CO_FTNP_FLFO_900(1)_Pavements_Report_Signed.pdf

FLORISSANT FOSSIL BEDS NATIONAL MONUMENT

VISITOR CENTER PARKING LOTS & ROAD

TELLER COUNTY, COLORADO

CO FTNP FLFO 900(1)

PAVEMENT AND MATERIALS REPORT

AUGUST 2017

Report prepared by:

U.S. Department of Transportation Federal Highway Administration

Central Federal Lands Highway Division Lakewood, Colorado http://www.google.com/imgres?sa=X&biw=1280&bih=819&tbm=isch&tbnid=gtpyJEKxSQX6SM:&imgrefurl=http://portal.hud.gov/hudportal/HUD?src=/press/press_releases_media_advisories/2010/HUDNo.10-242&docid=0hzyuk4oobnONM&imgurl=http://portal.hud.gov/hudportal/images/hudimg?id=dot_logo_41193.jpg&w=520&h=528&ei=uGw7Uoy6Ksjk4AOC_IDQBw&zoom=1&iact=hc&vpx=567&vpy=131&dur=635&hovh=226&hovw=223&tx=151&ty=150&page=1&tbnh=154&tbnw=162&start=0&ndsp=30&ved=1t:429,r:26,s:0,i:171

CO FTNP FLFO 900(1) Florissant Fossil Beds Parking Lots & Road ii

Written by: ________________________________________________________ Robert Norick, Staff Pavements & Materials Engineer

Reviewed by: ________________________________________________________ Mike Voth, Pavements & Materials Team Lead

Approved for distribution by:

Mike Voth, Pavements & Materials Team Lead Date

Electronic Distribution:

Construction Project Development Project Management Technical Services iii

TABLE OF CONTENTS

I. INTRODUCTION

II. CLIMATE

III. GEOLOGY

IV. EXPLORATION

V. EXISTING PAVEMENT & SOILS

VI. PAVEMENT DESIGN INPUTS

VII. PAVEMENT RECOMMENDATIONS & DISCUSSION

VIII. MATERIALS RECOMMENDATIONS

APPENDICES

A – Location, Site, & Soils Maps B – Boring Log, DCP Data, and Lab Report C – Site Investigation Photos D – Pavement Design Calculations E – LTPPBind & Climate Data F – Pipe Selection Criteria

I. INTRODUCTION

This report is written to document the existing road conditions and provide pavement recommendations for the planned CO FTNP FLFO 900(1) project for the parking lots and road at the Florissant Fossil Beds National Monument in Teller County, Colorado. The monument is located two miles south of the town of Florissant along Teller County Road 1. The Town of Florissant is located 35 miles west of Colorado Springs along US Highway 24. Location and site maps are provided in Appendix A. The project consists of the following three improvements:

• Reconstruct and reconfigure the existing road and parking lot (60 parking spaces) to improve safety and pedestrian and vehicle traffic flow, including sidewalks and RV/bus parking and unloading areas. The entrance road width will remain 22 feet wide with two 10 foot lanes and 1 foot shoulders and a 20 mph posted speed limit.

• Pave existing gravel administrative parking lot including minor regrading to promote drainage and provide an accessible route to interpretive and picnic areas.

• Construct a formal paved parking lot with 60 additional parking spaces at the location of the existing informal gravel/grass peak season overflow parking lot.

II. CLIMATE

Climate data was obtained from Western Regional Climate Center data for the Florissant Fossil Beds weather station. The data is summarized in Table 1 below and provided in Appendix E. The average annual precipitation for this area is approximately 14.65 inches.

The project ranges in elevation from ≈8,360 feet to ≈8,385 feet. The project is located at an elevation that receives both snow and rain, depending upon the time of year. The Florissant Fossil Beds receive approximately 56 inches of snow annually.

Table 1. Weather Data

Month Average

HIGH

Record

HIGH

Average

LOW

Record

LOW

Average

PRECIP.

January 39.1 61 4.6 -28 0.39”

February 40.6 62 6.3 -34 0.33”

March 47.9 70 15.0 -29 0.94”

April 55.0 79 22.0 -12 1.14”

May 64.5 86 29.2 9 1.26”

June 74.2 90 36.3 22 1.45”

July 78.4 92 41.5 28 3.08”

August 75.2 89 40.8 27 3.13”

September 69.6 87 32.9 12 1.36”

October 59.4 76 22.6 -13 0.76” November 46.5 68 13.1 -21 0.47” December 38.2 60 4.3 -30 0.34”

Temperatures are in °F and precipitations are in inches.

