California Department of Transportation
 

DIB 83-02 - 2.1 Culvert Structures

DESIGN INFORMATION BULLETIN No. 83-02
CALTRANS SUPPLEMENT TO FHWA CULVERT REPAIR PRACTICES MANUAL

         
2.1 CULVERT STRUCTURES
  2.1.1 Material
    2.1.1.1 Rigid
      2.1.1.1.1 General
      2.1.1.1.2 Concrete Pipe
      2.1.1.1.3 Other Rigid Materials
        2.1.1.1.3.1 Glass Fiber Reinforced Polymer Mortar (Reinforced Polymer Mortar) or Fiber Reinforced Polymer Concrete Pipe
        2.1.1.1.3.2 Polymer Concrete Pipe
        2.1.1.1.3.3 Fiber Reinforced Concrete Pipe
        2.1.1.1.3.4 Ductile Iron
        2.1.1.1.3.5 Fiberglass - Fiber Reinforced Plastic
    2.1.1.2 Flexible
      2.1.1.2.1 Metal Pipe
      2.1.1.2.2 Plastic Pipe
    2.1.1.3 Culvert Coatings
      2.1.1.3.1 Coatings for Concrete and other Culverts
      2.1.1.3.2 Coatings for Metal Culverts
  2.1.2 Service Life for Culvert Rehabilitation; Geotechnical Factors
    2.1.2.1 Hydrogen-Ion Concentration (pH), Soil Resistivity, Chloride and Sulfate Concentration of the Surrounding Soil and Water
    2.1.2.2 Material Characteristics of the Culvert
    2.1.2.3 Abrasion

2.1 Culvert Structures

2.1.1 Material

The most common materials used in culvert conduits are reinforced concrete, corrugated steel, and corrugated high-density polyethylene. Other materials that may be found in culvert conduits are corrugated aluminum, non-reinforced concrete, ribbed polyvinyl chloride (PVC), welded steel, timber, and masonry. Refer to HDM Chapter 850, for guidance on Material Selection, Design Service Life and Kinds of Pipe Culverts. Refer to FHWA Culvert Repair Practices Manual Volume 1, pages 2-18 to 2-30 for a description of culvert materials and coatings for culvert materials. Refer to Table 857.2 in the HDM for allowable alternative pipe materials for various types of installation.

These various pipe materials will have differing types of response to applied load. Based on this response, the pipe material can be categorized as either rigid or flexible, as described in Indices 2.1.1.1 and 2.1.1.2. This distinction in behavior is important not only in understanding how a pipe will perform under various soil and live load conditions, but will also affect failure mechanisms and repair considerations.

The following flow chart offers a general guide to the thought process and factors involved in selecting allowable alternative materials in accordance with HDM Topic 857:

DESIGN FACTORS
DESIGN GUIDANCE
DESIGN SELECTION

Chart illustrating general guide to selecting allowable alternative materials

 


2.1.1.1 Rigid

2.1.1.1.1 General

If the culvert material is rigid (usually reinforced concrete), the load is carried primarily by the structure walls. Refer to FHWA Culvert Repair Practices Manual Volume 1, pages 2-7 to 2-8, 2-11 and 2-31 to 2-35 for a description of pipe loading, rigid culvert behavior and installation. As described on page 2-33 and in Figures 2.20 and 2.21 on pages 2-34 and 2-35, it is very important to have uniform bedding to distribute the load reaction around the lower periphery of the pipe. Adequate support is critical in rigid pipe installations, or shear stress may become a problem.  Excavation, backfill and culvert beddings shall conform to the details shown on the Standard Plans numbered A62D, RSP A62DA, A62E and to the provisions in Section 19-3, “Structure Excavation and Backfill” of the Standard Specifications. In addition, slurry cement backfill or controlled low strength material (CLSM) may be used in lieu of structure backfill. Where cover heights above culverts are less than the values shown in HDM 856.5, stress reducing slab details available from the Headquarters Design drainage detail library using the following web address may be used: http://onramp.dot.ca.gov/hq/design/drainage/library.php. Where cover heights are less than the values shown in the stress reducing slab details, contact Office of State Highway Drainage Design or Underground Structures Branch of DES - Structures Design.

