WO1995013431A1

WO1995013431A1 - Modular retaining walls

Info

Publication number: WO1995013431A1
Application number: PCT/AU1994/000692
Authority: WO
Inventors: Robert John Stubbs; Arvo Tinni
Original assignee: Ts Modular Systems Pty. Limited
Priority date: 1993-11-12
Filing date: 1994-11-09
Publication date: 1995-05-18

Abstract

A modular retaining wall arrangement, such as finds use in road and railway embankments, is described. The retaining wall (10) consists of spaced-apart T-post units (14) stacked as courses on a footing located on the ground. The footing is formed by a front strip footing (17), a rear deadman anchor (18) and a tie beam (19). The T-post units (14) consist of a web (12) and a pair of cantilevered wings forming a face portion (13). Each web (12) of a T-post unit (14) is anchored to either the deadman anchor (18) or an adjacently stacked web (12) in a lower course of T-post units (14). Wall planks (15) are placed to the inside of the face portions (13) to span the space between adjacent stacks of T-post units (14). Fill material is provided at least to a partial height of the wall (10) and also covers the portions of the base rearward of the planks (15). The deadman anchor (18) is two-way in nature, providing fixidity and stability, thus resisting sliding or overturning of the retaining wall (10).

Description

MODULAR RETAINING WALLS Field of the Invention

The invention relates to modular retaining walls. Such retaining walls typically find application for example in road and railway embankments, bridge approaches, seawalls and as riverbank protection.

Background of the Invention

Known methods for containing embankments to achieve structural stability include (i) cast-in-situ retaining walls, (ii) reinforced soilmass blocks with facings and (iii) modular systems. The modular systems typically are crib type mass walls of limited height, or utilise unitary support structures which suit either uniform height walls (typically for stepped configurations) or must be pre-designed for each structure location and hence require constant mold adjustments. These known systems are impractical for retaining wall configurations in steep or undulating country and also are limited by transportation constraints.

Specific examples of prior art retaining wall systems are disclosed in U.S. Patent No. 4,684,294 (O'Neill) issued on 4 August 1987 and U.S. Patent No. 4,572,711 (Benson et al) issued on 25 February 1986.

Disclosure of the Invention

Preferred objectives of the invention are to provide a retaining wall arrangement that can be rapidly erected in the field and offers superior fixidity and stability over prior art arrangements, and that also can reduce time constraints of associated earthwork operations. Therefore the invention discloses a retaining wall comprising: a footing; at least one course of spaced apart T-post units stacked on said footing, said T- post units each having a web portion and a face portion, the face portion forming part of the face of said retaining wall and the web extending in a direction away from the face portion; anchor means for anchoring each said web portion to said footing or to a respective web of one of said T-post units of a lower course; at least one panel spanning the space between adjacent T-post units; and fill material placed rearwardly of the panels and covering the web portions and footing at least partially to the height of the retaining wall.

Advantageously, the footing comprises a front strip footing on which the face portion of the T-post units and the panels are stacked, and a rear deadman anchor beam connected to the front strip footing by a tiebeam, the web portion of each T-post unit being stacked on the tiebeam.

The invention further discloses component parts for a retaining wall, the parts comprising: a footing; a plurality of T-post units each having a web portion and a face portion, and whereby, in use, at least one course of the T-post units is stacked in spaced apart relation on the footing, the face portion of each T-post unit forming part of the face of the retaining wall and the web extending rearwardly of the face portion, each said web portion being anchored to said footing or to a respective web of one of said T-post units of a lower course; and a plurality of panels whereby, in use, at least one panel spans the space between each adjacent T-post units.

The invention yet further discloses a method of construction of a retaining wall, the method comprising the steps of: forming a footing on the ground; stacking at least one course of spaced apart T-post units on the footing, the T- post units each having a web portion and a face portion, the face portion forming part of the face of the retaining wall and the web portion extending rearwardly from the face of the retaining wall; anchoring said T-post units to said footing or to a respective web of one of the T-post units of a lower course by anchor means; spanning the space between each adjacent T-post units with at least one panel, said panels forming the remainder of the face of the retaining wall; and backfilling with fill material rearwardly of the panels to cover the footing and web portions to at least partially the height of the retaining wall.

