Drain Pan Void Fill Structural Support CDOT Region 1

A drain pan structure running adjacent to US-287 near Broomfield Colorado had experienced significant voids of varying severity beneath the structure. The drain pan was designed to move water away from the roadway during water events and run off; however, due to issues with the design of this particular structure, water was running beneath the concrete and eroding areas beneath the pan. The integrity of the structure was compro-mised due to the weakened and eroded supporting soil.

CDOT needed an effective solution to treat and repair the almost 800 foot long problem section of drain pan that would not only fill the voided areas, but also protect it against additional damage and structural failure that may also effect the safety of the adjacent highway.

A thorough evaluation of the site was conducted prior to design of the repair plan for the drain pan. It was determined that the more severe voids were located on the uphill slope area of the structure. Alternate solutions, including a flowable fill, were taken into account while determining the most effective way to treat the area. However, due to the advanced features of CST’s proprie-tary injection process, and the unique characteristics of the specialized expanding structural polymer, it was determined that filling the voided areas using this process would most effectively and most efficiently solve the problem. Injections were made directly through the drain pan, filling voids, and strengthening the supporting soils.

The entire stretch of affected drain pan was void filled and stabilized in four days without any disruption to traffic flow along the adjacent highway.

The treatment method allowed CDOT to extend the use life of the structure and avoid the expense of tearing out and replacing the structure.

The specifically designed repair not only eliminated the void space beneath the pan and strengthened the soils, but also provided protection to the structure against future erosion.

Repair costs came in under budget for this project.

Culvert Annular Void Fill

Utah DOT Culvert Annular Void Fill

Objective of this project was to fill annulus between culvert and surrounding embankment. The outer pipe was rusted out at the bottom and water was leaking in between the two pipes and coming out bottom of joint. Goal was to seal leaks in an outer pipe, surrounding smaller pipe and fill voids.

Critical elements of this project were dealing with the rusted out bottom of the outer surrounding pipe. Large amounts of water needed to be pushed out and fill resultant voids to assure pipe support and stability.

CDOT HWY 52 CMP Rhabilitation – Hudson, CO

The Problem

The deterioration of Corrugated Metal Pipe, (CMP) at the flow line is a result of exposure to oxygen and moisture mixed with metal, which causes rust. Other factors such as soil conditions and the acidity of the water flow will also affect the rate of deterioration.

When CMP deteriorates, water runs under the pipe instead of through and undermining of the structure occurs. Sink holes above the structure will begin as the soil collapses. The underlying bedding material or support fill is then exposed to water flow, and begins to erode away, causing voids and loss of structural support. This creates a potentially dangerous situation with the possibility for failure of the entire structure and collapse of the overlying roadway.

Concrete Stabilization Technologies, Inc.’s Field Consultant, Richard Hess was contacted by Colorado Department of Transportation Maintenance Department representative for Region 4, Zach Junk, concerning a deteriorated culvert beneath Colorado State highway 52 near Hudson, Colorado. The traditional method of tearing out and replacing eroded culvert pipe had proven to be a time consuming and disruptive process which had lead CDOT to seek a less disruptive solution.

The Solution

CST met on site with Mr. Junk and after reviewing the area, determined that our CMP repair process was an ideal fix for this particular culvert and overlying roadway. Subgrade stabilization injections from the roadway surface were included in the repair plan where exfiltration of soils through the rusted out pipe had caused variable settlement in the road surface above the culvert, requiring steel plates as a temporary fix against further damage to the road surface and vehicles. Thus, part of the CST complete solution was to not only secure the metal sheets to the old CMP but to also inject from the road surface above to 3′ to 4′ to reinforce the subgrade while replacing soil lost to exfiltration.

CDOT maintenance representative Zach Junk stated that he, “liked the fact that they didn’t have to close the road or detour traffic like they normally do when having to replace pipe.”

Structural integrity of the existing pipe was a concern and it was discussed that not only would the structural integrity of the pipe be restored, but also restoration of correct flow into the repaired pipe.

The ditch company expressed concern of subsequent debris buildup such as weeds and silt that may disturb the water flow. The repair design and installation is such that this concern is positively addressed and re-establishes water flow with no added obstruction.

