My neighborhood in Seoul got a new subway line while I grew up, I believe they used cut-and-cover (it was almost at the outskirt, so they didn't have anything e

My neighborhood in Seoul got a new subway line while I grew up, I believe they used cut-and-cover (it was almost at the outskirt, so they didn't have anything else underground) and it took several years. So, while it's doable, it's not exactly "Just dig a hole, build the tunnel and cover, done." It's a major disruption to shops along the street.