MECHANICAL EARTH STABILIZING SYSTEM INCLUDING REINFORCING MEMBERS WITH ENHANCED SOIL SHEAR RESISTANCE

Abstract

A mechanical earth stabilizing system is provided that includes at least one facing panel that retains compacted soil, and at least one reinforcing member connected at one end to the facing element and disposed within the retained soil. The reinforcing member is formed from a pair of parallel, bar-shaped legs disposed in a horizontal plane. Each of the bar-shaped legs includes a plurality of deformations along its length to resist axial movement of the leg through the surrounding soil. The parallel legs are spaced apart a distance of no more than about four times the thickness of the legs in order to synergistically increase the resistance of the legs to axial shearing through the compacted soil. The legs are preferably formed from a single length of bar-shaped material having a U-shaped bent portion that integrally connects the legs in parallel. Such a structure facilitates manufacture and the rounded portion of the integrally formed U-shaped portion provides a strong and convenient site for connecting the reinforcing member to a facing element.

Description

FIELD OF THE INVENTION

The present invention generally relates to a mechanical earth stabilizing (MSE) system for forming structural components from compacted soil reinforcing members formed from a pair of parallel legs that are spaced apart a selected distance to synergistically increase the resistance of the legs to axial shear movement through the compacted soil.

BACKGROUND OF THE INVENTION

Mechanically stabilized earth (MSE) is used to build a variety of structures such as retaining walls, bridge abutments, and sea walls. These structures are formed from a network of soil reinforcing members embedded in a volume of engineered frictional backfill formed from soil that has typically been compacted to a high percentage (>90%) of its maximum dry density. The reinforcing members are connected at one end to a structural facing that retains the engineered backfill. Stresses in the engineered backfill are partially transferred to the reinforcement members by way of frictional forces acting between the reinforcing members and the engineered backfill, or passive resistance between protruding surfaces on the reinforcing members and the surrounding soil, or a combination of both, resulting in a composite structural material of reinforced soil, the strain of which, in the working condition, is limited by the strain in the soil reinforcing element. The tensional forces in the reinforcing members are also partially transferred to the structure facings, which most commonly include precast concrete facing panels, welded wire facing forms, or modular blocks.

A number of different types of soil reinforcing members are known in the prior art, including steel strips, bar mats, ladder-type reinforcements and geosynthetic sheets, grids and strips. Ideally, the soil-reinforcing members should carry the tensile loads applied to them by the surrounding compressed soil in a uniform manner along their lengths. In order for the forces in the soil to be transferred to the reinforcement, the reinforcing member must effectively engage the surrounding soil along its length through friction, or bearing resistance on protrusions, or a combination of both mechanisms. The ability of soil reinforcing elements to engage the surrounding soil is commonly referred to by practitioners in the art as “pull out resistance.” Ladder-type reinforcements, usually made of steel, are commonly formed by welding cross bars at regular intervals to parallel steel bars. The cross bars on this type of reinforcement are particularly good at providing pullout resistance. However, ladder-type reinforcements are relatively expensive to produce in view of the welding required in mounting the large number of cross bars. The cross bars also add significantly to the unit weight of the reinforcing member, increasing the cost of transportation and installation. Finally, the welds may make ladder-type reinforcing members more susceptible to accelerated corrosion in service.

While steel strip-type reinforcements are easier and less expensive to manufacture, they typically provide less resistance to shearing through the soil than do ladder-type reinforcements even when manufactured with ribs or other types of protrusions to enhance soil engagement. Moreover, the applicant has observed that reinforcing members that are wider than they are thick require a greater weight of steel per unit of tensile strength, since a loss of thickness due to corrosion (generally on the order of 1.5 mm to 2 mm) is assumed to occur over the design life of the structure. Additionally, narrow relatively flat reinforcements also suffer from the need to create a penetration at the connection with facings to accommodate a connection member, commonly a bolt, which in turn reduces its structural capacity at the location of the penetration.

Accordingly there is a need in the field of MSE for a soil stabilization system having reinforcing members that generate a high resistance to pullout, are relatively simple and easy to manufacture, provide maximum tensile strength with a minimum amount of material, maintain full strength at the connection with the facing, and maintain structural efficiency in tension over the design life of the resulting MSE structure.

