Hydro-Mechanical Properties of an Unsaturated Frictional Material

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CHAPTER 7. ANALYSIS AND INTERPRETATION OF THE EXPERIMENTAL
RESULTS
Influence of loading path direction
Influence of loading path direction, i.e. main drainage and imbibition process was investigated
in the modified pressure plate apparatus and in sand column test I, where the imbibition re-
sults are scanning imbibition curves. These results are given in Fig. 7.5. The main imbibition
and drainage curves show significant influence of loading path on the shape of the suction-
water content curves. Draining and imbibition processes of the specimen show non-unique
behavior. For a suction value the corresponding volumetric water content (degree of satura-
tion, water content) during imbibition process is smaller than during drainage process. The
curves are characterized by the phenomena of hysteresis. The scanning imbibition curves are
located between the main drainage and imbibition loop.
Whereas after imbibition procedure an initially saturated specimen was reached again for
the tests performed in the modified pressure plate apparatus, in the sand column test I an
initially saturated specimen was not reached (θ ′
s,loose = 39%, θ′
s,dense = 37%). The results are
characterized by occluded air.
Volumetric water content (%)
Volumetric water content (%)
50
40
30
20
10
0
50
40
30
20
10
0
θs=θ's
specimen - drainage Loose specimen - imbibition Dense specimen - drainage Loose
0.1 1 10 100
Suction
Dense specimen - imbibition
(kPa) specimen - drainage Loose
θ's= 39% (loose)
0.1 1
specimen scanning imbibition Loose specimen
10
θ's=
100
37% Dense (dense) -
0.89 Dense specimen Initial void ratio = 0.66 = ratio void Initial
Suction (kPa)
specimen - scanning imbibition Dense specimen - drainage Loose
Figure 7.5: Influence of loading path direction (drainage, imbibition process) on the shape of
the soil-water characteristic curve (steady state tests)