Best Practices for Building High-Performance Resource Roads. Road Drainage. Developed by: The Roads and Infrastructure Group

Transcription

1 Best Practices for Building High-Performance Resource Roads Road Drainage Developed by: The Roads and Infrastructure Group

2 THIS GUIDE IS INTENDED FOR EQUIPMENT OPERATORS CONSTRUCTION CONTRACTORS FIELD SUPERVISORS Developed by: The Roads and Infrastructure Group Introduction 2

3 The goal is to teach you the benefits of building resource roads with effective drainage which can prolong road life and reduce maintenance costs. You will learn about the available drainage options, where each one is most applicable, and the criteria for using that form of drainage succesfully. Developed by: The Roads and Infrastructure Group Introduction 3

4 PROBLEM STATEMENT Water is the enemy of any road structure. The accumulation of water on the road s surface or inside its structure can lead to: - pothole development; - erosion of fine-grained materials into streams; - loss of fine particles from the surface; - slippery conditions during wet weather; - reduced load-bearing capacity. Developed by: The Roads and Infrastructure Group Introduction 4

5 SOLUTION Effective drainage The most important element to ensure good road performance is drainage. - provides a long-lasting road - reduces road failures and surface damage; - reduces maintenance costs; - increases transportation efficiency; - reduces erosion problems and prevents the transport of sediment into streams. Developed by: The Roads and Infrastructure Group Introduction 5

6 We will focus on when to use and how to build: - crowns and cross-slopes - ditches; - off-takes; - cross-drainage; - other drainage systems. Developed by: The Roads and Infrastructure Group Introduction 6

7 CROWNS AND CROSS-SLOPES On a flat surface, water will not go anywhere. The purpose of a crown is to provide enough of a slope that water will drain off the road surface. Crowns are used in most cases, whereas crossslopes are used on steep slopes, cut-slopes and in curves. Developed by: The Roads and Infrastructure Group Crowns and Cross-Slopes 7

8 AMOUNT OF CROWNING Slope = Drop / Distance x 100 = % 4cm / 100cm x 100 = 4% The amount of crowning that is necessary depends on the nature of the road. We recommend a minimum crown of 4% for unpaved roads. This means a drop of 4cm for 1m of distance from the centre of the road. Developed by: The Roads and Infrastructure Group Crowns and Cross-Slopes 8

9 TABLE FOR CALCULATING A CROWN for a 4% crown Drop from centerline to the edge of the road (to the shoulder) (cm) Road width (m) Developed by: The Roads and Infrastructure Group Crowns and Cross-Slopes 9

10 INSUFFICIENT CROWNING Slope = 3cm / 100 cm x 100 = 3% A 2% or 3% crown is not enough to drain water from the road surface, especially on wide roads. 2% is sufficient for paved roads but not for gravel roads. Developed by: The Roads and Infrastructure Group Crowns and Cross-Slopes 10

11 Potholes Ruts caused by water infiltration that weakens the surface. Wet conditions that reduce traction during heavy rain. Insufficient crowning allows water to accumulate on the surface, causing surface damage. Each of these kinds of damage can reduce driver safety. Developed by: The Roads and Infrastructure Group Crowns and Cross-Slopes 11

12 TOO MUCH CROWNING A crown more than 6% is too high If crown is too high (e.g., more than 6%): 1. Increase erosion of fine particles into ditches. This reduces cohesion of the surface material, loosening surface materials, and increasing rutting. 2. Force drivers to travel at the center of the road. Developed by: The Roads and Infrastructure Group Crowns and Cross-Slopes 12

13 Gradually eliminate the crown as you approach road intersections and railway crossings, where the meeting of the crowns would create a bump and a safety concern. Developed by: The Roads and Infrastructure Group Crowns and Cross-Slopes 13

14 CUT-BANK IN-SLOPED ROADS An in-sloped road drains water from the entire road toward the cut-bank. This technique can be used on steep slopes to avoid road erosion on the downslope side. Provides a safer surface that reduces the risk of sliding off the road under wet or icy driving conditions. Developed by: The Roads and Infrastructure Group Crowns and Cross-Slopes 14

15 FILL SLOPE OUT-SLOPED ROADS Drains water from the entire road towards the fill slope. This technique can be used to avoid the accumulation of water in a ditch. Outward slopes are also useful where side slopes are gentle and building a ditch on the cut-slope side would be difficult or expensive. Developed by: The Roads and Infrastructure Group Crowns and Cross-Slopes 15

16 A SINGLE CROSS-SLOPE This design is easier for graders to maintain. On narrow single-lane roads of 5 to 6m wide, a single 4% cross-slope can be used instead of a crown. Developed by: The Roads and Infrastructure Group Crowns and Cross-Slopes 16

17 SUPER ELEVATIONS Recommended slope is 6% but may vary depending on design speed and curve radii. When you approach a curve, you should gradually transform the crown into a superelevation, in which the curve s outside edge is higher than the inside edge. Developed by: The Roads and Infrastructure Group Crowns and Cross-Slopes 17