2.1.1.1.2 Concrete Pipe

Per Topic 852 of the HDM, for reinforced concrete pipe (RCP), box (RCB) and arch (RCA) culverts maintenance free service life, with respect to corrosion and abrasion and/or durability, is the number of years from installation until the deterioration reaches the point of exposed reinforcement at any location on the culvert.

Refer to Standard Plan D88 for required minimum cover for construction loads on reinforced concrete pipes and arches.

For non-reinforced concrete pipe culverts, per HDM Topic 852.1 maintenance free service life, with respect to corrosion and abrasion and/or durability, is the number of years from installation until the deterioration reaches the point of perforation or major cracking with soil loss at any point of the culvert.

2.1.1.1.3 Other Rigid Materials

2.1.1.1.3.1 Glass Fiber Reinforced Polymer Mortar (RPMP) or Fiber Reinforced Polymer Concrete Pipe (FRPC)

Reinforced Polymer Mortar pipes (RPMP) are made by mixing a high strength thermosetting polyester resin, aggregate/sand and chopped glass fiber roving to form a type of concrete. The resin within the mix provides for bonding the aggregate much like Portland Cement does in traditional concrete pipes. Cement and water are not used and this product may be used in corrosive applications. It is also lightweight compared to RCP and uses push-together joints instead of a bell and spigot. RPMP is available in diameters from 18 inches to 102 inches and section lengths of 5, 10 and 20 feet. See FHWA Culvert Repair Practices Manual Volume 1, page 2-27 and refer to ASTM D3517.

Currently, Caltrans does not contemplate developing new Standard Specifications for this product; however, this product is approved for jacking and microtunneling for permit installations. See Indices 9.1.2.2.1 and 9.1.2.2.2. There is a very limited use for RPMP in typical direct burial culvert applications due to its relatively high cost. However, in addition to jacking and microtunneling applications, there is potential usage for RPMP as a slipliner if site conditions dictate a special design. See Index 6.1.3.1.

Since RPMP is specially designed to fit specific site loading and hydraulic characteristics, the Underground Structures Unit within Caltrans Division of Engineering Services (DES) should be contacted for a project-by-project review. See Index 7.1.6.2.

Maintenance free service life, with respect to corrosion and abrasion and/or durability, is the number of years from installation until the deterioration reaches the point of perforation or major cracking with soil loss at any point of the culvert.

2.1.1.1.3.2 Polymer Concrete Pipe - also known as Polyester Resin Concrete (PRC), this type of pipe is currently not included in Caltrans standards. The materials used in polymer concrete include resin, sand, gravel, and quartz powder mineral filler. Similar to RPMP pipes, Polymer concrete pipes are lightweight compared to RCP and use push-together joints with gaskets. PRC pipes may be viable for use in some specialized applications including corrosive environments (pH ranges of 1 to 10) and pipe jacking or microtunneling (high compressive strengths of up to 13,000 psi), see Indices 9.1.2.2.1 and 9.1.2.2.2.

2.1.1.1.3.3 Fiber Reinforced Concrete Pipe - the fiber cement industry has grown out of the asbestos cement industry. Fiber reinforced concrete pipe consists of cellulose fiber, silica sand, cement, and water. Fiber reinforced concrete pipe is potentially a durable, lightweight option to non-reinforced concrete pipes. It is not approved or included in Caltrans Standards for use as a direct burial alternative pipe. However, in large diameter man entry pipes the material may be viable for use as a segmental liner. See Index
6.1.3.7.1.

2.1.1.1.3.4 Ductile Iron is a strong, durable semi-rigid pipe. Even though ductile iron has been used for culvert and storm drains, it is generally not a cost effective option and there are no Caltrans Standards. Occasionally this material may be a consideration for use as a slipliner.

