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3.2.1 Tank foundations may be classified into slope protected foundation，ringwall foundation，outside ringwall foundation and pile foundation.
3.2.2 Foundation shall be properly selected for the tank based on the type and volume of tank，geological conditions at site，subgrade treatment methods，construction technologies and economic effectiveness，etc.
3.2.3 When selecting the foundation type according to the site and geological conditions，the following requirements shall be followed:
1 When the characteristic value of subgrade bearing capacity is larger than or equal to the mean pressure at foundation base surface，subgrade deformation satisfies the allowable limits specified in Article 6.1.3 of this Code and there are no field constrains，slope protected foundation should be used，and ringwall foundation or outside ringwall foundation may also be used(Figure 3.2.3-1 to Figure 3.2.3-3).
Figure 3.2.3-1 Slope Protected Foundations
2 When the characteristic value of subgrade bearing capacity is less than the mean pressure at foundation base surface，but subgrade deformation satisfies the allowable limits specified in Article 6.1.3 of this Code，and the subgrade after treated or pre-loaded by tank hydrostatic test satisfies the bearing capacity requirements，ringwall foundation should be used，and outside ringwall foundation or slope protected foundation may also be used(Figures 3.2.3-1 to Figure 3.2.3-3).
3 When the characteristic value of subgrade bearing capacity is less than mean pressure at foundation base surface，subgrade deformation fails to satisfy the allowable limits specified in Article 6.1.3 of this Code and the subgrade is subject to liquefaction under earthquake action，but the subgrade after treated or preloaded by tank hydrostatic test satisfies the bearing capacity requirements and the allowable limits specified in Article 6.1.3 of this Code，or proper elimination of liquefied soil layer satisfies related requirements，ringwall foundation should be adopted(Figure 3.2.3-2)，and when subgrade is difficult for treatment or is not treated，pile foundation should be adopted(Figure 3.2.3-4).
Figure 3.2.3-2 Ringwall Foundation
b —width of ringwall(m)； h —height of ringwall(m)
Figure 3.2.3-3 Outside Ringwall Foundation
b —width of ringwall(m)； h —height of ringwall(m)； b 1 —distance from the inner side of outside ringwall to the inner side of tank shell(m)； H —height from tank bottom to outside ringwall bottom(m)
Figure 3.2.3-4 Pile Foundation
4 When there are field constrains and the tank is designed with special requirements，ringwall foundation shall be selected(Figure 3.2.3-2).