Terzaghi’s one-dimensional consolidation assumptions: Which statements are included in Terzaghi’s classical theory for vertical (1D) consolidation of saturated clay layers?

Introduction / Context:
Terzaghi’s consolidation theory provides the framework for predicting settlement versus time in saturated clays subjected to load. The theory employs simplifying assumptions to obtain closed-form solutions and practical design charts for average degree of consolidation U.

Given Data / Assumptions:

• Saturated, homogeneous soil layer; constant properties in space and time.
• Small strains; one-dimensional deformation (vertical only).
• Drainage occurs vertically (single or double drainage).
• Water and soil grains are incompressible relative to skeleton rearrangement; time lag due solely to permeability.

Concept / Approach:

Under these assumptions, excess pore pressure dissipation is governed by a diffusion-type equation with coefficient of consolidation C_v = k / (m_v * γ_w), linking permeability k and compressibility m_v. The boundary conditions define drainage path length d, used with the time factor T_v = C_v * t / d^2 to compute U.

Step-by-Step Solution:

Verification / Alternative check:

Oedometer tests are designed to satisfy these assumptions, validating the model for design within its limits.

Why Other Options Are Wrong:

Since (a)–(d) are all part of the classical model, “All the above” is the correct aggregate statement.

Common Pitfalls:

Applying the model to anisotropic layers without adjustment; ignoring secondary compression and property changes with stress.

Final Answer:

All the above