FACINGS FOR EARTHWORKS

Abstract: A facing for an earthwork comprises earth pressure bearing sections 2 adapted to be held rigidly relative to the rearwardly adjacent earth, for example by means of stabilising elements 3 embedded in the earth, and moveable facing panels 4 resiliently permitting movement of the earth substantially perpendicularly to the plane of the facing whereby earth pressure on the facing panels is reduced by establishment of arching forces between the rigidly held sections 2.

Description: This invention concerns improvements in or relating to facings for earthworks. Facings for earthworks are conventionally relatively thick in order to withstand earth pressures, even when the earth is stabilised, for example by inclusion of stabilising members such as reinforcement strips or grids, anchor systems or soil nails. The pressure of the earth on the facing, while often greatly reduced by interaction with stabilising members in the earth, is usually still sufficiently large to require an earth retaining facing comprising concrete panels of some 14-25cm in thickness or other panels of equivalent strength. Such panels are, however, expensive and there is a demand for a modified system using less expensive panels. We have found that the pressure on the facing is not uniformly distributed but that the areas of the facing close to the points of attachment to stabilising members tend to carry the greater part of the pressure while at more distant locations the pressure is lower. Thus, in a system in which substantially rectangular abutting facing panels are attached to the ends of rows of embedded stabilising elements, the pressure at the centres of the units is significantly lower than that at the periphery where the stabilising members are attached. This observation appears to be due to the phenomenon of arching within the earth mass. At the present time this phenomenon has not been fully explained and there are at least three theories of its mode of action. (Karl Terghazi, Theoretical Soil Mechanics, Whiley, p66 et seq). In principle, however, in particulate earth, compressive forces at a point are transferred by shear stresses in the earth to more distant points and the forces involved can be shown to follow an arched path within the earth mass. Where, as in the case of panels attached to stabilising members, the earth is rigidly constrained at a number of relatively close adjacent points, the arched lines of force within the earth emanating from adjacent fixed points join to form complete arches within the mass. These arches serve to retain more rearward earth and have the effect of reducing pressure at the facing at locations distant from the fixed points, e.g. at the centres of the facing panels. Our calculations, as given in greater detail hereinafter, have shown that although arching reduces the earth pressure on the central area of a rigid panel supported between two rigidly held beams, such forces are still large even at parts on the panel at a significant distance from the rigidly held beams. In contrast, where the rigid panel is replaced by an elastic membrane the earth pressure on the elastic surface is greatly reduced even close to the rigidly held beams, although the pressure on the beams is correspondingly increased. Furthermore, the deformation of the elastic membrane is only of the order of a few millimeters, not greatly different from that of a relatively thin conventional concrete panel. In practice, however, deformations of 1-2 cm might be expected. The present invention is based on the concept of designing the facing to take the greater part of the earth pressure in the vicinity of the points of attachment to stabilising members in the earth mass and, in order to reduce pressure at other points, to provide surfaces of the facing capable of resilient outward movement substantially perpendicular to the plane of the facing. In this way it is possible to design facing systems in which substantial areas are at reduced pressure and may thus be thinner and hence less costly, so reducing the overall cost of the facing system. It is known from US-A-3 802 205 (on which the precharacterising parts of the independent claims are based) to provide rigid piles which support facing blocks in a manner which resiliently permits movement of rearwardly adjacent earth perpendicular to the plane of the facing. It is known from FR-A-830 584 to provide a facing having facing elements carried by support elements rigidly held by soil anchors, wherein the support elements are narrower at the back than at the front. According to the present invention therefore we provide a facing for an earthwork comprising earth pressure bearing sections adapted to be held rigidly relative to earth and moveable or deformable sections resiliently permitting movement of rearwardly adjacent earth substantially perpendicularly to the plane of the facing, characterised in that the pressure bearing sections are narrower at the back than at the front to promote arching of compressive forces in the earth between said pressure bearing sections, whereby earth pressure on the moveable or deformable sections is reduced. According to a further aspect of the invention we provide a stabilised earthwork including a facing comprising earth pressure bearing sections adapted to be held rigidly relative to earth and moveable or deformable sections resiliently permitting movement of rearwardly adjacent earth substantially perpendicularly to the plane of the facing, characterised in that the pressure bearing sections are narrower at the back than at the front to promote arching of compressive forces in the earth between said