interfere with or impede the construction of outer wall portion 58 of the wall structure 50 the particular size of shear blocks 10 of the present invention is not believed to be critical the size of blocks 10 will generally vary according to the magnitude of the expected forces to be resisted and the strength of the material used to fabricate the blocks as was set forth previously when shear blocks 10 are used to resist shear forces caused by backfilling preferably the blocks vary in size depending upon their proximity to the expected forces to further illustrate the present invention the following example is given as a particular application of the subject shear blocks in a prestressed concrete tank it should be realized that the example is presented for the purpose of illustration only and the example does not limit the invention as has heretofore been described in a particular application of the present invention in a tank having an outer diameter of approximately 140 feet thirty shear blocks 10 were utilized on each side of foundation 20 the blocks placed in a pattern as illustrated in fig2 in each group of thirty shear blocks 10 fifteen are on each side of a line perpendicular to the uphill direction the fifteen downhill shear blocks 10 and the adjacent group of twelve uphill blocks are all of a shape as shown in fig1 and have a length of about two feet a width of ten inches a front height of about eight inches and a rear height of about six inches adjacent to the uphillmost block 10.