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Important/significant foundation soil physical properties

Color Texture StructureConsistence Coarse fragments Reaction

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Important/significant foundation soil physical properties

• Texture – the composition (sand, silt, clay), the feel, the classification (triangle) - micropores

• Structure – how the particles are aggregated, bound together – macropores

• Consistence – how the soil holds together, feels, can be worked when wet

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Texture is:

What the soil feels like – that’s texture

A classification method: whether the soil is a ‘clay’, ‘sand’, ‘silt’, ‘loam’, or one of the other eight textural categories – based on percentage sand, silt, and clay

Texture (the proportion of sand, silt, and clay) influences porosity, water holding capacity and flow, compaction, aeration status, structure, microbial behavior, and soil chemistry.

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There are two generally accepted methods for assessing texture: one is by feel and appearance and the other is by mechanical analysis (particle size analysis)

The site evaluator will use feel and appearance, will possibly confirm or check the assessment against soil survey data, and may follow up with a laboratory mechanical analysis

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Textural TriangleSilt goes to

sand goes toclay to silt

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WITH REGARD TO TEXTURE:  There are some obvious characteristics of different soils which help identify thepredominant texture – the feel and appearance of soil.

Sand - feels gritty, does not bind together when dried, and maintains individual particle identity when rubbed between the forefinger and thumb; has a distinct grinding sound. Will not form a ribbon when wet.

Silt feels like talcum powder, slippery and smooth, but not sticky when wet. Will form a weak, short ribbon. Silt is often very hard and crusty after drying and it usually does not crack much when it dries.

Clay can't be seen with unaided eye; will remain in the water almost indefinitely. When dry and powdery, clay feels like silt - soft, smooth, very fine, When clay is wet it is "sticky", like 'tacky' dough or wood glue. Dries very hard, may shrink and swell.

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Horizontal flow

Vertical flowVertical flow

Tortuous flow

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Blocky structure

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Moderate, coarse granular

Moderate to strong, medium prismatic

Moderate to strong, medium subangular blocky

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Moderate, coarse prismatic

W weak to moderate, medium to coarse subangular blocky

XTRA SLIDES

17Crumb, granular

Blocky

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Wet soilsMoist soils Dry soils

Stickiness Plasticity

Nonsticky Nonplastic Loose Loose

Slightly stickySlightly plastic

Very friable Soft

Sticky Plastic Friable Slightly hard

Very sticky Very plastic Firm Hard

Very firm Very hard

Extremely firm

Extremely hard

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Questions?