Storage Facility With Integral Foundation

This invention relates to storage facilities. More specifically, this invention relates to a partially submerged storage facility such as a circular tank and a process for the construction of such a storage facility.

Storage facilities for holding liquid products, such as petroleum, have commonly heretofore consisted of steel tanks. Such steel tanks have static heads of product in them which, with increasing heights, require increasingly thick conventional steel sidewalls to resist the static heads of fluid pressure within the tank. Typically, the tanks, at their steel plate, resist pressure internally of the tank with tension. As the tank height increases, especially above the level of 72 feet, the plate necessary to provide the requisite tension at the bottom of the tank to counteract internal static heads of pressure has to be so thick that the tank often becomes uneconomical.

A further problem with existent steel storage facilities, such as tanks, is that such storage facilities have to be placed on conventional foundations. These storage facilities on conventional foundations with their interior heavy loads have been found to settle. Slight angular settlement of the tank presents structural difficulties and can result in tank failure. Moreover, where tanks are provided with a circular floating top, the respective sides of the tank become elliptical in horizontal section when differential settlement on a conventional foundation occurs. As the floating top remains circular, it can bind and therefore remain unable to rise upwardly and downwardly of the tank sidewalls as the level of product stored within the tank rises upwardly and downwardly.

Finally, it is noted that "farms" of storage facilities containing combustible or corrosive products are required world-wide to be subdivided with soid dikes. Each separate storage facility must contain a soil dike about it capable of containing the entire contents of the surrounded storage facility in the event that the storage facility is ruptured. This diking requirement uses much land, requires additional expense in the excavations required to make the dikes, and finally produces storage facility "tank farms" that become a double eyesore not only because of the presence of the discrete storage facilities or tanks themselves, but also because of the required dikes.

A process of constructing a storage facility, such as a tank, and the resultant storage facility product having an integral foundation is disclosed. Typically, piles having conjoining sides (preferably of the tongue and groove variety) are driven into the earth along a proposed storage facility perimeter and pressure grouted along their conjoined sides to form a watertight perimeter. The piles forming the closed pile perimeter penetrate into the earth a substantial portion of their length and preferably extend into impervious soil strata. This penetration into impervious soil strata occurs to a depth where either the percolation of any acquifier into the storage facility or the leakage of product from the storage facility can be prevented by ambient soil strata. After installation of the closed pile perimeter, soil is thereafter excavated below the existent ground level from the interior of the closed pile perimeter to the intended storage facility depth. The excavated soil is placed in a preferably compacted embankment immediately exterior of the closed pile perimeter where it extends above the ambient ground level. The compacted soil embankment forms a static head inwardly on the pile perimeter that exceeds anticipated static heads for the stored product within the storage facility. This compacted embankment together with the subterranean portion of the pile perimeter is maintained in a closed fluid-tight relation by the soil pressure arching adjacent piles compressively together. During excavation, wales are placed against the storage facility sides, preferably by casting the wales in place as excavation proceeds. When the excavation reaches the full tank depth, the tank bottom is finished typically by a concrete rat slab. A conventional top is then provided. The resultant finished storage facility utilizes pile sidewalls, has an integral foundation, and is held together with an earth dike to provide an inexpensive storage facility preferable for the storage of petroleum or other fluid products.

An object of this invention is to disclose a process for storage facility construction which utilizes concrete construction in lieu of steel construction. According to this aspect, a closed pile perimeter is first constructed. Upon excavation of the interior of the closed pile perimeter, the pile perimeter is compressed together and the interior storage volume is simultaneously defined.

An advantage of this invention is that pile sidewalls under compression are substituted for steel sidewalls under tension for resisting loading due to stored products within the facility. Concrete under compression can be substituted for steel under tension. Cost of the storage facility is vastly reduced.

A further advantage of this invention is to substitute modern foundation construction techniques for steel fabricated techniques in the construction of a storage facility, such as a tank.

A further object of this invention is to disclose piles for providing a closed pile perimeter suitable for forming the sides of a liquid product storage facility. According to this aspect, adjacent piles are provided with conjoining adjacent sides having mating tongues and grooves to form a closed pile perimeter. Additionally, the piles, when driven in the ground, are tapered so that each driven pile biases towards an adjacent previously installed pile.

An advantage of the piles utilized with this invention is that they are urged into a contiguous conjoinder in side-by-side relation when driven. The achieving of a side-by-side liquid impervious barrier between adjacent piles is facilitated.

A further object of this invention is to disclose a storage facility which uses underground soil pressure to hold it together. According to this aspect of the invention, a closed pile perimeter has its interior excavated. Soil pressure from the outside exceeds stored product pressure from the inside. The result is that the sidewalls of the storage facility, formed from contiguous and conjoined piles, is always under radial compression between adjacent piles to assure a fluid-tight storage facility perimeter.

