3.1.1　Prior to design of tank foundations，geotechnical investigation shall be done for the tank construction site.

3.1.2　The design classes of tank foundation shall conform to the current national standard GB 50007:Code for Design of Building Foundation.

3.1.3　When the tank foundation is constructed on particular soil or the subgrade soil that is subject to liquefaction under earthquake action，or the bearing capacity of subgrade soil and the differential settlement fail to satisfy the design requirements，measures such as subgrade treatment or deep foundation shall be adopted and if adverse geological actions and geological disasters are foreseen，special geotechnical engineering investigations shall be made.

3.1.4　Geotechnical engineering investigations for tank construction site shall conform to the current national standard GB 50021:Code for Investigation of Geotechnical Engineering，and shall comply with the following requirements:

1　Exploration points should be provided at the center and along the shell of the tank，and number of exploration points shall be determined depending on the tank types，volumes and subgrade geological complexity.In detailed geotechnical investigation stage，the number of exploration points provided for tank subgrade may be selected from Table 3.1.4-1，where the number of control exploration points should be 1/5-1/3 of the total number of exploration points.

2　Depth of boreholes shall comply with the following requirements:

1)Depth of general borehole:it may be determined in accordance with Table 3.1.4-2 depending on the subgrade geological complexity and volume of tank，or the borehole shall be drilled to the top of bedrock.

2)Depth of control borehole:it shall be the depth of general borehole plus 10m for soil，and it shall be the depth of general borehole plus 5m for rock，and should be drilled into moderately weathered rock in a depth not less than 1m.

3　Geotechnical engineering investigation report shall include the following contents:

1)General subgrade:the report shall include site landform and geomorphy，geological configuration，earthquake effect，adverse geological actions，stratum formation conditions，physical-mechanical properties of each soil stratum，site stability，soil uniformity，characteristic values of soil bearing capacities，coefficient of compressibility，compression modulus，corrosion to construction materials from ground water，soil and water，standard frost penetration as well as the conclusions and recommendations for geological issues due to construction activities，and the attached arrangement drawings of exploration points，engineering geologic profile，engineering geologic columnar profile and related test charts.

2)Soft soil subgrade:the report shall include the soil composition，category，distribution extent，coefficient of permeability and coefficient of consolidation by vertical and horizontal drainage，the relationship between consolidation pressure and void ratio，triaxial consolidated undrained shear strength，unconfined compression strength，triaxial unconsolidated undrained shear strength，cohesion intercept in terms of effective stress，angle of shearing resistance in terms of effective stress undrained shear strength from the field vane test，sensitivity and the recommendations for subgrade treatment in addition to the contents covered in the report for general subgrade.

3)Mountainous subgrade:In addition to the requirements stipulated in general subgrade，the report shall include the adverse geological conditions at construction site such as landslide，karst，karstic earth cave，eboulement and debris flow，the site stability assessment conclusions，the inhomogeneity distribution range of subgrade and the recommendations for subgrade treatment.

4)Special soil subgrade:In addition to the requirements stipulated in general subgrade，the report shall include the recommendations proposed on service，treatment and retrofitting of particular soil subgrade in accordance with the current national codes and standards.

3.1.5　Cultivated soil，soft soil，covered ponds，covered channels and household waste under the tank foundation shall be removed，and plain soil，graded sand and stones or lime soil shall be backfilled and compacted(rammed)layer by layer，the mechanical properties of compacted(rammed)subgrade soil should be the same as those of the untreated soil layer under the same foundation.When removal is not feasible，other proper treatment measures shall be taken.

3.1.6　Tank foundation should not be constructed on alternating hard and soft subgrade，when it is not avoidable，proper treatment measures shall be taken.

3.1.7　When the tank is not provided with anchor bolts，design of its foundation may not consider wind load action.

3.1.8　When the tank is not provided with anchor bolts，design of non-pile foundation may not consider earthquake action，but it shall satisfy the seismic measures requirements.

3.1.9　When the soil and ground water at site are corrosive to concrete，anticorrosion measures shall be provided for tank foundation and shall be in accordance with those specified in current national standard GB 50046:Code for Anticorrosion Design of Industrial Constructions. uQauygArS1sW65M4fgcZPnfnTxCGWAfZ6L1MAp06T6/nAMxgHXVWiMXOhlbop7v8