OR/15/065 Appendix 6 - Corrosivity classification descriptions

Entwisle, D, Lee, K A, and Lawley, R S. 2015. User guide for ‘BGS Civils’ - a suite of engineering properties datasets. British Geological Survey Internal Report, OR/15/065.

Corrosion Property	Value	Score
pH (a)	<4.5	3
	4.5–8.5	0
	>8.5	3
Moisture conditions (b)	Sand	0
	Sand > loam	0
	Sand > loam > clay	1
	Loam	1
	Loam > sand	1
	All	1
	Loam > clay	1
	Clay + loam	1
	Clay > loam	1
	Clay	2
	Peat	2
Resistivity, Ohm.m (c)	<7	10
	7–10	8
	10–12	5
	12–15	2
	15–20	1
	>20	0
Redox status (d)	Well oxidised soils e.g. coarse and highly permeable soils	0
	Soils prone to seasonal waterlogging e.g. clay soils	4
	Very wet or waterlogged soils e.g. peat and salt marsh soils	5
Suphates/sulphides (e)	Primary	3.5
	Secondary	3.5
	Not present or unlikely	0

Classification descriptions

Class	Score	Legend	Recommendation	Backfill	Typical Material Description
1	<9	Ground conditions beneath topsoil are unlikely to cause corrosion to iron.	Special protection probably not required, unless the ground is clay or peat or likely to contain saline water (estuarine or marine) if so see class 3.	Do not use peat or salty materials for backfill. Only use clay materials if they do not contain sulphide or sulphate crystals or are of low pH.	Most rocks e.g. sandstone, limestone, chalk, igneous and metamorphic rocks, boulders, cobbles, gravel, sand and silt.
2	9–11	Ground conditions beneath topsoil may cause corrosion to iron.	Special protection probably required if materials at site are clay, peat or likely to contain saline water (estuarine or marine). If so see class 3. Do not use peat or salty materials for backfill. Only use clay materials if they do not contain sulphide or sulphate crystals or are of low pH.	Do not use peat or salty materials for backfill. Only use clay materials if they do not contain sulphide or sulphate crystals or are of low pH.	Mostly ‘clays’ and mudstones with relatively low clay size content and do not contain iron sulphide or calcium sulphate.
3	>11	Ground conditions beneath topsoil are likely to cause corrosion to iron.	Special protection probably required if materials at site are clay, mudstone, peat or likely to contain saline water (estuarine or marine). If so, further ground investigation is required to assess whether the hazard exists. Do not use peat or salty materials for backfill. Only use clay materials if they do not contain sulphide or sulphate crystals or are of low pH.	Do not use peat or salty materials for backfill. Only use clay materials if they do not contain sulphide or sulphate crystals or are of low pH.	A variety of material types depending on the lithostratigraphical classification. The following indicate corrosivity hazard: i)  Grey to black clay, brown near surface. May be mudstone at depth. May contain white or translucent ‘soft’ crystals (gypsum) at a few metres depth. ii)  Red clay or mudstone, may contain white or translucent ‘soft’ crystals (gypsum) at a few metres depth. iii)  Peat. iv)  Contains saline water

Score = a + b + c + d + e