7/28/2019 Tank Settlement

http://slidepdf.com/reader/full/tank-settlement- 1/2

Tank Settlement CriteriaAPI 650 Appendix B Chevron SHELL

“Criteria for Settlement of Tanks”

From Journal of Geotechnical Engineering Division, Proceedings of the

American Society of Civil Engineers, Vol. 108, August 1982

Recommended Performance Criteria for Differential Settlement of 

 Tanks

Allowable Tank Bottom Differential Settlement

1) For New Tanks with Floating roofs

2) For New Tanks with Fixed roofs

Dss

⎟⎟

 ⎠

 ⎞

⎜⎜

⎝ 

⎛  ++=Δ

4

461.02

 

where:

Δ =Allowable differential settlement edge to center of tank, in.

D =Tank diameter, ft:

S =Intial bottom slope (positive when coned up), in/ft

Most soils-related damage to tanks is due to differential settlement.

 Tank (bottom) settlement

As a general rule, one must assume that the tank center will settlesubstantially more than the tank edge because of variation in stress

distribution.

After settlements due to hydrostatic testing and a number of years of 

operational service, the remaining minimum elevation of the tank pad

measured at the position of the tank wall shall be 0.60 m above the highest

floor level of the bunded area.

During hydrostatic testing of the tank, 30 to 70% of the total settlement

will take place already and the remaining settlements will take place

mainly during the first few years when the tank is in operation.

Settlements will gradually become less, as can be seen in the typical

settlement curve below. 

MONITORING OF FOUNDATIONS

Especially foundations on soft soil and weak rock should be evaluated by

monitoring of settlement at intervals of:

y  2 to 6 weeks during construction of the superstructure,

y  6 months during the first two years after construction/water testing,

y  3 to 5 years in the period thereafter.During the water test the tank settlements shall be monitored. If the

maximum settlement of the tank shell during the water test is more than 50

mm, the tank settlements should also be monitored during operation.

three types of differential settlements:

y  differential settlements along the tank shell

y  differential settlements between tank centre and perimeter

y  overall tilting

7/28/2019 Tank Settlement

http://slidepdf.com/reader/full/tank-settlement- 2/2