Pit-in-pit usually occurs in pit engineering practices

making the soil at the bottom of the foundation pit become a limited soil. Thus

Rankine earth pressure theory based on conventional semi-infinite space is not applicable for calculating the earth pressure acting on retaining structure in case of pit-in-pit. This also makes it difficult to correctly estimate the excavation depth of the foundation pit for design. Based on the limited equilibrium theory and the hypothesis of planar sliding plane

four formulas for calculating passive earth pressure are deduced with cohesion force and different shapes of sliding soil mass taken into account

and corresponding mathematical expressions of shear failure angles are given. By example

the values and variation trends of passive earth pressures for different internal pit positions are calculated. The results show that the angle of shear failure is a variate that are related to the friction angle of soil

the cohesion of soil

the depth

the size and the position of inner pit. The inner pit will lead to decrease of the passive earth pressure acting on retaining structure

and there is a most unfavorable position for inner pit

where the value of passive earth pressure is minimum. This study provides a theoretical basis for the calculation of passive earth pressure in foundation pit design.