Topics What Are the Basics of a ¾ Ten Commandments for Good Roads ¾ Types of Soils Good Road? ¾ Permeability ¾ Capillarity Soils ¾ Compaction ¾ Frost Action and Potholes Vincent Drnevich, P.E., Professor ¾ Selection of Soils for Roads School of Civil Engineering, ¾ Improvement of Soils for Roads z Stabilization

Purdue University z Geotextiles ¾ Summary and Conclusion March 10, 2004 Drnevich on Basics of a Good Road - Soils 3/10/04 2

Ten Commandments for Good Types of Soils Roads (from: Vermont Local Roads Program) 1. Get Water Away from the Road* ¾ Boulders – Larger than 12-inches 2. Build on a Firm Foundation* 3. Use the Best Soils Available* ¾ Cobbles – 3 to 12 inches 4. Compact Soils Well* 5. Design for Winter Maintenance ¾ Gravels – approx. ¼ to 3 inches 6. Design for Traffic Loads and Volumes 6. Design for Traffic Loads and Volumes ¾ Sands – 0.003 (#200 sieve) to ¼ inch 7. Pave Only Those Roads That Are Ready* 8. Build From the Bottom Up* ¾ Silts - smaller than #200 sieve but no 9. Protect Your Investment 10. Keep Good Records strength (cohesion) when dried ¾ Clays - smaller than #200 sieve but *6 of the 10 are related to soils significant strength (cohesion) when dried

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Silts and Clays (referred to as “fines”) Determine Soil Types (Sieving) Silts and Clays (referred to as “fines”) Determine Soil Types (Sieving) are Easily Identified by Behavior

Put Soil in at top ¾ Silts – exhibit no plasticity; crumble when Cobles - soil retained on 3” sieve rolled into a thread; when dry, can easily broken by hand into a powdery form Gravel - soil retained on #4 sieve ¾ Clays – exhibit plasticity; can be rolled into a Coarse Sand - soil retained on #10 sieve thread without crumbling; when dry forms hard lumps which cannot be From Das, B. (2002) Fine Sand - soil retained on #200 sieve readily broken by hand Silt and clay - soil passing the #200 sieve Drnevich on Basics of a Good Drnevich on Basics of a Good Road - Soils 3/10/04 5 Road - Soils 3/10/04 6

1 Classification of Soils (AASHTO) Permeability

¾ Granular Soils – Soils that have less than 35 % ¾ Ability of soil to allow water to flow through it. silts and clays z Drain well – depends on amount of clay and silt Gravel: ~ 10,000 ft/day (2 mi/day) z Good support for pavements Sand: ~ 10 ft/day ¾ Silt-Clay Soils – Soils that have more than 35% Silt: ~ 0.01 ft/day (1/8”/day) silts and clays Clay: ~ 0.00001 ft/day (1/2”/year) z Generally prevent drainage z Behavior strongly determined by the amount of water Gravels and sands allow water to be drained from in the soil (wet → mud; dry → very strong) beneath pavements assuming that there is a place for z Generally not good for pavement support the water to drain

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Capillarity Compaction

¾ How water is absorbed in a soil (analogous to ¾ Increasing density of soil z Increases strength of soil – how a sponge attracts water) reduced likelihood of failure

z Increases stiffness of soil – reduces deformation and Height of Rise: settlement Small Gravel: 0.1-0.4 feet ¾ Depends on the water Coarse sand: 0.5 feet content of soil at the time Fine sand: 1-3 feet of compaction Silt: 3-30 feet z Some water in soil aids in Clay: 30-90 feet compaction z Too much water in soil From Das, B. (2002) impedes compaction

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Water Content at the Time of Compaction Specifications for Highway Compaction Obtainable Density Embankments (Percent of Max. Density)

Saturated Maximum Dry conditions Unit Weight The Maximum Dry Unit Weight and Optimum Moisture Content vary with soil type.