The gist of the invention is the provision of a two-way deadman anchor providing fixidity and stability for a retaining wall regardless of its height. Put simply, the retaining wall resists both sliding and overturning under the influence of dead weight of the wall and contained fill material.

Brief Description of the Drawings Fig. 1 is a front isometric view of part of the retaining wall constructed in accordance with a first embodiment;

Fig. 2 is an exploded isometric view of a portion of the retaining wall shown in Fig. 1;

Figs. 3a and 3b are cross-sectional views of two types of the precast component wall panels;

Fig. 4 is an elevation view of the stress bar anchor assembly;

Fig. 5 is an elevation view of the stressing system of the anchor bars;

Fig. 6 shows the structural principle of the retaining wall;

Fig. 7 is a schematic diagram summarising the forces acting on the retaining wall;

Figs. 8a-8g show cross-sectional views of various configurations of a retaining wall;

Fig. 9 shows plan arrangements of the T-post units; Fig. 10 is a plan view of a retaining wall; and Fig. 11 is a front view of a retaining wall.

Detailed Description and Best Mode of Performance A retaining wall 10 of a first embodiment is illustrated in Fig. 1. The retaining wall 10 usually supports the near vertical faces of embankment fills up to 20 metres in height, and consists of spaced-apart T-posts 11 which preferably are 5-7 metres between their centres. The T-posts 11 are formed by courses of T-post modular units 14 that preferably are 2.4 metres in height. The T-post units 14 are constructed from steel reinforced concrete, and consist of a web 12 and a pair of cantilevered wings forming a face portion 13. The face portion 13 forms part of the front face of the retaining wall 10 and the web 12 projects perpendicularly (rearwardly) from the retaining wall 10.

Spanning the space between adjacent T-posts 11 are precast extruded wall panels or planks 15 (or 15a) of pre-cast pre-stressed concrete which abut against the inside portion 16 of the corresponding face portions 13. The planks 15 preferably are 1.2 metres high, hence in the embodiment show there are two planks per T-post unit 14.

The retaining wall 10, including the T-posts 11 and planks 15, is positioned on a footing formed by a front strip footing 17, a rear deadman anchor 18 and a tie beam 19. The footing is cast on site from reinforced concrete to be located on or under the ground surface. This allows the required levels and sure contact with the ground to be obtained.

Fig. 1 shows only two adjacent T-posts 11, however there is repetition of further T-posts/planks along the front footing 17 to the full width of the retaining wall 10.

As best seen in Fig. 2, the front strip footing 17 is cast with an integral shear key /bearing face 20. The deadman anchor 18 has a stress bar anchor assembly 21 accurately located and cast into the concrete during construction of the footings 17, 18 and 19. The deadman anchor 18 functions to resist both vertical (overturning) and horizontal (sliding) forces, and its method of construction/location provides for uninterrupted soil pressures generating a very high shearing capacity in the soil, as will be further explained presently.

The web 12 of the T-post units 14 has a variety of present lengths selected according to height and load requirements. The T-post units 14 having the longest webs 12 are positioned on the concrete footings 17, 18 and 19 for the appropriately sized T-post 11. The web 12 of the T-post units 14 has a shear key 22 integrally formed at the top edge thereof, and a corresponding mating recess 23 on the lower edge. The shear key 22 and the recess 23 on an adjacent course mate during erection to correctly position the T-post units 14. and prevent relative lateral movement between the units 14, and further transfer horizontal shear forces. The first T-post unit 14 is positioned on the base and levelled with steel strip spacers and then bedded on a mortar bed. Subsequent units 14 are accurately aligned by the centring pins 24 (not shown) incorporated in the face portion 13 of the T-post units 14 and fixed by "LaZee" plates (also not shown) on the webs 12.

Adjacent courses of T-post units 14 are tied together with anchor bars 25 located towards the rear extremities of the webs 12. The bottom unit 14 is fixed to the deadman anchor 18 by anchor bars 25 passing through a coupler 26 to the anchor plate assembly 21 cast in the concrete.

