California Department of Transportation
 

DIB 83-02 - 6.1 General Culvert Barrel Rehabilitation Techniques

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

         
6.1 GENERAL CULVERT BARREL REHABILITATION TECHNIQUES
  6.1.1 Caltrans Host Pipe Structural Philosophy
  6.1.2 Grouting Voids in Soil Envelope
  6.1.3 Rehabilitation Families
    6.1.3.1 Sliplining (General)
      6.1.3.1.1 Sliplining using Plastic Pipe Liners
        6.1.3.1.1.1 Allowable Types of Plastic Liners
        6.1.3.1.1.2 Strength requirements
        6.1.3.1.1.3 Pipe Dimensions
        6.1.3.1.1.4 Grouting
        6.1.3.1.1.5 Joints
        6.1.3.1.1.6 Installation
        6.1.3.1.1.7 Other Considerations
    6.1.3.2 Lining with Cured-In-Place pipes
    6.1.3.3 Lining with Folded and Re-Formed PVC Liner (Fold and Form)
    6.1.3.4 Lining with Deformed-Reformed HDPE Liner
    6.1.3.5 Lining with Machine Wound PVC Liner
    6.1.3.6 Sprayed Coatings
      6.1.3.6.1 Air Placed Concrete & Epoxy or Polyurethane Lining for Drainage Structures
      6.1.3.6.2 Cement Mortar Lining
    6.1.3.7 Man-Entry Lining with Pipe Segments
      6.1.3.7.1 Fiberglass Reinforced Cement (FRC)
      6.1.3.7.2 Fiberglass Reinforced Plastic (FRP)
    6.1.3.8 Other Techniques

6.1 GENERAL CULVERT BARREL REHABILITATION TECHNIQUES

6.1.1 Caltrans Host Pipe Structural Philosophy

In general, if the host pipe cannot be made capable of sustaining design loads, it should be replaced rather than rehabilitated. This is a conservative approach and when followed eliminates the need to make detailed evaluations of the liners ability to effectively accept and support dead and live loads. Prior to making the decision whether or not to rehabilitate the culvert and/or which method to choose, a determination of the structural integrity of the host pipe must be made. See Index 2.1 of this D.I.B. for a discussion on loading, bedding and behavior of flexible and rigid pipe. Existing voids within the culvert backfill or in the base material under the existing culvert should be filled with grout to re-establish its load carrying capability prior to rehabilitating any type of culvert (see Index 6.1.2 below).

Also, see Index 11.1.1 for a discussion on supporting the roadway and traffic loads.

Other entities have adopted procedures for assigning structural capacity to liners. While this is presently not Caltrans practice, under unique circumstances, or where extraordinary costs for rehabilitation are likely, it is recommended that the designer consult with the Headquarters Office of Highway Drainage Design within the Division of Design to determine if consideration of these alternative analysis methods is justified.

6.1.2 Grouting Voids in Soil Envelope

External grouting is the introduction of a chemical or Portland cement based grout (possibly with special admixtures including polymer resins) into void space or areas of loose soil directly behind or beneath a culvert. This discussion will focus on grouting, see Index 11.1.1 for a more detailed discussion on voids. Grouting may be accomplished from the inside of the culvert through prepared grout holes in the culvert wall or from grout tubes drilled through the fill. See Index 5.1.1.1.3 for a discussion on grout types.

There are basically three alternative procedures for grouting voids behind the culvert as described in FHWA Culvert Repair Practices Manual Volume 2, Appendix B-30, page B-135:

  • Gravity flow from above the void
  • Gravity flow through a tremie pipe or tube (from bottom up)
  • Pressure grouting (see below)

The above-referenced description for Pressure Grouting refers to a low-pressure method for grouting voids directly behind the sides of culvert and is the same as the Caltrans method called “Contact Grouting”. Voids or loose soils not immediately adjacent to the culvert (i.e., beyond about 12 inches) that developed through infiltration of fines into the culvert may indicate more serious problems affecting the roadway prism that will need to be addressed with other grouting methods. See Indices 11.1.1 and 11.1.2, for discussions on supporting roadway and traffic loads and compaction grouting. Also refer to Index 7.1.6.3 for guidance on Coordination with Geotechnical Design.

For bidding purposes, contract plans should include these details:

General site conditions, access, end treatments, (profiles and grade), staging, voids, special situations, restrictions, etc. The Geotechnical Engineer should be contacted for material selection items for filling voids in the backfill. See Index 7.1.6.3.

6.1.3 Rehabilitation Families

See HDM Index 853.4 "Alternative Pipe Lining Materials."

6.1.3.1 Sliplining (General)

Refer to FHWA Culvert Repair Practices Manual Volume 1, pages 6-23 through 6-29.

Note: Caltrans host pipe structural philosophy in Index 6.1.1 is intended to supersede any discussion by FHWA for restoring structural strength with slipliners. A major deficiency in sliplining may be an ultimate lack of soil-structure interaction. For flexible pipe, this is a crucial physical characteristic, which directly relates to the structural integrity of the pipe. Therefore, thorough grouting of the space between the culverts should be specified for construction.

Rehabilitation of culverts with slipliners is one of several methods available for extending the life of an existing culvert. Sliplining is not suitable for all situations. Prior to any proposal to rehabilitate a culvert with a pipe liner a thorough examination of the existing culvert and consultation with the District Hydraulics Unit to discuss possible alternatives and cost effective solutions must be performed.

Sliplining consists of sliding a new culvert inside an existing distressed culvert as an alternative to total replacement. This method is much faster to complete than a remove and replace option and often will yield a significant extension of service life at less cost than complete replacement, particularly where there are deep fills or where trenching would cause extensive traffic disruptions.

When choosing the material for a culvert liner, consideration should be given to the environment and the physical needs of the installation including handling and weight of the liner and construction footprint. In some cases, a smoother culvert material will offset the reduction in culvert diameter. The adequacy of outfall protection should be evaluated when the culvert liner results in higher discharge velocities.

