Soil reinforcement method and apparatus

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method and apparatus for reinforcing soil by improving the stiffness of soil.

In a further respect, the invention relates to a method and apparatus for constructing a structure at a selected building site.

In another respect, the invention relates to a method and apparatus for inexpensively improving the stiffness of soil supporting freeway embankments, water tanks, and other large loads which occupy large areas of ground, especially in situations where the soil supporting the large load is soft and is compressible by relatively light loads.

In still a further respect, the invention relates to a method and apparatus for supporting smaller structures, including buildings, storage silos, etc. which generate a smaller load on soil and occupy smaller areas of ground.

2. Description of the Related Art

My U.S. Pat. No. 5,249,892 describes aggregate piers which are constructed to improve the stiffness of soil. Each aggregate pier is constructed by forming a cavity in the ground and by then compacting layers of aggregate in the cavity to form a substantially stiff, dense aggregate pier. Each aggregate pier is typically ten to forty-five times stiffer than soil. The aggregate pier and soil surrounding the pier comprise a cell which has a composite stiffness about five to fifteen times greater than the stiffness of the soil without the pier. Although the aggregate pier is effective in increasing the stiffness of soil, the pier has disadvantages. In particular, it is not practical to install an aggregate pier which extends to great depths. If it is therefore desirable to improve the stiffness of soil at depths of greater than about twenty feet, an aggregate pier is not practical. In addition, in some cases it is not necessary to stiffen soil to the degree provided by an aggregate pier.

Accordingly, it would be highly desirable to provide an improved method and apparatus for increasing the stiffness of soil at depth of up to one hundred and fifty feet and at a cost which is significantly less than the cost of utilizing aggregate piers.

SUMMARY OF THE INVENTION

Therefore, it is a principal object of the invention to provide an improved method and apparatus for stiffening soil.

A further object of the instant invention is to provide an improved method and apparatus for stiffening soil at depths of up to one hundred and fifty feet.

Another object of the invention is to provide an improved method and apparatus which can be utilized to stiffen soil at a cost which is significantly less than that encountered in using aggregate piers or other soil reinforcing systems.

These and other further and more specific objects and advantages of the invention will be apparent to those skilled in the art from the following detailed description thereof, take in conjunction with the drawings, in which:

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1

is a side elevation view illustrating apparatus being installed in the ground at a building site to improve the stiffness of soil comprising the ground;

FIG. 2

is a side elevation view of the apparatus of

FIG. 1

illustrating further steps taken to install the apparatus in the ground at a building site;

FIG. 3

is a side elevation view illustrating a structure constructed at a building site using apparatus of the type shown in

FIGS. 1 and 2

;

FIG. 4

is a cross-section view of a portion of the apparatus of

FIG. 2

illustrating further construction details thereof;

FIG. 5

is a side elevation view illustrating one procedure for installing in the ground at a building site the apparatus illustrated in

FIGS. 1 and 2

;

FIG. 6

is an elevation view illustrating another procedure for installing in the ground at a building site apparatus constructed in accordance with the invention;

FIG. 7

is a perspective view illustrating a rectangular plate utilized in the procedure illustrated in

FIG. 6

;

FIG. 8

is a perspective view illustrating another plate which can be utilized in the procedure illustrated in

FIG. 6

; and,

FIG. 9

is a section view taken along section line

9

—

9

and illustrating further construction details of the procedure of FIG.

6

.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Briefly, in accordance with my invention, I provide an improved building site. The building site includes a section of ground including existing soil having an in situ density and in situ stress state, and includes a structure constructed on the section of ground. The improvements increase the stiffness of the soil and comprise a soil stiffening system. The soil stiffening system includes a cavity beneath the structure in the section of ground; and, at least one elongate expandable member in the cavity. The expandable member has a normal configuration, and an expanded configuration in which the member is distended. The soil stiffening system also includes a composition in the expandable member. The composition expands the expandable member from the normal configuration to the expanded configuration. The soil stiffening system further includes densified, stressed, strained soil adjacent the expandable member. The densified soil consists of at least one portion of the existing soil densified, stressed, and strained when the expandable member is expanded from the normal configuration to the expanded configuration.

