavation. Unloading radial stress distribution around model tunnel indicates that stress adjustment is quite different for three excavation methods. Non-monotonic distribution is also shown in radial stress for extraction and blasting excavation. Due to deterioration of mechanical properties and damage during blasting excavation, both unloading strains and stresses are much bigger than those for digging or extraction excavation, especially close to model tunnel boundary. Moreover, the non-monotonic distribution of unloading radial strains and stresses indicates a tendency of zonal disintegration in deep rock mass after excavation.