Calculation method of the earth pressure for parallel pipe jacking with small spacing

With the increase in the urban underground buildings and the limitation of underground space, there are increasing double-line or even multi-line pipe jacking projects with small spacing. In the process of pipe jacking with small spacing, due to the influence of pipe-pipe interaction, the earth pressure distribution around the pipes changes greatly, which leads to difficulties in the load determination, structure calculation, and jacking force prediction and control. Combined with the back analysis of numerical simulation, based on Terzaghi’s theory of consolidation and limit equilibrium theory, the soil loosening line and the retaining line of the existing pipe are assumed, and a new calculation method of vertical earth pressure on the vault of parallel pipe jacking with small spacing is established. The effects of soil shear strength, pipe diameter, and pipe spacing on the earth pressure are analyzed, and the calculated earth pressure on the vault of the new pipe is compared with those calculated by the soil column theory and Terzaghi’s theory without considering the influence of the existing pipe. The results show that the vertical earth pressure of the new pipe jacking vault increases with the increase in the soil shear strength, but the earth pressure on both sides of the new pipe jacking decreases. When the shear strength is large, the earth pressure on the vault calculated by this method is smaller than that calculated by Terzaghi’s theory. When the shear strength is small, the earth pressure on the vault calculated by this method is larger than that calculated by Terzaghi’s theory. When the buried depth of the pipe increases, the earth pressure on the vault of the new pipe jacking increases, but compared with the soil column theory and Terzaghi’s theory, the earth pressure increment is smaller. With the increase of the spacing between the two pipes, the earth pressure on the vault of the new pipe jacking arch increases.