Selection of the appropriate liner material should take into account the reasons and mode of failure of the existing pipe.  High-density polyethylene and polyvinyl chloride pipes in both solid wall and ribbed profiles have become common materials for sliplining culverts, particularly in diameters up to 72 inches and are discussed in detail in this section.  However, for any plastic liner or slipliner, if the diameter exceeds 60 inches, headquarters approval will be required. See Index 7.1.6.1.

Corrugated metal pipes are sometimes used for larger diameter sliplining projects. See Index 7.1.7 for maximum push distance for large diameter flexible pipe liners and Appendix H, which includes a CMP sliplining example. Liner pipes with smooth exteriors usually will allow for easier insertion, particularly if the culvert being rehabilitated has a corrugated profile. Almost any type of culvert can be sliplined with an appropriately sized commercially available pipe. See ‘Products’ on pages 6-25 and 6-26 of FHWA Culvert Repair Practices Manual Volume 1. Note that some of the products described on page 6-26 under plastic pipe (Nu-Pipe and U-Liner) belong under the Fold and Form family rather than sliplining and are described elsewhere in this document. Not listed, but also a viable alternative, is fiber reinforced polymer mortar (RPMP), or fiber reinforced polymer concrete (FRPC), which is about a third of the weight per foot of precast RCP. FRPC can be manufactured in "short sections" (2-3 foot lengths) for use in curves that can accommodate a 1-1.5 degree deflection angle at each joint. Alternatively, if needed, beveled sections can be customized. Either way, at curves the short sections are placed by bobcat or pulled through the curves and then installed with a winch. See FHWA Culvert Repair Practices Manual Volume 1, page 2-27 and Index 2.1.1.1.3.1. Other viable materials for sliplining may include: fiber reinforced concrete pipe (FRCP), Polyester Resin Concrete (PRC) pipe, fiber reinforced plastic (FRP), ductile iron and welded steel. See Indices- 2.1.1.1.3.2-5.

Inserting a PVC slipliner
Inserting a PVC slipliner

Prior to sliplining, the existing culvert must be surveyed carefully to determine the maximum diameter of culvert that can be inserted through the entire length of the host pipe. Any deflections in the culvert walls will become control points and any alignment changes coupled with deflections can reduce the slipliner diameter significantly. Major deflections may indicate the need for other rehabilitation techniques. It may be necessary to install rails on which to slide the liner culvert.

Once stream diversion methods are in place and the work area is stabilized, the liner pipe is moved into the culvert either one section at a time or as an entire unit. All water and debris must be removed from the existing pipe prior to grouting.  The liner is pushed with jacks or machinery such as a backhoe.  When the liner is in place, the space between the culverts generally must be grouted to prevent seepage and soil migration and to establish a connection between the liner, the host pipe and the soil thus providing uniform support and eliminating point loads.  Grout may be either gravity fed into the annular space between the liner and the existing culvert or pumped through a hose or small diameter pipe (1-1/2”- 2 inch PVC) laid in the annular space.  When the lining is fairly long (100 feet or more), gravity feeding of grout will be difficult unless additional openings in the top of the existing culvert are made for intermediate insertion of the grout.  When grout is pumped, the small pipe or hose is typically removed as the space is gradually filled.  When this is difficult due to field conditions, the small pipe or hose may be banded to the liner with "tees" placed a 5 ft intervals.

To avoid floating of the liner and ensure a uniform grout thickness around the liner pipe, the grout should be placed in lifts. Each lift of grout should be allowed to set before continuing further up the culvert walls. Alternatively, the liner can be plugged at the ends and filled with water to prevent floating during the grouting operation, or blocks can be used (at least two sets per pipe section) to effectively rest between the liner and the existing culvert.


PVC lined storm drain with grout tube at upper right and drain tube at bottom
PVC lined storm drain with grout tube at upper right and drain tube at bottom

The grouting process will apply pressure to the liner pipe. Minimum liner pipe stiffness must be selected such that the pipe strength exceeds the maximum specified grouting pressure. See Index 6.1.3.1.1.4 for grouting plastic pipe slipliners.

In accordance with the specifications, the contractor will be required to perform a test on each type of grout and grout system proposed and shall submit a grouting plan to the Engineer.

Each project will have its own unique site-specific conditions that will require a unique grouting plan for that site. The pipe length and slope are directly related to grouting pressure and the plan must outline the proposed grouting method and procedures to stay below the maximum grouting pressure. Most grouting work will be sub-contacted and the quality of grouting contractors can vary considerably. For quality assurance purposes it is recommended that the following list of submittals and calculations required by the grouting sub-contractor should be forwarded by the Project Engineer and included within the Resident Engineer file:

1) The proposed grouting mix
2) The proposed grout densities and viscosity
3) Initial set time of the grout
4) The 24-hour and 28-day minimum grout compressive strengths
5) The grout working time before a 15 percent change in density or viscosity occurs
6) The proposed grouting method and procedures
7) The maximum injection pressures
8) Proposed grout stage volumes (e.g., Stage 1, to spring line; Stage 2, fully grouted)
9) Bulkhead designs and locations
10) Buoyant force calculations during grouting
11) Flow control
12) Provisions for re-establishment of service connections
13) Pressure gauge, recorder, and field equipment certifications (e.g., calibration by an approved certified lab)
14) Vent location plans
15) Written confirmation that the Contractor has coordinated grouting procedures with the grout installer and the liner pipe manufacturer

Data for 1) through 5) shall be derived from trial grout batches by an approved, independent testing laboratory.

For each different type of grout or variation in procedure or installation, a complete package shall be submitted. The submittal shall include each of the above items and the sewer locations or conditions to which it applies. The Contractor shall obtain approval from the Engineer for any changes to be made in grout mix, grouting procedure, or installation prior to commencement of grouting operations.

