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    Strength and Stress-Strain Characteristics of Clays Subjected to Seismic Loading Conditions

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    An attempt is made to relate the results of unconfined compression tests on saturated clays to the strength and bilinear stress-strain parameters which will govern the behavior of the clay during and after earthquakes.

    Simple-shear pulsating-load tests on three soils indicate that while the decrease in dynamic strength with number of cycles increases with the failure strain observed in static strength tests, a plot of the product of failure strain x dynamic strength (in percent of static strength) against number of cycles is about the same regardless of the failure strain.

    Cyclic-loading triaxial compression tests in which the peak strain was controlled were also performed on the three soils. After 200 cycles of loading the compressive strength was measured under static conditions. It was found that when the peak cyclic strain is less than one half the static failure strain, the strength after cyclic loading is at least 80 percent of the original strength. For larger strains higher strength losses were observed.

    The nonlinear stress-strain curves obtained from various cycles in the cyclic loading tests were approximated by a bilinear model defined by three parameters (two moduli and a yield strain). The decrease in the ratio of dynamic modulus/ original static modulus with the ratio of cyclic strain-failure strain is about the same for all three soils for a given number of cycles. A similar relationship for yield strain was found, although this parameter increases with cyclic strain and is virtually unaffected by number of cycles.

    The static modulus of each soil tested was greatly reduced by the cyclic loading, decreasing to about one half its original value in tests where the cyclic strain was one half the failure strain.


    clay soils, earthquake, dynamic loads, compression tests, soil mechanics, soil dynamics, earth (soil)

    Author Information:

    Thiers, GR
    Assistant Professor of Civil Engineering, Carnegie-Mellon University, Pittsburgh, Pennsylvania

    Seed, HB
    Professor of Civil Engineering, University of California, Berkeley, California

    Committee/Subcommittee: D18.10

    DOI: 10.1520/STP33635S