EP3201399B1 - Method of manufacturing an underground storage tank and corresponding tank - Google Patents

Description

FIELD OF THE INVENTION

The present invention relates to the construction of buried structures, more particularly buried storage tanks designed to contain a fluid, in particular a liquid, for example water.

BACKGROUND OF THE INVENTION

It is already known to store fluids such as water in tanks partially or completely buried in the ground.

These tanks typically comprise an outer wall buried in the ground and forming a ground support system delimiting a first volume to be excavated, a raft, and an inner coating covering the outer wall and sealingly connected to the lower slab, so to seal a storage space for the fluid. This inner liner is traditionally formed of steel or reinforced concrete cast directly against the outer wall and in one piece with the raft.

The outer wall and liner face significant tensile and compressive forces due to ground and groundwater pressures as well as internal fluid pressure. In particular, the inner lining needs important reinforcements to withstand the shrinkage of the concrete that constitutes it, the thermal stresses during the setting of said concrete, and high circumferential stresses, which can lead to cracking.

To comply with recent standards for water storage structures, it is necessary to further limit the maximum width of cracks in structures. With common construction methods, this leads to increasing the dimensions of the coating in the case of a steel coating, or to increasing the amount of reinforcement in the case of a concrete coating. However, the additional costs can be significant because of the quantities of steel to be used. Moreover, in the case of a concrete lining, the density of the reinforcement may be very to the point that it is difficult to properly place and compact the concrete. Finally, the tightness of structures and their durability can depend heavily on the quality of execution and control during the construction of the coating.

An object of the present invention is to provide a method of manufacturing a buried storage tank, in particular a buried tank for storing a fluid, in particular a liquid, having improved and durable resistance to cracking, easy to implement, economical and not requiring the use of a significant amount of materials.

Another object of the present invention is to provide a buried storage tank having improved and durable crack resistance.

The patent BE 418786 discloses a method of manufacturing a buried storage tank with radial prestressing, but without means to easily adjust this prestressing.

SUMMARY OF THE INVENTION

• on forme dans le sol une structure comportant une paroi extérieure formant un premier contour fermé délimitant un premier volume, un radier, et une paroi intérieure formant un deuxième contour fermé délimitant un espace de stockage étanche pour un fluide à l'intérieur du premier volume, de façon à ce que la paroi extérieure et la paroi intérieure soient espacées l'une de l'autre, de sorte qu'un espace intermédiaire est formé entre elles, et
• on applique sur la paroi intérieure une force de précontrainte orientée vers l'intérieur de l'espace de stockage, en remplissant l'espace intermédiaire avec au moins un fluide de précontrainte, de sorte que la paroi intérieure est soumise à une contrainte circonférentielle de compression, le fluide de précontrainte exerçant la force de précontrainte radiale sur la paroi intérieure, le fluide de précontrainte étant une matière durcissable, plus particulièrement une matière autodurcissable, et comprenant du béton, en particulier du béton à prise lente. Un deuxième volume de béton est introduit dans l'espace intermédiaire seulement une fois qu'un premier volume de béton a déjà fait prise (durci) à l'intérieur de l'espace. La pression maximale mesurée dans le béton peut ainsi être limitée.

A method of manufacturing a buried storage tank according to the present invention comprises at least the following steps:

• a structure is formed in the ground comprising an outer wall forming a first closed contour delimiting a first volume, a slab, and an inner wall forming a second closed contour delimiting a sealed storage space for a fluid inside the first volume, so that the outer wall and the inner wall are spaced from each other, so that an intermediate space is formed between them, and
• a prestressing force facing the inside of the storage space is applied to the inner wall, filling the intermediate space with at least one prestressing fluid, so that the inner wall is subjected to a circumferential compressive stress. , the prestressing fluid exerting the radial prestressing force on the inner wall, the prestressing fluid being a hardenable material, more particularly a self-hardening material, and comprising concrete, in particular slow setting concrete. A second volume of concrete is introduced into the intermediate space only once a first volume of concrete has already taken (hardened) inside the space. The maximum pressure measured in the concrete can thus be limited.

