Earth anchors can be used to limit lateral movement of retention walls or soils that have been vertically shored, allowing the face of the soil to remain free from obstruction. Earth anchors are beneficial when conventional tiebacks or excavation with internal bracing cannot be used. A variety of materials, designs and installation lengths are used depending upon the load to be carried and the bearing strength of the soil.
Featured Project
US 31
Petoskey, MI
Little Caesars Arena
Detroit, MI
University of Michigan Ross School of Business
Ann Arbor, MI
University of Michigan Law School
Ann Arbor, MI
5th Avenue Parking Structure
Ann Arbor, MI
Project Details
Team Hardman Construction opened up the year 2019 with a precise and detailed undertaking. Located along US-31 on the north side of Petoskey, Michigan, Hardman Construction was hired by DJ McQuestion to install a retaining wall approximately 450 feet in length with a maximum height of nearly 22 feet at its highest point. There were many aspects to this job, including but not limited to the following key items:
- 57 drilled shafts at 17.5’ deep
- HP14x117 H-piles up to 22’ above top of drilled shaft
- 56 earth anchors with a capacity of 113 kips each
- Waler system which demanded a tolerance between installed H-piles of less than one half inch
- Timber lagging structure to retain backfill/subgrade and expedite the road building process
- Permanent reinforced 16” thick concrete wall
- Simulated stone masonry finish
It was clear from the beginning that this job would require adherence to a tight schedule and having multiple crews working on the wall at the same time while performing different tasks would be the way to accomplish that goal. At the beginning of the job, Hardman worked closely with Rohrscheib Son’s Caissons to get the shafts drilled. Rohrscheib would drill all the shafts, and Hardman would follow behind setting cages and beams in the shafts, verifying the tight tolerances were met by bracing the steel in place, and then tremie pouring the shaft with a crane, concrete pump and a tremie pipe.
Following behind the shaft crew was the anchor crew. Hardman installed one anchor between each pair of H-piles. Since the ground elevation on site was approximately 590’ and anchor elevations went up as high as 601.5’, Hardman construction had to work off of an elevated dirt work platform for the middle 80% of the wall. This provided many logistical challenges with so much moving equipment around a narrow jobsite. Good communication was required to ensure there was enough sand moved in front of the anchor crew for them to work, Rohrscheib had to continually move their drill spoils, and several concrete trucks moved in and out of the site every day for the drilled shaft pours.
Behind the anchor crew was the anchor testing crew to perform verification proof tests on every anchor before they are tied into the wall. At this point we were ready to install wood lagging and begin backfill behind the wall. For this application Hardman chose to band the 8’x6”x10” (LxWxH) wood lagging together and set the boards as 2 to 6 board panels. This method saved a lot of time and allowed Hardman to begin installing the wale system almost one week ahead of schedule. With a crew following the lagging crew mag drilling holes for the walers and bolting them in place, all that was left for the main structure was to set the final lagging panel on top of the waler to bring the wall to design height and lock off all of the anchors to complete the structure.
At this point DJ McQuestion could begin grading on top of the wall, and Hardman could put finishing touches on the wall, and began tying and hanging resteel for the concrete pour. Steel forms had to be put together, and all of the simulated stone texturing had to be fixed to the forms before they were stood up against the wall. A single pour could be up to almost 22 feet high and would be either 48 or 72 feet in length along the wall. Once all of the texturing was in place and pouring concrete commenced, it was our goal to pour 48 to 72 feet of wall every 3 days. We achieved this goal and placed the last concrete on May 15, 2019.
Hardman Construction managed to finish the project ahead of schedule and ended with a structurally sound and aesthetically pleasing product, making an iconic land mark for the City of Petoskey to enjoy for years to come.
The Joe Louis Arena located along the banks of the Detroit River has been the home of the 11-time Stanley Cup Champion Detroit Red Wings since 1979. The “Joe” replaced the Olympia Arena where the Detroit Red Wings had played since 1927. Just as the Olympia Arena was replaced by the Joe, the time had come for the Joe to be replaced by the new Little Caesars Arena. Located in downtown Detroit, this multi-purpose building has become the new home for the Detroit Red Wings (NHL), the Detroit Pistons (NBA), as well as a facility for hosting special events. Construction began in April 2015 and the 785,000 square-foot development which seats approximately 20,000, opened its doors September 5, 2017. As a geotechnical construction contractor, Hardman Construction was tasked with building the temporary earth retaining system around the main and practice ice arenas. The earth retention system was composed of four 40′ tall retaining walls which spans more than 1,700′. The ERS design combines augercast piles, tiebacks, and lagging. The augercast piles are installed a set distance apart, and lagging boards are used to span the space between piles. Each augercast pile is constructed by drilling a large diameter vertical hole. The hole is then filled with grout, and a steel H-beam is installed in the hole. After a short period of time, the grout is removed from the face of the beams so the lagging can be installed. The ERS achieves its retaining strength by the use of tiebacks, which are a type of earth anchoring system. Although the schedule was tight and the construction process complex, the project was completed on schedule.
