MinImpactLVRManual_CH12_PartialDRAFT.pdf

DRAFT

Contents – Chapter 12, Materials 1

12. CHAPTER 12 ROADWAY MATERIALS ........................................................................................... 4 2

INTRODUCTION TO MATERIALS..................................................................................................... 4 12.1.3 PROPERTIES AND CLASSIFICATION OF SOILS ............................................................................. 7 12.2.4

12.2.1. Description and Identification of Soils ............................................................................................ 7 5

12.2.2. Soil Tests .......................................................................................................................................... 8 6

12.2.3. Soil Classification .......................................................................................................................... 12 7

PROPERTIES AND REQUIREMENTS FOR AGGREGATES .......................................................... 20 12.3.8

12.3.1. Crushed Aggregate ........................................................................................................................ 20 9

12.3.2. Pit Run, Grid Roll, or Marginal Aggregates ................................................................................. 25 10

12.3.3. Blending Materials ........................................................................................................................ 25 11

UNBOUND AGGREGATE SURFACING DESIGN ........................................................................... 26 12.4.12

12.4.1. Subgrade Strength ......................................................................................................................... 29 13

12.4.2. Surfacing Strength ......................................................................................................................... 30 14

12.4.3. Traffic ............................................................................................................................................ 31 15

12.4.4. Selection of Materials .................................................................................................................... 31 16

12.4.5. Reduced Tire Pressure ................................................................................................................... 32 17

12.4.6. Weather ......................................................................................................................................... 33 18

12.4.7. Other Considerations .................................................................................................................... 34 19

12.4.8. Design Charts ................................................................................................................................ 34 20

12.4.9. Sediment Reduction Study Results ................................................................................................. 36 21

12.4.10. Surface Maintenance ................................................................................................................... 36 22

QUARRY AND BORROW PIT DEVELOPMENT, OPERATION, AND RECLAMATION............. 38 12.5.23

12.5.1. Quarry Site Selection ..................................................................................................................... 38 24

12.5.2. Sand and Gravel Pit Selection ....................................................................................................... 40 25

12.5.3. Pit and Quarry Development Plans ............................................................................................... 40 26

12.5.4. Roadside Borrow Sites ................................................................................................................... 43 27

12.5.5. Reducing the Impacts of Pit and Quarry Mining ........................................................................... 44 28

12.5.6. Reclamation ................................................................................................................................... 47 29

12.5.7. Materials Source Inventories ......................................................................................................... 48 30

SHRINK AND SWELL FACTORS IN EARTHWORK/ROCKWORK .............................................. 51 12.6.31 COMPACTION .................................................................................................................................... 56 12.7.32

12.7.1. Compaction Criteria ...................................................................................................................... 58 33

12.7.2. Types of Compaction Equipment ................................................................................................... 65 34

SOIL STABILIZATION METHODS, SURFACING ALTERNATIVES, AND GEOSYNTHETIC 12.8.35

REINFORCEMENT...................................................................................................................................... 69 36

12.8.1. Drainage ........................................................................................................................................ 70 37

12.8.2. Compaction .................................................................................................................................... 70 38

12.8.3. Capping Soil .................................................................................................................................. 70 39

12.8.4. Corduroy Roads ............................................................................................................................. 73 40

12.8.5. Chunkwood .................................................................................................................................... 73 41

12.8.6. Cobblestone Roads ........................................................................................................................ 74 42

12.8.7. Concrete or Brick Pavers .............................................................................................................. 77 43

12.8.8. Fiber Reinforcement ...................................................................................................................... 77 44

12.8.9. Chemical Soil Stabilization ........................................................................................................... 77 45

12.8.10. Limiting Use/Reduced Tire Pressures ......................................................................................... 81 46

12.8.11. Thermal and Electrical Stabilization ........................................................................................... 81 47

12.8.12. Geosynthetic Reinforcement ........................................................................................................ 81 48

MARGINAL AND PROBLEMATIC SOILS--SILTS, EXPANSIVE CLAYS, ETC. .......................... 82 12.9.49 IN-SITU TESTS, DCP, SPT, CBR, AND DRIVE PROBE USE ........................................................ 83 12.10.50 DUST ABATEMENT ........................................................................................................................ 83 12.11.51

12.11.1. Dust Palliative Basics .................................................................................................................. 84 52

12.11.2. Suppressant Selection Tips .......................................................................................................... 88 1

12.11.3. Suppressant Application Tips ...................................................................................................... 92 2

12.11.4. General Application Tips ............................................................................................................. 93 3

12.11.5. Environmental Impacts ................................................................................................................ 95 4

BITUMINOUS SURFACE TREATMENTS AND SEAL COATS .................................................... 98 12.12.5

12.12.1. WHEN TO PAVE A GRAVEL ROAD .......................................................................................... 98 6

12.12.2. BITUMINOUS SURFACE TREATMENT ( CHIP SEALS) ........................................................ 104 7

12.12.3. Other Seal Coats and Bituminous Concrete Pavement ............................................................. 110 8

12.12.4. Bituminous Concrete Paving ..................................................................................................... 112 9

CHAPTER 12 SUPPLEMENT ............................................................................................................ 114 12.13.10 SELECTED REFERENCES – CHAPTER 12, MATERIALS .......................................................... 117 12.14.11