pressure bearing sections, whereby earth pressure on the moveable or deformable sections is reduced. According to a still further aspect of the invention we provide a method of constructing an earthwork, comprising the steps of: rigidly mounting earth pressure bearing sections of a facing relative to the earth, and arranging moveable or deformable sections of the facing resiliently to permit movement of rearwardly adjacent earth substantially perpendicularly to the plane of the facing, characterised in that the pressure bearing sections are narrower at the back than at the front to promote arching of compressive forces in the earth between said pressure bearing sections, whereby earth pressure on the moveable or deformable sections is reduced. The sections which resiliently permit earth movement may be relatively rigid elements resiliently mounted to permit movement of the whole element (i.e. moveable sections) or they may be deformable elements such as membranes or compressible pads wherein only a part of the element moves (i.e. deformable sections). The reduction in earth pressure on the above movable or deformable sections is relative to that pressure which would be exerted if the sections were not capable of permitting earth movement. In principle, the rigidly held sections of the facing may be held in position by any suitable means. Thus, for example, the facing may be a gravity wall in which the rigidly held parts of the facing are maintained rigidly in contact with the earth by their weight and stiffness and thus carry the earth pressure using the arching phenomenon, while intermediate thinner sections are moveable relative to the earth. However, the present invention is principally of interest in relation to stabilised earthworks, that is earthworks in which stabilising members are embedded and provide a regular array of points to which a facing can be attached and the invention is largely described herein in relation to such stabilising systems. Thus, in general, the rigidly held sections of the facing will carry means for attachment to stabilising members embedded in the earthworks. The stabilising elements to which the facing is attached may include reinforcing strips as described in British Patent GB-A-1563317 and GB-A-1324686 or grids or other elements embedded in layers in the earth, for example using the Reinforced Earth technique described in said British patents; other stabilising elements include tie-rods attached to anchors or "deadmen" embedded in the earth at the rear of the structure, as well as soil nails driven into existing earth masses (including rock masses). The stabilising elements will advantageously be in the form of elongate, galvanised steel strips (e.g. having a rectangular cross-section 5mm thick by 40 mm wide) with their larger faces lying horizontally in the earth. In some cases, the reinforcing strips may each be provided with a ground anchor, e.g. a vertical plate, at their ends remote from the facing, and while this assists anchorage of the strip, the earth in the region of the facing will still be stabilised by the frictional forces between soil particles and the strip itself. The strips may be provided on their upper and lower faces with transverse ridges to assist frictional interaction with the earth. The stabilising elements may alternatively take the form of a metal mesh or plastic net or the like. A further possibility is that a single stabilising element extending rearwardly from the facing may be connected to a pair of further stabilising elements which extend rearwardly and diverge from each other. The connection between each stabilising element and the facing may be arranged to permit relative vertical movement between the stabilised earth in which the stabilising element is embedded and the facing element to which the stabilising element is connected. Such a connection may for example comprise a pair of horizontally spaced joints allowing pivotal movement in a vertical plane. In general it is preferred that a significant area of the rearward side of the facing in the vicinity of the points of attachment to the stabilising member should be exposed to the direct pressure of the earth. The resistance to earth movement created by the rigid attachment to the stabilising members establishes the required arching phenomenon and permits a measure of resilient movement of the earth to take place in the vicinity of the moveable or deformable surface elements without failure of the structure. In general, it is preferred that the ratio of the non-movable area of the facing to the movable area should be in the range 5:1 to 1:2, more preferably 2:1 to 1:1. The forward movement of earth in contact with the movable sections of the facing will generally be in the range 1-4 cm, e.g. 2-3 cm, depending on the distance from the rigidly fixed points of attachment to the stabilising members. In general, the distance of such forward movement may be 0.5% to 2% of the distance between the points of attachment in the vicinity of the movable section. The invention may be applied to a wide variety of facing systems and the following systems are illustrative. 1. A continuous relatively thin concrete facing with points of attachment to arrays of stabilising elements embedded in the earth mass, pads of resilient material such as foam rubber or expanded polystyrene being positioned in areas between said points of attachment. Such a continuous wall, for example constructed from reinforced concrete, is suitable where little or no settlement of the structure is anticipated and/or for low walls. The areas of facing covered by the resilient pads may be significantly thinner in cross section than the areas in the vicinity of the points of attachment, thus reducing the overall cost of the facing. 