Because it is a design drawing, it shows that the concrete label is C30 when the pile is above the water surface or above the amplitude range of groundwater, and C35 is used when the pile is immersed in water (including rivers and groundwater) for a long time, so as to improve the compactness and impermeability of concrete. If groundwater is corrosive, there will be requirements for impermeability grade on general drawings, which is generally to improve the durability of concrete.

Similar to underwater concrete pouring is a construction consideration.