579
The use of hydro test results for design of steel tanks on stone column improved
ground - a case history
L’emploi des résultats des essais hydrauliques dans l’étude des réservoirs en acier sur le sol
amélioré par colonnes de pierre – histoire de cas
Matešić L.
Geokon-Zagreb, Zagreb, Croatia; University of Rijeka, Faculty of Civil Engineering, Rijeka, Croatia
Mihaljević I., Grget G.
Geokon-Zagreb, Zagreb, Croatia
Kvasnička P.
University of Zagreb, Faculty of Mining geology and petroleum engineering, Zagreb, Croatia
ABSTRACT: This paper describes hydro tests performed on five large storage tanks (80.000 m
3
each) located at the Sisak Oil
Terminal, Croatia. Because of its small stiffness and low water permeability, foundation soil for each tank was improved with 660
stone columns. In order to reduce the risk of accidents, such as fire, breach or leak, a crude oil storage tank requires stringent security
measures. In the case of the Sisak tanks, the hydro tests were conducted as part of technical monitoring to determine a set of
documented and interconnected activities which would provide proof of proper functioning of all elements of a tank structure. In case
of critical deviations from the operation expected, such activities ensure that such deviations are removed or corrected on time by
taking necessary measures approved by experts. Under a procedure for the hydro tests, the phases of tank and bund filling were
defined and each phase was followed by visual inspection and measurements of settlements and deformations of the steel structure.
Design directions for future foundation and hydro tests of tanks were made accordingly.
RÉSUMÉ : Les essais hydrauliques conduits sur cinq réservoirs de grande taille (chacun de 80,000 m3 ) situés dans le Terminal
pétrolier de Sisak en Croatie, sont décrits dans l’ouvrage. Compte tenu de petite rigidité et perméabilité à l’eau peu importante, le sol
de fondation pour chaque réservoir a été amélioré avec 660 colonnes de pierre. Les mesures très rigoureuses doivent être prises pour
les réservoirs à pétrole brut afin de réduire le risque d’accidents tels que feu, rupture ou fuite de pétrole. Dans le cas des réservoirs de
Sisak, les essais hydrauliques ont été conduits dans le cadre de la surveillance technique dont le but était de définir une série des
activités bien documentées et interconnectées visées à prouver le fonctionnement impeccable de tous les éléments structurels du
réservoir. Dans le cas d’une déviation critique par rapport au fonctionnement normal, ces activités permettent l’élimination ou la
correction prompte de ces déviations en prenant les mesures appropriées approuvées par les experts. Dans la procédure pour les essais
hydrauliques, les phases de remplissage du réservoir et de la cuvette de rétention ont été définies, et chaque phase a été suivie par une
inspection visuelle et par mesurage du tassement et des déformations de la construction en acier. Les instructions d’études sont
fournies pour les essais hydrauliques et les essais des fondations futurs.
KEYWORDS: steel tank, stone columns, hydro test, monitoring, settlement
1
INTRODUCTION
During the years 2010 and 2011, five new crude oil storage
tanks were built at the Sisak Oil Terminal.
80.000 m
A-2510
N
50
100
150
200 m
0
3
80.000 m
A-2509
3
80.000 m
A-2508
3
80.000 m
A-2507
3
80.000 m
A-2511
3
A
A
cross section A-A
bund
floating roof
tank
Figure 1. The layout plan of the tanks
All the tanks are of the same size and have an identical steel
structure with a floating roof and steel bund wall designed in
accordance with API 650. The diameter of the tanks and bunds
is 73,2 m and 78,2 m respectively. The tanks have 80.000 m
3
in
volume and their total and overflow height is 20,6 m and 19,5 m
respectively (Figure 1.).
Foundation soil is horizontally stratified and, therefore, the
soil under all the tanks is of almost the same properties. Because
of its small stiffness and low water permeability, the foundation
soil for each tank was improved with hundreds of stone
columns, which is a technology applied in similar cases of soil
improvement (Raju et al 2004, Ambily and Gandhi 2004).
In order to prevent industrial accidents, viz. fire, breach or
leak of a tank, etc. to happen, a crude oil storage tank requires
special safety measures. For this reason, all tank development
stages such as ground investigations, design, construction,
hydro tests and exploitation, were strictly controlled according
to a highly elaborated plan as laid down in API 653 and EN
14015.
On the basis of in situ and laboratory tests, a numerical
model was created in Plaxis, and all phases of hydrostatic tests
were checked before testing.
2
DESIGN REQUIREMENTS
In the near vicinity of the new tanks, three 80.000 m
3
tanks with
floating roofs were installed 30 years ago. During the hydro test
performed on one of them, the yielding of foundation soil
