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Undrained cyclic simple shear test

In an undrained cyclic simple shear test the specimen is sheared back and forth in simple-shear conditions (the deformation mode that most closely represents level-ground seismic loading) with drainage prevented. As in the cyclic triaxial test, excess pore pressure accumulates and the soil may approach liquefaction, but under a stress state more representative of many field situations.

What it constrains

Cyclic simple shear tests constrain the cyclic shear response and liquefaction behaviour in simple-shear conditions. They are widely used in earthquake geotechnics and provide an important, independent check on models calibrated for cyclic loading, complementing the cyclic triaxial data.

How numgeo-ACT simulates it

numgeo reproduces the cyclic simple shear test as a single solid finite element (U4-solid-red), a plane element rather than an axisymmetric one, since simple shear is not an axisymmetric deformation.

The conditions under which the test is simulated are:

  • Base: fully fixed (u₁ = u₂ = 0 on nbottom).
  • Consolidation: the recorded normal stress is applied to the top, bringing the specimen to the prescribed normal stress and \(K_0\) state.
  • Cyclic shearing: the top is sheared horizontally by a prescribed cyclic horizontal displacement (u₁ on ntop), while its vertical displacement is held at zero (u₂ = 0 on ntop). Keeping the height constant enforces a constant-volume (undrained) simple-shear condition; the shear stress, the developing pore-pressure ratio and the cyclic response are compared with your data.
  • Loading control: the shear is applied through a cyclic loading signal at the amplitude and cycle count taken from the sheet.

The drained monotonic counterpart

The same element and the same specimen geometry are used for the drained direct simple shear test (DSS-#). There the top is free to move vertically under a constant normal load, so the specimen may dilate or contract, whereas here u₂ = 0 enforces constant volume.

Data mapping (USScyc-# sheet)

Cell Meaning Units
B1 initial void ratio \(e_0\) –
C1 test name (informational) –
B2 shear-stress amplitude kPa
B3 initial normal stress \(\sigma_{n,0}\) kPa
B4 lateral earth-pressure coefficient \(K_0\) –
B5 pore-fluid bulk modulus \(K_w\) kPa
Column (from the data row) Meaning Units
column 0 time s
column 1 shear strain (in %) %
column 2 shear stress kPa
column 3 normal stress kPa
column 4 normal strain (in %) %
column 5 stress ratio –
column 6 cycle number –
column 7 double-amplitude shear strain (in %) %
column 8 accumulated stress ratio –

Record what you have

Not every column is available in every test; provide the quantities your apparatus recorded. The shear, normal and double-amplitude strains are read in percent.

The full specification is on the Excel sheet reference. A USScyc-1 example sheet is included in the template.