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Bridge & Roadway

By applying unique solutions to increase the safety and longevity of our environment.

MSE Wall Backfill

The Job

The geotechnical investigation for a double bridge replacement in Amelia County, Virginia found a layer of compressible soils below four proposed abutments.

Anticipated settlement exceeded allowable settlement, so the abutments were designed to be backfilled with expanded shale lightweight aggregate.

The two parallel bridges have an AAWDT of 14,000 and carry a rural divided highway (US-360) over Norfolk Southern Railway & Business 360 in Amelia Courthouse, Virginia.

The Challenge

Lightweight fill placement had to be unaffected by frequent rail traffic, have a limited footprint, and be economical.

The Solution

CJGeo provided a value engineering proposal to utilize 30lb/cuft cellular concrete in place of the expanded shale lightweight aggregate. This significantly reduced the unit weight of the lightweight fill, given the 70lb/cuft density used in the design, further reducing the anticipated settlement.

CJGeo mobilized a 200CY/hour cellular grout plant to the site and placed lifts ranging in size from 35 to 300CY. Wall erection crews were able to walk on the in-place cellular concrete without leaving footprints as quickly as 4 hours after each placement.

The total project volume was approximately 7200CY.

Stone Arch Lightweight Backfill

The Job

A stone arch bridge constructed in the 1800s was experiencing significant scour at the bases of the arch. This caused differential settlement of the structure, and deterioration of the wing walls.

The bridge, which was adjacent to a historic mill structure, could not be removed and replaced with a modern structure, it had to be rehabilitated in a fashion which preserved its historic nature.

The bridge was constructed on shallow stone foundations.

The Challenge

As part of rehabilitating the structure, structural engineers designed two new mass footings in the stream bed to underpin the edges of the stone arch. Then, to strengthen the arch designed a 12″ thick reinforced concrete arch overlay on top of the stone arch for the full length/width of the bridge.

In order to compensate for this additional weight, designers determined that a lightweight fill material was needed to reduce the chances of inducing settlement.

Designers also evaluated remedial deep foundations but determined that lightweight fill was the fastest and most economical solution.

The Solution

After the structure had been rehabilitated, CJGeo installed 325CY of 30lb/cuft cellular concrete to backfill the structure. Placed in lifts up to 4 feet thick, the work was completed over a period of three days.

By using 30lb/cuft non-permeable cellular concrete, the dead load on the underlying soil decreased by up to 935lbs/sqft relative to compacted soil backfill.

Because cellular concrete is self-consolidating and can easily be pumped hundreds of feet, single side access was not a problem, and no compaction equipment was necessary.

A crew of two workers completed the pour using continuous wet batch generation. Wet batch generation was chosen due to the relatively small daily volume of material placement.

PA Turnpike Undersealing

The Job

As part of a 24 lane mile mill & pave rehabilitation on the Pennsylvania Turnpike, slab stabilization was required. The Turnpike’s specification for stabilization is either liquid asphalt or polyurethane.

The Challenge

In order to keep MOT in place continuously, work had to be done 24 hours per day. Due to work on three bridges within the repair area, undersealing also had to be phased.

The Solution

CJGeo proposed undersealing with CJGrout 40NHL, a 4.0 lb/cuft free rise polyurethane grout formulated specifically for undersealing thick pavements in transportation environments. 40NHL is hydro insensitive, so performs well in wet environments, as confirmed with NYSDOT GTP-9 testing.

Using a double gang drill and single grout truck, CJGeo crews undersealed up to 1.8 lane miles per shift. Drilling was completed at night, and grouting during the day, to allow the general contractor to keep MOT in place continuously.

Bridge Approach Polymer Grouting

THE JOB

The George Washington Memorial Parkway connects Washington, DC with Fairfax and Alexandria Counties in Virginia. Originally designed as a scenic route, the road has transformed into a heavily used commuter route in and out of Washington. The road runs along the Potomac River, with bridges crossing deep ravines, including Windy Run.

THE CHALLENGE

Our biggest challenge with this project was making sure this heavily populated commuter route was completed in a timely fashion.

THE SOLUTION

CJGeo proposed polyurethane compaction grouting using CJGrout 30NHL, which is specifically formulated for improving the bearing capacity of loose soils. Grouting was performed on 4’ centers, at 5’, 10’ & 15’ below grade, until surface movement was detected. Top-Down grouting was used to help ensure maximum densification of underlying soils, and approximately 25,000 pounds of grout were used over two mobilizations. Due to polyurethane grout’s nearly immediate cure, CJGeo helped ensure that ground improvement stayed out of the critical path of this accelerated project. Pre and Post Grouting DCP Testing was performed by Schnabel Engineering to quantify the soil density improvement.

MD 355 Lightweight Fill

THE JOB

As part of the construction of a pedestrian underpass at the Medical Center WMATA station, an open cut tunnel was installed. The tunnel crossed under MD-355, but over the underlying Metro Red Line tunnel. To maintain vehicular traffic during construction, a temporary bridge was constructed spanning the H-pile & lagging open cut walls.  

After the tunnel was completed, the 7′ of space between the top of the new pedestrian tunnel and the bottom of the temporary bridge had to be filled. Numerous utilities, including gas transmission mains, a power vault & duct bank, municipal water, gravity sewer, and numerous communication duct banks and lines all passed through the fill area. The tunnel designers had planned on lightweight fill material being used for the majority of the backfill in order to reduce loads on the new pedestrian tunnel.

The extensive utilities and limited working space made other lightweight fill materials such as EPS blocks and lightweight aggregate impractical to place. The Clark Foundations project team reached out to CJGeo to come up with a pumpable lightweight fill solution.  

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THE CHALLENGE

CJGeo proposed using cellular concrete for the lightweight backfill.  Cellular concrete had a few distinct advantages:

  • Unit weight: the 30lb/cuft density met the designer’s requirement for unit weight, and also reduced buoyancy of to-be-embedded utilities
  • Strength: the 125psi at 28 days strength far exceeded the requirement, and allowed for nearly immediate final backfill & paving
  • Safety: since cellular concrete is pumped into place, just a few hours of labor were required in the tunnel to set the grout placement pipes
  • Constructibility: aside from being lightweight, the primary concern was ensuring that all utilities were fully encapsulated and that there were no voids left. Since the fill had to go to within 12″ of the bottom of the temporary bridge beams, this would have been exceptionally difficult with any type of non-pumped lightweight fill.

THE SOLUTION

CJGeo mobilized a single cellular concrete crew to the site, capable of producing up to 150CY/hour of cellular concrete. Over the course of three days, CJGeo placed 990CY of 30lb/cuft non-pervious cellular concrete, using Aerlite preformed foam. The placement schedule was primarily driven by DOT-imposed maximum lift thicknesses. Placement into the tunnel was done via sacrificial tubes suspended from the bridge decking, in addition to hose discharge into the tunnel ends.

7 day breaks on the cellular concrete exceeded the minimum strength for backfilling. This allowed the customer to stay on their targeted schedule.

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