to find the volume of the slios, or anything round, you need to know the formula, which is:
$${\mathtt{\pi}}{\mathtt{\,\times\,}}{{\mathtt{r}}}^{{\mathtt{2}}}{\mathtt{\,\times\,}}{\mathtt{h}}$$
first, we will do area
radius as you know is half of the diameter
so divide 10 by 2=5
5^2=25
so, $${\mathtt{25}}{\mathtt{\,\times\,}}{\mathtt{\pi}} = {\mathtt{78.539\: \!816\: \!34}}$$
now lets times it by 20 meters, for 20 meters is the height
$${\mathtt{78.539\: \!816\: \!34}}{\mathtt{\,\times\,}}{\mathtt{20}} = {\mathtt{1\,570.796\: \!326\: \!794\: \!896\: \!62}}$$
most accurate answer: 1570.79632679489662 meters
rounded answer (to the nearest whole number):1571 meters