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Excavation/Structural Support


Barberton, OH: Soil-Mixed Temporary Retention Wall

soil-excavation-structural-support-barberton-oh

An area within an existing manufacturing facility containing precision machinery required the construction of a new massive machine tool foundation. The foundation soils primarily consisted of loose poorly graded sands, which were prone to piping and settlement from even moderate vibration. Geo-Con worked with project engineers to develop a plan utilizing Shallow Soil Mix (SSM) methods to install the retaining wall while protecting nearby precision machinery within the building from potentially damaging vibrations.

Geo-Con was then contracted to install soil-mixed temporary retaining wall system to facilitate excavation and construction of the 25-foot deep foundation structure. The wall would also serve as a groundwater seepage barrier during installation of the machine tool foundation. Geo-Con mobilized a specialized track-mounted SSM rig capable of operating within a confined area having less than 60 feet overhead clearance within the existing building.

The initial phase of work involved installation of 195 soil mix columns to create a rectangular wall system. The columns were each 36 inches diameter and spaced on 27-inch centers to create an effective wall thickness of 24 inches. A steel beam was installed in every second column to provide the required wall system strength. SSM columns and steel beams were installed to within vertical tolerance of 0.5 degrees. The majority of columns extended 50 feet below the ground surface to key into the underlying clay layer to provide required lateral stability for the retaining structure and create an effective groundwater cutoff.

soil-excavation-structural-support-barberton-oh

The second phase of the project consisted of jet grouting to provide support to existing crane bent foundations adjacent to the retaining wall in areas inaccessible by the SSM rig. Holes were typically placed on 2-foot centers and grouted using the single stem jet grout method at pressures of 5,000 psi using a cement grout to yield the required twenty four inch wall thickness and desired permeability. Pressure and lifting rates varied beneath the crane bents to assure complete contact to the existing concrete bent foundations. Jet grout columns were also installed behind the SSM wall in areas where columns may have deviated more than 0.5 degrees from vertical to provide suitable overlapping of the SSM columns.

The final phase of work consisted of installing 68 auger cast piles within the excavation by the intrusion grout method to provide for the machine tool foundation. Once the piles were completed the foundation was excavated to seven feet below grade to allow Geo-Con to install the supporting wale and strut system. The exposed surface of the soil-mix columns were trimmed and wales were tied directly into the steel columns placed within the soil-mix columns.

The temporary foundation was completed within a tight construction schedule driven by the planned delivery date of the machine tool equipment. Critical aspects of working within an existing building housing precision machinery included operating mobile equipment within a confined area, management of equipment emissions, control of fugitive dust and containment of drill cuttings and excess grout.

In addition to the initial design mix testing, a rigorous Quality Control program was implemented to monitor grout viscosity, grout flow rates, and pressures to insure consistency throughout the project. In situ samples were taken from the completed soil mix and jet-grout columns for permeability and compressive strength. Laboratory testing results indicated the SSM material developed an average unconfined compressive strength of 226 psi within 28 days of cure. Hydraulic conductivity results ranged from 1.1E-8 cm/sec to 2.7E-6 cm/sec with an average of 8.5E-7 cm/sec. In addition, Geo-Con installed monitored several inclinometers to measure the response of the soil-mix column retaining structure during excavation of the foundation.

Project was completed in less than 10 weeks.



 

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