SUMMARY OF THE INVENTION

The present invention solves or at least ameliorates all of the aforementioned shortcomings associated with the prior art. To this end, the mechanical earth stabilizing system comprises at least one facing element that retains compacted soil, and a plurality of reinforcing members connected at one end to the facing element and disposed within the retained soil, the reinforcing member including a pair of legs, each of which includes a plurality of deformations along its length that generate passive resistance to sliding through the soil. The longitudinal axes of the legs are mutually parallel and preferably disposed in a same horizontal plane. Preferably, the legs are spaced apart a distance of no more than about four or five times the thickness of the legs. The applicant has surprisingly found that such spacing synergistically increases the resistance of the legs to shearing through the compacted soil. Stated differently, the total amount of shear resistance for both legs when such spacing is present is greater than the sum of the shear resistance of the individual legs when such spacing is not present.

The legs are preferably formed from a continuous bar-shaped member and formed into a U-shaped configuration, with the U-shaped bend connected to the facing element. Such a structure facilitates manufacture and the rounded portion of the integrally formed U-shaped portion provides a strong and convenient site for connecting the reinforcing member to a facing element. Alternatively, the legs may be independent elements connected to a separate facing connection apparatus.

The legs have a same or substantially same cross-sectional shape which is preferably round or oval, but which could be square or hexagonal or any other regular polygon, the only constraint being that the legs are not substantially flat. The deformations along the length of the legs may be protrusions such as ribs or ridges which circumscribe the outer surface of the legs. Alternatively, the deformations may take the form of crimps or bends in the legs, such as an undulating pattern of sinusoidal bends in the legs. In order to effectively engage the surrounding soil, the deformations should have a regular pattern and be spaced at regular intervals of not more than about 200 mm. If the deformations are protrusions, then they preferably protrude between about 2 and 4 mm.

The present invention further includes a connection assembly that fixedly connects the reinforcing member to the facing element. One embodiment of the connection assembly includes a loop member fixedly mounted to the facing element and having a rounded section that overlaps with the rounded portion of the U-shaped bar element. A tubular linking element is disposed in the overlapping rounded portion of the U-shaped bar element and the rounded section of the loop element. The tubular linking element is secured to the rounded section of the loop element and the rounded portion of the U-shaped bar element by opposing cotter pins. Another embodiment of the connection assembly includes a mounting plate that projects from the face of the facing element and that overlaps with the rounded portion of the U-shaped bar element. A bolt in combination with a thick washer, nut, and clamping plate clamps the U-shaped bar element to the mounting plate extending from the facing element.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and, together with the written description, serve to explain various principles of the invention.

FIG. 1 is a cross sectional view of a typical MSE structure that the system of the invention may be applied to.

FIG. 2 is a partial isometric view of the MSE system of the invention that includes an enlarged view of the connections between the reinforcing elements and the facing panels.

FIG. 3 is a plan view of a single reinforcement member and a first embodiment of a connecting assembly that connects the U-shaped end of the reinforcing member to the loop connector of a facing element.

FIG. 4 is a side view of the single reinforcement member and a first embodiment of a connecting assembly shown in FIG. 3.

FIG. 5A is an enlarged side view of the tubular linking element and cotter pins used in the connection assembly shown in FIGS. 3 and 4.

FIG. 5B is a plan view of the tubular linking element illustrated in FIG. 5.

FIG. 6 is an enlarged side view of one of the parallel legs of the reinforcing members, illustrating the soil-engaging deformations in the legs.

FIGS. 7 and 8 are side and plan views, respectively, of a single reinforcement member and a second embodiment of a connecting assembly that connects the U-shaped end of the reinforcing member to a plate connector of a facing element.

FIG. 9 is the plan view of FIG. 8 with the bolt removed to illustrate the washer used in the connection assembly illustrated in FIG. 7 and FIG. 8.

FIG. 10 is a partial isometric view of the MSE system of the invention that uses the second embodiment of the connecting assembly including an enlarged view of the connections between the reinforcing elements and the facing panels.

FIG. 11 illustrates how the spacing of the parallel legs of the reinforcing members generates synergism in the ability of the reinforcing member to engage with the surrounding compacted soil.