After an in depth investigation and review of the site, it was assured that this would be an ideal repair process for the deteriorated culvert and CST was given the approval to begin the project.

Crews arrived on the job site around 10:00 a.m. to begin repairs. A significant amount of water was running in the ditch containing the culvert. While water was shut down, crews began deep injection to stabilize the sub-grade on the overlying roadway. Injections were made from the surface at a depth of approximately 3 ½ feet on 5 foot centers, while monitoring at the surface for move-ment. After the subgrade stabilization was complete, it was determined that one of the two overlying road lanes was in good shape and the other lane would only require select asphalt patching once repairs were complete.

The Results

Neither lane required any excavation during repair, due to CST’s unique in situ polymer injection process. Once stabilization of the roadway was complete, the crew began repairing the corrugated metal pipe. Repairs and cleanup were completed in one working shift. The Frico Ditch Company representative confirmed that “the ditch is flowing well”.

Benefits of CMP Repair

The patented CMP repair process is quick and non-disruptive. The pipe is first cleaned of any sticks, rocks, and other debris. Repairs begin on the outlet-side of the pipe where the new sheets of specially coated metal are laid, ensuring the corroded water line is covered. The metal sheets are then attached to the ribs of the pipe with corrosion resistant fasteners. Overlapping sheets are then continuously added and secured in place until the length of the pipe is completely reinforced. In this case, the culvert being repaired was approximately 50 feet long and 5 feet in diameter with the corrosion/water line reaching approximately one third of the way up the side wall of the culvert. Once the new metal sheets are all placed, and secured, expanding structural polymer is injected beneath the metal sheets, to fill any voids beneath the pipe. Excess material is removed and a tar coating is applied to the top edge of the new metal sheeting as an extra protective measure to deter rusting and to ensure longevity.  The benefits include:

  • No-excavation
  • Less disruptive
  • Reduces costs
  • No road or rail closure or downtime
  • Repair equipment & material are easily mobilized
  • Extends lifetime of invert
  • No loss of flow
  • Environmentally inert materials
  • Completely restores structural integrity

 

Battle Mountain Highway Frost Heave – Encampment, WY

Abstract

This project investigated a novel procedure to reduce or prevent subgrade freezing non-destructively by injecting a two part rigid polymer foam at the top of the subgrade. Controlled injection of a CST expanding structural polymer foam created a continuous three inch thick layer of insulation that significantly reduced the heat loss from the deeper soil and prevented the upward movement of water from the warmer regime under the foam to the upper frozen regime above the foam, preventing segregational freezing in the upper zone. The construction time for the 170 foot section was one week for injection and milling the surface. Construction was contained in one lane, leaving a lane open for the entire duration without a detour, increasing safety and minimizing impact for the driving public.

Additionally, a procedure is developed for estimating the thickness of the foam layer required for other sites with different average temperatures.

Objectives

  • Can foam be injected nondestructively to level the road surface and make the road safer to drive without full reconstruction?
  • Will the foam layer provide a sufficient thermal barrier to prevent heat loss and reduce frost heave?
  • Will a continuous layer of foam create a barrier to vertical water movement and reduce spring thaw degradation?

Background

  • This section of Highway WY-70 was constructed in the early 1980’s. The highway crosses a crystalline caprock ridge outcrop that the contractor had difficulty removing.
  • The contractor was allowed to alter the design to leave the ridge intact and place three feet of compacted silty sand fill over the rock with the sub-base and base course on top over a distance of 150 feet.
  • Lateral drains and cross drains have not completely removed the water under the pavement. .
  • The combination of a frost susceptible silty sand, extended cold temperatures and the availability of water provide the necessary pieces for segregational frost heave.
  • Measured heaves of three inches and reported heaves of four to six inches created a dangerous bump over a short distance of 75 feet. In addition, a drain installed over the caprock was backfilled with non-heaving backfill which created a dip significant enough to flip snowmobiles off of trailers when traveling faster than the posted speed.

Proposed Solution

A standard technique to control frost heave is to place several layers of foam insulation panels below the sub-base course. This requires a full reconstruction of the site. A process was proposed to inject a three inch thick layer of a two part structural polymer foam at the bottom of the sub-base without removing the existing road surface.

