Influence of weathering-induced iron precipitation on properties of sandstone in a tropical environment

Abstract

Weathering-induced iron dissolution and precipitation in rock masses lead to reduction in shear strength of discontinuities, amongst others, while precipitation leads to an increase, and precipitated iron may reduce the susceptibility to future weathering. This effect is investigated in fieldwork campaigns with detailed rock mass characterization and chemical analyses in Kota Kinabalu, Malaysia. Many cut slopes in this area consist of different zones in which iron in various forms is either dissolved or precipitated. Iron-coated and -cemented discontinuities have a marked higher shear friction, while staining has little influence on friction. Discontinuities with iron-coating and -cementing reduce the susceptibility to weathering of a rock mass as weathered material is less easily eroded and underlying material is protected from further weathering. On the other hand, dissolution zones, which are mostly found below the precipitation zones, have considerably lower rock mass quality. In engineering works the latter are invisible before excavation. Just assuming the continuation downward of the surface rock mass with precipitated iron, or, worse than this, assuming a less weathered rock mass with better characteristics, may be very erroneous. This study emphasizes that forecasting the susceptibility to weathering should include the influence of morphology, environment and climate.

Weathering, Erosion, and Susceptibility to Weathering

“…Inversely, erosion causes the insulation to be removed, exposing the groundmass to the environment, accelerate weathering, and allow further progressive weathering in depth of new fresh ground. Erosion thus increases the rate of weathering of the underlying material (Huisman et al 2011;Tating et al 2019).…”

The Influence of Discontinuities on Rock Mass Quality and Overall Stability of Andesite Rock Slope in West Java

“…In contrast, Ehlen (2002) studied the effects of the weathering process on the discontinuity properties of weathered granitic rocks and found no clear relation between the spacing and length of the discontinuities and weathering grades. A study on the effect of weathering on the properties of sandstone discontinuities (Tating et al, 2018) showed that the iron-oxide precipitation in the discontinuities reduces the susceptibility of sandstones to weathering and increases their shear strength. Although many previous studies have shown how the properties of main discontinuities contribute to rock mass quality, none of them have attempted to evaluate the contribution of other types of discontinuities, such as integral discontinuities, to rock mass quality and slope stability.…”

Tropical sandstone degradation with time : case study in Kota Kinabalu Sabah, Malaysia

“…The thesis comprises of a collection of research papers submitted or published in peer review international journals and conferences (chapters 3 (Tating et al, 2013a;2013b;2013c); chapter 4 (Tating et al, 2015a); chapter 5 (Tating et al, 2015b)) with additionally an introduction, chapter on the description of the study area, and concluding chapter (chapters 1, 2 and 7). Chapter 6 describes the use of an exposure time parameter in the assessment of landslide susceptibility.…”

“…This chapter described the discontinuity development mechanism in thick to very thick bedded sandstone due to weathering and their implication in the engineering works on rock mass. This is based on the article "Weathering effects on discontinuity properties in sandstone in a tropical environment: Case Study at Kota Kinabalu, Sabah Malaysia" (Tating et al, 2015b).…”

“…The influence of iron precipitation on the condition of discontinuities is also discussed. This chapter is based on the articles "Influence of weathering-induced iron precipitation on properties of sandstone in a tropical environment" (Tating et al, 2015b; submitted for publication).…”