News and Events - "DS Article"

Welcome to our newsroom! Here you will find the latest information about our company, projects and people. Browse articles published by our engineers and scientists in national publications and conference proceedings, view our press releases and read through news coverage of Terracon.

If you are a member of the media, you may contact our media relations representative at

All News and Events

Deep Excavation Support: Innovative Geodesign in an Urban Environment

When you plan to construct a 35-story high-rise in Downtown Seattle, you must also plan to go into the ground as well as up.  Structures of this type can commonly require temporary excavations on the order of 50 to 75 feet below grade.  The challenge of such construction is the design of a temporary retaining system that allows such excavations amid the existing infrastructure and adjacent buildings without inflicting damage on your neighbors. In fact, the City of Seattle requires documentation that the designs will not inflict deflections in excess of 1-inch in the existing structures.

Unique Challenges

As part of the Tower 12 Building project, a 60-foot-deep excavation was required to construct five levels of below-grade parking and the foundation system for the new high-rise building. Excavation was facilitated by soldier piles with lagging, along with ground anchors that provided additional lateral restraint. Along the west side of the excavation, the temporary retaining wall was required to maintain support of the adjacent infrastructure which included an existing 20-story tower with three levels of below-grade parking separated from the project by an 18-foot wide alley. The below-grade parking did not permit continuation of the soil nail system used at the other excavation faces, and a site-specific approach was required to accommodate the physical obstructions.

Unique Solutions

The solution combined two temporary excavation support systems, soil nailing and anchored soldier piles, to work within the site constraints.  The adjacent building basement limited the horizontal distance available for placement of anchors in the upper half of the excavation. Densely-arranged, short-length soil nailing was used to support the top 30 feet of the excavation, while the bottom 30 feet of the excavation was supported with soldier pile combined with steeply-inclined, high-capacity (200,000 pound) ground anchors which extended below the adjacent 20-story high-rise building foundation. The solution is shown on the West Wall Section illustration.  Notice how the geometry of the existing basement and underground utilities were accommodated with the combination retaining wall system. This system also eliminated the need for internal bracing, which would have increased the project’s construction cost and schedule.

The performance of the temporary retaining wall was monitored with an inclinometer to measure ground displacement from surface down to rock as well as optical survey monitoring of the top of the excavation, adjacent roadways, and buildings. The monitoring program demonstrated the performance of the unique design met the City’s maximum deflection requirement of 1 inch.

Teamwork Provides Solutions

Other services Terracon professionals provided for the 35-story high-rise building included geotechnical design recommendations for foundation support, site specific seismic design criteria, geotechnical special inspection, and environmental observation to determine if impacted soils were present during excavation. Through a collaborative approach, the team was able to bring to our client an innovative and cost-effective design while meeting the project budget and schedule.


All News and Events

How to determine the best window type

The amount of light coming through a building’s windows determines not only the relative brightness of the interior, but also generates heat. If the building has the wrong type of windows for its climate, more energy will be needed to provide air conditioning or heating to reach a comfortable indoor temperature.

Taking a holistic approach to the window selection can identify risk, enhance performance, optimize comfort, and provide savings. Performance modeling analysis is key to informing decision-making at the early stages of building design.


Visual comfort

Thermal comfort

Building energy consumption

Building aesthetic

Condensation resistance

As an example, a building located in a northern climate may be designed with larger windows when facing south that allow more light, and thus heat, ultimately saving on heating costs. Conversely, a building in a warmer environment typically achieves better energy performance with smaller windows when facing east and west, different orientation, and more tinting and shading. Condensation on windows is a sign of a wrong window type.

When working with a client, Terracon’s facilities professionals consider location, window-to-wall ratio, solar heat gain coefficient (SHGC), orientation, placement and type (single clear, double clear, and double clear low-energy, double low-energy with shade and more). Exterior features such as an overhang or fins also have an impact on energy usage. Local code requirements that mandate specific materials are another key variable. Once all relevant data is compiled, advanced performance modeling software is used to simulate the impact on building façade performance.