FIG. 12 is a plan view of an alternate embodiment of the invention wherein the deformations are an undulating pattern of sinusoidal bends in the legs.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to various exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. The following detailed description is provided to give details on certain embodiments of the invention, and should not be understood as a limitation on the full scope of the invention.

FIG. 1 illustrates the principal components of the MSE system 100 of the invention. This system 100 includes facing elements 102 which in this example are pre-cast concrete wall panels, a network of horizontally-oriented soil reinforcing members 104, and connecting assemblies 106 that affix the free ends of the reinforcing members 104 to the facing elements 102. While not specifically shown in FIG. 1, the other ends of the reinforcing elements 104 are secured into or on the structural member 107 opposite the facing elements 102. The facing elements 102 retain a volume of engineered backfill, which in this example is soil 108 that has been compacted to about 95% of its maximum potential dry density. The compacted soil 108 forms a solid matrix of material around the network of reinforcing members 104. Mechanical engagement between the reinforcing members 104 and the compacted, surrounding soil 108 caused by friction and passive resistance between the soil 108 and protrusions on the members 104 forms a composite structural material of reinforced soil. Accordingly, lateral deformation of the reinforced compacted soil 108 in response to gravity and externally applied loads is resisted by the tensile strength of the reinforcing members 104 in combination with the compressive capacity of the reinforced soil structure.

The ability of the MSE structure formed by the system 100 to carry a load is dependent upon the ability of the reinforcing members to generate pullout resistance 108 and to withstand tensile loads. So, if the soil easily shears between the reinforcing members 104 and surrounding soil 108, it will pull out of the soil long before reaching the tensile capacity of the element. While pullout resistance may be increased by increasing the number of reinforcing members in the system 100, such a solution would require substantial increase in material and labor. Accordingly, the reinforcing members 104 are designed to provide a high degree pullout resistance.

With reference now to FIGS. 2 and 3, each of the reinforcement members 104 includes a pair of bar-shaped, parallel legs 110a, 110b oriented in a horizontal plane as shown. While each of the legs has a generally round cross-sectional shape in this example of the invention to facilitate manufacture, cross-sectional shapes that are ovular, square, or any type of regular polygon are within the scope of the invention. Preferably, the cross-sectional shape is not substantially longer than it is wide (as would be the case if the legs 110a, 110b were substantially flat) so that the reinforcing members 104 will maintain their strength over the expected lifetime of the resulting MSE structure despite a 1.0 to 1.5 mm loss in material over all exposed surfaces of the legs due to corrosion. In this application, the “thickness” of the legs 110a, 110b refers to the average distance across their non-deformed cross-section. Accordingly, “thickness” corresponds to diameter in the case of legs 110a, 110b having round cross-sections. In the preferred embodiment, the legs 110a, 110b range from between about 5 and 25 mm in thickness and more preferably between about 9 mm and 20 mm in thickness. The legs 110a, 110b are preferably of the same thickness to facilitate manufacture. While the outer surface of bar material used to form the legs 110a, 110b may be smooth, it preferably carries a base texture such as that rolled into concrete reinforcing bars in order to increase frictional engagement between the legs 110a, 110b formed thereby and the surrounding soil 108.

With reference to FIGS. 2, 3 and 6, in order to enhance the engagement of the legs 110a, 110b and the surrounding compacted soil 108, each of the legs 110a, 110b includes a plurality of deformations which in this example are a series of annular ribs 112 that completely circumscribe the legs 110a, 110b. In order to ensure a high degree of soil engagement, the outer edges 114 of each of the annular ribs 112 should radially extend between about 2 and 4 mm from the surface of the legs. Additionally, there should be at least one rib 112 every 200 mm length of the legs 110a, 110b. Preferably the annular ribs 112 are integrally formed around the bar-like legs 110a, 110b by a hot rolling or cold drawing process of the type well known in the prior art.

