Culvert structures deteriorate over time and present a range of levels of damage. While joint separation or shifting is a common form of culvert decay, more severe damage includes collapsed, distorted, and crushed culverts. Let’s discuss how to properly repair a crushed culvert.
Inspecting a Crushed Culvert
When performing an inspection for a crushed or distorted culvert, structural and hydraulics engineers must:
- Identify the problem
- Determine the cause of the damage
- Evaluate repair options
- Implement designs
- Maintain the repairs
Roadway project designers and maintenance staff can identify problems related to deteriorating culverts by noting the prevalence of sinkholes, ponding water, distorted guardrails, and roadway settlement.
Determine the Cause and Problem Type
Structural deterioration can result in collapsed or distorted culverts, but there are other potential causes of culvert damage and decay.
Some structural culvert problems include loss or erosion of the invert, joint separation in reinforced concrete pipe (RCP) culverts, soil infiltration, and fractures or cracks in flexible pipe culverts. Causes vary from installation damage to the pipes, excessive culvert loads, erosion, corrosion, improper joint seating, and excessive movement.
Once inspectors identify the probable cause (or causes) of culvert damage, their every effort focuses on reducing or eliminating those sources of deterioration. Remediation may include replacing materials with more durable alternatives or redesigning and reconstructing the culvert to make it less susceptible to further deterioration.
Evaluating Repair Options
When evaluating crushed culverts, there are different repair methods to help maintain their future structural integrity. Over time, corrugated culverts change shape and bend due to environmental factors and surrounding pressure.
The state of Minnesota developed the HydInfra database to compile information on all state-maintained bridges into a single database. It published suggested repair methods for steel and concrete culvert pipes. The suggestions include factors to consider before repair and flowcharts to guide repair processes.
HydInfra Pipe Suggested Repair Method
Minnesota’s HydInfra flowcharts help sort characteristics through a computer program. Then, the designer in the field reviews the culvert to verify HydInfra data for specifics that can affect the constructability of the chosen repair method. This includes site access, flow diversions, and staging area requirements.
Culvert repair and rehabilitation both in and outside of Minnesota can use repair techniques such as:
- Spot fixing/patching
- Cured-in-place repairs
- Rigid slip-liners, or
- Spray on techniques.
Preparation for Culvert Repair
Before moving forward with repairs to distorted or crushed culverts, proper preparation is necessary to prevent further damage in the culvert and surrounding area. First, the repair team must protect adjacent lands, waterways, fauna, and flora and obtain any required permits.
Repair crews should determine the flow capacity and variations in both high and low water levels to aid in planning temporary water flow diversions that may be necessary during the repair process. As long as there are no adverse effects on surrounding areas, workers can temporarily divert flow around damaged culverts. Coffer dams and bypass pump systems are some of the most common methods used to temporarily divert water sources.
Before repair work begins, crews clean culverts to remove debris and install necessary fixes or equipment to keep debris from reentering the culvert. Culvert cleaning operations may use high-pressure water jets, push buckets, reaming, augers, vacuum trucks, pull buckets, or brushing to dislodge debris. Larger culverts may require skid steer loaders to remove large heavy debris.
Finally, the culvert repair preparation team checks culvert clearance to determine if there are any obstructions or deformations that impact flow capacity, and implements safety procedures to ensure the repair team is protected when working in and around culverts.
Measuring and Evaluating Culvert Distortion
Flexible corrugated metal pipe (CMP) culverts interact with surrounding soil to maintain load-bearing metrics. It follows that shifts in traffic loads and supporting soil pressure will impact the structural load-bearing capacity of CMP culverts. Over time, culverts can bend and become misshapen due to uneven compaction of supporting soil.
In addition, environmental conditions, infiltration, exfiltration, piping, and erosion at the culvert ends can cause bending and shape deformation. Repairs require an accurate survey of the existing condition of the culvert.
One way to measure the shape and dimension of a culvert is with a traditional survey. A traditional survey uses a manual theodolite, an instrument that measures angles between visible points in horizontal and vertical planes with manual calculations and data recording. This survey technique is relatively inexpensive, but it can be difficult and risky to get measurements this way.
A “total station” survey is an alternative technique using an electronic theodolite with data storage adapters for recording survey readings. While the survey equipment may cost more, the data transfers directly to computer systems for analysis to determine the shape of the culvert cross-section. Uploading data directly avoids the risk of errors in manual data entry.
Lastly, the photogrammetric survey technique requires highly trained individuals to use a special 35mm camera to create large-size prints for analysis, plotting, and determining any shape changes. Other technologically advanced methods like LIDAR and 3D imaging provide exceptionally detailed and accurate measurements and renderings of the terrain in and around culverts.
Repairing Distorted Culvert Sections
The variety of external loads and changing soil positions can cause localized distortion and cracking in a culvert post-installation. Total collapse is possible, especially in cases of uneven soil pressures. The complexity of remedial steps varies depending on the culvert type, the level and severity of distortion, and local site conditions.
There are a handful of ways to impose spot repairs on culvert distortion, including strengthening the culvert with a tunnel liner plate ring, replacing distorted sections with a liner plate ring, and forming a complete shotcrete ring. The use of tunnel liner plates helps repair distorted culverts due to their rigid and covered design.
It’s also possible to replace a liner plate ring if severe distortion occurs. Lastly, if there are instances of cracking and deformation along the entirety of the culvert barrel, repair teams can use rigid slip-liners to rehabilitate the full length of the structure.
Re-Rounding and Reshaping Culverts
Distorted culverts can be re-rounded and reshaped, working from the outside and inside of the culvert, or solely from the inside. The former procedure removes the backfill from the culvert, reshapes the interior, and replaces the backfill to repair and strengthen the crown of the culvert.
When the culvert is too deep to remove the backfill above it, it must be reshaped solely from within the structure. There are a few instances that require interior repair, such as when only one section of the culvert is affected, and the culvert size is only marginally adequate, with reduced hydraulic capacity. The objective is to restore the cross-sectional area and optimal flow characteristics.
Culvert Maintenance Procedures
To ensure a culvert continues to function as it should, culvert repair and rehabilitation projects require follow-up inspections. It’s prudent to plan for ongoing culvert monitoring and maintenance.
Culvert movement can cause joint separation or leakage. InfraSteel culvert liners are joined together by full penetration welds. This radically reduces the possibility of joint failure. Ensuring culverts receive the necessary care and inspections will help ensure solid culvert foundations and stability, and prevent further warping or distortion.
InfraSteel offers quality structural steel pipe culvert rehabilitation services to the nation’s stormwater and trenchless rehabilitation industries. Our arched and elliptical culverts are designed to match the radii of existing culvert structures, maximizing hydraulic flow. They’re made with high-quality domestic steel materials for strength and dependability. Contact our team today if you have questions regarding our culvert rehabilitation services.