Abstract: In order to study the distribution of spatial active earth pressure against retaining walls in square shaft excavations, a 3-dimensional finite element analysis model of orthogonal rigid retaining walls is established, and the distribution of spatial active earth pressure and variation of the spatial slip block against translating retaining walls with different aspect ratios are studied. A theoretical model for determining spatial active earth pressure against translating rigid retaining walls with different aspect ratios is proposed. The definition of deep shaft excavations is given. The theoretical formulae for the resultant earth pressure and its acting point and the active earth pressure in the middle section of the wall are presented. Comparing the theoretical and numerical results, it is found that the two are in good agreement. The studies indicate that the spatial slip block consists of Coulomb’s active soil wedge in the middle of the wall and object with curved surfaces in the corner when the aspect ratio of the retaining walls is larger than the critical aspect ratio. When the aspect ratio of the retaining walls is less than the critical aspect ratio, it can be defined as a deep shaft excavations whose sliding block does not have straight section. As the decrease of aspect ratio, the active earth pressure coefficient decreases gradually from the Coulomb’s solution and the sliding angle increases.

Key words: deep shaft excavations, orthogonal retaining walls, translation model, active earth pressure, critical aspect ratio of retaining walls