In another embodiment of the invention, I provide an improved method for building a structure at a building site including a section of ground including existing soil having an in situ density and an in situ stress state. The method includes the steps of forming a cavity in the section of ground; and, providing at least one elongate expandable member. The expandable member has a normal configuration, and has an expanded configuration in which the member is distended from the normal configuration. The method also includes the steps of inserting the expandable member in the cavity in the normal configuration; of at least partially filling the expandable member with a composition to expand the expandable member to the expanded configuration, and to densify, strain, and stress portions of the soil adjacent the expandable member; and, of constructing the structure at the building site above the cavity and the expandable member in the cavity.

In a further embodiment of the invention, I provide an improved method for building a structure at a building site. The building site includes a section of ground including existing soil having an in situ density and an in situ stress state. The improved method includes the steps of forming a cavity in the section of ground; and, providing at least one elongate expandable member. The expandable member has a normal configuration, and has an expanded configuration in which the member is distended from the normal configuration. The method also includes the steps of inserting the expandable member in the ground beneath the cavity in the normal configuration; of at least partially filling the expandable member with a composition to expand said expandable member to said expanded configuration, and to densify, stress, and strain portions of the soil adjacent the expandable member; inserting aggregate in the cavity; of compacting the aggregate; and, of constructing the structure at the building site above the cavity and the expandable member in the cavity.

Turning now to the drawings, which depict the presently preferred embodiments of the invention for purpose of illustrating the invention and not by way of limitation of the scope of the invention, and in which like reference characters refer to corresponding elements throughout the several views,

FIG. 1

illustrates a soil stiffening system being constructed in accordance with the principles of the invention in a section of ground including soil

10

having an in situ density and an in situ stress state. The in situ density of the soil comprises the density prior to a building or other structure being constructed on the soil and prior to the insertion in the soil of aggregate piers or other structure to increase the stiffness of the soil. The in situ stress state includes the horizontal stress of the soil prior to a building or other structure being constructed on the soil and prior to the insertion in the soil of aggregate piers or other structures to increase the stiffness of the soil. The section of ground includes an upper surface

11

. During construction of the soil stiffening system, a cylindrical cavity

12

is formed in the ground. The shape and dimension of cavity

12

can vary as desired. The soil at the bottom

13

of the cavity is compacted to densify the soil at the bottom of the cavity. An elongate expandable member

14

is inserted in the ground in elongate cavity

15

. Cavity

15

extends downwardly from the bottom

13

of cavity

12

. Member

14

includes an upper section

16

and a lower section

17

. If desired, cavity

12

need not be formed in the ground, and member

14

(and cavity

15

) can simply extend downwardly from surface

11

. In addition, member

14

can extend downwardly from beneath a loaded member such as a footing, mat, or slab.

After member

14

is positioned in the ground in the position shown in

FIG. 1

, a hose

18

is used to direct, in the direction of arrow A, air, slurry, sand, foam, or another gas, liquid, or solid substance or composition or combination thereof into member

14

to expand member

14

into a desired shape and dimension.

FIG. 2

illustrates segments

16

and

17

after they have expanded into, by way of example, ellipsoid shapes. Segments

16

and

17

can, as noted, expand into any desired shape and dimension. When expandable segments

16

and

17

expand in the directions indicated by arrows E, F, H, and J, they displace, stress, strain, and densify soil which is adjacent segments

16

and

17

.

After segments

16

and

17

are expanded as desired, the lower portion of cavity

12

is filled with a quantity of loose, well-graded aggregate

19

. Other granular material besides loose, well-graded aggregate can be utilized. Well-graded aggregate is presently preferred because the larger particles in the aggregate impart substantial strength. The smaller particles in the aggregate fill the interstitial spaces between the larger particles. The depth or height of the layer of aggregate

19

can vary as desired but is presently in the range of six inches to three feet, preferably about eighteen inches.

The layer of aggregate is compacted with tamping apparatus including beveled head

21

and shaft

20

attached to head

21

. Head

21

and shaft

20

are displaced in the direction of arrow D, retracted in a direction oppositive arrow D, displaced in the direction of arrow D, etc. until the aggregate

19

is densified and produces lateral forces acting in the directions indicated by arrows B and C. The amount by which the layer of aggregate

19

is compressed by the tamping apparatus can vary as desired, but presently tamping reduces the height of the aggregate

19

layer by about one-third.

