Introduction to Road Soil

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Introduction to Road Soil Characterization By: Dr. Curtis F. Berthelot P.Eng.

Infrastructure t Road Soil Introduction Roads are constructed of layered heterogeneous

1 Introduction to Road Soil Characterization By: Dr. Curtis F. Berthelot P.Eng. Department of Civil and Geological Engineering Centre of Excellence for Transportation ti and Infrastructure t Road Soil Introduction Roads are constructed of layered heterogeneous multiphase geo-materials that exhibit internal friction, cohesion, dilation, and viscoelastoplastic behavior under load. Behavior is often influenced by confinement because the material is non-linear stress dependent. Several methods have evolved to quantify performancerelated properties or road soils. 2 1

2 Granular Pavement Structure Asphalt wearing coarse Granular Base Subbase Subgrade Subgrade: in-situ material used to construct grade. Subbase: select material (usually low quality granular) that is borrowed from a pit and placed over the subgrade. Base: high quality granular layer placed directly under asphalt concrete. Wearing coarse : asphaltic or hydraulic bound aggregate 3 PCC Cross Section Portland Cement Concrete Granular Base Subgrade Subgrade: in-situ material used to construct grade. Subbase: none. Base: high quality coarse crush with high air voids for drainage. Wearing coarse : Portland Cement Concrete 4 2

3 Permanent Deformation HMAC Materials Pouching Asphalt Concrete Pavement Failures and Distresses 5 Permanent Deformation Substructure Asphalt Concrete Pavement Failures and Distresses 6 3

4 Fatigue Cracking Asphalt Concrete Pavement Failures and Distresses 7 Fatigue Cracking and Substructure Rutting Asphalt Concrete Pavement Failures and Distresses 8 4

5 Frost Action Asphalt Concrete Pavement Failures and Distresses 9 Frost Action Asphalt Concrete Pavement Failures and Distresses 10 5

6 Soil Definition Soil: All earthen materials including: Organics Sands Clays Gravels Silts 11 Soil Definition Definition of Soil and Soil Components: Soil is a layer of disintegrated rock material lying on the surface of the earth Two broad groups of soils: Residual Soils Soils developed in place from the rock or parent soil Transported Soils Residual soils eroded and redeposited by wind, ice or water 12 6

7 Road Soil Characterization Physical properties: Grain size analysis (AASHTO T27, ASTM C136) Sand equivalent (AASHTO T176) Classification (ASTM D3282): Unified Soil Classification System AASHTO 13 Road Soil Characterization Phenomenological properties: Atterberg limits and plasticity index (ASTM D4318, AASHTO T89, AASHTO T90) Proctor water-density (AASHTO T99, ASTM D 698) California bearing ratio (AASHTO T193, ASTM D1883) Hveem Resistance 14 7

8 Soil Volumetrics Soil mass is comprised of: Soil Air Water Soil-water interface Water-air interface 15 Soil Volumetrics V V V W Air Water-Air Interface Water Soil-Water Interface W W V T V S Soil Solids W S W T 16 8

9 Grain Size Analysis Aggregate gradation is the distribution of particle sizes. AASHTO T27, ASTM C136. Size of soil particles has an effect on the engineering behavior of soil. Affects strength through inter-particle interlock. Affects mixing: more fines = more surface area to coat. Well-graded soils compact to higher density increasing strength. th 17 Grain Size Analysis Uniformly Graded Well Graded 18 9

Grain Size Analysis Mechanical Sieve: Used to

series of different sized screens Results are

performed first to accurately quantify fines in

10 Grain Size Analysis Mechanical Sieve: Used to determine particle size distribution of aggregates larger than 0.075mm Weighed sample of aggregate passed through series of different sized screens Results are used to classify soils May have wet sieve performed first to accurately quantify fines in the material. 19 Aggregate Particle Size/Gradation Individual Sieve Stack in Mechanical Shaker 20 10

