Abstract: In foundation pit engineering, the depth of embedment of retaining structures into the pit bottom affects both the failure mode of the pit against basal heave and the magnitude of the safety factor. Adopting the finite element limit analysis and incorporating the concept of critical embedment depth into the analytical framework, this study revealed the effect of the geometrical parameters of the foundation pits and the strength parameters of the soil on the critical embedment depth of foundation pits. Based on the results of numerical simulation, this study proposed an applicable formula on calculating the critical embedment depth of circular foundation pits. With the help of numerical and practical engineering examples, this study validated the formula and systematically analyzed the magnitude of the formula’s error. Therefore, the reliability of the formula was demonstrated.