III. GEOLOGY

Based upon the USGS-NPS Vegetation Mapping Survey for the monument, the monument’s access road through the valley is underlain by Fourmile-Lymanson-Vabem complex soils; decomposed granite and alluvial deposits up to 5 foot depth (see Appendix A). Clay soils are derived from the various deposits. In the area of the administrative parking lot (base of mountainside), hard granite can be expected at depths of 3.5 feet (Guffrey-Raleigh association). The valley’s deposits (5 foot depth) lie on top of the Florrissant Formation and Fossil Beds (34 million years old and 150 foot deep) which lie on top of Pikes Peak granite (1 billion years old). The Florrissant Formation and Fossil Beds are the result of the area’s volcanic activity: Grizzly Peak, Mount Aetna, and Bonanza calderas, as well as, Guffrey and Thirtynine Mile volcanic fields. There are six described units within the Florissant Formation: lower shale unit, lower mudstone unit, middle shale unit, caprock conglomerate unit, upper shale unit, and upper pumice conglomerate unit. During the various volcanic events, the valley was dammed by volcanic debris flows creating a lake with lake deposits (shale). The mudstone was created by stream deposits, while conglomerates were from large volcanic debris flows.

IV. EXPLORATION

On June 8, 2017, a pavement and subgrade investigation was conducted for the project consisting of six in-situ dynamic cone penetration (DCP) tests coupled with six shallow hand augered borings (1.5 to 4 foot depth). The locations of the DCPs and soil borings (BH-1 through BH-6) are shown on the Boring Locations exhibits in Appendix A. CFL personnel logged the findings including DCP measurements, depth of boring, visual soil classification, pavement thickness, and areas of distress. During the site visit, four subgrade soil samples were collected. These samples were submitted to the CFLHD laboratory for soil classification and to determine engineering properties. The boring log, DCP data sheets, and laboratory reports are provided in Appendix B.

V. EXISTING PAVEMENT & SOILS

The existing pavement was found to be asphalt concrete pavement in poor condition. The existing pavement exhibits transverse, block, and alligator cracking that comes with an old age hardened pavement. The pavement thickness ranges between 2 and 3 inches.

Beneath existing asphalt is a layer of aggregate base/clayey sand with gravel; thickness ranging between 3 and 8 inches. In general, the underlying subgrade soils through the project limits are fairly consistent; soft sandy fat clays and clayey sands. The soil classifications for the four subgrade samples are shown in Table 2 below.

Table 2. Subgrade Soil Classifications Soil Boring Designation B-1 B-5 B-6A B-6B AASHTO Classification A-7-6(6) A-7-6(22) A-2-6(1) A-6(3) ASTM Group Symbol SC CH SC SC ASTM Group Name Clayey sand with gravel Sandy Fat

Clay Clayey sand with gravel

Clayey sand with gravel

VI. PAVEMENT DESIGN INPUTS

The pavement design for CO FTNP FLFO 900(1) utilized design criteria established in the Federal Lands Highway Project Development Design Manual (PDDM) and the 1993 AASHTO Guide for Design of Pavement Structures (AGDPS). The criteria shown in Table 3 below were selected based on the project’s scope and traffic levels.

Table 3. Design Criteria Design Performance Period (3R) 20 years Initial Serviceability 4.2 Terminal Serviceability 2.0 Design Reliability Level 75% Overall Standard Deviation 0.49 Annual Traffic Volume Growth Rate 2.0% Directional Distribution 50%

Traffic

The parking lots and entrance road at the Florissant Fossil Beds are used primarily for tourism with the vast majority of vehicles being passenger vehicles, pickups, SUVs, recreational vehicles (RVs), and school buses. There are occasional garbage trucks, dump trucks, and delivery trucks for servicing the park visitor center. The existing parking lot has 60 parking stalls for cars, pickups, and SUVs and 6 parking stalls for RVs and school buses. According to the national park service website, 73,564 people visited the park in 2016. This number includes visitors to the Hornbeck Homestead and Barksdale Picnic Area which do not visit the visitor center, but excludes NPS personnel visits. It is assumed that the estimated vehicle visits to the Hornbeck and Barksdale sites are offset by the excluded NPS vehicles. An average annual two way road ADT of 140 vehicles per day (or 70 vehicle visits per day) is assumed for the project with 95% Class 2-3 cars, pickups, and SUVs and 5% Class 4-6 RVs, school buses, and 3-axle trucks. Buses are assumed to constitute 30% of the Class 4-6 vehicles. The assumed traffic data equates to 77,562 annual visitors as tabulated below (persons per vehicle provided by NPS).

