This study explores interpretation methods for determining the preconsolidation stress from one-dimensional consolidation test results. Twelve reconstituted clay specimens with targeted preconsolidation stresses of 60 and 120 kPa were prepared using commercial kaolinite and marine clays collected from coastal regions of South Korea. Five representative interpretation methods were applied, and the influence of maximum applied stress levels of 320, 640, and 1280 kPa was evaluated. The results indicate that the estimated preconsolidation stress varies considerably depending on both the interpretation method and the maximum applied stress, particularly for rounded compression curves with gradually changing virgin compression slopes. To address these limitations, a new interpretation approach is proposed. The method utilizes the rebound slope obtained from an unload–reload cycle and defines the virgin compression line through linear regression without identifying the recompression–virgin compression boundary. The proposed method demonstrated reduced sensitivity to the maximum applied stress and provided more reproducible estimates for rounded compression curves, although further validation using natural clays considering sample disturbance effects is required.

Although the long-term behavior of ground anchors depends fundamentally on interfacial behavior, the independent effect of the strand–grout interface on load loss has not been comprehensively investigated. This study establishes a physical model testing method that isolates the strand–grout interface and systematically investigates both short-term and long-term load loss behavior. Pull-out tests and long-term monitoring tests were conducted using grout uniaxial compressive strength ($q_u$ = 18–30 MPa) and bond length ($L_b$ = 900–1500 mm) as primary design variables. Long-term monitoring confirmed that prestress loss at the strand–grout interface is induced by the progressive pull-out displacement of the strand over time, following a logarithmic decay pattern. The load reduction coefficient n was significantly more sensitive to $L_b$ than to $q_u$; n increased sharply from 0.015 to 0.069 as $L_b$ decreased. Anchors with insufficient bond length exhibited secondary load reduction behavior that disrupted the stable log-linear decay, posing significant risk to long-term performance. Based on RMSE analysis of the fitted logarithmic model, a minimum monitoring period of approximately 50 days is recommended for reliable long-term prediction when bond length is adequate. These findings identify $q_u$ and $L_b$ as the governing parameters, providing a quantitative basis for optimizing prestress design and enhancing the long-term reliability of anchor systems.