California Department of Transportation

DIB 83-02 - 12.1 Appendixes


  Appendix A - Butt Fusion Procedures for Solid Wall HDPE Slipliner
  Appendix B - Flow Chart of the New Product Approval Process
  Appendix C - Caltrans Condition Tables Example
  Appendix D - Typical Resistivity Values and Corrosiveness of Soils
  Appendix E - Crack Repair in Concrete Pipe
  Appendix F - Sources of Information and Industry Contacts
  Appendix G - CIPP Guidance for Resident Engineers
  Appendix H - Case Studies

12.1 Appendixes Page

Appendix A – Butt Fusion Procedures for Solid Wall HDPE Slipliner

Copied with permission from Chevron Phillips Chemical Company LP

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Appendix B

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Appendix C – Caltrans Condition Tables Example

The table below is part of a larger set developed for inspectors participating in the Caltrans Culvert Inspection program.

The rating system developed by Caltrans is compatible with the Caltrans Culvert Inventory Database and not related to the FHWA rating system in the Culvert Inspection Manual. See for complete set.

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Appendix D - Typical Resistivity Values and Corrosiveness of Soils

See Index 5.2.5

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Appendix E – Crack Repair in Concrete Pipe Using a Maximum Strength, Non- Shrink, Portland Cement or Mortar (Refer to Index

Dimensions of "V" Grind shall be 0.25 inch wide minimum and approximately 0.5 inch deep.  1 inch deep Grinds may damage reinforcement.  The Grind shall be cleaned of any grinding dust and surface thoroughly moistened before filling with non- shrink Portland cement or Mortar (e.g. Jet PlugTM by Jet Set California Inc, see Appendix F) to ensure a good bond.

The mortar mix should be mixed to a low-slump consistency with only enough water added to gain a consistency of heavy glazing putty. Allow repair to become firm to touch 6 to 10 minutes after installation. Then shave to grade with a trowel edge. Do not overwork

If the new patch is not under water, a curing agent shall be used to cover the new patch plus 1 inch on either side of the new patch immediately after patch is firm.  It should be noted that when longitudinal cracks are found at the crown of the pipe, usually the invert of the pipe is also cracked.

Appendix F - Sources of Information and Industry Contacts

In addition, to the following web sites, see FHWA Culvert Repair Practices Manual Volume 2, Appendix D, for Sources of information and assistance. A comprehensive index of trenchless contractors and services is provided in the Directory published annually by the Trenchless Technology magazine. See
for buyer’s guide link. Caltrans does not endorse any of the firms referenced below or listed in the Trenchless Technology magazine annual Directory and there may be many other firms not listed equally capable of performing specific services.

Internal joint seals:
CREAMER In-Weg® internal joint seals

AMEX-10® /WEKO-SEAL® by Miller Pipeline Corp.

Victaulic Depend-O-Lok, Inc.

Internal Repair Sleeves
905-886-0335 ext 302

Chemical Grouting
Avanti International
822 Bay Star Blvd.
Webster, TX 77598
(281) 486-5600
(800) 877-2570 United States & Canada

Concrete Pipe Crack Repair
Jet Set California, Inc.
2144 Edison Avenue, San Leandro, CA 94577
(510) 632-7800

Cement-Mortar Lining
Spiniello's SpinCo.

Spirally Wound PVC companies:

Danby Pipe Renovation

Rib Loc Group Limited

Sekisui SPR Americas, LLC:

Plastic Pipe Manufacturers:
ADS Pipe


KWH Pipe

J-M Manufacturing

Metal Pipe Manufacturers :

Pacific Corrugated Pipe Company

General Pipe Rehabilitation:
Gelco Services
1705 Salem Industrial Dr NE
Salem, OR 97303
Phone: 503-364-1199

1244 Wilson Way
Woodland CA 95695
Phone: 530-406-1199

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Appendix G – CIPP Guidance for Resident Engineers

The following information should be included with the R.E. file when CIPP is included as a contract item:


Cured-in-place pipe (CIPP) lining is a resin-saturated, flexible fabric that is inverted (turned inside out by water or air pressure) or winched into the host pipe. Water or air/steam pressure is introduced to invert the tube into the host pipe (or inflate the already winched-in tube) and hold the tube tight against the existing pipe wall. Next a suitable heat source is introduced which activates a catalyst, causing the resin to begin to harden.

With water inversion, the lining is inverted under water pressure from a hydrostatic head and cured by circulating hot water. With air inversion, the lining is inverted under air pressure and cured by introducing steam.

With winched (i.e., pulled in place) installations, the liner is inflated against the existing pipe wall by use of another internal liner (so-called “calibration hose”) which is either inverted on site into the liner under air/steam or water pressure or pre-installed off site and then inflated with air, water or steam. Both liners carry resin. The pulled in place liner can be cured by circulating hot water or steam, depending on the inflation method. 

After 3 to 6 hours of curing, the hardened resin gives the new pipe liner its strength.   

After the resin sets, the downstream closed end is carefully cut and removed and a final video inspection is performed. A remote controlled cutting device may be used to open lateral connections after dimples are visually located with the camera or by referring to previously recorded information.
In general, the following steps are performed:

  1. Install diversion (if needed)
  2. Clean, inspect and prepare host pipe for lining (voids in backfill may need grouting, remove protrusions greater 0.5 inch, record exact locations of lateral pipes)
  3. Prepare liner: The tube is vacuum impregnated with resin (on or off site depending on length and size of liner) and may be stored in ice for transportation to the site.
  4. Install preliner or insulation liner depending on host pipe material (see “liner”below)
  5. Install liner
  6. Cure liner
  7. Take test samples
  8. Final inspection
  9. Repair as needed
  10. Remove diversion (if needed)

Basic equipment and materials:


In the pre-lining state, the liner typically consists of reinforced 3 mm layers of non woven needled polyester fiber felt formed into a seamed tube of the required diameter with an impermeable plastic (polyethylene) inner membrane. The purpose of the plastic membrane is to keep water/steam separate from the resin impregnated felt during the cure.

For inversion installations the liner will be delivered to the job site plastic side out prior to inversion. For pulled in place installations, a sandwich-like combination of two liners will be delivered with plastic on the outside and inside. The pulled in place ASTM also allows an onsite inversion installation option for the inner liner (“calibration hose) for pulled in place installations.

The Caltrans spec does not reference ASTM F 2019 “Conduits by the Pulled in Place Installation of Glass Reinforced Plastic (GRP) Cured-in-Place…” which is for a pulled in place fiberglass and felt composite tube that has higher physical property values and can be UV cured (which we do not allow and is not feasible for felt-only tubes). However , this type of tube also falls under the “combination of non-woven and woven materials” description from ASTM F 1743 & F 1216 and therefore may be accepted provided it is steam or air cured and pulled in place because these products cannot be inverted.

