The volume of the cone is given by:

where r is the radius and h is the height.
In this case we have that the radius is 8 meters, this comes from the fact that the radius is half the diameter. Now the height is 1.5 times the radius, this meand that the height is:

Plugging the values into the formula we have that the volume is:

Therefore the volume is 804.2 cubic meters.