After the layer of aggregate

19

is compacted, an additional layer of loose aggregate is inserted in cavity

12

on top of the compacted layer of aggregate

19

. This additional layer is then compacted in a fashion similar to that utilized to compact the layer of aggregate

19

, and the process is repeated (i.e., additional layers of loose aggregate are inserted in cavity

12

and are compacted on top of existing previously compacted layers) until cavity

12

is filled.

Once cavity

12

is filled, additional cavities

50

to

54

are formed in the ground. The bottom of each cavity

50

to

54

is compacted (but, if desired, need not be compacted), and elongate expandable members

61

,

62

,

64

,

65

,

66

are each inserted into the ground through the bottom of a different one of the cavities

50

to

54

and are inflated or filled to expand into the ellipsoid-type shapes illustrated in FIG.

3

. When members

60

and

63

are inserted, a cavity

12

or

50

to

54

is not formed in the ground. Instead, members

60

and

63

are inserted in the ground, extend downwardly from the surface

11

, and are expanded to form the ellipsoid-type segments shown in FIG.

3

.

If desired, an expandable member

60

can be inserted in the ground such that the top end

60

A of member

60

is not positioned at surface

11

, but is spaced apart from and at a desired distance beneath surface

11

. In this scenario, member

60

is in the same vertical configuration illustrated in

FIG. 3

, with bottom end

60

B positioned beneath and spaced apart from top end

60

A. This occurs, for example, in

FIG. 3

if member

65

remains in the same position and if both cavity

53

and the aggregate in cavity

53

are not utilized.

The shortest distance Y between each pair of cavities

12

,

50

to

54

can vary as desired, but is presently preferably in the range of about one to ten feet. The maximum diameter or width of each cavity

12

,

50

to

54

can vary as desired, but is presently preferably in the range of about six inches to forty-eight inches. The shortest distance between each pair of expandable members

14

,

60

to

66

can vary as desired, but is presently preferably in the range of about two to ten feet. The maximum width G of each inflated or distended member

14

,

60

to

66

or segment

16

,

17

thereof can vary as desired, but is presently preferably in the range of about six inches to thirty-six inches.

After cavities

12

,

50

to

54

are formed and filled in the manner shown in

FIG. 3

, and after expandable members

14

,

60

to

66

are installed and expanded in the manner shown in

FIG. 3

, a water or other storage tank

40

or other structure is constructed on the ground. Alternately, as earlier noted above, under some circumstances, expandable members

14

,

60

are installed without the need for cavities

12

,

50

to

54

, and expandable members

14

,

60

to

66

are expanded generally in the manner shown in

FIG. 3

or in any other desired manner. Tank

40

generates significant or other forces on or in the soil generally beneath tank

40

in an area generally indicated by dashed line

70

. As is evidenced by dashed line

70

, some of the soil affected by and supporting tank

40

is not immediately beneath tank

40

. It is often advantageous to reinforce soil which is not directly beneath tank

40

but which still functions to reinforce and stiffen soil supporting tank

40

. Member

60

, for example, fulfills such a function.

The construction of an expandable member

14

,

60

to

66

can vary as desired.

FIG. 4

illustrates in greater detail a presently preferred construction of expandable segment

16

of member

14

. In

FIG. 4

, reference character

16

A indicate segment

16

prior to its being inflated. Reference character

16

B indicates segment

16

after it is inflated. Segment

16

includes an inner sealing layer

24

formed from a rubber, polypropylene, plastic or other expandable material. Layer

24

prevents the air or other composition which is used to fill and expand segment

16

from passing through layer

24

such that segment

16

deflates or contracts. In the event a concern exists that, for example, air utilized to inflate and expand a segment

16

will over time gradually permeate and escape outwardly through layer

24

and allow segment

16

to deflate, then segment

16

can be filled with sand, grout, foam, slurry or another material which solidifies and hardens. In the event segment does deflate or contract, one alternative is that air or another composition may be re-introduced in segment

16

to expand segment

16

a desired amount.

As illustrated in FIG.

1

and earlier noted, an expandable member

14

can include a plurality of separate segments. Or each segment

16

,

17

can comprise a separate member which can be utilized alone and stacked on or besides another segment.

