Interlocked gridwork for retaining walls, and the like

A gridwork or crib structure is formed from reinforced, injection molded plastic or injection molded structural foam plastic crossbeams, stringers and fascia members by interlocking the members and pinning the stringers together to form a structure which can function as a gravity retaining wall to retain earth, as a structural wall, or as a water wall. The individual crossbeams are laid end-to-end on conventional base footings and define elongated slots and holes into which are connected the stringers, which are then locked and pinned together, thereby forming an initial crib or grid layer at ground level. This crib or grid layer can be built up in height and depth to provide an open structure defining securement channels into which earth is filled. Use of slot and hole connections produce an adjustable interfitted grid which can assume a convex or concave curvature, or the usual linear form, or the grid can form a square corner. Consequently, it is relatively easy to build the crib or grid layers to follow uneven perimeters such as property lines, roads, hill sides, etc. Since the plastic crossbeams and stringers are quite light, it is very easy to erect the crib or grid, compared to working with metal, timber or concrete reinforcement beams. This enables its installation in inaccessible locations, since it does not require heavy equipment for its construction. Also, the opening in fascia elements of the crib or grid enables planting of vegetation into the earth fill for soil retention or decoration.

BACKGROUND OF THE INVENTION 
This invention relates to a new and improved structure formed as a gridwork 
of interlocked, lightweight, injection molded plastic or injection molded 
structural foam plastic components. The structure may be used as an earth 
retaining wall by filling earth in between the plastic components of the 
gridwork, or the structure may be used simply as a structural wall. When 
used as an earth retaining wall, the earth in the structure can be 
stabilized by means of growing vegetation, or by means of earth retaining 
panels, or both. When used in conjunction with closed fascia, the 
structure can be used as a water wall to protect earthen banks. 
Prior art structures are stabilized by means of the weight of the concrete, 
timber, metal beams, etc., and with the weight of the retained earth; 
hence, the term `gravity wall` is used to describe these structures. These 
prior art structures are stabilized by the rigidity of the components and 
also their heavy weight. Thus, the strength of the structure is related to 
their rigidity and weight a well as the weight of the earth which is 
retained by the structure. 
But the use of timber, metal beams, concrete or building blocks is 
expensive both in terms of material cost and labor. Also, they are 
expensive in terms of installation costs due to the weight of the 
materials employed, since these heavy components require the use of large 
lifting cranes, heavy powered equipment and manpower. 
Various publications of earth retaining wall systems include U.S. Pat. Nos. 
4,514,113; 4,661,023; 4,718,792; 4,725,168; 4,798,499; 4,914,876; 
4,917,543; 4,929,125; 4,930,939; 4,952,098; 4,961,673; and, 4,968,186. 
But, these patents involve structures which employ concrete, building 
blocks, steel or timber as an essential reinforcement, and these prior art 
components are immobilized in position. 
However, when using these prior art components, the round on which the 
structure is installed may shift due to water absorption, or due to earth 
movement such as soil subsistence or hill slides, or due to earthquake, 
etc. Consequently, if the structural components are in a fixed or 
immobilized position, they will tend to be placed under a greater degree 
of compressive or tensile stress, and the entire structure could fail or 
become badly deformed. 
Hence, it is desired to provide an earth retaining system which can also 
function as a structural wall, and which employs inexpensive and 
lightweight components that may be installed quickly and inexpensively. 
Also, an earth retaining system is desired in which the components are 
adjustable, thereby enabling the structure to follow curved o straight 
lines, and where the components are resilient to earth movement, 
earthquakes, and the like. 
It is also desired to provide a structure that ca shift slightly vertically 
or horizontally to adjust to ground movement, which gives rise to the term 
`diaphragm wall`. 
It is also desired to provide a structure which relies solely on 
lightweight, interlocked components as well as on the weight of earth to 
maintain stability. 
