Soil Steel Composite Bridges (SSCB) are buried structures relying on the structural collaboration of corrugated steel plates (CSP) and engineered soil and have been in use since the end of the 19th century. Lacking regular maintenance (partially due to their frequently modest spans), many SSCB show significant corrosion issues but require service life extension. The presented research explored the potential of retrofitting SSCB with a thin layer of textile-reinforced mortar (TRM), offering the necessary strengthening and corrosion protection, in addition to not overly affecting the SSCB’s clearance (compared to other retrofitting methods). Two typical circular SSCB shapes with 1.5 m and 3.5 m diameter, respectively, and standard CSP profiles were evaluated. The assumed soil cover depths vary between 0.6 m and 3.0 m. The comprehensive project encompassed full-scale load tests as well as numerical simulations, aiming at identifying key parameters in the structural response of retrofitted elements, such as the influence of normal force (or effects of soil cover, respectively) and sensitivity to flexural stiffness. These experimental and theoretical evaluations resulted in a practice-oriented approach to design the retrofitting of SSCB with thin TRM layers. This paper discusses the main results from experimental evaluations.