Table 4. Park Visitor Calculations

Vehicles Persons per Vehicle

Vehicle Visits/Day

Annual Visitors

Cars/Pickups/SUVs/RVs 2.5 69 62,962 School Buses 40 1 14,600

Total Annual Visitors 77,562

Accurate traffic load estimates expressed as 18-kip equivalent single axle loads (ESALs) are critical for the pavement design. Load estimates are based on vehicle counts and classifications with a 20-year, 2% growth factor of 24.3. Standard load equivalency truck factors are used to convert the various vehicle axle loads to 18-kip ESALs. The following truck factors were assumed for the aforementioned vehicle classifications in accordance with PDDM Exhibit 11.2-A: 0.004 for Class 2-3 and 1.0 for Class 4-6. Based upon the design criteria and assumptions shown above and the 1993 AASHTO pavement design procedure, the project’s 20-year-18-kip equivalent single axle loads (ESALs) are calculated to be 33,399 (see Appendix D). According to PDDM Section 11.2.1.2, a minimum of 50,000 ESALs shall be used for the design of paved roads.

Subgrade Soil Resilient Modulus

Six in-situ DCP tests (ASTM D6951) were conducted to determine the California Bearing Ratio (CBR) and Resilient Modulus for the subgrade soils beneath the proposed parking lot and road improvements. Table 5 below summarizes the subgrade DCP index values (mm/blow) for the six boring locations, in addition to, the design DCP, CBR, and Resilient Modulus values. The field DCP data sheets are provided in Appendix B. In accordance with ASTM D6951, the California Bearing Ratio can be estimated from the DCP index value using the following US Corps of Engineers equation. The subgrade Resilient Modulus is calculated from the CBR using the subsequent correlation equation from the AGDPS (Page I-14, Equation 1.5.1).

CBR (%) = 292 / DCP1.12

Resilient Modulus, MR (psi) = 1,500 x CBR (%)

Table 5. Subgrade DCP Resilient Modulus Boring Number Location DCP Index

(mm/blow) Moisture & Consistency

BH-1 Administrative Lot 12 Moist & firm BH-2 Visitor Center Cul-de-sac 10 Moist & firm BH-3 Corner of Parking Stall 43 Very wet & soft BH-4 Overflow Lot Entrance 41 Very wet & soft BH-5 Overflow Lot 17 Moist & soft BH-6 Entrance Road 25 Moist & soft

Design DCP Index Value 43 mm/blow Design CBR Value 4.3%

Design Resilient Modulus 6,500 psi

Additionally, two subgrade soil samples were submitted to the CFLHD lab for testing to determine their respective R-Values (AASHTO T 190) for correlation purposes. These test results and their calculated Resilient Modulus values are summarized in Tables 6 below. The subgrade Resilient Modulus is calculated from the R-Value using the following correlation equation from the AGDPS (Page I-14, Equation 1.5.3). The aforementioned Design Resilient Modulus (Table 5) is within the range of the R-Value Resilient Modulus values (Table 6).

Resilient Modulus, MR (psi) = 1,000 + 555 x (R-Value)

Table 6. Subgrade R-Value Resilient Modulus Sample Number Location R-Value Resilient

Modulus B-5 Overflow Lot 5 3,775 psi

B-6B Entrance Road 12 7,660 psi

Structural Layer Coefficients

Standard CFLHD structural layer coefficients were selected for asphalt concrete pavement (0.44) and crushed aggregate base (0.12) in accordance with Exhibit 11.2-C of the PDDM. A drainage coefficient of 1.0 was utilized for all proposed layers.

Structural Number Calculations

The Pavement Interactive App for the 1993 AASHTO pavement design procedure is used to determine the required pavement structural numbers (SN) for the CO FTNP FLFO 900(1) paved road and parking lots. Based upon the ESALs, the subgrade Resilient Modulus, and the aforementioned design criteria, the following required pavement design structural number is calculated.

Required SN for Florissant Fossil Beds = 2.05 inches

VII. PAVEMENT RECOMMENDATIONS & DISCUSSION

Project Recommendations

In accordance with the 1993 AASHTO design procedure, a 20 year pavement design requires a Structural Number (SN) of 2.05. After evaluating alternatives, the following pavement structural section is recommended for the paved parking lots and roads:

3 inches Asphalt Concrete Pavement (SN = 3” x 0.44 = 1.32”) 6 inches of Compacted Aggregate Base (SN = 6” x 0.12 = 0.72”)

TOTAL SN = 2.05 inches

The existing pavement thickness ranges between 2 and 3 inches. Beneath the existing asphalt is a layer of aggregate base/clayey sand with gravel; thickness ranging between 3 and 8 inches. It is recommended that the existing asphalt pavement be recycled for use as aggregate base through the process of a 4” deep full depth reclamation of the existing pavement with subsequent excavation, placement and compaction; to be paid for with the 30201 and 30402 line items (see below). Further, the pavement investigation identified a soft clayey subgrade beneath the parking lots and road. To avoid subexcavation, excavation into the existing base should be avoided. Preferably, borrow material and aggregate base should be placed directly on top of the existing base.

