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CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is an U.S. national phase application under 35 U.S.C. §371 based upon co-pending International Application No. PCT/AU2006/000501 filed on Apr. 13, 2006. Additionally, this U.S. national phase application claims the benefit of priority of co-pending International Application No. PCT/AU2006/000501 filed on Apr. 13, 2006, Australia Application No. 2005901902 filed on Apr. 18, 2006 and Australia Application No. 2005903270 filed on Jun. 22, 2005. The entire disclosures of the prior applications are incorporated herein by reference. The international application was published on Oct. 26, 2006 under Publication No. WO2006/110943. 
   FIELD OF THE INVENTION 
   The present invention relates to a masonry block for use in a retaining wall, and a method of construction of a retaining wall including the provision of soil stabilising members. 
   BACKGROUND TO THE INVENTION 
   It is known to require the use of soil stabilising members in conjunction with retaining walls. Typical soil stabilising members comprise sheets of mesh-like material known as “geogrid”. The sheets are affixed between courses of masonry blocks used in the retaining wall construction, and extend behind the retaining wall to reinforce and stabilise the soil being retained. 
   There are several known methods for affixing the sheets between masonry block courses. Typically, these use pins or similar devices passed through the blocks and the sheet to restrain movement of the sheet relative to the blocks. 
   This process can be time consuming. Additionally, it must be done during the building of the wall, with the sheets being placed between appropriate courses whilst the wall is be constructed. This greatly reduces the efficiency of labour during construction of the retaining wall. 
   An alternative method which has been proposed is to use hollow blocks having a vertically aligned inner cavity, and to pass strips of soil stabilising material through the cavities of adjacent blocks. The strips can then be passed out between courses as required. 
   This method shares many of the disadvantages of the use of sheets described above. It requires the strips to be fed through the blocks during construction of the wall, and greatly adds to the complexity and time of the wall building process. 
   The present invention attempts to overcome at least in part some of the aforementioned disadvantages of previous masonry blocks and methods of affixing soil stabilising members thereto. 
   SUMMARY OF THE INVENTION 
   In accordance with one aspect of the present invention there is provided a masonry block having a front face and a rear face, characterised in that the rear face includes a back wall and an extension portion extending outwardly therefrom, the extension portion including a channel passing therethrough, the channel having openings at either end thereof, wherein, in use, when the extension portion of a first block in a first course is located adjacent the back wall of at least one adjacent second block in an adjacent second course, the front faces of the first and second blocks being substantially co-planar, a channel opening of the first block locates adjacent to, and outside of, the back wall of the second block, and whereby a portion of a soil restraining member may be restrained within the channel. 
   In accordance with a second aspect of the present invention there is provided a method of construction of a retaining wall, the method characterised by including the steps of laying courses of masonry blocks to form a wall having a rear face, at least one of the masonry blocks having an extension portion which extends beyond the rear face, the extension portion having a channel passing therethrough; passing a portion of a soil stabilising member through the channel to be retained thereby; moving an outer portion of the soil stabilising member away from the rear face; and filling against the rear wall face with filling material to cover the outer portion of the soil stabilising member. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
       FIG. 1  is an isometric view of a masonry block in accordance with the present invention; 
       FIG. 2  is a rear isometric view retaining wall constructed of masonry blocks as shown in  FIG. 1 ; and 
       FIG. 3  is a rear isometric view of the retaining wall of  FIG. 2  including a plurality of soil stabilising members located therewithin. 
   

   DESCRIPTION OF PREFERRED EMBODIMENTS 
   Referring to the Figures, there is shown a masonry block  10  having a substantially planar front face  12  and a rear face  14 . 
   The rear face  14  has a back wall  16  substantially parallel to the front face  12 , and an extension portion  18  extending outwardly from the back wall  16 . The extension portion  18  in the embodiment of the drawings is trapezoid in shape, with an outermost face  20  which is substantially parallel to the front face  12 , and two angled side faces  22  which taper from the back wall  16 . The back wall  16  is thus divided into two substantially equal portions  16   a  and  16   b , each of which are about two-thirds the width of the outermost face  10 . 
   A substantially rectangular channel  24  passes through the extension portion  18  from a top face  26  of the block  10  to a bottom face  28 . The channel  24  is substantially parallel to, and of approximately equal length to, the outermost face  20 . The channel  24  is entirely contained within the extension portion  18 , and is thus outside a plane determined by the back wall  16 . The channel  24  has an openings at either end, with an upper opening  30  at the top face  26  and a lower opening (not shown) at the bottom face  28 . 
   The portion of the block between the side walls  22  and the channel  24  is a shear-supporting portion  25 . 
   In use, a retaining wall  40  as shown in  FIG. 2  is constructed from a plurality of masonry blocks  10 . The wall is constructed by laying the masonry blocks  10  in a plurality of courses  42 . The blocks are layed such that the front faces  12  of the blocks  10  are substantially co-planar, as are the back walls  16 . The back walls  16  combine to form a rear face  44  of the retaining wall  40 . 
   Each course  42  is offset from an adjacent course  42  by 50%. In this way the extension portion  18  of a first block  10   a  in a first course  42   a  is adjacent a portion  16   a  of the back wall  16  of an adjacent second block  10   b , and adjacent a portion  16   b  of the back wall  16  of an adjacent third block  10   c , the second and third blocks  10   b ,  10   c  being in a second course  42   b.    
   It will thus be apparent that the lower opening of the channel  24  of the first block  10   a  locates outside the back wall  16  of the adjacent blocks  10   b ,  10   c , and is thus accessible even after subsequent courses  42  have been laid. 
   Once the retaining wall has been constructed as shown in  FIG. 2 , it is possible to introduce soil reinforcing members in the forms of strips  46  of geo-grid material into the retaining wall. In a preferred deployment of such strips, an inner portion  48  of a strip  46  is passed through the channels  24  of two parallel blocks  10   a ,  10   d , the parallel blocks being in first and third courses  42   a ,  42   c  separated by a second course  42   b . The strip  46  has two outer portions  50  extending from the upper opening  30  of the first block  10   a  and the lower opening of the fourth block  10   d.    
   Preferably, strips  46  of geo-grid material are arrayed through the retaining wall  40  as shown in  FIG. 3 . 
   In an alternative deployment, strips  46  can be passed through a single block  10 . 
   The outer portions  50  of the strips  46  are moved away from the rear face  44  of the retaining wall  40  as shown in  FIG. 3 . The rear face  44  can then be filled against with filling material such as soil, the strips  46  acting to both stabilise the soil and strengthen the wall. 
   It will be appreciated that the shear supporting portion  25  of the blocks  10  must be sufficiently strong to withstand shear forces introduced through the strips  46  when the retaining wall  40  is in use. It will also be appreciated that the channel is sized so as to allow the strip to pass within without restriction. In particular, the width of the channel is larger than that of the reinforcing member. 
   Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.

Summary:
A masonry block ( 10 ) has a rearwardly extending portion ( 18 ) which includes a vertical channel ( 24 ). In use, soil stabilizing members ( 46 ) are passed through channels of aligned masonry blocks ( 10 ) and extended rearwardly behind a retaining wall ( 40 ).