Causes of spatial variation in geomaterials Spatial variation in properties in the horizontal and vertical directions arises from multiple weathering processes. Identify the correct grouping.

Introduction / Context:
Engineering properties of soils and rocks vary spatially due to the complex interplay of geological processes. Recognising the origins of variability helps in site investigation planning, sampling strategies, and uncertainty quantification for design.

Given Data / Assumptions:

• Near-surface geomaterials undergo weathering.
• We consider physical, chemical, and biological mechanisms.
• Variations are both lateral and vertical.

Concept / Approach:
Physical weathering (e.g., freeze–thaw, thermal stress) fractures rock and increases porosity. Chemical weathering (e.g., hydrolysis, oxidation) alters mineralogy and fabric. Biological weathering (roots, microbes) enhances disaggregation and chemical alteration, creating heterogeneous profiles.

Step-by-Step Discussion:

Verification / Alternative check:
Borehole logs typically show gradations from residual soils to partially weathered rock, evidencing combined mechanisms.

Why Other Options Are Wrong:

• Each single mechanism contributes; excluding others misrepresents reality.
• None of these: Incorrect because all mechanisms operate in nature.

Common Pitfalls:
Assuming homogeneity from limited samples; ignoring scale effects; extrapolating 1D profiles to site-wide conditions.

Final Answer:
All of these