Instability of Amuay Cliffside

by T. William Lambe, (F.ASCE), Prof.; Dept. of Civ. Engrg., Massachusetts Inst. of Tech., Cambridge, Mass. 02139,
W. Allen Marr, Jr., (M.ASCE), Prof.; Dept. of Civ. Engrg., Mass. Inst. of Tech., Cambridge, Mass. 02139.,
Francisco Silva, Consulting Geotechnical Engr.; 12 Baskin Rd., Lexington, Mass. 02173,

Serial Information: Journal of the Geotechnical Engineering Division, 1981, Vol. 107, Issue 11, Pg. 1505-1520

Document Type: Journal Paper


This paper presents a case study of cliffside instability. Geotechnical analyses employing field measurements and laboratory test results obtained over a 30-yr period indicate that rising pore pressures trigger slides along the cliff. Visual observation, surveys, and field exploration show that most of the landslides have wedge-type failure geometry. Shear occurs through a nearly horizontal stratum of weak clay, brown fat clay. The strength of the fat clay decreases with deformation. Fluids generated by domestic and industrial activities have resulted in a perched water layer above the stratum of fat clay. For more than two decades, the pore pressure on top of the fat clay has risen. A wedge type of stability analysis can give the correct factor of safety — i.e., 1.0 — for the slides which have occurred.

Subject Headings: Clays | Case studies | Laboratory tests | Pore pressure | Soil strength | Soil deformation | Soil pressure | Geotechnical investigation

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