it would be better to build, oh I don't know...a train line instead?
There is a 16,000 mile train link from China to Spain. It takes 4 months for goods to arrive and they are subject to extremes of weather that make a lot of shipments impractical. It's also slower and more expensive than sending goods by sea. Any fixed link is going to be subject to delays, breakdowns, politics and difficulty in "overtaking" slower vehicles ahead of you.
It sounds like a neat idea, but we've already got better solutions: depending on whether you want speed or low cost.