2.1.1.1.3.5 Fiberglass – Fiber Reinforced Plastic (FRP) is not included in the Caltrans Allowable Alternative Materials Table 857.2. FRP is typically not economically competitive for use as a direct burial alternative culvert material. However, in large diameter man entry pipes the material may be viable for use as a segmental liner (see index 6.1.3.7.2) or in some specialized applications including: pipe jacking or microtunneling. See Indices 9.1.2.2.1 and 9.1.2.2.2. FRP pipe is available in diameters from 12 inches to 144 inches. For further discussion on FRP, see FHWA Culvert Repair Practices Manual Volume 1, page 2-26 and refer to ASTM D3517.

2.1.1.2 Flexible

If the culvert material is flexible (usually metal or plastic), a soil-pipe interaction must be present in order that the pipe is able to transfer the bulk of the load to the surrounding soil. In other words, the soil, not the pipe, carries and supports most of the live and dead load. Suitable backfill material and adequate compaction are of critical importance – especially below the springline. A well-compacted soil envelope of adequate width is needed to develop the lateral pressures required to maintain the shape of the culvert. The width of the soil envelope is a function of the strength of the surrounding in-situ soil and the size of the pipe. This is achieved by meeting the requirements that are outlined in Section 19-3 of the Standard Specifications for Structure Excavation and Backfill and conforming to the details shown on Standard Plan A62F. Refer to FHWA Culvert Repair Practices Manual Volume 1, pages 2-9 to 2-10 for a description of flexible culvert behavior. Also, refer to Standard Plan D88 for required minimum cover for construction loads on plastic pipes and metal culverts. See Index 2.1.1.1.1 for discussion of structure backfill alternatives. See HDM Topic 856.5 and Table 856.5 for minimum thickness of cover required for design purposes.

2.1.1.2.1 Metal Pipe

For all metal pipes and arches that are listed in Table 857.2A in the HDM, maintenance free service life, with respect to corrosion and abrasion and/or durability, is the number of years from installation until the deterioration reaches the point of perforation at any location on the culvert. This is primarily a function of corrosivity and abrasiveness of the environment into which the pipe is placed. See Figure 855.3A - Minimum Thickness of Metal Pipe for 50 Year Maintenance Free Service Life and Figure 855.3B – Chart for Estimating Years to Perforation of Steel Culverts (California Test 643) in the HDM. Note that the service life estimates referenced in Figures 855.3A and 855.3B, are for various corrosive conditions only, and both these charts require, as a minimum, site-specific pH and minimum resistivity data from District Materials in order to determine the pipe’s corrosion resistant service life. For a detailed discussion of maintenance free service life and durability of metal pipe, refer to Topic 855.1 and 852.4 (2) Durability, in the HDM. For a detailed discussion of corrosion, see Index 5.1.2.4 of this document. For a detailed discussion of metal pipe abrasion see Indices 2.1.4.1 and 5.1.2.2.

The following is a brief summary of the material design step considerations for metal pipe:

1. Metal thickness adequate to support fill height (see HDM Tables 856.3A-P)
2. Use Figures 855.3A and 855.3B to determine the minimum thickness and limitation on the use of steel, aluminum or aluminized steel (corrugated or spiral rib) pipe.
3. Consider Aluminized Steel or Aluminum if applicable
4. Consider Protective Coating using Table 855.2C (knowing channel bedload material and stream velocity) if necessary
5. Increase Metal thickness to offset abrasion effects per Table 855.2D
6. Check material design meets design service life per Topic 855.1(1)

