worker in a culvert

What to Know About Culverts and Grouting

According to the Federal Highway Administration, there are approximately 110,000 tunnels and culverts that serve U.S. highways, many of which are experiencing some degree of reduced functionality due to lack of maintenance or rehabilitation.

So, what are our obligations to restore or repair the current state of our culvert infrastructure network?

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For starters, what are culverts and why do they exist? Culverts are tunnel-like structures that are a substantial part of our infrastructure. These critical structures are designed to serve several purposes such as wildlife passages, preventing flooding, erosion, and other water-related concerns by allowing the safe passage of stormwater from one side of an obstruction such as highway, railway, or embankment, to another.

Culverts are constructed in various shapes and sizes like round, box, and elliptical, and made from materials like concrete, corrugated metal, or HDPE plastic. Proper design, installation, and maintenance of stormwater culverts are essential to ensure they function effectively and prevent issues like blockages, structural failure, and sediment buildup. Culverts are a vital component of stormwater management systems.

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debris in pipe

What are some issues that culverts face?

  • Infiltration/Exfiltration: Excessive groundwater infiltration into stormwater culverts can lead to loss of soil fines — a form of soil erosion — which can compromise structural integrity. Alternatively, exfiltration of stormwater through culvert walls can also result in internal erosion which is the movement of fines through soils due to hydraulic flows and pressure. Infiltration and exfiltration can cause settlement which can lead to structural damage of the culvert, collapse of the structure in extreme circumstances, and damage to above-grade assets through subsidence.
  • Reduced Conveyance Capacity: The effects of infiltration and exfiltration can reduce the cross-sectional area of culverts through structural degradation, thus limiting capacity to convey stormwater and adjusting flow coefficients. This can result in increased flooding and potential damage to surrounding infrastructure.
  • Sediment Transport: Infiltrating groundwater can transport soil and sediment into culverts, leading to reduction in its conveyance capacity due to siltation in the pipe.
  • Maintenance Concerns: Infiltration and exfiltration can make it challenging to inspect and maintain culverts. Sediment buildup, erosion and structural damage may not be easily visible, requiring more frequent and thorough inspections.
  • Environmental Concerns: Groundwater exfiltration can alter moisture conditions in surrounding soils, which can affect soil stability, vegetation, and ecosystems. Infiltration may contribute to localized groundwater depletion, changes in water table levels, and transport of contaminants.
Avanti culvert grouting

Doing nothing to restore these structures can cause the problem to intensify leading to costly repair, more expensive replacement, or worse – harm to human life and community.

To mitigate these challenges, proper design, construction, and maintenance practices are crucial. This may involve the use of appropriate rehabilitation materials, installation of protective measures, regular inspections, and addressing issues promptly to ensure the long-term functionality and stability of stormwater culverts.

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One cost-effective, long-lasting technology for groundwater control and soil stabilization is the use of injection grouts.

grouted culvert

Injection grouting is a process used in civil engineering and construction to seal the system from infiltration and exfiltration. Additionally, injection grouting solidifies exterior soils by improving the stability of culverts or other underground pipe structures without the need to dig and replace. There are multiple families of injection grouts including acrylics, polyurethanes, epoxies, and Ultrafine cements. Each grout is specifically designed for different applications – including leak sealing, soil stabilization, structural repairs, and void filling.

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Injection grouting is one of the only processes which can benefit culverts in each of the following ways:

  • Soil Stabilization: Injection grout can greatly enhance the surrounding soil characteristics. Grouting can reduce permeability, bind soils together, and densify soils resulting in reduced erosion, subsidence, and restoring compromised bearing capacities. This helps maintain the integrity of the culvert bedding and prevents shifting of the culvert and subsidence of neighboring infrastructure.
  • Sealing Leaks/Infiltration: Culverts may develop leaks over time due to failing joints, corrosion, soil erosion, and settlement. Injection grouting can be used to seal leaks by injecting grout into or behind the defect, effectively creating a waterproof barrier with the surrounding soil that prevents groundwater from infiltrating or exfiltrating.
  • Sinkhole Prevention: Sinkholes can form around culverts when soil erosion causes voids to develop beneath the surface. Injection grouting fills voids, both open and within porous soils, reducing the risk of sinkholes and helps ensure stability of the ground or roadway around the culvert.
  • Enhancing Structural Integrity: By stabilizing the surrounding soil, sealing leaks, and filling voids, injection grouting contributes to the overall structural integrity of the culvert. This can extend culvert lifespan and reduce maintenance frequency.
  • Improved Load-Bearing Capacity: Injection grouting can be used to increase the load-bearing capacity of soils beneath and around culverts. This is especially important in projects where soil compaction has been compromised or when lining of the culvert will add to the overall weight of the structure.
  • Inspection and Maintenance Enhancement: Once injection grouting has been performed, it becomes easier to inspect and maintain culverts. By sealing and stabilizing the structure, buildup of sediment will be minimized resulting in less frequent cleaning requirements. It also helps reduce structure movement which can cause offset joints and challenges for some inspection equipment.

It is important to note the specific grouting materials and techniques used may vary depending on the project requirements, soil conditions, and the type of culvert being rehabilitated. Consulting with knowledgeable professionals experienced in culverts, soils, and injection grouting is essential to ensure the most effective and appropriate solution for a specific culvert project.

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Jessica Williams marketing manager at Avanti International. Jacob Swanson is Midwest regional manager at Avanti International.

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