For further general information on the procedures for sliplining culverts, refer to FHWA Culvert Repair Practices Manual Volume 2, Appendix B-39, page B-174.

6.1.3.1.1 Sliplining using Plastic Pipe Liners

The following information is intended to provide design guidance regarding the rehabilitation of existing pipe culverts with plastic pipe liners. Indices 6.1.3.1.1.1 through 6.1.3.1.1.7 below, supersede DIB No. 76 dated January 1, 1995.

6.1.3.1.1.1 Allowable Types of Plastic Liners

Plastic pipe made of polyvinyl chloride (PVC) and high-density polyethylene (HDPE) is commercially available in a variety of diameters and styles that are adequate for the purpose of relining existing culverts. Any plastic culvert that is discussed in Section 64 of the Caltrans Standard Specifications will perform adequately. In addition, many types of solid wall, profile wall and ribbed PVC and HDPE are manufactured that are also capable of performing the necessary function. No attempt is made to list every type of plastic pipe that could be used. The following information describes some of the most likely alternatives that are readily available.

The most economical types currently manufactured are SDR 35 PVC sewer pipe (AASHTO M-278), PVC ribbed pipe (AASHTO M-304), Type C (corrugated interior) and Type S (smooth interior) corrugated HDPE (AASHTO M-294). HDPE solid wall fusion welded or Snap-TiteTM (ASTM F-714) is relatively expensive but has a variety of diameters and wall thicknesses. HDPE solid wall pipe is listed by Standard Dimension Ratio (SDR) classification (Standard Dimension Ratio given by the ratio of outside diameter to wall thickness with the lower SDR's having thicker walls). Also available is PVC profile wall sewer pipe (ASTM F-794 and F-949). Also relatively expensive, this smooth interior and smooth exterior pipe (closed profile) with an internal rib can be easier to install than other types and does not require couplers, belling, or other connectors that would increase the pipe diameter at the joints. Several pipe products are made specifically for sliplining with joint systems designed to maintain a constant outside and inside diameter. Some examples of these are the Contech A2 Liner PipeTM (PVC), the Vylon PVC Slipliner PipeTM, and the WeholiteTM Culvert Reline System (HDPE).

6.1.3.1.1.2 Strength Requirements

Pipe used as a liner will not typically be subjected to the degree of loading experienced by the original culvert (see Caltrans host pipe structural philosophy). In most cases, although the invert of the original culvert has deteriorated, the load carrying capacity has not been significantly diminished. As a result, strength requirements of liner pipe are more dependent on a determination of potential grouting pressures and the need for the liner pipe to withstand handling and installation stresses.

Pipe stiffness is a common term used in describing plastic pipe's resistance to deflection prior to placing any backfill. The higher the number, the stiffer the pipe, and the better the pipe's resistance to grouting pressure and handling.

The following table lists minimum pipe stiffness in PSI.  Testing for pipe stiffness is performed in accordance with ASTM D-2412:

Nominal
PVC*
PVC
PVC*
HDPE
HDPE Solid Wall (SDR)
Dia.(in)
SDR-35
Ribbed
Profile
Type S
15.5
17
21
26
32.5

15

46

NA

46

42

NA

NA

NA

NA

NA

16

46

NA

NA

NA

86

71

22

11

6

18

46

32

46

40

86

71

22

11

6

20

NA

NA

NA

NA

86

71

22

11

6

21

46

28

46

NA

86

71

22

11

6

21.2

NA

NA

NA

NA

86

71

22

11

6

24

46

24

46

34

86

71

22

11

6

27

46

22

46

31

86

71

22

11

6

30

NA

19

46

28

86

71

22

11

6

33

NA

NA

NA

25

NA

NA

NA

NA

NA

34

NA

NA

NA

NA

NA

71

22

11

6

36

NA

166

46

2

NA

71

22

11

6

39

NA

NA

NA

NA

NA

NA

NA

NA

NA

42

NA

14

46

20

NA

NA

NA

11

6

45

NA

NA

NA

NA

NA

NA

NA

NA

NA

48

NA

12

46

18

NA

NA

NA

11

6

54

NA

NA

46

NA

55

NA

NA

NA

NA

60

NA

NA

46

14

63

NA

NA

NA

NA

*No Caltrans Standards

6.1.3.1.1.3 Pipe Dimensions

When determining the appropriateness of relining an existing culvert, an assessment of the discharge capacity of the liner must be made to verify that the liner pipe, due to its smaller diameter than the existing culvert, will allow the design discharge to be passed. To make this assessment, selection of the liner must consider the effect on the liner diameter due to liner wall thickness and, in particular, the space requirements of the liner joints. This maximum exterior dimension of the liner must be able to be inserted through the existing culvert, while also considering deformations in the existing culvert, minor culvert bends, and any other disturbances in the bore of the existing pipe. These considerations make it imperative that the designer obtains accurate field measurements of the existing culvert to determine the minimum available clearance prior to selecting liner types and diameters. A good rule of thumb for sizing the liner is to select a liner diameter that is 20% less than the diameter of the host pipe. Be aware that manufacturers occasionally delete existing products and often bring new products to the market. Contact with industry representatives is encouraged to verify the availability of any products that will be specified.

The following tables provide industry-supplied pipe inside and outside diameters. Dimensions will vary somewhat between different manufacturers and must be verified prior to being specified. Also see FHWA Culvert Repair Practices Manual Volume 2, pages A-40 to A47.

