Due to the lack of a clear definition for some key parameters in engineering design specifications

the wrong estimation of earth pressure produced by the inner pit excavation often results in accidents. The existing researches of  earth pressure in the passive zone of pit-in-pit have not considered the soil arching effects

which widely exist in geotechnical engineering. As a result

an accurate analysis on passive earth pressure is impossible. In this paper

an earth pressure mechanical model of cohesionless soil is established by presuming the inner pit support structure with large stiffness and very close to the outer pit support structure. Coefficient of earth pressures and the large principal stress rotation angle are obtained by analysing the horizontal earth pressure between two pit supporting structures at a limit state based on soil arching effects

and then the theoretical formulae and the force point are obtained. The case study shows that this method can better reflect the actual situation by analysing horizontal differential elements comparing to the classical earth pressure theory.