Caltrans Culvert Rehabilitation Project

OVERVIEW

The Caltrans Culvert Rehabilitation project scope was to rehabilitate 13 culverts along I-8 in Alpine, California. Some of these culverts are more than 50 years old. Culverts 1-2, 4, 6-7, 9, 10, a portion of 11, 12-13 were lined with a Cured-in-Place (CIPP) liner while Culverts 3, 5, 8, and a portion of Culvert 11 were rehabilitated with concrete invert paving.

JWF performed the concrete invert paving.  The work included the following:

  • Full culvert cleanout (Performed by GC)
  • Rust removal on corrugated peaks where nelson studs were welded
  • Grouting/fill of any voids in the flow line
  • Stud installation
  • Wire mesh installation
  • Shotcrete placement (Performed by JWF’s sub)
  • Contact grout of discovered voids along walls above spring-line  

Culverts 3, 5, 8, and 11 were to be lined with steel nelson studs welded to wire mesh for reinforcement and lined with 6000-psi shotcrete. JWF self-performed the reinforcement installation, and a subcontractor placed the shotcrete.

CHALLENGES

Schedule

JWF was to start work in May 2020 however only 2 culverts were available to begin work on, Culvert #5 & #11. Due to environmental restrictions at Culverts #3 and #8, these culverts were not available for access until late September 2020. This was anticipated at bid time and incorporated into JWF’s schedule. The main crew working on the project was moved to other jobs during this period.

Owner

The Caltrans inspection team was a challenge to work with as the materials department in this district is extremely strict. Due to a vague special provision for the material used for the invert paving, the DOR held strict to a variety of standards which caused the mix design for the 6000-psi shotcrete to almost impossible to meet. After 4 reviews and revisions, the DOR finally accepted a mix. Only one supplier in all of San Diego County would supply this specific mix design.  

Differing Site Condition (DSC)

JWF was responsible to divert groundwater from the flowline of each culvert with an approved diversion plan. After implementing the diversion plan for the first time on Culvert #5, it was discovered that perched groundwater was still infiltrating the flowline to the point that the Inspector required further measures to be taken. As the contract was written, the diversion plan was the only means of water diversion required by the contractor. The Geotechnical Baseline Report (GBR) indicated that perched groundwater would not be an issue and would not affect construction activities. To remove the perched groundwater JWF installed wells 18” below flowline with additional pumps routed to the main diversion line every 50 feet. This was performed on all culverts except #8.

Equipment Restrictions

Each culvert only had main access from one portal where all materials and work would only be able to progress from one end. Large equipment was not allowed down to the culverts resulting in having materials delivered offsite and manually brought into each culvert.

PERFORMANCE

Each culvert was different and possessed its own challenges, but all were rehabilitated in the same overall manner. Due to the prevalent challenges, size and nature of Culvert #3, this location will be highlighted below in detail to give the reader an understanding of how the work was performed and what was encountered on this project as a whole.

Culvert #3 was the final culvert rehabilitated and was the largest (15’ diameter / 600 LF). This culvert presented many challenges including a significant settlement along the middle 200’.

Figure 1: Portal of Culvert #3 and settled portion.

It was discovered when JWF gained access that the mid 200 LF of Culvert #3 had significantly settled (about 1ft from the original flowline). The initial concern was that entry would not be safe but after meeting with the Caltrans inspection team it was decided safe for entry and construction.  The flowline was repaired by filling the 200 LF void with a 3-sack slurry to match the unsettled flowline.

Figure 2: Filling the settled portion of Culvert #3 with slurry

After the flowline was repaired JWF installed the nelson studs and wire mesh. The mesh had an arc length of over 15’ and could only be rolled in 12×6 sections. To cover the entire length 2 pieces had to be made for each 6’ section along the radius.

Figure 3: Galvanization removal and Nelson stud installation.

A substantial saving on the project was the ability to self-perform the galvanization removal on the culvert corrugation peaks and the nelson stud welding. A large cost of the project would have been utilizing a certified welding subcontractor to perform this. The project specifications did not require a certified welder for this scope. The picture above is of JWF crew members removing the galvanization and welding studs on Culvert #8. Two Studhorse 1200i welding guns were utilized for the welding and the crew was able to average about 2,000 studs a day. There were 18,000 studs on Culvert #3. Once the studs were in place the wire pash was placed 1” above the surface and tack welded to the studs.

Figure 4: Shotcrete placement on Culvert #3

After the mesh was placed, JWF’s subcontractor Superior Gunite was able to move in and perform the shotcrete placement. For Culvert #3 Superior was able to place the entire length in the three full days just before Thanksgiving. After the shotcrete was complete JWF removed the dewatering wells and cleaned out the culvert. A concrete coring sub then took concrete cores for every 50 CY that was placed and performed a break test after the 42-day cure time.

CONCLUSION

The project faced many challenges but the JWF team forged forward through each of them. The project from the top down was a success. The estimate package allowed room for creativity and provided multiple options on how to approach the work. The field team’s creativity and superb work ethic were key to finishing the project on time and well under budget.

Matthew Mills
Project Engineer
James W. Fowler Co.