The design of flexible retaining structures is very frequently conducted using simplified soil-structure interaction schemes such as the well known non-linear spring method. With this method, several distinguishing aspects of flexible wall behaviour can be usually captured with reasonable accuracy with regards to construction stages and static conditions. Seismic design, however, still represents a challenging aspect. In this paper some common issues of seismic analysis with the spring method are addressed and a proposal to include seismic effects within a pseudo-static framework is presented. Some examples analyzed with the proposed approach are finally discussed.