Practical prediction method on frost heave of soft clay in artificial ground freezing with field experiment

Artificial ground freezing (AGF) is a method of paramount importance for underground construction in soft soil area. There were numerous studies concerned on field observations and the theoretical formulations on frost heaves. However, the field observations and validity of the theoretical models from practical points were lack. This paper focused on a more accurate practical prediction method of frost heave by multilayer field experiments and segregation potential (SP) model, for a strict deformation requirement AGF project in a non-stopping airport during construction. Thus, a large-scale area (3.5 times than actual frozen curtain) field experiment of multi layered temperatures and displacements was conceived and developed, to evaluate the freezing effect and deformation characteristics. Temperature variations show that the additional freezing tubes at the tunnel opening can only achieve faster cooling rate initially but could not descend the final stable temperature, and so substantially increasing freezing tubes at the tunnel opening may not be best choice to keep excavation safe. Multilayered temperatures and displacements show that deformation of multi-layers is directly relevant to the position of frost front. A simplified frost heave prediction method using segregation potential concept is proposed based on field experimental data. The temperature gradient and frost front function have been calculated based on field monitoring results and served for the model computation. This prediction method was further validated by both other's published and our field experimental data. 2-8% relative errors surrounding the axis of frozen curtain prove the applicability of this practical prediction model is much well. This paper provides valuable reference for urban tunneling under extreme conditions such as non-stopping airport or adjacent to existing structures.