The new Bozeman Public Safety Center has been constructed at the site of the former MDT yard facility, located on the southwest corner of N. Rouse Avenue and W. Oak Street on the northeast side of Bozeman. This 8-acre site development includes a large, multi-story building and several asphalt parking lots and roadways. The building houses the police department, the municipal court facilities, and one of the City’s fire stations.

AESI first became involved with the project in 2014 during the initial concept phase. At that time, we were retained for a preliminary geotechnical investigation and report of the subject property. In 2019, as the project design progressed, we performed additional field explorations to better characterize the site conditions. This was followed by the preparation of the final geotechnical report for design and construction.

The two biggest findings of the geotechnical work were that the site was blanketed by a 1.5 to 2.0-foot layer of asphalt millings/roadmix gravel and that the “target” bearing material for the building was the native sandy gravel at a depth of generally 5.0 to 7.0 feet. To save a substantial amount of money, we recommended stripping/salvaging all of the existing asphalt-laden gravel materials from the surface of the site and re-using these materials as part of the sub-base gravel section under new asphalt areas. This saved on both the haul-off of the material and the importing of all new gravel. Due to the footprint size of the building and the number of interior footings, we recognized that traditional footing over-excavation/replacement down to the “target” native gravel would be impractical and uneconomical. Instead of standard foundation earthwork, we recommended a ground improvement system consisting of rammed aggregate piers under all foundation elements (including perimeter, interior, and exterior footings). This foundation system was chosen and designed to include over 650, 30-inch piers that extended down into the “target” native gravel.

AESI has been involved with the site and foundation construction since it began in the spring of 2020. We observed the stripping/salvaging of the asphalt-laden gravel materials, the preparation of subgrade, and the placement of the sub-base gravel sections under new asphalt areas. In the building area, we monitored the construction of the gravel building pad, provided QA inspection/oversight during the installation of the rammed aggregate piers, and observed the foundation excavation and the exposed tops of the piers under footing locations.

Site Conditions: The site was covered by a 1.5 to 2.0-foot layer of asphalt millings/roadmix gravel, which required careful management to reuse these materials effectively and economically.

Foundation Design: The native sandy gravel, identified as the “target” bearing material, was located at a depth of 5.0 to 7.0 feet. Traditional footing over-excavation and replacement were impractical and uneconomical due to the building’s footprint and the number of interior footings.

Ground Improvement: Implementing a ground improvement system with over 650 rammed aggregate piers was a significant undertaking. This required precise installation and quality assurance to ensure the stability and integrity of the foundation.

Material Management: Stripping and salvaging the existing asphalt-laden gravel materials and reusing them as part of the sub-base gravel section under new asphalt areas required meticulous planning and execution to save costs and reduce waste.

Coordination and Oversight: Continuous involvement from AESI for site and foundation construction, including monitoring subgrade preparation, gravel building pad construction, and the installation of rammed aggregate piers, was essential to address any issues promptly and maintain project timelines.

Reuse of Existing Materials: Stripped and salvaged the existing asphalt-laden gravel materials from the site and reused them as part of the sub-base gravel section under new asphalt areas. This approach saved on both the cost of hauling off the material and the expense of importing new gravel, making the project more economical.

Ground Improvement System: Instead of traditional footing over-excavation, a ground improvement system using rammed aggregate piers was implemented under all foundation elements. This method provided a stable foundation for the building, with over 650, 30-inch piers extending into the native sandy gravel, ensuring the structural integrity of the building.

Cost Savings: The reuse of existing materials and the innovative foundation solution significantly reduced project costs.

Structural Integrity: The ground improvement system ensured a stable and durable foundation, capable of supporting the large, multi-story building.

Efficient Project Execution: Continuous monitoring and quality assurance helped maintain project timelines and addressed any issues promptly, leading to a smooth construction process.

In the summer of 2024, AESI provided comprehensive geotechnical engineering and survey services for a new 4,250-square-foot residence in Bridger Canyon, Montana. The project site, a 20-acre property with a moderately steep southeast-facing slope, required detailed analysis and innovative solutions to ensure stability and functionality. Our team conducted extensive site investigations, including test pit explorations and laboratory testing, to assess subsurface conditions. We identified clayey residual soils and recommended over-excavation to stable weathered siltstone/sandstone, supported by 12 inches of structural fill. Additionally, we designed and monitored the installation of boulder walls up to 12 feet high to retain driveway cuts, ensuring both slope stability and aesthetic appeal.