VIII. MATERIALS RECOMMENDATIONS, SCRs, AND

CONSTRUCTION CONSIDERATIONS

Selection of Asphalt Binder

LTPPBind was utilized for the selection of the asphalt binder for the project (See Appendix E). A PG 58-34 binder is recommended for the project’s asphalt pavement.

This binder grade is readily available and commonly used by the Colorado DOT.

Tack Coat and Fog Seal

A Tack Coat applied between asphalt lifts, and a Fog Seal applied to the final pavement surface are recommended.

Subexcavation and Drainage

The pavement investigation identified a soft, saturated clayey subgrade beneath the parking lots and road, but did not identify specific areas requiring subexcavation. To avoid subexcavation, excavation into the existing base should be avoided. Preferably, borrow material and aggregate base should be placed directly on top of the existing base.

For the County Road 1 tie-in, subexcavation is recommended based upon the extensive alligator cracking and the fixed road grade (excavation into the subgrade is unavoidable).

Subexcavation should be to a depth of 2 feet with the placement of a geotextile separation fabric (nonwoven, Class 1,Type E) in the bottom of the excavation and the placement of suitable backfill material on top of the fabric. Additional areas of soft subgrade may need to be stabilized during construction, and therefore, it is recommended that an additional 200 cubic yards of subexcavation be included in the contract to be used at the discretion of the CO. Further, ditch maintenance is needed to prevent water from saturating the subgrade.

Materials for Culvert Pipe / Cement

The project’s sandy clays were found to be fairly corrosive with resistivity as low as 928 ohm-cm. To address the corrosive soils, it is recommended that galvanized steel pipe should have either a polymer coating or a 12 gage wall thickness.

SCRs and Construction Concerns

CFLHD standard SCRs related to pavements and materials are expected to be used with the project apart from the Sections 302 and 304 SCRs for the use of the recycled pulverized asphalt as aggregate base. Any additional SCRs may be developed as needed.

Bid Items

Suggested FP-14 pay items for the proposed structural section are shown in Table 7.

Table 7: Recommended Pay Items Item Number Item Description Unit 20402-0000 Subexcavation CUYD 30201-2000 Roadway Aggregate, Method 2 (Recycled Pulverized Asphalt) CUYD 30202-2000 Roadway Aggregate, Method 2 TON 30402-5200 Full Depth Reclamation, Method 2, 4-Inch Depth CUYD 40301-0100 Asphalt Concrete Pavement, Type 1 TON 40601-0000 Fog Seal TON 41201-0000 Tack Coat TON

APPENDICES

A – Location, Site, and Soils Maps

B – Boring Log, DCP Data, and Lab Report

C – Site Investigation Photos

D – Pavement Design Calculations

E – LTPPBind & Climate Data

F – Pipe Selection Criteria

APPENDIX A – Location, Site, & Soils Maps

LOCATION MAPS

SITE MAP - FLORISSANT FOSSIL BEDS NATIONAL MONUMENT – VISITOR CENTER PARKING LOTS & ROAD

BORING LOCATIONS

BH-2

X

BH-1

X

BH-3

X

BH-4

X

BH-5

X

BORING LOCATIONS

BH-6

X

APPENDIX B – Boring Log, DCP Data, and Lab Report

P ro je ct

B o ri n g

N u m b e r

Lo ca ti o n D e p th o f

B o re t o to

.5

.5 t o to

.5

.5 t o to to t o to t o

' t o t o to to

N o te

B H

-5

' n o rt h o f w o o d c h ip p ile in o ve rf lo w p ar ki n g lo t

G re y sh ad in g in d ic at es s am p le lo ca ti o n

B O

R

IN

G L

O G

N o

S am p le s

P av e m e n t In ve st ig at io n

S h al lo w

B o ri n gs w it h

H an d A u ge r

B ro w n c ru sh ed a gg re ga te b as e

(m o is t f ir m

D ar k gr ey is h b ro w n c la ye y sa n d w it h g ra ve l ( m o is t f ir m

R ef u sa l o f h an d a u ge r

A sp h al t

B ro w n c ru sh ed a gg re ga te b as e

(m o is t f ir m

G re y sa n d y cl ay w it h y el lo w r u st ve ry w et v er y so ft

B o ri n g O b se rv at io n s (m o is tu re c o n si st e n cy

D ar k gr ey is h b ro w n s an d y cl ay ve ry w et v er y so ft

Sa m p le

N u m b er

C o n ta in er

G ra ve l a d m in is tr at iv e lo t, so u th o f so u th ea st b u ild in g co rn er

B H

-1

.5

C O

F

TN

P F

LF

O

(1

Fl o ri ss an t Fo ss il

B e d s

P ar ki n g Lo ts

R o ad

W it h in a lli ga to r cr ac ke d as p h al t at e n tr an ce t rf lo w p ar ki n g lo t

