Note: Descriptions are shown in the official language in which they were submitted.
lZ~ 17
-- L -
SYSTEM FOR STORING LIQUID_OR GAS I A ROCK CHAMBER
The present invention relates to a system for sealed
lining of a rock chamber for storinq liquid or gas, also
under very high pressures, as stated in the preamble of
claim 1.
The ceiling, walls and floor of the storage space are
lined with a sandwich construction comprising drainage
material, concrete affixed to the wall, and a sealing
membrane of e.g. stainless thin sheet.
By making a sealed lining in which the pressure from
the product kept in the storage space is absorbed by the
surrounding rock, it is possible to store e.g. gas or air
under excess pressure at a considerably smaller depth
below the ground surface than in an unlined storage space
where the water pressure in the rock must be higher than
the gas or l:iquid pressure from the product in the storage
space. According to this invention, the gas pressure or
the liquid pressure is balanced by the weight of the rock
volume activated on failure or by the lithostatic pressure
only.
The lining should also be able to withstand a water
pressure from the surrounding rock which is higher than
the pressure in the storage space. Such loads occur, for
example, when petroleum is stored below the phreatic
surface or when storing gas after the storage space has
been emptied.
90'7
By this method, a na~ural gas store having an excess
pressure of 80 bars can be loca~ed with a rock overburden
of about 70-80 meters, whereas 800 meters are required if
S no lining is used.
An object of the invention is a system for storing a
fluid in a cavity defined in a rock formation, that avoids
the necessity of dimensioning for outside water pressure
but is still capable to employ the rock as means for
absorbing the inside pressure.
The object of the invention is achieved by providing
a fluid storage system, comprising:
- a concrete lining adjacent a wall of the cavity in
the rock formation
- a drainage layer of granular material between the
cavity wall and the concrete lining, the drainage layer
completely enclosing the concrete lining and transmitting
fluid pressure from the cavity to the wall thereof;
- a plurality of drainage channels in the drainage
layer;
- sealing means facing the cavity, including a
plurality of extensible thin metal sheets attached
together and being movable relatively to the concrete
lining;
- means for mounting the concrete lining to the wall
and allowing the concrete lining to move with respect to
the wall, including a plurality of bolts retained to the
concrete lining and extending through the drainage layer,
12~6907
the bolts being slidinyly received in respective holes in
the wall, whereby allowing the concrete lining to expand
toward the wall under the effect of fluid pressure in the
cavity by sliding in the respective holes.
I~ preferred embodiment of the invention will now be
described with relation to the annexed drawings in which:
- Figure 1 is a cross-section of a storage space
according to the invention;
- Figure 2 is an enlarged cross-section of a portion
of the wall construction with the anchoring member 5;
- Figure 3 is an enlarged cross-section of a portion
of the transition between the wall and floor with drain
pipes 9 and a specific construction 6, 7 for the drainage
of water between the metal sheet and the drainage layer;
- Figure 4, on a larger scale, shows the part 7 as
seen from inside the storage space; and
- Figure 5 shows a portion of the assembly of the
sealing function and the manner in which it is secured to
a sheet-metal strip in the concrete surface.
The construction comprises, in addition to rock 1,
also a drainage layer 2 which is attached to the rock and
from which water is pumped off such that no outside
pressure is exerted on the lining 3, 4. The drainage
layer should also serve to transmit, upon a certain
deformation, the pressure to the surrounding volumes. The
drainage layer may consist of natural material, e.g. sand,
gravel (pebbles).
.
.
lZ~6907
Inwardly of the drainage layer 2, concrete 3 is cast
which is force-transmitting and serves as a base for the
sealing function 4 which may be a membrane 4 (e.g.
stainless thin sheet). The concre~e is crack control
reinforced in order to distribute the cracks which, in
connection with deformation, are formed when the concrete
exerts a pressure on the drainage layer 2 and the rock 1.
The concrete is anchored in holes drilled in the rock by
means of bolts 5. The bolts must be able to move in the
drill holes towards the rock upon application of the gas
or liquid pressure in the storage space to avoid
penetration of - - _
~296907
the concrete around the bolts 5 which are expansion-type
~olts.
Since pressure can be transmitted to the rock
via the concrete layer 3 and the drainage layer 2
and, also, the outside water pressure is removed by
means of the continuous drainage layer 2, the sealing
function 4 need not be dimensioned for this pressure.
The deformation will make the metal sheet expand
slightly. Since the metal sheet is thin, it will plasti-
cize in connection with irregularities and cracks inthe concrete, thereby eliminating any bending stresses
which, in connection with deformations, will appear in
heavier and more rigid sheets.
By using a thin metal sheet, welding can be car-
ried out by an automatic seam welding method 12 inFig. 5, which is a known technique used in connection
with, for example, roof coverings.
The sheets, which are delivered in rolls, are
bent in a special bending machine and welded together
by seam welding to an L-section 12 having a thickness
of about 0.5 mm and being spot welded ll to a sheet-
metal strip lO inserted in the ccncrete surface.
In this case, the bent seam 12 has a function
not previously utilized in that the welding seam will
not be subjected to tensile loads when the bent seams
of the metal sheet are compressed by the gas or the
liquid pressure in the storage space.
The use of sheets having such a small thickness
(about 0.4 mm) that automatic welding can be used,
and the simplified assembly work entail a cost of
about one third as compared with the use of a conven-
tional welding technique.
Since the concrete is allowed to crack, the cracks
can be filled with water. If the water pressure should
exceed the inside pressure in the storage space, the
metal sheet will rise to some extent from the concrete,
.;
~2~6907
and the water wil] llow between the sheet 4 and the
concrete 3, resulting in a pressure drop.
Maximum pressure will occur in the lower portion
of the wall where the metal sheet also will rise first.
This water is collected via drain pipes 6 which commu-
nicate with the drainage layer 2. To make the thin
sheets 4 bear across the drain pipes 6, the connec-
tion is designed as a perforated strip 7, see Figs. 3
and 4.
When gas is stored, the drainage layer 2 may
also serve to absorb leaking gas in the event of gas
leakage through the metal sheet, in that the pressure
of the escaping gas holds atmospheric pressure in
the drainage layer 2. Since water pressure is exerted
in the rock, if the storage space is located below
the phreatic surface, the gas will not migrate into
the rock in an uncontrolled manner but can, via a
shaft in the upper part of the storage space, be col-
lected and pumped into the storage space or to a gas
pipe.
Nor will liquids, such as jet fuels, migrate
into the rock without control but be collected to-
gether with the drainage water.
By constructing the lining as a sealing function
according to the present invention, two essential
advantages are obtained:
1. It is possible to store products which cannot
be stored against water, e.g. ammonia or deli-
cate petroleum products, such as jet fuels
and possibly unleaded gasoline, and to store
any products where there is no groundwater
at reasonable levels.
2. By using the volume of the rock for pressure
absorption, it is possible to store e.g. pres-
surized gas at considerably smaller depth
--~ than when the water pressure is used to prevent
- gas or liquid from flowing out.
i~6907
There are a number of lining systems, but none
that combines force transmission and force deflection,
i.e. ensures continuous drainage in a natural material,
which also requires a construction withstanding the
deformations which occur when the construction is
subjected to pressure in the storage space, without
jeopardizing the sealing function (the metal sheet).
