Method and apparatus for forming successive overlapping voids in the ground along a predetermined course of travel and for producing a subterranean wall therein

A method and an apparatus is provided for forming successive overlapping voids in the ground along a predetermined course of travel and for producing a subterranean wall therein. The apparatus includes a mandrel for forming voids in the ground, and a pattern guide templet having repeating contours arranged on the ground for accurately guiding the mandrel along the predetermined course of travel during successive mandrel insertions. The mandrel includes a plurality of downwardly projecting spaced-apart cutting teeth for facilitating penetration of the mandrel into the ground, and a plurality of downwardly projecting high pressure nozzles for discharging an injectable material (e.g., slurry material or water) into the ground as the mandrel is inserted therein. The repeating contours of the pattern guide templet accurately receive and accommodate the cross-sectional shape of the mandrel during successive mandrel insertions so that successive overlapping voids are formed in the ground along the predetermined course of travel. The apparatus of the present invention further includes an installation rig for inserting structural elements into the successive overlapping voids formed by the mandrel. In this way, a subterranean wall comprised of liquid impervious slurry material and/or contiguous structural elements may be conveniently produced in the successive overlapping voids.

TECHNICAL FIELD OF THE INVENTION 
The present invention relates generally to the formation of subterranean 
voids and walls and, more particularly, to a method and apparatus for 
producing successive overlapping voids in the ground along a predetermined 
course of travel so that a subterranean wall comprised of liquid 
impervious slurry material and/or contiguous structural elements may be 
accurately formed therein. 
BACKGROUND OF THE INVENTION 
It is frequently desirable and sometimes necessary to construct 
subterranean voids and walls. Subterranean walls are commonly used, for 
example, to insulate and protect a site (e.g., an environmental clean-up 
site, a construction site, etc.) from ground water seepage. Such walls are 
typically formed of slurry material (i.e., a gradually solidifying 
grout-like bonding agent which provides a liquid impervious shield) and/or 
structural elements (e.g., sheet metal pilings). Conventional slurry 
materials include cement, bentonite, and/or clay. Of course, a suitable 
subterranean void is needed to accommodate such a subterranean wall. 
Various techniques for constructing subterranean walls are known in the 
art. A first, somewhat rudimentary, technique involves excavating a trench 
with a backhoe or the like, and then filling the trench with a barrier 
material, such as sheet metal pilings and/or slurry material, to produce a 
subterranean wall therein. A second, more advanced, technique involves 
driving a beam or mandrel into the ground to form a void, injecting slurry 
material into the void as the beam is extracted therefrom to fill the 
void, and then advancing the beam along the ground to a position where the 
beam overlaps a portion of the previously formed and filled void. This 
procedure is repeated until a desired length of successive overlapping 
voids is formed in the ground. Because the overlapping voids are 
immediately filled with slurry material, a subterranean slurry wall is 
produced therein. 
Both of these techniques, however, suffer from noted deficiencies. The 
first is expensive, time consuming, and labor intensive, while the second 
is somewhat unreliable in terms of precision. More specifically, the 
second technique provides no reliable way to accurately guide the beam 
during successive beam insertions. As a consequence, the successive 
overlapping voids and the resulting slurry wall often deviate from the 
planned course of travel. The second technique is also inadequate for 
penetrating through dense soil layers. 
OBJECTS AND SUMMARY OF THE INVENTION 
Accordingly, a primary object of the present invention is to provide a 
method and apparatus for accurately forming successive overlapping voids 
in the ground along a predetermined course of travel. 
A related object of the present invention is to provide a method and 
apparatus for constructing a uniform subterranean wall in the successive 
overlapping voids. 
A more specific object of the present invention is to provide a method and 
apparatus for constructing a subterranean wall comprised of liquid 
impervious slurry material. 
A related object of the present invention is to provide a method and 
apparatus for constructing a subterranean structural wall comprised of 
contiguous structural elements (e.g., interconnected sheet metal pilings). 
A further related object of the present invention is to provide a method 
and apparatus for constructing a subterranean wall comprised of liquid 
impervious slurry material and contiguous structural elements. 