Implementation of an energy-efficient glazing design strategy on the high-performance façade is one of the key factors to impact mechanical systems. Selection and integration of the appropriate energy efficient windows is key to maximizing the performance of a building’s façade.

All News and Events

Leveraging Technology: Reducing Environmental Compliance Risk at an International Airport

An Environmental Management Information System (EMIS) is frequently a critical component of an effective Environmental Management System (EMS). Many regulated entities, including airports and airlines are investing in EMIS solutions to help manage their environmental compliance data and streamline compliance activities. This leveraging of technology is giving them a greater ability to maintain environmental compliance and effectively use their data to reduce overall risk. This impactful benefit makes an EMIS solution one of the most important components of an overall EMS program.

Beginning The EMIS Journey

A practical approach to EMIS implementation used by many airports is to focus first on activities with the greatest potential to impact day-to-day operational efficiency and jeopardize compliance with regulatory requirements. For example, at some California airports this has meant utilizing EMIS to assist with complex air quality compliance requirements, while smaller airports with less staff often require a strong focus on compliance submittals and due dates. At the Minneapolis-St. Paul International Airport (MSP), an EMIS was developed with an initial focus on stormwater and de-icing management, two challenging tasks that are data-intensive and can cause regulatory compliance issues. In all of these instances, a phased approach can immediately reduce compliance risk for operations. Considering what organizational elements are most critical will help determine the right EMIS application for your situation.

The Metropolitan Airports Commission (MAC), who own and operate MSP, began using an EMIS to manage various compliance-related tasks and requested Terracon’s assistance in developing a solution to centralize environmental data, increase business continuity, and streamline compliance activities. The MAC team began their EMIS journey using a phased approach with an eye toward continual improvement. The first system utilized macro-enabled Office applications that provided automated task scheduling and weekly reporting. With the success of this system, MAC recognized the value that could be realized with a cloud-based Software as a Service (SaaS) EMIS, adding data centralization, dash-boarding, online inspections, and reporting. In addition, Terracon partnered with MAC to develop online Process Fact Sheets to detail each aspect of environmental compliance and provide links to necessary documents and reference materials. These fact sheets helped to capture the best practices employed by various staff and consultants in maintaining compliance and greatly enhanced the organization’s business continuity.

These robust EMIS systems provide the organization with necessary business continuity, increased performance, and overall reduced risk.

Why would I need an EMIS?

What will happen if one of your key environmental staff leaves? Their institutional knowledge will leave with them. Getting their knowledge into an EMIS will keep your operations running smoothly during staff transition.

What mechanism do you or senior leadership have to perform a quick review of key compliance tasks and if they have been completed? Effective managers delegate to trusted staff and have the responsibility to ensure these tasks are completed on schedule.

How do you and your organization efficiently access and interact with your environmental compliance data? Often data accessibility is limited to those in control of the data, sometimes residing on a single computer. When that person is unavailable, access to your data is be challenging at best.

Are your reports generated in a consistent and timely manner? Nearly all compliance activities include a reporting function. Manual report generation is time consuming and introduces the potential for error if relying on re-keying of data or manual data consolidation.

What Does the Future Hold?

During the past decade, airports have been rolling-out sustainability programs that include environmental transparency often in the form of public facing dashboards and reporting elements. An EMIS can play a key role in collecting, managing, and reporting the necessary information to the interested parties in a systematic and efficient manner. A robust EMIS solution that has been developed with thoughtful consideration to your specific needs and desired technological investment will help organizations effectively and efficiently manage compliance now and well into the future.

All News and Events

Innovating a safer work site

Terracon was recently recognized by the Ohio Bureau of Workers Compensation for their 2018 BWC Safety Innovation Awards. The awards, designed to encourage and recognize innovative solutions to reduce the risk of workplace injuries and illnesses, are given to employers that showcase successful innovations that can help other Ohio employers in their safety efforts or inspire innovation solutions of their own.