PVC SDR 35 PIPE DIMENSIONS
(AASHTO M 278* and ASTM F 679)

Nominal Dia.
(in)

Min. Average Inside Dia.
(in)

Average Outside Dia.
(w/o bell)** (in)

15*

14.42

15.30

18

17.63

18.70

21

20.78

22.05

24

23.38

24.80

27

26.35

27.95

30

29.69

31.50

33

33.40

35.43

36

37.11

39.37

42

41.95

44.50

48

47.89

50.80

  *   AASTO M278 applies to nominal sizes of 15” or smaller
  ** Tolerance on Average Outside Diameter varies from +/- 0.028 in to +/- 0.075 in

 

PVC RIBBED PIPE DIMENSIONS
(AASHTO M 304)

Nominal Dia.
(in)

Min. Average Inside Dia.*
(in)

Outside Dia. (Inc. Joint)**
(in)

18

17.51

20.88

20

20.66

24.16

24

23.41

27.38

27

26.37

30.80

30

29.39

34.08

36

35.37

40.67

42

41.37

46.24

48

47.36

52.61

  *    Tolerance on inside diameter is + 2 percent, but not to exceed 0.5 in
   **  Outside dimension may vary from manufacture example shown here

 

HDPE TYPE S PIPE DIMENSIONS
(AASHTO M 294)

Nominal Dia.
(in)

Average Inside Dia.*
(in)

Average Outside Dia.
(in)

15

14.98

17.57

18

18.07

21.20

24

24.08

27.80

30

30.00

35.10

36

36.00

41.70

42

41.40

47.70

48

47.60

53.60

60

59.50

66.30

  *    Tolerance on inside diameter is +4.5 percent (but not more than 1.5 inches) and – 1.5 percent


HDPE SDR PIPE DIMENSIONS
(ASTM F 714)
Minimum Wall Thickness (in)

Nom. Dia

Avg. OD

SDR 32.5

SDR 26

SDR 21

SDR 17

16

16

0.492

0.615

0.762

0.941

18

18

0.554

0.692

0.857

1.059

20

20

0.615

0.769

0.952

1.176

22

22

0.677

0.846

1.048

1294

24

24

0.738

0.923

1.143

1.412

26

26

0.800

1.000

1.238

1.529

28

28

0.862

1.077

1.333

1.647

30

30

0.923

1.154

1.429

1.765

32M

31.594

0.969

1.213

1.500

1.854

32

32

0.985

1.231

1.524

1.882

34

34

1.046

1.308

1.619

2.000

36

36

1.108

1.385

1.715

2.117

40M

39.469

1.213

1.516

1.874

2.315

42

42

1.292

1.615

2.000

2.471

48M

47.382

1.453

1.819

2.246

2.780

48

48

1.477

1.846

2.286

2.824

54

54

1.662

2.077

2.571

3.176

55M

55.295

1.697

1.118

2.626

3.244

63M

63.209

1.987

2.421

3.000

 

 

HDPE SDR PIPE DIMENSIONS (Continued)
(ASTM F 714)
Minimum Wall Thickness (in)

Nom. Dia

Avg. OD

SDR 15.5

SDR 13.5

SDR 11

16

16

1.032

1.185

1.455

18

18

1.161

1.333

1.636

20

20

1.290

1.481

1.818

22

22

1.419

1.630

2.000

24

24

1.548

1.778

2.182

26

26

1.677

1.926

2.364

28

28

1.806

2.074

2.545

30

30

1.935

2.222

2.727

32M

31.594

2.031

-

-

32

32

2.065

2.370

2.909

34

34

2.194

2.519

3.091

36

36

2.323

2.667

3.273

42

42

2.710

3.111

-

48

48

3.097

-

-

 

PVC CLOSED PROFILE WALL PIPE DIMENSIONS
(ASTM F 1803 and ASTM  F 794 (Series 46))

Nominal Dia.
(in)

Min. Inside Dia. *
(in)

Outside Dia. **
(in)

18

17.60

NA

21

20.69

22.68

24

23.43

25.43

27

26.42

28.43

30

29.41

31.43

32

32.41

33.43

36

35.40

37.93

39

38.39

NA

42

41.38

44.38

45

44.37

NA

48

47.36

50.78

54

53.35

57.13

60

59.34

NA

  *    Tolerance on Minimum Inside Diameter varies from + 0.11 in to + 0.32 in per ASTM F 1803
  **   Vylon Slipliner outside diameter example shown, dimensions may vary from manufacture example shown

 

PVC CORRUGATED - SMOOTH INTERIOR PROFILE WALL PIPE DIMENSIONS
(ASTM F 949 and ASTM F 794 (Series 46))

Nominal Dia.
(in)

Average Inside Dia. *
(in)

Outside Dia. **
(in)

12

11.72

12.80

15

14.34

15.66

18

17.55

19.15

21

20.71

22.63

24

23.47

25.58

27

26.44

28.86

30

29.47

32.15

36

35.48

38.74

***42

41.37

-

***45

44.37

-

***48

47.36

-

  *    Tolerance on Average Inside Diameter varies from to +/- 0.028 in to +/- 0.105
  **   For slipliners without bell, tolerance on Average Outside Diameter varies from to +/- 0.018 in to +/- 0.079 in from dimensions shown per ASTM F 949
  ***  Minimum inside tolerance varies from + 0.255 in. to  + 0.285 per ASTM F 794. Minimum outside diameter controlled controlled by bell not shown.

6.1.3.1.1.4 Grouting

See Index 6.1.3.1 for general grouting considerations, contractor submittals, grouting plan, and quality control.

Unless site constraints make it infeasible, full length grouting of the liner is recommended. This not only provides a more secure attachment to the existing culvert, but also reduces the potential for joint leakage to create piping problems. Although generally not a concern, it also provides additional strength if there is deterioration of the existing culvert, particularly where fill heights exceed currently recommended values for plastic culverts.

The grout should be a low-density foam concrete consisting of Portland cement, fly ash and additives. This type of mix should allow the grout to flow easily and completely fill the entire annular space around the liner pipe (see below).

Grouting of annular space between inserted pipe and culvert.
Grouting of annular space between inserted pipe and culvert.

