Normal-Load Sharing and Base Shear Resistance of Rigid Circular Foundations on Partially Cement-Treated Ground: Implications for Marine Gravity Anchorages

Large gravity anchorages founded on soft marine deposits often rely on partial cement-based ground improvement, creating a composite-foundation base in which treated area and mechanical contribution are not equivalent. This study develops a normal-load-sharing framework for evaluating base shear resistance of rigid circular foundations on partially cement-treated ground. Large-scale interface shear tests and three-dimensional finite-element analyses were used to determine constituent interface properties and examine composite-interface behaviour. The normal-load replacement ratio RN was introduced to distinguish the actual normal load carried by treated ground from the area replacement ratio RA. For a rigid circular foundation at RA = 76.7%, the homogeneous solution gives geometric normal-load fractions of 0.8756 for outer-ring treatment and 0.5170 for centre treatment. Idealised elastic analyses showed a saturating increase in outer-ring RN with stiffness ratio, represented by a one-parameter relation with β = 2.42 (R2 = 0.9998). Under measured 35% and 40% CTS conditions, the simplified relation overpredicted regional load concentration, while overall horizontal-resistance estimates remained within about 7% of full finite-element results. The framework provides a first-order basis for assessing treatment layout, stiffness contrast, and base shear resistance.