2. A system of interlocking facing units, for example relatively thin panels of reinforced concrete, the units being sufficiently spaced apart, usually by resilient bearing material, to permit flexibility in the plane of the facing, such units carrying a rearward panel of flexible material attached to the central area while the outer area, which also carries the means of attachment of the stabilising members, is in direct contact with the earth. Again, the areas covered by the flexible material may be thinner, thus reducing costs. 3. A system of interlocking frames, for example of reinforced concrete, secured to the ends of stabilising members, the remaining areas of the facing being capable of movement substantially perpendicular to the plane of the facing and being resiliently mounted on said frames, the frames being spaced apart sufficently to permit flexibility in the plane of the facing. 4. A system of beams (or lines of beams arranged end to end) attached to the ends of stabilising members, the substantially linear areas of the facing between such beams being capable of movement substantially perpendicularly to the plane of the facing. Such beams may be continuous or may be constructed of units and they may run vertically or horizontally or, indeed, at other appropriate angles. 5. A facing system comprising areas of facing rigidly secured to the ends of stabilising members separated on all sides by areas of facing which are capable of movement substantially perpendicularly to the plane of the facing. In order to optimise the establishment of arching within the soil mass, in the preferred embodiments the rearward surfaces of those sections of the facing rigidly secured by attachment to stabilising members are substantially perpendicular to the direction of the arching forces generated in the earth at their origin on the facing surface. These surfaces are thus preferably at an angle between 30° to 60° to the plane of the facing, more preferably 40° to 50°. Thus, in the case of a beam secured to the ends of a line of reinforcing elements, the cross-section of the beam is substantially triangular, (the stabilising members being attached at the point of the triangle) to assist generation of arching forces radiating rearwards on either side of the beam. Such arching forces will combine with those from neighbouring beams to form complete arches. If the beams are parallel, the arches in the earth will form essentially linear vaults which serve to retain the rearward earth. If the beams form part of a frame system, the arches from the side frame members and from the upper and lower frame members can join to form substantially domed vaults. Where the rigidly held facing elements attached to each of the stabilising members are completely separated by moveable areas, these facing elements advantageously have angled rearward surfaces generating arches towards each of the adjacent rigidly held facing elements. In an array of stabilising members the ends of which form an essentially rectangular pattern, the facing elements will have four such angled surfaces and will be shaped essentially as four-sided pyramids attached via the point of the pyramid to the stabilising members. The angled surfaces may advantageously be provided with grooves or other textural features which enhance frictional interaction between the surface and the earth and thus optimise the transmission of the required compressive arching forces. The present invention is particularly beneficial in the case of a framework facing system as described in (3) above. Such frame systems are now described in greater detail. The permitted movement of the frames in the plane of the facing should be sufficient to accommodate those movements of the earth structure which are found in practice. In general the movement of each frame in any direction in the plane of the facing, particularly the vertical direction is preferably at least 0.25%, more preferably at least 0.5%, most preferably at least 1.0% of the dimension of the frame in that direction. In general the movement of each frame will be less than 3%, more usually less than 2% of the dimension of the frame in that direction. In general, greater vertical spacing of the frames will be required where substantial vertical movement of the earth fill is expected after compaction for example when the fill is relatively lightly compacted during construction or where the earth structure is relatively high. Lateral movement of the frames needs to be accommodated to allow for the possibility of different vertical movements of the fill at points along the facing thus requiring the frames to tilt slightly in the plane of the facing. In a preferred form of frame structure the corners of the polygonal frames are adapted to engage via securing means permitting relative movement of said corners. Thus, for example, the securing means may comprise pins or lugs adapted to cooperate with holes or slots in the opposed corners of vertically adjacent frames, suitable resilient bearing means being provided to ensure the required movement of the frames in the plane of the facing. Such securing means may also, for example, comprise 'nails' each having a shank carrying resilient bearing means which engage with shaped surfaces at the corners of the frames to permit the required movement in the plane of the facing, and preferably a head portion which engages with the front of each polygonal frame to prevent forward movement perpendicular to the plane of the facing. Thus for example, the frames may be provided at their