We also completed a comprehensive slope stability analysis, confirming the site’s stability under typical foundation loading and moderate seismic events. We provided foundation support recommendations, allowable bearing criteria, and anticipated settlements to ensure a robust and durable foundation.

The success of this project depended on utilizing drone survey data and soil logs to create detailed AutoCAD Civil 3D soil horizon models. We also assisted with the layout of proposed horizontal drains and the design of access roads, improving site accessibility and drainage. Notably, we employed MASW (Multi-channel Analysis of Surface Waves), a geophysical analysis, to provide a site-specific seismic classification, ensuring the residence’s resilience against seismic activity.

Our integrated approach and expert solutions ensured the successful planning, design, and construction of this beautiful residence.

Subsurface Conditions: The presence of clayey upper residual soils required careful management. These soils needed to be over-excavated to reach stable weathered siltstone/sandstone, which added complexity to the foundation preparation.

Slope Stability: Ensuring the stability of the moderately steep southeast-facing slope was crucial. This involved conducting a comprehensive slope stability analysis and designing appropriate measures, such as boulder walls, to retain driveway cuts and prevent erosion.

Seismic Considerations: The project required a site-specific seismic classification to ensure the residence’s resilience against seismic activity. This was addressed using a MASW (Multi-channel Analysis of Surface Waves) geophysical analysis, which provided detailed insights into the site’s seismic characteristics.

Integration of Data: Creating accurate soil horizon models and stability models required integrating various data sources, including drone surveys and borehole logs. This necessitated advanced software tools like AutoCAD Civil 3D and SLOPE/W to develop detailed and reliable models.

Foundation Design: Over-excavated the clayey upper residual soils to reach stable weathered siltstone/sandstone and used 12 inches of structural fill for foundation support. This provided a solid and stable foundation, ensuring the long-term durability of the residence.

Slope Stability Measures: Conducted a comprehensive slope stability analysis and designed boulder walls up to 12 feet high to retain driveway cuts. These measures effectively stabilized the moderately steep slope, preventing erosion and ensuring the safety of the structure.

Seismic Resilience: Employed MASW (Multi-channel Analysis of Surface Waves) geophysical analysis to provide a site-specific seismic classification. This ensured the residence was designed to withstand seismic activity, enhancing its resilience and safety.

Integrated Data Modeling: Utilized drone survey data and soil logs to create detailed AutoCAD Civil 3D soil horizon models and SLOPE/W stability models. These models provided a comprehensive understanding of the site conditions, informing better design and construction decisions.

In the summer of 2019, AESI provided geotechnical engineering and construction support services for the renovation of the historic Romney Hall gymnasium at Montana State University. As part of the foundation design process, AESI observed initial helical pier load testing to verify performance under site-specific conditions. Our team conducted laboratory testing to assess the reusability of native foundation soils and monitored the placement of the first phase of production helical piers. Throughout the project, AESI oversaw the successful installation of nearly 100 helical piers, ensuring the foundation system met engineering and structural requirements for the building’s modernization.

The renovation of Romney Hall presented several challenges, including the complexity of foundation design and the installation of helical piers in variable soil conditions. Environmental factors and soil inconsistencies required adaptive engineering solutions to ensure stability and load-bearing capacity. Scheduling and budget constraints added another layer of complexity, requiring efficient coordination between engineering teams and contractors. Additionally, the project required balancing historic preservation goals with modern engineering standards to enhance the building’s structural integrity while maintaining its historical significance.

AESI provided a comprehensive geotechnical assessment to inform foundation design and optimize soil reuse. Our oversight of helical pier installation ensured precision placement and structural reliability despite variable subsurface conditions. By implementing efficient testing, monitoring, and adaptive engineering strategies, AESI helped strengthen the foundation system, extending the lifespan of Romney Hall and preserving an important historic structure for future generations.

As part of their IDIQ contract with the USFS Region One, Allied Engineering provided engineering and surveying services for the repair of the Sullivan Bridge gabion abutment on the north side of the east abutment of the bridge.