11 Wet Sieve Analysis 21 Wet Sieve Analysis 22 11

12 Aggregate Particle Size/Gradation Mineral Filler: aggregate with at least 70% passing the 75 m (No. 200) sieve. Fine Aggregate: aggregate passing 4.75mm (No. 4); or 2.36mm (No. 8); or 2.00mm (No. 10) sieve. Coarse Aggregate: aggregate retained on 4.75mm (No. 4); or 2.36mm (No. 8); or 2.00mm (No. 10) sieve. Nominal Maximum Size: smallest sieve size through which 90% passes. Maximum Size: smallest sieve size through which 100% passes. 23 Grain Size Analysis 100 Percent Finer Than Grain Size (mm) Clay Subgrade (Hydrometer Sieve) Clay Subgrade (Mechanical Sieve) Clay Till Subgrade (Hydrometer Sieve) Clay Till Subgrade (Mechanical Sieve) Subbase (Mechanical Sieve) Granular Base (Mechanical Sieve) 24 12

Grain Size Analysis Hydrometer Sieve: Fine

075 mm are further graded by a hydrometer

13 Grain Size Analysis Hydrometer Sieve: Fine particles smaller than mm are further graded by a hydrometer analysis Mix fines with water/flocculants and measure density of water as the particles settle Large particles settle faster than fine particles Settlement changes density of water 25 Hydrometer Grain Size Analysis Silty-Sand Clay-Till 26 13

14 Grain Size Analysis COS Subbase Aggregate Percent Finer Than Grain Size (mm) Gradation Boundaries Mean 27 Grain Size Analysis COS Base Aggregate 100 Percent Finer Than Grain Size (mm) Gradation Boundaries Mean 28 14

15 Grain Size Analysis SDHT Granular Base Type 33 Percent Finer Than Grain Size (mm) Gradation Boundaries Mean 29 Grain Size Analysis COS Subbase & Base Mean Crossplot Percent Finer Than Sieve Size 0.45 (mm) Subbase Base 30 15

16 Atterberg Limits Introduction Water significantly affects behavior of fine grained soils Different fine grained soils behave differently How can different fine grained soils be categorized? 31 Atterberg Limits Define water contents at which fine grained soils behavior changes (states of consistency) Upper Limitit Liquid Limit: water content where clay begins to act like a liquid Sticky Limit Cohesion Limit Plastic Limit: water content where clay begins to exhibit plasticity Shrinkage Limit Plastic Index: LL-PL 32 16

17 Atterberg Limits Free Flow Limit Liquid State Liquid Limit Plastic Limit Shrinkage Limit Plastic State Semisolid State Solid State Liquid Limit minus plastic limit equals plasticity index; equals range in moisture content through which soil is plastic Dry Limit 33 Atterberg Limits Plastic Limit Test: Sieve soil through #40 (0.425 mm) sieve Add enough moisture to be able to knead the material Roll soil into 3mm thread Plastic limit defined as the point when soil crumbles at 3mm diameter 34 17

18 Atterberg Limits 35 Atterberg Limits 36 18

Atterberg Limits Liquid Limit Test: Mix fine

Cut groove into soil Drop bowl 1 cm until

19 Atterberg Limits Liquid Limit Test: Mix fine grained soils with enough water to get soil to consistency of peanut butter Spread 1 cm layer into bowl on liquid limit apparatus Cut groove into soil Drop bowl 1 cm until groove closes 13mm (1/2 ) 37 Atterberg Limits 38 19

20 Atterberg Limits 39 Atterberg Limits 40 20

21 Soil Classification Most common methods: USCS: Unified Soil Classification System. AASHTO: American Association of State Highway and Transportation Officials. 41 USCS Soil Classification Four main groups of soils: 1. Coarse-grained 2. Fine-grained 3. Organic soils 4. Peat Used by Saskatchewan Highways Originally developed for airfield construction 42 21

22 USCS Soil Classification Letter system for soil classification: G Gravel S Sand M Silt C Clay W Well Graded P poorly graded U uniformly graded L low liquid limit I intermediate liquid limit H high liquid limit V very high liquid limit 43 USCS Soil Classification ASTM D 2487 Group symbol GW GP GM GC SW SP SM SC ML CL OL MH CH OH Pt Group name well graded gravel, fine to coarse gravel poorly graded gravel silty gravel clayey gravel well graded sand, fine to coarse sand poorly-graded sand silty sand clayey sand silt clay organic silt, organic clay silt of high plasticity, elastic silt clay of high plasticity, fat clay organic clay, organic silt peat 44 22