The inner wall forms an inner liner which delimits, within the first volume, a sealed storage space for a fluid to be stored. According to the present invention, this inner wall may be subjected to a radial prestressing force oriented towards the interior of the storage space before a fluid is introduced into this space for storage.

The inner wall is deformed inwardly of the storage space, and is subjected to a circumferential compressive stress.

In the case of a circular section structure extending about an axis, a radial direction is defined as a direction perpendicular to the axis of the structure and passing through this axis.

A circumferential stress applied to said structure is in this case orthoradial, that is to say perpendicular to such a radial direction and to the axis of the structure.

When the storage space is then filled with the stored fluid, the latter exerts on the inner wall a radial internal pressure, so that the inner wall tends to return to its initial position.

The circumferential stress due to the preload compensates for a portion of the circumferential tensile stress in the inner wall induced by said inner pressure, so that resulting tensile stresses in the inner wall are maintained at sufficiently small amplitudes to not require the implementation of substantial reinforcements, or even completely avoid the implementation of a reinforcement. The inner wall experiences limited traction, and crack formation is limited or even avoided.

As is known, the concrete walls usually retract during the setting of the concrete. With conventional construction methods where the inner wall is cast directly against the outer wall, creating a space between the two walls due to the shrinkage allows the inner wall to deform outwardly when filling the space storage with the stored fluid. The inner wall must then be further strengthened to limit cracking.

With the method according to the invention, the circumferential compressive stress created in the inner wall due to prestressing blocks the relative movement of the inner and outer walls so that the tension created in the inner wall, and consequently the width of the cracks created in it, are limited. Reinforcing means of the inner wall can therefore be even more limited or even omitted.

The rheology of the fluid and the casting sequence are advantageously chosen to adjust the pressure applied to the inner wall.

The method according to the invention may also comprise controlling the rate of introduction of the prestressing fluid into the intermediate space.

The method may also include controlling at least one pressure within the space.

According to an exemplary implementation, limit values for the minimum and maximum pressures of the prestressing fluid within the intermediate space are established before starting the casting.

According to an exemplary implementation, before the prestressing step, compression limit values of the inner wall during the filling of the intermediate space are predetermined.

According to an exemplary implementation, the top of the intermediate space is sealed, the sealed intermediate space remaining connected to pressurized feed means into a filling substance, and the filling substance is introduced into the space intermediate via said supply means so as to increase the prestressing force applied to the inner wall. Note that the filling substance is generally a fluid, which may be the prestressing fluid or which may be a different fluid, which may in this case be added after introduction of the prestressing fluid for example to adjust the prestressing pressure or increase this pressure during the life of the work, if it decreases.

To obtain the final compression aimed at any location of the coating, the prestressing of the inner wall can also be obtained (in addition or as an alternative to the method described above) using conventional methods. For example, the inner wall may be prestressed using prestressing frames, including frames installed horizontally around the inner wall. The reinforcements may be for example cables or bars.

The present invention also relates to a buried storage tank, in particular a tank for storing a fluid such as water, which can be obtained by the manufacturing method mentioned above.

The buried storage tank according to the invention comprises an underground structure comprising an outer wall forming a first closed contour delimiting a first volume, a slab, and an inner wall forming a second closed contour delimiting a fluid-tight storage space for a fluid. within the first volume, the reservoir being adapted to be in a filled state in which a fluid is stored in the storage space or in an empty state in which the storage space is empty, the reservoir comprising means preloading means for applying on the inner wall a prestressing force directed towards the inside of the storage space in at least one configuration, so that in the empty state of the reservoir the inner wall is stressed circumferential compression.