Sullivan Bridge is located on National Forest System Road 895 in a remote area on Hungry Horse Reservoir. An initial site visit was conducted in July 2016 by Allied Engineering and the US Forest Service. Following the field visit, it was decided that the failing gabions should be removed, the slope re-shaped and protected to minimize erosion and channelization, and an engineered toe should be built and backfilled with riprap up to the existing road shoulder. All survey, evaluation, and construction needed to consider steep slopes and cliffs inaccessible to most equipment.

The site was surveyed with a combination of high-definition scanning, bathymetric surveys with GPS integrated depth finder, and conventional survey and GPS. Several different design and construction options including barge access, long reach excavators, and specialty drilling and anchoring equipment, and techniques were then considered and discussed by Allied Engineering and the Forest Service. The preferred alternative included removing the existing gabion baskets entirely and replacing them with a stacked riprap fill slope. Because the catch point is a thin section of steep bedrock, the toe of the riprap is supported by gabion reno mattresses anchored into the rock with driven rebar pins. These pins and mattresses help to buttress the bottom of the riprap slope along with providing some vertical clearance between the bottom of the rock and the existing bedrock catch point. Construction documents were developed in September 2016 including plans, engineer’s opinion of probable construction cost, supplemental specifications, and schedule of items. A report was also prepared to summarize the design process and describe how and why the final design was chosen.

Remote Location Access: Sullivan Bridge is located in a remote area on Hungry Horse Reservoir, making access challenging. Transporting personnel, equipment, and materials to such an isolated site would require careful logistical planning, potentially increasing costs and project duration.

Steep Slopes and Inaccessible Terrain: The project area included steep slopes and cliffs that were largely inaccessible to standard construction equipment. Working on these slopes required specialized surveying and construction techniques and equipment, adding complexity to the planning and execution.

Erosion and Slope Stability: The site’s steep and unstable slopes posed a risk of erosion and channelization, particularly after removing the failing gabions. The team had to carefully re-shape and reinforce the slope to prevent future erosion and maintain long-term stability, which required precise engineering and innovative solutions.

Technical Survey Requirements: The combination of high-definition scanning, bathymetric surveys, GPS, and conventional survey techniques presented technical challenges. Integrating and analyzing data from different survey methods required advanced expertise and coordination to ensure accuracy.

Limited Equipment Options: Due to the site’s inaccessibility, traditional construction equipment was unsuitable. The team had to consider alternative approaches, such as barge access, long-reach excavators, and specialty drilling and anchoring equipment, requiring significant planning and potentially high equipment rental costs.

Anchoring in Bedrock: The design required that the toe of the riprap slope be anchored into steep bedrock using gabion reno mattresses and rebar pins. Anchoring into thin, steep bedrock presents challenges with securing materials effectively, requiring precise drilling and reinforcement to ensure stability.

Environmental Protection: Working near a reservoir necessitated additional precautions to protect water quality and surrounding habitats. Implementing these environmental safeguards while conducting construction on steep and fragile slopes would add another layer of complexity to the project.

Design Complexity and Safety: The unique challenges of the site required careful design considerations and coordination between Allied Engineering and the US Forest Service. Safety for workers on steep slopes, handling heavy materials, and dealing with specialized anchoring and drilling techniques added risk that required stringent safety protocols and oversight.

Development of Comprehensive Construction Documents: Given the site’s complexities and remote nature, developing thorough construction documents, specifications, cost estimates, and schedules would be essential to mitigate the high risks and unpredictability associated with this project.

Comprehensive Site Surveying: Allied Engineering used a combination of high-definition scanning, bathymetric surveys with GPS-integrated depth finders, and conventional surveying methods to accurately map the complex terrain. This multifaceted approach ensured precise data collection, which was essential for creating a tailored engineering solution.

Specialized Equipment for Inaccessible Terrain: The project team considered various options to overcome the remote, steep terrain, including barge access and long-reach excavators. Ultimately, they opted for specialty drilling and anchoring equipment that allowed work on steep slopes and difficult-to-reach areas, improving safety and effectiveness in the challenging environment.

