It is all to common a story these days.  A municipality spends hundreds of thousands of dollars to reline all the culverts under a stretch of busy highway with the intention of correcting the eroding pipes so the road won't be damaged above.  Then a few years down the road sinkholes and subsidence begin to occur and the road has to be replaced anyway.  The reasons for this are varied and can be summed up concisely, “The contractor only did half the job”.  
What we mean by that is that in almost any scenario where a pipe is failing there has been some sort of erosion, scouring of the pipe or roadbed around the pipe.  These voids or poorly compacted zones are further impacted by the cleaning methods used in preparation for pipe repairs.  It is not sufficient in many cases to simply repair the pipe or joint, you also need to fill the voids and stabilize the surrounding soil.  That way the situation is permanently addressed and the overhead infrastructure will not be affected by further issues.  
In some large culverts where the pipe is fundamentally sound but had joint issues grouting can extend into dozens or even hundreds of yards of grouting material to fill the voids which can extend for a long distance from the actual pipe.  Pipe grouting is an extremely important facet to a comprehensive pipe rehabilitation solution.