I disagree as to the comment it is an addition to basis of the land - this definitely has a useful life and is required to use the land for rental purposes.
I would treat this as a repair and expense it (if not you could do 100% bonus depreciation), per IRS Pub 946 :
How Do You Treat Repairs and Improvements?
If you improve depreciable property, you must treat the improvement as separate depreciable property. Improvement means an addition to or partial replacement of property that is a betterment to the property, restores the property, or adapts it to a new or different use. See section 1.263(a)-3 of the regulations.
You generally deduct the cost of repairing business property in the same way as any other business expense. However, if the cost is for a betterment to the property, to restore the property, or to adapt the property to a new or different use, you must treat it as an improvement and depreciate it.