LIST OF TABLES 14

Table 12-1 (Table 12.2.1) Unified Soil Classification System .................................................................... 16 15 Table 12-2 (Table 12.3.1) Commonly Specified Base Aggregate Gradations for Rural Roads ................... 20 16 Table 12-3 (Table 12.3.2) Common Quality Requirements for Aggregates ................................................. 21 17 Table 12-4 (Table 12.4.1) Typical CBR Range for Various Materials ......................................................... 30 18 Table 12-5 (Table 12.4.2) Tire Pressures and ESALs .................................................................................. 31 19 Table 12-6 (Table 12.6.1) Typical Shrinkage Factors ................................................................................ 55 20 Table 12-7 (Table 12.6.2) Typical Swell Factors ....................................................................................... 55 21 Table 12-8 (Table 12.7.3) More Typical Properties of Compacted Materials ............................................ 62 22 Table 12-9 (Table 12.8.1) Summary of Soil Stabilization Techniques by Modification ............................ 79 23 Table 12-10 (Table 12.8.2) Summary of Soil Stabilization Techniques by Cementing Agents ................. 80 24 Table 12-11 (Table 12.8.3) Summary of Soil Stabilization Techniques by Bridging/Covering ................. 80 25 Table 12-12 (Table 12.11.1) Summary of Dust Palliatives ........................................................................ 86 26 Table 12-13 (Table 12.11.2) Additional Information About dust Palliatives ............................................. 89 27 Table 12-14 (Table 12.12.1) Typical Bituminous Surface Treatment Gradations .....................................105 28 Table 12-15 (Table 12.12.2) Typical Chip Seal “Recipe” .........................................................................105 29

LIST OF FIGURES 32

Figure 12-1 (Figure 12.1.1) Commonly Used Road Surfacing Types ........................................................... 4 33 Figure 12-2 (Figure 12.2.3) Soil Particle Shapes ........................................................................................ 12 34 Figure 12-3 (Figure 12.2.6 or12.2.5?) Hand Soil Classification For Fine Sediments .................................. 18 35 Figure 12-4 (Figure 12.3.2) Gradation Curve Specifications for Road Aggregates .................................... 24 36 Figure 12-5 (Figure 12.3.3) Aggregate Blending Chart .............................................................................. 26 37 Figure 12-6 (Figure 12.4.1) Flowchart ........................................................................................................ 27 38 Figure 12-7 (Figure 12.4.2) Rutting/Pavement Deflection ......................................................................... 28 39 Figure 12-8 (Figure 12.4.3) Aggregate Surface Design for 30mm Minus Aggregate of High Quality ........ 34 40 Figure 12-9 (Figure 12.4.4) Aggregate Surface Design for 70mm Minus Aggregate of Low Quality ......... 35 41 Figure 12-10 (Figure 12.4.5). – Pavement Design Chart from AARB ........................................................ 35 42 Figure 12-11 (Figure 12.5.1a) Example Pit Development Plan .................................................................. 41 43 Figure 12-12 (Figure 12.5.1 b) Example Pit Development Plan Notes ...................................................... 42 44 Figure 12-13 (Figure 12.5.2) Roadside borrow areas. ................................................................................. 44 45 Figure 12-14 (Figure 12.5.3 a) Volumes of Conical Stockpiles ................................................................. 46 46 Figure 12-15 (Figure 12.5.3 b) Volumes of Kidney-Shaped Stockpiles...................................................... 47 47 Figure 12-16 Figure 12.5.xx Key Elements of Forest Materials Inventory ................................................ 50 48 Figure 12-17 Figure 12.5.xx Example Quarry Inventory ........................................................................... 51 49 Figure 12-18 (Figure 12.6.1) Shrink-Swell Relationships .......................................................................... 53 50 Figure 12-19 (Figure 12.6.2) Volume and Density Relationships in Rock ................................................. 54 51 Figure 12-20 (Figure 12.7.1) Compaction Process ..................................................................................... 57 52 Figure 12-21 (Figure 12.7.2) Summary of Laboratory Compaction Concepts ............................................ 60 53 Figure 12-22 (Figure 12.7.3) Compaction Test by Standard and Modified Proctor Methods .................... 63 54 Figure 12-23 (Figure 12.7.4) Types of Compaction Equipment ................................................................. 67 55 Figure 12-24 (Figure 12.8.1) Aggregate Options ....................................................................................... 72 56

Figure 12-25 (Figure 12.8.2) Cobblestone and Concrete Block Road Surfacing ....................................... 76 1 Figure 12-26 (Figure 12.11.1) Guidelines for Selection of Dust Palliatives .............................................. 90 2 Figure 12-27 ( Figure 12.11.2) Cost Record for Dust Control Program ...................................................... 91 3 Figure 12-28 (Figure 12.11.3) Benefits of Dust Control Program .............................................................. 92 4

12. CHAPTER 12 ROADWAY MATERIALS 1

Draft PB,GK 2010 2

INTRODUCTION TO MATERIALS 12.1.4

This chapter discusses the characteristics and properties of materials used in the design 5 and construction of road embankments and road surfacing. These materials include, but 6 are not limited to, soil, local sand and gravels, crushed aggregate, and stabilized or 7 improved in-place materials. Figure 12-1 shows the range of surfacing materials and 8 types typically used on low-volume roads. Techniques used to optimize production, 9 design and construction with these materials for road surfacing and the structural section 10 are also addressed. 11