THE INVENTION 
According to the invention, an adjustable, interlocked gridwork of 
structural components is provided useful as an earth retaining wall, or a 
self supporting structural wall. The gridwork components are adjustable 
during construction to follow uneven contours of the ground and the 
perimeter, and to self adjust to subsequent changes in ground support due 
to earth movement, earthquake, slides, etc., with reduced tendency of the 
structure to deform or crack, compared to concrete, and other prior art 
materials. Thus the present invention not only functions as a gravity wall 
but also functions as a structural wall and as a diaphragm wall. 
The structural wall of this invention is held in place due to the 
engineered design in which all the components are interlocked and pinned 
together and alternate in position to form a crib or grid system. The 
structural components are manufactured of an injection molded plastic 
which may be reinforced with fiberglass or any other suitable, filamentary 
material. These components are interlocked to form a lightweight gridwork 
into which earth is usually filled. 
Since the load bearing component of the earth filling is basically 
downward, the internal grid or crib structure functions to retain the 
earth in place without excessive outward force being placed on the overall 
structure, while downward, load bearing forces on the components are not 
excessive. Also, if a shift occurs in the foundation of the gridwork 
structure, due to subsistence, water absorption, earthquakes, landslides, 
or soil movement, etc., the gridwork components will deform or articulate, 
thereby compensating and reducing the risk of structural failure. Hence 
the structure of this invention gives rise to the term, `gravity wall`. 
Basically, the components of this invention include a system of lightweight 
(about four pounds for each component), reinforced, injection molded, 
plastic crossbeams, and interlocking stringers and fascias formed into a 
grid structure having reasonable rigidity, but with elasticity, 
flexibility and adjustability characteristics. The stringers are 
beam-shaped, such as an I-beam or H-beam, and configured for end fitting 
over a cross beam. The end fitting around the crossbeams and the interfit 
of the stringer into the crossbeam provide structural continuity and 
integrity to the gridwork. 
Additional horizontal adjustability of the structure arises by virtue of 
the connection between the crossbeams and the stringers. The cross beams 
define a slot and hole arrangement into which the molded pivot on the 
stringers are inserted, with a locking means being provided to connect the 
stringers and crossbeams to each other. Certain of the cross beams are 
provided with slots instead of holes, and these crossbeams are coursed 
back into the wall. The slots enable a concave or convex curvature to be 
imparted to the retaining wall and this permits the structure to follow 
property lines, curved frontage lines, etc., besides the usual straight 
lines. 
The combination of slots and holes in the crossbeams and engaging 
corresponding pivots in the stringers, the use of locking pins which 
secure the stringers together, the use of pinned joints which still can 
articulate, the use of alternating components in the structure, and the 
inherent elasticity and flexibility of the plastic material of the 
components, produce a `diaphragm wall` and enables the structure to 
articulate, thereby accommodating for minor changes in soil movement due 
to cracking, subsistence, upheaval, and earthquakes, as well as 
temperature variations.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The structure 10 of this invention is shown in FIGS. 8, 9, 10 and 11, and 
comprises a gridwork of injection molded long crossbeams 11 and short 
crossbeams 12 interlocked with stringers 13 and fascias 14. A typical long 
crossbeam 11 is shown in greater detail in FIGS. 2A and 4A, and comprises 
a U-shaped, rectangular cylinder 15 with integrally formed reinforcing 
panels 16. Holes 17, two of which are shown, are provided on both the 
upper and lower sides of the long crossbeam to enable interfitting with 
the stringer 13, by means of a pivot pin 26, infra, as shown in FIG. 1. 
The stringers and crossbeams components of this invention are easily 
manufactured of conventional plastics such as PVC, high density 
polyethylene, polypropylene, etc. Obviously, other plastic materials which 
may be developed in the future may be used, where suitable. A present 
production size of stringer 13 is about 2".times.12".times.48", and 
weighs about four pounds; a long cross beam 11 is about 
4".times.4".times.48" and weighs about four pounds; and a short cross beam 
12 is sized about 4".times.4".times.38", and weighs about three pounds. 
