DISROC Materials

hiDCon elements are used to control the deformation of the concrete lining in tunnels, located in areas of high rock pressures. A typical stress-strain curve for these elements under simple axial compression is represented on the following figure. The stage of elastic deformation ends with a peak stress followed by a large stage of plastic deformation deformation with small variation of stress. The deformation in this stage can attain values exceeding 50%. Then the stress begins to increase significantly with a tendency near to a parabolic shape. An example of the strain-stress curve of variety of hiDCon produced by SOLEXPERTS is given in the following figure (www.hiDCon.ch)

Figure 1: Experimental strain-stress curve of a hiDCon material (www.hiDCon.ch)

In Disroc model for hiDCon, under a uniaxial stress, the deformation is elastic and linear up to the stress sigma_0 for the axial strain Epsilon_0=Sigma_0/E. Then a perfect plastic deformation takes place according to a Mohr-Coulomb criterion F and a non-associate plastic potential G. This perfect plastic deformation continues up to a total axial strain Epsilon_M. After this stage, the stress increases with the plastic strain (hardening law). The compressive strength Rc in this stage is quadratic function of the plastic strain.

Figure 2: Theoretical stress-strain curve of hiDCon material in Disroc

All the parameters of the model can be determined from the test data. The parabolic shape of the stress-strain curve in the hardening stage is controlled by a parameter Beta which can be determined by curve fitting as illustrated in the following figure. The first fitting in this figure is obtained by taking Sigma_0=9.85 MPa, corresponding to the perfect plasticity level of the curve. Then the parameters Epsilon_M=0.29 and Beta=0.07 are found to provide a good fitting of the curve. The second fitting consists in taking a slightly greater value for Sigma_0, equal to 10 MPa, in order to take into account the existence of a peak stress. This moves the best fitting values for the two other parameters to Epsilon_M=0.26 and Beta=0.05.

Figure 3: Identification of the parabolic hardening parameter of the model by curve-fitting (Courtesy to SOLEXPERT (www.hiDCon.ch) for test data)

For more details see the Disroc Materials Catalog.