Hardman Construction worked on the University of Michigan Ross School of Business demolition and expansion project. The old School of Business was demolished to make room for the new one, which features a new facade as well as additional rooms below grade. In order to complete the extensive renovations, the site required an earth retention system. The excavation depth for the new building was 20’ to 27’ below grade, with the overall wall length just under 1,000 lineal feet. Hardman Construction installed a tangential augercast wall. Every third augercast pile was reinforced with an H-pile. The reinforced piles are installed in front of the non-reinforced or filler piles. Filler piles are installed behind the beam piles and do not have steel reinforcement. By doing this, the soil load is transferred into the beams. To resist lateral loads, earth anchors were used. The earth anchors were installed through anchor pockets which are fabricated in the H-pile reinforcement. Depending on the depth of excavation, up to two rows of ties were used. Another interesting aspect of the project was that approximately 150 lineal feet of the earth retention system had to be installed with limited headroom of 15′, which was required to protect a 250-year old oak tree. We utilized a low headroom drill rig and had to splice the H-piles while in place. An ongoing challenge faced was where the new Ross building tied into the two existing buildings. The new foundations were 15’ deeper than the two existing buildings. If the foundations for the new building were excavated, it would undermine the foundations of the existing buildings. Conventional earth retention systems could not be used due to space constraints. The only option was to stabilize the soil using micro fine cement and conventionally underpinning the existing foundations. We installed 40,000 gallons of micro fine cement to help stabilize the soil while the foundations were then segmentally underpinned. Ross School of Business opened for the 2016 school year.
The new University of Michigan Law School required the installation of augercast tangential walls, chemical grouting, and underpinning for the construction of the new buildings. The ERS was a tangential pile wall with earth anchors. Our contract was held by Walbridge and our scope of services was a prime contract. Our work included the tangential walls, grouting and permanent underpinning of adjacent structures. The North Addition was in the existing courtyard and presented some very difficult challenges for the project team. The existing foundation required grouting and underpinning as the proposed footings were to be 8’-10’ below the existing foundations. In addition, a tangential earth retention wall was required for access into the work area. This work had to be performed during the university’s summer break and an extensive amount of overtime and coordination was required to complete this work on time. The inside work demanded limited access equipment and signifcant scheduling. The South Addition was an augercast tangential pile wall with earth anchors. The wall was over 1,000 LF long and enclosed the perimeter of the site. The South Addition was started in the fall and completed throughout the winter. There were areas of the tangential wall where a permanent shotcrete facing was required. This area of shotcrete was performed in the winter and required heating and housing to protect the work. The interesting part of this project is that the south addition ERS walls connected to the previously installed tangential walls that U of M first used on the Gerald Ford Public Policy Building. The previous project was a trial ERS wall that U of M, selected after having diffculty achieving successful ERS walls on campus. The installation, construction, pricing and settlement results of the Gerald Ford project, have continued to be used on future work at U of M. The two building areas were extremely limited, and delivery of materials had to coordinated daily. The settlement of the existing structures was monitored by settlement points. These points were checked throughout the project’s duration and no settlement was recorded in the adjacent structures or utilities. The settlement of the existing building was a concern for all parties, and it was successfully completed by using good construction techniques and engineering. The anchors were installed and tested per the specifcations. The permanent shotcrete facing was placed using wet mix methods.
The $50 million dollar 5th Avenue parking structure required the installation of a temporary Earth Retention System consisting of a tangential auger cast pile wall & soldier pile & lagging system. Augercast tangential walls were selected over secant walls for the tangential pile areas, and the soldier pile & lagging system was per the original scope of services. The primary reason for the augercast wall was the economics and schedule constraints that the secant wall presented. The project was set up as a secant wall design, however when the final bids were received, the project team decided to use the tangential auger cast pile wall as it was a substantial saving to the project. The scope of services was the construction of the new parking garage adjacent to the existing downtown buildings. The site was extremely congested, and deliveries had to be scheduled days in advance because of this. The existing buildings were still in service and our work could not affect these operations. The project required an ERS system to support the existing residential, & commercial building that were on site, numerous utilities that serviced the existing buildings, and tower cranes. The ERS system had to be vibration free, due to the sensitive nature of the existing operations, which were directly adjacent to our work. Due to the site conditions, weekly meeting with project managers were held throughout the project. Daily activity meeting with the site superintendent and look-ahead schedules were required. The settlement of the existing structures were monitored by settlement points. These points were checked throughout the project’s duration and to date there has been no settlement of any adjacent structures or utilities. The project included 1,510 lineal foot of tangential auger cast pile wall (855’) & soldier piles & lagging (656’). The excavation depths were up to 71’ deep. There were over 40,000 lineal foot of augercast pile drilling installed, 1,130,000 lbs. of reinforcing steel installed, and over 6,000 cubic yards of grout used for the project. To our knowledge, this is one of the deepest excavation depths which utilized this type of system. The tangential auger cast pile wall utilized earth anchors which were installed using duplex drilling and self-drilling/grouted anchors. Over 700 earth anchors were installed. All of the anchors were tested and locked at their required loads. The duplex drilled earth anchors were tested to maximum of 235 Kips and the self-drilling anchors were tested to 144 Kip. The duplex-drilled anchors were installed using water, grout, and air as the drilling mediums.