EarthworksModule #7

Prepared by

Dr. Randy R. RappJuly 2005

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Soil Classification

• Texture, consistency, mineralogy, and structure

• Unified Soil Classification System (USCS)

• American Assn. of State Highway and Transportation Officials (AASHTO)

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USCS

• Coarse-grained vs. fine-grained• Coarse:

– Gravels– Sands– Sieve analysis size distribution: well and poorly

graded• Fine:

– Silts– Clays: kaolinite, illite, montmorillonite or smectite– Mineralogy and geological history matters: Atterberg

liquid and plastic limits (LL or wl; PL or wp)• Chart, pp. 152-53

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Compaction

• Standard or Modified Proctor test: optimum moisture content (OMC) to achieve γdry,max (lb/ft3, pcf) for compactive effort

• Specifications usually % range of γdry,max and ± 1.5 to 2% of OMC

• Proctor suffices for most soils, but relative density might be applied for coarse soils

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Compaction Molds and Hammers

• Standard Proctor– Mold, 4-in I.D.

• 0.333-ft3 or• 944-cm3

– Hammer blow• 5.5-lb• dropped 12-in

• Modified Proctor– Mold, 6-in I.D.

• 0.0752-ft3

• 2,130-cm3

– Hammer blow• 10-lb• dropped 18-in

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Field Compaction

• Roller types

• Behavior of rollers during multiple passes

• Relating Proctor to field density: test strips

• Field density testing:– Random, at least every few thousand yd3

– Nuclear density gauge (or meter)– Sand cone density test to check the nuke

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Inspection Control

• Observation of passes• Borrow pit concerns (p. 163)• Embankment (pp. 163-64)• Determining average depth of lift• Payment

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Stabilizing Additives

• Additives– Portland cement– Lime (hydrated and quick)– Bituminous materials

• Curing requirements are critical

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OSHA

• Competent person– Knowledge– Authority

• Expedient soil classification (pp. 167-69; 174-76)• Rock and Soil Types, for trench shoring

– A, ¾:1– B, 1:1– C, 1-½ : 1