ROCKSLOPE DETERIORATION ASSESSMENT (RDA)

Co-workers: Dr Steve Hencher (Halcrow Geotechnical Hong Kong) and Alastair Lumsden (University of Leeds). This research was conducted with some financial and technical support from the School of Earth Sciences at the University of Leeds.

Go straight to links for downloadable .pdf RDA documents

Existing slope hazard assessment schemes often give scant attention to the effects of dynamic, shallow surface weathering processes on slope deterioration. This is because deterioration of rockslopes is often not perceived as a significant risk, it is difficult to quantify and its mechanisms are poorly understood. However, published records demonstrate that falls of material from excavated rockslopes such as quarry faces and highway cuttings are actually a significant source of serious accidents. Methods which are widely used to investigate slope instability are inappropriate for the analysis of weathering-related deterioration. Despite years of research into weathering processes, progressive deterioration of slopes cut into rock is not predictable, other than on a conceptual basis Images of rockslope and rock deterioration

Field investigation of over 200 excavated rockslopes in the UK was conducted. The aims of this fieldwork were:

1. To determine the extent of the problem of rockslope deterioration and identify common consequences and approaches to its assessment and mitigation.
2. To characterise deterioration and its effect on the form of slopes.
3. To assess the role of dynamic weathering processes in deterioration.
4. To develop an adequate, systematic evaluation method for deterioration of rockslopes.

The field investigation found deterioration to be widespread in man-made excavations (eg road cuts and quarry faces). There is little evidence of a systematic approach to its assessment or mitigation. Deterioration commonly necessitates considerable maintenance and remedial work and presents a safety hazard for workers, public and traffic flow. Deterioration manifests in a range of distinctive transport mechanisms such as block and grain ravelling, rockfall, scaling and wash erosion. These mechanisms can be classified according to constituent material size, velocity of movement and frequency of occurrence. Deterioration transport mechanisms correlate well with the type of rock mass in which they occur. Deterioration results in a range of distinctive erosional and depositional changes to slope morphology. A range of weathering process indicators were identified (eg dissolution of fracture walls, corestone development, and root 'wedging'). Data collected have also enabled the relative importance of intrinsic and extrinsic parameters on deterioration susceptibility to be assessed.

The primary result of this research was the development of a new, three stage approach to slope hazard assessment called Rockslope Deterioration Assessment (RDA). RDA deals with shallow, weathering-related breakdown. In stage one, deterioration susceptibility is assessed through a ratings approach to intrinsic and extrinsic influences and controls. In stage two, likely deterioration hazard is qualitatively reviewed through an assessment of likely deterioration transport mechanism, slope morphology and rock mass type. In stage three, guidance on appropriate mitigation is provided. Field investigation is continuing in the UK and overseas in order to further refine ratings and rating adjustments. Though RDA was designed for UK climatic conditions, modifications to ratings will enable its use in a wider range of conditions.

Please feel free to download any of the .pdf files listed below. However, these documents are copyright of Dawn T. Nicholson (2004) and should only be used for educational or non-commercial purposes. By this I mean that you may use the materials for research, investigation, training or personal interest, but do not offer them for sale or pass them off as your own. I would appreciate a reference in anything you publish. All published references relating to RDA are listed on the publications page of this web site. If you wish to obtain electronic copies of any images, tables or diagrams please contact me by e-mail at d.nicholson@mmu.ac.uk. Please note that some of the documents listed below (those not in bold font) are not yet available but will added progressively over the winter 2004/2005.

1. Complete RDA Technical Handbook: Complete RDA handbook containing all of the components listed below plus details of derivation and theoretical basis. (kb). Not yet available.
2. Introduction to RDA: Introduction to RDA and its overall structure. (196 kb). Added 23rd December 2004. Slightly modified 16th March 2005.
3. RDA Stage One: Ratings charts, explanatory notes and guidance. Adjustment factors, detailed descriptions and guidance on aplication. (366kb). Added 10th March 2005. Slightly modified 16th March 2005.
4. RDA Stage Two (rock mass types): Guidance notes for determining and interpreting rock mass type. (307kb). Added 16th March 2005.
5. RDA Stage Two (deterioration transport mechanisms): Guidance notes for determining and interpreting deterioration transport mechanisms. (kb). Not yet available.
6. RDA Stage Two (deterioration morphology): Indicative images and descriptions of deterioration morphology. (1065 kb). Soon to be updated.
7. RDA Stage Three (mitigation matrix): Matrix of remedial and maintenance works based on RDA Rating and deterioration transport mechanism. (325 kb). Updated 23rd December 2004.
8. Example applications of RDA: Some completely worked examples of how to use RDA stages one, two and three. (kb). Not yet available.

A shortened version of the RDA method is presented in QJEGH. The full .pdf version of this paper is available from here.

You can also refer to the Rockslope and Rock Deterioration Page of this web site to see some macro and micro images.

 
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