Abstract: Pit-in-pit excavation is becoming more and more popular, and concerns are increasing on the influence exerted by the interior pit. However, the calculating depth in design remains a puzzle, taking the exterior pit excavation depth is a risk, while the interior is conservative. This paper raises a concept of equivalent depth and two parameters called equivalent depth coefficient and equivalent impact angle based on analysis of various relative position of interior and exterior pit, width and depth of the former, whose feasibility is proved. The equivalent depth converts the pit-in-pit into normal excavation model, and the equivalent depth factor quantifies this kind of conversion.

Key words: pit-in-pit, equivalent depth, equivalent depth coefficient, equivalent impact angle, deformation control