Designing a Better Tool

Terracon’s team was recognized for the development of a tool, known as the YankMeister 3000 (YM3000) pin puller, that reduces the potential of back or wrist strains from pulling nuclear density gauge pins.  This new tool helps reduce fatigue, increases technician productivity, increases data quality and improves morale.

Senior Industrial hygienist, Mike Meister, CIH, CSP, of Terracon’s Cincinnati office, developed the tool after observing and recognizing the hazards to the employees due to their awkward postures and excessive pulling forces needed to pull pins with the old, manufacturer provided pin puller.  The YM3000 pin puller allows employees to retain good ergonomic posture and use the stronger muscles of the legs when pulling pins from the ground for soil density readings. The tool was made and tested locally, reviewed by ergonomics specialists, and tested by field staff, supervisors, and safety professionals.

Improving an Industry Practice

The puller eliminates the need to bend, twist, and stoop when performing the pin pulling task, creating an alternative to a 30-year old practice. More than 1,000 units have been mass produced for Terracon Operations, are included with each nuclear density gauge, and used by more than 900 technicians company-wide. The tools are used up to 15,000 times per day. Since their implementation there have been no related back injuries reported related to pin pulling operations.

“The improvement process is pretty simple,” Mike Meister remarked.  “Just talk to workers about what is the most strenuous part of their job, then get creative and find alternatives that reduce those stresses.  Then repeat”.   It’s part of Continuous Improvement and how we demonstrate care and concern for our employees.


All News and Events

Modernizing an Airport Terminal: Expanding Concourse to Improve Customer Experience

As one of Arizona’s main transportation hubs, the Phoenix Sky Harbor International Airport has experienced a significant amount of growth and expansion in the last five years. To meet the needs of its nearly 40 million passengers annually, the airport is working to improve services for its airlines and travelers alike. To help in the expansion, Terracon’s experienced aviation and materials professionals provided quality assurance consulting and non-destructive testing services on various building components to verify that future travelers would be safe during seismic events and that the quality of construction would meet the intended life cycle costs.

The original terminal was built in 1979 and needed improvements to keep the airport competitive. The most recent work involves a $590 million design-build, expansion to the existing Terminal 3, which consists of a new customer processing terminal, South Concourse, and enhancements to the North Concourse. The existing South Concourse of Terminal 3 was razed, and a 15-gate concourse was constructed to replace the existing structure. The makeover included adding windows throughout the facility and even a new garden and dog park – all to bring a more open and modern experience to its visitors. The new structures were constructed of reinforced concrete, structural masonry, structural steel moment frames, and metal decking.

Depth of Services Differentiates

For this signature project, Terracon initially provided materials testing to supplement the City of Phoenix Aviation Department as a part of the quality assurance team during construction. Terracon provided a full-time, experienced aviation technician to perform compaction verification, concrete and grout sampling, and construction observation. Having on-site knowledge and expertise with respect to FAA specifications, materials, and typical construction practices that occur during airport construction was an immediate benefit to the owner and contractor. As an added benefit, our local staff was also well versed with City of Phoenix requirements which enhanced communication, and kept the project moving forward without unnecessary delays.

During our scope development, it was also noted by the airport team that the project would require visual welding inspection and ultrasonic testing of the moment connections for the structural steel welding construction. Based on the project needs, Terracon provided two experienced, local certified welding inspectors with non-destructive testing expertise to the project to observe and test 100 percent of the moment connections as well as standard welding inspection services for the welded connections for the South Concourse. High-strength bolting special inspection, structural steel erection observation, and fabrication inspection of steel was also provided.

Reporting Adds Value

During the construction, Terracon provided daily reports and test data, including location descriptions and photos which were rapidly turned around to the project team — most within 24 hours after performing the service. This allowed the team to quickly confirm the information produced met the project specifications and allowed the contractor to perform minor rework as necessary without losing time. Terracon tracked all non-conformances separately on a deviation log as the work continued, keeping all outstanding non-conformities at a high attention level to all concerned parties.