Preliners (including insulating liners for metal pipe)

For all inversion installations, a preliner will be needed. If the host pipe is RCP, a continuous reinforced plastic sheet formed into a preliner tube sized to fit the host pipe being lined is installed before installing the liner. Polyester resin is most commonly used in CIPP, which won’t stick to anything damp. Therefore an outer impermeable pre-liner acts as both a barrier and “mold” to span voids, open joints and damaged pipe etc. It is installed by first folding the ends 45 degrees, then it is attached to a cable or camera and pulled in flat. Once pulled through, the end is slit and attached to a fan. The fan inflates the preliner and inversion through the opposite open end is possible. See Griffolyn Type-55 FR by Reef Industries, Inc (Houston, TX) 800-231-6074 or 713-507-4251

If the host pipe is corrugated metal, a 3 mm thick flexible needled felt insulation tube with a plastic inner liner (i.e. simply another liner) is used as a preliner and insulator before installing the liner. It is installed by being pulled in first and layed flat. Then it is slit and anchored to the same end of the host pipe inversion begins. Soap and water may be applied during inversion.
For pulled in place installations , if the host pipe is RCP, a reinforced plastic preliner is not used because the liner itself will have a polyethylene outer layer. But if the host pipe is corrugated metal, the 3 mm thick felt insulation tube described above will be needed as an insulator and is installed as follows:

The insulation can be pre-ordered to be already attached (felt side out) to the outside of the liner upon delivery, or, two pull-ins are performed. During the pull-in of liner through the insulating liner, soap and water may be used for lubrication and the insulating liner is anchored to host pipe at the opposite end from the winch.


Three types of resin are allowed and will cure readily when heated with air, steam or hot water; polyester, vinylester or epoxy. Epoxy is difficult to use for liners greater than 15” in diameter and is less commonly used than the other two. Recycled resins are excluded. See resin fingerprint analysis below.

The curable thermosetting resin is impregnated into the resin absorbent layers of the liner by a process referred to as the " wet out ." This can occur on or off site at a plant, depending on the length and pipe diameter. Pipes over 400 feet long, 48 inches or larger in diameter, and tube thickness’ of 24 mm or more will typically be wet out on site. The wet-out process generally involves injecting resin into resin absorbent layers through an end or an opening formed in the outer impermeable film, drawing a vacuum and passing the impregnated liner through rollers. It is important during the impregnation process that air be excluded from the resin absorbent material to the maximum possible extent. This, in itself, gives a test as to the soundness of the liner since in a damaged bag, it would be impossible to draw and maintain a vacuum within the system.

Care should be taken to keep the resin material away from direct exposure to sunlight; ultraviolet rays tend to deteriorate the composition of the material. Prolonged exposure in the presence of heat can cause a thermosetting reaction. The saturated liner temperature should be kept at or below 70 degrees Fahrenheit during transportation and storage – which may be several weeks depending on the type of resin system. A refrigerated truck may be needed to maintain temperature level.  After “wet out” the impregnated liner is laid into a truck for transport to the job site.  This is done by folding the liner in layers stacked one above the other (see picture below). In between each layer of liner is a layer of ice to retard the resin from curing.  This situation creates a great deal of weight bearing down on the lower layers of liner.  The weight on top of the lower layers can cause resin to be squeezed out, leading to a thin wall in those layers of liner.

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Resin – continued

Once a catalyst (commonly used systems consist of a low temperature and high temperature peroxide) is added to the resin, the resin is considered to be in the promoted or reactive state.

Inversion Installations

See “overview” above.

Typically an inversion platform, reinforced polyester tube, and 90 degree steel elbow are the three pieces of equipment unique to inversion installations if water is used for inversion and cure.

The scaffold height for the platform varies with the depth below grade and the diameter of the host pipe being lined as well as the thickness of the liner. The larger the diameter, the smaller the head needed for inversion.

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For air/steam inversions and cure, an air compressor and a steam source of sufficient capacity equipped with monitoring and control equipment for adjustment of air/steam temperature and pressure in accordance with the manufacturer’s instructions submitted. The liner is first inverted with air pressure and then cured using steam.


Thermocouples are temperature-sensing devices placed between the liner and the preliner or insulating liner to read the temperature during the cure and post-cure periods; these give accurate indications of the cure status of the material.  

Potential problems

Pinholes or tears in the polyethylene coating

One of the first and ongoing procedures throughout the entire installation is the visual inspection of the bag for any obvious flaws such as pinholes or tears in the polyethylene coating. Occasionally defects may have been caused in manufacturing the bag, but more often occur during job site handling or shipping. If there is a defect in the liner, it is much better to detect it before the liner is installed into the host pipe than to realize the recirculating water (or steam) is leaking.

After the liner is unpacked from its shipping container, a vacuum pump is attached to the bag to evacuate the entrapped air from the felt liner material. This, in itself gives a test as to the soundness of the liner since in a damaged bag it would be impossible to draw and maintain a vacuum. Depending where the “wet out” occurs, most often this will occur offsite at a plant. See “resin” above.

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Example of liner tear during installation and subsequent repairs.

Heat sink of ground

Monitoring of the thermocouple temperature shows the actual increase in temperature of the liner bag. The heat sink ability of the ground around a pipe can greatly vary with groundwater, backfill and host pipe material. Therefore, the temperature of recirculating water (or steam) verses liner bag outer surface temperature may vary. For this reason, the temperature of the circulating water should never be used as the only indication of the extent to which the process has proceeded.

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Examples of delamination, bubbling and rippling in lined CMP host pipes

Styrene boils

If the amount of heat given off (i.e., the temperature of the exotherm) is not controlled properly the styrene in the resin may boil, forming microscopic air bubbles in the wall of the liner. The formation of these bubbles can reduce the physical properties of the finished liner by as much as 75%.

Fillers in resin

The Caltrans specification states the resin shall not contain fillers, except those required for viscosity control, fire retardance, air release or extension of pot life.

Poor dispersion of fillers during mixing into the resin can result in areas of high filler concentration in sections of the liner wall
High levels of fillers will make the liner more brittle and more susceptible to damage by impact.

Banding liner (inversion installations)

The proper banding to the inversion shoe (reinforced polyester tube – see “inversion installations” and photo) is critical. If the bag comes loose from the shoe, or a leak develops at the connection, the inversion may have to be stopped because curing could not proceed. If the problem cannot be corrected quickly, the entire insertion might have to be abandoned; this most likely would result in the loss of the liner bag, resin, and all preparatory work.  

