Dynamic Moduli and Damping Ratios for a Soft Clay

by William D. Kovacs, (A.M.ASCE), Asst. Prof. of Civ. Engrg.; Univ. of Missouri-Rolla, Rolla, MO; Staff Consultant, Law Engrg. Testing Co., Birmingham, AL,
H. Bolton Seed, (M.ASCE), Prof. of Civ. Engrg.; Univ. of California at Berkeley, Berkeley, CA,
Clarence K. Chan, (M.ASCE), Assoc. Res. Engr.; Inst. of Transp. and Traffic Engrg., Univ. of California at Berkeley, Berkeley, CA,

Serial Information: Journal of the Soil Mechanics and Foundations Division, 1971, Vol. 97, Issue 1, Pg. 59-75

Document Type: Journal Paper


Cyclic, simple shear, and free vibration tests were performed on 12-in × 12-in × 6-in block samples of a remolded 3:1 kaolinite-bentonite clay mixture of various water contents. The simple shear tests were performed by using predetermined sinusoidal displacements at frequencies ranging from 1 cps to 10 cps. A free-vibration damping factor was obtained from the logarithmic decrement of the free-vibration decay curve. By using the theory of the transverse vibration of shear beams, it was possible to obtain the shear modulus from a known period of free vibration. The shear moduli, established by simple shear and free-vibration tests, were in good agreement. The modulus for a given strain decreased as the shear strain increased and as the number of cycles increased. The damping value, which is also strain-dependent, increased with increasing strain. The value of free-vibration damping was always higher than the value of hysteretic damping for a given strain value.

Subject Headings: Shear tests | Shear modulus | Vibration | Soil dynamics | Strain | Dynamic modulus | Soil modulus | Damping

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