As airports throughout the United States prepare for update and expansion, Terracon continues to offer comprehensive services and solutions for facilities of all sizes. With a national footprint, we already serve many large and regional airports from our local offices. Our aviation team is well-versed with FAA specifications, specific reporting requirements, and special inspection and ready to assist with any facility needs.

All News and Events

Stormwater: A Frequently Overlooked but Potentially Costly Construction Management Issue

Storm management can be an overlooked aspect of construction management that can result in a multitude of unanticipated costs and the need for additional contractors on a project. For property owners, stormwater may be a low priority when building a multi-story high-rise or shopping center. However, failure to consider potential stormwater problems could result in making them an unforgettable part of a construction project. For contractors, responsibility for who will be managing stormwater services should be identified in the bid phase of a project. If not managed well, nearby business could be negatively impacted by mud in the streets and may file a complaint with local inspectors, assigning responsibility for stormwater management.

Planning for stormwater permitting and compliance

Well in advance of breaking ground, it should be determined who is responsible for planning and managing stormwater permitting and compliance. Frequently, this item occurs at the beginning of the rainy season when the contractor notifies the owner or stormwater permit holder that someone should manage the stormwater to prevent any scheduling delays. Since this responsibility is often specifically excluded in bids, it can become a last-minute scramble to resolve. While early partnership offers owners the greatest value, Terracon is available to collaborate with the project team after the project has begun with a focus on quickly bringing the site into compliance, and can even help after a violation has occurred.

With proper planning, stormwater design challenges can be addressed, corrected with a licensed contractor, and then monitored with weekly inspections. Common recommendations may include catch basin inlet protections or other best management practices. However, the associated costs can affect project budgets and profit if post-violation recommendations need to include operation of a chemical treatment system to manage the stormwater.

Ready to respond

When a client in the Northwest received a permitting violation letter following a recent inspection regarding the lack of stormwater management, the Terracon team was quickly to respond. The project setting included the demolition of a multilevel structure to be redeveloped with a larger multilevel structure.  The violations included the lack of properly installed or management of best management practices. These practices included track out of mud and failure to sweep daily; excess concrete on the ground not contained in a designated washout area; and cleaning or missing catch basin inlet protection. It was also required that the permit holder have weekly inspections completed by a certified erosion and sedimentation control lead. Other administrative record keeping violations included failure to report discharge monitoring reports from the permit start date and failure to maintain stormwater records/inspection sheets onsite and readily available upon request. Terracon team worked closely with the agency and inspector to bring the site into

Stormwater permitting and management requirements vary widely among states, making it important for contractors to maintain a good working relationship with their state and local agencies. Understanding local stormwater management requirements can help prevent significant potential fines and project delays. With offices in more than 140 locations nationwide, Terracon can provide you with a local, trusted stormwater professionals familiar with your area regulations and can recommend the right solutions for your stormwater issues.

All News and Events

Building A Strong Foundation: Laying Groundwork for a Successful Hospital Project

Excellent healthcare facilities are essential to vibrant communities. The recently constructed Florida Hospital for Women is a great addition to the healthcare system in Orlando.  The way that the geotechnical engineer collaborated with the design team to expedite its construction demonstrates how collaboration between key design partners can produce significant dividends in the budget-driven and time-sensitive healthcare industry, ultimately benefiting an entire community.

“This project is a prime example of the power of collaboration among the design and construction team members paying big dividends,” said Amr Sallam, Ph.D., P.E., Terracon’s principal geotechnical engineer. In fact, the partnership led to a final project design that saved the client more than $1 million and allowed the facility to open two months earlier to begin serving the community.

Facing settlement challenges with experienced team

The new facility would subject columns to loads of up to 2000 tons.  Such loads are routinely founded on deep foundations, extending 75 feet or more into the ground.  Conventional shallow foundations may create excessive settlements under such heavy loads. In addition to the challenge of high column loads, this was a constricted urban site on the main campus, adjacent to a heavily-used rail line, with connections to adjacent existing buildings, adding complexity.

