Deeper plastic zone

At a pressure of 4.665 MN/m (I.TSPgd), a wider and deeper plastic zone appeared (mark 6) in the top cap. It is interesting to note that the top haunch plastic zone has also been increased. In addition, a minor plastic zone has been predicted by FE at the bottom cap haunch. Moreover, at the upper part of the side wall a wider radial crack has occurred and this crack has also been confirmed by the model tests. 

At larger stresses, beyond SSY, for which the plastic zone extends deeper into the undeformed ligament t = D - a as shown in Fig. 12.6(b), the stress and strain distributions at the crack tip inside the yield zone are now very significantly altered, such that the strongly attenuated stresses are accompanied by more concentrated crack-tip plastic strains. To deal with a family of such problems a form of non-linear crack-tip analysis was introduced independently by Hutchinson (1968) and by Rice and Rosengren (1968). This approach is referred to as the HRR crack-tip analysis. 

Fig. 2.10 Rock beds in a subsidence basin. The part above the terminal base of drainage, for example, the sea, functions as a through-flow system (arrows). The deeper rock beds are fossil through-flow systems that host stagnant groundwater as they are (1) covered by impermeable rocks, (2) bisected by plastic impermeable rocks that have been squeezed into stretch joints in the competent rock beds and in between bedding plane thrusts, and (3) placed in a zone of zero hydraulic potential.

---