State College, PA
CMT Laboratories’ initial Geotechnical Report prepared for the 320 W. Beaver Ave. Student Apartment Project, The Palmerton, was issued on March 30, 2005. This evaluation indicated the depth to bedrock increased considerably in a general southeast to northwest direction. To better define the top of rock and to better investigate bearing materials, additional borings were performed and the logs issued in a March 1, 2007, report.
In September, 2006, excavation of the underground parking levels commenced. This was performed following temporary shoring installation along the north and west sides of the site. Excavation procedures required blasting along the eastern portion of the structure. Less blasting was required toward the western portion of the site as a result of a change in grade and softer, deeper soils.
As foundation excavation continued along the north side, it became apparent that suitable bearing materials were not going to be present within close proximity to the raised floor elevation
To further evaluate subsurface conditions, 24 air-rotary test borings were drilled along the centerline of the wall footing as well as adjacent column footings. Based upon this analysis, a foundation modification was required in the northwest corner of the building due to the significant presence of clay seams and pockets. The total length of wall requiring modification was an estimated 70 feet.
To adequately support wall foundations along this length, it was recommended that a series of minipiles be used to provide support. This type of foundation element utilizes a frictional bond between the pile and the bedrock rather than an end-bearing element. A total of 36 minipiles were installed along the length of the wall originating at the northwest corner with pile depths ranging between 17 and 74 feet. The piles were designed to attain a 60-ton capacity. A load test, performed on a representative pile, revealed a deformation of 0.341 inches when loaded to twice the design load of 120 tons. Following successful installation of the minipiles, a grade beam was constructed to transfer the wall loads to the deep foundation elements.
Implementation of cold weather concrete practices (ACI 306R) was required for the project to move forward. Practices included heating and tenting formed areas, refinement of the concrete mix, testing of field-cured specimens and temperature monitoring during initial concrete curing. These procedures were monitored by CMT and allowed the contractor to continue construction without sacrificing quality. The majority of the structure’s foundations were constructed utilizing these procedures.