Small wind / Buyer questions
Structure and civil works
Why can adequate soil bearing capacity still leave a wind foundation unsuitable?
The short answer
Adequate bearing capacity addresses one potential failure mechanism. A wind foundation can remain below that resistance while moving enough to compromise its intended support conditions. The assessment therefore needs separate limits for settlement, differential movement and rotation, together with the soil stiffness used in the tower model.
Strength and movement answer different questions
Bearing failure concerns loss of ground resistance under the loaded footing. Settlement concerns displacement as stresses change in the soil profile. A competent surface layer may support the footing without shearing yet transmit stress into a deeper compressible layer. That layer can govern movement even though the surface bearing calculation appears satisfactory.
Ask whether the reported bearing recommendation is controlled by shear resistance, an assumed settlement allowance, or both. An unlabeled pressure value cannot resolve this distinction.
Examine the loading and geometry together
Compare the investigation depth and interpreted layers with the foundation footprint and loaded depth. Then separate sustained vertical loading from repeated overturning that shifts pressure across the base. A centered vertical settlement estimate does not automatically predict rotation under eccentric loading.
A wider footing can reduce average pressure while influencing a larger volume of compressible ground. Consequently, increasing area is a design alternative to assess, not proof that every displacement will decrease proportionally.
Set the decision around the supported tower
The structural reviewer should identify acceptable movement for the assembled tower and its interfaces. The geotechnical reviewer then assesses whether the proposed foundation meets those criteria under the relevant loading conditions and time periods.
Request predicted total settlement, differential settlement or rotation, the controlling soil layers, and sensitivity to uncertain stiffness. If movement governs, compare foundation geometry, ground treatment or a different support location before fixing construction quantities. MARSTON turbine power class does not establish the allowable ground movement or complete foundation design.
Sources
Examples are illustrative. Confirm product-specific performance, compatibility and supply scope in the applicable documents.