Grouting pressure resistance of the liner varies with pipe stiffness. The gauged pumping pressure shall not exceed the liner pipe manufacturer's approved recommendations or the values shown below:

HDPE Solid-Wall:

SDR

Maximum Safe Annular Grouting Pressure
(psi)

32.5

4

26

8

21

16

19

21

15.5

36

Maximum safe annular grouting pressure (psi) for other materials:

  • Divide minimum pipe stiffness shown in Index 6.1.3.1.1.2 by 4.5
  • Centrifugally cast glass fiber reinforced polymer mortar (RPMP): 6 psi or pipe stiffness divided by 3
  • Divide minimum pipe stiffness by 4.5 for CMP and Fiber Reinforced Plastic

Verification must be made that the joint type specified is also able to withstand anticipated grouting pressures.

6.1.3.1.1.5 Joints

In general, joints in pipes used for slipliners will not be subjected to the same performance requirements, as are joints in direct burial applications.  The encasement provided by both the host pipe and the annular space grouting will typically isolate slipliner pipe joints from problems associated with infiltration/exfiltration, separation or misalignment.  What is important is an understanding of the physical dimensions of various pipe joints (see tables in Index 6.1.3.1.1.3) to ensure that there is adequate space to both insert the liner pipe and feed in the annular space grout (at least 1 inch of space on all sides is desirable), and to ensure that the joint is sufficiently tight to preclude migration of grout through the joint during the annular space grouting operation (which may have operating pressures of several psi).  At a minimum, joints described as soil tight in Index 853.1(3) of the HDM should be specified, and where it is anticipated that grouting pressures are likely to exceed 4 psi, joints meeting watertight requirements should be considered.

Several manufacturers have developed modified joints for their pipes specifically for sliplining applications. This generally is accomplished by routing out male and female ends of the pipes and eliminating the bell end. As such, the increased external dimension of the bell is eliminated, minimizing the loss of host pipe cross sectional area. Several of these specially modified pipes are available in both PVC and HDPE. Some examples are given in Index 6.1.3.1.1.1. To date, however, one of the most commonly used plastic slipliners is solid wall HDPE. The sections of this pipe are most typically "joined" via a fusion welding machine which results in a continuous pipe structure with no change in inside or outside dimension at the locations where pipe segments are fused. Butt fusion procedures for solid wall HDPE are described in Appendix A.

Also to be considered in specifying the type of pipe, and its attendant type of joint, is the likely method of insertion of the liner into the host pipe being rehabilitated. Most plastic joints used in sliplining applications have little to no ability to resist tensile forces. As such, they must be pushed, or jacked through the pipe being rehabilitated. Only fusion welded joints and some of the types with routed ends with overlapping tabs will allow a combination of pushing and pulling the liner through the host pipe. The need to also be able to pull as well as push can be important where very long (or heavy) segments are being inserted, or where deflections, discontinuities or angle points in the host pipe increase the force needed to bring the liner into place.

6.1.3.1.1.6 Installation

Prior to insertion of the liner pipe, the existing culvert must be cleaned of all debris either by flushing or manual removal. Any rust or spalls must be cleaned and removed as well as protrusions into the pipe.

A jacking pit must be constructed with adequate size to contain lengths of pipe to be inserted, grouting equipment and any other equipment necessary to perform the insertion. The liner is normally pushed into the existing culvert, but occasionally it is pulled, or a combination of pulling and pushing is used. Due to the often-large pressure load needed to push the last sections of a long or heavy liner into place, pulling may be the preferred method as long as adequate provisions have been made to avoid joint separation.

Illustration of Pull and Push insertion technique

The difficulty encountered in inserting the liner will be primarily dependent upon the roughness of the existing culvert (either corrugations, other protrusions, or minor displacements) and the type of exterior on the liner. Corrugated or ribbed liners will be the most difficult to insert, particularly if the existing culvert is also corrugated, corroded, and/or distorted.

6.1.3.1.1.7 Other Considerations

1. For any plastic slipliner, if the liner diameter exceeds 60 inches, headquarters approval will be required. See Index 7.1.6.1.

2. PVC pipe as typically manufactured will become brittle and experience a significant reduction in impact resistance due to freezing temperatures and/or long-term exposure to ultra-violet radiation. Therefore, ends of completed installations should not be exposed if they would be subject to very low temperatures or direct sunlight. Temperature considerations are only important if the pipe is likely to be handled or impacted (falling rocks/debris or maintenance equipment) during periods of low temperatures.

3. Ribbed PVC must be protected from rib cracking/breaking during handling and installation. This may be of particular concern if skids or other devices are not used to help slide the liner into place in an existing corrugated culvert.

4. Design discharge for the liner must be evaluated with consideration of conditions that may have changed since the original culvert was placed. It is incorrect to assume that if a liner will pass the discharge for which the existing culvert was designed that all design requirements have been met.

5. The nominal pipe diameters given in the tables in Index 6.1.3.1.1.3 reflect nominal U.S. customary unit designations for current round pipe sizes.  It is imperative that designers use the most current information available from manufacturers when specifying products in order to know the exact dimensions of pipe products that will be delivered to the job site.

6.1.3.2 Lining with Cured-In-Place Pipes

Cured-in-place-pipe (CIPP) is a method of complete culvert relining employing a thermosetting, resin-impregnated flexible tube either;

a) Inverted in place using water or compressed air, or
b) Pulled in place with a winch.

The lining does not come in standard sizes, but is designed specifically for the individual pipeline to be rehabilitated, with variable diameters/shapes (i.e., round, elliptical, oval, etc.) and wall thickness. When necessary, a minimum thickness of the liner can be specified to provide additional service life for abrasive conditions. No grouting is required, and there is no annular space between the host pipe and liner. Historically, the most common application of this method has been in small diameter (less than 48 inches) storm drains and sanitary sewers, although larger sizes have also been successfully rehabilitated.  Concrete culverts subject to sulfate attack are especially good candidates for this repair method or metal pipes where the reduction in diameter using other lining methods is not acceptable. CIPP is quite resistant to abrasion from bedload with small particle sizes.

