Which Stone is Commonly Used for Switch Yard in Bangladesh?

Which Stone is Commonly Used for Switch yard In Bangladesh?

     Different sizes and patterned stone/gravel are available in Bangladesh which  (most of) are collected from many rivers and some other sources. But all sizes are not suitable for Electric Switch yard. The commonly used stone size and details are:

          Stone Type:             Diamond/ White Color
          Stone Size in MM:   (25 mm - 50mm)
          Stone Size in Inch: (2 inch-3 inch)

25mm to 50mm Stone