corners with channels perpendicular to the plane of the frame which cooperate with the resilient bearing and the securing means. In the case of rectangular frames, the facing may advantageously comprise spaced frames arranged to abut only at their corners, as in the arrangement of the black squares of a chess board. Thus, the frames in each horizontal row may be spaced laterally by about one frame width and the frames of the vertically adjacent rows will join the corners of said spaced frames. In this way, there will only be two frames abutting at each point of contact and the securing means will advantageously include resilient bearing means positioned between two L-shaped channels, each channel being provided by a respective frame. The resilient bearing means may be a rubber material preferably formed with external grooves to increase flexibility and facilitate relative movement of the polygonal frames. The corners of the frames may advantageously be provided with locating means such as the above mentioned pins or lugs which cooperate with the corners of vertically adjacent frames to permit limited lateral movement while assisting in locating the frames in their correct positions during assembly. Each lug may be in the form of a projecting end portion of a member embedded in the frame body, for example a concrete reinforcing bar. Nail securing means are advantageously provided with means for attachment to the ends of stabilising elements, for example a suitably placed hole through an extended portion of the shank. However, it is also possible for the frames to be attached to stabilising elements directly, via lugs projecting rearwardly therefrom and having a hole for a bolt connection to the stabilising element. Such lugs may conveniently be extensions of the metal bearing surfaces at the corners of the frames. The frames are advantageously constructed from uniform members comprising the sides of the polygonal shape required. This provides the advantage of simplicity of production and transport. The frames will normally be each constructed prior to assembly, for example by bolting to shaped metal brackets which, in a preferred form, may also serve as the shaped surfaces, e.g. channels, which abut the flexible bearing surfaces. Alternatively the frames may be assembled in situ from the side members and if so it may be desirable temporarily to stiffen each frame during construction by using a bar extending between diagonally opposite corners. In an alternative embodiment, the polygonal frames may be provided at their corners with diagonal bearing surfaces which, when the framework is assembled, are separated by resilient bearing means. In this case, the diagonal bearing surface may be a metal plate serving also as securing means in the assembly of the frame, for example by cooperation with bolts protruding from the separate side members of the frame. One or both of the diagonal plates may conveniently be provided with means for attachment to the earthwork, for example a short linkage so shaped as to permit one end to be bolted to the diagonal plate while the other end is bolted to the substantially horizontal end of a stabilising element in the earth. In such an embodiment, it may be convenient to provide at each pair of bearing surfaces a pin cooperating with holes in the respective frames to prevent relative movement of the frames perpendicular to the plane of the facing. However, this is not essential, for example where both of the diagonal plates are secured to stabilising elements or to each other. It is desirable to provide means whereby, during construction, the frames cannot overturn in the forward direction. This is conveniently achieved by extending the metal plates providing bearing surfaces at the corners of the frames sufficiently far rearwards to permit a bolt to join the two abutting plates and thus prevent their separation at that point. Alternatively, a strong substantially rectangular ring member, e.g. of steel, may be slid over the said extended metal plates to prevent such separation while not hindering the required vertical movement of the frames. It is also desirable to provide means for keeping the horizontal front surfaces of such plates apart to prevent rotation of the upper frame due to compression of the resilient bearing material, for example a bolt which can subsequently be removed. Tilting of an upper frame may also be prevented by using an elongate device which hooks on to an appropriately adapted portion at the front of the metal plates and which extends vertically to engage both a lower frame and the upper frame. The side members of the frames are desirably of sufficient depth in the direction perpendicular to the plane of the facing to provide adequate strength and stability. In the case of concrete frames, the side members may, for example have a thickness of 100-200 mm, e.g. 130mm, a length of 1000 to 1500 mm, e.g. 1350 mm, and a width of 200-300 mm e.g. 240 mm. The movable resilient sections of such frame structures, may be constructed from flexible, resilient material of adequate strength to resist soil pressure, for example a plastic or metal mesh secured at the edges to the frame but allowing soil movements of at least one or two cm at the center for a 1.5 metre frame. Alternatively, solid or other panels which are relatively rigid may be mounted on the frames in such a way as to permit relative movement perpendicular to the facing. If necessary, a flexible bearing can be interposed between the cover and the frame to permit such movement while maintaining a firm connection. This flexible bearing may be made from flexible material such as rubber or may be