foundation drawings prepared by the mill supplier. The second is the need for dynamic foundation analysis. The mill to foundation interface is prescribed by the mill supplier and includes the foundation bolting details, shear key geometry, baseplate requirements, and the dimensional constraints necessary to avoid clashes and ensure adequate space for operation and maintenance. Unfortunately, there have been several cases where the mill supplier’s foundation drawings have been taken as a complete foundation design and used directly for the installation arrangement (Belke & Berger, 2014). The dimensions and drawings provided by the mill supplier are intended only to communicate interface requirements and constraints; they do not constitute a full foundation design. Instead, they should be treated as an envelope within which the civil designer develops the surrounding structure, adding concrete volume and detailing as required to achieve the desired foundation performance. In addition to static strength checks, dynamic loading passing from the mill into its foundation must be considered as part of the mill foundation design. Although not all mill suppliers proactively provide dynamic foundation loads, it is a critical aspect that should not be overlooked. There are two primary sources of excitation passing from the mill into its foundation. The first is charge motion, which acts at lifter passing frequency. The second is drive dynamic loading, which can act at gear mesh frequency, pole passing frequency or converter excitation frequency depending on the drivetrain configuration. Mill foundation dynamic analysis should include both a modal analysis and a harmonic response analysis. Harmonic response analysis enables a quantitative assessment of vibration levels by applying excitation forces to the system and evaluating the resulting response. In doing so, interference points (where mode shapes and forcing frequencies overlap) can be identified and compared against a predefined vibration acceptance criterion such as ISO 10816 (Bordi et al., 2023). The analyses discussed above are typically run by the owner’s engineer and are conducted within a foundation design model. This simulation typically compromises of a detailed foundation geometry and appropriate soil modelling, but the mill and mill drive details are simplified or excluded. An additional risk mitigation step available for foundation design is validation via system analysis. Originally created to address vibration and air gap sensitivity issues for Gearless Mill Drive (GMD) mills, system analysis is a highly detailed assessment comprising of mill, GMD, foundation and soil. In addition to assessing GMD air gap reduction throughout the span of anticipated loading scenarios, system analysis remains a powerful tool to ensure long-term reliable operation of the combined
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