Figure 12-1 (Figure 12.1.1) Commonly Used Road Surfacing Types 13

Some influences these materials have on roads embankments and surfaces are: 1

• The structural support of the road subgrade and materials placed over the subgrade; 2

• The drivability and need for maintenance of the road surface. The gradation and 3 amount of plastic fines greatly influences the tendency of a road to washboard and 4 ravel; 5

• The quality of fill material and degree of compaction of theat material that affect the 6 subgrade strength and likelihood of fill failures; 7

• The ability of the road surfacecut and fill slope surfaces to erode or be revegetated; 8

• , or tThe ability of the road surfacing material to resist the formation of potholes; 9

• Compaction of roadway materials that can greatly improve the material's strength and 10 structural support value, and that can make the surface less permeable and less 11 erosive. Soil strength increases directly with density (achieved through compaction); 12 and 13

• Use of borrow pits or quarries that can realize major cost savings for projects. 14

Materials from local quarries and borrow pits can be substantially less expensive than 15 commercial or imported materials. However, once used, quarries should be 16 rehabilitated. 17

Materials used in road construction and for surfacing of roadways can make a significant 19 difference in the performance or usefulness of the road, the comfort of the user, the 20 amount of erosion which comes off the road surface, and the cost of construction and 21 maintenance of the road. Use of high quality, well-compacted roadway materials, when 22 available, produces a durable, structurally sound road with minimum maintenance costs. 23

Good roadway surface and subsurface drainage, to help keep roadway materials dry (as 24 discuss in Chapter 7), is one of the most cost-effective actions that can be taken to 25 maintain or improve quality and strength of any soil or aggregate. 26

A working knowledge on the properties and characteristics of soils commonly found 27 during construction are addressed in Section 12.2. The subgrade is the term commonly 28 given to the soils supporting the imported portion of the road structure. How well the soil 29 will support vehicle traffic is a function of the soil type and how much moisture is in the 30 soil. Soil types are typically grouped according to the Unified Soil Classification System 31

(USCS) or the AASHTO Classification System. Know Thy Soil!! 32

Preferably good, coarse, structurally sound materials should be used for the roadway 33 surfacing material. Crushed aggregate with a small percentage of plastic fines as “binder” 34 is probably the best roadway surfacing aggregate. Section 12.3 discusses the properties 35 and characteristics of crushed aggregate. Higher standard paved roads also typically 36 require some crushed base course aggregate for structural support of final pavement 37 surface, typically capped with 2 to 4 inches (50 to 100 mm) of asphalt concrete. Standard 38 gradations for aggregate used as base and surfacing materials are generally specified. 39

Cobblestone or concrete block roads offer a reasonable alternative to gravel or paved 1 roads under some circumstances. 2

Ruts and potholes are common problems on unsurfaced and gravel-surfaced roads, as 3 well as on structurally inadequate pavements. They are caused by local soft soils and thin 4 layers of gravel that are then magnified by the action of traffic. An adequate structural 5 section with well graded aggregate, plus good drainage, all helps minimize the formation 6 of ruts and potholes. Section 12.4 addresses how to determine the necessary aggregate 7 thickness to prevent rutting and excessive surface deformation. 8

Use of local borrow pits or quarries as sources of materials (in lieu of import from remote 9 commercial sources) should be considered since they can result in major cost savings for 10 a project. They can help insure better quality and quantity of construction materials, and 11 use of borrow areas can keep the area of disturbance off the road or in a location which is 12 hidden and whose impacts can be minimized. Pit development plans, as discussed in 13

Section 12.5, are desirable to define the source of materials, sequence of operations, and 14 to describe needed work in a quarry or borrow pit to make the site work well and 15 efficiently, and minimize environmental impacts. Good planning, materials investigation, 16 and site reclamation are each key aspects of quarry management. Section 12.6 presents 17 information on shrink and swell factors that affect the volume and density of materials in 18 an in-place, loose, or compacted state. This should be considered in quarry operations and 19 any earthwork. 20

Information on soil compaction, how it is specified, achieved, tested for, and its benefits 21 can be found in Section 12.7. Second only to drainage, compaction is a very important 22 aspect of materials work and the most cost-effective way to improve the strength of a 23 soil. 24

Where either the roadway surfacing material or the subgrade material is not structurally 25 sound, and where the cost or availability of crushed rock makes its use impractical, other 26 soil stabilization measures may be used. These include measures such as cement or lime 27 stabilization, cobblestone surfacing, use of wood chips, improved compaction, drainage 28 or encapsulation, and use of geosynthetics for subgrade reinforcement. Also road use may 29 be limited to dry periods. Section 12.8 discusses a wide variety of soil stabilization 30 options. 31

Although we try to utilize quality construction materials, at times marginal or poor 32 quality materials problematic to road projects are encountered and have to be removed, 33 utilized, or dealt with. Section 12.9 discusses marginal and problem materials such as 34 silts, fine sands, expansive clays, organic deposits, collapsing soils, and lateritic soils. 35

Section 12.10 discusses some of the useful tools and methods available to help evaluate 36 or characterize materials or in-situ deposits. These methods include use of the California 37

