Influence of Boundary Insulation on the Growth of Frozen Soils during AGF Modeling

To clarify the influence of boundary insulation on the development of frozen soils, seven artificial ground freezing (AGF) models of Ottawa sand were performed with different thermal impedance Z-values of the boundary insulation system. Results of testing show that the greater the Z-values, the larger the frozen soil areas for a given time of freezing. When the Z-value is more than 2.27 m(2) K/W, however, the extent of frozen soils appears to be stabilized for the AGF model with dimensions of 100 cm (L) by 100 cm (W) by 15 cm (H). Two-dimensional finite element analyses were also conducted to verify the performance of boundary insulation systems of the physical model. Numerical simulations show the development of frozen soils is significantly affected by the ambient temperature if no insulation is covered on the boundary of the AGF model, and the growth of frozen soils would cease at a freezing time of less than 6 h. However, when the Z-value of the boundary insulation system is more than 2.27 m(2) K/W, the pattern of the temperature field and the size of frozen soils in the model resemble those for a system with a perfectly insulated boundary with an elapsed time of freezing up to 24 h. Hence, it can be concluded that the thermal impedance Z-value should be at least 2.27 m(2) K/W for the boundary insulation system of the current AGF model to be free from the influence of an ambient environment and have a similar temperature response as the perfectly insulated model for a test time up to 24 h.

Automated summary

The study found that the development of frozen soils is significantly affected by the Z-values of the boundary insulation system, with a Z-value of at least 2.27 m(2) K/W necessary for stable frozen soil development.