Aggregate Columns on the Jane Byrne Interchange Ramps: Tight Quarters, Poor Soil, and a Customized Approach

As we head into winter, we’re making progress on the Jane Byrne Interchange Ramps project, and recently, the contractor began installing aggregate columns for the new Taylor Street exit approach.

This ramp will connect the proposed eastbound I-90/94 Kennedy Collector-Distributor, or C-D Road, to the proposed Taylor Street Exit Ramp by flying over both inbound and outbound I-290, the CTA Blue Line, and I-290 ramps to westbound and eastbound I-90/94.

Phase II Investigations

Phase II design investigations identified this area of the Jane Byrne Interchange to have poor soils which are unable to support the new roadway without ground improvements. These type of improvements that modify the existing ground to make it more stable are also known as geotechnical improvements

The existing clay soils in area are too weak to support the proposed roadway and bridge structures. Because of this, the plans called for the contractor to utilize aggregate columns as geotechnical improvements.

Aggregate columns are shafts of compacted stone installed in tight groups in poor soil to increase the bearing pressure that the soil can safely hold and mitigate settlement under structural footings.

Not only do we have to consider the type of columns used, but we also must consider the best way to install the column. Two typical installation methods include vibrator compacted or tamper compacted aggregate columns. This is a unique challenge and we’ve captured a few photos and thoughts on the process.

Vibrator Compacted Aggregate Columns

The contractor working on this project is using the vibrator compacted method to install the aggregate columns. Vibrator compacted aggregate columns are installed using a vibroprobe to penetrate the soil by vibration to a required depth. Compressed air can be used to aid in reaching the proper depth if penetration is exceedingly difficult or not possible with standard vibratory methods.

The column is then constructed in steps by repeatedly raising the vibroprobe about three feet to create a void or opening in the soil into which gravel is released through the nose cone located at the tip of the hollow probe. The probe is then lowered back into the gravel pocket to consolidate and compact it, using the same vibrating motion and energy that created the void. 

As the vibroprobe is being raised, positive air pressure is maintained in the hollow probe (tremie pipe) containing the gravel to prevent surrounding soil and water from entering the tremie pipe. This action of releasing gravel and compacting it in steps is repeated until a column of well compacted aggregate reaches the top of the ground. 

Aggregate Columns on the Jane Byrne Interchange

The contractor’s submittal lists 126 aggregate columns, each approximately 20 feet deep, at this ramp within the Jane Byrne Interchange. The orange marks and flags in the photo below shows the field layout of where the aggregate columns will be constructed for the southbound Taylor Street exit approach.

 

Below, equipment is being prepared to begin aggregate column construction including the excavator (yellow CAT machine) with the vibroprobe attachment. The blue aggregate hopper is on the top of the hollow pointed probe. Cables and hydraulic hoses from the vibroprobe are attached to the excavator to supply power to the probe. A separate machine called a loader (not shown) will scoop aggregate (stone) out of a pile near the work, lift it and dump it in the hopper. The hopper acts as a funnel to direct the stone to the tip of the hollow probe.

 

Working on a project of this scale requires a lot of coordination, and as construction engineers, we’re  responsible for documenting the progression of the completed work. Working together with the contractor as a team to resolve issues is an important way to reduce delay time or eliminate potential conflicts before they arise all together.

“The subcontractor Menard was very knowledgeable.”stated Ramsey Salahat, PE, one of the construction engineers on the job. “Their crew discussed all foreseen issues with me, and we developed a solution to prevent any potential delays.”

An example of this teamwork was the coordination between contractor and OMEGA during aggregate column installation adjacent to the abutment’s drilled shafts. The plan location of the first row of aggregate columns presented a conflict between the vibroprobe’s hopper and the previously installed abutment drilled shafts. The contractor and OMEGA worked together to relocate the first row of aggregate columns within the allowable tolerances so as not to delay the work.

 

OMEGA is serving as the Phase III consultant for the Illinois Department of Transportation providing construction oversight and management on the Jane Byrne Interchange Ramp project. This project, which is scheduled for construction from 2019 to 2020, involves reconstructing five ramps of the Jane Byrne Interchange to have wider radii and shoulders. This reconstruction will improve the interchange’s overall safety, capacity, and operation while eliminating existing geometric deficiencies.  

The ramps OMEGA is overseeing include: 

  • Ramp West North (WN): Westbound I-290 (Ida B Wells) to Northbound I-90/94 
  • Ramp West South (WS): Westbound I-290 (Ida B Wells) to Southbound I-90/94 
  • Ramp South East (SE): Southbound I-90/94 to Eastbound I-290 (Ida B Wells) 
  • Taylor Bypass Ramp: Southbound I-90/94 to Southbound Taylor Exit Ramp 
  • Eastbound Taylor Exit Ramp
  • Westbound Ida B Wells Viaduct 
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