Project Information
Name: Six Point
Product: AB Vertical INDOT
Size: 2,800 ft2 (850 m2)
Wall Builder:
White Construction
Wall Designer:
Infrastructure Engineering
Allan Block Manufacturer:
Reading Rock
AB Rep:Jill Fouts
Using Geosynthetic Reinforced Soil-Integrated Bridge System
As technological innovations increase over the years, so has the growth in the possible uses for Allan Block Retaining Wall Systems. The Geosynthetic Reinforced Soil – Integrated Bridge System (GRS-IBS) is employed to address the increasing national need for replacing small, single-span bridges. Advocated by the Federal Highway Administration (FHWA) for over a decade, this method offers an economical and robust alternative, significantly reducing construction timelines.
One of the most recent successes was a GRS-IBS Bridge design out of Hamilton County in rural Indiana. Located directly outside the heart of Indianapolis in Sheridan, is known for its authentic downtown vibe and has been growing in popularity due to its affordable living and easy urban access. It was no surprise in this specific case that the city was emphasizing and pushing for a more aesthetically pleasing site solution over a natural creek along one of the most common interstate roads in the county.
The project constraints called for a relatively fast construction process as the bridge system design was impacting a prominent roadway and its absence would cause the city major traffic delays. Due to the versatility, time effectiveness and aesthetics of Allan Block, the product was chosen to provide the perfect solution, and the result didn’t disappoint.
Plan:
At the time, Hamilton County was undergoing a transition to redesign 4 bridge structures in the area, and this was the last one to be finalized. With 3 already in the ground, there was a basic understanding of the process on the design side, but as we know, each site provides its own unique challenges to plan for and overcome. There were several factors to be considered as the county reviewed their budget options. Since there was a heavy constraint on time for construction and considering GRS-IBS structures had already been in place within county, conventional designs and driven pile systems were not ideal solutions presented at initial meetings. GRS-IBS came to fruition as building time could be cut down from months to weeks. Although the county had allocated an initial budget for the project, it was estimated that the decision to go GRS-IBS saved the county thousands of dollars in project cost.
The local Allan Block sales rep, Jill Fouts, with Reading Rock, can be largely credited for the success of this project. She had played a key part in working with the other 3 projects in the area and was more than happy to help tie the bow on the last one. Jill highlighted the benefits of Allan Block’s durability, versatility, and height tolerance, in contrast to a CMU block. With the plan now approved for implementation, the county focused on gathering proper materials to ensure successful execution and product. Hamilton County, like much of the northern United States, faces extended and harsh winters that require a long-lasting solution. This led to the design decision for Reading Rock to deliver a block mix design with a near vertical setback, approved by the Indiana DOT, ensuring durability of the wall project through freeze/thaw cycles throughout the different seasons.
Design:
To incorporate Allan Block into the GRS-IBS structure, civil design professionals from Infrastructure Engineering created site and grading plans then handed over the wall designs and construction drawings to White Construction, who was awarded the bid. The aim was to provide consistency with the other existing structures and develop a recipe that could serve as a framework for tackling similar bridge crossings throughout the county in future years and nationwide.
The engineers knew there were limitations with space and excavation. Therefore, the AB Vertical INDOT block was approved, whose near vertical design would align the structures blueprint more closely with the existing road, leading to less excavation and also minimizing the setback of the abutment structures.
The next design decision involved the surrounding reinforcement for the structure. Being able to extend grid with strong tensile strength to hold the superstructure loading and vehicular weight was imperative. Designers went with TERRATEX HPG-57 geotextile, from TerraTex High Performance. Not only is the grid a reinforcement material specifically designed for the GRS-IBS applications, but its highly resistant polypropylene properties make it one of the most stable polymers to design projects with during different seasons. When it was all said and done, based on the project’s nature and on-site engineering decisions, there were over 5,000yds2(465m2) of this grid used in this project. One of the key features that made this project special was the use of grout with rebar in the cores for the top 3 rows of block. This was done to increase the walls’ strength and stability.
By grouting the cores, it helped disperse the load from the superstructure and bridge across the support system evenly.
The totality of the project’s height reached 18ft (5m) with each of the IBS spanning 81ft(25m) in total length. There were 3 leveling pads on both sides made up of approved aggregate to help stabilize the entirety of each foundation the block was sitting on. It was expected, based on the previous county projects, that the new bridge would take up over 1,600ft2(150m2) of block and require over 1,000yds2(835m2) of reinforced backfill that would be brought in. Now, let’s dive into how it physically got done.
Build:
After the plans and designs were finalized, the project was turned over to White Construction to start putting block in the ground. This was the first GRS-IBS project for the crew based out of Ohio and upon its completion allowed them to achieve their first level of the Allan Block Contractor Certification Program. Jill, the local Allan Block sales representative, played a part as well. Along with the initial training, she provided tips and tricks learned from overseeing the previously built structures in the county by working with those crews.
Construction of the two abutments started in early June of 2021 and was wrapped up toward the end of the month. A key step during the initial stages of the project was the use of the red Allan Block that was installed below the finished grade. This was so scour could easily be identified along with instilling a baseline for where the buried block should start in the future.
Installation of the superstructure followed with the bridge sitting on the beam seat within the bearing bed reinforcement zone. Single course spacing was required on the top 4 layers in the reinforcement zone to secure bridge loading and take pressure off the soil and grid.
A re-occurring rave from the county was how the much quieter vehicular crossing was over the structure and how the built-in front-lip of the block led to an upgraded look aesthetically and made the installation process easy. This part of the construction process was completed by mid-July - within the desired time constraints allotted with the resources budget.
All in all, the project went smoothly and was deemed a win as it ended at the end of July 2021. While not the fastest of the county’s series of 4 installations, their results spoke for themselves, and the county was thrilled.
The GRS- IBS concept and application is growing in popularity throughout the states as a more cost-efficient solution that designers are recognizing as a more aesthetically pleasing facing unit in comparison to CMU’s. Successes like this one in Hamilton County are just the start for helping spread awareness to over 25% of bridges nationwide looking for an upgrade.