Terracon believed that alternatives to deep foundations could save time and money, but it took collaboration with the design and construction team to consider its suitability for the project.  Understanding both the geotechnical and structural aspects of the design, Sallam progressed beyond a typical geotechnical engineering study to an interactive design with the structural engineer, Kevin Casey, P.E., (Paul J. Ford), all in collaboration with the contractor (Brasfield and Gorrie), and the owner’s representative, Mohammed Alai, A.I.A. (with Florida Hospital).

Mat foundation saves construction time

After considering several options at the preliminary stage, Terracon proposed the use of a mat foundation. The design of a mat for such heavy and variable loading conditions required an iterative process between the structural engineer running the SAFE model, the structural engineer’s finite element software program, and the geotechnical engineer utilizing PLAXIS model, a finite element software. The structural model generated a preliminary contact pressure distribution. Terracon used the PLAXIS model to estimate settlement, redefining the contact pressure estimates using aspects of slab rigidity and subgrade support. The revised contact pressures were input into the structural model, and this iterative approach was repeated until estimated settlements became congruent.

The iteration produced a final mat design with predicted maximum settlements of 2.5 inches at the interior core to about 1.5 inches along two adjacent buildings.

The contractor determined that the cost of the mat foundation would be slightly lower than deep foundations. A more substantial benefit associated with the mat alternative is reduced construction time. The client and design team decided that the expected settlements were acceptable, and the estimates allowed the design of appropriate connection points to existing structures. The design achieved a reduction in the construction schedule of two months.  Settlement monitoring confirmed settlements were well within the maximum values predicted.

Since opening in April 2016, the Florida Hospital for Women has provided enhanced medical care to the Orlando community, providing additional labor and delivery suites, operating rooms, postpartum bed space and an area for equipment that offers minimally invasive surgery options for patients.

Key Facility Features

  • 12 story patient tower with basement
  • 322 beds
  • Three floors of shell space for additional beds
  • 14 labor and delivery suites,
  • 13 operating rooms for obstetrics and women’s services,
  • 2 postpartum care beds, mother-baby beds and high-risk beds.
  • Operating rooms accommodate the DaVinci Surgical System for robotic minimally invasive surgery.

All News and Events

Helping A Hospital: Diagnosing Indoor Air Quality and Building Operation Issues

Hospital culture demands that nothing is as important as the people in its care and those who serve them. So when a healthcare facility experienced elevated relative humidity levels, condensation on ductwork, and mold growth following general renovations and building additions, the building owner contacted Terracon. Our team began an evaluation of the performance of the heating, ventilating, and air conditioning system (HVAC) to determine if the system was maintaining cooling, dehumidification, relative humidity, and positive indoor air pressure per the original design.

A diagnostic assessment of the building mechanical HVAC and exterior enclosure systems were conducted to determine the potential causes of elevated humidity levels and related issues. Additionally, spotted ceiling tiles and mold growth on interior walls was found in several care rooms and common areas. Our facilities experts determined that the HVAC system was operating at a negative indoor air pressure and was in need of repairs along with recalibration of the automatic controls. With help from the commissioning agent, mechanical contractor for the project, and owner’s maintenance personnel, the automatic controls of the HVAC were re-calibrated and air balanced to provide a net positive indoor air pressure in the building and to correct and maintain relative humidity levels in the acceptable performance range.

The Terracon team of building specialists also provided extensive diagnostics of the building exterior to determine the pathways of moisture infiltration into the building interiors. Partial destructive investigative work was required to the building façade to observe the condition of the building exterior construction, air barriers, and sealants. The building height and limited access to the façade necessitated the expertise of our building exterior professionals trained to access the exterior façade via rope access. Architectural details for the building renovations and additions were studied to understand the designed versus installed methods of weather proofing and placement of air barriers. Extensive visual observations of the building exterior wall sections were also conducted to locate potential pathways of outside air infiltration and air movement between the outdoor environments and the indoor conditioned areas.


