SPWA Fall Rural Roads Workshop

Transcription

1 SPWA Fall Rural Roads Workshop Gravel Roads Material Analysis, Surfacing and Maintenance Manoj Jogi Saskatchewan Ministry of Highways & Infrastructure Saskatoon October 19, 2017

2 Basic Objectives of a Road 1. Support traffic loads 2. Protect roadbed from water infiltration 3. Minimize loss of surface material 4. Provide reasonable surface texture 5. Provide resistance to weathering

3 Typical gravel road section Credit: FHWA

4 1. Drainage from the road surface 2. Allow water to leave the road as a shallow, non erosive sheet Crown ½ inch per foot or 4% crown recommended AASHTO recommends ½-1 inch foot crown Credit: Penn State University Center for Dirt and Gravel Roads Studies

5 Crown Credit: Penn State University Center for Dirt and Gravel Roads Studies

6 Maintaining Crown Credit: Penn State University Center for Dirt and Gravel Roads Studies

7 Sections without crown Credit: FHWA

8 Parabolic crown Less crown in the middle No room for drainage Credit: FHWA

9 Blade wear at center Modify usage to reduce wear Parabolic crown Credit: FHWA

10 Placement for Surface Aggregates Address all surface drainage issues before placement Road instability issues must be addressed before placement Flat A crown profile, shape the subgrade Credit: Penn State University Center for Dirt and Gravel Roads Studies

11 Crown gauge Credit: FHWA Credit: Skorseth, 2015

12 Good vs Poor Construction Credit: Maine Dept. of environmental Protection

13 Aggregates / Soil Testing 1. Sieve Analysis Test Categorize coarse-grained soils in terms of particle size distribution. 2. Atterberg Limit Test Categorize fine-grained soils in terms of the material s consistency (plasticity index). 3. Percent fracture To determine percent fracture faces in coarse portion of the material Organic soils are generally not tested unless they pose a risk to the failure on a project.

14 Sieve Analysis Test Credit: Klimochko

15 Sieve Analysis Test Procedure for describing a coarse-grained soil in terms of particle size (gradation). Percent Passing Agg A Agg B Agg C Agg D 100% 92% 70% 40% 97% 82% 60% 0% 40% 52% 55% 8% 26% 48% 4% 12% 25% 1% 7% 7%

16 Importance of Sieve Analysis Sieve analysis test results on a coarsegrained soil indicates the following: How clean or dirty the aggregate is. How well the aggregate can compact How will be the aggregate matrix in place How suitable the aggregate is. Confirm if aggregate is in spec?

17 Atterberg Limit Test

18 Atterberg Limit Test Used for identifying soil s water content causing the material to pass from one condition state to another. From liquid to plastic = Liquid Limit (w L ) From plastic to plastic solid = Plastic Limit (w P ) Plastic Index (PI) = Liquid Limit (w L ) Plastic Limit (w P )

19 Atterberg Limit Test Apparatus

20 Liquid Limit Test Apparatus Liquid Limit = soil moisture at which the bottom of the groove in soil sample closes approx. 12 mm after 25 rotations of crank.

21 Plastic Limit Test Apparatus In field roll the soil with water to thickness of a matchstick tip till it starts crumbling Plastic Limit = soil moisture at which the threads of soil sample start to break up when 3 mm in diameter.

22 Importance of Plastic Limit Value Plastic Limit (w P ) value identifies the approx. optimum water content of a soil at which it should be compacted. Soil goes into a plastic state deforms without rebound

23 Importance of Plasticity Index Value Plasticity Index (PI) value indicates the relative compressibility of a soil. The higher a number, the more compressible the soil. How well the soil can pack depends upon plasticity index Good indication of binding characteristics

24 Dry Density - kg/m3 Determining Optimum Moisture Standard Proctor Test Optimum Moisture = 6.7 % Proctor Dry Density = 2234 kg/m % Percent Moisture 4 Klimochko, 2008

25 Compaction vs. Optimum Moisture Wet of optimum moisture - dried to optimum by blading or disking before compacting. Dry of optimum moisture - it should be sprayed with water to get the soil to optimum before compacting.