Bearing Ratio, Dynamic Cone Penetrometer, Williamson Drive Probe, and Standard 38

Penetration Test. 39

At times an unsurfaced or even an aggregate surfaced road gets to the point that traffic 40 generates an unacceptable amount of dust. To combat dust, Section 12.11 discusses the 41 various key ingredients of a dust abatement program as well as the various palliatives 1 used on today's market. 2

Finally, Section 12.12 discusses use of Oils, various Seal Coat options, and Bituminous 3

Surface Treatments. Some information concerning selection of seal coats and bituminous 4 concrete pavement is also presented, but asphalt concrete pavements are not uncommon 5 on Forest Service low-volume roads and their design and maintenance are well 6 documented elsewhere. Thus asphalt and concrete pavement use and design are beyond 7 the scope of this Manual. 8

PROPERTIES AND CLASSIFICATION OF SOILS 12.2.11

It is very important for the engineer, to have some type of information about the 12 characteristic of the materials where the road will be built and about the materials that 13 will be added as borrow-pit, subbase, base and road surface. Consequently, a good design 14 step, must include, a preliminary field study to classify the soils and to locate areas with 15 potential settlement and instability problems. Additional laboratory tests may also be 16 done to define with greater detail the soil’s mechanical properties. 17

12.2.1. Description and Identification of Soils 19

Soil, in an engineering sense, is a relatively loose agglomerate of mineral grains, organic 20 material, water, and gases. Soils can be relatively easily broken down into their 21 constituteconstitutive mineral, or organic particles. The sizes of particles present in a 22 given soil play an important role in classifying the soil and influencing its engineering 23 properties. The following terms are used to describe the various particle sizes: 24

• Boulders – particles larger than 12 inches ( 300 mm) in diameter; 25

• Cobbles – particles between 3 and 12 inches (75 and 300 mm) in diameter; 26

• Gravel – particles between 3/16 and 3 inches (4.75 and 75 mm) in diameter; 27

• Sand –particles between 0.003 and 3/16 inches (75 µm and 4.75 mm) in diameter; 28

• Fines – silt and clay sized particles smaller than 75 µm in diameter. 29

Cohesionless soils are materials composed of granular soils that are non-plastic. They are 30 made up of rounded or angular particles, and their strength depends largely upon particle-31 to-particle contact (sometimes calledmeasured by the shear strength or the angle of 32 internal friction). They tend to be stable under static loading, but shock or vibration may 33 cause loose deposits to densify. The compactness of granular material is referred to as 34 loose or dense, which may be expressed mathematically as “relative density”. 35

Cohesive soils are soils composed of fine-grained materials that are plastic. Clay minerals 36 require special attention because of the influence of individual minerals on the 37 engineering properties of soils. Clays are made up of flat plates and for this reason tend to 38 compress easily. They are stable in dynamic loading; but because they have a great 39 affinity for water, they will expand when wetted. Understanding the “shear strength”, a 1 fundamental property of cohesive soils that can vary depending on soil moisture and rate 2 of loading, is important for solving many problems. 3

There are three principle groups of clay minerals: 4

• Kaolinite – most stable of the three common types 5

• Illite – somewhat expansive 6

• Montmorillonite – very unstable and expansive; (bBentonite is a form of 7 montmorillonite from volcanic ash, used commercially as drilling mud and reservoir 8 sealing). 9

Various soils tests are used to determine soils engineering properties., Tthese are 11 described below. Information is also presented on how to classify soils, both in the 12 laboratory and in the field. 13

12.2.2. Soil Characteristic Tests 15

The most common tests used to identify the engineering propertiescharacteristics of soil 16 and to assist classification of the soil are the gradation analysis (AASHTO T-11 and T-17

27) and Atterberg Limits (AASHTO T-89 and T-90). Particle shape and shrinkage limit 18

(AASHTO T-92) are other important soil characteristics that needs to be evaluated and 19 documented. 20

12.2.2.1. Grain Size Distribution 22

The grain size distribution (gradation) of a soil is the relative distribution of the various 23 particle sizes. Gradation is determined through a simple test consisting of sieving or 24 screening a measured quantity of dry material through successively smaller sieves as seen 25 in Table 6.3.xx. The contents retained on each sieve are weighed and expressed as a 26 percentage of the total sample weight. Soil particles are often referred to by size such as 27 the x1/4 inch (4.756.3 mm) or the 75 µm. 28

The entire size distribution of a soil is best shown on a gradation chart where particle size 29 is plotted horizontally on a logarithmic scale against the cumulative percent passing on a 30 vertical linear scale. To plot a gradation curve, the test results should be tabulated as 31 percentage passing each sieve. After calculating the percent passing, the grain size 32 distribution can easily be plotted on the gradation curve as shown in Figure 12-2. 33

Figure 12-2 (Figure 12.2.1) Soil Gradation Curve 2

The shape of the gradation curve gives an indication of the size distribution of the 3 material in the sample. The steeper the curve, the more one-sized material present 4

(uniform gradation); the flatter the curve, the wider the range of grain sizes present (well-5 graded). Two coefficients, the coefficient of uniformity (Cu), and the coefficient of 6 curvature (Cc), are used to measure the uniformity and how well graded the soil. Details 7 on using these coefficients are discussed below under soil classification. 8