Layer

23

is attached to and circumscribes layer

24

. Layer

23

is also expandable, but is porous and permits air, gas, or liquid to permeate layer

23

and travel upwardly to the surface

11

of the ground. Porous layer

23

facilitates the densification of soil because when air, gas, water or another fluid is permitted to escape from the soil, soil particles more readily travel toward one another and reduce the average distance and or space between the particles.

In

FIG. 4

, aperture

25

interconnects segments

16

and

17

such that when (in

FIG. 1

) air or another composition is directed in the direction of arrow A through hose

18

into segment

16

, the air can readily pass from segment

16

into segment

17

. A member

14

,

60

to

66

can consist of one or more segments

16

,

17

.

The installation of an expandable member

14

in soil can be accomplished by any desired method. One procedure for installing an expandable member

14

,

60

to

66

in the ground is to drive or push a hollow rectangular conduit or mandrel

32

into the ground to form a rectangular cavity

75

in the soil. When conduit

32

is being driven or pushed into the ground, lines

30

and

31

extend into the conduit

32

, through end

33

, and up and around the outside of conduit

32

. While conduit

32

is driven into the ground, lines

30

and

31

also are fed into the ground such that both ends of a line

30

,

31

remain above the ground and such that each line continues to extend into conduit

32

, through the bottom

33

of conduit

32

, and up along side the outer surface of conduit

32

to the surface

11

of the ground. When conduit

32

has reached its desired depth, one end of each of lines

30

and

31

is tied to the bottom

14

B of member

14

. Lines

30

and

31

are pulled in the directions indicated by arrows K and L, respectively, to draw the bottom

14

B down to the bottom

33

of conduit

32

. If desired, an anchor

70

can be attached to the bottom

14

B of member

14

to anchor bottom

14

B in the ground at the bottom of conduit

32

. Conduit

32

is then removed from the ground. Any other means can be utilized to anchor member

14

in the ground. Expanding segments

16

and

17

into the ellipsoid shapes shown in

FIG. 2

may function of its own accord to anchor member

14

in the ground such that additional anchoring mechanisms are not required.

In the relevant industry in which the invention is utilized, the terms hard, soft, loose, and dense sometimes refer to soil consistency, sometimes to soil strength, and sometimes to soil stiffness. For the sake of clarity and certainty, the following terms when utilized herein have the meanings set forth when used to describe soil consistency:

Hard:

not easily penetrated.

Soft:

easily penetrated.

Loose:

composed of particies capable of free

movement.

Dense:

composed of particles which are crowded

close together and which, because they are

crowded close together, tend to resist free

movement.

Stress:

the internal forces interacting between

particles of soil, caused by the extemal forces,

such as compression or shear, which produce

the strain.

Strain:

to cause alteration of form, shape, or volume

of a selected portion of soil.

Soil stiffness is the ability of soil to resist being compressed when subjected to a compressive load.

Soil densification is reducing the average space between particles making up soil.

Based on the foregoing, it is, for example, possible to have a soft soil like a rich, dry, loamy “peat moss”. It is also possible to have a soft soil comprised of small, interlocking volcanic particles. The particles are close together, but the soil is readily penetrated because the particles are each porous and are filled with air or water cavities. However, because the volcanic particles interlock, the volcanic particles may (unless the compressive force are sufficient to cause the volcanic particles to break) not readily compress and the soil may have significant stiffness and provide significant resistance to densification.

One application of anchor members

14

,

60

to

66

is for reinforcing subsoils at depths greater than the depths to which the aggregate piers extend. Members

14

,

60

to

66

presently extend to depths of two hundred feet, preferably to about one-hundred and fifty feet. If, for example, the aggregate pier comprised of cavity

12

and the tamped aggregate in cavity

12

extends from surface

11

to a depth of twenty feet, then member

14

can extend from a depth of twenty feet to a depth of one hundred feet such that end

14

B is one hundred feet beneath surface

11

.

The distance, indicated by arrows X in

FIG. 3

, between each adjacent pair

62

-

63

of expandable elastic members is in the range of two to ten feet, preferably about three to six feet. In loose sandy soil, utilizing elastic members

14

,

60

to

66

which are spaced apart about five feet enables the soil to support from 1000 to 7000 psf. If expandable members

14

,

60

to

66

are spaced apart three feet (instead of five feet), then the soil may support from 1,500 to about 10,000 psf.