Termination points

If the CIPP liner does not fit tightly against the host pipe at its termination point(s), the space between the liner and host pipe shall be filled with a quick-set epoxy mortar or high viscosity epoxy such as Neopoxy NPR-3501 or equivalent, or a hydrophilic vulcanized expansive rubber strip such as Swellseal 8 by De Neef Construction Chemicals or equivalent.

Neopoxy NPR-3501:
Phone: 510-782-1290 
Web address:

De Neef Construction Chemicals:
Phone: 936-372-9185 Web address:

Cool down time

The Caltrans specification states: “Curing temperatures and schedule shall comply with submitted data and shall include an adequate "cool down" in accordance with these special provisions.”

According to one source, the minimum cool down time should be no less than the boiler start time to end of the high temperature cure.


Special consideration should be given to safety factors during installation and curing. Care to protect workers, spectators, and equipment from hot water or steam should be observed by the use of rubber wear and protective shrouds. Any time workers enter the drainage structures and pipes; all confined space procedures must be strictly followed. Strong volatile styrene fumes are created by this process to which prolonged exposure must be avoided. Also, because most polyester resins are water soluble, the uncured resin may pollute ground water. For this reason, all curing water must be captured.


It should be recognized the Caltrans specification was developed as a “performance-based specification” of the finished product. One necessary aspect in successful implementation of the performance specification is testing. Attention is directed to the Submittals and Quality Control sections of the specification for in-house pre-testing, quality assurance requirements, and independent laboratory testing, as well as a field thickness test.  

For testing physical properties, three aluminum plate clamped molds containing flat plate samples are placed inside the installed liner during the curing period of the CIPP tube. Each flat plate sample is sealed in a heavy-duty plastic envelope inside the molds. Enclosing the sample in plastic keeps the resin and water separated during cure (similar to the inner plastic coating of the liner). A sample transmittal form is included with this document.

For testing liner thickness over corrugated metal host pipes, it is important to measure the thickness over a corrugation crest in the pipe invert which is usually the place with the least resin and experiences the most wear. Note there may be a minimum thickness provided by the designer in the specifications. The thickness calculated by the contractor and provided in the submittals must not be less than the minimum thickness (if specified). A sample form is included with this document.

To verify the type of resin used, a liquid resin sample (114 g min. of unreacted resin) shall be shipped to the Transportation Laboratory for infrared fingerprint analysis as part of the pre-job submittals.

Also, for the first test performed, and for at least one, randomly selected by the Engineer, of every 5 subsequent tests, the Contractor shall concurrently prepare an additional resin sample for quality assurance infrared fingerprint analysis, which shall be shipped to the Transportation Laboratory in Sacramento, 5900 Folsom Blvd., Sacramento, CA 95819 (Attention: Chemical Laboratory).

Thickness sampling and repair

Caltrans specification requires lining through an "insulating liner" in CMP host pipes. If Contractor chooses the alternative method allowed in the specifications for thickness sampling - using a 10 feet long like diameter pipe extension butted up against the host pipe (in place of coring the host pipe 10 feet from the ends), it is important that the temporary pipe extension is made of the same combination of materials (i.e., CMP and insulating preliner). This is the only way to replicate what is happening in the host pipe during the lining process regarding temperature, resin flow, exotherm heat dissipation, and thickness over corrugation crests. The sample should be taken within 1 ft or so of the temporary joint where like pipe/insulating material extension is butted up against the host pipe. This ensures the specified sample location of approximately 10 ft. from the termination point of the liner, avoiding any thinning.

Figure 1 on the next page depicts core sampling and repair to host pipe.

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Project No. ___________________________
Project Title __________________________
Segment No. __________________________ on Map No. _______________________
*Sample No. _________________________             *Sample No. ___________________
Location: ____________________________ ______________________________
Sample Date: _________________________ ______________________________
Sample tested by: _____________________  ____________________________________
Measurements: ________________________mm       __________________________mm
                          _______________________ mm      __________________________mm
                          _______________________ mm      __________________________mm
Sub-Total =        _______________________ (A)      __________________________(B)
Average Thickness       (A+B/6) = ___ + ___/6   =    __________________________mm
Required Thickness (Bid Form)    = ________________________________________ mm
Results (Pass/Fail) _______________________________________________________
Contractor Representative Present ___________________________________________
Engineer Representative Present ______________________________________________
Date ___________________  Time ___________________

*Sample Number is Segment Number with a -1 or -2 added for Sample Designators.


Project No. __________________________________
Project Title _________________________________
Sequential Submittal No. _______________________
Segment No. _____________________ on Map No. _____________________________
Location: _______________________________________________________________
Requirements:   Modulus _______________________ PSI (250,000 PSI Minimum)
Flexural Strength ________________ PSI (4,500 PSI Minimum)
Thickness (this segment, minimum) ______________________
Sample No. _______________________ Sample by _____________________________
Sample on  _______________________  Total No. Samples _______________________
Test for:

Modulus (ASTM D-79)
Flexural Strength (ASTM D-790)
I.R. Fingerprint
Other: ____________________

Independent Lab ___________________       Submitted to:    _____________________
            Phone:      ___________________
            Fax:          ___________________
Translab Contact (Random Q/A samples only): _______________________________________     
Phone:    __________________
Fax:        __________________

Caltrans Intranet website to access ASTM’s:

Then click on the following IHS Specs and Standards search link:;

Appendix H – Case Studies

Example 1:  Ed-50-PM 14.0 (4C9104) Culvert Repair Summer 2003

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Approximate pipe location shown in blue

In June 2003, a sinkhole was identified by maintenance adjacent to the number one lane of the westbound traveled way on Highway 50 in El Dorado County at Post Mile 14.0 just east of El Dorado Road Overcrossing (Br. No 25-76) in the vicinity of a 96 inch Structural Steel Plate Pipe (SSPP). This section of Highway 50 was constructed 35 years prior. The 820 foot long SSPP was constructed as a cross drain for Indian Creek which was realigned from its original location to the east and uphill. A 230 foot long 36-inch diameter bitumen coated CMP connects into the SSPP at the center in the median and a 56 foot long 18-inch diameter CMP connects into the SSPP approximately 150 feet from the outlet. Both pipes collect drainage from the north side of the freeway and outlet into the SSPP.

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Measuring the sinkhole

Initial Investigation and Problem Identification

The District Hydraulics and Maintenance Branches and Headquarters Offices of Roadway Drainage Design and Maintenance made initial investigations. Subsequently a team was assembled consisting of representatives from these units and also from Geotechnical Design, the Corrosion Technology Unit and Underground Structures from within the Division of Engineering Services (DES).

In the interim, District Maintenance attempted to backfill the initial large void/sinkhole at the surface with approximately 9 cubic yards of concrete slurry after an earlier attempt to backfill the void with aggregate base.