A further advantage of this invention is that the natural inwart thrust of the ambient soil is utilized to hold the foundation of the storage facility in place.

A further object of this invention is to disclose an underground storage facility having an integral foundation. According to this aspect, the interior of a closed pile perimeter is excavated. The soil exterior of the excavation becomes the storage facility foundation.

An advantage of this integral foundation is that a conventional foundation for the storage facility is not required. Rather, the foundation perimeter and the storage facility perimeter are one in the same.

A further object of this invention is to construct integrally with a submerged storage facility, such as a petroleum storage tank, an integral soil dike. According to this aspect, portions of the closed pile perimeter are allowed to protruce upwardly and above the ambient ground level. Soil excavated from the interior of the pile perimeter is stacked around and about those portions of the soil perimeter extending above ambient ground level.

An advantage of this aspect of the invention is that the soil dike can be used to hold the tank together at elevations above ground level by compressing inwardly on the closed pile perimeter above ground level.

A further advantage is that the soil dike can simultaneously serve as an emergency barrier to contain product in the event that the pile perimeter is ruptured.

Yet a further advantage of this aspect of the invention is that the soil dike forms a convenient location immediate the excavated storage facility for the placement of soil from the interior of the storage facility.

Yet another advantage of this aspect of the invention is that adjacent storage facilities can be placed in closer relationship. The expanse of land used in forming a so-called "farm" of storage facilities can be vastly reduced.

Yet another advantage of this aspect of the invention is that the eyesore resulting from a storage facility "farm" is minimized. The bulk of the storage facility is subterranean. That portion of the storage facility above ground is embanked in soil, and capable of blending on an unobtrusive basis into the landscape.

Yet another advantage of the storage facility of this invention is that the resultant tank is virtually maintenance free. As the sidewalls of the tank are typically concrete and not metal, preservative techniques utilized in the maintenance of metal storage facilities need not be used to maintain storage facilities constructed in accordance with this invention.

Other objects, features and advantages of this invention will become more apparent after referring to the following specification and attached drawings in which:

FIG. 1 is a vertical section of soil strata taken through the ground illustrating in phantom the partial installation of a closed pile perimeter with a series of piles installed and one pile being driven to form the closed pile perimeter;

FIG. 2 is an enlarged vertical section in perspective taken along lines 2--2 of FIG. 1 vertically broken away, illustrating the pile being driven alongside of a previously installed pile and showing the conjoinder of the piles at adjacent tongue and groove section;

FIG. 3 is a perspective vertical section similar to FIG. 1 illustrating the placement of a ground level concrete wale around the interior of closed pile perimeter with excavation occurring interior of the storage facility, and the excavation spoils being stacked and compacted exterior of the storage facility to form a dike about the upper portion of the storage facility; and,

FIG. 4 is a cross sectional configuration of the storage facility similar to FIG. 1 with the storage facility constructed to its full depth, the respective cast-in-place concrete wales reinforcing the storage facility sidewalls, a finished rat slab poured on the bottom of the storage facility, and the side of the storage facility finished in concrete "gunite" construction.

Referring to FIG. 1, a vertical cross section is shown taken through a typical site for the installation of the storage facility. Various soil strata, typically of the sedimentary type, are illustrated in strata 14, 16, 18 and 20. It is preferable that the storage facility be installed to penetrate to an impermeable soil strata, here indicated as stratum 20.

A closed pile perimeter A is formed about the boundary of the storage facility. PErimeter A includes a series of discrete piles 24 driven in conjoined and contiguous side-by-side relation. These piles, as hereinafter will be more fully set forth, constitute the sidewalls of the storage facility.

Referring to FIG. 2, the installation of adjacent piles 24a and 24b is illustrated. To understand the adjacent installation of the piles 24a and 24b, the configuration of the piles will first be discussed. Thereafter, the process of their installation can be easily set forth.

Pile 24a is typical. Preferably, each pile is made from pre-cast concrete having a compressive strength of the concrete on the order of 8000 psi. The piles are preferably prestressed. Pile 24a is installed to a predetermined depth. This installation occurs by typical pile installation techniques such as pile drivers using conventional leads and the like.

Pile 24a at side 25a includes a groove 27a which is semicircular in shape. Groove 27a extends along side 25a to the bottom of pile 24a. This groove enables conjoinder of one pile to an immediately adjacent pile and further permits pressure grouting of the two piles along their adjoined sides to assure a fluid-tight interface between the two piles. This conjoinder, by pressure grouting, forms a grout cylinder 29a which will hereinafter be discussed.

Pile 24a includes a second side 26a. Side 26a includes a groove 28a. Groove 28a is semicircular in section and extends along the entire side 26a from the top of the pile 24a to the bottom of pile 24a.

The bottom of pile 24a includes two features. It includes a tapered end which can be driven into the ground and a short tongue. These features can best be observed at the bottom of pile 24b, which bottom is identical to the bottom of pile 24a (not shown).