Four examples of gradation curves for various soils are plotted in Figure 12-2. The soils 9 on the left are more coarse-grained and those on the right are more fine-grained. Note the 10 differences in the shapes of the curves representing the uniform soil, the well-graded soil, 11 and the gap-graded soil. 12

12.2.2.2. Atterberg Limits 14

Plasticity is the property of a soil that allows it to be deformed beyond the point of 15 recovery without cracking or with appreciable volume change. Soils that pass the No. 200 16

(75 µm) sieve are classified according to their plasticity characteristics -- as this 17 determines their strength, settlement, and other properties. In the laboratory, arbitrary 18 limits called the Atterberg limits are used to determine the plasticity characteristics of a 19 soil. These tests are based on the changes in soil consistency with varying moisture 20 contents, as shown in Figure 12-3. The following terms are used to describe each stage: 21

• Plastic Limit (PL) - the boundary between the semisolid and plastic state 1

• Liquid Limit (LL) - the boundary between the plastic and liquid state 2

• Plasticity Index (PI) - the range of water content where the soil is plastic, the 3 difference between the LL and PL 4

• Shrinkage Limit (SL) - the water content at which the soil reaches its minimum 5 theoretical volume and no more volume reduction can take place with continued 6 drying 7

The Liquid Limit test consists of molding a soil pat in a brass cup of standard 9 dimensions, cutting a groove in the pat with a special standard cutting tool, and dropping 10 the cup onto a solid base from a constant height using a standard dropping tool. The 11

Liquid Limit is that moisture content (percent by dry weight) at which the groove closes 12 for a length of 0.5 x inches (13 mm) underafter 25 impacts. 13

The Plastic Limit test consists of rolling a soil sample into a thin thread. The soil thread is 14 made by rolling a wet sample with the hand. This procedure is repeated until the sample 15 crumbles when the diameter of the thread is equal to 0.1x inches (3 mm). The moisture 16 content (percent by dry weight) of the soil in this latter condition is the Plastic Limit. 17

Large values for the Liquid Limit or Plastic Limit indicate a poor soil for engineering 18 purposes. A high Liquid Limit indicates a very compressible soil, thus poor for 19 foundation purposes. A large value for Plasticity Index indicates a soil of high plasticity 20 and low permeability with the ability to absorb large amounts of moisture and still remain 21 plastic (typical of clays). 22

The Liquid Limit varies widely, with values of 40 to 60 typical for clay soils (however, 23 values as high as 80 to 100 are not uncommon). For silty soils, values of 25 to 50 can be 24 expected. Highly compressible soils are those with Liquid Limits over 50. The Plasticity 25

Index can be as high as 70 to 80 for the very plastic clays. Commonly, clays will have a 26

Plasticity Index between 20 and 40. The silty materials normally have a Plasticity Index 27 between 10 and 20. The Liquid Limit and Plastic Limit tests will not produce a result for 28 cohesionless soils; therefore, they are reported as "non-plastic". 29

Figure 12-3 (Figure 12.2.x) Soil Consistency Limits 2

12.2.2.3. Particle Shape 4

The shape of individual particles is at least as important as the grain size distribution in 5 affecting the engineering behavior of granular (cohesionless) soils. A visual estimate is 6 sufficient for classifying particle shapes. Coarse-grained soils are commonly classified 7 according to the shapes shown in Figure 12-4. 8

Figure 12-4 (Figure 12.2.3) Soil Particle Shapes 2

12.2.3. Soil Classification 4

Soil can be classified in a variety of ways, depending on the use of the information. If the 5 soils will be used for agriculture, the soils would be grouped according to their drainage 6 capabilities. The USDA Soil Conservation Service has developed a textural classification 1 scheme shown in Figure 12-5. Figure 12-5 presents this same textural “soil triangle” 2 with approximate Unified Soil Classification System limits drawn upon it. This 3 information presents commonly used terms for soils, as a function of the amount of sand, 4 silt, or clay they contain. This classification scheme is commonly used for agricultural 5 purposes, but can be applied to engineering projects as well. 6

Soils for engineering purposes are grouped based on resistance properties, bearing 7 capacity, plasticity, etc. The basis for soil classification used in engineering are the 8 plasticity characteristics and the grain size distribution, eliminating in this way expensive 9 research and additional tests. 10

Figure 12-5 (Figure 12.2.4a) USDA Textural Soil Classification System 12

Figure 12-6 (Figure 12.2.4b) Soil Textural Classification by USDA and USCS. 3

12.2.3.1. Unified Soil Classification System 5

The Unified Soil Classification System (USCS) uses prefixes and suffixes to describe the 6 soil as noted in Table 12-1. It is the most common engineering classification system in 7 use worldwide. This classification system, as well as others like the AASHTO system, 8 was specifically developed for engineering purposes, based upon laboratory soil testing. 9

The first step of the USCS is to determine if the soil is coarse grained or fine grained. 10

Classification is performed only on material passing the 3 inch (75 mm) sieve (largest 11

“gravel” size particle). Larger materials - cobble and boulders - are noted, but do not 12 affect the classification. Coarse-grained soils are those that have more than 50 percent by 13 weight of the sample coarser than the No. 200 (75 m) sieve. It is given the prefix “G” 14

