Geotechnical, structural & civil engineering — Australia
Crack assessment detail
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Comparison
An overview only. Every entry below is described cautiously and is not an engineering limit; suitability is always confirmed against site-specific data.
| In detail | Best suited to | Key consideration |
|---|---|---|
| Shrinkage & Thermal Cracking | Typically non-structural, appearing early in the life of the element. | Identified by pattern, age and absence of associated distortion or level change. |
| Reactive Soil (Shrink-Swell) Movement | Very common in Queensland clay profiles on residential slabs and footings. | Assessed with soil classification, moisture profiling, tree influence and site drainage review. |
| Differential Settlement Cracking | Sites with variable profiles, uncontrolled fill or cut-and-fill platforms. | Level survey, footing exposure and ground testing to compare actual with assumed founding conditions. |
| Subsidence & Loss of Support | Leaking services, poorly compacted service trenches, and sites with erodible or dispersive soils. | Investigation of services, voids and the erosion path; the leak or flow path must be fixed first. |
| Lateral & Retaining-Related Movement | Structures near retaining walls, batters and sloping ground. | Assessed with wall condition, drainage function, slope stability and evidence of ongoing movement. |
| Crack Mapping & Monitoring | Any case where whether movement is continuing changes the remedial decision. | Baseline plus repeat readings across at least a seasonal cycle where reactive movement is suspected. |
| Level & Floor Surveys | Distinguishing distortion from cosmetic cracking and locating the movement centre. | Compared with distortion limits appropriate to the construction type. |
| Drainage & Moisture Correction | The first and most cost-effective step in most reactive and erosion-related cases. | Targets the moisture mechanism identified in the assessment rather than generic landscaping works. |
| Underpinning & Foundation Retrofit | Confirmed inadequate founding conditions or continuing settlement of a defined area. | Requires exposure of existing footings, load assessment and staged installation to limit further movement. |
| Structural Repair Interface | All retrofits — geotechnical cause and structural repair must be resolved together. | Cause addressed first, then repair sequencing and tolerance for residual movement agreed. |
In detail
Crack width alone is a poor diagnostic. Pattern, location, orientation and whether movement is continuing matter far more.
In detail 01
Fine, often uniform cracking in concrete, render and masonry from drying shrinkage or temperature change.
Typically non-structural, appearing early in the life of the element.
Identified by pattern, age and absence of associated distortion or level change.
Can be mistaken for movement cracking; monitoring may be needed to distinguish them.
In detail 02
Seasonal cyclic movement of expansive clays, often worse near trees, leaks or poor drainage.
Very common in Queensland clay profiles on residential slabs and footings.
Assessed with soil classification, moisture profiling, tree influence and site drainage review.
Cyclic movement may reopen repairs unless the moisture regime is addressed.
In detail 03
Tapering diagonal cracking with associated distortion where part of a structure has settled more than the rest.
Sites with variable profiles, uncontrolled fill or cut-and-fill platforms.
Level survey, footing exposure and ground testing to compare actual with assumed founding conditions.
Requires enough investigation to locate the weaker zone before designing a retrofit.
In detail 04
Localised collapse, erosion or washout removing support beneath a footing or slab.
Leaking services, poorly compacted service trenches, and sites with erodible or dispersive soils.
Investigation of services, voids and the erosion path; the leak or flow path must be fixed first.
Filling voids without stopping the water responsible generally leads to recurrence.
In detail 05
Cracking, rotation or displacement associated with earth pressure, slope creep or retaining wall distress.
Structures near retaining walls, batters and sloping ground.
Assessed with wall condition, drainage function, slope stability and evidence of ongoing movement.
May indicate a stability problem beyond the structure and require a slope assessment.
In detail 06
Documented mapping of crack location, width and orientation with gauges or repeat surveys over time.
Any case where whether movement is continuing changes the remedial decision.
Baseline plus repeat readings across at least a seasonal cycle where reactive movement is suspected.
Takes time; interim measures may be needed on structures with safety concerns.
In detail 07
Relative level survey of floors, footings and wall lines to quantify distortion.
Distinguishing distortion from cosmetic cracking and locating the movement centre.
Compared with distortion limits appropriate to the construction type.
A single survey gives shape, not direction of travel — repeat surveys establish that.
In detail 08
Correcting surface grades, downpipe discharge, subsoil drainage, leaks and vegetation influence.
The first and most cost-effective step in most reactive and erosion-related cases.
Targets the moisture mechanism identified in the assessment rather than generic landscaping works.
Movement may take seasons to stabilise; structural repair should generally follow, not precede, this work.
In detail 09
Extending or supplementing existing foundations using mass concrete, screw piles, micropiles or grouting.
Confirmed inadequate founding conditions or continuing settlement of a defined area.
Requires exposure of existing footings, load assessment and staged installation to limit further movement.
Partial underpinning can shift the differential elsewhere if the mechanism is misdiagnosed.
In detail 10
Coordination with the structural engineer on crack repair, stitching, stiffening and finishes.
All retrofits — geotechnical cause and structural repair must be resolved together.
Cause addressed first, then repair sequencing and tolerance for residual movement agreed.
Cosmetic repair before the cause is addressed usually recurs.
Selection considerations
These factors tend to narrow the options faster than any single test result. Every recommendation remains site-specific and subject to the available data.
Method
Scope is adjusted to the project, the risk and the information already available.