A thin layer of thaw-unstable permafrost over bedrock or over thaw-stable soil can be replaced with thaw-stable soil. More often such replacement is not feasible or not economically justified. The other method of permafrost modification prior to construction is its preliminary thawing to a specific depth. Steam and water points and electrical heating have been applied for thawing. This method has been infrequently used in Alaska and Russia.
Preliminary thawing of foundation soils is most effective in the case of coarsegrained soils where settlement is practically complete during thawing. Ice-rich clayey soils reach 60-80% of their total settlement upon thawing, and their settlement continues during and after construction. Their water content upon thawing is greater than their liquid limit and shear strength is insufficient. Thus, preliminary thawing cannot by effectively applied to such soils.
There are successful and unsuccessful examples of application of the method. This method is the first to consider in areas of degrading coarse-grained perennially frozen soils.
Was this article helpful?