Correlating Uniaxial Compressive Strength with Non-Destructive Testing (NDT) for Marl-Limestone from Taza, Morocco: Implications for Field Geotechnical Characterization

Identifying suitable local materials for civil engineering is a key challenge for geotechnical engineers. This study characterises the physico-mechanical properties of Taza marl-limestone (Morocco), focusing on the correlation between uniaxial compressive strength (UCS) and non-destructive tests. Twenty-eight samples from various sites underwent physical, mineralogical and mechanical tests. UCS showed a strong positive correlation with P-wave velocity, Vp (R2 = 0.95; internal leave-one-out cross-validated Q2 = 0.94, RMSE = 2.8 MPa) and a moderate correlation with Schmidt rebound hardness (R2 = 0.79; Q2 = 0.75, RMSE = 5.6 MPa). Eleven published UCS–Vp equations gave much larger errors on the same specimens (RMSE ≥ 11 MPa), partly because the Taza data lie outside their calibration ranges; they therefore cannot be transferred to this material without recalibration. The average CaCO3 content is 75.07%. Degradability and fragmentability tests classified the samples, informing long-term behaviour under mechanical and hydric stress. Within the calibrated ranges, these site-specific correlations enable a preliminary non-destructive evaluation of intact Taza marl-limestone and may support local-material use and field-investigation optimisation. However, predictive performance was only internally cross-validated, and the specimens could not be traced to individual outcrops; independent validation (new specimens, other locations, field and moisture conditions) is therefore required before wider use.