Optimum Moisture Content

Ref.: Hilf, J.W., Chapter 8 - Compacted Fill, Foundation Engineering, Second Ed., Edited by Fang, H-Y, Van Nostrand Reinhold, Drnevich on Basics of a Good New York, 1991, p. 313. Drnevich on Basics of a Good Road - Soils 3/10/04 11 Road - Soils 3/10/04 12

2 Effects of Water on Well Keeping Water from Soils Beneath Compacted Soils Pavements ¾ Design road to minimize ground water access to the soils beneath the pavement

¾ Good pavement maintenance minimizes the water getting into the soils beneath the pavement

Do you want this soil ¾ Provide for removal of water from beneath pavements beneath your pavements z Free draining base material pavements? Free draining base material z Place for water to drain – side ditches

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Freeze-Thaw and Potholes Common Pavement Profile

What causes potholes? Pavement ¾ Water

z If water is not drained from beneath pavements, it Base freezes and expands Subbase z The depth of freezing could go well into the subgrade

z Thawing occurs from the roadway downward Subgrade z Upon thawing the frozen soil surrounds the thawing soil beneath the pavement ▼Groundwater Table▼

z Loose saturated soil provides very little support for the pavement

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Prolonged Freezing Temperatures in Water- Thawing Occurs from Top Down - Saturated Soils Form Ice Lenses and Cause Saturated Soil in Thawed Zone Cannot Drain Pavement Heave Bathtub Effect = Little Support for Pavement Water saturated base, subbase, and Zone of Pavement subgrade expands Pavement thawed, forming ice lenses saturated soil Plowed Plowed snow snow Base Base Subbase Subbase

Depth of Freezing Depth of Freezing Subgrade Subgrade ▼Groundwater Table▼

Water drawn into the zone of freezing from groundwater by capillarity

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3 Selection of Soils for Roads Details at Pavement Edges – Selection of Soils for Roads Collect water that gets beneath pavement and get rid of it

¾ Subgrade – natural soil at the site z If soft or loose soil, compact it or stabilize it ¾ Subbase – first layer above the natural soil Pavement Shoulder z Should prevent clays and silts from penetrating into Base the base layer. Edge drain z Dense-graded aggregate is frequently used (Indiana Subbase 53’s) ¾ Base – layer immediately below the pavement Subgrade z Open graded, free draining material (# 8 or #9 aggregate http://www.dot.state.ny.us/cmb/consult/cpdmfiles/CPDM_Chap_09.pdf z Attention to removing water at edge of pavement into Transverse drains to drainage drainage ditches ditch or storm sewer

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Improvement of Soils for Roads Use of Geotextiles

¾ Stabilization of Subgrades ¾ Many types exist z Filter fabrics placed on z Clayey soils, especially ones which are wet – subgrades prevent use quicklime or lime kiln dust silts and clays from • Mix with soil migrating into the base materials and • Compact to make dense contaminating them z Granular soils – if cannot be compacted

consider mixing in small amounts of cement z Geogrids are and water before compacting geotextiles that act like reinforcing steel does in concrete http://www.mtcsg.com/ http://syllabus.syr.edu/CIE/SKBHATIA/Cie584/dave/index1.htm Drnevich on Basics of a Good Drnevich on Basics of a Good Road - Soils 3/10/04 21 Road - Soils 3/10/04 22

Summary and Conclusions; References Basics of Good Roads - Soils

¾ Das,B. (2002) Principles of Geotechnical Engineering, ¾ Build roads on good soils; if soils are not good, Brooks-Cole Publishers, 5th Ed., ISBN 0-534-38742-X compact and/or improve them ¾ http://personalweb.smcvt.edu/vermontlocalroads/FactSheet%20files/B asics_of_a_Good_Road_Fact_Sheet.htm ¾ Use a subbase to prevent subgrade soils of http://www.dot.state.ny.us/cmb/consult/cpdmfiles/CPDM_Chap_09.pdf contaminating the pavement base ¾ http://www.usroads.com/journals/rmej/9803/rm980304.htm contaminating the pavement base ¾ http://www.sacdot.com/services/Potholes.asp ¾ Use a free-draining base material and make ¾ http://www.freep.com/news/weather/weahome/potholes.htm ¾ http://www.in.gov/dot/div/contracts/standards/dm/ sure that water drains away from the pavement ¾ http://syllabus.syr.edu/CIE/SKBHATIA/Cie584/dave/index1.htm ¾ Maintain the road to: ¾ http://www.mtcsg.com/ (Mt. Carmel Sand and Gravel)

z Reduce water infiltration through the pavement

z Allow base layer to drain

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