The outer wall and the inner wall are separated from each other by an intermediate layer, the intermediate layer comprising, as prestressing means, concrete that has set, which, in its fluid state, is provided for applying a force radial prestressing on the inner wall. More specifically, the intermediate layer comprises a first volume of set concrete and a second volume of concrete introduced only after the first volume has set.

The inner wall may be a concrete wall, particularly a reinforced concrete wall, or may be formed of steel.

The subterranean peripheral structure may have a circular or oval shape.

According to one embodiment, the intermediate layer can extend continuously over the entire periphery of the inner wall.

Except in the case of obvious incompatibility and unless otherwise indicated, features of an example embodiment or implementation described here may be applied to other examples of embodiment or implementation described.

BRIEF DESCRIPTION OF THE DRAWINGS

• La figure 1 est une vue en perspective d'une cuve de stockage enterrée selon la présente invention ;
• Les figures 2 à 5 sont des vues en coupe schématiques selon II-II de la figure 1, montrant les différentes étapes de fabrication de la cuve de stockage enterrée de la figure 1 selon un exemple de mise en œuvre de la présente invention ;
• Les figures 6a) à 6c) illustrent un deuxième exemple de mise en œuvre dans lequel un fluide de précontrainte est introduit dans l'espace dans un processus pas à pas ;
• La figure 7 illustre un troisième exemple de mise en œuvre dans lequel l'espace est scellé avant d'y introduire le fluide de précontrainte ;
• La figure 8 illustre un quatrième exemple de mise en œuvre dans lequel une précontrainte de la paroi intérieure est en outre obtenue à l'aide d'armatures de précontrainte horizontales ;
• Les figures 9, 9A et 9B illustrent un cinquième exemple de mise en œuvre dans lequel la paroi intérieure est en outre comprimée en utilisant des armatures de précontrainte verticales.

The invention will be better understood on reading the following description of embodiments of the invention given as non-limiting examples, with reference to the accompanying drawings, in which:

• The figure 1 is a perspective view of a buried storage tank according to the present invention;
• The Figures 2 to 5 are schematic sectional views along II-II of the figure 1 , showing the different stages of production of the underground storage tank of the figure 1 according to an exemplary implementation of the present invention;
• The Figures 6a) to 6c ) illustrate a second example of implementation in which a prestressing fluid is introduced into space in a step-by-step process;
• The figure 7 illustrates a third example of implementation in which the space is sealed before introducing the prestressing fluid therein;
• The figure 8 illustrates a fourth example of implementation in which a preload of the inner wall is further obtained using horizontal prestressing reinforcements;
• The Figures 9, 9A and 9B illustrate a fifth example of implementation in which the inner wall is further compressed using vertical prestressing bars.

In the drawings, identical references to the different views generally refer to the same elements.

DETAILED DESCRIPTION

The Figures 1 to 5 illustrate a buried storage tank according to an exemplary embodiment of the present invention, in particular a tank provided for storing fluids, and in particular liquids such as water. Such a reservoir has for example an outer diameter of between 10 and 60 meters, and a total height of between 10 and 100 meters.

The tank 100, shown in the figure 1 , comprises an underground structure comprising an outer wall 20 forming a first closed contour delimiting a first volume V1, a base 10, and an inner wall 30 forming a second closed contour delimiting, inside the first volume V1, a storage space S-tight for a stored fluid W.

In the present description, unless otherwise indicated, the bottom and the top of a structure are defined along a vertical axis, the lower part referring to the lower part of the structure, directed towards the depth of the ground.

In the example illustrated, the tank 100 is open at its upper end 100a. However, although this is not shown, it is also possible that the tank is provided with a cover structure.

In the present description, a filled state of the tank 100 is defined as a state in which a fluid is stored in the storage space S. On the other hand, a state where the storage space S is empty (that is, there is no fluid stored inside this space) is defined as an empty state of the tank 100.