(for gravel) if more than half of the coarse particles, by weight, are coarser than the No. 4 15

(4.75 mm) sieve (largest “sand” size particle) and “S” (for sand) if more than half are 16 smaller. The G or S is followed by a second letter that describes the gradation; “W” 17 means, well-graded with little or no fines; “P,” means poorly-graded, uniform or gap-18 graded with little or no fines; “M”, means containing silt or silt and sand; and “C,” means 1 containing clay or sand and clay. The coefficient of uniformity (Cu), and the coefficient 2 of curvature (Cc) are used to help classify the soil. 3

The Uniformity Coefficient Cu is defined as D60/D10 where Dx is the diameter of the 4 particle at x percent passing. Soils with a Cu less than 4 are called uniform soils (poorly 5 graded). Soils with a Cu greater than 6 are well graded, if the gradation curve is soft and 6 relatively symmetric (the Unified System uses a minimum of Cu = 4 for well graded 7 gravel and 6 for well graded sands). 8

The Curvature Coefficient Cc is defined as (D30) 2/(D60xD10.) Soils with a Cc between 1 9 and 3 are well graded. 10

Fine-grained soils are soils that have more than 50 percent by weight finer than the No. 11

200 (75 m) sieve. Fine-grained soils are divided into three groups: C, clays; M, silts and 12 silty clays; and O organic silts and clays. These prefixes are followed by a suffix that 13 denotes the Liquid Limit or relative compressibilityplasticity: “L,” means low plasticity a 14

Liquid Limit less than 50; and “H,” means high plasticity a Liquid Limit exceeding 50. 15

With laboratory testing, a plasticity chart as shown in Figure 12-7 can be used to classify 16 the fine-grained soil. 17

Figure 12-7 (Figure 12.2.5) Soil Plasticity Chart 19

Formatted: Subscript

Table 12-1 shows the criteria for soil classification according to the Unified Soil 1

Classification System. 2

Table 12-1 (Table 12.2.1) Unified Soil Classification System 4

Once soil has been classified Table 12-2, developed by the U.S. Bureau of Reclamation, 6 can be used to estimate the expected range of strength values, workability as a 7 construction material, recommended compaction equipment, value as a subgrade, 8 compressibility, drainage characteristics, and unit weight. 9

Table 12-2 (Table 12.2.2) Construction Characteristics of Various Soils 1

12.2.3.2. Field Classification 4

A simple hand texture and classification test is shown in Figure 12-8 where basic soil 5 properties can be determined by the working a handful of soil and observing its behavior. 6

If the moist soil cannot form a ball, it is likely predominantly a sand. If the soil can be 7 squeezed into a ribbon, it is likely clay. If it is fine grained but will not make a ribbon it is 8 likely a silt or silty sand. To describe a soil in the field in more detail and when no other 9 resources are available, engineers frequently use classifications based on additional tests 10 and texture. Supplement 112A, titled “Soil Classification in the Field” presents a useful 11 write-up for basic field classification of soils if laboratory testing is not available. Field 12 methods are based upon simple “hand” tests to indicate the soil properties needed 13 classification. 14

Figure 12-8 (Figure 12.2.6 or12.2.5?) Hand Soil Classification For Fine Sediments 2

In this case, the following characteristics must be taken into account: 2

• Consistency (loose, strong, uniform, soft, etc.) 3

• Resistance and compressibility (crackable, plastic, compressible, etc.) 4

• Color 5

• Composition (well graded, uniform, plastic, organic, rounded, silty, sandy, coarse, 6 etc.) 7

• Additional details (porous, decomposition state, fractured, wear, moist, etc.) 8

As an example, a soil may be described as we can have: “soft clay, lightly plastic, with 10 some gravel size quartz particles; hard gravel, yellowish coffee color, cemented with 11 sand.” If the soil iswas a mix of different particle sizes, it must be described by order of 12 importance. A sandy silty clay, would be a clay with some sand and a small amount of 13 silt and it would behave as a silt. An excellent reference of this type of soil description is 14 the ASTM test method D2466 (visual procedure manual). 15

References 17

Soil Classification Handbook – Unified Soil Classification System, Training Manual No. 19

6, Geotechnical Branch of the Bureau of Reclamation, Department of the Interior, Denver 20

Colorado, 1986 21

Standard Classification of Soils for Engineering Purposes, ASTM D-2487, American 23

Society of Testing Materials, Volume 4.08, 1999 24

Standard Practice for Description and Identification of Soils (Visual Manual Procedure), 26

ASTM D-2488, American Society of Testing Materials, Volume 4.08, 1999 27

Classification of Soils and Soil-Aggregate Mixtures for Highway Construction Purposes, 29

AASHTO M-145, Standard Specifications for Transportation Materials and Methods of 30

Sampling And Testing, Part I Specifications, American Association of state Highway 31

And Transportation Officials (AASHTO), 1998 32

Engineering Manual – A Water Resources Technical Publication, Bureau of Reclamation, 34