The components have a wall thickness of approximately 3/16 inches. By 
comparison, the same size of concrete components weigh in the order of 
about 125 pounds. The present production sizes of the components were 
selected as convenient and economical, however, a large range of component 
sizes could be readily manufactured. 
A typical short crossbeam 12 is shown in greater detail in FIG. 2B, and 
comprises a U-shaped rectangular cylinder 18 having integrally formed 
reinforcing panels 19 and elongated slots 20 on both the upper and lower 
sides of the short crossbeam. This arrangement enables interfitting of a 
crossbeam with a stringer 13 by means of a pivot pin 26, and it will be 
apparent that the crossbeam and stringer can move relative to each other 
along the slots 20. The fascia 14 is shown in FIGS. 3 and 4C, and 
comprises a rectangular flat plate with two ribs 31 on the front, a 
rectangular dish 32 and a flat open area 33. An awning portion 34 is 
formed on the rear of the fascia (FIGS. 4C and 7) and functions to shield 
the open area 33 from movement of earth therethrough. 
The stringer 13 is shown in greater detail in FIGS. 1, 4B, 6 and 7, and 
comprises an elongate body 21 with an I-beam cross section and U-shaped 
end members 22. As shown in FIGS. 6 and 7, when assembled, the end members 
22 function to partially envelope the sides of the cross beams 11 and 12, 
and assist in rigidifying the gridwork structure 10. 
As shown in FIGS. 6 and 7, the end members 22 comprise integrally formed 
upper and lower upstanding retainer sections 23 and intermediate floor 
portions 24. Each floor portion comprises a central ridge 25, bearing a 
pivot pin 26, and adjacent channel portions 27; only the upper retainer 
sections are shown. The stringers are then locked together by means of 
T-pins 28, one of which is shown in detail in FIG. 5A. 
As shown in FIG. 6, the channel portions 27 are sized to receive clips 29, 
which are used to stabilize two stringers 13, following locking by the 
T-pins 28, when they are placed end-to-end and side-by-side to form 
additional courses of gridwork. Four clips 29 are shown in FIG. 6 
connecting two stringers 13, and this locking arrangement enables lateral 
shear strength to be imparted to the stringers 13. 
As shown in FIG. 8, to construct a retaining wall using the present 
invention, initially a ground base is first graded 35, followed by say 
installing a drainage system , and then forming the gridwork structure 10. 
For a `gravity wall` method of construction, a ground base is graded on a 
1:4 reverse incline, which is approximately 15 degrees. This reverse 
incline places more weight of the earth in a lower or gravity position. 
FIG. 9 shows the initial construction which is one tier high and three 
courses deep, and involves laying out the long cross beams 11 to form the 
front perimeter of a wall or earth retaining structure followed by laying 
out the short cross beams 12. The centers of the short cross beams 12 are 
directly behind the joints 37 between each long cross beam 11. By 
alternating the joints 37 as the crossbeams 12 progress into the wall by 
courses, and alternating the joints as the cross beams 11 and 12 are 
stacked in successive tiers, a structural gridwork system is formed where 
all components are interconnected. Crib channels 36 are formed internally 
in the gridwork and function to contain the retained earth into discrete 
columns. This prevents the retained earth from moving as a single mass, 
that might otherwise overload a portion of the gridwork. 
The stringers 13 are then installed between the cross beams 11 and 12. This 
involves inserting the stringer pivot pins 26 into the holes 17 and slots 
20 of the cross beams, as shown in FIGS. 1, 2 and 3. Since the slots 20 
are longer than the smaller pivot pins 26, the pivot pins can move along 
the slots, and hence, the grid structure can be formed in various types of 
curves so that it can follow along ground contours, straight lines, etc., 
to form convex, concave or straight walls, as shown in FIG. 10. 
