trails manual section3

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Hard Surface Multiple Use Trails

Concrete Trail Specifications

Objectives for Concrete Trail Surfaces

A properly constructed concrete trail on a good subgrade will last for 30 to 50 years or more. Modernconcrete handling techniques can be used to form a continuous smooth and skid resistant surface. The useof saw cut joints and careful handling of construction and expansion joints eliminates the feel of joints andmakes the trail safer and easier to use for baby carriages, inline skaters, wheelchair users, and bicyclists.

Trails are to be constructed to the widths specified elsewhere in this Handbook, including changes of width athazard zones and other points. The standard thickness is 6 with saw cut joints every 10. Pitch andsuperelevation must also be built into the trail. The concrete can be poured directly on a compactedsubgrade unless subgrade soils are poor. Plain Portland cement concrete without tinting can be used formost trails. Use of joint sealer is suggested in order to reduce subgrade moisture and to reduce the smallbump at expansion and construction joints.

Concrete work is best done early in the summer so that the concrete is as strong as possible before its firstwinter. The first month should have many daytime hours of 55 or higher temperatures.

Initial Grade Preparation

See Hard Surface Path Cross Sections, p. 2-30.

Subgrade Preparation

Necessary preparation of the subgrade depends on soil type:

Excellent subgrade soils unaffected by moisture or frost include well-graded clean sharp sands andgravels.

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Good subgrade soils retain a substantial amount of load supporting capacity when wet. Theyinclude clean sands and sand gravels and soils free of detrimental amounts of plastic materials suchas bentonite and gilsonite.

Medium subgrade soils (loams, silt sands, and sand-gravels containing moderate amounts of clayand fine silts) retain a moderate degree of firmness under adverse moisture conditions.

Poor subgrade soils (those having appreciable amounts of clay and fine silt which become soft andplastic when wet, and coarser silts and sandy loam) are susceptible to frost.

On excellent to good subgrade soils, the concrete can be poured on a subgrade of the native soil compactedto 95%. On medium subgrade soils, a compacted porous base course of suitable materials (river run or pitrun gravels, etc.) should be used if the material is available on site. On poor subgrade soils, use a minimumof 12 compacted porous base.

Root barriersRoot barriers should be considered where riparian or aggressively suckering vegetation is found along thetrail. Willows, poplar, and sumac are all aggressively spreading plants. On trails where irrigated land is onone side and non-irrigated land is on the other, water-seeking vegetation on the dry side may try to sendroots to the irrigated side, consider a root barrier here. Some geotextiles can serve as weed barriers.

Specifications for Concrete WorkMaterial shall be:

Concrete 32 MPA, no wetter than 3.5 slump with 6% air and limestone. Aggregate shall be bothcoarse and fine with a maximum coarse aggregate size of 1-1/2. Any admixture except airentrainingagent must be approved by the Town, including accelerators and retarders.

Cement Cement in concrete shall conform to the Standard Specification for Portland Cement.

Aggregate Aggregate in concrete shall conform to the Standard Specification for ConcreteAggregate.

Wire reinforcement - Welded steel wire fabric shall be a minimum size of 6 x 6 inch 10/ 10 wire.

Water - Water used for mixing or curing concrete shall be clean and free from injurious amounts ofoil, acids, salt, alkali or organic substances harmful to concrete.

Equipment

Regular finishing equipment for finishing concrete pavements shall be mechanical, self-propelled spreadingand finishing machines of either the slip-form or form riding types, and shall be capable of compacting andfinishing the concrete. For small projects or projects with variable widths, a vibratory screed may be used inlieu of a finishing machine.

Forms

If side forms are used for straight sections, the forms shall be straight and of a depth equal or greater thanthe specified thickness of the pavement. All forms shall be in sections not less than 10 in length and have abase width sufficient to prevent displacement from line or grade during paving. For curved sections, flexibleor curve forms shall be used for construction of circular pavement where the radius is 200 or less.

The supply of forms shall be sufficient to permit their remaining in place for a minimum of six hours after theconcrete has been placed. Each section of form shall be straight and free from warps and bends. Themethod of connection between sections shall be such that the joint just formed is tight and free from



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The concrete shall be deposited on the subgrade to the required depth and width in successive batches andin a continuous operation. The concrete shall be placed as uniformly as possible to minimize the amount ofspreading necessary. While being placed, the concrete shall be spaded and/or vibrated with suitable tools toprevent the formation of voids or honeycomb.

