A Long Island, N.Y., shore property has been experiencing significant ground movement, causing the hill slope to slide toward the Long Island Sound. East Coast Geoservices LLC, out of Huntington Station, N. Y., was retained to perform a series of borings to document the underlying soil and clay. Using 2 1⁄4-inch hollow-stem augers, borings were conducted on both the uphill and downhill sides of the silage fault line. The borings, along with soil sampling and blow counts, document the underlying soil conditions, including the identification of a 12-foot layer of perched water over the clay uphill of the fault line. The soil information obtained is being used by the project’s consulting engineers to evaluate alternative mitigation proposals.
Geotechnical borings were used to determine the depth and thickness of a clay layer that is causing a slope to slide toward Long Island Sound. Two borings, using 2 1⁄4-inch hollow-stem augers, were completed at the subject property. The first boring was positioned on the top of the slope adjacent to the fault line of the slide. This boring, which was required in order to determine the location of the clay layer, was completed to a depth of 75 feet. Clay was present approximately 73 feet below grade. During the completion of this boring, blow counts were collected every 5 feet for the first 20 feet, and every 10 feet for the remainder of the boring. A perched water layer was encountered approximately 62 feet below grade.
The second boring was located at the top of the bluff, running along the shore of Long Island Sound. This boring, which was required to determine the thickness of the clay layer, was completed to a depth of 65 feet. During the completion of this boring, blow counts were collected every 5 feet for the first 40 feet, and every 10 thereafter for the remainder of the boring. The clay layer was encountered approximately 40 feet below grade, and extended past the end of the boring depth. A perched water layer was encountered approximately 35 feet below grade. Based on the finds of the borings, engineers were able to prepare a detailed report on the existing conditions of the slope, and present alternatives to the landowner for potential mitigation measures to prevent further sliding.
East Coast Geoservices is a full-service geotechnical company, specializing in geological and environmental sampling, and ground water monitoring well installations. The company currently has two AMS PowerProbe sampling systems that have both direct-push and auger capabilities. The 9100 unit, mounted on a Bobcat MT-52, is a small unit that is utilized to collect soil and ground water samples in restrictive space environments. This unit can be taken into wooded areas without having to clear a path, and inside buildings through 36-inch doorways. The 9600 unit, situated on a Ford F-550 flatbed truck, is a heavy-duty machine that can go deeper than the 9100, and utilizes larger augers – allowing the installation of larger ground water wells at deeper depths. The 9600 unit also has an auto drop hammer, which is utilized to obtain blow counts needed for geotechnical information.