困扰的语法题as...as

什么时候用as....as什么时候用than

The EEC exported just under 400billion in goods in 1988,60% more than the US did and twice as much as Japanese did.

这里为什么可以用twice as...as的形式，为什么有的地方就一定要用twice more than？？？

这两个是不同的意思啊