FIG. 6 shows the stringers connected together by inserting T-pins 28 into 
the pivot pin holes on all the stringers, i.e., four T-pins (two on the 
top and two on the bottom) for each stringer, and clips 29 are then 
snapped into the channel portions 27 at every side-by-side stringer. The 
structure 10 is then continued, shown in FIGS. 8, 9, 10 and 11 by laying 
courses and stacking tiers until the pre-designed retaining wall has been 
completed. Back filling with back fill 38 and tamping are accomplished on 
a continuous basis as every one or two tiers are installed. 
FIGS. 7 and 9 show the fascias 14 which function to assist in stabilizing 
the earth enclosed in the gridwork. The fascias are installed between the 
stringers by fitting them into the recesses 30 of the stringers. The 
fascias define strengthening ribs 31 which rest both on top of, and below 
a crossbeam 11, thereby supporting and spacing the crossbeams; the ribs 31 
also prevent earth from sifting out of the wall. The fascias can be open 
33 to allow vegetation to grow therethrough and present a pleasing 
appearance, or alternatively, the fascias can be molded without the 
opening 33, if vegetation is not desired. 
Square corners can be formed with the molded plastic components of this 
invention. Special configurations (FIGS. 12A and 12B) of the stringer 38 
and 39, cross beam 40 (FIG. 13.) and fascias 41 and 42 (FIGS. 14A and 14B) 
are used for a corner construction. These components form an interlocked 
gridwork system by physically fitting and pinning components 38, 39, 40, 
41 and 42 together, unlike concrete or wood components which use only 
gravity to maintain their assembly. 
FIG. 15 shows an outside 90 degree corner which is constructed by starting 
on the 1st, or bottom most tier, and all odd numbered tiers, i.e, 3rd, 
5th, etc., are similarly constructed. For this purpose, a cross beam half 
40 is substituted for the normal long crossbeam 11 in front of the wall 
where the corner is desired. A stringer 38, with two notches 43 (FIG. 12A) 
is assembled and pinned to the cross beam half 40. At the rear of this 
stringer 38 a normal short cross beam 12 is assembled and pinned together. 
A cross beam long 11 is placed at 90 degrees at the end of the cross beam 
half 40. Two stringer halves 39 are assembled to this 90 degree long 
crossbeam 11. The notch 44, as shown in FIG. 12B, on each stringer is 
fitted into its corresponding notch 43 (FIG. 12A) on the stringer notch. 
The fascia corner piece 42 is fitted into the front of the wall and the 
fascia corner piece 41 is fitted into the 90 degree side of the wall. A 
second long crossbeam 11A is placed end-to-end with the long cross beam 11 
that is forming the 90 degree corner. A stringer 13 is pinned on top of 
the long cross beam 11A and a cross beam half 40A is pinned underneath the 
rear of stringer 13. This configuration completes the 1st and all odd 
numbered tier assemblies for a 90 degree corner. The retaining wall on odd 
numbered tiers is then continued in both 90 degree directions using a 
straight wall method of assembly. 
FIG. 16 shows a 90 degree corner on the 2nd, 4th, 6th and all even numbered 
tiers which are constructed by assembly and pinning together a series of 
three crossbeams. Initially, a long crossbeam 11 is assembled on top of 
the crossbeam half 40 and the notch stringer 38 that were assembled as 
part of the lower 1st tier. This long cross beam will extend to the last 
stringer 13 of the front wall on the 1st tier. A second cross beam half 40 
is placed at 90 degrees to, and at the end of, this first long cross beam 
11. An additional, long cross beam 11B is then placed end-to-end to the 90 
degree cross beam half 40. A notched stringer 38 is assembled on top of 
the long cross beam 11 on the front wall, and a cross beam half 40B is 
assembled underneath the rear of this notched stringer. A stringer half 39 
is assembled on top of the 90 degree crossbeam half 40 and its end-to-end 
long cross beam 11. A second half stringer 39B is assembled on top of the 
cross beam 11B and stringer 38. The rear of these two stringer halves 
define notches 44 which are fitted into the notches 43 of the stringer 38. 
