negative pore water pressure. Tensiometers require
sum blocks require tedious calibration of electrical
resistivity for each soil and dissolved salts greatly in-
constant maintenance, while gypsum blocks and psy-
chrometer tend to deteriorate with time and may be-
fluence the results. Thermocouple psychrometer can-
not measure soil suctions reliably at negative pres-
come inoperable within one year. A routine field meas-
sures that are less than one atmosphere and require a
urement of soil suction is not presently recommended
because of the limitations associated with these de-
constant temperature environment. Psychrometer
vices. Alternatively, laboratory measurements of soil
also measure the total suction that includes an osmotic
suction can be easily performed (para 4-2a).
component caused by soluble salts in the pore water, as
well as the matrix suction that is comparable with the
3-6
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