2.1.1.2.2 Plastic Pipe

“Plastic” pipe is as unspecified a term as is “metal” pipe. The two most commonly used plastics are polyvinyl chloride (PVC) and high-density polyethylene (HDPE). The limited data that is available regarding plastic pipe for culvert applications suggests that plastic materials may provide equivalent service life in a potentially broader range of environmental conditions than either metal or concrete. Both PVC and HDPE are unaffected by the chemical and corrosive elements typically found in soils and water. In addition, both types have exhibited excellent abrasive resistance. Plastic pipe materials are also subject to some limiting conditions that often are not a consideration in selecting other culvert types which include: extended exposure to sunlight (specifically ultra-violet radiation) and a higher potential for damage from improper handling and installation. See Index 5.1.4. Plastic is also flammable; PVC will melt/burn under high temperatures but is inherently difficult to ignite and will self-extinguish once the heat source is removed. PVC will become brittle due to temperatures below 37 degrees Farenheit and/or long term exposure to ultra-violet radiation. However, temperature considerations are most important if the pipe is likely to be handled or impacted during periods of low temperatures. HDPE will continue to burn as long as adequate oxygen supply is present.  Based on testing performed by Florida DOT, this rate of burning was fairly slow, and often "burned itself out" if there wasn't sufficient airflow through the pipe. End treatments using metal or concrete (flared end sections or headwalls) will limit the possibility of fire damage.

Per Topic 855 of the HDM, maintenance free service life, with respect to corrosion and abrasion and/or durability, is the number of years from installation until the deterioration reaches the point of perforation at any location on the culvert or at the onset of wall buckling and/or for further discussion on durability and strength requirements. See Section 64 of the Standard Specifications for pipe material, joints, earthwork and concrete backfill requirements. See Index 2.1.1.2 for a general discussion on flexible pipe behavior and excavation and backfill considerations. See Index 6.1.3.1.1 for sliplining using plastic pipe liners. For further discussion on plastic pipe, see Index 5.1.4 and FHWA Culvert Repair Practices Manual Volume 1, pages 2-25 and 2-26.

2.1.1.3 Culvert Coatings

2.1.1.3.1 Coatings for Concrete and other Culverts

As discussed in FHWA Culvert Repair Practices Manual Volume 1, pages 2-28 to 2-30, a variety of coating types may be used either singularly or in combination to protect culverts from corrosion and or abrasion and meet design service life requirements.

Caltrans abrasion test panel installation showing various culvert materials and coatings

Caltrans abrasion test panel installation showing various culvert materials and coatings

Polyvinyl Chloride (PVC) Lined RCP is not listed in the FHWA Culvert Repair Practices Manual. It is primarily used for protection from corrosion, but also provides some sacrificial abrasion resistance to RCP in lieu of additional cover and/or admixtures. PVC Lined RCP uses Polyvinyl Chloride sheet liners that cover three hundred sixty degrees (360°) of the interior surface of the pipe. It was originally designed specifically to protect new concrete sewer pipe against hydrogen sulfide gas/sulfuric acid attack.

Example Polyvinyl Chloride (PVC) Lined RCP using T-Lock Polyvinyl Chloride (PVC) sheet liners manufactured by Ameron Protective Linings Division

Example Polyvinyl Chloride (PVC) Lined RCP using T-Lock TM Polyvinyl Chloride (PVC) sheet liners manufactured by Ameron Protective Linings Division

Designers need to be aware that both the cement in concrete as well as the reinforcing steel in RCP are susceptible to chemical attack and will occasionally need to be protected.  For pH ranging between 7.0 and 3.0 and for sulfate concentrations between 1500 and 15,000 ppm, concrete mix designs conforming to the recommendations given in Table 855.4A of the HDM should be followed.  Higher sulfate concentrations or lower pH values may preclude the use of concrete or would require the designer to develop and specify the application of a complete physical barrier.  Reinforcing steel can be expected to respond to corrosive environments similarly to the steel in CSP.  Referring to Figure 855.3A it is apparent that combinations of pH and minimum resistivity will lead to corrosion of reinforcing steel if water can penetrate through the concrete.  In a similar fashion, waters with high chloride concentrations (e.g., marine environments) can also lead to corrosion of reinforcing steel.  However, properly designed and installed RCP (i.e., minimal cracking due to handling/construction loading) will typically provide adequate concrete coverage over the reinforcing steel to provide protection to the steel, except under extreme conditions.  Contact the District Materials unit or Corrosion Technology in Engineering Services for design recommendations when in extremely corrosive conditions.   Non-Reinforced concrete pipe is not affected by chlorides or stray currents and may be used in lieu of RCP (with additional concrete cover and/or protective coatings) for sizes 36 inches in diameter and smaller. See Table A in Index 2.1.2.2, HDM Table 855.4A, and HDM Index 852.1(4).