26 Optimum Moisture vs. Soil Type Optimum moisture contents for various soil types are as follows: Granular Base Course: 6 % Sandy Glacial Till: 13% 3 Silty Glacial Till: 15 % Clayey Glacial Till: 17% Highly Plastic Clay: 30 % Low Plastic Clay

27 Soil Compaction Proper compaction equipment is essential. Uniform water application is essential. Work zones should be kept short ( 500 m) to help ensure uniform moisture application during compaction. If sections are too long, compacting soil at optimum moisture content becomes more difficult to achieve.

28 Soil Compaction Use sufficient amount of water. Use sufficient number of passes. Use proper equipment. Self propelled Pneumatic or steel wheel No steel rollers on steep grade

29 Soil Compaction Check densities (Quality Control) Check with Probe

30 Gradation Types Open graded has only a small percentage of aggregate particles in the small particle size range. This results in more air voids. Gap-graded - contains coarse and fine-graded soil particles but no intermediate sizes. Well/Dense graded has a uniform distribution of all particles sizes.

31 Gradation Open graded Gap graded Dense graded

32 Surface gravel Stone + Sand + Fines (dust) Good gradation is a good blend of stones, sand and fines.

33 Properties for surface gravel Fracture Percent Very important property Crushing is needed for this Better embedment than rounded aggregates Resistance to movement under traffic better than rounded aggregates

34 Surface gravel Ideally some amount of crushed stones (fractured faces) More gravel than sand (excess sand = no stability) Blending different sizes allows the pieces to lock together to form a strong tight surface Good gravel road can not be made with bad gravel Credit: USDA Forest Service No fines Excess fines Right amount of fines

35 MHI Traffic Gravel Specifications Sieve Designation Percent by Weight Passing Canadian Metric Sieve Series Type mm mm mm mm mm mm mm mm µm Fractured 50.0 Minimum Face %

36 MHI Base Course Specifications Base Course Type Jan 1996 Sieve Designation Percent Passing (by weight) 50 mm 31.5 mm mm 22.4 mm 18 mm mm 12.5 mm mm 5 mm mm µm µm µm µm Plastic Index Fracture, Min (50/75 Blow) % Min 50 Lightweight pieces % Max 5

37 Properties for surface gravel AASHTO Minimum 8% passing 71µm sieve and PI 4 9 Maximum liquid limit 35 Soil aggregate surface course Sieve C D E Designation 75.0mm mm mm mm mm mm µm µm

38 Recycled asphalt (RAP) Can be used but few issues In hot weather it behaves as a weak pavement Hard to maintain and can develop potholes Good idea to blend 50/50 with virgin gravel Good binding and workability with 50/50 blend Credit: Granite Construction Company

39 Properties for surface gravel Top size inch Typical Ministry gravel is 22.5 mm (7/8 inch) top size Desirable 8 to 15 % passing 71µm sieve (dust) some amount of clay for binding Plasticity, PI 4-9 range Good abrasion resistance Wet conditions -- Less PI and fines Dry conditions -- Can have PI and fines on higher side of the range

40 Surface Gravel Can be placed at in an 8 depth and compacted to 6, or in a 6 depth and compacted to 4½ Higher top size (Coarse)for wet area Lower top size (Finer) for dry area Pneumatic rollers, Wobbly or 10 tonne steel roller can be used. Pneumatic / rubber rollers work on most gravel surfaces and they do not crush the rock.