Another object of the present invention is to provide a method and 
apparatus for forming successive overlapping voids through dense soil 
layers. 
A related object of the present invention is to provide a method and 
apparatus for installing structural elements (e.g., sheet metal pilings) 
through dense soil layers. 
A collateral object of the present invention is to provide a method and 
apparatus for insulating and protecting a site from ground water seepage. 
Still another object of the present invention is to provide a method and 
apparatus having the foregoing characteristics which is dependable, 
durable, and convenient to use. 
In accordance with these and other objects, a method and an apparatus is 
provided for forming successive overlapping voids in the ground along a 
predetermined course of travel and for producing a subterranean wall 
therein. The apparatus includes a mandrel for forming voids in the ground, 
and a pattern guide templet arranged on the ground for accurately guiding 
the mandrel along the predetermined course of travel during successive 
mandrel insertions. More specifically, the mandrel includes a plurality of 
downwardly projecting spaced-apart cutting teeth for facilitating 
penetration of the mandrel into the ground, and a plurality of downwardly 
projecting high pressure nozzles for discharging an injectable material 
(e.g., slurry material or water) into the ground as the mandrel is 
inserted therein. The pattern guide templet accurately receives and 
accommodates the cross-sectional shape of the mandrel during successive 
mandrel insertions so that successive overlapping voids are formed in the 
ground along the predetermined course of travel. The apparatus of the 
present invention further includes an installation rig for inserting 
structural elements into the successive overlapping voids formed by the 
mandrel. In this way, a subterranean wall comprised of liquid impervious 
slurry material and/or contiguous structural elements may be conveniently 
produced in the successive overlapping voids. 
These and other objects, features, and advantages of the present invention 
will become apparent upon reading the following detailed description of 
the preferred embodiment, and upon reference to the accompanying drawings.

While the present invention will be described and disclosed in connection 
with a preferred embodiment and procedure, it will be understood that we 
do not intend to limit our invention to what is shown and described. On 
the contrary, we intend to cover all such alternatives, modifications, and 
equivalents that fall within the spirit and scope of the present invention 
as defined by the appended claims. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, an apparatus constructed in accordance with 
the teachings of the present invention is generally designated by 
reference numeral 20, as shown, for example, in FIG. 1. In use, the 
apparatus 20 accurately forms successive overlapping voids 12 in the 
ground 10 along a predetermined course of travel 18, and also produces a 
subterranean wall comprised of liquid impervious slurry material and/or 
contiguous structural elements therein, as schematically illustrated in 
FIGS. 6-8. Such walls are frequently used, for example, to isolate 
environmental clean-up sites, and the like, from ground water seepage. 
In accordance with certain objects of the present invention, the apparatus 
20 includes a mandrel 30 which is inserted into the ground 10 to form 
voids or cavities, and a pattern guide templet 130 which accurately guides 
the mandrel 30 along the predetermined course of travel 18 during 
successive mandrel insertions. As best shown in FIG. 6, the pattern guide 
templet 130 comprises a plurality of repeating contours 132 attached to a 
stabilization member 134. Each repeating contour 132 is configured to 
receive and accommodate the mandrel 30. 
In the illustrated embodiment, a crane 90 is provided for vertically 
supporting the mandrel 30 during each insertion. As best depicted in FIGS. 
1, 7, and 8, the crane 90 is maneuverable along the ground 10 by crawler 
tracks 92 and includes a boom 94 and a hoist line 96. Suspended from the 
hoist line 96 is a vibratory driver 100 which is also coupled to the 
mandrel 30. In operation, the vibratory driver 100 applies a substantially 
vertical vibratory force to the mandrel 30 which causes the mandrel 30 to 
penetrate the ground 10. A guide support 110 attached to the crane 90 
vertically aligns and slidably guides the mandrel 30 as the mandrel 30 is 
driven into the ground 10 by the vibratory driver 100. 