In soft clay soil, utilizing expandable members

14

,

60

to

66

which are spaced apart about three feet will enable the soil to support from about 1,000 psf to 5,000 psf. When members

14

,

60

to

66

are spaced five feet apart, the soft clay soil will support from about 500 to 2,500 psf.

Members

14

,

60

to

66

can be formed in the ground beneath cylindrical tank

40

in a pattern generally similar to the pattern of holes which are formed in a calender in order to permit water to drain from the calendar. While the pattern of members

14

,

60

to

66

can vary as desired, it is presently preferred that each adjacent pair of members

14

,

60

to

66

be about one to ten feet apart.

The greatest inflated or distended width, indicated by arrows G, of a member

14

,

60

to

66

is presently in the range of about one-half to three feet, preferably about two feet. The soil which is densified by a member

14

,

60

to

66

extends from the outer surface of a segment

16

,

17

out to about fifteen to twenty inches from the outer surface of each segment

16

,

17

.

One advantage of members

14

,

60

to

66

is that the cost per foot of building and installing a member

14

,

60

to

66

is only about 15% to 30% of the cost per foot of building an aggregate pier. Another advantage is that members

14

,

60

to

66

can each readily extend to great depths of seventy-five feet or greater.

Each inflated member

14

,

60

to

66

preferably has a stiffness which can vary as desired but which presently is in the range of about five to twenty times greater than the stiffness of the soil in which member

14

,

60

to

66

is utilized. A cell includes the inflated member

14

,

60

to

66

in soil and includes the soil which is adjacent the inflated member and extends outwardly from member

14

,

60

to

66

a distance equal to the distance from the outer surface of member

14

,

60

to

66

(for example, member

62

in

FIG. 3

) to about half-way between a member

14

,

60

to

66

and the closest adjacent member

14

,

60

to

66

(for example, member

63

in FIG.

3

). The cell has a stiffness which typically, but not necessarily, is two to ten times the stiffness of the soil in which member

14

,

60

to

66

is utilized.

Utilization of members

14

,

60

to

66

in accordance with the invention produces a greater proportional increase in soil stiffness when members

14

,

60

to

66

are utilized in soft clays, soft silts, and loose sands. The invention can, however, be utilized to stiffen clays, silts, and sands which are harder and denser than said soft clays, soft silts, and loose sands; can also be utilized to stiffen peat and organic soils and landfills; and, can be used to generate stresses and strains in almost all types and classifications of soils.

When the stiffness of a soil need only be increased by two to five times, members

14

,

60

to

66

can often be utilized without aggregate piers or other soil reinforcement or modification systems or components. Examples of circumstances where a system of members

14

,

60

to

66

can be utilized alone are (1) the existing soil is not very compressible, (2) the load which must be supported by the soil is limited, and (3) the allowed settlement of the structure on the existing soil (i.e., the distance a building or load compresses or displaces soil and “sinks” after a building or other load is placed on the soil) is greater than normal. An example of the latter is a highway embankment. The settlement allowed for a highway embankment can be six to twelve inches. An example of a light load is the load generated by a large 200 foot diameter water tank which is forty feet high. The water tank will generate a load of about 2500 psf.

In

FIG. 3

, the depth of the upper zone of soil equal the depth to which each cavity

12

,

50

to

54

is drilled (say, for example, twenty feet) plus the diameter of each cavity (say two feet). Consequently, the depth of the upper zone is twenty-two feet. The lower zone comprises the soil below the upper zone and has a depth which extends downwardly from the upper zone to the bottom of the lower zone. The soil in the upper and lower zones performs in large part the function of supporting tank

40

. By way of example, and not limitation, the greatest depth of the lower zone typically is about equal to twice the diameter of tank

40

.

In

FIG. 3

, members

14

,

60

to

66

are particularly useful in stiffening soil in the lower zone. This is especially the case because it is not presently economically practical to build aggregate piers which extend to a depth beyond about twenty feet.

As noted earlier, in

FIG. 4

dashed lines

16

A indicate member

16

prior to its being expanded. Prior to its being expanded, the member

16

illustrated by way of example, and not limitation, in the drawings has the generally rectangular cross-sectional area shown in FIG.

4

. Reference character

16

B indicates member

16

after it has been inflated or otherwise expanded into an arcuate shape having the elliptical cross section illustrated in FIG.

