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Chapter 16 Subgrade Materials. Components and Functions.

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Presentation on theme: "Chapter 16 Subgrade Materials. Components and Functions."— Presentation transcript:

1 Chapter 16 Subgrade Materials

2 Components and Functions

3 Subgrade Supports and distributes the loadings Facilitates drainage Serves as a working platform Can be either foundation or embankment

4 Use Typical Soils/Geotechnical Technology Very Important TTehnology Very Important Subgrade

5 Subgrades Vary Must Evaluate Consider Stabilizing Top 2 Feet Important Stabilize ??? Top 2 feet important Subgrade

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10 Classification Gravel>2.0 mm Sand 2.0 mm to 0.06 mm Silt 0.06 mm to mm Clay<0.002 mm Unified System – Based on Grain Size and Plasticity

11 Unified Soil Classification System G—gravel S—sand M—silt C—clay O—organic soil Pt—peat W—well-graded and clean P—poorly graded, relatively clean F—poorly graded, dirty H—high plasticity L—low plasticity

12 Index Properties

13 Atterberg Limits

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16 Strength – Resist deformation and be stable under loads Granular – function of shearing strength and cohesion. Fine Grained – Stability is measured by q u Φ S p S = p tan Φ ququ S C = q u /2 Ult. Bearing cap. (q d ) = 5c = 2.5 q u P c = 20 psi Φ=0 Q u /2 C

17 Soil Surveys – obtain information about the surface and subsurface soils Ideal Soil Properties – Uniformity 1. Free of excess moisture 2. High internal friction 3. High cohesion? 4. High density 5. Low compressibility 6. Low capillary 7. Low elasticity 8. High compaction

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19 Location and Selection 1. Move alignment 2. Improve drainage 3. Borrow materials 4. Stabilize 5. Waterproof

20 Track Design Assume P a max is 65 psi on ballast  P c = 16.8 P a / h 1.25 (Talbot) Where, P c ≤ 2.5 q u or ≤ 1.67 q u q d 50% fs

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