23 Coarse grained soils more than 50% retained on No.200 (0.075 mm) sieve Fine grained soils more than 50% passes No.200 (0.075 mm) sieve USCS Soil Classification ASTM D 2487 Major divisions gravel > 50% of coarse fraction retained on No.4 (4.75 mm) sieve sand 50% of coarse fraction passes No.4 (4.75 mm) sieve silt and clay liquid limit < 50 clean gravel gravel with >12% fines clean sand sand with >12% fines Group symbol GW GP GM GC SW SP SM SC Group name well graded gravel, fine to coarse gravel poorly graded gravel silty gravel clayey gravel well graded sand, fine to coarse sand poorly-graded sand silty sand clayey sand ML silt inorganic CL clay organic OL organic silt, organic clay MH silt of high plasticity, elastic silt silt and clay inorganic liquid limit 50 CH clay of high plasticity, fat clay organic OH organic clay, organic silt Highly organic soils Pt peat 45 USCS Soil Classification CV Plasticity Index CI CH CL 10 CL-ML ML Liquid Limit (%) 46 23

24 AASHTO Soil Classification Developed for farm to market road construction. Based on observed performance of different soils under highway h pavements (moisture susceptibility). Seven main groups of soils, A-1 to A-7. Grouped by gradation, liquid limit, and plasticity index. One of first soils classification schemes related to road performance. Correlate subgrade soil type and observed road performance. 47 AASHTO Soil Classification Modified by Highway Research Board and later AASHTO into the present AASHTO Group Index (GI) soil classification system. Categorizes soils into 8 classes based on grain size distribution: A-1 to A-3 (well-graded to poor-graded granular soils) A-4 to A-7 (fine-grained soils) Extension of AASHTO soil classification scheme which further classifies road soils based on correlations of physical soil properties and Atterberg limits to observed road performance

25 AASHTO Soil Classification A-1 to A-3: Excellent to good material for subgrade: A-1: most stability, less than 50% passing No. 40 sieve, less than 25% passing No. 200 sieve A-2: less than 35% passing No. 200 sieve A-3: fine sand A-4 to A-7: Fair to poor material for subgrade materials: More than 36% passing No. 200 sieve Separated by liquid id limit it and plasticity it index 49 AASHTO Soil Classification Group Index (GI): Used to further evaluate soils within a group Based on service performance of soils Range from 0 to 20 GI = (Fines-35)[ (LL-40)]+0.01(Fines-15) (PI-10) Fines = % passing 0.075mm sieve LL = Liquid limit PI = Plasticity Index 50 25

26 AASHTO Road Soil Classification AASHTO M-145 and ASTM D 3282 General Classification General rating as a subgrade Group Classification Usual types of significant constituent materials A-1 stone fragments, gravel and sand Granular Materials (35% or less passing mm) excellent to good A-3 fine sand A-2 silty or clayey gravel and sand Silt-Clay Materials (>35% passing mm) fair to poor A-4 A-5 silty soils A-7 clayey soils 51 AASHTO Road Soil Classification AASHTO M-145 and ASTM D 3282 General Classification Group Classification 2.00 mm (No. 10) (No. 40) (No. 200) Liquid Limit Plasticity Index Usual types of significant constituent materials General rating as a subgrade A-1-a 50 max 30 max 15 max A-1 6 max A-1-b 50 max 25 max stone fragments, gravel and sand Granular Materials (35% or less passing mm) A-3 51 min 10 max 35 max 40 max 35 max 41 min A-2 35 max Characteristics of fraction passing mm (No. 40) N.P. fine sand A-2-4 Sieve Analysis, % passing 10 max excellent to good A max A max 11 min A max 41 min 11 min silty or clayey gravel and sand Silt-Clay Materials (>35% passing mm) A-7 A-4 A-5 A-6 A-7-5A-7- A min 40 max 10 max 36 min 41 min 10 max silty soils 36 min 40 max 11 min fair to poor 36 min 41 min 11 min 1 clayey soils Note (1): Plasticity index of A-7-5 subgroup is equal to or less than the LL Plasticity index of A-7-6 subgroup is greater than LL

27 Proctor Moisture-Density Compaction improves engineering properties of soils Minimizes settlements in road surface. Increases soil density - strength. Increases bearing capacity. Helps control volume change. Amount of moisture in the soil affects compaction. 53 Proctor Moisture-Density Developed by R.R. Proctor in 1930 s: Engineer for Los Angeles County. Earth dams. Consists of rammer that falls vertically onto soil that is placed in a cylindrical mold. Different procedures for different soil gradations. Two specified compaction efforts: Standard. d Modified

