Minimum practical depths for building foundations by soil type: Select the typical minimum depth ranges used in practice for shallow foundations on: (i) sandy soils, (ii) clayey soils, and (iii) rock.

Introduction / Context:
Shallow foundation embedment must ensure bearing capacity, protection against seasonal effects (scour, frost, shrink–swell), and construction feasibility. Practical minimum depths vary with soil type and site conditions even when ultimate capacity is ample.

Given Data / Assumptions:

• General building practice in non-frost to moderate climates.
• Sound rock outcrops may permit very small embedment where protection and seating are adequate.
• Numbers represent typical ranges rather than code-mandated values.

Concept / Approach:
On sands, embedment of roughly 0.8–1.0 m helps limit scour and seasonal disturbance. On clays, slightly greater depths (about 0.9–1.6 m) mitigate shrink–swell and seasonal moisture fluctuations. On competent rock, only enough embedment to seat and key the footing (5–50 cm) may be required, provided bearing surface is sound and protected.

Step-by-Step Solution:

Verification / Alternative check:
Local codes may specify frost depth controls; where frost is significant, minimum depths exceed these general ranges.

Why Other Options Are Wrong:

• Picking a single range ignores differing soil behaviors.

Common Pitfalls:
Using ultimate capacity alone to set depth; neglecting erosion or desiccation effects; ignoring local code requirements.

Final Answer:
All of the above