From the initial site investigations and problem identification the following factors were identified:

  • Corrosion of the lower 180 degrees throughout the pipe
  • Deformation of up to 1 foot squeezing inward in the x-axis
  • Invert perforations throughout pipe with significant loss of invert in the vicinity of the sinkhole
  • Abrasion negligible – most nuts showing little sign of wear
  • Rock hammer blows to the side of the culvert made hollow sound at multiple locations in lower portions of the pipe indicating potential for voids or loose soil throughout much of the length
  • The 3 foot diameter bitumen coated pipe was perforated in the invert

Detailed investigation

After initial investigations were made it was determined that more detailed investigations would be needed to provide the following information:

  • Soil and Water samples to obtain pH and Minimum Resistivity
  • Thickness measurements of metal
  • Survey of dimensions within pipe
  • Detailed hydraulic investigation to determine hydraulic parameters of existing pipe and potential rehabilitation alternatives
  • Geotechnical investigation using Ground Penetrating Radar (GPR) and Cone Penetrometer (CPT) to determine location and extent of the voids

Using the original metal gage (thickness) as input for Culvert 4, the corrosion samples from the soil and water indicated that the site was corrosive (soil: pH=5.6-6.3, Minimum Resistivity =10,000 ohm-cm, water: pH=7.5-7.8, Minimum Resistivity = 3400-3500 ohm-cm, Sulfate content = 12 mg/kg, Chloride content = 12 mg/kg ) but as designed, the pipe should have met the 50-year design service life based on our existing predictive method. From Figure 854.3C in the HDM using a pH of 5.6 and minimum resistivity of 10,000 ohm-cm for the soil, a service life of 22 years for an 18-gage is obtained which is equivalent to 48 years for the 12 gage portion and 62 years for the 10 gage portion.

However, groundwater is present at the site year round and the Indian Creek realignment has resulted in the backside of the pipe often being in a state of saturation from the invert up to mid point (springline) where the groundwater could leach in. Due to the condition of the pipe, it was assumed that higher corrosion levels than the test results indicated must be present.  

Thickness measurements using an ultrasonic thickness gage indicated that the upper 180 degrees (above the springline) showed minimal to no loss, while the lower 180 degrees indicated varying conditions of rust stain, pitting, perforation and total loss (in the invert). There was total loss of the invert starting at 350 feet and extending to about 500 feet of the 820 foot long pipe and perforations for the entire invert. See pictures and table of results the on following pages.

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Taking thickness measurements. Note evidence of leaking horizontal seam at springline

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Total loss of invert and existing nuts showing minimal wear

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Typical local corrosion cells. Note that the corrosion is coming in from the backside, thus the pipe is in worse condition than it appears. See picture of void found from probing during construction.

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36 inch Bitumen coated CMP tie-in.  Note rust stain below from perforated invert. Perforations in invert to 36 inch CMP allowed water to leak behind 96 inch culvert

Culvert Thickness Readings (in)


Clock Position







































































































Culvert Ga. 12 = 0.109 inches from 0-660 ft*
Culvert Ga. 10 = 0.138 inches from 660-840 ft*

Position is measured from inlet side.  Mouth of inlet side is 0 ft.  Clock positions were assigned assuming standing at the inlet, and facing the outlet.

* Culvert thickness change due to fill height.

The CPT and GPR test results did not indicate the presence of any additional major voids other than the sinkhole. However, below the springline and beyond the limits the freeway pavement and median, further information was still needed. 

Using the measurements of the original pipe to size a circular liner, hydraulic investigations indicated that the resulting increase in headwater from the reduced cross section would be unacceptable to adjacent property owners. The alternatives selected for consideration were all first analyzed to be hydraulically viable.

Alternative Selection and Design

The following alternatives were studied and discussed in a meeting consisting of members from the previously referenced units and Construction:

  • Total replacement with a combination of jacking under deeper fills and trenching at the shallow section of the pipe under the freeway
  • A combination of full-lining and jacking a parallel pipe to supplement the reduced cross section
  • Full-lining using a custom sized Fiber Reinforced Segmental liner system (Channel Line)
  • Paving invert with concrete

As an emergency project, there were significant scheduling constraints for both the plans preparation and construction window, i.e., number of working days available. Alternative number 4 above was deemed to be the most viable for completion within the narrow time frame and preliminary plans had already been initiated by Maintenance.

The initial invert-paving plan proposed by Maintenance was further developed to pave the entire lower 180 degrees of the pipe and a thrust connection was incorporated in the design to transfer thrust from the upper half of the pipe to the new concrete lining. The thrust transfer design comprised of tack welding L3.5” x 3.5” x 5/16” Bearing Angles to each side of the culvert longitudinally with each Bearing Angle connected to transverse L2” x 2” x 1/8” x 7.75" long Attachment Angles welded with 1/16 fillet welds at every corrugation (see detail on next page).

As outlined above, the GPR and CPT testing was incomplete relative to the voids below the springline directly behind the pipe and outside the limits of testing (i.e., ramps). Therefore, Geotechnical Design recommended exploratory probing for voids at 2, 4, 8 and 10 o ‘clock positions every 6 feet along culvert using a ½ inch (No. 4), 4 foot long rebar. Any voids found, were to be filled by low-pressure contact grouting with a maximum injection pressure not to exceed 5psi measured at the nozzle. The exploratory work and subsequent contact grouting was included into the contract and paid for by Extra Work (see detail on next page).

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An 32 inch plastic slip liner was also included into the contract to rehabilitate the 230 foot long, 36 inch diameter, and bitumen coated CMP connecting into the SSPP at the center in the median.


Since the envirnmental permits would take too long to obtain under normal project process, Maintenance Engineering proceeded with a Director’s Order Informal Bid contract.

Initially construction was delayed until Cal-OSHA approved the Contractor’s ventilation plan on site for welding operations inside a confined space.  Prior to bidding, the Underground Classification of “Nongassy” had been assigned by the Mining and Tunneling Unit within the Division of Occupational Safety and Health.

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Bulkhead and fan at culvert outlet to facilitate venting during welding

In general, the order of work performed was as follows:

  • Cleaning (by hand)
  • Welding angle iron
  • Placing and tack welding WWM
  • Exploratory probing for voids at 2,4,8 and 10 o ‘clock positions at 6 feet centers
  • Grout port installation
  • Shotcrete application (including voids below invert)
  • 3-sack sand slurry filling of large voids
  • Slipliner installation (for lateral 36 inch CMP)
  • Annular space grouting for slipliner
  • Contact grouting remaining voids in large pipe

The shotcrete and 3-sack sand slurry were performed as change orders (CCO’s) to the original contract.