18 NORMAL CROWN TRANSITIONS SUPER ELEVATIONS SUPER ELEVATIONS Curves should be banked to help moving vehicles remain on the road. The super-elevation increases vehicle stability and safety while also providing efficient drainage. Developed by: The Roads and Infrastructure Group Crowns and Cross-Slopes 18

19 SUBGRADE BASE LAYERS SURFACE Start building the crown early. CONSTRUCTION TIPS This ensures ongoing drainage even if the subgrade is not graveled immediately after construction. This is recommended for secondary and tertiary roads to allow drying of the subgrade (clays and silts). It reduces the volume of aggregate required at the center of the road during graveling, which reduces gravel transportation costs. Developed by: The Roads and Infrastructure Group Crowns and Cross-Slopes 19

20 An inexpensive slope meter can be installed in a grader or bulldozer to help achieve the desired slope. Alternatively using a straight board with a level and measuring tape can also work. Developed by: The Roads and Infrastructure Group Crowns and Cross-Slopes 20

21 DITCHES The purpose of a ditch is to collect water and move it away from the road. Developed by: The Roads and Infrastructure Group Ditches 21

22 An effective ditch should direct water into the forest around the road at frequent intervals rather than transporting the water over long distances. Developed by: The Roads and Infrastructure Group Ditches 22

23 Poor ditching Good ditching Once water drains from the surface of the road, it must be moved away from the road so that it does not enter the road structure. Developed by: The Roads and Infrastructure Group Ditches 23

24 BACK SLOPE SIDE SLOPE DITCH PARTS OF A DITCH Ditches have 3 key components. The slope of the ditch (bottom of the ditch) should follow the same slope as the road and natural terrain and drainage patterns. Developed by: The Roads and Infrastructure Group Ditches 24

25 Rock Sand Gravel Clay and silts Side slope 1:1 Back slope 1:4 to 1:1 Side slope 3:1 Back slope 3:1 Side slope 1.5:1 Back slope 2:1 Side slope 2:1 to 3:1 Back slope 2:1 to 5:1 DITCH DESIGN Design the ditch s side slope and back slope to minimize the soil s susceptibility to erosion. Developed by: The Roads and Infrastructure Group Ditches 25

26 ABOUT 0.5M WIDE Where prolonged, heavy rain is rare, a v-shaped ditch is effective. Flat-bottom ditches offer a lower flow velocity and can handle larger volumes of water Developed by: The Roads and Infrastructure Group Ditches 26

27 U-SHAPED DITCHES Avoid U-shaped ditches Their steep sides make them difficult to maintain, and the sides are likely to cave in, leading to blockage of the flowing water, erosion, and sediment transport. Instead, a V-shaped ditch with a rounded bottom will help to slow and disperse water. Developed by: The Roads and Infrastructure Group Ditches 27

28 Ditches can get obstructed by debris and vegetation. Ditches can be mechanically cleared with a grader or excavator. Maintain the ditch whenever necessary to ensure that water continues to flow smoothly. Developed by: The Roads and Infrastructure Group Ditches 28

29 CHECK STRUCTURES See FPInnovations Advantage report Vol. 9 no. 5 for more design information Ditch check structures are used to slow the flow within a ditch, promote deposition of suspended soil particles, and reduce erosion within the ditch. - they can be built from aggregate (or rocks), geotextile, logging debris or commercial products. - spacing is determined by the gradient of the ditch and the height of the structure. Developed by: The Roads and Infrastructure Group Ditches 29

30 DITCH ARMORING Reinforced matting, aggregate, and mulch or straw can be used as armor. Armoring ditches protects the soil against erosion and deepening of the ditch ("downcutting"). Developed by: The Roads and Infrastructure Group Ditches 30

31 Excavator preparing brushmat from branches, stumps and tree tops left on right-of-way after harvesting F ill Brushmat No defined ditch Bulldozer spreading imported fill and shaping the road NO DITCHES REQUIRED This technique is often used on soft soils where the organic layer must be kept undisturbed. Roads built on a brushmat or corduroy road covered with gravel may not require ditches because the road is elevated and drains more easily. Developed by: The Roads and Infrastructure Group Ditches 31

32 STREAM OFF-TAKE OFF-TAKES: DITCH TURNOUTS An off-take is an extension of a ditch that channels water away from the road and disperses it onto the forest floor, where it is absorbed by the soil. DITCH Developed by: The Roads and Infrastructure Group Off-Takes 32

33 Build off-take ditches, also known as ditch turnouts, outside the streamside buffer zone to carry suspended sediment away from the stream. Locate off-takes in places where the outlet will empty into a catchment area. If you can t direct an off-take into the forest, use other techniques such as the construction of a sediment pond (settling basin) or create cross-drainage using culverts. Developed by: The Roads and Infrastructure Group Off-Takes 33