a form of spring which allows forward movement e.g. a cylindrical pipe or a U-shaped section of metal which can compress. Alternatively, the required resilient movement may be provided by deformability of the connection between the cover and the frame which connection can comprise lateral, resilient projections, for example relatively thin shaped metal bars, e.g. the elements of metal grids, which fit into slots at the rear of the frames and deform under the action of the earth pressure, thus, permitting the cover to move in the frame. The movable section is conveniently mounted on the soil side of the frame but may be mounted inside the frame or even at the front. The moveable elements should not themselves be so closely spaced at any point that they interfere with the free movement of the individual frames. In general, the moveable sections should be free to move 1-3, e.g. 2 cm in the perpendicular direction i.e. about 0.5% to 2% of the length of each side of the frame. The facing may be vertical with a generally flat or alternatively a curved or angled profile in plan view. In each case the shapes of the various facing components will be appropriately designed. In one alternative embodiment, a frame facing of the structure might be at an angle to the vertical, for example about 30°, with joints between adjacent frames extending generally horizontally. There will be a significant tendency for the facing frames in such a stucture to tilt rearwardly before they have been backfilled, and this may be prevented by bolting together the brackets of the frames in adjacent rows at the front of the facing, in addition to the previously described bolted connections at the rear. The stabilising elements in such a structure will also extend generally horizontally. The stabilising elements for frame structures are largely described herein as being connected to the facing at the joints between facing frames. However, the stabilising elements may instead be secured to the side members at points away from the joints. For example, a square facing frame may have two stabilising elements secured to each side member respectively one third and two thirds of the distance along its length, the frame thus having altogether eight stabilising elements extending therefrom. The stabilising elements may be secured to plates cast into and projecting from reinforced concrete side members. Similarly, where the rigidly fixed part of the structure comprises beams connected essentially linearly, the points of attachment of stabilising members may be at or near the ends of the beams or at intermediate points. Apart from rectangular or triangular facing frames, other shapes may be provided, such as parallelograms. One possible frame is in the form of a parallelogram with sides at 60° to the horizontal and with the lateral spacing between the joints being equal to the height of the frame. Similarly, in the case of facing structures in which the rigidly fixed members are essentially linear beams, these may be arranged in straight lines, for example as vertical pillars, or may be arranged in a zig-zag or other non-linear configuration. The design of the resiliently moveable sections in facing systems of the invention has been described, for convenience, largely in terms of framework facing structures, which are, indeed, preferred. It will be appreciated that similar considerations apply to the design of moveable sections for use with rigidly held beams or plates. The following calculations demonstrate the arching effect in relation to an earth retaining wall comprising vertical pillars spaced at 2m intervals and supporting a thinner facing of either concrete or an elastic membrane. The deformation of the thinner intermediate section at varying distances from the pillar is calculated when a pressure of 20 kPa is exerted on the earth behind the wall. Young's modulus of the earth (E earth) is taken to be 50,000 kPa and Poissons coefficient for the earth is taken to be 0.3. Model 1 The intermediate facing is concrete (Young's modulus = E concrete = 107 kPa). The vertical pillars are of 20 cm x 20 cm square cross section. Four thicknesses of concrete facing, e, are considered, namely Om, 0.0125m, 0.025m and 0.0375m. These correspond to the following values of E x S (where S is the surface area of one vertical metre of facing over the half distance between pillars): 0kN/m, 125,000 kN/m, 250,000 kN/m and 375,000 kN/m. Figure 25 shows the deformation of the facing for the various values of e and Figure 26 shows the pressure exerted by the earth on the concrete taking into account the deformation of the concrete facing as shown in Figure 25. It can be seen that the flexural rigidity of the concrete facing permits the transmission of the forces exerted by the pillars to a significant area of earth adjacent to the pillar, in contrast with the situation where an elastic membrane is used as can be seen hereinafter. Model 2 In this system, the concrete facing is replaced by an elastic membrane having a stiffness per linear metre = K of OkN/m, 125,000 kN/m, 250 kN/m and 375 kN/m, i.e. corresponding to the values of ES in Model 1. In a first calculation, the pillars are 20 cm x 20cm in cross section. Figure 27 shows the deformation of the facing at varying distances from the pillars and Figure 28 shows the distribution of earth pressure exerted on the membrane. It can be seen that there is little significant pressure on the elastic facing at distances greater than 0.1m from the pillar; the initial 0.1m is the surface presented by the pillar itself and the increasingly large value for the pressure over that area is due to arching of compressive forces