In a further effort to investigate the potential areas of air movement between the outside environment and inside conditioned areas, and due to the urgency and target height, an infrared camera was mounted to an unmanned aircraft system (UAS) to scan the southern façades and identify variations in building surface temperatures. Scanning revealed isolated areas of the building façade that were possible areas of air movement between the outdoor ambient and indoor areas. To perform even more in-depth diagnostics, one area was selected for testing. A propeller blower door fan was installed with calibrated airflow and differential pressure measurement software to accurately determine air movement through the building façade. By testing a baseline of air leakage at an indoor air pressure of approximately 0.01-inches water gauge, air movement was quantified through the selected test area for comparison to any future repairs and improvements to the façade and air barrier. Safe smoke was introduced into the ceiling plenum of the test area to trace movement of air through the façade and other pathways in the exterior wall. The results from testing indicated that careful, detailed repairs to the façade and air barrier would be needed to reduce air movement from the outside environment to the inside areas, mitigating condensation and biological growth inside the building.

To develop a plan for detailed repairs to the elements of the building façade, Terracon assisted the design and contracting team in selecting fire-rated materials and sealants suitable for use in performing needed repairs that would improve the effectiveness of the air barrier and withstand typical building pressures generated by the HVAC system. Terracon performed a test of a prototype of the detailed repair for the test area and identified further areas in the façade for repairs.


As the detailed repairs were being performed, Terracon provided observations and testing of the installed repairs. Terracon will also observe the ongoing operation of the mechanical HVAC system to verify that the representative,interior areas in the building are maintained at desired positive pressure and an acceptable relative humidity. This hard work has paid off, providing a safer, more comfortable environment for the facility’s occupants.

All News and Events

Experience Prevails: Uncovering Hidden Obstacles

Located just 10 nautical miles from the Atlantic Ocean in Jacksonville, Fla., Dames Point Marine Terminal is JAXPORT’s newest marine facility. Opened in 2009, it includes a state-of-the art container terminal capable of handling an annual volume of 800,000 to 1 million Twenty-Foot Equivalent Units (TEUs). With an increase in container volume, JAXPORT recognized the need for an effective rail connector and the development of an efficient intermodal transfer facility (ICTF). In 2014, it decided on a design-build delivery for the project. Terracon partnered with TranSystems and D.B. Kenyon to deliver a quality project while optimizing the budget within a tight time frame.


The new facility was constructed on approximately 45 acres of JAXPORT property and required relocating a mile-long public road that bisected the site. Components included remediation of lead from an old gun range facility, wetland mitigation, clearing and grubbing, unsuitable material removal, excavation and filling, importing base material, rock, asphalt pavement, reinforced concrete, roller compacted concrete, high mast LED lighting, buildings, gates, canopy, and railroad track.

According to Tom Selfridge, senior geotechnical engineer in Terracon’s Jacksonville, Fla., office, the team decided to further investigate a minor mention made in a preliminary report of possible debris buried in the soil at the construction site. Historic aerial photos were quickly reviewed and indicated relatively large areas of disturbed ground. These areas were scanned with a geophysical survey, utilizing ground penetrating radar (GPR) and electromagnetic induction, to look beneath the ground surface for possible voids or debris deposits. Finally, suspect areas were ground-truthed with backhoe-excavated test pits. Results of the testing were significant. More than eight acres of the construction site had debris hidden under ground level, including pieces of charred wood timbers and sheets, and shredded metal intermixed with sand.

“Without a thorough investigation of the site, the debris could’ve been missed and negatively impacted the construction,” said Selfridge. Terracon’s early awareness and resolution of the debris issue protected the project’s budget and schedule. Additional value was added by Terracon’s recommendation to screen the excavated debris deposit which allowed for re-use of its sand component and reduction in the volume and cost of the off-site waste disposal. Terracon’s resourcefulness continued to the construction phase as Chris Martin, Terracon materials specialist also in the Jacksonville office, adopted use of a geophysical tool (Kessler MIT Scan T2) to obtain real-time measurements of layer thicknesses during placement of roller-compacted concrete (RCC) pavements. After an initial test strip was completed to calibrate the contractor’s equipment and methods, the RCC was placed in multiple lifts up to a maximum total thickness of 20 inches. In addition to the value of real-time data, the scanner tool saved approximately $20,000 in testing cost as compared to the conventional rotary coring method, according to Martin.

