Soils of Wisconsin Topic C

Soil Uncemented aggregate of mineral grains and decayed organic matter with liquid and gas in the empty spaces between the solid particles. Topic C

Types of Soils 1.Granular Soils – Sand and Gravel 2.Fine Grained Soils – Clays and Silts 3.Organic Soils – Topsoil and Peat Topic C

1.Granular Soils Sand and Gravel Excellent foundation, embankment and backfill material. Not susceptible to frost High permeability Settle rapidly while loaded Develops strength through particle contact/friction. Topic C

Granular Soils – Structure Strength Development Topic C

1.Granular Soils Sand and Gravel Excellent foundation, embankment and backfill material. Not susceptible to frost High permeability Settle rapidly while loaded Develops strength through particle contact/friction. Topic C

Gravel Larger Particles More pervious More stable Less affected by water or frost Sand Finer Particles – Feels gritty Finer and smoother it is closer to silt. – Decreased permeability – Reduced stability in water Topic C

2. Fine Grained Soils 1.Silts – Nonplastic 2.Clays - Plastic Topic C

Plastic Capable of being shaped or formed. Topic C

2. Fine Grained Soils Soil passing a No. 200 sieve Silts = mm to mm (0.003 in to in) Clays – less than mm ( in) Topic C

2. Fine Grained Soils Characteristics Low shear strengths Poor construction material Practically impervious Highly susceptible to frost Develops strength from particle bonds Higher amount of energy needed to compact (particularly clay soils) Topic C

Clay Particles Structure Topic C

Clay Particles Structure Topic C

Non-plastic Unstable in water. Change volume when shape changes. Pulverized by finger when dry. Silts Clays Plastic Compressible Wet – Low resistance to deformation. Hard cohesive mass when dry. Impervious. Topic C

3. Organic Soils Topsoil Peat Rootmat Organic matter Topic C

3. Organic Soils Not suitable for foundations or construction materials. Unacceptable roadway material. Topic C

Organic Soils 1.Reduced load-carrying capacity 2.Low Shear Strength 3.Increased compressibility 4.Releases toxic gases upon decay Topic C

Water and Soil Necessary Evil Critical to compaction effort Reduces strength of soil Loss of Stability Groundwater moves soil particles Erosion Amount of water influences permeability and frost action. Topic C

Effects of Water on Soil Concentrated zones of groundwater on a cut slope cause the soils to flow down the slope. – Often exists where a fine sand or silt overlays an impervious soil (clay). Topic C Seepage zones in backslopes causes slumping or sliding of slopes.

Topic C