It should be noted that the initial data from formulas (2) and (3) were obtained for ice whose 

 temperature was near -10°. Tests have not yet revealed the temperature dependence of the 

 flexural strength of ice. If one assumes that this dependence is proportional to the temperature 

 dependence of the compressive strength, one may use Royen's formula which already has been 

 given in Section 76: 



k ' (4) 



where a is the normal load, h is the coefficient characterizing the ice, t Is the temperature. 



But inasmuch as the normal loads are inversely proportional to the square of the thickness, 

 we obtain from formula (4) 



It is clear that if we make use of the coefficients of formulas (2) and (3) and consider that 

 these coefficients are obtained at an ice temperature of -9°, we obtain from formulas (2) (3) and 

 (5): 



,=.|/^.,„l/75, 



(6) 



^'~ 100 10 ' (7) 



where hf is the thickness of the ice at temperature t, capable of supporting a load p, p^. is the 

 weight of the load supported by the ice of thickness h and temperature t- 



In actual work it is very difficult to determine the temperature of the ice, especially sea ice, 

 since the vertical distribution of the temperature is a complex and variable curve. Because of 

 this, it is recommended that the average air temperature for the last 10 days be used instead of ice 

 temperature. 



For sea ice of about 6 o/oo salinity and -9° temperature, I consider it possible to assume 



/?.= 16i/7. (8) 



P = -^ (9) 



^250 



It develops from the comparison of formulas (2) and (8) that winter sea ice should be 1. 6 

 times thicker than fresh in order to support the same load. 



Inasmuch as the salinity of sea ice to which I consider formulas (8) and (9) applicable, is 

 about 6 o/oo, we can with a certain approximation write 



A, =/?„(] +0.1 S,.), (10) 



where S ■ is the salinity of sea ice. 



But on an average, the salinity of sea ice is about 5 times less than the salinity of the water 

 from which the ice had been formed. Hence it follows that the thickness of the sea ice which sup- 

 ports the same load as fresh ice would be equal to 



hs = {i + 0.02 S) ho, (11) 



where 5 is the salinity of the sea water from which the ice had formed. 



192 