Probing revealed the presence of a large, long void in the backfill between the sinkhole beginning near the mid point and ending approximately 620 feet from the inlet at the 4 o’clock position. After shotcreting was completed it was decided to core some additional ports and fill the large void with a 3-sack sand slurry prior to contact grouting work previously described. In addition, the long void that was found through probing extended to the surface near the original sinkhole and was also filled with slurry placed from the surface. See below.

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Large, long void that was located by probing. Note corroded back side of culvert on right side of picture.

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Freshly placed slurry where void migrated to surface.

No (contact) grout was pumped through any of the holes at 10:00 & 2:00 because no voids were found above the springline except for the original sinkhole and the large void described above, both of which were filled from the surface. Only the lower holes were pumped in the vicinity of a long void found in the backfill between the sinkhole beginning near the mid point and ending approximately 620 feet from the inlet.

The following is a summary of the various grout and slurry volumes that were placed to fill voids:

  • 9 cubic yards of slurry in original sinkhole (right side of pipe facing downstream) at edge of shoulder, under the traveled way and a portion of median by District Maintenance
  • 19 cubic yards of 3-sack sand/slurry in large void adjacent to pipe at 4:00 and 8:00 (between sinkhole and almost 200 feet downstream)
  • 4 cubic yards of slurry where large void described above day-lighted at surface on left side of pipe in the vicinity of the original sinkhole
  • 23.5 cubic yards of contact grout in vicinity of large void described above.
    The volume placed of shotcrete included filling the voids below the invert and was very close to the volume of 202 cubic yards for Minor Concrete that was shown on the plans.

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Tack welding WWM

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                   Placing Shotcrete                                             Contact grouting through grout port

Lessons learned

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  • Thrust transfer design was labor intensive and vertical angle iron design needed modifying in the field to make better contact with pipe (see pictures above); the original design did not work for the field conditions because the deformed host pipe resulted in several areas of poor contact with the longitudinal angle iron (see picture with hand). Therefore, it is incumbent for the designer to make sure their design will meet field conditions.
  • A possibly more efficient rehabilitation alternative for similar metal pipes in need urgent need of repair (i.e., large enough for human entry, relatively minor deformation, invert failure with concerns about future structural degradation due to soil side corrosion and ability to support roadway and traffic loads etc) suggested by Geotech may be to shotcrete with reinforcement the entire 360 degrees (different to cement mortar lining), and, in effect, creating a custom sized new pipe inside the existing pipe. If fiber reinforced shotcrete is used (either synthetic or steel), the need for steel WWM can be eliminated entirely. On another concrete invert lining project constructed this summer, shear connector welding studs (“Nelson Studs”) were used as a thrust connector at the outer edges of the invert lining.
  • California Test 643 can have environmental conditions that can vary dramatically depending upon the time of year the soil and water samples were taken. If available, use condition of existing metal culverts to determine if corrosion is present to supplement soil and water testing.
  • CPT and GPR testing is limited for finding voids directly behind the pipe below the springline and should be supplemented by probing from inside the pipe.
  • Repairs from CPT testing damage should be included in contract (see picture next page):

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  • Design changes made in field by Construction without communication to other units: 3- sack sand slurry in lieu of contact grout design used to fill largest void and decision to introduce “weepholes” in invert that were not shown on the plans (see pictures on following page):

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“Cored” grout hole in shotcrete used to fill large void with 3-sack sand slurryleaking groundwater during contact grouting. Note capped contact grout port.

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PVC pipe “weep” placed in rock below invert. Later, larger weeps were “cored” in addition in addition to these.

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Cored weep in shotcrete invert

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Non-woven polypropylene geotextile material and 3/8” – ¾” inch diameter gravel from gravel bag headwall used to make filters.

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Installed gravel filter bag in invert weep.

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Outlet of 96-inch pipe after repair.

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Inlet of 96-inch pipe after repair.

  • Costs: Engineers estimate---$407,000   Low bid---$472,420   Not including $100,000 for grouting around the pipe (force account). Actual completed construction cost: $480,500.

Example 2: 03-Nevada-80 PM 4.0 Culvert Repair (Castle Creek) EA 03-4C3601  Summer 2003


This section of Interstate 80 in Nevada County at Post Mile 4.0 was constructed over 40 years ago in 1961. At this location there are two, 144 inch diameter, Structural Steel Plate Pipes (SSPP), one under each direction of traveled way, which were constructed with the freeway as cross drainage for Upper Castle Creek. The lengths of the pipes are 169 feet (eastbound) and 179 feet (westbound).

Since 2001, under service contract, maintenance had been repairing depressions in the pavement in the vicinity of the culverts by slab jacking or slab replacement with asphalt.

During the summer of 2002, depressions in the pavement were identified by maintenance adjacent to the number one lane of the eastbound traveled way and under the entire westbound pavement in the vicinity of each culvert. See pictures below.

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         Dip in Number 1 EB Lane.  Summer 2002     Dip in entire WB freeway section.  Summer 2002

Problem Identification

Due to high flows, inspection of the culverts was not feasible in 2001; however, inspections conducted the following year (2002) revealed a corroded invert and deflection in each pipe.

Corroded and overlapping invert. Note oval shape of pipe.

Due to the deterioration of the invert plate and the subsequent loss of hoop strength, these culverts were deforming at the invert as revealed by a wide variation in cord length measurements (eastbound: 0-15 inches, westbound 0-13 inches) between the edges of the two plates (one edge on either side of the bottom or invert plate) that overlap the invert plate. The loss of chord length represented the amount of deformation in the bottom of the culvert due to external pressures that were no longer resisted by the hoop strength of the culvert at the invert.

Over the years the bottom of the culvert had deteriorated - possibly due to corrosion from de-icing salts placed on the roadway above during winter. Once the pipe had perforated, stream flows could then pass beneath the pipe carrying away soil fines (either within the stream flow or by moving outward into the voids of the courser graded surrounding highway fill material). The as-built plans indicated the freeway fill was constructed with ‘shot rock’ consisting of larger diameter material than the finer grained and potentially erodible backfill adjacent to the pipes.

As the fine material from beneath the pipe was evacuated, fill from the midline of the pipe could then settle down to fill the void left by the lower evacuated material. Surrounding and surface fill material would then begin to settle into the voids left by the fill that used to surround the midline of the pipe. The structural section beneath the PCC slabs began to fail and settle in and fill the voids of the settled fill material. The PCC slabs were left bridging the void left by the failed structural section. Ultimately, the slabs began to settle unevenly and created the surface dip.

This process may have been accentuated from the vibrations of truck traffic on the relatively shallow cover of 10 – 15 feet above the pipes.

At the time of inspection in 2002, a 4 to 6-inch void existed beneath the invert throughout most of the length of each culvert. 2-inch sized aggregate from the original bedding/fill could be seen below the pipe. There were also some large voids present at the endwalls where some stream flow was seeping out.