FIG. 16 also shows a fascia corner (two pieces 41 and 42) which are fitted 
in a reverse manner to that of the 1st tier. The fascia corner piece 42 is 
fitted into the 90 degree side of the corner and the fascia piece 41 is 
fitted into the front of the wall. This completes the 2nd, and all even 
numbered tiers for a 90 degree corner. The retaining wall on the even 
numbered tiers is then continued in both 90 degree directions as a 
straight wall method of assembly. 
FIG. 17 shows both ends 45 of a retaining wall that should, in the 
preferred design, taper down to a height that does not leave an open end 
to the wall, which otherwise would court failure. In the preferred wall 
design, both ends of the wall should provide a 90 degree outside corner 
extending back into wall 46 at least as far as the height of the wall end. 
An inside 90 degree corner 47 (FIG. 15.) is constructed by overlapping one 
of the intersecting walls. The overlap 48 should be sufficient so that the 
wall which is overlapped does not have side or end pressure but is only 
required to retain the rear tension pressure. 
If desired, the gridwork structure may be secured into the earth either 
within or adjacent the structure, as shown in say FIGS. 9, 10 and 11. For 
this purpose, a coarsely woven sheet 49, typically of plastic material, is 
wrapped one or more times around one or a plurality of stringers 12 and 
then extended for an appropriate distance into the earth in and/or 
adjacent to the gridwork structure. Backfill dirt applied on top of the 
plastic sheet will penetrate and then interlock with the sheet. The weight 
of the dirt combined with the interlock will produce a strong frictional 
force to secure the sheet against lateral movement, thereby further 
immobilizing the gridwork structure. This optional method may be utilized 
by the design engineer, depending on the nature of the retaining wall and 
overall requirements. 
When the production components of the gridwork system 10 of this invention 
were tested by applying pressure in the directions 51 as shown by the 
arrows in FIG. 11, a force in excess of 10,000 pounds was required to 
produce failure. In the test, a measured twenty inches of the stringer 13 
was stretched over two inches. Notwithstanding, the failed stringer 
nevertheless returned to its normal configuration of twenty inches upon 
conclusion of the test. Thus the test indicated both an adequate 
elasticity of the plastic material, and also an adequate design of the 
component and gridwork system. 
In another test, by applying pressure to the stringer component 13, as 
shown by the directions 53 of the arrows in FIG. 1, failure of this 
component exceeded 4,800 psi. The failure occurred at holes drilled in the 
beam portion of the stringer to accommodate for test holding fixtures. 
As indicated in FIGS. 4A and 4B, the test forces that were applied in the 
directions shown by the arrows 54 and 55 and that were required to shear a 
section of a production component, exceeded 2,000 psi. However, the 
configuration of the component, and the elasticity of the material used 
would enable the component to flex and bend long before the shear limit is 
reached. Hence, in actual use, the failure mode would be that of breaking, 
rather than shearing. 
As shown in FIG. 6, the tested lateral forces 57 applied in the directions 
of the arrows and which were required to separate an unrestrained joint, 
exceeded 850 pounds, at which level the clips 29 became disengaged. In 
actual use, it is considered that these lateral forces required to produce 
failure would be much greater, both because the joint would be part of a 
larger pinned wall system, and also because the joint would be restrained 
by the earth backfill. 
All tests were conducted using high density polyethylene having a low flow 
modulus, employing 15% by weight of fiberglass reinforcement, and with the 
production components having the dimensions described, supra. 
The use of reinforced plastic material has obvious advantages such as 
lightness in weight, which enables ease of transportation to inaccessible 
sites and during construction. Also, the plastic material employed is 
resistant to rot, alkali, and insect infestation, and U.V. deterioration 
is considerably reduced due to the use of anti-oxidants and U.V. 
inhibitors, and additionally because a large portion of the gridwork is 
buried. The selection of a specific plastic depends on its resistance to 
sunlight, U.V. and oxidation, in addition to strength. Although the 
components may be molded in any color, hue or shade, the preferred colors 
are black and green because these colors also reduce the effects of ultra 
violet sunlight.