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FIELD AND LABORATORY MEASUREMENTS OF SMALL STRAlN
STIFFNESS OF DECOMPOSED GRANITES
C. W. W. NG and Y. WANG
ABSTRACT:Non-linear stress-strain characteristics and
stiffness-strain relationships of sedimentary soils and sands at small
strains have been reported by many researchers. Research work on the
behaviour of weathered or decomposed granites at small strains however,
has rarely been reported. This paper compares some stiffness measurements
of decomposed granites from field investigations involving crosshole
seismic, self-boring pressuremeter (SBPM), and high pressure dilatometer
as well as results from laboratory tests using bender element and internal
transducers. The in-situ crosshole measurements show that the elastic
stiffness of Moderately Decomposed Granite (MDG, approximately 7000 MPa)
is about 25% greater than that (about 5500 MPa) of Highly Decomposed
Granite (HDG), which is in turn approximately 18 times higher than that
(about 300 MPa) of Completely Decomposed Granite (CDG). This is likely
attributable to the materials' different bond strengths and structures. A
new method has been adopted to interpret the SBPM data. Measured data from
crosshole seismic and self-boring pressure meter tests for CDG are found
to be consistent. Bender element laboratory tests on CDG indicate that the
measured A-coefficient in the expression of Go /pr
=A(p/pr)n lies between the results from clay and
sand as reported in the literature. However, the measured n- value for CDG
is generally larger for clays and sands. The measured bender element
results are consistent with data from internal transducers. Highly
non-linear characteristics of CDG were observed in both the laboratory and
field tests. Generally the elastic stiffness of CDG as determined by
laboratory tests is about 50-80% Of that from field tests. Some possible
reasons are discussed.
Key words:bonding and structure; decomposed granites; non-linear;
shear and bulk modulus; stiffness (IGC:D6/D3)
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