28 Proctor Moisture-Density Standard Three layers 12 inch drop 4.5 lb. Rammer 12,400 ft-lb/ft 3 600kN-m/m 3 Modified Five layers 18 inch drop 10 lb. Rammer 56,000 ft-lb/ft kN-m/m 3 55 Proctor Moisture-Density Using specific amount of compaction effort, density and moisture content varies. Test used to determine optimum moisture content to get maximum soil density for a level of compaction energy. Standard Proctor is minimum acceptable. Modified is preferred 56 28

29 Proctor Moisture-Density 57 Proctor Moisture-Density 58 29

30 Proctor Moisture-Density Dry Density (kgs/m3) Gravimetric Moisture Content(%) GranularBase Sand Clay Till Silt Clay 59 California Bearing Ratio (CBR) Developed in late 1920 s. Used by highway departments for evaluation of all road soils and granular. Bearing ratio of soils determines amount of load that soil can carry. Saskatchewan Highways uses bearing ratio for pavement design. Higher soil bearing ratio = thinner pavement, base, or sub-base layers = less $$$

31 California Bearing Ratio (CBR) Soaked Swell Test Soil sample prepared according to Proctor compaction procedure. Sample is soaked for 4 days. Swelling during soaking is measured. 61 California Bearing Ratio (CBR) Soaked Swell Test 62 31

California Bearing Ratio (CBR) Soaked Strength Test Determined by pushing a cylindrical

5mm intervals up to a penetration depth of 12.5mm. Measures the relative shearing resistance of soil.

32 California Bearing Ratio (CBR) Soaked Strength Test Determined by pushing a cylindrical piston with an area of 1935 mm 2 into a prepared soil sample at a standard rate of f mm/min to 2.0 mm/min. Applied pressure required to maintain the penetration rate is recorded at 2.5mm intervals up to a penetration depth of 12.5mm. Measures the relative shearing resistance of soil. Does not directly relate to field loading conditions, but it does provide a repeatable relative measure of soil strength. 63 California Bearing Ratio (CBR) Soaked Strength Test 64 32

6 mm Surcharge 200 mm 15 mm 1 Compacted Soaked

(mm) (MPa) 2.5 6.9 5.0 10.4 7.6 13.1 10.2 15.

33 California Bearing Ratio (CBR) Soaked Strength Test 65 California Bearing Ratio (CBR) Soaked Strength Test P 49.6 mm Surcharge 200 mm 15 mm 1 Compacted Soaked Sample Crushed Rock CBR Penetration Pressure (mm) (MPa) mm dia

34 California Bearing Ratio (CBR) Soaked Strength Test CBR is calculated as ratio of pressure at a given penetration increment during the soil test to that of a standard high-quality crushed rock. CBR F F 2.5mm to12.5mm penetration Crushed 2.5mm to12.5mm penetration 67 SDHT GI-CBR Correlation y = -3E-05x x x x x R 2 = CBR Group Index 68 34

35 SMHI Pavement Structural Design Conventional Flexible Pavement Structural Design 69 Substructure Moisture 20 yrs+field Measurements WB EB Chainage (km) Dielectric Permittivity SB NB Chainage (km) Dielectric Permittivity 70 35

Moisture Induced Sub-Structural Failure Asphalt

Join in the spirit and camaraderie of making

There are many ways and places to make a living.

36 Moisture Induced Sub-Structural Failure Asphalt Concrete Pavement Failures and Distresses 71 Discussion Don t hold back. You have a great deal to contribute. Join in the spirit and camaraderie of making something exciting ii happen. There are many ways and places to make a living. We must do that, but each of us also desires to accomplish something more exhilarating and create lasting value through our efforts

SOIL MECHANICS Assignment #2: Soil Classification Solution.

SOIL MECHANICS Assignment #2: Soil Classification Solution. Geotechnical Engineering Research Laboratory One University Avenue Lowell, Massachusetts 01854 Edward L. Hajduk, D.Eng, PE Lecturer PA105D Tel: (978) 934 2621 Fax: (978) 934 3052 e mail: Edward_Hajduk@uml.edu