Mechanical Properties of Virtual Block-in-matrix Colluvium

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 Specimen Size Various block (a) proportion, (b) orientation, (3) aspect ratio

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-ecurves 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 • 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. Specimens containing rock blocks without preferred orientation Specimens containing aligned rock blocks

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

10. Parametric Study –Effect of Block Orientation (block proportion=45% & aspect ratio=3 ) • 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. Effect on Strength Effecton E

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

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. s3=200 kPa As the specimen size gradually enlarges, the s-e curves appear less varied among the curves. • s-ecurves 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-independentblock-size distribution.

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