As will be apparent from reading the description which follows, the reservoir comprises, in the example of the figure 1 , prestressing means provided in at least one configuration for applying to the inner wall 30 a radial prestressing force oriented towards the inside of the storage space and for applying at the same time to the outer wall 20 a Radial preload force oriented outward of the storage space. Because of said means, in the empty state of the reservoir, the inner wall 30 is subjected to a circumferential compressive stress.

When the reservoir 100 is filled with a stored fluid as shown in FIG. figure 1 , an internal pressure due to the stored fluid is exerted on the inner wall 30, inducing a circumferential tensile stress in said wall. Due to the prestressing, this tensile stress in the inner wall 30 is balanced by the already existing compressive stress, thus preventing the formation of cracks in the inner wall 30.

The structure of such a tank will be better understood in light of the manufacturing steps thereof described below with reference to Figures 2 to 5 .

Usually, the outer wall 20 is first formed in the ground G and the soil contained in the first volume V1 thus defined is then excavated. The raft 10 is then formed. The outer wall 20 and the base 10 thus form the basic structure of the reservoir shown on the figure 2 , which defines in the soil a correspondingly shaped excavation.

As shown for example on figures 1 and 2 the outer wall 20 forms a thick vertical retaining wall having its outer surface 20c in contact with the ground G. In the example illustrated, the outer wall 20 has a generally cylindrical shape extending around a main vertical axis X1 . In the example, when viewed in projection in a horizontal plane, the outer wall 20 has a circular shape. In other embodiments, however, the outer wall 20 may have any other suitable shape, particularly an oval shape.

The outer wall 20 is typically made of reinforced concrete. It can for example be realized by the technique of the walls molded in situ, in particular by producing a plurality of individual molded panels, afterwards or alternately. This example is not, however, limiting, and the outer wall can be manufactured also by the known technique of the Berlin walls or by sheet piling systems or any other technique suitable for the realization of deep foundations. The techniques mentioned above are well known to those skilled in the art and are not described in more detail here.

The raft 10 is connected to the outer wall 20, preferably sealingly. The raft 10 extends horizontally from the lower part of the outer wall 20, and is generally made of reinforced concrete.

As shown on the figure 3 the inner wall 30 is then formed to delimit, within the first volume, a sealed storage space S for the stored fluid W.

The inner wall 30 covers the outer wall from the inside and is connected to the base 10 in a sealed manner. Advantageously, watertight seals (not shown) may be provided at the junction of the inner wall 30 with the raft 10.

The inner wall 30 may be made of concrete, especially fiber-reinforced concrete. It can for example be constructed using the sliding formwork technique.

In the exemplary embodiment illustrated, the inner wall 30 has a cylindrical shape centered on the axis X1 and thus extends parallel to the outer wall 20. The inner wall 30 is spaced from the outer wall 20 in a radial direction ( that is to say a direction perpendicular to the axis X1 and intersecting this axis), over its entire circumference and here over its entire height. A ring or intermediate space 40 is thus formed between the inner and outer walls 30, 20.

In the present embodiment, the aforementioned compression circumferential stress in the inner wall 30 is obtained by introducing a prestressing fluid into the space 40, in a step illustrated in FIG. figure 4 .

In the example, the prestressing fluid is concrete (marked C in the drawings), which can be poured directly into the intermediate space 40 via one or more hoppers 42.

When the concrete C contained in the space is in its fluid state, due to the pressure of the concrete C, the inner wall 30 undergoes an inward deformation of the storage space, resulting in a circumferential compressive stress . The dashed lines D1 in the figure 4 show amplified the deformation of the inner wall 30.

Advantageously, limits for the minimum pressure and the maximum pressure of the concrete C inside the intermediate space are established before starting the casting, and means are used during the casting of the concrete C in the space intermediate 40, to monitor the pressure inside this space 40.

These means may comprise sensors 50 as illustrated on the figure 4 , such as pressure sensors, connected to the surface to provide real-time results to operators.

