Precast concrete is used in elements, handleable by lifting equipment, which can be mass-produced at casting yards for repetitive inclusion in structures. Commonly these elements are beams but they may be piles, pipes, wall sections or architectural features. While it is difficult to move very heavy precast concrete elements on land, there have been many large-scale waterborne lifting applications such as for bridge foundation caissons or deck sections, immersed tube tunnels under estuaries and oil production platforms. In much simpler technology, lightweight concrete blocks are a common substitute for bricks, especially when brick clay is not readily available or for walls whose surfaces are going to be covered.