It was concluded that corrosion was far more problematic than abrasion as a contributor to the invert perforation.  Invariably, the corrugation valleys were what was perforated and not the corrugation crests.  In addition, while there was some wear apparent on the connecting nuts/bolts that were in the invert, the extent of upstream side wear was very slight - again indicating that while there is/was enough abrasion to remove the zinc coating, it was not severe and some chemical action is attacking the steel.

As is typical, there were a number of small spot locations on the culvert barrels where excessive compaction (or poor handling) during construction caused the zinc coating to chip off or delaminate.  In all of those locations rust had formed - most of which were well above the area where water had ever flowed.  This was another indicator of the corrosive environment.

In August 2003, at the request of the District Maintenance Engineer, the corrosion technology staff conducted a corrosion investigation; this included taking culvert thickness measurements using an ultrasonic thickness gage and visual observations.

The measurements indicated that corrosion damage was limited to the lower 90 degrees.

There were perforations along the flow line for the entire length of both pipes and corrosion stains were present throughout the lower 90 degrees.

There was no corrosion present in the upper 270 degrees along both pipes.


Because a bid contract was not possible due to environmental lead-time, work was done under Emergency Force Account.

The original plan by Maintenance Engineering was to place a reinforced concrete invert lining in each of the culverts with no thrust connection. However, District Hydraulics expressed concerns that the loss of hoop strength may continue to allow these pipes to collapse even farther, therefore, a structural stiffening system was considered in the invert to regain the lost hoop strength. 

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Eastbound pipe prior to Concrete placement with temporary HDPE by-pass, WWM and Nelson studs.

The Contech Construction Products Co. repair method employing bearing angles as used on another emergency culvert invert retrofit repair in District 3 under Highway 50  (03-ED-50-14.0) was initially chosen by the District as the thrust connection design.  However, the Construction Resident Engineer requested the Underground Structures Branch within the Division of Engineering Services to provide additional alternatives for thrust transfer. 

The Underground Structures Branch provided the District with the following three alternatives:

Alternative I. 

  1. Attach longitudinal bearing angles to culvert wall (normal to corrugations) with Nelson Studs.
  2. Install (2) 1/2" dia. x 1-1/4" long CPL Spec 1 Threaded Nelson Studs at each corrugation peak (6" o/c).
  3. Attach L5” x 3” x ¼” (LLV) longitudinal Bearing Angles to Nelson Studs.  Holes in angles can be shop punched.
  4. Fasten L5” x 3” angles onto wall with Nelson Studs using 1/2" dia. hex nut and flat washer.
  5. Nelson Studs should be attached to only non-corroded portions of culvert wall.
  6. Tack weld 4” x 4” – 6” x 6” WWF mesh to culvert invert at 12" o/c ea way, in order to provide composite action. 
  7. Pour 4" thick (minimum thickness above crest) concrete invert slab (f'c = 2500 psi).
  8. Extend concrete paving above the bearing angles.  Slope concrete to provide for drainage.

Alternative II.

  1. Attach longitudinal bearing angles to culvert wall (normal to corrugations) with plug welds.
  2. Initially tack weld L5” x 3” x ¼” (LLV) longitudinal Bearing Angles to culvert wall.  Holes in angles can be shop punched.
  3. Fasten L5 x 3 angles onto wall with (2) 1/2" dia. plug welds at each corrugation peak (6" o/c).
  4. Plug welds should be placed at only non-corroded portions of culvert wall.
  5. Tack weld 4” x 4” – 6” x 6” WWF mesh to culvert invert at 12" o/c ea way, in order to provide composite action. 
  6. Pour 4" thick (minimum thickness above crest) concrete invert slab (f'c = 2500 psi) to cover bearing angles.
  7. Extend concrete paving above the bearing angles.  Slope concrete to provide for drainage.

Alternative III (selected).

Observations were made that the Route 80 culverts have severe out-of-plane sidewalls due to invert buckling and overlapping.  Due to the undulations in the culvert invert and walls, the pre-fabricated longitudinal Bearing Angles would have to be cut into many shorter lengths in order to obtain a flush fit with the culvert walls.  Also the corrugation spacing varies between the original 6" o/c to 5" o/c due to the culvert invert/wall undulations.  This would prevent shop punching of holes in the longitudinal support angles due to varying spacing requirements.  Consequently, a simpler repair method employing only Nelson Studs for locations with severe out-of-plane sidewalls was requested.  While not as desirable as Alternatives I or II, Alternative III entails the following:

  1. This procedure does not employ longitudinal Bearing Angles.
  2. This repair method should only be used for culvert repairs where sidewalls are still in excellent structural condition.
  3. Nelson Studs are used as shear anchors to transfer culvert wall thrust into the new concrete invert slab.
  4. Weld (3) 1/2" dia. x 3-1/8" long H4L Headed Nelson Studs, spaced 3" apart vertically, at each corrugation peak (6" o/c).  Nelson Studs to be attached to only non-corroded portions of culvert wall.
  5. Tack weld 4” x 4” – 6” x 6” WWF mesh to bottom 90 degrees of culvert invert at 12" o/c ea way, in order to provide composite action.
  6. Pour 4" thick (minimum thickness above crest) concrete invert slab (f'c = 4000 psi) to cover Nelson Studs.
  7. Concrete lining to cover lower 90-degree internal angle.  Slope top portions of concrete to provide for drainage.

A structural bond to the host pipes can be achieved by using shear connector welding studs (Nelson Studs) attached with a stud welding gun as shown below:

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Shear connector welding studs (Trade name Nelson Headed Anchors and Nelson Threaded Studs are acceptable structural fasteners.  Nelson studs are regularly used in bridge superstructure construction. They are relatively inexpensive (roughly 25 cents each) and depending upon the overfill height and culvert pipe thrust, Nelson Headed Anchors can function to anchor and transfer the culvert thrust load from the wall into the concrete invert lining through shear transfer.  In addition, they are welded electrically which avoids the gaseous fumes resulting from normal structural welding. Six longitudinal rows of studs (3 running left of center and 3 running right of center) 6 inches apart on each corrugation were installed.  Approximately, 4300 studs were installed in a few days at a cost of about $7,000.

Paving Invert

The concrete design for the invert included a 4000 psi compressive strength and 3/8 inch aggregate along with air entraining for the freeze-thaw conditions. The 4-inch thick minor concrete invert lining was limited to the lower quadrant of the culvert (i.e., 90 degrees coverage from the 4:30 to 7:30 clock positions).

The voids directly below the invert were filled with the same concrete.

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View of both pipes after concrete invert paving.