Construction

Concrete Stabilization Technologies, Inc (CST) injected the foam through a series of 3/4 inch diameter, 18 inch deep holes drilled through the road surface on a 6 foot grid. Three inches of foam were injected over the area with the most heave. Additional injections provided tapered zones to smooth the transition from the original road surface to the full thickness zone.

The process required two trucks and a four person crew to complete the work in four days. All the work was performed in one traffic lane at a time while keeping the other lane open for traffic. Because of the poor road surface before the injection, the surface was milled at a later time. The subsequent road surface was sufficiently leveled to make the mediation unnoticeable.

Injection and Instrumentation Locations

  • Thirty survey points at 10 feet centers were measured over a 300 foot distance on five rows located at:
    • The centerline of the road,
    • The centers of the two lanes, and
    • The north and south edges of the lanes.
  • Five piezometers located in the north and south shoulders of the road.
  • Six boreholes with thermistors to measure the temperatures in the soil profile. One thermistor in each hole was located:
    • Above the injection point and the foam layer,
    • Below the foam layer, and
    • Ten inches below the foam.
    • One or two other thermistors were located lower depending on the depth to bedrock.

Results

The upper figure shows the measured elevation changes from the summer baseline along the center of the east bound lane.

    • The thin solid black line shows the heave in January prior to the injection of the foam. The dip at STA 2+10 is the location of a French drain that was backfilled with non-heaving sand.

 

    • The heavy black line shows the foam thickness averaging 3 inches with tapered edges to the east (STA 2+40 to 2+70) and west (STA 1+70 to 1+40).

 

    • The colored lines show the elevation differences in the two winters after injection. The total heave over the treated zone is generally less than 0.5 inches and is less than the natural heave outside the treated zone. The lower figure

 

    • shows the elevation changes along the centerline of the west bound lane. Substantial heave is shown where the foam thickness is only 1.0 to 1.5 inches.

 

 

The upper figure shows the measured elevation changes from the summer baseline along the center of the east bound lane.

  • The thin solid black line shows the heave in January prior to the injection of the foam. The dip at STA 2+10 is the location of a French drain that was backfilled with non-heaving sand.
  • The heavy black line shows the foam thickness averaging 3 inches with tapered edges to the east (STA 2+40 to 2+70) and west (STA 1+70 to 1+40).
  • The colored lines show the elevation differences in the two winters after injection. The total heave over the treated zone is generally less than 0.5 inches and is less than the natural heave outside the treated zone. The lower figure
  • shows the elevation changes along the centerline of the west bound lane. Substantial heave is shown where the foam thickness is only 1.0 to 1.5 inches.

The lower figure shows the elevation changes along the centerline of the west bound lane. Substantial heave is shown where the foam thickness is only 1.0 to 1.5 inches.

This figure shows the elevation changes along the centerline of the west bound lane. Substantial heave is shown where the foam thickness is only 1.0 to 1.5 inches.

The heavy black line in the below graph shows the thickness of the foam being about 3 inches under the east bound lane and tapering to zero under the west bound lane.

  • The thin colored line is the measured heave in the year before construction.
  • The other colored lines are the measured heaves during the two winters after construction.
  • The heave on the south edge (-12 feet) is caused by edge effects and local freezing.
The heavy black line in this graph shows the thickness of the foam being about 3 inches under the east bound lane and tapering to zero under the west bound lane. The thin colored line is the measured heave in the year before construction. The other colored lines are the measured heaves during the two winters after construction. The heave on the south edge (-12 feet) is caused by edge effects and local freezing.

Conclusions

  • Transferability of the control strategy is possible if the weather conditions in the new corridor are similar (i.e. defined by the same weather variables) to the corridor where the control strategy was developed.
  • It would be beneficial to train the decision trees with the storm data collected at the new corridor.
  • The system should be monitored till it is recommending desirable speed limits based on real time weather and traffic information.
  • From the simulation results it is observed that proposed control strategy is performing slightly better than WYDOT’s manual protocol.
  • If the control strategy is to transfer a completely new corridor, it would be ideal to collect some storm data and train the decision trees before using the control strategy in real time.