Any evidence of lack of consolidation shall be regarded as sufficient reason for requiring the removal of thesection involved and its replacement with new concrete. The Contractor shall be responsible for any defectsin the quality and appearance of completed work.

Cold weather concreting

Except by specific written authorization, concrete shall not be placed unless the air temperature is 350F, andascending and placing shall cease when the descending air temperature in the shade and away from artificialheat falls below 400F.

When concreting is permitted during cold weather, the temperature of the mix shall be not less than 500F atthe time of placing. Aggregates or water shall not be heated to a temperature exceeding 1500F. The concreteimmediately after placement shall have a temperature between 500F and 800F. Materials containing frost orlumps of frozen material shall not be used.

Ice, snow and frost shall be removed from the forms and subgrade before placing concrete. In no case shall

concrete be placed against frozen ground or against ground containing frost. After placing, the temperatureof the concrete shall be maintained above 500F for at least four days, or the concrete temperature shall bemaintained above the freezing point for at least ten days by the use of not less than 1 of loose, dry straw orwith insulated curing blankets. With the use of high early strength cement, the concrete temperature shall bemaintained above 500F for two days or above freezing by the use of straw or blankets for five days. Concreteinjured by frost action shall be removed and replaced at the Contractors expense.

Consolidating and finishing

The pavement shall be finished by an approved slip-form paver or form riding finishing machine operatedover each section of pavement to produce the specified results. Excessive working of the surface will not bepermitted. A medium transverse broom texture shall be applied to provide a uniform gritty non-skid texture.

The surface shall be continuously checked for trueness with 10 straightedges. If the pavement surface isdragged with a diagonal or V-shaped float, only occasional straightedge surface checks will be required.

Before the pavement has taken its initial set, the edges of the pavement along each side shall be workedwith an approved tool and rounded to radius of 1/4. The edges along each side of an expansion orconstruction joint shall be rounded to a radius of 1/8. All tool marks left by the edging shall be eliminated,including all marks on the visible surface.

Joints shall be constructed of the type, dimensions, and at locations specified.

Contraction joints -- These shall be constructed by sawing to a minimum depth of one-fourth of thespecified pavement thickness and a maximum width of 1/8. Joints shall be sawed as soon as the sawcan be operated without damaging the concrete. Unless otherwise specified, transverse joints shall besawed at a maximum spacing of 10.

Longitudinal joints -- If the pavement exceeds 12 feet in width, a longitudinal joint shall beconstructed along the pavement centerline by sawing. Sawing shall be done to a minimum depth ofone third the specified pavement thickness and a maximum width of 1/8. Joints shall be sawed assoon as the saw can be operated without damaging the concrete.

Construction joints -- These shall be constructed at the end of each days work and whenevernecessary to suspend work for more than 30 minutes. Construction joints shall be plain butt joints.



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Expansion joints -- These should be placed:

On all sides of an intersection at a distance of about 40 from the center of the intersection. On either side of a bridge, underpass, or other fixed structure at approximately 20 and 60

from the structure. In a continuous trail, expansion joints should not be necessary except as stated above.

No trowel marks or bumps of any kind shall be left on the surface. The preformed filler shall be 3/4 in

thickness and extend the full width and depth of the concrete pavement. The top of the filler should beflush with the pavement surface. If joint sealing is specified, an opening 3/4 in width by 1 in depthshall be formed for installation of the joint sealer.

Cold joints -- Cold joints shall be pinned with 3/4 diameter 18 long smooth coated steel pins on 1foot centers 3 beneath the surface. No trowel marks or bumps of any kind shall be left on the surface.The preformed filler (with holes drilled for the pins) shall be 3/4 in thickness and extend the full widthand depth of the concrete pavement. The top of the filler should be flush with the pavement surface. If

joint sealing is specified, an opening 3/4 in width by 1 in depth shall be formed for installation of thejoint sealer.

Curing

Concrete shall be cured by protecting it against moisture loss, rapid temperature change, rain, flowing waterand mechanical injury for a period of not less than five days after placement. It shall be the Contractorsresponsibility to protect the concrete from traffic and the elements.

Any concrete showing injury or damage due to inadequate or improper curing shall be repaired or replacedby the contractor at no additional cost.

Defaced concrete

It shall be the Contractors responsibility to protect fresh concrete from damage as a result of vandalism orother cause; damaged concrete shall be removed and replaced by and at the expense of the Contractor.

Surface smoothness

Sections of pavement containing depressions that cannot be removed by grinding shall be repaired orreplaced by the contractor to the satisfaction of the Town or its representative.