Filling Voids behind the culvert

Before paving the invert, coupons were cut into the culvert wall in order to probe for voids. Most of the voids found were below the springline, however, a significant void was discovered near the outlet of the eastbound pipe above the springline at the 10 o’ clock position. In both pipes the most significant voids were found at the inlet.

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Coupons cut in sidewall of culvert for probing and grouting

A decision was made to use polyurethane foam grout rather than cementitious grout to fill the voids behind the culvert. The decision to use polyurethane grout was based primarily on the fact that an agreement with the cementitious grouting contractor regarding Force Account rates could not be reached. Furthermore, the District already had a Maintenance service contract with a company called Uretek for slab jacking and had some success with the material for jacking operations (including this site in January 2003). Although the foam has been used in PCC slab raising work for several years on many California State Highways, there were concerns that the Uretek foam may have environmental impacts and durability issues, since it had not been used for this type of application. The Resident Engineer explained the environmental concerns with cementitious grout migrating into the creek during placement and stated that Uretek had provided data showing the foam to be inert and that it would not leach into the creek. This material is supposed to be inert in a live stream environment and will not absorb water. When first placed, high-density polyurethane rigid closed cell hydro-insensitive grout is supposed to form a mechanical seal by expanding twelve times its liquid volume in 8-12 seconds.

During grouting operations approximately 110 cubic yards of expanding grout were used. Laser and string-line monitoring of the culvert were performed to monitor deflection.

The Engineers estimate for repairs was $400,000. The Resident Engineer estimated final costs to be closer to $380,000.
Lessons Learned

  • Use of Nelson studs can expedite repair procedures, although preliminary investigation is required to verify that plate thickness and conditions (minimal loss due to corrosion) are satisfactory for their use. In this case, the decision to solely use Nelson Studs and totally omit using welded longitudinal bearing angles proved to be a major time saver for the District during construction. 
  • Use of polyurethane foam grout rather than cementitious grout to fill the voids behind the culvert or any other material that has not been tested by the Department requires approval from HQ before being shown on plans or recommended in emergency or any other repair strategies.  Communication and collaboration between functional areas is key when addressing any changes that occur in the field. Polyurethane foam grout has not been tested or approved by Geotechnical Design to determine applicability and use for culvert repairs.  The main issues are whether material is inert and whether it develops strength comparible to compaction grouting. This material cannot be pumped to a specified density.  Its durability in this application also needs to be monitored for longevity.

However, it should be noted that the Uretek grout, while not approved, provided some features that cementitious grouts could not provide and thus made void filling viable in this location. These include:

  1. Environmentally friendly in a live stream environment.
  2. Potentially higher percentage of void space sealed from mechanical seal and short expansion time of expanding polyurethane foam grout.
  3. Hydro-insensitive
  • Corrosion Investigation was limited to wall thickness measurements. No soil or water samples were taken, therefore, no recommendations were provided for the concrete mix design placed in the invert.

Prior to jacking or repairing subsiding pavements, an initial check to locate drainage structures (culverts) below should first be undertaken. In this case, roadway slabs were either jacked or replaced prior to inspection, problem identification and subsequent repairs had been completed in the culverts below.

Example 3:     03-Yub-49 KP 9.5/PM 5.9 (3C3504) Emergency Repair of CMP Summer 2003

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In 2002, Area Maintenance reported that the soffit of a 108-inch x 262 feet Structural Steel Plate Pipe (SSPP) culvert was collapsing causing the pavement above the pipe to crack.  This culvert was originally constructed in 1940 as cross drainage for Campbell Creek on Highway 49 near Camptonville (see map above).

Inside the culvert, corrosion, a perforated invert (up to 0.5 inch perforations) and missing nuts and bolts from the steel plating were observed as a result of the corrosion. Also, the bolt pattern of the steel plates were originally constructed “in-line” with each adjacent plate instead of being offset, which might have contributed to structural weakness.

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Inlet of original pipe                                                       Outlet of original pipe

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Inside original pipe barrel

Initially Maintenance Engineering proceeded with a regular rehabilitation/repair contract and an environmental document that restricted the start of work to August (water levels, etc).  However, since the rehabilitation work needed to be done before the coming winter, an Informal Bid contract by Director’s Order was executed in order to complete the repair work on time.

A study was performed by the District Hydraulics Branch to identify the condition of the existing pipe and make recommendations for pipe lining or replacement. Due to distress in both the invert and the soffit, complete lining of the pipe was selected.

Based on velocity concerns for smooth-bore pipe, the recommendation made was to use a “liner” pipe using the largest corrugated steel pipe that could be inserted.

Internal measurements of the failing original pipe were taken and hydraulic analysis verified that the diameter could be reduced to 84-inch with a CSP liner without detrimental impact. A 0.168-inch thick (8 gage) CSP liner was selected from the Alternative Pipe Culvert recommendation prepared by the District Materials Branch to provide 50 years of service life based on a soil pH of 5.85 and soil Minimum Resistivity of 2900 and assuming non-abrasive flow conditions.


The insertion process consisted of sliding individual 20 foot segments one at a time, coupling them and then pushing the combined pieces into the host pipe - initially using one excavator at the upstream end. After the liner was inserted to approximately the mid point of the host pipe, a second excavator was added to pull from the outlet end.  While the jacking operation was aided by the welded skids on the bottom of the CMP liner (see detail on next page), the existing bolts in the host pipe were problematic.

Once all of the liner was in place, continuous grouting of the annular space was performed.

The resulting hydrostatic pressure at the downstream end from continuous grouting of the annular space between the existing culvert and the 84-inch CSP liner placed inside caused the liner to float and buckle with grout leaking out of the liner’s joints which had been specified as watertight with gaskets. The grouting operation was immediately stopped and a Contract Change Order (CCO) was developed.

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Grouting through grout port in soffit of liner           Grout from leaking joints in invert

The CCO modified the design to welded joints for the CSP liner and the grouting from continuous to grouting in 3 sections (lifts). The continuous grouting was originally anticipated to take 2 days. The sectional grouting took 6 days. The installation of 8 welded skids as shown on the plans (see end view) was omitted to avoid additional welding.
The total completed construction cost was $340,000.

Lessons Learned

  • Preliminary Investigations

To more completely determine the reasons for the culvert’s failure the following studies were warranted but not performed prior to selecting a repair strategy:

  1. Wall thickness measurements in host pipe
  2. Waterside pH and resistivity
  3. Structural analysis of host pipe and proposed repair
  4. Void detection and geotechnical investigation

At the time of repair, it was still unclear what the failure mechanism for the host pipe was. In general, coordination with Underground Structures and Geotechnical Design from within the Division of Engineering Services (DES), and Headquarters Hydraulics should be made for any liner larger than 60 inches diameter. The repair work performed may well provide an effective solution, however, because several unknowns still exist there is a potential for reduced service life if all of the underlying mechanisms that led to failure of the original pipe have not been addressed by the repair.

