ROCK WEATHERING

This research was partly funded by the Nuffield Foundation NAL programme

 

INTRODUCTION

The aim of this research is to examine the extent to which rock mass deterioration is controlled by rock properties and their modification due to weathering. Specific objectives are to:

  1. Determine if the spatial distribution and characteristics of microcracks and pores are reflected in macrofracture properties.
  2. Infer the nature of weathering processes operating and establish the relative importance of climatic controls compared with rock properties.
  3. Examine variations in rock properties in relation to small scale weathering forms.
  4. Refine preliminary spatial and temporal models of fracture modification due to weathering (developed in earlier research).
  5. Consider temporal variation in properties of rocks subjected to experimental weathering and model the development of fractures from microcracks and pores.

The research will be conducted with reference to natural rockslopes in Norway and the UK to obtain data from similar lithological rock masses in different environments.

A fundamental hypothesis of the proposed research is that rock mass breakdown by fracturing and fragmentation is preceded by modification at the micro scale. Such modification includes microcracking, pore coalescence and enlargement, both of which lead directly to the generation and propagation of macrofractures and large-scale fragmentation. In granular rocks such as granites and sandstones, rock mass deterioration occurs via disintegration of the material (Nicholson and Nicholson 2000) around grain boundary microcracks and also via development of macrofractures visible at the rock surface. If sufficiently persistent, these macrofractures isolate blocks which are then available for removal from the rock mass. It is reasonable to expect, therefore, that macroscale evidence of deterioration will be reflected in variations in the spatial distribution of micro-scale rock properties.

In experimental weathering of limestones conducted previously (Nicholson 2001) evidence was provided that changes to the internal pore structure of rock was a precursor to more substantial deterioration at the macro scale. A two stage process was proposed linking micro- and macro-scale deterioration in which increased pore connectivity by modification of the existing pore structure precedes an increase in the total volume of new void due to microcracking and pore coalescence. Earlier work demonstrated the importance of textural, lithological and structural flaws in controlling the nature and severity of breakdown (Nicholson and Nicholson 2000). Several models describing the influence of pre-existing flaws on deterioration were proposed. These described the relationship between rock strength, porosity and the presence of small scale structural weaknesses.

CURRENT RESEARCH

Field investigations

Laboratory testing of rock properties