For the pulled in place installation method, a winched cable is placed inside the existing pipe. The resin-impregnated liner is connected to the free end of the cable and then pulled into place between drainage structures or culvert ends. The cable is disconnected, the ends are plugged and the liner is inflated and cured with hot water or steam.

For the inversion process, manufacturers use a number of different systems to insert the tube. This method generally consists of inserting a polyester felt tube, saturated with a liquid thermosetting resin material, into the culvert. The tube is inserted inside out (inverted) and filled with water or compressed air. During inversion the lining tube turns inside out and travels down the pipeline resulting in the plastic outer sleeve surface becoming the inner surface of the repaired pipe with the resin system being in contact with the pipeline. Pressure inside the inverted tube, due to the water or compressed air, presses the resin-impregnated tube against the carrier pipe wall. Once the tube has reached the far end of the pipe section under repair, either heated water or steam is fed into the inverted tube to cure the thermosetting resin.


Typical inversion tube insertion process


Inserting polyester felt tube, saturated with a liquid thermosetting resin material, into manhole

Inserting polyester felt tube, saturated with a liquid
thermosetting resin material, into manhole

If water is used for curing, it must be heated continually and circulated during the curing process. The application of heat hardens the resin after a few hours, forming a jointless pipe-within-a-pipe. Once set, remote controlled cutters are used to reinstate junctions and laterals.  Any stream flow must be diverted during construction.  Additionally a water source to fill the tube must be accessible to the site when water is used for inversion and curing.

The maximum length of pipe run that can be rehabilitated in this manner will vary with diameter, but over 400 feet is not uncommon. Due to potential environmental concerns including the capture and disposal of hot and possibly styrene-contaminated process water, using this lining method with heated water for curing should generally be limited to urban drainage systems that discharge to treatment plants, otherwise all residual water will need to be captured for proper disposal.

Large boiler on site to heat the water

Large boiler on site to heat the water

When curing using steam the pros and cons will be similar to water cure except for a slightly increased cure time and much less water to dispose of.

Site set up is a high proportion of costs on small projects. The site footprint is relatively large compared with some lining methods, but it is also somewhat flexible. In general, trained personnel with specialized equipment are required. When lining metal culverts with bituminous coatings containing high sulfur grades, there may be a problem with the resins used for CIPP; to find out what the sulfur grade is, take a bottle/jar of styrene or polyester and brush some onto the bituminous coating. If the black comes off on the brush, it probably has a high sulfur grade. Then it is recommended to:

  • Perform further lab tests if needed
  • Specify using a pre-liner or
  • specify an epoxy resin (which may be expensive)

For additional information on CIPP, see Appendix G.

6.1.3.3 Lining with Folded and Re-Formed PVC Liner (Fold and Form)

This method (per ASTM F 1504) involves the insertion of a continuously extruded, folded PVC pipe into the existing pipeline or conduit and the reformation of the pipe to conform to the shape of the existing pipeline or conduit without excavation. Although this method may be capable of expanding in diameter by up to 10 percent, it is primarily limited to a maximum nominal diameter of 15 inches and therefore non-applicable to most Caltrans applications. In order to allow the deforming and reforming process to take place without damaging the liner, it is manufactured from PVC compounds that are modified from those used in standard ribbed PVC pipe or other PVC pipes used for direct burial.  At present, there is no definitive information available on the long-term durability or abrasion resistant properties of PVC compounds of this type.

Fold and Form PVC Line

Fold and Form PVC Liner

6.1.3.4 Lining with Deformed-Reformed HDPE Liner

The HDPE method currently being marketed uses HDPE solid wall pipe with a Standard Dimension Ratios (SDR – pipe diameter/wall thickness ratio) of 35, 32.5, 26 and 21, which is adequately flexible to be folded for insertion into existing pipes. Lengths of individual pipe runs that can be rehabilitated by this method vary depending on pipe diameter – larger diameters require sections that need to be butt-fused together on site.

If the nominal diameter of the liner is 18 inches or smaller, it is delivered to the jobsite in a folded form on a spool. Larger diameters are brought to the jobsite in individual sections and then butt-fused and deformed on site by means of thermo-mechanical deforming equipment into a “U” shape (see pictures below).

On-site mechanical deforming equipment required for large diameter HDPE liner On-site mechanical deforming equipment required for large diameter HDPE liner

On-site mechanical deforming equipment required for large diameter HDPE liner.

This technique is generally applicable to rehabilitating pipes of 18 inches diameter or less. However, Caltrans has recently been testing this method with pipe sizes up to 30 inches.

After the liner is pulled through the pipe to be rehabilitated, heat is introduced into the folded liner using pressurized steam to force it out to shape. A remote controlled cutter reconnects connections and laterals without excavation.

The advantages of this method compared to sliplining include, no joints, no grouting and insignificant annular space thus providing increased hydraulic capacity if the reduction in diameter was a concern.

Smaller diameter liner (450 mm) being installed through a drainage inlet from a spool

Smaller diameter liner (450 mm) being installed through a drainage inlet from a spool

The main limitations of this method are that the range of available pipe diameters is limited and this method cannot accommodate oval or odd shapes of the old pipe, diameter variations, possible joint settlement and pipe bends for liners over 18 inches in diameter. Smaller diameter liner (18 inches) is delivered to the job site on a spool and has a significantly improved bending radius than the larger diameters that may require digging a jacking pit (see picture below).

Steam being introduced into 30 inch HDPE liner

Steam being introduced into 30 inch HDPE liner

6.1.3.5 Lining with Machine Wound PVC Liner

This method involves the insertion of a machine made field fabricated spiral wound PVC liner pipe into an existing pipe (either flexible or rigid). After insertion, the spiral wound PVC liner pipe is either:

a) Inserted at a fixed diameter and then expanded until it presses against the interior surface of the existing pipe; or,
b) Inserted at a fixed diameter into the existing pipe and is not expanded, and the annular space between the spiral wound PVC liner pipe is grouted; or,
c) Wound against the host pipe walls by a machine that travels down the pipe.

