1. Maximum impact load
The impact loads described in this section are those resulting from large weights falling from
significant heights. In this case, the use of an impact factor F , as applied in Section 4, is not
sufficient to estimate the effect of the impact load on the buried pipe. The surface impact load
due to the weight W of a fallen object
2.Penetration and PPV
For impact near the pipe location, the increased pressure transmitted to the pipe can be evaluated
as described in Section 4 where Pmax is the applied surface load. This evaluation considers the
ovality, through-wall bending, side wall crushing, and ring buckling. In addition, the burial depth
should be sufficient to guard against ground penetration by falling objects.
Example problem see the link
http://www.4shared.com/document/pfUVB8pb/Example_problem_for_Maximum_Im.html