immediately behind the pillar. This contrasts with the effect shown in Figure 25, where there was significant pressure on the facing even at 0.4m from the pillar. On the other hand, the deformation of the elastic facing as shown in Figure 27 is not markedly greater than when an essentially rigid concrete facing is used and consequently such an elastic membrane can readily serve to retain the earth between the pillars. Such deformation is still further reduced if the thickness of the pillars is increased slightly. Some preferred embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a horizontal section of a facing according to the invention provided with resilient pad sections; Figure 2 is a perspective view of a facing according to the invention in which rigidly fixed elements are separated by moveable panels; Figure 3 is a horizontal section of a facing according to the invention in which vertical beams are separated by resilient moveable cover sections; Figure 4 shows a frame constructed from side members which are narrower at the rear than at the front; Figure 5 shows an array of the frames of Figure 4; Figure 6 shows a horizontal section through a frame as shown in Figure 4 and includes a resiliently mounted cover; Figure 7 shows a perspective view of a channel member for use with a frame as in Figure 4; Figure 8 shows a section through abutting corners of frames carrying the channel members of Figure 7; Figure 9 shows a section through two abutting channel members of Figure 7 along the line A-A; Figure 10 shows a section through two abutting channel members of Figure 7 along the line B-B; Figure 11 shows a side member of a frame according to the invention together with part of an associated resiliently mounted cover; Figure 12 shows a perspective view of another form of flexible connection, with certain parts omitted for clarity; Figure 13 shows a longitudinal section in a vertical plane through the connection of Figure 12; Figures 14, 15 and 16 respectively show sections on the line A-A, B-B and C-C of Figure 13; Figure 17 shows a perspective view of attachment means for a stabilising element at the rear of the flexible joint shown in Figure 12; Figure 18 shows a device for temporarily stabilising the facing frames of Figures 12 to 17 during construction; Figure 19 shows the stabilising device of Figure 18 in use during construction; Figure 20 shows a perspective view of another form of flexible connection; Figure 21 shows a section through the connection of Figure 20 parallel to the plane of the facing; Figure 22 shows a nail for use in the connection of Figures 20 and 21; Figure 23 shows a perspective view of part of another form of flexible connection; Figure 24 shows a vertical section through the connection of Figure 23; and Figures 25-28 relate to the calculations discussed above. In the embodiment shown in Fig. 1, a facing panel 201 is provided with strengthened portions 202 having angled edges which serve to promote arching of compressive forces. Stabilising elements 203 embedded in the earth in regularly spaced horizontal arrays are attached to the rearward sections of the strengthened portions 202. Expanded polystyrene 204 is attached on the rear side of the panel to provide the required resilience. The sections covered by the polystyrene may be significantly thinner and incorporate less steel than corresponding areas of a conventional facing panel. The strengthened portions 202 may take the form of four-sided pyramids each attached to a separate stabilising element or of 2-sided linear beams each attached to more than one stabilising element; such beams may link with other such beams to form polygonal frames. The dotted lines indicate schematically the lines of arching compressive forces. In the embodiment shown in Figure 2, strengthened earth retaining portions substantially in the form of four-sided pyramids 205 are secured to stabilising members 203 embedded in the earth. Cruciform thin concrete panels 206 are mounted in interlocking relationship with the four-sided pyramids 205 and with each other, being restrained from forward movement by resilient engagement between the angled corners 207 of the panels 206 and the angled surfaces 208 of the pyramidal retaining portions, a resilient pad (not shown) being situated between the said angled surfaces 207 and 208 to permit resilient forward movement of the panels 206 relative to the four-sided pyramids 205. In the embodiment shown in horizontal cross-section in Figure 3, vertical earth retaining pillars 209 are secured to stabilising elements 203 embedded in the earth. Relatively thin unreinforced concrete panels 210 are mounted between the pillars 209 and resilient pads 211 are inserted between the angled surfaces 212 of the beams and the angled edges 213 of the panels 210 to permit resilient forward movement of the panels 210. The vertical pillars 209 may be continuous over the height of the wall or a series of relatively short beams may rest one on the other, preferably separated by resilient pads similar to the pads 211. Similarly, the panels 210 may be continuous vertical concrete 'planks' or may be shorter panels stacked vertically and also advantageously separated by resilient pads. The dotted lines indicate schematically the lines of arching compressive forces. In the embodiment shown in Figures 4, 5 and 6 the side members 6 of a facing frame 3 are narrower at the rear than at the front, thus presenting angled rear surfaces 6A which assist establishment of compressive arching forces indicated by dotted lines. A cover 4 is provided as shown in Figure 6 which is constructed from concrete. A resilient block 120 is provided