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GMAX OF
FINE-GRAINED SOILS AT WIDE VOID RATIO RANGE, FOCUSING ON TIME-DEPENDENT
BEHAVIOR
TARA NIDHI LOHANI , GORO IMAI , KAZUO TANI and
SATORU SHIBUYA
ABSTRACT: Effect of creep as well as initial water
content at deposition on the pseudo-elastic shear modulus, Gmax,
of finegrained soil are studied in a consolidometer equipped with bender
elements. The state boundary (SB) concept is discussed in void ratio (e)-Gmax-Effective
Vertical Stress (s'v)
space and the condition of metastability associated with t-term creep
and long-term natural creep are exemplified from laboratory creep tests
and in-situ soil test results, respectively. In addition to the
conventional laboratory reconstitution method adopted for almost all
clay samples that n initial water content of twice the liquid limit, the
soil samples from Minato-Mirai (MM) site were also prepared directly
consolidating the slurry with a water content ranging from I .5 to 5.0
times the liquid limit. The larger primary metastable region or higher
degree of on-depositional structuration associated with the samples at
higher initial ratio is confirmed. However, no appreciable difference
was found in the increase in Gmax
with time, represented by NG,
between the samples prepared by the two different methods. In addition
to the highly plastic MM clay, the study of NG
also covered other clayey soils of different origin and
plasticity index range from 29 to 78. Metastability index MI(Gmax)e
that manifested the aspect of structuration and
destructuration reaches a maximum value at the end of sustained loading
and vanishes slowly with any increase in stress level. By using
liquidity index instead of void ratio in the e-log Gmax
plot, the metastability index, MI(Gmax)LI,
is found to represent a wider variety of soils with minimum scatter. A
slight stress level dependency of metastability increase was observed
yielding smaller values at higher stresses. For the present test
conditions and duration, subsequent stressing of I .5-2.0 times the
creep stress brought about complete destructuration of the creep-added
soil-structure formed in the previous creep step.
key words: aging, clays, creep. Gmax,
metastability index, shear modulus, small strain, soil structure (IGC:
D6)
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