2.1.1.3.2 Coatings for Metal Culverts

Coatings for metal culverts are designed to provide either a corrosion barrier (generally covering the entire periphery of the pipe) or a sacrificial layer of abrasive resistant material (generally concentrated in the invert of the pipe). While increasing the pipe’s metal thickness to offset corrosive or abrasive effects can also be specified, coatings are typically more cost effective and should be given first consideration.

HDM Table 855.2C lists all of the plant-applied approved coatings for steel culverts and constitutes a guide for estimating the added service life that can be achieved based upon abrasion resistance characteristics only. Field application of a concrete invert lining or even special abrasion resistant tiles or linings can also be specified to increase service life due to abrasive conditions.

Under most conditions, plain galvanizing of steel pipe is all that need be specified. However, the presence of corrosive or abrasive elements may require the use of various coating products, used either individually or in combination. The Department of Fish and Game (DFG) has approved the use of both polymeric sheet coating and polymerized asphalt; however, DFG will restrict the use of bituminous coatings as discussed in the HDM. It should be noted that polymeric sheet coating was originally developed as a corrosive barrier although it can also provide additional protection from abrasion. Polymerized asphalt should be considered for use when abrasion is present.

Where significant soil side corrosion and abrasion are present, a composite steel spiral rib pipe, which is externally pre-coated with a polymeric sheet, and internally polyethylene lined, may also provide additional service life. Index 854.2 (2) (a) of the HDM discusses these approved protective coatings and their application to protect against corrosion, abrasion, or both. Section 66-1.02C of the Standard Specifications outlines the requirements for the approved coatings.

Determining when a coating is needed, and what type to call for will depend on the results of the materials/geotechnical investigation and an assessment of the corrosive and abrasive potential of the site by the designer. Minimum resistivity; pH; sulfate concentration; type, size and hardness of bedload materials can affect both durability and selection of appropriate coating. In many cases, multiple coating types may be effective and as such the contractor should be given the option of selecting the most cost effective of those that meet minimum service life requirements.

While generally perceived as an alternative pipe product as opposed to a coating, the application of a thin layer of aluminum over steel (i.e., aluminizing) can often be a very effective mechanism to enhance the durability of steel pipe. Per the material design selection considerations listed in Index 2.1.1.2.1, if the channel bedload is non-abrasive, the pH of the soil, backfill, and water is within the range of 5.5 to 8.5, inclusive, and the minimum resistivity is 1500 ohm-centimeters or greater, the use of Aluminized Steel (type 2) should be considered prior to considering alternative coatings or increasing the thickness of the steel. Aluminized steel should be considered to be equivalent to galvanized steel when abrasion is a factor. See Index 852.4 (2) (b) of the HDM.

Where soil side corrosion is the only concern, polymeric coated steel pipe service life should be evaluated using Figure 855.2C (to determine steel thickness necessary to achieve 10-year minimum life of base steel), with the assumption that the (exterior) polymeric coating will provide additional protection to attain the 50-year service life requirement.

For locations where water side corrosion and/or abrasion is of concern, recently developed coating products, like polymerized asphalt, polymeric sheet, and polyethylene can provide superior abrasive resistant qualities (as much as 10 or more times that of bituminous coatings of similar thickness).

