Sand piles for ground improvement — typical construction features Which statements correctly describe sand pile construction and usage for improving foundation performance?

Introduction / Context:
Sand piles (a form of granular piles) are installed to improve weak or compressible soils by providing reinforcement, drainage, and densification. They are common under individual footings and heavily loaded columns where settlement control is required.

Given Data / Assumptions:

• Granular piles are formed in pre-bored holes or by displacement.
• Compaction and controlled moisture are necessary for target density.
• Concrete caps or plug zones are used to spread load into the granular column.
• Typical application is under column footings or heavily loaded spots.

Concept / Approach:
Well-compacted moist sand achieves higher relative density and stiffness, enhancing load-sharing and reducing settlement. A concrete top cap provides a firm seat for footings and prevents surface ravelling. Granular piles also function as vertical drains, accelerating consolidation when combined with preloading in cohesive soils.

Step-by-Step Solution:

Verification / Alternative check:
Ground improvement manuals illustrate sand/granular piles with top plugs, preload options, and their role as drainage inclusions.

Why Other Options Are Wrong:

• Any single statement alone is incomplete; all listed practices together best characterise sand piles.

Common Pitfalls:
Neglecting quality control of relative density; omitting the top cap; assuming granular piles behave like rigid piles (they are deformable inclusions).

Final Answer:
all of the above