34 Off-take Stream Off-take INSTALLATION The terrain characteristics often determine the location of off-takes. Off-takes must be frequent enough to ensure that water has no chance to accumulate and overflow the ditches. On steep slopes, you may require more than one off-take every 100m. Developed by: The Roads and Infrastructure Group Off-Takes 34

35 lead off-takes away from the road The ditch turnout depth should be equivalent to or slightly deeper than the ditch, to eliminate barriers to the water s flow Build off-takes at an angle of 45" to 70 to the road Extend off-takes 20 to 50m, far enough to fully dissipate the water Developed by: The Roads and Infrastructure Group Off-Takes 35

36 CROSS-DRAINAGE: CULVERTS Cross-drainage controls water volume and speed. Where water cannot be easily dispersed on one side of the road, cross-drainage can transfer water to the opposite side of a road and reduce the accumulation of standing water. Install cross-drainage to transfer water from the high side of the road to the low side, so that water will be able to follow its natural flow path. Developed by: The Roads and Infrastructure Group Cross-Drainage 36

37 Select the culvert size based on the size of the road and the anticipated maximum flow. The diameter should be at least 30cm. The culvert must be long enough to reach natural ground at the outlet. Culverts with outlets positioned on the fill slope require armoring beneath the outlet to prevent erosion (scouring) of the fill material. Developed by: The Roads and Infrastructure Group Cross-Drainage 37

38 INSTALLATION Cross-drainage controls water volume and speed. Install culverts at an angle of 30" to 45" to the road, with the entry point farther uphill than the exit point to improve the flow of water into the culvert. Developed by: The Roads and Infrastructure Group Cross-Drainage 38

39 Firmly compact the fill around the culvert, particularly under the haunches. Minimum thickness of 30cm. Install the culvert on a well-compacted surface to prevent future settling. Cover the culvert with fill at least 1/3 the pipe s diameter in thickness, to prevent vehicles from damaging the culvert. Developed by: The Roads and Infrastructure Group Cross-Drainage 39

40 SPACING BETWEEN CULVERTS Define the spacing between culverts based on the road s slope and the soil type. Maximum distance between culverts (m) Slope (%) Low erosion risk* Significant erosion risk** *Coarse rocky soils, gravels, and some clays **Fine, friable soils, silts and some clays, fine sands Developed by: The Roads and Infrastructure Group Cross-Drainage 40

41 OTHER DRAINAGE ALTERNATIVES: - Broad-based dips - Open-top surface designs - Above-ground deflectors Developed by: The Roads and Infrastructure Group Other Drainage Alternatives 41

42 BROAD-BASED DIPS This low point must lie outside the stream s buffer zone. Broad-based dips (also called «rolling dips») are designed to remove water from the road surface. Construct the dip deep enough to provide adequate drainage. Design the dip so that it is sufficiently long and gradual that it will not affect vehicle traffic. Developed by: The Roads and Infrastructure Group Other Drainage Alternatives 42

43 Open-top surface drains are drainage structures that are placed to collect and direct surface flows off the road. These drains can be built from metal, lumber, small logs or any other material that can be laid side by side to support traffic while allowing drainage. Developed by: The Roads and Infrastructure Group Other Drainage Alternatives 43

44 ABOVE-GROUND DEFLECTORS Place above-ground deflectors across the road to direct the surface flow to the side. On long slopes, where water may flow downhill along the surface of the road, it is important to direct the flowing water to the sides of the road. Deflectors can be made from any durable material that does not create a large bump in the road. Recycled rubber conveyor belts are often used. Developed by: The Roads and Infrastructure Group Other Drainage Alternatives 44

45 SUMMARY The optimal combination depends on the location of the road, the soil material, and the amount of water that must be managed. An effective drainage system lets water follow its natural course. Accomplishing this requires a combination of the following techniques: - proper design of crowning, cross-slopes, and super-elevations; - efficient ditches with adequate capacity; - effective cross-drainage and off-take systems; - the use of drainage options such as broad-based dips, open-top surface drains, and deflectors. Developed by: The Roads and Infrastructure Group Conclusion 45

46 CONCLUSION Proper construction and design techniques will provide effective drainage, offering the following advantages: - increased road performance; - reduced erosion and sediment transport into streams; - increased safety; - increased transportation efficiency; - reduced maintenance costs. Developed by: The Roads and Infrastructure Group Conclusion 46

47 SUGGESTED READINGS Gillies, C Erosion and sediment control practices for forest roads and stream crossings. FPInnovations, Advantage Vol.9, no p. Keller, G.; Sherar, J Low-volume roads engineering Best Management Practices Guide. U.S. Agency for International Development (USAID) 158 p. Skorseth, K.; Selim, A. A Gravel roads maintenance and design manual. U.S. Department of Transportation, Federal Highway Administration. 64 p. Developed by: The Roads and Infrastructure Group 47

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