Methods including providing a hydrajetting tool comprising a housing having a top end and a bottom end and having a plurality of jetting nozzles disposed thereon, the top end of the housing fluidly coupled to a tool string; providing at least one sub-soil-surface cavity adjacent to or in unstable soil, the unstable soil having a plurality of channels therein; introducing the hydrajetting tool into the at least one sub-soil-surface cavity; injecting a cement slurry through at least one of the jetting nozzles and into the sub-soil-surface cavity; permeating the cement slurry into the plurality of channels in the unstable soil; filling the at least one sub-soil-surface cavity with the cement slurry; and curing the cement slurry, thereby forming a stable soil and a cement pillar in the at least one sub-soil-surface cavity.