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 = 0onnbottom). - 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 (
u₁onntop), while its vertical displacement is held at zero (u₂ = 0onntop). 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.
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.