Sealing joints

If joint sealing is specified, joints shall be sealed as soon after completion of the joint sawing as is feasibleand before the pavement is opened for use. Just prior to sealing, each joint shall be thoroughly cleaned of allforeign material by a jet of water or air under pressure. The joint faces shall be clean and their surfaces drywhen the seal is applied.

Backfilling

When side forms are removed, the space adjoining the concrete shall be promptly backfilled with crusherfines or soil as specified in the design, properly compacted, and brought flush with the surface of theconcrete and adjoining ground surface. The backfilled surface should be sloped as specified in Hard SurfacePath Cross Sections, p. 2-30.

Opening to traffic

Concrete trails shall not be opened to pedestrian traffic for at least 24 hours after placement. The Contractorshall maintain suitable barricades to comply with the foregoing requirements.



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Asphalt Path Specifications

Initial Grade Preparation

See Hard Surface Path Cross Sections, p. 2-30.

Subgrade Classification

Since the subgrade, base, and site conditions usually determine the success of asphalt trails, differentspecifications are to be used depending on these conditions. As subgrade and site conditions vary along thetrail, different specifications can be used. If necessary, concrete sections can be used in asphalt trails.

For the purpose of determining the appropriate specification for any given part of a trail, subgrade soils areclassified as follows:

Excellent subgrade soils unaffected by moisture or frost include well-graded clean sharp sandsand gravels free of detrimental amounts of plastic materials.

Good subgrade soils retain a substantial amount of load supporting capacity when wet. Theyinclude clean sands and sand gravels and soils free of detrimental amounts of plastic materials suchas bentonite.

Medium subgrade soils (loams, silt sands, and sand-gravels containing moderate amounts of clayand fine silts) retain a moderate degree of firmness under adverse moisture conditions.

Poor subgrade soils (those having appreciable amounts of clay and fine silt which become soft andplastic when wet, and coarser silts and sandy loam) are susceptible to frost. Soils containing bentoniteor gilsonite are poor subgrade soils.

Selecting the Appropriate Specification

Using the table on the following page, choose site, surface moisture, subsurface moisture, and subgradesoils that most closely match each part of the path. The numbers 1, 2, and 3 in the table refer tospecifications 1 through 3, respectively, which are given beginning on the next page. The table entryConcrete means that concrete should be used for at least the sections of the path with these site andsubgrade conditions. In the site condition listings, the phrase immediately on one side of trail also includesplaces where the adjacent soft surface trail is touching the outside edge of the pavement.



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Site conditions Excellent Good Medium Poor

Very dry surface conditions, minimal surface runoff, little snowaccumulation or sustained snowmelt, site slopes away from trail at10% on one side or slopes sharply away on one side. Very lowsubsurface moisture.

1 1 2 Concrete

Generally dry surface except for rain and snowmelt, site slopesaway from trail at 10% immediately on one or both sides of trail,low subsurface moisture, no irrigation.

1 2 2 Concrete

Generally dry surface except for rain and snowmelt, site slopesaway from trail at < 10% immediately on one side of trail, low tomoderate subsurface moisture, no irrigation.

2 2 3 Concrete

Regular irrigation, site slopes away from trail at 10% immediatelyon one side of trail.

2 2 3 Concrete

Regular irrigation, site slopes away from trail at


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of imperfections. Where asphalt meetsconcrete or other hard surfaces, the jointmust be smooth and even across the twosurfaces. Seams in the asphalt (such aswhen work is stopped) shall be butt seamsrather than taper seams.

Plan to seal the entire asphalt surface in

the second year. Sealing is expensive but

the lifespan of the asphalt material can beeasily doubled or even tripled by sealing itduring its second year. Early sealing greatlyhelps to keep out the moisture whichdestroys asphalt, helps prevent the surfacefrom drying out in the absence of a liveload, and prevents raveling (the loss ofindividual rocks from the surface). Use

sand slurry to form a more skid-resistantseal coat.



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4 asphaltmat

Geotextile (Mirify or

equivalent) underlaymentbetween asphalt and base

Base course to extend

18 from edge of asphalt

before tapering tosubgrade


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Cut/Fill Construction

Cut and fill construction can be used on cross slopes up to 30% in areas where all three following conditionsare met:

a. Soils are stable enough to use as fill

b. The prospects of revegetation are good

c. Vegetation disturbed by the cut and fill is easily replaced

Cut and fill sections can be alternated with full bench sections where trailside vegetation needs to bepreserved (see Full Bench Construction, following).