B H

-4

R ed c ru sh ed a gg re ga te b as e

(m o is t f ir m

R ef u sa l o f h an d a u ge r

B H

-3 Ed ge o f as p h al t at c o rn er o f p ar ki n g st al l

D ar k gr ey is h b ro w n s an d y cl ay ve ry w et v er y so ft

A sp h al t

D ar k gr ey is h b ro w n s an d y cl ay m o is t s o ft

N o

S am p le s B ro w n w el l g ra d ed g ra ve l ( m o is t f ir m

R ef u sa l o f h an d a u ge r

A sp h al t

N o

S am p le s

B ag

S am p le

B H

-1

In st ig at io n D at e

-J u n -1 ag

S am p le

B H

-6 A

B u ck et

S am p le

B H

-6

H

-2 N o rt h e d ge o f as p h al t n so u th s id e o f cu l-d e-sa c at tr an sv er se c ra ck

.5

A sp h al t

B H

-6 W it h in a lli ga to r cr ac ke d as p h al t o f w es tb o u n d la n e f en tr an ce r o ad

G o ld en b ro w n c la ye y sa n d w it h g ra ve l ( m o is t s o ft

G o ld en b ro w n c la ye y sa n d w it h g ra ve l ( m o is t s o ft

G o ld en b ro w n c la ye y sa n d w it h p eb b le s (m o is t s o ft

B u ck et

S am p le

B H

-5 t o

APPENDIX C – Site Investigation Photos

BH-1 in Gravel Administrative Lot (20’ South of SE Building Corner, Sample Taken)

BH-2 at North Edge of Asphalt on South Side of Cul-de-sac (Looking North)

BH-3 at Edge of Asphalt at Corner of Parking Stall (Looking East)

BH-3 - 8” Depth of Red Aggregate Base over Dark Greyish Brown Clay

BH-3 Material - Red Aggregate Base and Dark Greyish Brown Clay Subgrade

BH-4 within Alligator Cracked Asphalt at Overflow Lot Entrance (Looking East)

BH-4 within Alligator Cracked Asphalt at Overflow Lot Entrance (Looking South)

BH-4 Grey Clay Subgrade Material with Yellow and Rust Colors (from 4’ Depth)

BH-5 - 20’ North of Wood Chip Pile in Grass Overflow Lot (Looking North)

BH-5 - Dark Greyish Brown Clay Subgrade Material to 4’ Depth (Sample Taken)

BH-6 within Alligator Cracked Asphalt in Westbound Lane (Two Samples Taken)

Subgrade Samples Submitted for Lab Testing (BH-5 on Left and BH-6 on Right)

APPENDIX D – Pavement Design Calculations

Florissant Fossil Beds Parking Lots & Road, Colorado

Pavement Design Structural Number (SN) Calculation

APPENDIX E – LTPPBind & Climate Data

LTPPBind Online

LTPPBind V3.1 Data

Climate Data

Climate Data (Cont.)

APPENDIX F – Pipe Selection Criteria

Hydrology and Hydraulics December 2012

7-48 Roadway Hydraulics

7.3.5.5 Recommended Methods

Design and evaluate the performance of energy dissipators according to the methods presented in HEC 14. HEC 14 also contains procedures for estimating scour hole dimensions at pipe outlets.

7.3.5.6 Reporting

The design of outlet protection for culvert, ditch, or storm drain outlets should be supported by documentation containing, at a minimum, the following information:

● Project identification

● Location of proposed installation

● Hydraulic design calculations

7.3.5.7 Plans

For the location and design of riprap outlet protection, prepare plans showing all details necessary to construct the improvements according to the hydraulic design, including the following:

● Location

● Dimensions and extent of riprap

● Gradation

● Bedding and Filter Material or Geotextile

● Grading or slope details

7.3.6 ALTERNATIVE PIPE MATERIALS

It is Federal Lands Highway policy to specify alternative drainage pipe materials on all projects where feasible and to comply with the provisions of 23 CFR 635.411. All suitable pipe materials, including reinforced concrete, steel, aluminum, and plastic will be considered as alternatives for all new cross culverts and storm drain pipes on Federal Lands Highway projects.

Not all pipe materials are appropriate or applicable for all storm drain applications. The design of alternative drainage pipe materials should consider functionally equivalent performance in three areas: structural capacity, durability and service life, and hydraulic capacity. The service life and hydraulic capacity issues are addressed in this section.

