Diagnosing damage – Ruling out consolidation 

Ruling out Consolidation

Consolidation of soils happens in naturally occurring loose soils and in fill. In structural engineering, consolidation is normally associated with the addition or removal of an external load.

The factors contributing to the amount of vertical movement caused by consolidation are:

  • Depth of loose soil
  • Degree of consolidation (compaction)
  • Weight of applied force.

When attempting to identify or rule out consolidation, assess the vertical movement and damage in the building in relation to:

  • How deep the loose soil is.
  • How the weight of the building is distributed.

Sources of Information

The information on the depth of loose soil will come from the original soil test and the independent soil test.

  • Look for the term “loose” in the borelogs.
  • Look for the term “uncontrolled fill” in the borelogs.
  • Ask the soil tester for an assessment of settlement of loose soils.

Assessment Criteria for Consolidation

Look for the following conditions:

  • Sufficient depth of loose soil that when consolidated might equate to the amount of movement observed.
  • Increased downward movement under heavier loads such as external walls and load-bearing walls.
  • Some consolidation occurring immediately after construction (see timeframe of damage) with gradually decreasing new indications of live movement as the soil consolidates under the weight of the building.
  • Some consolidation can be linked to an crease of moisture content in soils. Soil moisture decreases the friction between soil particles and allows voids to be reduced.

Conditions that might Exclude Consolidation

  • Fill has been placed as controlled fill and DCPs and density results back this up.
  • Terminology in the borelogs such as dense, firma and hard.
  • Differential vertical movement in the slab that is higher under the slab than under loadbearing walls.

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