Network protection mechanisms are critical in the design of IP-based networks. In GMPLS networks, backup path protection and Shared-backup protection have been widely studied. More recent protection mechanisms, Self-Protecting Multipath (SPM), can be implemented in GMPLS networks. In this paper, we evaluate the traffic provision in SPM GMPLS networks where events of up to two simultaneous link failure can occur. We present a mathematical formulation to perform optimal capacity allocation in an SPM network environment. Network Service Provider (NSP) could use this mathematical model to design a network with certain availability requirement according to Service Level Agreement(SLA) of each connection requirement in dual link failure scenarios.