ser no 09 687 445 filed on oct 13 2000 which is incorporated by reference in its entirety to introduce the fill material under the slab to fill the space 170 one or more through holes 150 see fig1 a can be drilled through the slab 120 so that the fill material can be injected into the space 170 via the through hole 150 although one through hole 150 is illustrated any suitable number of through holes can be drilled through the slab to achieve appropriate filling the through holes 150 can be disposed at any location on the slab 120 one finds suitable for backfilling the space 170 in the illustrated embodiment the through hole 150 is disposed close to the edges 114 of the roadway 110 so that a central region of the roadway 110 can remain open for traffic e g vehicles and pedestrians after filling the through holes 150 are filled in an appropriate way such as by using concrete fill material alternatively the fill material can be injected into the space 170 from the side of the road for example as shown in fig1 a an injection device 155 can be introduced into the space 170 from the side of the road to inject the fill material into the space 170 turning to fig1 d after the slab 120 is lifted and the space is filled with fill material the hose 140 is deflated deflation of the hose 140 leaves a void resulting from the space occupied by the inflated hose additional fill material is then introduced again to fill the void as shown in fig1 d the sunken slab is thus returned to its original level 116 fig2 a and b illustrate another embodiment where.