Referring to pile 24b of FIG. 2, the lower end of semicircular groove 27b can be observed. This groove terminates at a tongue 30b. Tongue 30b is semicircular in shape and made to ride interiorly of groove 28a of pile 24a.

The tapered end 32 of pile 24b can be observed. This end tapers from side 25b of pile 24b to side 26b. This taper assures that pile 24b, when driven, is biased towards pile 24a.

The installation of the conjoining piles can now easily be explained. With at least one pile 24a installed, a pile 24b is moved into juxtaposition to pile 24a with side 25b of pile 24b confronted to side 26a of pile 24a. Tongue 30b of pile 24b is placed interiorly of groove 28a of pile 24a. Thereafter, pile 24b is conventionally driven downwardly into the ground in precise side-by-side juxtaposition to pile 24a. During this driving, tapered end 32 of pile 24b urges pile 24b towards pile 24a to closely confront side 26a of pile 24a with side 25b of pile 24b.

When pile 24b has been fully driven into the ground, it will be seen that the two grooves 28a of pile 24a, and 27b of pile 24b will confront one another. The two semicircular section grooves 28a and 27b will define a cylindrical volume. This volume is first drilled clean to remove earth and the like. Thereafter, grout is forced into the groove preferably by a tremie installation to provide a fluid-tight seal between adjacent piles. This process is commonly referred to as "pressure grouting" and forms a grout cylinder similar to grout cylinder 29a.

It should be realized that the process of installing adjacent piles, drilling clean the cylindrical volume defined between the piles, and pressure grouting the cylindrical volumes between them can occur at different portions of the pile perimeter at different times. For example, all of the piles could first be driven in place. Thereafter, all of the piles could have their respective confronting grooves drilled, and finally all of the piles could be pressure grouted. Alternately, the sequence of driving the piles, drilling the holes, and pressure grouting the holes can be varied to conform to the efficiencies of construction. Typically, the piles will be driven to form a circular or elliptical continuous and closed pile perimeter. Referring to the views of FIGS. 3 and 4, a circular perimeter is illustrated. It will be immediately realized that only one half of the circular perimeter is there shown. The remaining half is omitted so that the internal construction of the storage facility can be more easily illustrated.

Referring to FIG. 3, the remaining steps of construction of the storage facility together with the finished product can be understood.

First, a concrete wale 36 is typically cast in place at ground level about the interior of the closed pile perimeter. As will hereinafter be more fully understood, when the storage facility is empty, ambient earth from the outside will tend to push inwardly towards the inside. In the event of non-uniform pressures against the perimeter wall, collapse of the pile perimeter could occur. Wale 36 serves to resist such collapse.

It should be further appreciated that although wale 36 is preferably herein described as being cast in place, it could just as well be pre-cast and later installed at the site. Likewise, such a wale could be used as a guide placed in the ground first. Thereafter the pile perimeter could be driven around it as heretofore described.

Once wale 36 has been cast in place, excavation of the volume 40 interior of the storage facility occurs. Earth spoils from the interior of the storage facility are embanked in a compacted embankment 42 above the ambient ground level and on the outside of closed pile perimeter 34. Thus, it is seen that excavation spoils are moved a relatively short distance. They are moved from the subterranean volume of the storage facility to the immediately adjacent and above ground outside perimeter of the closed pile perimeter 34.

Referring to FIG. 4, a cross section of the completed underground storage facility according to this invention is illustrated. The interior volume 50 of the storage facility has been completely excavated. A compacted soil embankment 42 has been placed peripherally about that portion of the closed pile perimeter 34 which extends above the ambient ground level. A bottom wale 38 has been cast around the bottom portion of excavated volume 50. This bottom wale prevents the closed pile perimeter 34 from collapsing inwardly. Likewise, an upper wale 39 has been poured over the topmost portion of closed pile perimeter 34. Upper wale 39 caps the pile perimeter and at the same time prevents the pile perimeter 34 at the top from collapsing inwardly.

Preferably, the wales 36, 38 and 39 are sized to permit radial compression of the closed pile perimeter. Thus, the ambient forces of the earth loading exteriorly of the pile perimeter 34 radially compresses the piles along their conjoined sides into close and contiguous side-by-side relation. A fluid-tight storage facility perimeter results.

The tank is finished at the bottom by rat slab 52. Dependent upon soil conditions, a thicker mat could be used. Likewise, along the tank side a gunite concrete finish 54 or thin sheet metal finish can be applied.

Upon completion of the storage facility, a top can be added. Preferably, the top used with this type of tank is a conventional fixed top to completely enclose the storage facility. It should be understood, however, that floating tops and the like can be used.

It should be understood that soil pressure from the storage facility exterior is always designed to be greater than product pressure from the tank interior. This effect is schematically illustrated by graphs 60, 62. Consequently, radial compression of closed pile perimeter 34 will always be present to maintain a fluid-tight perimeter.