Department of the Interior, Second Edition, 1974 35

PROPERTIES AND REQUIREMENTS FOR 12.3.1

AGGREGATES 2

Aggregate is granular material of graded and/or crushed sand, gravel or stone. It is the 3 most common material used for surfacing of secondary roads and collector road systems, 4 as well as used as a base course under pavements. Also it is a commonly used material 5 for stabilization of low standard roads in local, soft soil areas. Aggregate materials are 6 typically classified as either a quality crushed material or as pit run/borrow/jaw crushed. 7

12.3.1. Crushed Aggregate 9

Crushed aggregates are used for surfacing as well as a base material, such as under 10 pavements, where structural support is the primary function. Crushed aggregate used for 11 base courses can be either well graded or open graded. Well-graded aggregate will have 12 the highest density and strength, and lowest permeability. Maximum strength for base 13 course is typically achieved with 4 to 8 % fines (minus No. 200 ([0.75 µm]) Sieve). Some 14 commonly specified base aggregate gradations appropriate for rural roads are shown in 15

Table 12-3. Aggregate without plastic fines are preferred for structural support and 16 strength. There are criteria for the quality requirements of the material, such as percent 17 wear, durability and plasticity. Some common quality requirements are shown in Table 18

12-4. 19

Table 12-3 (Table 12.3.1) Commonly Specified Base Aggregate Gradations for Rural 20

Roads 21

Table 12-4 (Table 12.3.2) Common Quality Requirements for Aggregates 2

As a surfacing material, crushed aggregate should have structural support, but it also 2 needs to be very well graded and have some plastic binder to prevent ravel and wash 3 boarding. Maximum density is achieved with between 6 and 12% fines. Ideally aggregate 4 used for road surfacing materials or a wearing surface should have 10 to 15 % fines and a 5

Plasticity Index of 5 to 9. Recommended gradations for some surface course aggregates 6 are also shown in Table 12-3 and quality requirements shown in Table 12-4. In the case 7 of highways, the materials used for the surface, would ideally be smaller than 50 mm (2 8 in). For low specification standard roads, such as in the case of rural road, the maximum 9 aggregate size will be smaller than 4 inch (100 mm). Larger size aggregate, unless very 10 well graded and angular, is very difficult to drive upon. Aggregate smaller than 1/2 in (10 11

mm) looses structural support and becomes more erosive on the road surface. The 12 cCrushed stone versus rounded stone is stronger than rounded stone, less slippery and 13 interlocks better. 14

Fines beyond about 15% will reduce the structural strength of the material. With material 15 having more than approximately 30 % fines, point-to-point contact of the rock particles is 16 lost and the fines begin to control the strength of the aggregate. Figure 12-9 shows the 17 relationship of aggregate with no fines, with an ideal amount of fines, and aggregate with 18 excessive fines. Each blend of materials has distinct physical characteristics. Either too 19 little or too many fines are generally undesirable for road aggregates, particularly on the 20 road surface. An open graded aggregate base material without any fines can be desirable 21 for good drainage but the material must be confined, such as under a pavement for 22 drainage. Figure 12-10 graphically presents the requirements of road aggregate plotted on 23 a range of gradation curves. Very coarse material ravels, but moderately coarse, well 24 graded material is ideal for base aggregate that will be confined. Surface course 25 aggregate needs to be a bit finer to retain moisture and minimize raveling. A fines- rich 26 aggregate will lose its strength, be moisture- sensitive, and produce dust. Thus Base 27

Course Aggregate and Surface Course Aggregate each have their ideal gradation ranges. 28

Figure 12-9 (Figure 12.3.1) Physical States of Soil-Aggregate Mixtures 2

Figure 12-10 (Figure 12.3.2) Gradation Curve Specifications for Road Aggregates 2

Quality requirements are important to the service life of the aggregate,; this includes its 3 wear characteristics and durability. Aggregate wear, or abrasion resistance, is particularly 4 important to aggregate surfacing. The test (known as the “Los Angeles Rattler” test) 5 involves tumbling aggregate in a drum with iron balls to determine its wear loss after 100 6 or 500 revolutions (see AASHTO T96). A maximum aggregate loss of 35 to 40 percent is 7 commonly specified. Durability represents the aggregate's resistance to weathering and 8 softening or disintegration with time. A fairly durable aggregate is desirable, so a 9 specified Durability Index of 35 (minimum) is common. 10

Strength properties of aggregate are occasionally specified using the California 11

Department of Transportation (CALTRANS) specification of a minimum resistance (R-12 value) of 78. This test measures the horizontal deformation of a sample caused by a given 13 vertical load. Another test has also been developed called tThe California Bearing Ratio 14

(CBR) test (AASHTO T-193) is most commonly usedto measure aggregate strength. 15

Though testing with this method is more involved, this method is better known and is 16 used worldwide. A minimum CBR value of 50 is often specified to ensure a quality 17 aggregate. A major advantage of the CBR procedure is that soil or aggregate strength can 18 be determined for any specified density. Thus field conditions can more closely be 19 modeled in the laboratory. 20

Strength properties of aggregate are also occasionally specified using the California 2

Department of Transportation (CALTRANS) specification of a minimum resistance (R-3 value) of 78. This test measures the horizontal deformation of a sample caused by a given 4 vertical load. 5

There are vVarious other strength determination schemes exist, and most all schemes 6 involve at least some laboratory testing. To avoid laboratory testing, aggregates with 7 specific properties are commonly used and placed at specified compaction standards to 8 achieve a minimum density. With a given density of specified aggregate, then the 9 strength properties are predictable and have been determined by prior laboratory testing 10 and field observations. 11

