Top-down construction
Basement excavation proceeds downward while the superstructure rises, controlling schedule and ground movement on constrained urban sites.
Perimeter walls and intermediate slabs are built first, then excavation continues beneath them while permanent columns carry loads.
It suits dense sites and limits settlement around neighbors, but restricts equipment, ventilation, and material handling.
Engineering must analyze the load path at every excavation stage, not only the completed building.
Basement waterproofing, joints, column connections, and continuous monitoring determine safety and service life.