As illustrated in FIGS. 2-5, the mandrel 30 of the present invention 
includes a top portion 32 which is attachable to the vibratory driver 100, 
and a bottom portion 42 which penetrates the ground 10. The top portion 32 
of the mandrel 30 includes a clamping plate 34 which is releasibly 
attached to the vibratory driver 100 via a hydraulic clamp, or the like 
(not shown), while the bottom portion 42 includes a shoe 44. The mandrel 
30 also has a length 64, a longitudinal axis 66, and a cross-sectional 
shape. In practice, the length 64 of the mandrel 30 is contingent upon the 
desired depth of the voids 12, but may be on the order of one-hundred feet 
or more. 
In order to facilitate penetration of the mandrel 30 through the ground 10, 
the shoe 44 of the mandrel 30 includes a plurality of downwardly 
projecting cutting teeth 46. The cutting teeth 46 are preferably 
spaced-apart and include hardened surfaces for wear protection. The shoe 
44 of the mandrel 30 also includes a plurality of downwardly projecting 
high pressure nozzles 54 for discharging injectable material (i.e., slurry 
material or water) into the ground 10 as the mandrel 30 is inserted 
therein. In the illustrated embodiment, the high pressure nozzles 54 are 
fluidically connected to a manifold or plenum 52 disposed within the shoe 
44 which, in turn, is fluidically connected to high pressure piping 72 
arranged on either side of the mandrel 30. As best shown in FIGS. 2 and 4, 
the high pressure nozzles 54 are disposed between the spaced-apart cutting 
teeth 46. 
A pumping unit 120 is also provided for supplying pressurized injectable 
material to the high pressure piping 72 of the mandrel 30. As 
schematically depicted in FIG. 1, the pumping unit 120 includes a supply 
tank 122 which stores a quantity of injectable material, a pump 124 which 
pressurizes the injectable material, and a high pressure feed line 126 
which fluidically connects the pumping unit 120 to the high pressure 
piping 72 of the mandrel 30. In use, pressurized injectable material is 
pumped from the supply tank 122 to the high pressure piping 72 of the 
mandrel 30 for subsequent discharge through the high pressure nozzles 54. 
Although the pumping unit 120 is illustrated as a separately maneuverable 
vehicle, it will be understood by those skilled in the art that the 
pumping unit 120 may alternatively be carried by or form a part of the 
crane 90. 
In accordance with an important aspect of the present invention, the 
pumping unit 120 supplies injectable material at an extremely high 
pressure level (e.g., 3000-8000 psi) which is subsequently discharged 
through the high pressure nozzles 54 as the mandrel 30 is driven into the 
ground 10. In this way, a high pressure jetting action 56 is provided that 
erodes away soil in advance of the mandrel 30, as shown, for example, in 
FIG. 7. This high pressure jetting action 56, in conjunction with the 
vertical vibratory force provided by the vibratory driver 100 and the 
sharpness of the cutting teeth 46, facilitates penetration of the mandrel 
30 through dense soil layers by breaking-up and/or pushing aside rocks, 
hard soil, and the like. 
In order to provide a more effective high pressure jetting action 56, the 
high pressure nozzles 54 are disposed at dissimilar angles with respect to 
the longitudinal axis 66 of the mandrel 30, as shown, for example, in FIG. 
2. In particular, some of the high pressure nozzles 54 are disposed 
substantially parallel to the longitudinal axis 66 of the mandrel 30, 
while others are disposed at an angle relative to the longitudinal axis 66 
of the mandrel 30. In this way, a discharge spray that traverses 
substantially the entire cross-sectional shape of the mandrel 30 is 
advantageously provided. 
In the illustrated embodiment, the mandrel 30 has a cross-sectional shape 
which is substantially channel-like in configuration. More specifically, 
the mandrel 30 includes a generally flat central portion 82, sloping side 
portions 84, and outer edge portions 86. As shown in FIGS. 4 and 5, the 
sloping side portions 84 are disposed at an angle relative to the central 
portion 82, and the outer edge portions 86 are substantially parallel to 
the central portion 82. Although a channel-shaped mandrel 30 is 
specifically described and illustrated herein, it will be appreciated by 
those skilled in the art that other shapes may alternatively be used, 
provided they substantially match the repeating contours 132 of the 
pattern guide templet 130. 
