Geostatistical analysis in weathering studies: case study for Stanton Moor building sandstone

Abstract

Geostatistical techniques for spatial prediction and spatial simulation have been used in an innovative application to the study of weathering of natural building stone. The study investigates the differences in the spatial variation of permeability characteristics between fine-and coarse-grained Stanton Moor building sandstone. Non-destructive permeability measurements, using an unsteady-state Portable Probe Permeameter, were made on three adjacent faces of two cubic blocks representative of fine-to medium-grained and mediumto coarse-grained Stanton Moor Sandstone. The findings provide greater understanding in the investigation of the durability characteristics of the Stanton Moor Sandstone and show that the spatial distribution and variability of permeability is more important in predicting the overall strength and weathering properties than mean permeability and absolute minimum and maximum values. The results suggest that both primary textural characteristics (such as grain size) and extent of cementation appear to be important factors in determining the overall durability properties of Stanton Moor Sandstone as a building stone. Geostatistical analysis has been shown to be an important tool in the characterization of spatial variation for the investigation of weathering of building stones.

Spatial characterization of salt accumulation in early stage limestone weathering using probe permeametry

“…It is because of this that there has been a growing interest in the association between rock properties and the susceptibility of natural building stone to weathering processes that has been widely discussed in the literature (Drever, 1994;McGreevy, 1996;Goudie, 1999;Nicholson, 2001;Inkpen et al, 2004;Smith et al, 2005). Central to these analyses is the role of the rock parameters of porosity (McGreevy, 1996;Nicholson, 2001Nicholson, , 2002Bidner et al, 2002;Přikryl and Dudková, 2002;Jornet et al, 2002;Pera and Burlini, 2002) and permeability (Carey and Curran, 2000;Russell et al, 2002;Warke et al, 2006;McKinley et al, 2006a;McKinley and Warke, 2007). The significance of these parameters has been demonstrated through, for example, the identification of porosity and permeability as key petrophysical properties to monitor during exposure trials and laboratory simulations.…”

“…A key rock property which may subsequently control longer term rock decay is permeability. This rock characteristic controls moisture transfer and is seen by many as an important determinant of susceptibility to salt weathering (Carey and Curran, 2000;Warke et al, 2006;McKinley et al, 2006a). Permeability variations depend on pore size distribution, the connectivity of this pore network and the nature and concentration of salt.…”

Dynamical instability in surface permeability characteristics of building sandstones in response to salt accumulation over time

“…The spatial variability of permeability values in previous studies, even on sandstones that appear 'homogenous' to the unaided eye, has pointed toward the potential for using permeability measurement in combination with predictive geostatistics (estimating values between measured sites) to help understand how surfaces change as weathering progresses in the complex sequence from 'fresh' to 'failed' (Carey and Curran, 2000;McKinley et al, 2006aMcKinley et al, , 2008Warke et al, 2006;McKinley and Warke, 2007;McKinley and McCabe, 2010). The stone decay system is inherently complex (Smith, 1996), and these very small-scale differences across a surface may eventually have larger scale consequences as weathering progresses -especially where variation is greater to begin with, for example, in stones composed of immature, poorly sorted, sediments.…”

“…Permeability measurements were taken using an unsteady-state portable air probe permeameter (PPP 250TM, Core Laboratories Instruments Operators Manual 2001) -a detailed description of its use can be found in McKinley et al (2006a). Unsteady-state permeametry measures the decay of pressurized air being forced into a rock surface from a probe.…”

“…The area of each exposed stone surface was 200 mm × 200 mm, with PPP measurements taken every 20 mm providing a grid of 100 permeability values. The grid scheme was designed to provide sufficient data for geostatistical analysis given the block dimensions and the effective penetration of gas from the probe permeameter (McKinley et al, 2006a).…”