7.3.6.1 References

The following references provide source information for the development of the standards, criteria, and guidance of this subsection (most recent editions apply):

1. 23 CFR 635.411 Title 23 CFR 635.411 in 23 CFR 635D, General Material Requirements

Roadway Hydraulics 7-49

2. FHWA-FLP-91-006 FHWA, Durability of Special Coatings for Corrugated Steel Pipe, FHWA FLP-91-006

3. FHWA-RD-97-140 FHWA, Durability Analysis of Aluminized Type 2 Corrugated Metal Pipe, FHWA RD-97-140, 2000.

4. AASHTO HDG

Vol. IV

AASHTO Highway Drainage Guidelines, Volume IV – Hydraulic Design of Culverts

5. AASHTO HDG

Vol. XIV

AASHTO Highway Drainage Guidelines, Volume XIV – Culvert Inspection and Rehabilitation

6. Caltrans Chapter

California Department of Transportation Highway Design Manual, Chapter 850 – Physical Standards

7.3.6.2 Design Standards

7.3.6.2.1 Service Life

Design cross culvert and storm drain pipes with a minimum maintenance-free service life of 50-years, regardless of pipe material selection. A shorter service life may be used for temporary installations, and a longer service life may be considered in unusual situations.

7.3.6.2.2 Minimum Pipe Classification

Use Class II as the minimum for all reinforced concrete pipes. Determine appropriate pipe class from FLH fill height FLH Standard Drawings.

Use a minimum wall thickness of 0.0625” [1.63 mm] for all steel and aluminum pipes. The appropriate minimum structural metal thickness will be determined from approved FLH fill height tables.

7.3.6.3 Design Guidance

7.3.6.3.1 Service Life

The durability and service life of a storm drain pipe is directly related to the environmental conditions encountered at the site and the type of materials and coatings from which the pipe was fabricated. The two primary causes of early failure in drainage pipe materials are corrosion and abrasion.

Corrosion gradually wears away at the pipe walls by chemical action, and can occur from both the soil and water sides of the pipe. Abrasion wears away at the interior pipe wall by friction from suspended or bed-load sediment.

http://www.fhwa.dot.gov/publications/research/infrastructure/hydraulics/97140/97140.pdf http://www.fhwa.dot.gov/publications/research/infrastructure/hydraulics/97140/97140.pdf http://www.dot.ca.gov/hq/oppd/hdm/pdf/chp0850.pdf

7-50 Roadway Hydraulics

7.3.6.3.2 Data Collection

Corrosion

Representative pH and resistivity determinations are required in order to specify pipe materials capable of providing a maintenance-free service life. Samples are taken in accordance with the procedures described in AASHTO T 288 and T 289. Samples should be taken from both the soil and water side environments to ensure that the most severe environmental conditions are selected for determining the service life of the drainage pipe. Soil samples should be representative of backfill material anticipated at the drainage site. Avoid taking water samples during flood flows or for two days following flood flows to ensure more typical readings. In locations where streams are dry much of the year, water samples may not be possible or necessary. In areas of known uniform pH and resistivity readings, a random sampling plan may be developed to obtain the needed information.

In corrosive soil conditions where water side corrosion is not a factor, consider specifying less corrosive backfill material to modify the soil side environment. The mitigating effect of the specified backfill should be taken into account in making alternative pipe materials selections in situations where the soil side conditions control the design.

Abrasion

An estimate of the potential for abrasion is required in order to determine the need for invert protection. Four levels of abrasion are referred to in this guidance and the following guidelines are established for each level:

● Level 1. Nonabrasive conditions exist in areas of no bed load and very low velocities.

This is the condition assumed for the soil side of drainage pipes.

● Level 2. Low abrasive conditions exist in areas of minor bed loads of sand and velocities of 5 ft/s [1.5 m/s] or less.

● Level 3. Moderate abrasive conditions exist in areas of moderate bed loads of sand and gravel and velocities between 5 ft/s and 15 ft/s [1.5 m/s and 4.5 m/s].

● Level 4. Severe abrasive conditions exist in areas of heavy bed loads of sand, gravel, and rock and velocities exceeding 15 ft/s [4.5 m/s].

Abrasion levels are intended as guidance to help the engineer consider the impacts of bed-load wear on the invert of pipe materials. Sampling of the streambed materials is not required, but visual examination and documentation of the size of the materials in the stream bed and the average slope of the channel will give the designer guidance on the expected level of abrasion.

Where existing culverts are in place in the same drainage, the conditions of inverts should also be used as guidance. The expected stream velocity should be based upon a typical flow (i.e., 2-year flow and less) and not a 10-or 50-year design flood.

Roadway Hydraulics 7-51

7.3.6.3.3 Reinforced Concrete Pipe

Reinforced concrete pipe (AASHTO M 170M) is typically specified as an alternative whenever environmental conditions permit. The appropriate pipe class is determined from approved FLH fill height FLH Standard Drawings. If the following guidance on corrosion and abrasion limitations is used, reinforced concrete pipe can be assumed to have a minimum service life of 50 years.

