PSI - Issue 18

Kostina A. et al. / Procedia Structural Integrity 18 (2019) 293–300 Author name / Structural Integrity Procedia 00 (2019) 000–000

299

7

Caverns at the soil-pipe interface occur due to the well survey. During soil thawing the pore pressure in the caverns significantly reduces, since water flows out to a free volume generated by the phase transition of ice to water. As a result, nonhomogeneous mechanical pressure along the pipe boundary arises. The pressure leads to bending of the pipe in the caverns that induces significant shear stress. A numerical simulation has been conducted to study on an influence of the nonhomogeneous pressure distribution along the pipe boundary to its integrity. In this case the strength analysis is carried out in the three dimensional configuration. On the boundary with the exception of two circular domain of diameter of 0.1 m, that corresponds to caverns, an external pressure equal to 50 MPa is given. In Fig. 6(a) a distribution of horizontal component of strain tensor is shown. It can be seen, that nonhomogeneous pressure causes bending of the freezing pipe. In Fig. 6(b) a distribution of the damage parameter is presented. On the basis of the distribution it can be concluded, that the pipe does not damage.

a

b

Fig. 6. (a) distribution of horizontal component of strain tensor; (b) distribution of the damage parameter. Blue color corresponds to the value 0 of the damage parameter. 4. Conclusions In the work integrity of a freezing pipe subjected to an external pressure, that is induced by an artificial freezing process of a rock mass and it subsequent thawing, is studied by a numerical simulation. An estimation of the pressure has been conducted on the basis of the thermo-hydro-mechanical model. The proposed model describes in coupled statement of processes of non-stationary heat transfer with considering the first order phase transition, filtration of water and elastic deformation of rock skeleton. The model allows one to take into account strain induced by frost heave and soil thawing. According to the technical standard the strength analysis of the pipe has been performed in the elastic range with using the failure criterion based a limit value of nominal stress. Several critical situations for pipe integrity such as nonhomogeneous distribution of the external pressure along the pipe wall and corrosion of the pipe wall have been considered. It has been shown that the pressure acting on the freezing pipe wall abrupt rises at the interface of soil stratums with different material properties. This leap of the pressure induces failure of the pipe if corrosion of the pipe wall leads to reduce of the wall thickness by 30% and the location of the leap is in the interval where the wall thickness decreases. Caverns at the soil-pipe interface do not induce drops of the external pressure that lead to damage of the freezing pipe. Acknowledgements This research was supported by 17-11-01204 project (Russian Science Foundation). References

Sres, A., Pimentel, E., Anagnostou, G., 2006. Numerical and physical modeling of artificial ground freezing, in “Proceeding of International Conference of Numerical Simulation of Construction Processes in Geotechnical Engineering Urban Environment” . In: Triantafyllidis, T. (Ed.).