In cities, once again because there is no room to allow normal excavation, before any serious site excavation is done for the foundations, shoring must be installed. Its sole purpose is to keep the city sidewalks, utilities, and street stable while excavation on your site progresses.
Although there are many different methods of shoring, based on size of excavation, depth of excavation, soil type, moisture content of soil, etc, the most common methodology is to drill holes and drop in wide flange steel beams (soldier piles).
These are photos of the drilling auger rig (background) used to drill approximately 22′ deep holes to receive the steel soldier piles.