Stabilization of organic-rich marine soft soil by an innovative binder: Box–Behnken optimisation and micro-mechanistic insights

• AK-13 achieves 2.0 MPa UCS at 9% OM, 3.3 × higher than OPC. • OM tolerance breakthrough: effective stabilization beyond 5% OM threshold. • Synergistic mechanism: HA suppression, GGBS activation, AFt/C–S–H co-precipitation. • Optimized mix reduces binder dosage by 32% and curing time by 40%. • Field-validated in coastal reclamation: 48.6% lower dosage, 50% faster strength gain. Organic-rich marine soft soils present critical challenges to coastal infrastructure due to their poor mechanical properties and humic acid-induced inhibition of cementitious reactions. Traditional ordinary Portland cement (OPC) fails to achieve effective stabilization when the organic matter (OM) content exceeds 5%. To address this, an innovative OM-resistant binder, AK-13, was developed. Its stabilization mechanism was systematically investigated using Box-Behnken response surface methodology (RSM) and microstructural characterization. The unconfined compressive strength (UCS) was optimized by evaluating binder dosage (10–20 wt.%), water-to-binder ratio (0.5–0.7), and OM content (3–9 wt.%). X-ray diffraction and scanning electron microscopy elucidated the underlying mechanisms. Results show: (1) At 9 wt.% OM, AK-13 achieved a 28-day UCS of 2.0 MPa, 3.3 times higher than OPC (0.6 MPa), surpassing the conventional 5% OM failure threshold; (2) Binder dosage was the dominant positive factor for UCS, while OM content had a significant negative effect; (3) AK-13 develops strength via three synergistic mechanisms: quicklime-induced high alkalinity suppresses HA dissociation by 60.7%, activators enhance reactive SiO₂/Al₂O₃ release from GGBS by 45%, and desulfurized gypsum promotes co-precipitation of ettringite and C-S-H, reducing porosity by 38.6%; (4) The optimized mix (19.8 wt.% AK-13, w/b=0.58) yielded a 28-day UCS of 2.85 MPa at 9 wt.% OM, reducing binder consumption by 32% and shortening curing time by 40% compared to OPC. A case study of the Mangzhou Tunnel project demonstrates AK-13′s advantages in reducing dosage and carbon emissions. This study provides a validated design framework and mechanistic insights for stabilizing OM-rich marine soft soils in coastal reclamation and infrastructure projects.