Presentation on theme: "Important/significant foundation soil physical properties Color Texture Structure Consistence Coarse fragments Reaction."— Presentation transcript:
Important/significant foundation soil physical properties Color Texture Structure Consistence Coarse fragments Reaction
Important/significant foundation soil physical properties Soil reaction - The acidity or alkalinity status of a soil. Soils that are acid have an ‘acid reaction’; those that are not acidic (basic) have an ‘alkaline reaction’. Coarse fragments – coarse sand, pebbles, gravel, cobble, stones, rocks – particles with a diameter > ¼”: don’t hold water!
Soil reaction – a qualitative or quantitative assessment, based on visual observation of soil reaction to weak (10%) hydrochloric acid or a commercially available test kit, or based on a color comparison to known references.
Soil reaction – what and why? What – testing the soil reaction will provide an indication of whether the soil material is acidic, basic (alkaline, containing carbonate salts), or neutral. The scale – a measure of the hydrogen ion activity, i.e., the concentration of hydrogen in the soil solution. Scale ranges from 0 (very acidic) to 14 (very alkaline) Why - the acidity, alkalinity, or basicity of the soil is a function of: 1) the geologic parent material, 2) climate/weather – particularly rainfall, 3) the predominant vegetation, and 4) the drainage, leaching, or historic wetting conditions of the soil. Why – the acidity or alkalinity will influence the life of the septic system, the functioning of the biofiltration process; it also reveals the circumstances of the soil property.
Soil reaction and the drain field: Assessing ‘reaction’ Typically, the measure of ‘soil reaction’ is whether the soil reacts, effervesces, when the soil comes in contact with weak hydrochloric acid. Under such circumstances, the effervescences is caused by a reaction between hydrochloric acid and calcium carbonate, i.e., limestone. This reaction: no effervescence – pH < 7.0 weak effervescence - pH 7.4–7.8, mildly alkaline moderate effervescence - pH 7.9–8.4, moderately alkaline strong effervescence - pH 8.5–9.0, strongly alkaline violent effervescence - pH > 9.0, very strongly alkaline The presence of calcium carbonate, i.e., limestone, indicates that the parent material is sedimentary, that rainfall-induced leaching has occurred to a depth approximated by the depth of limestone accumulation, that ‘cementing agents’ are likely present in the soil.
In contrast, highly acidic soil indicates granitic parent material, abundance of alumino-silicates or acid-forming minerals (iron), excessively leached soils, or accumulations of excessive amounts of organic matter associated with poor or inadequate drainage and absence of oxidation of organic material, i.e., peat bogs. None of these conditions is conducive to properly functioning drain fields – either because of excessive drainage, lack of drainage, or a hostile environment for a functioning drain field.
About coarse fragments –coarse fragments facilitate good internal drainage; this is one purpose of the gravel envelope, whiere it is used – to facilitate drainage away from the drain line. However, once water has drained away from the line, the objective is to provide a storage mechanism and retention time in the soil for biodegradation of organics and destruction of bacteria and viruses in the waste water. 10% coarse fragments means ~ 5% reduction in pore space; 20% coarse fragments means ~ 10% reduction in pore space Gravel doesn’t hold water – that’s the point!
A ABAB C
Min – 10’ to seasonally high water table Max – 7-10% coarse fragments below the depth of the drain field