Advantageously, the concrete C is chosen to have a slow grip, so that it begins to take up the space 40 only after the intermediate space 40 has been completely filled, thus ensuring that the force of F1 pressure exerted by the poured concrete C at the lower end of the inner wall 30 is maximum.

As shown on the figures 1 and 5 the ring formed between the inner and outer walls 20, 30 forms an intermediate layer 70 of concrete. The intermediate layer forms a structure distinct from the outer and inner walls, a first and a second joining surface being clearly visible between the intermediate layer 70 and the outer wall 20 and the intermediate layer 70 and the inner wall 30, respectively. However, a molded construction between the outer and inner walls forms a unitary construction with said walls, preventing voids from being formed between them.

The figure 5 shows the reservoir once the concrete C has hardened and the storage space S has been filled with stored fluid, including water W.

The internal pressure exerted by the stored fluid W on the inner wall 30 is represented by the arrows F3, on the figure 5 .

The reaction of said inner wall 30, prestressed by the prestressing fluid C, is represented by the arrow F2.

As a result of the stored fluid pressure F3, the inner wall 30 tends to deform outward (i.e., out of the storage space), thereby inducing a circumferential tensile stress in the inner wall.

The circumferential compressive stress of the inner wall 30, due to the prestress, balances this tension resulting from the stored fluid pressure, so that the tensile stresses exerted on the inner wall remain at acceptable levels. The inner wall experiences limited traction, and crack formation is limited or even avoided.

The resulting deformation of the inner wall 30 is amplified by the dashed line D2, on the figure 5 .

In some cases, it is desired that the maximum pressure in the intermediate space does not exceed a predetermined value.

In addition, compression limit values applied to the inner wall 30 during filling of the intermediate space 40 may be pre-established and means (not shown) may be provided to control deformation of the inner wall 30 during prestressing, by example of strain gauges.

According to an exemplary implementation illustrated on the Figures 6a) to 6c ), it is possible, in order not to exceed these limit values, to control the rate of introduction of the concrete into the intermediate space.

In particular, the concrete C can be introduced in several phases in the space 40.

As shown on the figure 6a ), a first concrete volume C1 is introduced into the space 40 in order to fill a part (here the lower third) of the intermediate space 40.

After complete setting of the first volume of concrete, and as shown on the figure 6b ), a second volume of concrete C2 is introduced in the intermediate space, thus filling a second part (here a second third) of the space 40.

Then, after taking the second volume C2, a third volume of concrete C3 is introduced into space, above the first and second volumes C1, C2 ( Figure 6c )).

Since the maximum pressure in the concrete increases with the maximum height of liquid concrete, it is easily understood that, according to this multi-phase process, the maximum pressure measured in the concrete is limited in comparison with the embodiment described with reference to FIG. figure 4 . As a result, the prestressing force applied to the inner wall is also limited.

In other cases, on the other hand, the pressure obtained in the intermediate space at atmospheric pressure may not be sufficient.

In these cases, the top of the intermediate space can be sealed by a cover 62 as shown in FIG. figure 7 , and additional pressure can be applied.

The sealed intermediate space can be connected to supply means 60 configured to deliver a filling substance into this intermediate space, the filling substance being the same or different from the prestressing material, and the filling substance can be introduced into the intermediate space under pressure, via the supply means 60. The additional pressure can be applied from the top of the space, through a hole 64 formed in the cover 62, or through holes 66 placed in any locations of the inner wall 30, depending on the compression referred to each location.

The prestressing force applied to the inner wall is thus increased.

The exemplary embodiment of the figure 8 provides another solution to achieve the desired final compression at each location of the coating.

As illustrated, the prestressing of the inner wall is further improved here by prestressing reinforcements 80 arranged horizontally inside the intermediate space 40 and surrounding the inner wall 30. cables can be installed in the space 40 before introducing the prestressing fluid.

