Location of Repository

Deterioration of excavated rockslopes : mechanisms, morphology and assessment

By Dawn Theresa Nicholson

Abstract

Results are reported of laboratory simulated weathering processes on a range of sedimentary rocks and the investigation of the deterioration of rock masses as observed on engineered and quarried rockslopes.\ud \ud The simulated weathering processes include freeze-thaw, wetting and drying, salt weathering and slaking. It is found that the rock properties of pore volume, saturation coefficient and microporosity exert greatest influence on susceptibility to breakdown. For stronger rocks it is\ud found that durability correlates well with high strength and elasticity.\ud \ud A range of rock flaws visible in hand specimen are described and their influence on rock deterioration assessed. Linear flaws such as laminations and stylolites are more likely to be associated with breakdown, and the role of structural weaknesses is most evident in stronger\ud rocks. Rock breakdown mode due to experimental weathering is found to closely resemble material weathering of source slopes in the field. A range of rock breakdown mechanisms are inferred from changes in pore microstructure and rock strength. There are indications of a progression from deterioration which is invisible and involves modification of the existing pore structure, to macro deterioration resulting from generation of new void space and microcracks.\ud \ud After field investigation of more than two hundred rockslopes deterioration is found to be widespread, and there is little evidence of a systematic approach to its assessment or mitigation. Fracture spacing, rock strength and lithology are found to be the most influential factors in rockslope deterioration and these are used to define a characteristic range of rock mass types. A range of morphological forms attributed to deterioration are defined and described. An engineering classification of deterioration modes is presented, based on constituent material size, velocity of movement and frequency of occurrence. Deterioration modes correlate well with\ud rock mass type.\ud \ud A new rock mass classification, called Rockslope Deterioration Assessment (RDA) is proposed, dealing specifically with shallow, weathering and erosion-related rockslope processes. RDA is divided into three stages; a ratings assessment of deterioration risk, a qualitative review of the likely deterioration hazard, and guidance on appropriate mitigation. The findings of the experimental work are incorporated into stage one of RDA where appropriate. Notable in this respect is the emphasis in RDA on evaluation of fracture spacing on the basis of all fractures present, whether open or incipient, and whether natural, or induced by blasting, weathering or stress release. RDA is applied to the slopes investigated in the fieldwork and shows that certain types of rock mass are associated with higher risk of failure. There is also an element of predictability in the occurrence of deterioration modes. Correlation between stage one of RDA\ud and Rock Mass Rating is examined and it is shown that, although there are some similarities, a fundamental difference relates to the basis upon which fracture spacing is assessed

Publisher: Earth Sciences (Leeds)
Year: 2000
OAI identifier: oai:etheses.whiterose.ac.uk:334

Suggested articles

Preview

Citations

  1. (1982). (4 th edition). Atmosphere, Weather and Climate.
  2. (1988). A non-destructive method of determining rock strength. doi
  3. (1981). Artificial weathering of Carrera Marble: Relationships between the induced variations of some physical properties. The Conservation of Stone //, pre-prints of the contributions to the International Symposium,
  4. (1989). Cavern design for Hong Kong
  5. (1990). Chalk fabric and its relation to certain geotechnical properties.
  6. (1993). Classification of rock masses for engineering purposes: The RMFI system and future trends.
  7. (1971). Corrosion by mixing of karst waters.
  8. (1992). Description and classification of rock masses. doi
  9. (1990). Developments in a non-destructive method of determining rock strength. doi
  10. (1990). Discontinuities and their effect on rock mass. In: N. Barton and 0. Stephansson (eds) Rock Joints,
  11. (1974). Engineering classifications of rock masses for the design of tunnel support. doi
  12. (1989). Engineering Rock Mass Classifications, John Wiley and son,
  13. (1994). Erosion on highway slopes in upland Wales: problems and solutions. doi
  14. (1972). Experimental frost shattering.
  15. FOR TESTING MATERIALS C88.1990. Standard Test Method For Soundness of Aggregates by Use of Sodium Sulfate or Magnesium Sulfate. doi
  16. FOR TESTING MATERIALS C99-87.1987. Standard Test Method for Modulus and Rupture of Dimension Stone. doi
  17. FOR TESTING MATERIALS D5240.1992. Standard Test Method For Testing Rock Slabs to Evaluate Soundness of Riorap by Use of Sodium Sulfate or Magnesium Sulfate. doi
  18. FOR TESTING MATERIALS D5312.1992. Standard Test Method For Evaluation of Durability of Rock for Erosion Control Under Freezing and Thawing Conditions. doi
  19. FOR TESTING MATERIALS D5313.1992. Standard Test Method For Evaluation of Durability of Rock for Erosion Control Under Wetting and Drying Conditions. doi
  20. (1999). Fracture of Rock, doi
  21. (1992). Influence of weathering and discontinuities on the behaviour of rock masses. doi
  22. (1987). Introduction to fracture mechanics. doi
  23. (1987). Modelling slope stability: the complementary nature of geotechnical and geornorphological approaches. In:
  24. (1998). Point load testing of weak rocks with particular reference to chalk. doi
  25. (1976). Principles of Engineering Geology, doi
  26. (1992). Rock mass characterisation system for rock slope stability analysis.
  27. (1976). Rock mass classifications in rock engineering. doi
  28. (1991). Rock resistance to erosion: Some further considerations. doi
  29. Sandblast erosion tests for the physical characterisation of chalk. doi
  30. (1996). Slope Stability and Stabilization Methods. Wiley Interscience,
  31. (1996). Slope stability modelling: an overview. In:
  32. (1982). Stress relief buckles in the McFarland Quarry, doi
  33. (1960). Temperature observations in bergschrunds and their relationship to frost weathering.
  34. (1994). The effects of fire on rock weathering: an experimental study.
  35. (1999). The effects of fire on rock weathering: some further considerations of laboratory experimental simulation. doi
  36. (1979). The Geomechanics Classification in rock engineering applications. doi
  37. (1933). The insolation hypothesis of rock weathering. doi
  38. (1990). The longitudinal pulse velocity in finite cylindrical cores. doi
  39. (1972). The point-load strength test. doi
  40. (1983). The relationship between rock mass quality and ease of excavation. doi
  41. (1987). The theory of subcritical crack growth with applications to minerals and rocks. doi
  42. (1912). Water in the liquid and five solid forms, under pressure. doi
  43. (1989). Weathering and weatherability of rocks and its significance in geotechnics.
  44. (1998). Weathering: An Introduction to the Scientific Principles,

To submit an update or takedown request for this paper, please submit an Update/Correction/Removal Request.