Soil Mineralogy and Consistence

Soil Mineralogy and Consistence

NDWRCDP Disclaimer This work was supported by the National Decentralized Water Resources Capacity Development Project (NDWRCDP) with funding provided by the U.S. Environmental Protection Agency through a Cooperative Agreement (EPA No. CR827881-01 01-0) 0) with Washington University in St. Louis. These materials have not been reviewed by the U.S. Environmental Protection Agency. These materials have been reviewed by representatives of the NDWRCDP. The contents of these materials do not necessarily reflect the views and policies of the NDWRCDP, Washington University, or the U.S. Environmental Protection Agency, nor does the mention of trade names or commercial products constitute their endorsement or recommendation for use.

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Citation -Greene, S, D. L. Lindbo, M. H. Stolt, R. Miles, D. L. Mokma, and M. T. Hoover. 2005. 3. Field Description of Soils: Mineralogy and Consistence Power Point Presentation. in (D.L. Lindbo and N. E. Deal eds.) Model Decentralized Wastewater Practitioner Curriculum. National Decentralized Water Resources Capacity Development Project. North Carolina State University, Raleigh, NC.

Soil mineralogy and consistence Clay mineralogy Water movement Management Consistence Field method to relate soil properties to clay mineralogy

Clay Mineralogy

Building Blocks of Clay Silica Tetrahedron-four sides, four oxygen molecules and one silica (Si +4 ) Aluminum Octahedron-eight eight sides, six oxygen molecules and one Al +3 These are bound together by shared oxygen molecules into different layers

Tetrahedron and Octahedron

Sheets of Tetrahedron and Octahedron

Definitions Plane-plane of atoms, individual row in the composition and structure of the clay mineral Sheet-combination of planes Layer- combination of sheets i.e.. 1:1

Clay Structure

1:1 Clay Minerals Like an open face sandwich One silica tetrahedron (bread) to one aluminum octahedron (filling) The most common 1:1 minerals is Kaolinite

1:1 Clay Mineral

2:1 Clay Minerals Like a sandwich with two slices of bread Two silica tetrahedrons (bread) to one aluminum octahedron (filling) The 2:1 clays can be broken into 2 groups Expansive Non expansive

2:1 Clay Mineral

Non-expansive 2:1 Clays the sheets or layers are held together strongly neither water nor a change in the interlayer cations causes them to swell Illites are one group of non-expandable clays

Expansive 2:1 Clays Bound together by very weak hydrogen bounds (easily broken) Will swell upon wetting Smectites are one group of expandable clays

Surface Area Smectite group minerals have higher CEC Smectite group minerals have a higher surface area Isomorphic substitutions plays a role in the above and in the expansive nature of this group

Parent Material The 1:1 minerals are usually weathered from acidic or felsic parent materials The expanding 2:1 minerals are usually weathered from basic or mafic parent material Parent material plays the biggest part of whether the soil will be expansive

Why water causes the mineral to expand Water is dipolar- which simply means it can be attracted to a net negative charge or a net positive charge Water carries many different ions in soil solution Water has a physical size

Examples of management issues for expansive soils Self plowing and cracking soils (Vertisols) Watering the foundations to prevent them from drying and splitting (tensile forces) Cracking foundations due to the swelling pressures of the soil (compression forces) Disturbed or buckled roads Unsuitable soils for on-site wastewater treatment and dispersal

Lab Test for Mineralogy X-Ray Diffraction Apparent CEC Coefficient of Linear Extensibility

Consistence Rupture Resistance Manner of Failure Stickiness Plasticity Penetration Resistance

Rupture Resistance A measure of the strength of the soil to withstand an applied stress Separate classes are made for Blocks, peds, and clods Surface crusts and plates Moisture content is also considered Dry Moist (field capacity) Cementation classes obtained by submergence of overnight air-dried samples for at lease 1 hour before test

Rupture Resistance Classes: Blocks, Peds, and Clods Dry Moist Cementation Description Loose Loose n.a. Cannot get samp. Soft V. Friable Non-cem Very slight FF Sl. Hard Friable Ex. w. cem Slight FF Mod. Hard Firm V. w. cem Moderate FF Hard V. Firm W. cem Str. FF V. Hard Ex. Firm Mod. cem Moderate HF Ex. Hard Sl. Rigid Str. cem Foot pressure Rigid Rigid V. Str. cem Light Blows V. Rigid V. Rigid Indurated Strong Blows

Manner of Failure The rate of change and physical condition soil attains when subjected to compression Samples are moist or wetter 3 failure classes are determined Brittleness Fluidity Smeariness

Brittleness Failure Classes Use a 3 cm block Press between thumb and forefinger Fluidity Use a palmful of soil Squeeze in hand Smeariness Use a 3 cm block Press between thumb and forefinger

Brittleness Grade Brittle Description Rupture abruptly ( pops or shatters) Semi- Deformable Deformable Rupture occurs before compression to < ½ original thickness Rupture occurs after compression to > ½ original thickness

Fluidity Grade Nonfluid Slightly Fluid Moderately Fluid Very Fluid Description No soil flows through fingers at full compression Some soil flows through fingers,, most remains in the palm, after full pressure Most soil flows through fingers, some remains in the palm, after full pressure Most soil flows through fingers, very little remains in the palm, after gentle pressure

Smeariness Grade Non- Smeary Weakly Smeary Moderatel y Smeary Strongly Smeary Description At failure, the sample does not change abruptly to fluid, fingers do not skid, no smearing occurs At failure, the sample changes abruptly to fluid, fingers skid, soil smears, little or no water remains on fingers At failure, the sample changes abruptly to fluid, fingers skid, soil smears, some water remains on fingers At failure, the sample changes abruptly to fluid, fingers skid, soil smears, water easily seen on fingers

Stickiness The capacity of soil to adhere to other objects Estimated at moisture content that displays maximum adherence between thumb and fore finger

Stickiness Classes Non-Sticky little or no soil adheres to fingers after release of pressure Slightly Sticky soil adheres to both fingers after release of pressure with little stretching on separation of fingers Moderately Sticky soil adheres to both fingers after release of pressure with some stretching on separation of fingers Very Sticky - soil adheres firmly to both fingers after release of pressure with stretches greatly on separation of fingers

Non-Sticky

Very Sticky

Plasticity The degree to which puddled or reworked soil can be permanently deformed without rupturing Evaluation done by forming a 4 cm long wire of soil at a water content where maximum plasticity is expressed

Plasticity Class Non-Plastic will not form a 6 mm dia, 4 cm long wire, or if formed, can not support itself if held on end Slightly Plastic 6 mm dia, 4 cm long wire wire supports itself, 4 mm dia, 4 cm long wire wire does not Moderately Plastic 4 mm dia, 4 cm long wire wire supports itself, 2 mm dia, 4 cm long wire wire does not Very Plastic 2 mm dia, 4 cm long wire wire supports itself

Very Plastic 4 cm long 2 mm diameter

Penetration Resistance The ability of a soil in a confined (field) state to resist penetration by a rigid object of specified size An average of 5 or more measurements should be used to obtain a value for penetration resistance Measure in vertical and horizontal directions Record moisture content of soil

Penetration Resistance Penetration Resistance Class Extremely Low Very Low Low Moderate High Very High Extremely High Criteria: Penetration Resistance (MPa) <0.01 0.01 to <0.1 0.1 to <1 1 to <2 2 to <4 4 to <8 >8

Interpretations

Interpretations As consistency increases the movement of water will decrease due to expansive clay minerals, compaction, cementation or all of the afore mentioned.