separation layer grouting is an important technology to control the settlement
the formation and situation of separation layer is significant to exert separation layer grouting. The formation of separation layer grout needs three conditions: weaker plane shear failure
terrane integrality and lithology otherness. The criterion of separation layer formation is established from the proceeding conditions and Mohr-Coulomb criterition. The study shows that the formation and situation of separation layer is confirmed by analytic solution or numerical solution.