
70 Forensic Engineering Fundamentals
e plastic limit (PL) is the lowest water content at which a thread of the soil can be
just rolled to a diameter of 1/8 in. without cracking, crumbling, or breaking into pieces.
According to ASTM 424,
PL
weightof ovendriedd
100
soil
(3.3)
e plastic index (PI) AASHO T-91 is the numerical dierence between the LL and the PL or
(3.4)
For our example soil samples, we nd
so that the PI is
For bearing soils the P.I. should not exceed 6, and the L.L. should not exceed 25. is soil
is not capable of supporting footings.
Subsidence
Natural subsidence rarely occurs ...