2.1.2 Service Life for Culvert Rehabilitation; Geotechnical Factors

Generally, for culvert rehabilitation, the design service life basic concepts are the same as those defined in Index 855.1 of the HDM. Plastic pipe liners should be considered the same as plastic pipe with no additional service life added for annular space grouting. The estimated design service life for rehabilitation projects should be the same as indicated in Index 855.1 (1) of the HDM.

Regardless of the method or material selected to repair, rehabilitate or replace the culvert, the following influences must be assessed during any estimation of service life:

2.1.2.1 Hydrogen-Ion Concentration (pH), Soil Resistivity, Chloride and Sulfate Concentration of the surrounding Soil and Water: Both concrete and metal pipes can be subject to corrosion attack. In reinforced concrete culverts, a high sulfate concentration will cause the cement to deteriorate whereas the reinforcing steel can be corroded if there is a low pH or high chloride concentration. See Indices 2.1.1.3.1 and 2.1.1.3.2, Table A in Index 2.1.2.2, Table 855.3A and Figure 855.4A of the HDM.

2.1.2.2 Material Characteristics of the Culvert: a careful determination of geotechnical factors at the Culvert site should be made to assure proper material selection for any repair or restoration. Table A suggests limitations and potentials for culvert materials.

Table A

Material
Acceptable
pH range

Resistivity
Level (ohm-cm)

Abrasion Potential

Chloride/Sulfate resistance

Steel
See HDM Table 855.3 A
See HDM Table 855.3A
Low 3
See footnote 5
Aluminum
5.5-8.5 1
>1500 1
Varies 1
See footnote 5
Plastic
>4 6
NA
Generally Low 6
NA
Concrete
>3 2
NA

Low to High 4
Sulfates 2
Polymer Mortar
1-13
NA
Generally Low
NA


1. Aluminum corrodes differently than steel and is not susceptible to corrosion attack within the acceptable pH range of 5.5-8.5 when considering abrasion potential.  See HDM Index 852.5(2)(a) thru (e), abrasion potential dependent upon, velocity, size, shape and hardness of bedload, i.e., velocities > 5 ft/s only allowable for a small, rounded bedload.

2. See HDM Table 855.4A for recommended cement type and minimum cement factor when pH range is 3 to 5.5.

3. Assuming zinc galvanizing is present and base steel not exposed to corrosion attack.

4. Abrasion potential for concrete is dependent upon the quality, strength, and hardness of the aggregate and density of the concrete as well as the velocity of the water flow coupled with abrasive sediment content. There is a correlation between decreasing water/cement ratio, increasing compressive strength and increasing abrasion resistance.

5. Chlorides and sulfates combined with moist conditions may create a hostile corrosive environment. Minimum resistivity indicates the relative quantity of soluble chlorides and sulfates present in the soil or water. See HDM Figure 855.3A.

6. PVC may experience greater abrasive wear in an acidic environment.


2.1.2.3 Abrasion: Abrasion is the wearing away of pipe material by water carrying sands, gravels and rocks (bed load) and is dependent upon size, shape, hardness and volume of bed load in conjunction with volume, velocity, duration and frequency of stream flow in the culvert. For example, at independent sites with a similar velocity range, bedloads consisting of small and round particles will have a lower abrasion potential than those with large and angular particles such as shattered or crushed rocks. Given different sites with similar flow velocities and particle size, studies have shown the angularity of the material may have a significant impact to the abrasion potential of the site. All types of pipe material are subject to abrasion and can experience structural failure around the pipe invert if not adequately protected. Four abrasion levels have been developed by FHWA to assist the designer in quantifying the abrasion potential of a site. The abrasion levels in Table 855.2C of the HDM for abrasive resistant protective coatings needed for metal pipe, use the same four abrasion levels that have been developed by FHWA. The abrasion levels and recommended pipe/invert materials that are presented in the summary table at the end of this section are generally the same as the four abrasion levels that have been developed by FHWA, however, some modifications have been made based on research data. The descriptions of abrasion levels are intended to serve as general guidance only, and not all of the criteria listed for a particular abrasion level need to be present to justify defining a site at that level. Included with each abrasion level description are guidelines for providing an abrasive resistant pipe, coating or invert lining material. The designer is encouraged to use those guidelines in conjunction with the abrasion history of a site to achieve the required service life (see Index 2.1.2) for a pipe, coating or invert lining material.