The anchor bars 25 are galvanised high strength steel rods threaded on both ends, and are contained in precast flutes 31 on the web sections 12 to provide protection during backfilling. Stressing of the anchor bars 25 is achieved through the top anchor plate 27 on top of the web 12 of the last placed unit 14 and the bottom anchor plate 28 inserted into a precast slot 29 of the previously placed T-post unit 14. This is particularly shown in Fig. 5. The anchor bars 25 are tightened when a new unit 14 is placed on the stack, but not 'stressed' until the backfill reaches a level where easy access is available to use an air wrench. The stressing level is controlled by the use of calibrated load indicating washers. Both bottom 28 and top 27 anchor plates are bedded on grout, and the whole assemblies sealed with an epoxy coating before they are covered with backfill.

The length of webs 12 and the number of anchor bars 25 provide optimum support against soil loads at each of the T-posts 11 for the particular height.

After each course of T-post units 14 has been positioned, the planks 15 (see Fig. 3) are set in position. The planks 15 are temporarily held against the inside portion 16 of the face portion 13 by erection clamps 30 shown in Fig. 10. Ordinary backfill is then compacted behind the retaining wall 10 and the erection clamps removed when the fill height contains the planks 15. The backfill covers the deadman anchor 18, the rearwardly directed webs 12 and occupies the space behind the planks 15, with the mass of fill material holding the planks in place. The backfill most usually will extend to the full height of the retaining wall, although in some circumstances may finish immediately below the top-most plank 15.

The speed of construction of this retaining wall 10 is limited mainly by the speed of placing and compacting the backfill. With the rapid placement and fixing, it is possible for the height of the retaining wall 10 to be maintained at a level up to 4.8 metres higher than the backfill operation. Thus a full-time free standing construction noise barrier is provided during the embankment construction.

Fig. 6 shows a schematic representation of the structural principles of the retaining wall in accordance with the present invention. The structural face is tied to the deadman anchor. No slab-like base is required, rather a strip footing is utilised. It is sufficient to use only ordinary backfill, with stability being provided by forces transferred to the two-way deadman anchor. As previously noted, the 'two-way' nature of the deadman anchor resists overturning and sliding. The use of anchor bars to 'tie down' each course of T-post units provides resistance to lifting (overturning). The mass of backfill acting on the deadman anchor 18 results in high soil pressures about the anchor that resists shearing (sliding). In addition, the coupling of the front footing 17 to the deadman anchor 18 by the tie-beam 19 provides extra resistance to sliding movement. The deadman anchor 18 is located outside the 'active' zone relative to soil slippage that otherwise would occur on failure of a retaining wall, thus providing an inherent safety characteristic.

The aspect ratio (height:depth) is about 1:0.45 - 0.5, which is significantly less than prior art systems (e.g. cantilevered counter fort 1:0.6, and reinforced soil blocks 1:0.7).

Fig. 7 shows a detailed summary of the forces acting on the retaining wall 10. A number of minor friction forces have not been shown, for example down drag on the webs 12 of the T-post units 14. The following glossary explains each force:

1. Fb=horiztonal wall forces (backfill) : Pressure Pb 2. Fs=horiztonal wall forces (surcharge) : Pressure Ps

3. qs= surcharge pressure (ground surface)

4. Fd*=downdrag/friction (front wall)

5.

(webs): not included for deadman anchor only 6. Wf = weight facade of tee

7. Ww = weight of web of tee

8. Ws = weight soil on rear deadman anchor

9. Wr = weight rear deadman anchor

10. Wc = weight front footing 11. Rf = front footing reaction : components 4* overturning reaction

12. Ff = front footing sliding friction = Rf x tan(20)

13. Hf = front footing : thrust from wall soil forces

14. Mot = overturning moment about point (A) = (Fb + Fs) . E^" . 1.5 15. Mr = restoring moment about point (A) = Ww . S + (Ws = Wr) . dp etc.

