Determining the shear strength of soils by use of the Simple Shear Test, is there any remarkable difference between the shear strength obtained from the Force Control and the Displacement Control tests?
How the rate of Force or Displacement affects the results?
Hello Dear Samad
In strain control test you can record the residual strength of soil but in Stress Control it is not possible but in stress control test the load is applied gradually so you can get the exact failure stress
The rate of force or displacement for fine aggregates is determined by oedometer test and it must be as slow as the excess pore pressure doesn't build up, for granular soils because of quick drainage the rate is arbitrary
fell free to ask further question if needed
In theory both should produce same results but according to my experience I would recommend displacement control tests !
I prefer displacement control.The complete stress-strain curve is obtained, and soils with a peak of shear strength do not fail brusquely, as in stress-controlled tests. Also it is possible to make reverse cycles with the machine, and thus obtain an approximation of the residual stress value.
The advantage of the strain-controlled tests is that, for example for dense sand,
peak shear resistance (at failure) as well as lesser shear resistance (at a point after failure so-called ultimate strength) can be observed and plotted.
In stress controlled tests, only peak shear resistance can be observed and plotted. Note that the peak shear resistance in stress-controlled tests can only be approximated. This is because failure occurs at a stress level somewhere between the pre failure load increment and the failure load increment. Nevertheless, stress-controlled tests probably simulate real field situations better than strain-controlled tests and more user-friendly due to reverse control and possible use for tensile tests of cemented soils.
How to simulate the tests with displacement control instead of stress control
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