  • Material Selection

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Because the upper half of the culvert was failing, based on the Materials Report and hydraulic analysis, it was determined that lining with a full circumferential 84-inch diameter CSP liner was the appropriate repair strategy. With the information that was gathered, i.e., from visual inspection (flexible and deformed host pipe, crack in roadway above pipe), the as-builts (profile/grade), the Alternative Pipe Recommendation (based on a soil pH of 5.85 and soil Minimum Resistivity of 2900 and assuming non-abrasive flow conditions with velocities ranging from 5 ft/s to 6.5 ft/s (see paragraph following alternative repair strategies below), and known host pipe dimensions and profile, a number of alternative repair strategies could also have been considered. Some of these include:

  1. A Rigid liner design; This may have been preferable for the given design parameters to account for loading, resulting grouting pressures during construction and potential abrasive flow condition that was not identified in the Materials Report: RCP, Fiber Reinforced Concrete or Reinforced Polymer Mortar are all viable rigid liner material options.
  2. A flexible liner system with a modified high compressive strength structural concrete mix placed in stages in lieu of annular space grout with adequate consideration for bracing and joint type to handle pumping pressures. In effect, this is another “rigid liner” design to independently handle loading and assumes the host pipe no longer can. For CSP steel pipe, an abrasive and corrosion resistant lining would be preferred, otherwise PVC or HDPE could be used.
  3. A 360 degree shotcrete lining with welded wire mesh or synthetic fibers. Synthetic fiber reinforced shotcrete or shotcrete lining with welded wire mesh are preferred if ground movement is present. In tests conducted by others, at larger deformations (with consequent greater crack widths) the mesh and certain fiber reinforced shotcretes displayed exceptional residual load carrying capacity. This is another pipe within a pipe concept that is fairly easy to construct.

It should be noted that the Culvert Recommendation Report prepared by District Hydraulics identified the flow velocity to be 22 ft/s for the Design Storm discharge. The same report specifically recommended not using smooth-bore pipe. Therefore, most of the alternative repair strategies described above would also require consideration of an energy dissipator at the outlet.

If any voids behind the existing culvert had been detected, they usually require grouting before lining or other repair can proceed.

If the host pipe is deformed, any liner may be subjected to stress concentrations where host culvert is failing and soil loads are transferred. It is imperative that the host pipe can adequately handle loads by transferring stresses to the surrounding soil. For any liner placed inside of another flexible pipe, which is already under distress, some loads will be applied directly to the liner. Therefore, if it is not possible to make the host pipe capable of sustaining design loads, it should be either replaced, or lined with a structural system independently capable of handling loads.


A preferable alternative to the welded skids to aid the liner insertion process may have been to weld steel plate to the invert of the host pipe.

Particular attention to the contractor’s grouting plan for long, large diameter, flexible liners is needed for pipes on a steep grade where there is a potential for significant hydrostatic pressure. Both the specified gasketed water tight joints and method for continuous grouting needed modifying in the field to welded joints and grouting in separate lifts.

As previously discussed, the resulting hydrostatic pressure at the downstream end from continuous grouting of the annular space between the existing culvert and the 84-inch CSP liner placed inside caused the liner to float and buckle with grout leaking out of the liner’s joints. In this instance, the invert elevation difference between the inlet and outlet was 24 feet.

Example 4: Compaction Grouting

Project location:  Century Freeway, Los Angeles, California.
Construction period: August 1996 - August 1997
General contractor:  Denver Grouting Services, Inc.
Scope of work:  Approximately 6500 cubic yards compaction grouting
Contract value:   $7,700,000


In March of 1995, major sinkholes occurred along a new 4-mile section of the I-105 freeway between the San Gabriel and Los Angeles Rivers in Los Angeles, CA. The sinkholes were attributed to infiltration of soil into the storm-drain system through insufficiently sealed pipe joints. Caltrans issued a multi-phased contract to Denver Grouting Services, Inc. (DGS) to: (1) stabilize the sub-soils and fill voids along alignments of Corrugated Metal (CMP) and Reinforced Concrete (RCP) storm-drain pipes beneath the freeway pavement, (2) repair leaking pipe joints, (3) mitigate liquefaction-potential along the pipe alignment under one of the pump-station structures, and (5) install water and observation wells for subsequent ground water draw-down testing.

This freeway was built as much as 40 feet below surrounding ground levels, which required a major water-pumping system to be installed at the time of construction (1993). The storm drains were installed 15 to 20 feet below the road surface, which meant the storm drain pipes were as much as 60 feet below the original ground level. The groundwater table was less than 5 feet below the freeway pavement in some areas.


Compaction Grouting was the method chosen to support the roadway and traffic loads by stabilizing the soils surrounding 14,500 feet of RCP and CMP storm drains, and to densify liquefiable sands beneath one of the pump structures. Storm-drain sizes included 24, 30, 36, 42, 48, and 54 inch diameters. It should be emphasized that compaction grouting primarily applies to voids not immediately adjacent to the culvert (i.e., beyond 12 inches) to support the roadway and traffic loads. See Index 6.1.2 for grouting voids in the soil envelope immediately adjacent to the culvert.  

Geotechnical Conditions:

The storm drains were installed through alluvial deposits consisting of medium sand, silty sand, silt and clayey silt layers which varied in thickness along the alignment. A mixture of these native soils had been used as storm-drain "trench" backfill at the time of construction. In general, very low densities and voids existed around storm drains where they were below the groundwater table, and soil infiltration was maximized. Fluctuating water tables had also affected the remaining alignments to varying degrees, creating unacceptable densities and created some localized voiding. Because depths of the CMP and RCP drains varied between 15 to 20 feet. (below the road surface), it was determined that the ground improvement program should extend from a minimum of 5 feet below the storm drains invert up to within 5 feet of the road surface. The work was to be performed with minimal disruption of traffic.

Cut-off Criteria

The grout injection cutoff criteria included:

Maximum 0.5-inch allowable pavement uplift or 0.5-inch storm-drain deflection. A predetermined volume of grout per foot stage.

Maximum grout pressure "at the header" of 450 psi, or a sudden 50 psi drop in pressure, indicating soil shear or grout travel was occurring.


The Compaction Grout equipment employed met the requirements of Caltrans to minimize its operational "effects on traffic" and involved "The Denver System™" as developed by DGS, including:

Mobile Grout Batch Plants
DGS 2015 Mobile Grout Pumps
DGS 2" I.D. Grout Casing, 3 to 5 foot lengths
DGS Grout Casing Retrieval Systems
Specialized Casing Driving Systems







This page last updated August 20, 2011