16. Fp = prestress force = (Mot - Ww . d^") / dp

17. Pp = passive pressure (rear deadman anchor) 18. Tf = tie force (= Pp)

Figs. 8a-8g show various configurations for a retaining wall having a height ranging from 1.2 metres - 19.2 metres. The T-post units are conveniently labelled Tl- T6a respectively to indicate individual components.

The range of retaining wall heights for each configuration is as follows: Fig. 8a 1.2 - 2.4 metres

Fig. 8b 3.6 - 4.8 metres

Fig. 8c 6.0 - 7.2 metres

Fig. 8d 8.4 - 9.6 metres

Fig. 8e 10.8 - 12.0 metres Fig. 8f 13.2 - 14.4 metres

Fig. 8g 15.6 - 19.2 metres

The dimensions length x thickness x height of the respective web portion of each of the T-posts (Tl-T6a) are as follows:

Tl 1.8 m x 0.25 m x 2.4 m T2 2.8 m x 0.25 m x 2.4 m

T3 3.8 m x 0.25 m x 2.4 m

T4 4.8 m x 0.25 m x 2.4 m

T5 6.8 m x 0.25 m x 2.4 m

T6 8.8 m x 0.25 m x 2.4 m The face portion 13 of each T-post unit 11 has a thickness of 0.3 m and a

'width' (when viewed from the front) of 1.7 m. Fig. 9 shows the configuration of the T-post units 14 having the designation Tl and T4. All of the T-post units designated T2-T6 include two sets of fluting 31 to receive the anchor bars.

Fig. 10 shows a representative arrangement for a reinforcing wall showing only the bottom-most course of T-post units and the corresponding base. As can be noted, the front strip footings 17 and deadman anchors 18 are of differing size for the retaining wall sections of differing heights. For the T-post unit designated T2 the front strip footing 17 cross-sectional dimensions are approximately 0.7 m x 0.3 m and the deadman anchor cross-sectional dimensions are 0.5 m x 0.5 m. For the T-post unit designated T4, the front strip footing 17 cross-sectional dimensions are approximately 1.3 m x 0.3 m and the deadman anchor 18 cross-sectional dimensions are 1.8 m x 0.5 m. Finally, for the T-post unit designated T5, the front strip footing 17 cross-sectional dimensions are approximately 3.2 m x 0.6 m and the deadman anchor 18 cross-sectional dimensions are 2.6 m x 0.6 m. Fig. 11 is an elevational view of a retaining wall embodying the invention from which it can be seen that adjacent footings 36 are stepped in height to accommodate the ground contours, eg. some are located in a valley. The T-post 38 on the lowest footing 36 incorporates a half standard height T-post unit (T4(a)) to minimise the stepping requirements in the parapet wall 42 to suit the road grade and ground contours. At the steps in the footing levels 36, the T-posts 38, 39, 40 and 41 will have unbalanced loads on the lowest units 42, 43, 44 and 45 due to the soil pressure from the planks 46 being on one side only of the T-posts. In this case lean mass concrete is cast behind the unloaded face portion of the units 42, 43, 44 and 45 before backfilling against the planks 46. This provides for the balancing of the loads on the bottom units of the T-posts 38, 39, 40 and 41.

The parapet and coping 47 is cast on site, as is the case with all types of retaining walls, following the construction of the wall 35. The T-posts 38, 39, 40 and 41 can be provided with an optional architectural finish on the face portion by fitting liners inside the standard steel mold (not illustrated) or through alternative face portion molds. The precast extruded planks 15 and 46 can have optional colour finishes compatible with the extrusion process. An additional feature of the retaining wall system as described above is the ability to use the locating/fixing points on the topmost of the T-post unit 14 to provide fixing points for support of permanent sound barrier panels where required.

The advantages provided by the retaining wall embodying the invention are manifold, and include that the resultant retaining wall is economical and fast to construct, suitable for up to 20m heights and easily adaptable for any wall face shape. The wall utilises only two standard modular unit configurations for precasting off-site and with many applications. It relies on minimum field labour with no special skills for erection, and allows earthworks operations to proceed at a rate suitable for the capacity of the roadway spreading and compaction fleet. Further the wall does not require any special quality backfill or free draining layers and does not utilise sophisticated proprietary stressing systems or devices.