Re-shaping and Stabilizing the Slope: To address erosion and slope instability, Allied Engineering reshaped the slope and protected it with an engineered toe structure backfilled with riprap. This reinforced slope reduced erosion risk and prevented future channelization, providing long-term stability for the bridge’s foundation.

Anchoring with Gabion Reno Mattresses and Rebar Pins: The design called for removing the failing gabions and constructing a stacked riprap slope, reinforced at the base with gabion reno mattresses. These mattresses were anchored into the steep bedrock using driven rebar pins, which provided a stable foundation and prevented slope movement along the bedrock’s edge.

Collaborative Design Process: Allied Engineering worked closely with the US Forest Service to explore various design options, ensuring the chosen solution met safety, budgetary, and environmental considerations. This collaborative approach allowed the team to select the best possible alternative given the project’s unique constraints.

Improved Structural Stability: The re-shaped slope with stacked riprap and anchored gabion mattresses provided a stable, resilient foundation for the bridge, protecting it from erosion and future deterioration.

Extended Service Life of the Bridge: The reinforced abutment and stable slope foundation significantly enhanced the longevity of Sullivan Bridge, ensuring it can withstand environmental pressures and serve the public for years to come.

Enhanced Safety and Accessibility: By stabilizing the slope and creating a secure foundation, the project improved the overall safety and accessibility of National Forest System Road 895, benefitting those who rely on this remote route.

Environmental Protection: The engineered slope and riprap design minimized erosion and preserved the surrounding natural landscape, helping to protect the reservoir and local ecosystem from sedimentation and potential contamination.

In 2010, a soil nail and shotcrete wall was constructed to stabilize a landslide in Hyalite Canyon. Since 2012, the USFS has actively monitored this wall for any movement. AESI was engaged to conduct annual slope inclinometer readings from two devices located on the bench in front of the wall. In 2018, AESI submitted a report analyzing ongoing issues at the slide, noting an acceleration in slope movement. To address this, AESI was tasked with laying out proposed horizontal drains, designing the access road, installing additional slope inclinometers and piezometers, and assisting with the selection and acquisition of remote monitoring equipment. AESI also monitored and surveyed the horizontal drains, developed AutoCAD Civil 3D soil horizon models using drone survey data and borehole logs, and back-calculated initial slope failure parameters using SLOPE/W. They then drafted a current-state SLOPE/W stability model with soil nail parameters estimated from third-party documentation.

Monitoring & Data Collection: Continuously monitoring the soil nail and shotcrete wall for movement required precise and consistent data collection over several years.

Accelerating Slope Movement: The slope movement appeared to be accelerating, which posed a significant risk to the stability of the wall and surrounding area.

Design and Installation of Horizontal Drains: Designing and installing horizontal drains in challenging terrain required careful planning and execution.

Developing Accurate Models: Creating accurate soil horizon models and stability models required integrating various data sources, including drone surveys and borehole logs.

Coordination and Communication: Coordinating with multiple stakeholders, including the USFS and third-party documentation providers, was essential for the project’s success.

Monitoring & Data Collection: AESI conducted annual slope inclinometer readings and installed additional monitoring equipment, such as piezometers and remote monitoring devices, to gather accurate data. The implementation of slope inclinometers, piezometers, and remote monitoring equipment provided continuous and accurate data on slope movement. This allowed for timely interventions and adjustments as needed.

Enhanced Stability: AESI analyzed the data and proposed the installation of horizontal drains to manage groundwater and reduce slope movement. The installation of the soil nail and shotcrete wall, along with the horizontal drains, significantly improved the stability of the landslide area. This reduced the risk of further movement and potential damage.

Design and Installation of Horizontal Drains: AESI laid out the proposed drains, designed the access road, and monitored the installation process to ensure effectiveness.

Developing Accurate Models: AESI used AutoCAD Civil 3D and SLOPE/W software to develop detailed models and back-calculate initial slope failure parameters, ensuring a comprehensive understanding of the site conditions.

Coordination and Communication: AESI maintained clear communication and collaboration with all parties involved, ensuring that the project stayed on track and met all requirements.

Cost Savings: By using advanced modeling techniques and precise data analysis, AESI was able to design effective solutions that minimized unnecessary expenditures and optimized resource use.