Use of porous steel soil nails for enhancing dynamic stability of earth dams

Many failures of earth structures, slopes and foundations supported on saturated sands have been attributed to liquefaction of the sands. Recent studies have shown that many embankments and earth dams are seismically vulnerable.; An innovative retrofit technique combining the advantages of in-situ strengthening and improving drainage is the use of small diameter (5 cm) porous pipes containing highly permeable geotextile driven vertically into the embankment. The shear force due to an earthquake is counteracted by the shear capacity of the soil nails' cross-section. The excess porewater pressure is dissipated through the geotextile thereby increasing the effective stresses within the embankment and dramatically improving its stability. The feasibility of the Porous Soil Nailing (PSN) technique to seismically retrofit embankment dams was the objective of this research. A case history of a failed road embankment on Highway 94 in Michigan has been selected as a study model. Vibratory tampers conducting a seismic reflection survey on a roadway embankment in Michigan's Upper Peninsula triggered a liquefaction failure. The embankment was then subjected to the El-Centro earthquake time history and its response evaluated.; The two-dimensional finite difference computer program, FLAC 3.4, was selected to analyze the problem. The study has illustrated the viability of the Porous Soil Nailing (PSN) technique for seismically retrofitting dam embankments. The use of the PSN technique to increase shear strength and reduce liquefaction potential has the advantages of rapid construction, use of light equipment, and low cost.