41 Aggregate Sampling Make sure the sample obtained is: Representative (quartering) Not segregated by sampling Properly identified (label) Poor sampling makes test results misleading and worthless. Credit: Skorseth, 2015

42 Jar Test Surface aggregate 8 15% fines (dust) Base aggregate (0-7% fines) More stones than sand desirable

43 Gradation for surface gravel Poor surface aggregate Credit: FHWA

44 Gradation for surface gravel Good blend for surface gravel Fine material Coarse material Credit: Klimochko, 2008

45 Gradation for surface gravel Mixing clay with aggregates Credit: Skorseth, 2015 Credit: Klimochko, 2008

46 Gradation for surface gravel Good gradation Gradation makes a difference Poor gradation Credit: FHWA

47 Culverts Culverts are critical for natural flow of water Plugged or collapsed culverts can cause serious damage Installation at correct location and elevationsurvey Reasonable maintenance and cleaning for proper functioning Install culverts as close as possible to the natural stream bed

48 Culverts Install culverts at natural stream grade X X Do not change stream bottom elevation Credit: USDA Forest Service

49 Culverts Install culverts at natural stream grade Right Do not change stream bottom elevation Credit: USDA Forest Service

50 Culverts Culverts are critical for natural flow of water Credit: USDA Forest Service

51 Riprap Culverts Riprap at inlet Credit: USDA Forest Service Riprap at outlet

52 Culverts Piping due to poor installation or lack of riprap Credit: USDA Forest Service

53 Dust Control All gravel roads will give a certain amount of dust under traffic Volume of dust depends upon Type of gravel Volume and type of traffic Precipitation Limestone based gravel tend to dust more Glacial deposits with a portion of clay tend to resist the dusting

54 Dust Reduction Through gravel specifications A good gradation is important Good amount of fines (8-15%) Right plasticity (4-9) Chloride dust treatment is not effective with poor gradation Credit: FHWA

55 Dust Reduction Prevent loose fines generation Good crown Shoulder drainage Strategies for less maintenance Loosen surface aggregate to sufficient depth during grading Always ensure optimum moisture during maintenance operations

56 Wash boarding

57 Wash boarding Poor quality gravel low fracture percent, low fines and plasticity Harsh breaking or acceleration Lack of moisture Motor grader too fast

58 Frost Heave Frost heave upward movement of subgrade due to expansion of accumulated moisture as it freezes Thaw weakening weakening of subgrade when moisture melts Three conditions Frost susceptible soils - silt Water Temperature- freezing

59 Frost Heave Water in void space freezes along plane of freezing Water in void space freezes along plane of freezing Water in void space freezes along plane of freezing Credit: Washington DoT

60 Frost Heave Treatment Providing adequate drainage / Drainage improvement Excavation of subgrade below frost depth Replacement of frost susceptible material Daylight Replace with 300 or more mm base course or pit run Geotextile filter cloth Insulation can also be provided The use of granular, non-frost susceptible fill can also help to alleviate frost heave and subgrade softening problems

61 Frost Heave Treatment Failure Daylight at Sideslope Excavate Failure To Sideslope (Daylight) and Backfill with Granular Note: Bottom of Excavation sloped down towards ditch. Schematic showing typical deep patch used to repair small isolated areas experiencing various kinds of distress due wet base/subgrade.

62 Frost Heave Treatment / Deep Patch

63 References FHWA, Gravel Roads Construction & Maintenance guide, August 2015 FHWA, Gravel Roads Maintenance & Design Manual, SD-LTAP November 2000 Gravel Roads, Back to Basics. Montana State University, LTAP 2000 Klimochko D, 2007 ATPC Presentation Gordon Keller & James Sherar Low Volume Roads Engineering, USDA Forest Service/USAID Main Department of Environmental Protection, Gravel Road Maintenance Manual, 2010 Penn State University, Center for Dirt and Gravel Road Studies Skorseth K., 2015, SD-LTAP. Managing Gravel Road Maintenance, 2015 NACE Conference, FL Joe Mahoney, 1985 Washington DoT, Research Summary Report- Evaluation of Frost Related Effects on Pavements

64 Questions / Comments Manoj.Jogi@gov.sk.ca