between the angled side of the cover and the angled side of the frame. The dimensions of the cover are such as to allow a forward movement of the cover of about 2 cm. In the embodiment shown in Figures 7, 8, 9 and 10 the corners of the frame are provided with brackets 7 which serve to connect the side members via bolts and which further carry bearing surfaces 150 and 151 provided with resilient bearings 152 and 153. Lugs 154 and 155 are provided which cooperate like hooks to assist location of the frames during assembly while allowing some lateral movement. The brackets 7 extend rearwards and forwards of the frames and are provided with holes 156 and 157 which are adapted to engage with bolts joining the abutting channel members 6 of vertically adjacent frames; this serves to hold the upper frames in the vertical position during assembly, when they are otherwise unsupported. Further holes 158 are provided which may be bolted to stabilising elements such as strips embedded in the earth. In the embodiment shown in Figure 11, the side member 75 of a frame is provided with slots 76. A moveable section 77 constructed from concrete cast on wire mesh 78 has side elements of the mesh 79 which engage in the slots 76 and which are so shaped as to bend under the forward movement of the cover due to earth pressure. Referring to Figure 12, this shows a pair of facing frames similar to the frame of Figure 4 and having side members 6 narrower at the rear than at the front. The flexible connection between the frames consists of an L-section bracket 80,81 bolted to each frame, as seen in Figures 13 and 15. The attachment means for a stabilising element or elements at the rear of the frames includes a relatively short bracket 83 also of L-shaped cross section bolted to the rear of the lower L- section bracket 80 to form an inverted T-shaped rear projection, as seen in Figure 17. A pair of connecting plates 84 fit above and below the cross bar of the "T" formed by the brackets. The connecting plates are formed with suitable holes for bolting to the brackets and the upper connecting plate 84 is formed with a slot 85 for receiving the vertical portions of the brackets. A hole 86 is formed through the rear part of each connecting plate to receive a bolt for connection of a stabilising element. Instead of a single hole 86 a pair of laterally spaced holes may be provided for connection of a pair of stabilising elements. As shown in Figures 12 to 15, the upper bracket 81 of the upper facing frame has bolted thereto a relatively short L-section bracket 87 with a spacer plate 88 arranged between the two brackets. The bracket 87 projects forwardly so as to abut against a front plate 82 secured, e.g. by welding, to the lower bracket 80 and to define a space 130 between the front face of the upper frame and the front plate 82. As seen in Figures 13 and 16 a resilient block 89, e.g. of rubber, fits between the lower and upper brackets 80,81 to provide a flexible connection between the frames. The resilient block could alternatively be replaced by a C-shaped spring of steel or the like arranged to permit resilient relative movement between the frames. Thus in the embodiment of Figures 12 to 17 the rear of the lower bracket 80 is secured to one or more stabilising elements embedded in the earth backfill, thereby securely locating the lower frame, while the short front bracket 87 connected to the upper bracket 81 abuts against the front plate 82 of the lower bracket 80, thereby securely locating the upper frame. By this arrangement the frames are secured to the stabilising elements and restrained against forward movement, while the resilient block 89 permits relative movement of the frames in the plane of the facing. The purpose of the space 130 between the upper frame and the front plate 82 will be described with reference to Figures 18 and 19 which show a device 90 used during construction to ensure that a frame 91 of an upper row of frames does not tilt forwardly. The device 90 comprises an elongate member 92 having at its upper and lower ends abutment plates 93 arranged to engage the front of the facing in the region of the flexible connections, as seen in Figure 19. Midway of its length the device 90 has a hook member 94 with a downwardly projecting portion 95 arranged to engage in the space 130 between the upper frame 91 and the front plate 82 of the lower bracket 80. During construction as shown in Figure 19, the top part of the frame 91 is restrained against forward movement by the device 90 which is secured to the facing by the hook member 94. The device may be removed once the stabilising elements at the top of the frame 91 have been backfilled, thereby permanently securing the top of the frame 91. In the arrangement shown in Figure 20 the side members 97 of the frame 96 are each provided with a pair of U-shaped lugs 98 which can conveniently be formed as part of the conventional reinforcing bars of the side members. Adjacent side members are held together by a bar 99 which passes through the two lugs of each side member. As seen in Figure 21 two such frames 96 are connected together at their corners with a resilient block 160 arranged therebetween to permit relative movement between the frames. The connection is completed by a nail 100, shown in Figure 22, which has a front plate 101 for abutment against the front faces of the frame side members and a widened rear portion 103 having a vertical hole for attachment to a stabilising element. The front plate 101 should be of a size sufficient to ensure that its abutment area with these front faces is large enough to accommodate stresses caused by forwardly acting earth