Micropiles are high capacity 5″ – 12″ diameter, drilled and grouted-in-place piles designed with steel reinforcement. Micropiles can be used for new construction, remediation or enhancement. Micropiles are rapidly gaining in popularity for use in urban areas, locations with low headroom and in other places where larger machinery cannot be used. They are an ideal alternative for underpinning and emergency repairs since they’re well suited for the most difficult natural or artificial ground conditions with little to no vibration or disturbance to existing structures.
Featured Project
Theodore Levin U.S. Courthouse
Detroit, Michigan
University of Michigan East Quad
Ann Arbor, Michigan
Cobo Hall Addition & Renovation
Detroit, Michigan
Project Details
The renovation at the Theodore Levin U.S. Courthouse posed many obstacles that were overcome by SOLID BRIDGE CONSTRUCTION’s top-notch drilling crew and management team. The primary challenges associated with this project were air quality management, the excavation and removal of 600 cubic yards of dirt and rubble from the basement, working 12-hour midnight shifts, and drilling micropiles with a Klemm 702 hydraulic drill rig with a remote power pack over 150’ from the drilling area.
Having worked in close proximity of the Theodore Levin U.S. Courthouse in the past, SOLID BRIDGE CONSTRUCTION was well aware of the potential hazard of harmful Hydrogen Sulfide (H2S) gas and Methane (CH4) entering the basement of the courthouse. These hazards along with the need to run several pieces of equipment inside the courthouse required a well thought out and properly executed air quality management plan. Thanks to the utilization of proper drilling techniques for the situation, the use of several air monitors, proper safety equipment and tier 4 rated construction equipment, SOLID BRIDGE CONSTRUCTION did not have any issues maintaining quality breathing air in the basement.
Hardman’s scope originally included only 3’ of excavation throughout the drilling area to achieve enough headroom so the Klemm drill rig could operate at full stroke. Once excavation in the basement commenced, it was clear that SOLID BRIDGE CONSTRUCTION was going to have to do much more excavation than what was defined in the scope. After excavating 7.5’ of dirt, brick, sandstone and granite, good soil was finally exposed, and the drilling area was now excavated to bottom of pile cap elevation.
All of the spoils being generated by the excavation were taken to a containment area that was located on Shelby Street where SOLID BRIDGE CONSTRUCTION was provided with 2 lanes next to the courthouse to store equipment, materials, and an area to store spoils until it could be loaded out and taken to a landfill. Coordination between court security, the construction manager, and the trucking company used to haul off spoils was always a challenge due to Hardman’s hours of operation and the requirement that all spoils quantities and type be documented.
After excavation was completed and a ramp was constructed to move the drill rig into the hole, a test pile was installed in a centralized location in the drilling area; a reaction frame was then constructed around it that only measured about 14 feet wide by 20 feet long. The load test design load for the 8-5/8” in diameter by 126.5’ long micropile was 250 kips (125 ton). Since a factor of safety of 2.0 was used, the test load on the micropile was designed to be 500 kips (250 ton). Once the load test was verified, production began in mid-March and lasted through the beginning of May. All 33 production micropiles anywhere from 126.5’ to 131.5’ long and received a full-length threaded Williams center bar coupled together in 8-foot pieces. Along with the foundation piling that was installed, SOLID BRIDGE CONSTRUCTION also installed a total of 80 wall feet of micropile lagging earth retention. The primary purpose of the earth retention was to provide access to foundation pile locations that were within a few feet of an electrical duct bank running under the basement floor slab. This created a confidence inspiring drilling environment where SOLID BRIDGE CONSTRUCTION did not have to worry about the duct bank moving or getting wet during the drilling process.
As with any significant construction project undertaking, there were many challenges associated with the job. It required an experienced crew with ample knowledge of both the drilling process and the soil conditions in the Detroit area. These factors coupled with a highly competent and knowledgeable project management team made for a very successful job that satisfied the needs of all involved parties.
The renovations to University of Michigan East Quad residence hall presented quite a few challenges for the project team. East Quad required Chemical Grouting, H-Pile and Lagging, Low Head Augercast Piles, Tangential Augercast Pile Walls, Soil Nails, Drilled Low-Head Micropiles, Push Piles, and Underpinning.
Walbridge was the construction manager for the 90 million-dollar renovations and SOLID BRIDGE CONSTRUCTION Inc (HCI) was hired for all the above-mentioned aspects of the project. This project was particularly difficult due to the schedule that needed to be met. On similar scope projects it would have typically taken seven months, however Walbridge required for the contract to be executed within three months.
All together there were 21 separate areas that required some form of work from HCI. The basement provided some of the most challenging work. The work that was done in the basement had to be done within seven to eight feet of headroom. Most of the work in the basement was needed for all of the new underground utilities that needed to be installed; HVAC, Plumbing, Sanitary, and Electrical would all be run underground. This would allow the university extra space in the basement. The underground utilities were 4 to 10 feet below the bottom of the column footings. With over 200 column footings no more than 20’ apart, they needed a solution on how to excavate for the utilities without compromising the buildings structural integrity. The soils below the footings needed to be chemically grouted. HCI facilitated the injection of over 60,000 gallons of micro fine silica cement into the basement. There were some locations that required excavation to be 10’ below the bottom of footing right next to the footing. Some of the footings were also supported with Micro or push piles. The basement area also presented HCI with the opportunity to install low-head Tangential Augercast ERS (Earth Retention System). Elevator pits were required in the basement for this to happen and HCI had to install an ERS system that would allow the concrete contractor to form the walls. The piles that were installed were 15’ long and 24” diameter with a full-length cage. HCI also installed soil nails and underpinned in the basement.
As with any construction project unknown issues and problems arise, East Quad was no different. SOLID BRIDGE CONSTRUCTION worked closely with Walbridge and Soils & Materials Engineers to solve unexpected and emergency issues all while keeping the project on time. This project was a tough job that required a company with a wide array of skills and the ability to solve tough problems. HCI completed the job successfully and satisfied the needs of the construction manager as well as the needs of the owner.
The Cobo Hall Addition & Renovation required the installation of 6” Diameter 200 Kip Micro-Piles to facilitate the foundation changes & new construction. The Micro-Piles were installed utilizing Duplex Drilled Grouted Micro-Piles. Our contract was a direct contract for the Micro-Pile package, and it was held by the DRFCA & Administered by the Joint Venture of Turner/Tools Construction. Micro-Piles were selected due to the low headroom environment inside the building and due to the fact that dense rock was going to be encountered to develop enough capacity for the 200 Kip Capacity with a safety factor of 2.0 or a total test load of 400 Kips. The scope of services was the construction of the new addition to Cobo Hall adjacent to the existing Cobo Hall Building & the addition of a new structure inside of the existing Civic Arena. The site was extremely congested, and deliveries had to be scheduled days in advance of actual deliveries. The project required that we work 5 or 6 days a week with 2 crews in order to meet the delivery schedule inside & outside of the building. 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 project included approximately 47,000 lineal foot of 6” Diameter Micro-Piles. The drill depths were up to 128’ deep and never less than 118’. We performed 1 Compression Pile Load Tests to 400.0 Kips to verify the design load. The soil conditions are typically a mixture of fill material at the surface followed by loose clay and underlain by rock/hardpan material in the borings. The project was started in the Winter of 2011 and our services were completed on time and within the original schedule & contract value for our work.