With reference again to FIGS. 2 and 3, the legs 110a, 110b of each reinforcing member 104 are preferably integrally connected at one end by a U-shaped bent portion 116 having a rounded portion 118. The rounded portion 118 provides a convenient and strong means to interconnect the free ends of the reinforcing members 104 to the facing elements 102 via the connecting assemblies 106, as will be described in detail hereinafter. One preferred method of forming the reinforcing members 104 of the system 100 is to bend a single bar-shaped member in “hairpin” fashion to form two leg members 110a, 110b of equal length and thickness that are integrally connected via a U-shaped bent portion. Such a method is easy to implement, and creates an integral U-shaped portion without the need for welding. However the invention is not confined to such a manufacturing method or the particular embodiment of the reinforcing member formed thereby.

With reference now to FIGS. 3-5B, a first embodiment 106 of the connection assembly of the invention includes upper and lower anchor loops 122a, 122b, a tubular linking member 128, and a pair of cotter pins 130a, 130b. The anchor loops 122a, 122b are formed from bar stock, preferably plain round reinforcing steel, that includes an end portion 124a, a 90° bend extending the bar perpendicular to the facing element, a curved section 126 having an inner, semi-circular shape that is about the same size as the inner, semi-circular shape as the U-shaped bent portions 116 of the reinforcing members 104, a return elongated leg equal in length to the first, a 90° bend in the opposite direction of the first, and another end portion 124b which is approximately equal in length to the first end portion 124a. The end portions 124a, 124b are directly cast within the precast concrete panel forming the facing element 102, although any form of attachment of the anchor loops 122a, 122b to the facing element 102 is within the scope of the invention. The anchor loops 122a, 122b are spaced vertically at a distance reasonably close to, but not less than the maximum thickness of the U-shaped bent portion 116 of the reinforcing member 104. The diameter of the anchor loops 122a, 122b is sized such that their combined cross sectional area, at the end of the structure design life, is at least equal to, and not less than the cross sectional area of the parallel legs 110a, 110b of the reinforcing member 104 at the end of the structure design life.

The tubular linking element 128 has a cylindrical outer surface that is preferably complementary in shape to the circular opening made after the U-shaped bent portion 116 is inserted between the curved sections 126 of the anchor loops 122a, 122b. The tubular linking member 128 is disposed within this circular opening as shown. To secure the bent portion 116 and the curved section 126 to the tubular linking member 128, cotter pins 130a, 130b are slipped over the upper edge of the linking member as shown in FIG. 4. As best seen in FIG. 5, cotter pin 130a includes a single C-shaped section 132 for receiving the distal end of the U-shaped bent portion 116, while cotter pin 130b includes two such C-shaped sections to receive the distal ends of the curved sections 126 of the anchor loops 122a, 122b. The cotter pins 130a, 130b not only securely mount the tubular linking member 128 to the U-shaped bent portion 116 and the curved sections 126 of the anchor loops; they also rigidly affix the linking member 128, bent portion 116 and curved sections 126 together so that they cannot move relative to one another along the axis of the reinforcing member 104. This is important as any such axial, relative movement between these components could promote undesirable shear movement between the reinforcing members 104 and the surrounding compacted soil 108 and thereby diminish the engagement between the reinforcing members 104 and the surrounding soil 108. The thickness of the linking member 128 is sized such that the shear capacity of the tube, at the end of the design life of the MSE structure, is at least equal to the tensile capacity of the reinforcing member 104.

With reference now to FIGS. 7-10, a second embodiment 135 of the connection assembly includes a rectangular mounting plate 137 having a hole 139a, 139b at its distal and proximate ends, a steel mounting dowel 141, a washer 143 sized to fit closely within the U-shaped bent portion 116 of the reinforcing member, an L-shaped clamping plate 145 having a lip portion 147 and a hole 148, and a bolt 149 and nut of 150. The mounting dowel 141 secures the mounting plate 137 to the pre-cast concrete panel that forms the facing element 102. To this end, the dowel 141 is inserted through the hole 139a at the distal end of the mounting plate 137, and both are cast within the facing element 102 with the dowel 141 vertically oriented and the plate 137 horizontally oriented as best seen in FIG. 7. Next, as best seen in FIG. 9, the U-shaped bent portion 116 is aligned over the hole 139b at the end of the mounting plate 137 that projects out of the facing element 102. Washer 143 is then disposed within the semicircular inner periphery of the U-shaped portion 116 of the reinforcing member such that the opening in the center of the washer 143 is aligned with the hole 139b in the mounting plate 137. The clamping plate 145 is then positioned over the U-shaped portion of the reinforcing member 104 with the hole 148 of the clamping plate aligned with the hole 139b of the mounting plate 137 and the lip portion 147 overhanging the distal end of the U-shaped portion as shown in FIGS. 7 and 8. Finally, the shaft of the bolt 149 is inserted through the hole 148 of the clamping plate 145 and through the washer 143, and the nut 150 is tightened over the threaded end of the bolt shaft. The pressure that the bolt 149 and nut 150 applies to the clamping plate 145 in combination with the capture of the distal end of the U-shaped portion by the lip portion 147 fixedly connects the free end of the reinforcing member 104 to the mounting plate 137 cast into the facing element such that the reinforcing member 104 cannot move axially with respect to the facing element 102. The shear capacity of the both the mounting plate 137 and the bolt 149 at the end of the design life of the resulting MSE structure must at least equal to, but not less than the tensile capacity of the reinforcing member 104.

