<p>Creep in clay significantly influences the long-term performance of geotechnical structures. Although Hypothesis B, in which creep develops under evolving effective stress, is widely accepted for one-dimensional clay creep, many existing soil mechanics models still assume constant effective stress after the onset of creep and are therefore not explicitly formulated for evolving stress conditions. Conventional creep models are also limited by discrepancies between laboratory and field conditions, insufficient representation of over-consolidation ratio (OCR) effects, and reliance on elapsed time as the primary constitutive variable. This study proposes a creep model for clay based on the terminal creep line (TCL) concept. The volumetric creep strain rate is formulated as a state-dependent constitutive law governed by the current void ratio relative to the terminal state. The model provides a unified description of contractive and dilative volumetric creep and is consistent with both the isotache concept and Hypothesis B. An analytical relationship between pre-consolidation pressure and strain rate is derived from the model and is shown to agree well with experimental data. The formulation also reproduces the strong OCR dependence of creep behavior, including the marked reduction in contractive creep as OCR increases and unloading-related delayed volumetric expansion at high OCR. In addition, a time-shifted deviatoric creep law is reformulated into a time-independent incremental form and combined with the volumetric model to obtain a multi-dimensional creep strain-rate tensor, providing a constitutive framework for numerical implementation under evolving effective stress.</p>