12.3.2. Pit Run, Grid Roll, or Marginal Aggregates 13

Pit run aggregate, grid roll, mobile rock crusher, or tractor rolled aggregate are all ways 14 to produce aggregate at a relatively low cost. However, the minimal processing usually 15 results in a lower quality material, depending greatly on the characteristics of the original 16 material used. A well fractured, “dirty” rock source may make a good roadway surfacing 17 material or aggregate to fill in soft spots, particularly for a low-use road. It is often 18 appropriate and cost-effective to use poor or marginal quality aggregate for low-volume 19 roads. The tradeoff is usually a reduced construction cost but poorer performance on the 20 road and higher maintenance costs. Thus the savings in initial production of the aggregate 21 must be weighed against poorer performance and increased operation and maintenance 22 costs. Poor materials should usually not be placed under a pavement considering the high 23 cost of the pavement. 24

Cobbles or big stones without fines are suitable for the sub-base but make a poor 25 surfacing material. If they are used on the roadway surface, traction and trafficability will 26 be difficultreduced, particularly on steep grades, a rough driving surface will result, and 27 maintenance of the road will be difficult. A 3 to 4 inch (25 to 75mm) maximum size 28 aggregate is the largest size rock practical to drive upon, and even this large a size may 29 produce a very rough driving surface. Normally the maximum specified crushed 30 aggregate size is 2 inches (50 mm). 31

Add more Marginal Aggregate Info- TRL, Metcalf- 32

12.3.3. Blending Materials 34

Two or more different materials with specific gradations can be mixed together, or 35 blended in certain specific percentages to produce a more desirable composite gradation. 36

A coarse aggregate free of fines might be blended with a rocky soil to produce an 37 aggregate with moderate fines. Figure 12-11 shows a blending chart used to mix two 38 specific materials. 39

ADD MORE BLENDING INFO 40

Figure 12-11 (Figure 12.3.3) Aggregate Blending Chart 3

UNBOUND AGGREGATE SURFACING DESIGN 12.4.5

As previously mentioned, the primary purpose of roadway surfacing is to support the 6 traffic and minimize the amount of deformation in the roadway surface. Most natural 7 soils are not strong enough to support traffic without excessive surface maintenance and 8 vehicle operating costs. For this reason, a “surfacing structure” is placed over the native 9 materials to help distribute the load stresses and provide a longer lasting surface. There 10 are a multitude of secondary reasons to surface a roadway. These include, butand are not 11 limited to, the following: 12

• improving the ride and comfort of the user, 13

Comment [UFS1]: What are the open circle symbols on this graph?

• providing a long-term cost effective running surface, and 1

• minimizing the amount of sediment and dust coming from the road surface. 2

This section will address how to combine the knowledge of the materials characteristics, 4 along with information about the traffic, to ensure that the proper amount of surfacing is 5 placed to minimize surface deformation. 6

Figure 12-12 outlines a flowchart practitioners can follow to determine if surfacing may 7 be needed to prevent excessive surface deformation that can lead to high maintenance 8 and vehicle operating costs. Erosion Control? Typically higher standard roads will 9 receive an aggregate surface course. Less expensive materials should always be used 10 whenever possible, particularly on low standard roads. Cost savings may be realized by 11 using such materials as jaw-crushed aggregate, screened or pit run material, blended 12 coarse aggregate with fines, woodchips or chunkwood. Also soil stabilization measures 13 or surface mulching should be considered. However, less expensive materials often are 14 limited in volume and have hidden costs that must be evaluated including higher 15 exploration costs, higher maintenance costs, unknown performance, more road user 16 discomfort, and other risks. As a result of all these considerations, aggregate is the most 17 commonly used rural road surfacing material. 18

Figure 12-12 (Figure 12.4.1) Flowchart 20

Formatted: Highlight

This chapter addresses the use of aggregate for surfacing. The use of other materials for 1 surfacing is addressed in Section 12.8 and 12.12. Maintenance tips for aggregate surfaced 2 roads are also discussed in this chapter. 3

Surface deformation by traffic can take various forms. The primary surface deformation 4 created by traffic is rutting in the wheel tracks. Rutting is the downward movement of the 5 surface material with possible lateral or side heaving. The rutting can take place in either 6 the surfacing material or in combination with the underlying subgrade material as shown 7 in Figure 12-13. 8

Figure 12-13 (Figure 12.4.2) Rutting/Pavement Deflection 10

Another surface deformation commonly observed on aggregate road surfaces is wash 11 boarding. Wash boarding is a sinusoidal feature found in the wheel tracks that resemble 12 clothes washboards common in the early 1900’s. The last surface deformation observed 13 on aggregate surfaced roads is aggregate loss. This surface deformation is not as evident 14 as the previously mentioned deformations but it does occur. Aggregate loss is the loss of 15 aggregate thickness by the wear and tear of traffic and/or by maintenance activity such as 16 a motor-grader reshaping the road surface. 17

There are various methods one can use to determine the proper amount of surfacing to 18 mitigate surface deformation. The USDA-Forest Service has chosen the design algorithm 19 developed by the Corps of Engineers in 1978.