Preferably, the mandrel 30 is formed of a high-grade steel that is 
fabricated or cast to shape. In this way, the mandrel 30 has a 
substantially unitary construction. Although a steel mandrel 30 having a 
substantially unitary construction is specifically described herein, it 
will be appreciated by those skilled in the art that other constructions 
could alternatively be employed. For example, the mandrel 30 could be 
comprised of two separately shaped pieces that are welded together in the 
middle of the central portion 82 such that a weld disposed substantially 
parallel to the longitudinal axis 66 of the mandrel 30 runs along the full 
length 64 of the mandrel 30. 
In order to provide added strength, stiffness, and durability to the 
mandrel 30, a structural cover plate 62 is welded to either side of the 
bottom portion 42. In addition, a plurality of structural bars 74 are also 
welded to the sloping side portions 84. In the illustrated embodiment, the 
structural cover plate 62 abuts the shoe 44 and extends upwardly 
therefrom, as shown in FIG. 2. The structural bars 74 extend upwardly from 
the structural cover plate 62 and are disposed substantially parallel to 
the longitudinal axis 66 of the mandrel 30. 
The mandrel 30 of the present invention also includes a rigid guide fin 76. 
As shown in FIGS. 2-5, the rigid guide fin 76 extends upwardly from the 
bottom portion 42 of the mandrel 30 and projects outwardly from one of the 
outer edge portions 86. In FIG. 6, the mandrel 30 is shown oriented 
180.degree. with respect to FIG. 5 such that the rigid guide fin 76 
extends rearwardly from the predetermined course of travel 18. In use, the 
rigid guide fin 76 is placed within a previously formed void, as shown, 
for example, in FIGS. 6 and 8, such that it partially overlaps the void 
formed in the ground 10 during the previous mandrel insertion. In this 
way, the rigid guide fin 76 assures continuity between the successive 
overlapping voids 12. Preferably, the rigid guide fin 76 has a relatively 
long length (e.g., approximately one-third the length 64 of the mandrel 
30), and includes a sharp edge portion 78 which facilitates penetration of 
the mandrel 30 into the ground 10. The relatively long length of the rigid 
guide fin 76 not only provides increased lateral support to the mandrel 
30, but also facilitates proper alignment of the mandrel 30 as it is 
inserted into the ground 10. 
In accordance with certain objects of the present invention, the injectable 
material supplied by the pumping unit 120 may either be water or slurry 
material (i.e., a hardenable grout-like bonding agent which provides a 
liquid impervious shield). If water is used, the successive overlapping 
voids 12 formed by the mandrel 30 will either be substantially empty or 
substantially water-filled, depending upon the drainage of the soil. If, 
however, slurry material is used, the successive overlapping voids 12 will 
be substantially slurry-filled because slurry material is too viscous to 
flow through the soil. Of course, in order to completely fill the voids 
12, it may be necessary to continue to discharge slurry material as the 
mandrel 30 is extracted from the ground 10. In any event, the successive 
overlapping slurry-filled voids 12 will produce a liquid impervious 
subterranean slurry wall which, in time, will gradually harden or set. By 
way of example, a typical slurry material gels after about four hours, 
semi-hardens overnight, and fully strengthens into a paste after a couple 
of weeks. Slurry materials that are suitable for use with the present 
invention include: (1) cement and water; (2) cement, bentonite and water; 
and (3) clay, cement, and water. 
In keeping with another important aspect of the present invention, the 
repeating contours 132 of the pattern guide templet 130 are adapted to 
individually receive and accommodate the cross-sectional shape of the 
mandrel 30 during successive mandrel insertions, as depicted, for example, 
in FIGS. 6 and 8. In other words, each repeating contour 132 has a shape 
which is substantially similar or complemental to the cross-sectional 
shape of the mandrel 30. In this way, the mandrel 30 is conveniently 
placed within the repeating contours 132 during successive mandrel 
insertions. 