No counter balancing or similar devices are employed after connection of the base unit to the deadman anchor to completely eliminate interference with the backfill operations. The wall can be erected independently of the earthworks operations and up to 5m in height ahead of the working level. It does not require any temporary supporting during erection, and does not require the preparation of flat areas or slabs for commencement of the construction. It also has simple and minimum requirements for footing preparation.

Claims

CLAIMS:

1. A retaining wall comprising: a footing; at least one course of spaced apart T-post units stacked on said footing, said T- post units each having a web portion and a face portion, the face portion forming part of the face of said retaining wall and the web extending in a direction away from the face portion; anchor means for anchoring each said web portion to said footing or to a respective web of one of said T-post units of a lower course; at least one panel spanning the space between each adjacent T-post units; and fill material placed rearwardly of the panels and covering the web portions and footing at least partially to the height of the retaining wall.

2. A retaining wall as claimed in claim 1, wherein the base comprises a front strip footing on which the face portion of the T-post units and the panels are stacked, and a rear deadman anchor beam connected to the front strip footing by a tiebeam, the web portion of each T-post unit being stacked on the tiebeam.

3. A retaining wall as claimed in claim 2, wherein the web portion of a T-post unit has a recess formed in a horizontal edge thereof and a complementarily shaped shear key formed in the opposed horizontal edge, and whereby the key and recess of adjacent courses of T-post units mate to reduce lateral movement between stacked T-post units.

4. A retaining wall as claimed in claim 2, wherein the anchor means comprises a plurality of bars that extend over one or more adjacent stacked web portions, the bars being fixed at the ends thereof by locking means.

5. A retaining wall as claimed in claim 4, wherein said bars each are received within a fluted partial housing integral of the web portions.

6. A set of component parts for a retaining wall, the parts comprising: a footing; a plurality of T-post units each having a web portion and a face portion, and whereby, in use, at least one course of the T-post units is stacked in spaced apart relation on the footing, the face portion of each T-post unit forming part of the face of the retaining wall and the web extending rearwardly of the face portion, each said web portion being anchored to said footing or to a respective web of one of said T-post units of a lower course; and a plurality of panels whereby, in use, at least one panel spans the space between each adjacent T-post units.

7. A set of parts as claimed in claim 6, wherein the base comprises a front strip footing on which the face portion of the T-post units and the panels are stacked, and a rear deadman anchor beam connected to the front strip footing by a tiebeam, the web portion of each T-post unit being stacked on the tiebeam.

8. A set of parts as claimed in claim 7, wherein the web portion of a T- post unit has a recess formed in a horizontal edge thereof and a complementarily shaped shear key formed in the opposed horizontal edge, and whereby the key and recess of adjacent courses of T-post units mate to reduce lateral movement between stacked T- post units.

9. A method of construction of a retaining wall, the method comprising the steps of: a footing on the ground; stacking at least one course of spaced apart T-post units on the footing, the T- post units each having a web portion and a face portion, the face portion forming part of the face of the retaining wall and the web portion extending rearwardly from the face of the retaining wall; anchoring said T-post units to said footing or to a respective web of one of the

T-post units of a lower course by anchor means; spanning the space between each adjacent T-post units with at least one panel, said panels forming the remainder of the face of the retaining wall; and backfilling with fill material rearwardly of the panels to cover the base and web portions to at least partially the height of the retaining wall.

10. A method as claimed in claim 9, comprising the further step of casting the base onto the ground.

11. A method as claimed in claim 10, wherein the step of backfilling occurs after completion of the preceding steps at intervals corresponding to achievement of the partial final height of the wall, and the steps are repeated until the final height is reached.

12. A method as claimed in claim 11, wherein the anchor means comprise a plurality of bars that extend over one or more adjacent stacked web portions, being fixed at the ends thereof by locking means, and the method comprising the further step of tensioning the bars by the locking means following backfilling.