There are currently three manufacturers using this process.  One manufacturer offers three systems:

  • An expanding system, limited to host pipes ranging from 6 inches to 30 inches in diameter
  • A fixed diameter system for host pipes ranging from 15 inches to 108 inches in diameter
  • A full bore, traveling machine system for host pipes ranging from 30 inches to 108 inches in diameter.

One manufacturer offers two systems:

  • A fixed diameter system, machine applied, for host pipes ranging from 24 inches to 36 inches
  • A human-entry, fixed diameter manual application system for host pipes ranging from 42 inches to 96 inches

The other manufacturer offers one system specifically designed for installation in large (36” diameter and larger – both circular and non-circular) pipelines using a steel-reinforced PVC strip and a winding machine that locks the PVC materials firmly together while automatically moving down the pipeline.

Note that, as with any plastic liner or slipliner, if the liner diameter of any of the above systems exceeds 60 inches, headquarters approval will be required.  See Index 7.1.6.1.

The expanding system consists of a continuous plastic strip that is spirally wound into the existing deteriorated host pipe. The male and female edges of the strip are securely locked together via the winding machine. Once a section is installed, it is expanded against the wall of the host pipe, creating a watertight seal. Both flexible and rigid pipes can be rehabilitated with this system. This lining system is similar to the fixed diameter process except that the continuous spiral joint utilizes a water activated polyurethane adhesive for sealing, no annular space grouting is required (but the pipe ends are usually grouted) and the range of diameters given above is for smaller non-human entry pipes.

Rib Loc Expanda PipeTM lining system example shown above

Rib Loc Expanda PipeTM lining system example shown above

The fixed diameter machine spiral wound liner process produces a renovated pipe, which is a layered composite of PVC Liner (using ribbed PVC strips 8 inches to 12 inches wide that are supplied in 330 feet coils), cementitous grout, and the original pipe.  The combination of the ribbed profile on the PVC liner and the grout produces an integrated structure with the PVC liner "tied" to the original pipe through the grout similar to a slipliner.  Unlike the expanding system, after insertion, the annular space between the liner and the existing pipe is filled with grout as described in Indices 6.1.3.1 and 6.1.3.1.1.4. The composite structure also may provide a watertight system.

Rib Loc RibsteelTM lining system

Rib Loc RibsteelTM lining system shown above

There are variations to PVC profiles that are used by the different manufacturers for the fixed diameter machine spiral wound liner process.  One manufacturer uses a lining system that is capable of being steel reinforced.  This steel reinforced PVC lining system may be used for larger diameters than the expanding system, namely 21” to 108”, however, as with any plastic liner or slipliner, if the liner diameter exceeds 60 inches, headquarters approval will be required. See Index 7.1.6.1. For many smaller applications the steel reinforcing is not required as the plastic strip has sufficient stiffness to withstand the grouting pressure. The steel reinforced PVC lining system consists of a continuous plastic strip, which is spirally wound directly into the existing deteriorated host pipe at fixed diameter.  The male and female edges of the strip are securely locked together via the winding machine.  The plastic strip is designed with ribs on its outer surface to engage a continuous strip of profiled reinforcing steel, which is added to the outside of the plastic pipe when specified.  The resulting liner has a smooth plastic internal surface with increased stiffness from the steel reinforcing profile.  The liner is annular space grouted as described in Indices 6.1.3.1 and 6.1.3.1.1.4.  A watertight seal is achieved through sealing elements pre-applied to the male and female edges of the profile during manufacture. Both flexible and rigid pipes can be rehabilitated with this system.

The full bore, traveling machine system consists of a continuous plastic strip that is spirally wound into the existing deteriorated host pipe, with the option of a steel reinforcing section for increased load carrying capacity, by a machine that rotates and lays the profile against the host pipe walls as the machine traverses the host pipe.  The male and female edges of the strip are securely locked together via the winding machine.  The plastic strip is designed with ribs on its outer surface to engage a continuous strip of profiled reinforcing steel, which is added to the outside of the plastic pipe when specified.  For many smaller applications the steel reinforcing is not required as the plastic strip has sufficient stiffness to withstand the grouting pressure.  The resulting liner has a smooth plastic internal surface with increased stiffness from the steel reinforcing profile (if specified).  Both flexible and rigid pipes can be rehabilitated with this system. One manufacture uses a traveling machine capable of lining large diameter arches and box culverts.

 

Full bore, traveling machine system: Rib Loc RotalocTM lining system

Full bore, traveling machine system: Rib Loc RotalocTM
lining system shown above.

The annular space grouting procedure is described in Indices 6.1.3.1 and 6.1.3.1.1.4. A watertight seal is achieved through sealing elements pre-applied to the male and female edges of the profile during manufacture.

PVC liners are not recommended in conditions with combinations of impact abrasion and freezing temperatures where the pipe liner may become brittle and crack. PVC also may experience greater abrasive wear in an acidic environment than HDPE. See Index 2.1.2.3.

6.1.3.6 Sprayed Coatings

Sprayed lining systems can be used to repair drainage structures or to form a continuous lining within an existing pipe. Lining materials may include concrete, concrete sealers, silicone, vinyl ester, and polyurethane. The primary goals of the non-cementitious systems are improved corrosion resistance for concrete structures.

The application of any coating or lining requires correct surface preparation and cleaning in advance of application.

6.1.3.6.1 Air Placed Concrete and Epoxy or Polyurethane Lining for Drainage Structures

Placing a spray-applied Polyurethane protective lining on air-placed concrete is an effective method to rehabilitate concrete inlets and manholes; after the concrete has cured, a thin layer of moisture tolerant epoxy primer is applied by spray, followed by a thicker outer layer of polyurethane lining material.

