1. Mechanical Properties of Virtual Block-in-matrix Colluvium
Pan, Y.W., Hsieh, M.H. & Liao, J.J.
Department of Civil Engineering
National Chiao Tung University
Hsinchu, TAIWAN

2. Background Nature of colluvial materials Complex Composite Geomaterial
Block-In-Matrix (BIM) geomaterial similar to BIMROCK  “BIM Colluvium”
Mechanical behavior of a BIM geo-material likely depends on block characteristics.
Examples of BIM Colluvium

3. Motivation Difficulties in characterization of BIM colluvium
Cored specimen size << the REV size
Feasibility of numerical simulations of virtual mechanical tests for BIM colluvium
Virtual specimens
Virtual triaxial tests

4. Virtual Specimen Generation
Controlling Parameters:
block proportion
block shape
block orientation
block aspect ratio

5. Various Virtual Specimens
Various block (a) proportion,
(b) orientation, (3) aspect ratio
Various
Specimen Size

6. Virtual Triaxial Tests
Numerical simulation using FLAC
Strain concentration at failure
Tortuous Failure surface
With contribution from block interaction
Smooth Failure surface
Matrix controlled

7. Parametric Study – Effect of Block Proportion
s-e curves
for
block proportion
(a) 30%
(b) 45%
(c) 60%
s3 ↑Variation↓
Medium block proportion has a higher variation

8. Parametric Study – Effect of Block Proportion on Strength
Specimens containing rock blocks
without preferred orientation
Specimens containing
aligned rock blocks
For low block proportion, strength is close to the matrix strength; failure surface remains more or less planar.
For high block proportion, inter-block contact becomes prevalent and raises the strength.

9. Parametric Study – Effect of Block Proportion on E
Specimens containing rock blocks
without preferred orientation
Specimens containing aligned blocks
For low block proportion, E is close to Ematrix.
For high block proportion, inter-block contact raises E.

10. Parametric Study – Effect of Block Orientation
(block proportion=45% & aspect ratio=3 )
Effect on Strength
Effect on E
Similar to the effects of aligned discontinuities in a jointed rock mass.
The lowest strength occurs at block orientations ~45o.
E depends on block orientation as well.

11. Parametric Study – Effect of Block Aspect Ratio
(block proportion=45% & block orientation=60o )
Effect on Strength
Effect on E
Defined as the ratio of block length to block width.
As block aspect ratio > 2, its influence becomes insignificant.

12. Parametric Study – Effect of Specimen Size
The s-e curves converge to the mean s-e curve as the specimen size approaches to REV.
As the specimen size gradually enlarges, the s-e curves appear less varied among the curves.
s3=200 kPa
s-e curves for various specimen sizes
50mm x 100mm, (b) 70.5mm x 141mm,
(c) 100mm x 200mm, (d) 200mm x 400mm
block proportion=45%
block orientation=45o

13. Concluding Remarks
Virtual mechanical tests were used to investigate important factors for the mechanical properties of BIM colluvium. The results reveal
Strength/modulus increases with increasing block proportion;
Block orientation results in the anisotropy of mechanical behavior & properties;
Block aspect ratio has a minor influence on mechanical behavior & properties; &
Variation of mechanical behaviors tend to converge as specimen sizes approach to REV.

14. Concluding Remarks (Con’d)
It’s possible for adopting virtual mechanical tests
to complement insufficient laboratory tests;
to estimate the mechanical properties variance from small specimens; &
to examine the effect of scale-independent block-size distribution.

15. Thank you for Your Attention