While the facing elements 102 have been described as pre-cast concrete wall panels in the descriptions of both connecting assembly embodiments 106, 135 they may just as easily be cast-in-place panels or blocks or welded wire the facings.

FIG. 11 illustrates what the applicant believes is the synergistic mechanism behind the enhanced resistance to axial shear movement between the reinforcing members 104 and the surrounding compacted soil 108. As previously stated, the legs 110a, 110b of the reinforcing members are preferably spaced apart a distance D of between two and five thicknesses of the legs 110a, 110b, and most preferably a distance of about four thicknesses of the legs 110a, 110b. When tensile forces are applied to the legs 110a, 110b and the legs attempt to move axially relative to the compacted soil 108, the friction between the outer surfaces of the legs and the surrounding compacted soil 108, in combination with the passive resistance between the protruding ribs 112 circumscribing the legs 110a, 110b and the surrounding compacted soil 108 creates two interfering zones of dilation, i.e. zones where the compacted soil is being pushed away from the legs 110a, 110b in the radial direction. The interference between these two zones of dilation tends to compress the soil between the two parallel legs 110a, 110b and create a positive arching effect in the soil above and below the legs 110a, 110b, thereby increasing both the friction between the outer surfaces of the legs 110a, 110b and the surrounding soil 108 as well as the passive resistance between the protruding ribs 112 and the surrounding soil 108. These increased frictional and passive resistance forces in turn impart to the reinforcing member 104 enhanced resistance to shearing through the soil.

FIG. 12 illustrates a second embodiment 200 of the invention wherein the deformations 112 in the legs 110a, 110b are bends or crimps in the bar-like material forming the legs. In this particular example, such bends or crimps are a series of undulating sinusoidal curves 112 in the legs 110a, 110b having the same amplitude and wavelength. In one preferred embodiment, the length of each of the sinusoidal bends 112 is between about 25 and 40 cm The maximum distance “d1” between the legs 110a, 110b at opposing peaks 150a, 150b peaks of adjacent bends 112 is no more than about six diameters of one of the legs 110a, 110b and a minimum distance “d2” between the legs is at least one diameter of one of the legs 110a, 110b. Such proportioning of the distances d1 and d2 insures that the distance between the two legs 110a, 110b is between about two and five leg thicknesses throughout a substantial portion of the length of the legs 110a, 110b. Even though both of the legs 110a, 110b in the second embodiment have deformations in the form of sinusoidal bends 112, the central axes A1, A2 of these legs 110a, 110b are parallel as shown. This second embodiment has the advantage that the legs 110a, 110b may be formed from standard reinforcing bar material of the type commonly used to reinforce concrete structures. The naturally rough exterior surface of such reinforcing bar helps enhance the frictional forces between the legs 110a, 110b and the surrounding compressed ground fill.

The foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to exemplary embodiments, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.

Claims

1. A mechanical earth stabilizing system, comprising:

at least one facing element that retains soil;

at least one reinforcing member connected at one end to the facing element and disposed within the reinforced soil, the reinforcing member including a pair of legs, each of which includes a plurality of deformations along its length that resists axial movement of the leg through the surrounding soil, the pair of legs having mutually parallel longitudinal axes and being disposed in a same horizontal plane,

wherein the legs are spaced apart a distance of no more than about five times the thickness of the legs for at least a substantial portion of their lengths.