Cut and fill slopes should mimic natural landforms along the trail and should vary whenever it makes senseto vary (appropriateness). Where the soft surface trail is not adjacent to the hard surface, provide an 18shoulder at the outside edge of the hard surface. Where superelevation pitches the trail surface inward ormoderate runoff is expected from above, provide a side swale on the inside edge. See Superelevation, p. 2-35, and Path Drainage, p. 2-36.

Grading Specifications

Topsoil, which covers areas to be cut or filled, shall be removed and stockpiled for site restoration.

Suitable material removed from the excavations shall be used as far as practicable for embankments andbackfilling. Unsuitable material shall be excavated below grade and replaced with select material suitable forthe hard surface (see Concrete Path Specifications, p. 2-21, and Asphalt Path Specifications, p. 2-26).Excavated materials that are considered unsuitable and any surplus of excavated material not required forembankments or backfill shall be disposed of by the Contractor.

Fills and Embankments

Fills and embankments shall be constructed by depositing, placing and compacting materials of acceptablequality above the natural ground in accordance with the specifications below. Clearing, tree removal, andtopsoil removal shall be performed before any embankment is placed.

Remove and dispose of obstructions and rubbish to a minimum depth of 12 below subgradeelevation

Remove trees and stumps to a minimum depth of 8 below subgrade elevation

Remove sod to a minimum depth of 6

Site Restoration

Topsoil shall be replaced on all fill surfaces and on cut surfaces where possible. See Site Preservation,Restoration, and Revegetation, p. 2-103.



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Full Bench Construction

Full bench construction is to be used on any cross slope with one or more of the following conditions:

a. Cross slope exceeds 30%

b. Soils are not stable enough to use as fill

c. The prospects of revegetation are poor

d. Vegetation which would be disturbed by a cut and fill is difficult to replace (i.e., mature trees,fragile or unresilient vegetation)

Full bench sections can be alternated with cut and fill sections where conditions permit (see previous page).Remove and stockpile at least the top 6 of topsoil before excavating.

Where the soft surface trail is not adjacent to the hard surface, provide an 18 shoulder at the outside edge ofthe hard surface. Where superelevation pitches the trail surface inward or moderate runoff is expected fromabove, provide a side swale on the inside edge. See Superelevation, p. 2-35, and Path Drainage, p. 2-36.



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Superelevation

Curves with a radius of 300 or less will be banked, or superelevated, in high to moderate speed travel zones.

In the following table, High speed, uncongested zone refers to sections of trail which are not commonlybusy and where bicycle users are likely to be traveling fast. This zone does not include any intersections.

Moderate speed, mainline path refers to trail sections that are in somewhat busy areas. This zone alsoincludes mainline trail sections with a straightforward low-use intersection on a curve such as a low-use spurtrail which connects to a nearby open space access point - the mainline trail should be banked through theintersection.

Slow or congested zone includes all busy trail sections, marked slow zones, busy intersections, andsections with heavy pedestrian traffic.

The superelevations given in the table are to be the final pitch of the hard surface from side to side (asopposed to crowning). The table entry none means that only the minimum surface pitch for drainage is tobe used (see Path Drainage, p. 2-36) and that the direction of pitch does not have to be related to thedirection of the curve. Whenever practical, however, the surface should pitch toward the inside of the curve.

Curve Radii High speed,uncongested zone

Moderate speed,mainline path

Slow or congestedzone

>300 None None None

200-300 5/16 per ft. per ft. + None

120-200 3/8 per ft. 5/16 per ft. None

60-120 7/16 per ft. 3/8 per ft. None


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Example of geotextile encircling drainage rock to maintain dry trail surface.

Example of sheet drainage under trail surface



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Geosynthetics are designed for many trail construction applications.

For more information on Geosynthetic products contact the Specifiers Guide for Geosynthetic Materialpublished by Geosyntheics Magazine from Industrial Fabric Association International Resource Center, 1801County Road B.W. Roseville MN 55133-4061 (800)-225-4324 or Terrafix, Canadas Leader in Geosynthetics(416) 674-0363 www.terrafixgeo.com 178 Bethridge Rd., Toronto, Ontario, M9W 1N3

Culvert headwalls

Headwalls and tailwalls for culverts should consist of small stone walls of carefully fitted native stone. Asaesthetic elements along the trail that help set the solid character of the trail, they must be carefully crafted,preferably by skilled stoneworkers. These walls can either be dry laid, mortared from behind such that theylook dry laid, or mortared with deeply raked joints.

http://www.terrafixgeo.com/http://www.terrafixgeo.com/


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