According to yet another embodiment illustrated on the Figures 9, 9A and 9B , the inner wall may be further prestressed using vertical prestressing reinforcements 82, for example anchored in the concrete base 10 and fixed to the upper end of the inner wall 30. As shown in FIG. Figure 9A which is a sectional view along line IXA-IXA of the figure 9 a plurality of cables 82 may be distributed in the circumferential direction, preferably in a regular manner.

The embodiments described above are however not limiting of the present invention.

As an example, the prestress fluid may not be a hardenable material such as concrete. The prestressing fluid may for example be water or any other fluid remaining in a liquid state.

In this case, the intermediate layer 70 is made of a liquid, the liquid exerting a force on the inner wall 30 inwardly of the storage space 10 throughout the life of the reservoir.

In addition, in this case, openings such as holes 64, 66 described with reference to FIG. figure 7 can advantageously be kept accessible so that prestressing fluid or any other filling substance can be added to the intermediate space in order to maintain the adequate pressure on the inner wall 30 throughout the life of the reservoir 100 .

Claims (10)

1. A method of fabricating a buried storage tank (100) comprising at least the following steps:

   • forming below ground a structure comprising an outer wall (20) forming a first enclosed periphery defining a first volume (V1), a raft (10), and an inner wall (30) forming a second enclosed periphery defining a fluid-tight storage space (S) for a fluid inside the first volume (V1), so that the outer wall (20) and the inner wall (30) are spaced apart from each other, whereby a gap (40) is formed between them; and

   • applying a prestressing force on the inner wall (30) directed towards the inside of the storage space (S), filling the gap (40) with at least one prestressing fluid (C), whereby the inner wall is subjected to compressive hoop stress, the prestressing fluid (C) exerting the prestressing force on the inner wall (30), the prestressing fluid (C) being a hardening material and comprising concrete, in particular slow-setting concrete; the method being characterized in that a second volume of concrete is introduced in the gap (30) only once a first volume of concrete has already set within the gap.
2. A method according to claim 1, further comprising monitoring the rate of introduction of the prestressing fluid (C) into the gap (40).
3. A method according to any one of claims 1 or 2, further comprising monitoring at least one pressure inside the gap (40).
4. A method according to any one of claims 1 to 3, further comprising sealing the top of the gap (40), the sealed gap remaining connected to supply means (60) for supplying a filling substance, and introducing the filling substance in the gap via said supply means (60) so as to increase the prestressing force applied on the inner wall (30).
5. A method according to any one of claims 1 to 4, wherein the inner wall (30) is formed after the outer wall (20) has been formed and the earth inside the first volume (V1) has been removed.
6. A method according to any one of claims 1 to 5, wherein the inner wall (30) is prestressed using prestressing reinforcement (80, 82).
7. A buried storage tank (100) comprising an underground structure including an outer wall (20) forming a first enclosed periphery defining a first volume (V1), a raft, and an inner wall (30) forming a second enclosed periphery defining a fluid-tight storage space (S) for a fluid inside the first volume, the tank being adapted to be in a filled state where a fluid is stored in the storage space or in an empty state where the storage space is empty, wherein the tank comprises prestressing means adapted for applying a prestressing force on the inner wall (30) directed towards the inside of the storage space (S) in at least one configuration, whereby, in the empty state of the tank, the inner wall (20) is subjected to compressive hoop stress, the outer wall (20) and the inner wall (30) being separated from each other by an intermediate layer (70), and the intermediate layer (70) comprising, as prestressing means, concrete having set,
   the tank (100) being characterized in that the intermediary layer comprises a first volume of concrete having set and a second volume of concrete introduced only once the first volume of concrete has set.
8. A buried storage tank (100) according to claim 7, wherein the intermediate layer (70) extends continuously around the entire periphery of the inner wall (30).
9. A buried storage tank (100) according to any one of claims 7 to 8, wherein the inner wall (30) is a concrete wall.
10. A buried storage tank (100) according to any one of claims 7 to 9, wherein the inner wall (30) is made of steel.

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