Testing of the rail components required knowledge and application of requirements set forth by The American Railway Engineering and Maintenance-of-Way Association (AREMA). Field density testing was completed on the sub-ballast material and welding of the steel rail tracks was checked by ultrasonic testing.

In January 2016, the Port took beneficial occupancy of a $25 million state-of-the-art ICTF, delivered via design-build, on time and within budget.

All News and Events

Determining Stability: Evaluating a Tunnel to Predict Performance Under Catastrophic Loading

Could a tunnel constructed more than 50 years ago still rapidly drain a reservoir if a catastrophe happened? This was the question Terracon helped answer regarding the 185-foot deep reservoir at the Broken Bow Hydroelectric Dam in Broken Bow, Okla.

Following Hurricane Katrina in 2005, the United States Army Corps of Engineers (USACE) mandated that each public reservoir be retrofitted to drain if there was a catastrophic event threatening the stability of the reservoir’s dam. To comply with this requirement, Terracon joined the team led by Mead & Hunt to evaluate the complex geology, subsurface conditions, and the concrete tunnel liner condition to determine the stability of the existing tunnel. To make sure the 18-foot diameter diversion tunnel met stability requirements, the USACE needed a geotechnical study performed. In the study, the USACE requested that no test borings, rock coring, or destructive testing of the tunnel liner be performed.


As part of the team, Terracon developed a multi-stage work plan to understand the original tunnel construction and assess its current condition. Boxes of USACE files of the original dam construction documents were reviewed, including 14 soil test boring logs, geological studies of the steeply dipping rock formations, and construction plans and photographs of the 1960s construction.


After gaining a thorough understanding of the tunnel design and the geotechnical/geologic conditions, it was time to investigate the tunnel with the team. With the safety of the workers a priority, Terracon crafted a 200-plus-page safety plan including an activity hazard analysis for each team member responsible for accessing the wet tunnel and climbing the rock outcrops.

The work plan included a review and geologic mapping of nearby outcrops of the same rock formations cut by the original tunnel excavation and performing sensitivity analyses. Geologic strike and dip measurements were made, as well as joint spacing and the location of faults and discontinuities. The team then interpreted aerial Light Detection and Ranging (LiDAR) images of four major outcrops for joint patterns and bedding characteristics of the native bedrock. Rose Diagrams and Stereonet Pole plots were created to define structural geology properties such as the dominant orientation of bedding planes, folds, and faults. Using the collected data, Terracon provided calculated estimates for the Rock Mass Rating characterization parameters (RMR) and the Rock Quality Designation (RQD) for the rock along the tunnel alignment, as well as Headcut Erodability indices.


The next stage of work included conducting a detailed visual condition study of the concrete tunnel liner, documenting the location and width of all cracks, mapping areas of seepage, and estimating seepage flow. To approximate the compressive strength of the tunnel’s liner concrete, the team also performed Windsor Probe testing. Terracon performed ground penetrating radar (GPR) data acquisition to determine the concrete liner thickness, assess the presence of voids in the liner, and to detect the presence of delaminations within the concrete.

Terracon concluded that most of the original tunnel liner was in good structural condition and suitable for use as an emergency spillway of the Broken Bow Reservoir under high velocity flow. The conclusion that the 55-year-old liner could perform under catastrophic loading was great news. The report did document local areas where the concrete liner was detached from the bedrock face, as well as many areas where active seepage was occurring. To control seepage and fill voids in the liner created by the original wooden blocking points and rotted timber cribbing, Terracon recommended the tunnel liner be pressure grouted with chemical grout.

Controlled and engineered weep holes would be designed and placed through the concrete tunnel liner to relieve hydrostatic pressures. This fast-paced, detailed study was impacted by record rainfalls during the data-gathering field operation. This project was truly a collaborative and seamless effort with Mead & Hunt and the Tulsa District USACE personnel.