Soil Mechanics – Typical behavior of clayey soils in foundations and earthworks In geotechnical engineering practice, which of the following statements about clay soils (high plasticity, water-sensitive fine-grained soils) are generally true for structures resting on or constructed with clay?

Introduction / Context:
Clayey soils are fine-grained, often plastic, and highly sensitive to water content. Their engineering behavior controls how foundations, pavements, and earth structures perform over time. This question checks recognition of three hallmark behaviors: volume change (shrink–swell), time-dependent consolidation, and the tendency toward differential settlement.

Given Data / Assumptions:

• Soil type: clays with appreciable plasticity (for example, high PI).
• Seasonal groundwater or moisture variation is possible.
• Loads from typical buildings/embankments are applied.
• No special ground improvement unless stated.

Concept / Approach:

Clay mineralogy (for example, montmorillonite) leads to water adsorption and layer expansion, causing swelling when wetted and shrinkage upon drying. Consolidation in clays is governed by expulsion of pore water and rearrangement of particles under sustained load, a process controlled by low permeability and drainage path length, hence it can take years. Because clay properties and thickness vary laterally, different zones compress differently, producing differential settlements unless mitigated by foundation selection and construction staging.

Step-by-Step Solution:

Verification / Alternative check:

Case histories and settlement monitoring demonstrate multi-year settlement records in soft clays and seasonal movement in expansive clays. Design guides recommend moisture control, preloading, vertical drains, or stiffened rafts to reduce these effects.

Why Other Options Are Wrong:

Choosing any single behavior ignores the other well-established clay responses; “None” contradicts standard geotechnical knowledge.

Common Pitfalls:

Assuming sands and clays behave similarly; ignoring time effects; underestimating differential settlement risk in mixed soil profiles.

Final Answer:

All of the above.