Epoxies can also be used alone or as a topcoat to a cementitious product to provide a chemical barrier.

6.1.3.6.2 Cement Mortar Lining

Cement Mortar Lining

This alternative may be used to line corroded corrugated steel pipes ranging from small diameter (12 inches) to a maximum of 23 feet diameter. Prior to performing this technique, any voids around the pipe must first be pressure grouted as described Index 6.1.2. In addition to being an effective invert lining method, this method will also create a zone of alkalinity for the entire circumference of the pipe. Corrosion Engineers maintain that the cement in concrete prevents or significantly retards the oxidation of the interior base metal (rust).  Construction thicknesses from 1/8” to 3/4” per pass are attainable. Typically, two passes are made resulting in a 1 inch minimum thickness over the crests of the corrugation pattern.

Any grade (steepness) of pipe can be lined by this method and most bends do not present a problem. A polypropylene fiber mesh reinforcement additive will provide improvements in the strain capacity, toughness, impact resistance, and crack control, however, it is not a substitute to Caltrans host pipe philosophy outlined in Index 6.1.1 which must be adhered to. The mortar is made of one part cement, to one part sand. As with other liners, the pipes must first be thoroughly cleaned and dried. For diameters between 12 and 24 inches, the cement mortar is applied by robot. The mortar is pumped to a head, which rotates at high speed using centrifugal force to place the mortar on the walls. A conical-shaped trowel attached to the end of the machine is used to smooth the walls. The maximum recommended length of small-diameter pipe that can be lined using this method is approximately 650 feet. Although this method will line larger diameter pipes, it is mostly appropriate for non-human entry pipes (less than 30 inches).  Larger diameter metal pipes will generally only require invert lining. See Index 5.1.2.2.1.

6.1.3.7 Man-Entry Lining with Pipe Segments

Man-Entry Lining with Pipe Segments

For the rehabilitation of large (42 inches and larger) diameter storm drain systems, segmental liners can be manufactured in virtually any shape and length from a number of different types of materials, discussed below. The installation process is very labor intensive, largely due to the joining and grouting. These liners can be installed in single, short, circumferential sheets joined together longitudinally, or in multiple segments (usually invert and crown sections joined together longitudinally and circumferentially). The joints may be tongue and groove. Additional joint protection can be provided by the application of resin-based sealants following the installation of the units. This work generally needs to be accomplished in dry conditions; therefore, bypassing of flow may be required. Segmental liners can be installed with or without annular space grouting which is usually incorporated with mortar placement (shotcrete) or by pressure grouting applied after installation.

6.1.3.7.1 Fiberglass Reinforced Cement (FRC) Liners

Fiberglass reinforced cement (FRC) liners are prefabricated thin panels designed for large diameter (42 inches and larger) and odd shaped pipes. After the existing pipeline is thoroughly cleaned and dewatered the segments are provided in 4 to 8 foot lengths, which overlap at each end. The segment ends may be pre-drilled to accommodate screws or impact nails. The segmented rings are anchored on spacers and, upon final assembly; the section(s) are cement pressure grouted in the annulus provided. Laterals are cut in and grouted.

This method provides flexibility to be made specially to fit any portion (e.g., invert only), shape or size of host pipe and to accommodate variations in grade, slopes, cross-sections and deterioration. The linings are not designed to support earth loads, therefore, the host pipe must be structurally sound. Although the segmented sections are lightweight and easy to handle, the installation is labor intensive and slow.

The FRC liners are normally three eighth inches thick, but can vary. They are composed of Portland cement, fine sand and chopped, fiberglass rovings. They have high mechanical and impact strengths and also a high strength to weight ratio. FRC is more abrasion resistant than the concrete mix used in standard reinforced concrete pipe (RCP), however, their thickness is significantly less than the cover over the reinforcing steel in RCP.  See Index 2.1.1.1.3.3.

6.1.3.7.2 Fiberglass Reinforced Plastic (FRP) Liners

Irregular shape example using FRP Irregular shape example using FRP

Irregular shape examples using FRP

Invert lining with FRP

Invert lining with FRP

Fiberglass reinforced plastic (FRP) liners are similar in most respects to FRC liners, however, they are lighter weight and more resistant to chemical attack (e.g. sulfate) and therefore provide a better corrosion barrier (when used to line steel pipes) than FRC liners. They are also highly abrasion resistant with negligible absorption and permeability.

The FRP liners are normally one half inch thick, but can vary. They are composed of thermosetting plastic resin (polyester or vinylester) and chopped, fiberglass rovings and mostly constructed with the same materials that are used to make fiber-reinforced polymer concrete. See Indices 2.1.1.1.3.1 and 2.1.1.1.3.5. However, however, a sand free inner surface made of pure resin is provided for resistance to chemical attack and abrasion resistance. The fiberglass inner surface has a finish that is compatible with the type of resin employed. The outer surface is treated with bonded inert sand aggregate to enhance the adhesion to the annular space grout.

Channeline Sewer Systems (North America) Inc. offers a range of FRP segments up to 15 feet in diameter available in any shape or size.

Existing multi-plate arch before lining

Existing multi-plate arch before lining

After lining with FRP

After lining with FRP

 

6.1.3.8 Other Techniques

The following techniques are described elsewhere in this D.I.B. under the various referenced indices and are included the table of alternative repair techniques in Index 8.1.1:

  • 5.1.1.1.3.1 Internal chemical grouting
  • 5.1.1.1.3.2 Internal joint sealing systems and repair sleeves
  • 6.1.2 Grouting voids in soil envelope
  • 5.1.1.2 & 5.1.1.2.1 Crack repairs
  • 5.1.2.2.1 & 5.1.2.2.2 Invert paving
  • 5.1.2.2.3 Steel armor plating

This page last updated August 20, 2011