In use, the stabilization member 134 of the pattern guide templet 130 is 
anchored to the ground 10 along the predetermined course of travel 18, 
while the repeating contours 132 receive the mandrel 30 during successive 
insertions. In particular, after the mandrel 30 has been received by one 
of the repeating contours 132, the mandrel 30 is driven into the ground 10 
to form a void therein. Upon extraction, the mandrel 30 is advanced along 
the pattern guide templet 130 into an adjacent repeating contour 132 (by 
moving the crane 90 in a direction substantially parallel to the 
predetermined course of travel 18) such that the rigid guide fin 76 of the 
mandrel 30 partially overlaps the previously formed void, as shown, for 
example, in FIGS. 6-8. The mandrel 30 is then re-inserted into the ground 
10 to form a subsequent void therein. By repeating these steps, a desired 
number of successive overlapping voids 12 may be accurately formed in the 
ground 10 along the predetermined course of travel 18. Although the 
predetermined course of travel 18 shown in FIGS. 6-8 is a substantially a 
straight line, it will be appreciated by those skilled in the art that the 
pattern guide templet 130 of the present invention may be modified to 
conform to any predetermined course of travel (e.g., curved, circular, 
angled, etc.). 
In accordance with certain objects of the present invention, the apparatus 
20 further includes an installation rig 140 for inserting structural 
elements 150 into the successive overlapping voids 12 that were previously 
formed by the mandrel 30. In the illustrated embodiment, the installation 
rig 140 is a conventional pile driver (see, e.g., FIGS. 7 and 8), and the 
structural elements 150 are sheet metal pilings (see, e.g., FIG. 9). More 
specifically, the pile driver includes a crane 142 with crawler tracks 144 
and a pivotally mounted boom 146. A vibratory unit 148 suspended from the 
boom 146 is used to drive structural elements 150 into the voids 12. As a 
safety precaution, the crane 142 of the installation rig 140 and the crane 
90 supporting the mandrel 30 are spaced apart, preferably by a distance of 
at least forty feet. 
In operation, the installation rig 140 sequentially installs structural 
elements 150 into the successive overlapping voids 12 to produce a 
subterranean structural wall therein, as depicted, for example, in FIG. 7. 
Of course, prior to installation, the voids 12 may be substantially empty, 
substantially water-filled, or substantially slurry-filled, depending upon 
the drainage of the soil and the injectable material used to form the 
voids 12. As a consequence, the injectable material not only determines 
the content of the voids 12, but also dictates the substance of the 
resulting subterranean wall. For example, if water is used as the 
injection material, the voids 12 will either be substantially empty or 
substantially water-filled prior to installation, and the resulting 
subterranean wall will be comprised exclusively of contiguous structural 
elements. If, on the other hand, slurry material is used as the injection 
material, the voids 12 will be substantially slurry-filled prior to 
installation, and the resulting subterranean wall will be comprised of 
both contiguous structural elements and liquid impervious slurry material. 
In practice, the structural elements 150 are driven through the 
slurry-filled voids 12. Of course, in order to minimize installation 
resistance, the structural elements 150 should be inserted into the voids 
12 before the slurry material has an opportunity to set or harden 
appreciably. 
In order to facilitate insertion of the structural elements 150 into the 
voids 12, each structural element 150 has a cross-sectional shape which is 
substantially similar to the cross-sectional shape of the mandrel 30 
(e.g., compare FIGS. 3 and 4 with FIG. 9). The structural elements 150 are 
also advantageously provided with interlocking edge portions (i.e., a male 
coupling 152 and a female coupling 154) which facilitate the construction 
of contiguous subterranean structural walls. For example, after a first 
structural element has been installed into a first void 12, a second 
structural element is aligned with and connected to the first structural 
element via the interlocking edge portions before it is installed into a 
second adjacent void. In this way, a contiguous subterranean structural 
wall comprised of interconnected structural elements 150 may be 
conveniently produced in the successive overlapping voids 12.