Soil Nail Forces Caused by Frost

Soil nailing can be an effective solution for wall construction but is not common in colder climates because unknown frost forces may occur in frost-susceptible soils behind the wall. Currently, no design criteria exist for these walls in frost conditions, but development of design guidelines under frost conditions would promote the use of this technology in cold climates. Soil nail head force results are presented for 3 years of monitoring of a soil-nailed wall in Moscow, Maine, in a frost-susceptible environment. Also, proposed methods for estimating nail head tensions arising from freezing in frost–susceptible conditions are discussed. Instrumentation was installed to determine the effectiveness of the wall’s facial insulation and to determine the effects of frost on an uninsulated wall. One monitoring station was insulated and the other comparable station was not. Instrumentation, including thermocouples, thermistors, vibrating wire strain gauges, piezometers, and earth pressure cells, revealed wall performance. During three milder than normal winters, frost action in the uninsulated areas produced tensions that exceeded design tensions. A portion of the annually induced nail head tensions was permanent and cumulative. Facial insulation minimized frost loads on nail and wall components below the top nail row. For frost-susceptible conditions, the magnitude of frost-induced maximum additional nail-head tension was related to the seasonal freezing index. The ultimate permanent nail head tension caused by frost was estimated from measurement data to be 2.5 times the peak seasonal tension increase.