| Author | Lee, Young Huy |
| Call Number | AIT Diss. no. GT-86-01 |
| Subject(s) | Rockfills
|
| Note | A dissertation submitted in partial fulfilment of the
requirements for the Degree of Doctor of Engineering, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Abstract | A comprehensive set of laboratory investigations was carried out
to study the general behaviour of rockfill under various stress
conditions. The crushed graywacke rockfill used in the construction of
the Chiew Larn Dam (located in the southern part of Thailand) was studied
in this research by means of three different apparatus; the large-scaled
oedometer (730 mm in diameter), the large-scaled triaxial apparatus
(300 mm in diameter) and the conventional triaxial apparatus (100 mm in
diameter). The index properties of the crushed rockfill indicated that
the material was relatively sound, homogeneous and angular.
The experimental investigations by means of the large-scaled
oedometer show that rockfill sample constituted of well-graded material
is less compressible than that of poorly-graded material, but this is not
true when the sample contains much fine fractions. The effect of particle
size is not significant to the one-dimensional compressibility. However,
the compressibility of the rockfill is significantly influenced by
saturation. The axial strain of the saturated sample is 1.6 to 1.7 times
greater than that of the dry sample at different stress levels.
The results of the conventional drained triaxial tests for both
large and small samples reveal that the Mohr failure envelopes are
markedly curved, especially at low stress levels. This leads to the
variation of the internal friction angle from 51.6° to 40.5° for large
specimens when the confining stress increases from 5 t/m2 to 60 t/m2 •
Further, the internal friction angle of small specimens decreased from
47.6° to 38.0° as the confining stress increases from 5 t/m2 to 140
t/m2 • The influence of the maximum particle size on the stress-strain
behaviour of rockfill is not significant, provided that the material does
not contain much fine fractions. However, the method of sample
preparation appeared to be the most significant factor affecting the
stress-strain behaviour of rockfill .
A series of anisotropic consolidation tests on small triaxial
samples resulted in the volumetric yield point in the void ratio vs
logarithmic mean normal stress plot and also the distortional yield point
in the deviator stress vs shear strain plot. The above two yield points
(volumetric and distortional) are more or less the same in the stress
plane. Similarly, the plot of shear strain against volumetric strain is
bilinear at a given stress ratio, which implies that the strain increment
ratio is constant for any one value of the stress ratio and results in
distinct and different magnitudes for the stress states inside and outside
the yield locus. The coefficient of earth pressure at rest (K 0 ) of
rockfill was evaluated indirectly from the plot between stress ratio and
strain increment ratio. The estimated K0 -value is about 0 . 39 for the
stress state outside the volumetric yield locus .
The results of undrained shear show that the undrained stress paths
of rockfill are similar but cannot be normalized with respect to the
pre-shear consolidation stress. It is also found that the contours of
equal shear strain in the undrained tests are somewhat similar to those
exhibited by overconsolidated samples of sand and clays. The undrained
shear strains are dependent both on the stress ratio and the mean normal
stress. Bilinear relationships are established between the pore pressure
developed and the stress ratio, which can then be used to derive
expressions for the undrained stress paths.
Based on observations emerged from the undrained tests and the
anisotropic consolidation tests, an incremental stress-strain theory for
rockfill is proposed in a manner similar to that developed by Cambridge
Group for normally consolidated soils; the volumetric strain due to stress
increment is the same as the increment due to an undrained component
followed by an increment along the constant stress ratio path. The
strains in drained tests are predicted from those in the undrained tests
and in the anisotropic consolidation tests. An expression for the
undrained stress path is derived based on the bilinear relationship
between the pore pressure developed and the stress ratio observed during
undrained tests . Good agreement is found between the calculated and
measured strains. This trend in behaviour would be helpful in
establishing a stress-strain model for rockfill using the elasto-plastic
behaviour with the concept of plastic potentials and flow rules. |
| Year | 1986 |
| Type | Dissertation |
| School | School of Engineering and Technology (SET) |
| Department | Other Field of Studies (No Department) |
| Academic Program/FoS | Geotechnical and Transportation Engineering (GT) |
| Chairperson(s) | Balasubramaniam, A.S.
|
| Examination Committee(s) | Karasudhi, Pisidhi ;Chandra, Sarvesh ;Bergado, Dennes T. ;Towhata, Ikuo ;Burland, J. B.
|
| Scholarship Donor(s) | Government of Japan |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 1986 |