Protection schemes for WDM mesh networks are typically based on the single-failure scenario. However, the single-failure model is not realistic since the failure of network components is probabilistic. On the other hand, different applications or end users need different levels of fault tolerance. In this work, we assume a probabilistic failure environment and choose the connection reliability as a parameter to denote the level of fault tolerance. We propose a partial segment-based protection approach to accommodate lightpath requests according to their differentiated reliability requirements. We also consider incorporating backup sharing in such an environment. We conduct extensive simulation experiments to evaluate the effectiveness of the proposed scheme. Simulation results show that establishing connections according to their differentiated reliability requirements can effectively improve network blocking performance and the proposed partial segment-based protection scheme outperforms the partial path-based protection scheme proposed in the literature in terms of connection blocking probability.