Water pipes are to be buried underground in a wet soil (thermal diffusivity = 2.78 * 10 -3 m2/s) which is initially at 4.5 degree Celsius. The soil surface temperature suddenly drops to -5 degree Celsius and remains at this value for 10 hours. Calculate the minimum depth at which the pipe be laid if the surrounding soil temperature is to remain above 0 degree Celsius. The soil may be considered as semi-infinite solid

• A. 0.467 m
• B. 0.367 m
• C. 0.267 m
• D. 0.167 m