Corrosion

Reinforced concrete pipe should not be specified for extremely corrosive conditions where the pH is less than 3.0 and the resistivity is less than 300 Ω-cm. Where the pH is less than 4.0, or the pipe is exposed to wetting and drying in a salt or brackish water environment, protective coatings (e.g., epoxy resin mortars, poly vinyl chloride sheets) should be used. When the sulfate concentration is greater than 0.2% in the soil or 2,000 parts per million in the water, Type V cement should be specified. When the sulfate concentration is greater than 1.5% in the soil or 15,000 parts per million in the water, Type V cement should be used with a sulfate resistant pozzolan. A higher cement ratio may also be used (e.g., AASHTO Class V pipe design).

Abrasion

On installations in severe abrasive environments, consider using seven or eight sack concrete or increasing the cover over the reinforcing steel.

7.3.6.3.4 Steel Pipe with Metallic Coatings

Steel pipe will typically be specified as an alternative when the environmental conditions permit.

The appropriate minimum structural metal thickness is determined from approved FLH fill height tables. Federal Lands Highway design policy assumes that steel pipe will provide a useful, maintenance-free service life for a period of time beyond the point of first perforation. This assumes an acceptable risk for most Federal Lands Highway projects, but at locations with erodible soils, large traffic volumes, or high fills where replacement or repair would be unusually difficult or expensive, consider increasing the steel plate by one standard thickness. In unusual situations where very high fills and severe abrasion are combined, or where other environmental concerns would make replacement of a pipe culvert very costly or impractical, consider using a pipe one size larger in diameter to permit re-lining in the future by insertion of another pipe.

The following types of steel pipe with metallic coatings are considered as alternatives on Federal Lands Highway projects:

● Galvanized steel (AASHTO M 218)

● Aluminum coated steel (Type 2) (AASHTO M 274)

Corrosion

Under non-abrasive and low-abrasive conditions, the service life of steel pipe with metallic coatings may be determined based upon corrosion (i.e., pH and resistivity) factors determined from Exhibit 7.3-B, which shows the relationship between service life and corrosion for plain

7-52 Roadway Hydraulics galvanized steel pipe. It has been adapted from the California Department of Transportation “Method for Estimating the Service Life of Steel Culverts,” California Test 643. The curves have been modified to show the expected average service life of pipe with a steel thickness of 0.0625” [1.63 mm] assuming a useful, maintenance-free service life 25 percent longer than the number of years to first perforation. Under moderate and severe abrasive conditions, abrasion protection must also be considered.

Under nonabrasive and low abrasive conditions, the metal thickness of galvanized and aluminum coated steel (Type 2) alternatives should be determined from Exhibit 7.3-B based on the resistivity and pH of the site. The minimum metal thickness of steel pipe, as determined from FLH standard fill height tables, may have to be increased, or the additional life of a protective coating may have to be added, in order to provide a 50-year service life. The results included in FHWA-FLP-91-006 indicate that within the environmental range of 5.0 through

9.0 pH and resistivity equal to or greater than 1500 Ω-cm, aluminum coated steel (Type 2) can be expected to give a service life of twice that of plain galvanized pipe.

Exhibit 7.3-B can be used to determine various combinations of increased thicknesses, aluminum coated steel (Type 2), and protective coatings to achieve a 50-year service life, but in no case may the metal thickness specified by the structural requirements be reduced.

Abrasion

Under nonabrasive and low abrasive conditions, the metal thickness of the galvanized, galvalume, and aluminum coated steel alternatives, as determined from Exhibit 7.3-B, should be used.

On installations in moderate abrasive environments where protective coatings are not required for corrosion protection, the thickness of the metal should be increased by one standard metal pipe thickness determined from the diagram for average service life of plain galvanized culverts (see Exhibit 7.3-B) or invert protection should be provided. Invert protection may consist of bituminous coating with invert paving with bituminous concrete, Portland cement concrete lining, installation of metal plates or rails, or velocity reduction structures.

On installations in severe abrasive environments where protective coatings are not required for corrosion protection, the thickness of the metal should be increased by one standard metal pipe thickness determined from the diagram for average service life of plain galvanized culverts (see Exhibit 7.3-B) and invert protection should be provided. Invert protection may consist of installation of metal plates or rails, or velocity reduction structures.

Protective coatings are not suitable for corrosion protection in moderate-abrasive and severe abrasive locations. Metal pipes should not be specified in moderate and severe abrasive environments where coatings are required to protect against water-side corrosion.

Roadway Hydraulics 7-53

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7-54 Roadway Hydraulics

7.3.6.3.5 Non-Metallic Protective Coatings for Steel Pipe

Protective coatings may be used to provide additional protection from corrosion or abrasion resulting in an extended service life. Coatings to protect against corrosion may only be used in non-abrasive and low abrasive environments.

