Structural Concrete Removal Over Water: Methods, Challenges, and Best Practices from the Navy Pier Redevelopment

Planning Structural Concrete Removal in Waterfront Environments

Removing structural concrete in a waterfront environment presents a unique set of challenges that go well beyond typical demolition work. The recent redevelopment of Chicago’s Navy Pier provides an instructive example of how careful planning, specialized equipment, and innovative problem-solving come together in complex structural concrete removal projects. When 56 sections of massive structural concrete slabs and beams needed to be removed directly over Lake Michigan to make way for recessed tree pits, the project demanded meticulous preparation. Contractors faced the task of cutting through 31-inch railroad-track embedded slabs and 34-inch concrete beams, with individual concrete masses weighing in excess of 35,000 pounds per piece. Success in such an environment depends on a systematic approach that begins long before the first saw blade touches concrete.

Advanced remote controlled demolition techniques have transformed how contractors approach structural concrete removal, but even the best equipment requires a thorough upfront assessment. The first step is a detailed review of original structural drawings to understand reinforcement layouts, load paths, and the precise location of embedded elements. Engineers must calculate the weight of each section to be removed and determine how the remaining structure will redistribute loads during and after cutting. This structural analysis informs every subsequent decision, from selecting cutting sequences to positioning rigging points and crane placements.

Structural Assessment and Drawings Review

Before any cutting begins, the project team must meticulously dissect the original engineering drawings. This process identifies critical structural elements such as post-tensioning tendons, embedded conduits, and existing reinforcement patterns that must be avoided or carefully managed. The review should also identify any historical modifications or repairs that may have altered the original structural behavior. For the Navy Pier project, this thorough review allowed the contractor to develop a step-by-step cutting procedure that preserved the structural integrity of the 98-year-old pier throughout the demolition process.

Key Pre-Planning Considerations

• Identify all load-bearing elements and determine safe cutting sequences that prevent progressive collapse
• Calculate section weights to match crane capacity and rigging requirements
• Establish environmental protection measures for work over or near water bodies
• Plan for weather contingencies, especially when working in cold climates
• Coordinate with structural engineers to validate temporary load paths

The planning phase should also include a thorough concrete structure assessment using ground penetrating radar and other nondestructive testing methods. These tools help locate embedded utilities, post-tensioning cables, and reinforcement that may not appear on original drawings or may have been added during previous renovations. This information is critical for avoiding dangerous encounters with energized conduits or stressed tendons during cutting operations.

Equipment Selection for Heavy Structural Concrete Cutting

Structural concrete removal at the scale required for the Navy Pier redevelopment demands specialized cutting equipment capable of handling thick, heavily reinforced sections. The choice of equipment depends on several factors, including slab thickness, reinforcement density, accessibility constraints, and environmental considerations. For the pier project, the contractor deployed four different custom-built wire saws and a Diamond Products CC110 deep cut slab saw equipped with a 72-inch blade to cut through the formidable concrete sections.

Wire Saw Systems for Large Section Removal

Wire sawing is often the preferred method for cutting large structural concrete sections, particularly when working in confined spaces or over water. The system uses a diamond-impregnated wire cable that loops around the concrete section and passes through specially drilled pilot holes. As the wire travels at high speed, it abrades through concrete and reinforcement with precision. Wire saws offer several advantages for structural removal:

• Ability to cut through very thick sections in a single pass, up to 36 inches or more
• Minimal vibration compared to impact demolition methods, reducing risk to adjacent structures
• Clean, straight cuts that leave a smooth surface suitable for new construction connections
• Ability to cut in hard-to-reach locations where slab saws cannot fit
• Reduced dust and noise compared to traditional jackhammer demolition

Deep Cut Slab Saws for Embedded Elements

When concrete sections contain embedded elements such as railroad tracks, heavy utilities, or multiple layers of reinforcement, deep cut slab saws provide the necessary cutting depth and power. The CC110 saw used on the Navy Pier project, with its 72-inch blade, could cut through the full 31-inch depth of the railroad-track embedded slabs in a single pass. These machines use purpose-built diesel or hydraulic power units to deliver the torque needed for sustained cutting through heavily reinforced concrete.

Advancements in modern concrete cutting and removal methods continue to improve efficiency and safety on complex projects. New diamond tool technologies, water recycling systems, and automated cutting controls are making structural removal faster and more environmentally responsible than ever before.