2. The mechanical earth stabilizing system of claim 1, wherein the legs are integrally connected together at the end connected to the facing element.

3. The mechanical earth stabilizing system of claim 2, wherein the legs are integrally connected together by a U-shaped member.

4. The mechanical earth stabilizing system of claim 3, wherein the legs are formed by a single length of bar-shaped material having a U-shaped bent portion that integrally connects the legs in parallel.

5. The mechanical earth stabilizing system of claim 1, wherein the deformations are protrusions that extend from the surface of the legs at a distance of at least about 10% of the thickness of the legs.

6. The mechanical earth stabilizing system of claim 1, wherein the deformations are protrusions that extend from the surface of the legs at a distance of between about 2 and 4 millimeters.

7. The mechanical earth stabilizing system of claim 1, wherein the legs have a rounded cross-sectional shape, and the deformations are ridges that circumscribe the outer surface of the legs at least partway.

8. The mechanical earth stabilizing system of claim 1, wherein the deformations are spaced along the length of the legs a distance of not more than about 200 millimeters apart.

9. The mechanical earth stabilizing system of claim 1, wherein the deformations are spaced along the length of the legs a distance of not more than about twenty times the thickness of the legs.

10. The mechanical earth stabilizing system of claim 1, wherein the deformations are crimps or bends in the legs.

11. The mechanical earth stabilizing system of claim 10, wherein the deformations are sinusoidal bends in the legs.

12. The mechanical earth stabilizing system of claim 11, wherein the sinusoidal bends are of uniform length and amplitude.

13. The mechanical earth stabilizing system of claim 12, wherein the sinusoidal bends on both legs are uniformly spaced along the longitudinal axis of each leg.

14. The mechanical earth stabilizing system of claim 3, further comprising a connection assembly that fixedly connects the end of the reinforcing member to the facing element, wherein the connection assembly includes a loop member fixedly mounted to the facing element and having a rounded section that overlaps with the rounded portion of the U-shaped bar element.

15. The mechanical earth stabilizing system of claim 14, wherein the connection assembly further includes a tubular linking element disposed in the overlapping rounded portion of the U-shaped bar element and the rounded section of the loop element.

16. The mechanical earth stabilizing system of claim 15, wherein the connection assembly further includes a mounting element that fixedly connects the tubular linking element to one or both of the rounded portion of the U-shaped bar element and the rounded section of the loop element.

17. The mechanical earth stabilizing system of claim 15, wherein the mounting element includes at least one cotter pin.

18. The mechanical earth stabilizing system of claim 3, further comprising a connection assembly that fixedly connects the end of the reinforcing element to the facing element, wherein the connection assembly includes a plate element fixedly mounted to the facing element, and a fastener for fixedly mounting the U-shaped bar element of the reinforcing element to the plate.

19. The mechanical earth stabilizing system of claim 18, wherein the plate element includes an opening, and the fastener of the connection assembly includes a bolt that extends through the rounded portion of the U-shaped bar element and the opening of the plate, and a nut.

20. A mechanical earth stabilizing system, comprising:

at least one facing element that retains compacted soil;

at least one reinforcing element connected at one end to the facing element and disposed within the compacted soil, the reinforcing element including a pair of bar-shaped legs, each of which includes a plurality of protrusions along its length that resist axial movement of the leg through the surrounding soil, the pair of legs being mutually parallel and in a horizontal plane and having about a same cross sectional area,

wherein the parallel legs are spaced apart a distance of no more than about five times the thickness of the legs, and are connected together at the facing element by a U-shaped element.

21. The mechanical earth stabilizing system of claim 16, wherein the legs are formed by a single length of bar-shaped material having a U-shaped bent portion that integrally connects the legs in parallel.

22. The mechanical earth stabilizing system of claim 16, wherein the legs have a rounded cross-sectional shape, and the protrusions are ridges that circumscribe the outer surface of the legs at least partway.

23. The mechanical earth stabilizing system of claim 18, wherein the ridges extend from the surface of the legs at a distance of between about 2 and 4 millimeters.

24. The mechanical earth stabilizing system of claim 16, wherein the protrusions are spaced along the length of the legs a distance of not more than about 200 millimeters apart.