The additional service life noted below in bold for each type of protective coating, for corrosion protection, are from Part V of FHWA-FLP-91-006. The added service is applicable only to non-abrasive and moderate abrasive conditions. All of the following types of steel pipe with non-metallic coatings are considered as alternatives on Federal Lands Highway projects:

Bituminous coating

Bituminous coatings (AASHTO M 190) can be expected to add 10 years of service to the water side and 25 years life to the soil side service life of pipe as determined from Exhibit 7.3-B.

Bituminous-coated pipe should not be used in low abrasive environments.

Bituminous paving and coating

Bituminous paved invert with bituminous coatings (AASHTO M 190) can be expected to add 25 years life to water side locations. Under moderate abrasive conditions, bituminous paved pipe may be used for invert protection where corrosion protection is not required.

Concrete lining

Concrete lining (ASTM A 849) can be expected to add 25 years of service life. Due to the natural cracking of concrete, the concrete lining should be applied over an asphalt coating if corrosion protection is needed. Under moderate abrasive conditions, concrete lined pipe may be used for invert protection where corrosion protection is not required.

Polymer coating

Ethylene Acrylic Acid Film coatings (AASHTO M245 and M246) should provide an additional 30 years service life with a 0.009” [0.25 mm] thickness.

Aramid fiber bonded coating

Only limited data is available for the service life of aramid fiber bonded coated (ASTM A 885) and epoxy coated pipes. No additional service life is currently credited with this policy.

7.3.6.3.6 Aluminum Alloy Pipe

Aluminum alloy pipe (AASHTO M 196M) will typically be specified as an alternative when environmental conditions permit. The appropriate minimum structural metal thickness is determined from approved FLH fill height tables. Within the following limits of corrosion and abrasion, aluminum alloy pipe can be assumed to have a service life of 50 years. Additional service life may be achieved where required by abrasion with the addition of protective coatings or additional metal thickness as discussed below:

Roadway Hydraulics 7-55

Corrosion

An aluminum alloy should be allowed if the pH is between four and nine and the resistivity is greater than 500 Ω-cm. An aluminum alloy alternative can also be considered for use in salt and brackish environments when embedded in granular, free draining material.

Abrasion

On installations in non-abrasive and low-abrasive environments, abrasion protection is not required.

On installations in moderately abrasive environments, the thickness should be increased by one standard metal thickness or invert protection should be used. Invert protection may consist of bituminous coating and invert paving with bituminous concrete or Portland cement concrete, installation of metal plates or rails, or velocity reduction structures.

On installations in severe abrasive environments, the thickness of the metal should be increased by one standard metal pipe thickness from that determined for low-abrasive conditions and invert protection should be provided. Invert protection may consist of installation of metal plates or rails or velocity reduction structures.

7.3.6.3.7 Plastic Pipe

Polyethylene and polyvinyl chloride plastic pipe may be specified as alternatives for pipe diameters and minimum resin cell classifications shown in the AASHTO’s Standard Specifications for Highway Bridges, Division I Design, Section 18, Soil Thermoplastic Pipe Interaction Systems. The thickness of the plastic alternatives must meet the structural requirements of AASHTO’s Standard Specifications. The assumed service life of plastic pipe designed in accordance with AASHTO Section 18 is 50 years. The maximum allowable fill heights for pipe materials listed below is determined from approved FLH standard fill-height tables which include the following plastic pipe materials:

● Smooth wall polyethylene (ASTM F 714)

● Corrugated polyethylene (AASHTO M 294)

● Ribbed polyethylene (ASTM F 894)

● Smooth wall polyvinyl chloride (AASHTO M 278 and ASTM F 679)

● Ribbed polyvinyl chloride (AASHTO M304 and ASTM F 794)

Corrosion

Plastic alternatives may be specified without regard to the resistivity and pH of the site.

Abrasion

Under nonabrasive and low-abrasive conditions, polyethylene and polyvinyl chloride alternatives should be allowed. Plastic alternatives should not be used under moderate and severe abrasive conditions without invert protection.

7-56 Roadway Hydraulics

Maximum Size

Limit the size of plastic pipe to 48” [1200 mm] under mainline roads.

The locations selected for use of plastic pipes should address partner agency concerns of possible damage due to fire, ultraviolet sunlight, and rodents.

7.3.6.4 Recommended Methods

Design and evaluate the design service life for galvanized steel culvert and storm drain pipes by the Modified California method presented in Exhibit 7.3B. Refer to FHWA-RD-97-140, Durability Analysis of Aluminized Type 2 Corrugated Metal Pipe, for design guidance on aluminized material.

7.3.6.5 Reporting

Documentation of the design service life of culvert and storm drain pipes should be included in the design reporting.

7.3.6.6 Plans

For culvert and storm drain pipes, include information on pipe material, size, class, gauge, and any special coatings in the Plan Drainage Summary.