Rigging, Lifting, and Load Management

Once concrete sections are cut free from the surrounding structure, they must be safely rigged and lifted clear of the work area. This phase is among the most dangerous in any structural removal project and requires careful engineering of lift points, selection of appropriate rigging hardware, and precise coordination between cutting and crane operations.

Epoxy Anchoring Systems for Lift Points

For the Navy Pier project, after pre-cuts were made, the contractor drilled and set 1-inch Hilti HIT-HY 200-R epoxy anchors to create secure rigging points in the concrete sections. These adhesive anchoring systems develop high pullout strength by bonding threaded rods or reinforcing bars into drilled holes using specialized epoxy formulations. The selection of anchor type, embedment depth, and adhesive must be carefully matched to the concrete strength, section weight, and load angle expected during the lift.

Rigging Safety Checklist

1. Verify epoxy anchor cure time based on concrete temperature and manufacturer specifications
2. Calculate the weight of each section from measured dimensions and known concrete density (typically 145-150 lb/ft3)
3. Select lifting hardware with a safety factor of at least 5:1 for overhead lifting
4. Position crane to minimize swing radius and maintain stable load path
5. Conduct trial lift of each section to verify rigging integrity before full removal
6. Maintain communication between cutting crew, riggers, and crane operator at all times

A 50-ton rough terrain crane was utilized on the pier project to hoist concrete masses weighing up to 35,000 pounds per piece. The crane’s positioning on the pier structure itself required careful load analysis to ensure the existing deck could support both the crane weight and the lifted loads. This is a common challenge on waterfront and rooftop demolition projects where cranes must operate on the very structure being modified.

Environmental Protection and Winter Operations

Working over Lake Michigan introduced environmental protection requirements that added significant complexity to the concrete removal operation. The contractor fabricated and built three custom-made pontoons to catch concrete chips and slurry, preventing debris from entering the lake. This level of environmental stewardship is essential for projects regulated under the Clean Water Act and local environmental protection ordinances.

Cold Weather Concrete Cutting Solutions

The 2013-2014 Chicago winter ranked as the third snowiest on record and the coldest in 30 years, creating extraordinary challenges for the cutting operations. Water is essential for diamond saw cutting to cool the blade, lubricate the cut, and control dust. In freezing conditions, standard water supply systems become unusable. The project team implemented several innovative solutions:

• An electrically heated water hose kept cutting water flowing to the saw without freezing
• Two custom 32-foot by 24-foot heated work enclosures were fabricated from heavy gauge metal studs and reinforced poly fabric
• The enclosures incorporated lifting points so the crane could relocate them quickly between cutting locations
• Six Kasco 3/4 horsepower de-icers ran 24 hours a day to prevent ice formation around the debris containment pontoons

These heated enclosures allowed crews to continue working through snow and extreme cold, maintaining the project schedule despite conditions that would normally halt outdoor construction. The enclosures were designed for rapid relocation, allowing the team to move from one cutting location to the next without losing productive time to enclosure disassembly and reassembly.

Slurry Management and Containment

Concrete cutting generates slurry consisting of water, cement fines, and fine aggregate particles. Over water, this slurry must be contained and removed for proper disposal rather than allowed to discharge into the water body. The pontoon system deployed at Navy Pier represents a best practice for waterfront concrete work. Key elements of an effective containment strategy include:

• Physical barriers positioned below and around cutting areas to catch falling debris
• Vacuum systems to collect slurry at the point of cutting before it can spread
• Sedimentation tanks or filter bags to settle solids before water discharge
• Regular monitoring of water quality around the work area
• Contingency plans for extreme weather events that could compromise containment

The use of advanced concrete materials like glass fibre reinforced concrete in new construction adjacent to removal areas requires careful protection during demolition. The dust and debris from cutting operations can compromise bond strength and surface quality if not properly controlled, making containment measures doubly important on projects that combine removal with new installation.

Lessons for Future Waterfront Structural Removal Projects

The Navy Pier concrete removal project demonstrates that successful structural removal over water requires expertise that spans structural engineering, equipment operation, environmental management, and cold weather construction techniques. General contractors and specialty demolition firms undertaking similar projects should invest heavily in the planning phase, engage specialty concrete cutting contractors with proven experience in challenging environments, and develop robust contingency plans for weather and environmental conditions. The 50-plus years of combined experience that Alliance Concrete Sawing and Drilling brought to this project highlight the value of specialized expertise when the margin for error is minimal and the consequences of failure extend beyond project delays to environmental harm and public safety risks.