Sampling of the streambed materials is generally not necessary, but visual examination and documentation of the size and shape of the materials in the streambed and the average stream slopes will give the designer guidance on the expected level of abrasion. Where an existing culvert is in place, the condition of the invert should also be used as guidance.

The stream velocity should be based on typical intermittent flows and not a 10 or 50-year event. This is because most of the total abrasion will occur during these more frequent smaller events. For velocity determination of typical intermittent flow, the velocities in the table at the end of this section (and Table 855.2C of the HDM) should be compared to those generated by the 2-5 year return frequency flood.

Corrugated steel pipes are typically the most susceptible to the combined actions of abrasion in conjunction with corrosion – this has led to a wide range of protective coatings being offered. However, steel plate is a viable alternative for use as an invert lining. See Index 5.1.2.2 for abrasion and invert durability repairs of corrugated metal culverts.

Aluminum may display inferior abrasion characteristics than steel in non-corrosive environments, however, Aluminized Steel (Type 2) can be considered equivalent to galvanized steel for abrasion resistance. Furthermore, in some cases, Aluminum may display less abrasive wear than steel in a corrosive environment depending on the volume, velocity, size, shape, hardness and rock impact energy of the bed load.

Polymer Mortar, fiber reinforced plastic and other resin-based products such as Cured in Place Pipe (CIPP) offer good abrasion resistance and are not subject to corrosion effects. The same can be said for PVC and particularly HDPE; however, PVC may experience greater abrasive wear in an acidic environment (pH < 4).

Concrete pipes will counter abrasion through increased minimum thickness over the steel reinforcement, i.e., by adding additional sacrificial material. Abrasion potential for any concrete lining is dependent upon the quality, strength, and hardness of the aggregate and density of the concrete as well as the velocity of the water flow coupled with abrasive sediment content and acidity (see HDM Table 855.4A). There is a correlation between decreasing water/cement ratio, increasing compressive strength and increasing abrasion resistance. For further discussion on concrete invert paving, see Index 5.1.2.2.1.

Various culvert material test panels after 1 year of wear at site with moderate to severe abrasion

Various culvert material test panels shown above after 1 year of wear at site with moderate to severe abrasion (velocities generally exceed 10 ft/s, see table next page). Note the significant wear to abrasive resistant protective coatings, which, would typically not be recommended under these conditions (see table next page). The bed load material composed of 90% quartz sand. Also note the wear on the leading edges (right) of the steel nuts.

As discussed on the previous page, there are multiple factors that should be considered when attempting to estimate the abrasion potential of a site and associated service life of a culvert and/or lining material (size, shape, hardness and volume of bed load, in conjunction with volume, velocity, duration and frequency of stream flow in the culvert).

HDM Table 855.2A "Abrasion Levels and Materials" can be used as a “preliminary estimator” of abrasion potential for material selection to achieve the required service life (see Index 2.1.2), however, it uses only two of the factors that are outlined above; bed load size and flow velocity. As discussed above, the other factors that are not used in the table should also be carefully considered. For example, under similar hydraulic conditions, heavy volumes of hard, angular sand (see photo in Index 5.1.2.2) may be more abrasive than small volumes of relatively soft, large rocks. Furthermore, two sites with similar site characteristics, but different hydrologic characteristics, i.e., volume, duration and frequency of stream flow in the culvert), will probably also have different abrasion levels. See HDM Topic 855.2 for more comprehensive design guidance.

 



This page last updated August 20, 2011