4

. Reference character

16

C indicates the outer arcuate surface of member

16

after it has been expanded

16

B. The elliptical cross-sectional area of member

16

after it is expanded

16

B is presently 1.5 to 6.0 times greater, preferably about 2.0 to 5.0 times greater, than the rectangular cross-sectional area

16

A of member

16

prior to the expansion of member

16

. In addition, it is preferred that the cavity

75

which is formed in soil to receive member

16

conforms with as little deviation as practically possible to the outer shape and dimension of member

16

prior to member

16

being inflated or otherwise expanded. This is desirable because it means that member

16

ordinarily will have to densify, stress, and strain a greater volume of soil in order for member

16

to fully expand to its desired shape and dimension

16

B. In contrast, if the cavity

75

formed in the ground for member

16

has a greater width than the greatest width G of member

16

when member

16

is fully expanded, then member

16

will densify, stress, or strain little, if any, soil immediately adjacent the cavity formed for member

16

. Accordingly, not only does expanding member

16

after it is inserted in soil function to increase the cross sectional area of member

16

by a factor in the range of 1.5 to 6.0 times, such expansion also functions (when the cross-sectional area and shape and dimension of the cavity is similar to that of member

16

prior to expanding

16

A member

16

) to increase by about 1.5 to 6.0 times the cross-sectional area of the cavity

75

in which member

16

is inserted prior to expanding member

16

. Such expansion of member

16

and of the cavity

75

is important for several reasons. First, the expanded member

16

usually will have a greater stiffness than the existing soil. Consequently, the greater the expansion of member

16

, the greater the volume in the soil which is stiffened by member

16

. Second, the expansion of member

16

also increases the volume of the resulting cell. The resulting cell includes member

16

and soil which is in the immediate vicinity of member

16

and which is densified, stressed, and strained when member

16

is expanded. Third, expanding cavity

75

by expanding member

16

functions to density, stress, and strain soil adjacent member

16

.

As used herein, the cross-sectional area of a member

16

is the cross-sectional area at a selected point along the length of member

16

. The cross-sectional area of a member

16

typically, but not necessarily, will be determined at a point along member

16

where the cross-sectional area is greatest. This is the case, for example, in

FIG. 2

where the cross-section indicated by arrows

4

and illustrated in

FIG. 4

is taken at a point along the longitude of member

14

where the cross-sectional area of expanded member

16

is greatest. Similarly, the cross-sectional area of a cavity

75

is the cross-sectional area at a selected point along the length of cavity

75

. The cross-sectional area of a cavity

75

typically, but not necessarily, will be determined at a point along member

16

where the cross-sectional area is greatest.

FIGS. 6 and 9

illustrate another method of installing in the ground an expandable member

87

constructed in accordance with the invention. The apparatus utilized in

FIG. 6

includes a rectangular steel plate

81

, an expandable member

87

, and a hollow rectangular mandrel

86

. The lower end

89

of member

87

is permanently affixed to plate

81

. Elliptically shaped member

87

includes an arcuate front face

88

. Mandrel

86

includes rectangularly shaped interconnected sides

88

,

90

to

92

.

Opening or hole

80

is formed in the ground

11

by using mandrel

86

or other means to drive plate

81

into the ground in the manner illustrated in FIG.

6

. While mandrel

86

drives plate

81

into the ground, mandrel

86

extends over and temporarily “houses” member

87

as shown in

FIGS. 6 and 9

. After plate

81

is driven by mandrel

86

to a selected depth, mandrel

86

is withdrawn from the ground, leaving plate

81

and member

87

in the ground. Member

87

is then inflated or otherwise expanded to compress, stress, and strain soil adjacent opening

80

.

The shape and dimension of plate

81

can vary as desired. By way of example, and not limitation, the length P (

FIG. 7

) of plate

81

is presently in the range of six inches to eighteen inches. The width Q of plate

81

is presently in the range of one to six inches. Plate

81

may take on the oval shape of the plate

84

illustrated in

FIG. 8

, or can take on any other shape and dimension.

Number	Name	Date	Kind
4334345	Jenks	Jun 1982	A
5202522	Williams	Apr 1993	A
5249892	Fox et al.	Oct 1993	A

Soil reinforcement method and apparatus

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