Settlement analysis estimates how much a foundation or embankment sinks under load and how fast it happens.

Scope (settlement)

This page covers foundation settlement: immediate elastic deformation, consolidation of saturated clays (Terzaghi theory, oedometer parameters), and long-term creep where relevant. Serviceability limits for buildings and infrastructure are checked against total and differential settlement. In South Africa, geotechnical serviceability and partial factors are framed in SANS 10160-5 together with project-specific performance criteria.

Settlement review (concept)

  1. Estimate elastic settlement in coarse-grained soils using modulus E and ν from tests or correlations.
  2. For clays, compute consolidation settlement from stress increase, compressibility (Cc or M), and drainage path; assess time scale with cv.
  3. Compare total and differential settlement to limits (tilt, crack control, services) and refine foundation size or ground improvement.
  4. Use the calculator below for a rough elastic order-of-magnitude; use software for layered profiles and consolidation time lines.

Geotechnical Engineering — Settlement Analysis

Predict immediate, consolidation, and creep settlement of foundations under load.

Introduction

Settlement is vertical movement of the ground surface (or structure) under load. Immediate settlement occurs under undrained loading in clays and elastic deformation in sands. Primary consolidation in saturated clays is the slow squeezing of pore water; secondary compression (creep) may follow. Differential settlement between footings causes distortion and damage—often more critical than total settlement.

Elastic solutions (half-space, layered elasticity) give one component; oedometer and field tests calibrate compressibility for clays.

Terzaghi mechanical model with spring and piston representing soil consolidation
Terzaghi-style mechanical analogy for saturated soil consolidation (spring–piston model). See licence on Wikimedia Commons
Plan symbol for settlement monitoring recordings
Symbol for settlement recordings on geotechnical investigation drawings. See licence on Wikimedia Commons

What settlement analysis produces

  • Total settlement at critical points (centre/corner of raft, single footing).
  • Differential settlement and tilt between supports for structural and architectural limits.
  • Time–settlement curves for consolidation (when rate of settlement matters).
  • Documentation of assumptions (E, ν, layer thickness, drainage) for peer review.

Standards (South Africa)

Geotechnical design basis and serviceability: SANS 10160-5. Soil testing for modulus and consolidation: SANS 3001 series (oedometer, triaxial, etc.). Compare predictions with observed performance where monitoring is specified.

One-dimensional consolidation (concept):   ΔH/H = Δe/(1+e0)   with e from effective stress change.

Notation (common)

  • s — settlement (often mm in reporting).
  • E, ν — Young’s modulus and Poisson’s ratio (elastic estimates).
  • Cc, cv — compression index and coefficient of consolidation (clays).
  • Δσ′ — increment of effective vertical stress from foundation load.

Examples in practice

  • Pad footing on dense sand: mostly immediate settlement; check adjacent footings for differential.
  • Wide raft on soft clay: consolidation governs total settlement over months or years.
  • Embankment on compressible subsoil: staged construction or vertical drains to control rate.
  • Machine foundations: dynamic settlement and resonance checked separately.

Calculator — elastic settlement (order of magnitude)

Highly simplified elastic estimate for a flexible footing approximation: q and E in kPa, B in m. The script uses a fixed shape factor (0.8) as an order-of-magnitude guide—replace with Boussinesq influence factors or FE for real projects.

s ≈ 0.8 (1 − ν²) q B / E   (output in mm when q [kPa], B [m], E [kPa])

Approximate settlement

Order-of-magnitude elastic settlement s from contact pressure q, footing width B, E, and ν.

Key terms

Consolidation
Time-dependent volume change in saturated clays as pore water drains.
Modulus (E)
Stiffness of soil; use correlated values from in-situ or lab tests.

Software and settlement analysis

Layered soils, groundwater, and construction staging are usually modelled with geotechnical FEA or 1D/2D consolidation tools. Examples (official sites):

  • PLAXIS — deformation and consolidation in 2D/3D.
  • GeoStudio — consolidation, settlement, and slope interaction.
  • gINT — borehole data feeding parameter selection.
  • Autodesk Civil 3D — site surfaces and volumes with geotechnical modules.
  • Rocscience — Settle3 and related foundation tools.

No product endorsement—verify moduli and drainage boundaries against investigation data. This elastic shortcut does not replace consolidation analysis for soft clays.

Diagram sources

Educational schematics. Files in Images/settlement-analysis/ were downloaded from Wikimedia Commons into this repo (not copied from other topic folders). Confirm licence on each Commons file page before reuse.