It is a common law principle that a landowner has a duty to maintain lateral support to adjoining properties, which means your neighbor may not legally dig a hole that causes your land to collapse. However, the exception to this rule is that the neighbor is only responsible for providing enough support to the land in its natural condition and not for any of the buildings on it, unless you can prove that the land in its natural state was strong enough to support the structures. As long as your neighbor exercises reasonable care in supporting only the land itself, he will not be responsible for your damages. The limits of “reasonable care” here means the neighbor does not need to take extreme or burdensome precautions, but only a level of ordinary care and prudence. So, if your neighbor takes reasonable care to reinforce your land during the excavation and was not negligent, he will not be liable for your foundation slipping.
For more information, see: Walker v. Strosnider, 67 W.Va. 39, 67 S.E. 1087 (1910); McCabe v. Parkersburg, 138 W.Va. 830, 79 S.E.2d 87 (1953); Beaver v. Hitchcock, 151 W.Va. 620, 153 S.E.2d 886 (1967); Noone v. Price, 171 W.Va. 185, 298 S.E.2d 218 (1982); 1A Michie’s Jurisprudence Adjoining Landowners §§ 5-9 (2007); Restatement (Second) of Torts § 821D (1979); Doyle, D., Smith, D., Ferrise, A., Real Property: Landowners’ Rights and Responsibilities in West Virginia, http://www.wvu.edu/~agexten/forglvst/Bulletins/rd726.pdf (last visited June 15, 2015).