pressures on the frames. The shank 102 of the nail 100 is of circular cross section and is arranged to screw into a hole in the front plate 101 once the shank has been threaded through a central hole 104 in the resilient block. The nail 100 may alternatively have a shank of uniform rectangular cross section which may be threaded through a correspondingly shaped hole in the resilient block. At the front of such a rectangular nail a front plate may be welded, so that the nail is installed by threading through the staples in the direction from the front to the rear of the facing. It will thus be seen that in the arrangement of Figures 20 to 22 significantly less steel is used at the flexible connection between frames than in the previously described embodiment. In the embodiment shown in Figures 23 and 24 each frame consists of four side members 105 each having at its opposite ends a pair of plate-like attachment lugs 106. These lugs, preferably of steel, are provided integrally on the ends of members embedded in the concrete side member and each lug has a hole 107 therethrough for passage of a bolt for securing together adjacent side members 105 of a frame. Figure 24 shows how the attachment lugs 106 of upper and lower frames 110 and 111 fit together at the flexible connection with a resilient block 109 located in the space defined by the ends of the side members. The two pairs of lugs designated 106a secure together the side members of the upper frame 110 and the two pairs of lugs designated 106b secure together the side members of the lower frame 111. As seen in Figure 24 the lugs 106a and 106b associated with the respective frames are offset from each other along the axis of the connection so that the lugs nest together substantially coaxially. In such an arrangement the frames will normally be connected to stabilising elements at points on the side members spaced away from the flexible connections between frames. In the embodiment of Figures 23 and 24, each side member is formed with a pair of attachment lugs 106, but in an alternative arrangement each side member may instead be provided with a single lug. Each lug may be formed by a U-shaped bent plate having its bent portion embedded in the frame side member and its two end portions spaced apart and projecting from the side member, possibly with the space between the plates filled in with concrete to form a block-shaped lug.

Claims: A facing for an earthwork comprising earth pressure bearing sections (202;205;209;3;91) adapted to be held rigidly relative to earth and moveable or deformable sections (204;206;210;4) resiliently permitting movement of rearwardly adjacent earth substantially perpendicularly to the plane of the facing, characterised in that the pressure bearing sections are narrower at the back than at the front to promote arching of compressive forces in the earth between said pressure bearing sections, whereby earth pressure on the moveable or deformable sections is reduced. A facing as claimed in claim 1, wherein stabilising elements (203) are embedded in the earth and are attached to the pressure bearing sections to hold said sections rigidly relative to the earth. A facing as claimed in claim 2, in which the stabilising elements are reinforcing strips (203). A facing as claimed in claim 2, in which the stabilising elements are grids. A facing as claimed in claim 2, in which the stabilising elements are tie-rods secured to anchors. A facing as claimed in claim 2, in which the stabilising elements are soil nails. A facing as claimed in any of claims 2 to 6, in which the ends of the stabilising elements (203) are separately attached to pressure bearing sections (205) of facing which are separated on all sides by moveable sections (206) of facing. A facing as claimed in any of claims 2 to 6, in which the pressure bearing sections of facing comprise beams (209) attached to two or more stabilising elements (203) and separated on each side by moveable sections (210). A facing as claimed in any of claims 2 to 6, in which the pressure bearing sections are in the form of interconnecting polygonal frames (3) enclosing said moveable sections (4). A facing as claimed in any preceding claim, wherein the moveable sections (204;206;210;4) permit soil movement in the perpendicular direction of 2 to 4 cm. A stabilised earthwork including a facing comprising earth pressure bearing sections (202;205;209;3;91) adapted to be held rigidly relative to earth and moveable or deformable sections (204;206;210;4) resiliently permitting movement of rearwardly adjacent earth substantially perpendicularly to the plane of the facing, characterised in that the pressure bearing sections are narrower at the back than at the front to promote arching of compressive forces in the earth between said pressure bearing sections, whereby earth pressure on the moveable or deformable sections is reduced. A method of constructing an earthwork, comprising the steps of: rigidly mounting earth pressure bearing sections (202;205;209;3;91) of a facing relative to the earth, and arranging moveable or deformable sections (204;206;210;4) of the facing resiliently to permit movement of rearwardly adjacent earth substantially perpendicularly to the plane of the facing, characterised in that the pressure bearing sections are narrower at the back than at the front to promote arching of compressive forces in the earth between said pressure bearing sections, whereby earth pressure on the moveable or deformable sections is reduced.

Inventors: VIDAL, HENRI
Applicants: SOCIETE CIVILE DES BREVETS DE HENRI VIDAL
Application year: 1988
Main classification: E02D29
IPC codes: E02D17, E02D29