Theoretical Analysis of the Effect of Large-Section Rectangular Pipe Jacking on the Asymmetric Deformation of the Formation

Using the Baotou comprehensive pipe corridor pipe jacking project as background, this study examined how asymmetric additional thrust affects ground deformation during the boring of large cross-section rectangular pipe jacking machines. The additional thrust was decomposed into left and right components, and a theoretical analytical model was developed based on the Mindlin solution from elastic mechanics. An equilibrium coefficient m and an offset coefficient n were introduced to characterize the formation’s deformation state, and a deformation-pattern zoning of the formation was derived. The results indicate that, among the factors influencing stratigraphic deformation, the additional thrust force accounts for the largest proportion; if n ∈ (−1, 1), when m > 0, stratigraphic deformation manifests as left-lateral uplift, and when m < 0, it manifests as left-lateral subsidence. If n > 1, when m > 0, stratigraphic deformation manifests as a right-lateral uplift; when m < 0, it manifests as a right-lateral subsidence; if n < −1, when m > 0, stratigraphic deformation manifests as a right-lateral subsidence; when m < 0, it manifests as a right-lateral uplift. The conclusions are as follows: (1) Formation deformation induced by large-section rectangular pipe jacking is not necessarily symmetric. When soil compartment pressure is uneven, deformation in the surrounding strata becomes asymmetric. (2) Additional thrust is the primary cause of formation deformation. (3) Deformation on the left side is governed by the equilibrium coefficient, whereas deformation on the right side is governed by both the equilibrium coefficient and an offset coefficient; the ultimate deformation reflects the overall state of the strata. (4) The stratum deformation pattern zoning proposed in this paper enables rapid, intuitive identification of strata deformation patterns and can inform the safe excavation of rectangular roof pipes.