FALL 



r 



iff 



6 



WINTER 



3- DIA ALUMINUM DISK 

 WITH THREADED STUD 



WELD MARK (NO FLUID ABOVE) 



o 

 6 



-^ 



DRIVING HEAD WITH 

 THREADED STUD 



HEAT FLOW 



EVAPORATION )U 



FALL: The active layer starts 

 freezing from the top and 

 proceeds down. ice lenses 

 form creating heave forces in 

 upward direction. The thermo 

 bench mark is activated by the 

 air temperature dropping below 

 ground temperature. The 

 refrigerant is heated to the 

 boiling point by the higher 

 ground temperature along the 

 bottom of the mark, and 

 evaporates to the top, where it 

 condenses. The condensate 

 then returns to the bottom of 

 the mark through gravity. This 

 thermal cycling draws heat out 

 of the ground radially around 

 the thermo bench mark. The 

 radial freezing prevents ice 

 lense formation adjacent to the 

 mark and therefore upward 

 heaving forces. Higher 



temperatures near the top of 

 the mark also cause the frozen 

 soil to sublimate and relax its 

 grip on the mark. 



WINTER: The active layer is 

 completely frozen and the 

 potential for frost heave is past. 

 The thenno bench mark 

 continues to cycle and reduce 

 the grip of the frozen soil near 

 the surface. 



SPRIt^G/SUMMER: Air 

 temperature Is greater than 

 ground temperature and the 

 thermo bench marks thermal 

 cycling stops. No heave forces 

 are present during these 

 seasons. 



CONDENSATION 



Figure 11. Thermo Bench Mark 



29 



