About Differential Settlement

1. What is Differential
Settlement? - Civil &
Geotechnical
Engineering
Dr. Costas Sachpazis

2. What is Differential Settlement? - Civil & Geotechnical Engineering
Table Of Contents
De ne Differential Settlement of Structures? 3
What Causes Differential Settlement? 3
Signs of Differential Settlement 4
Prevention of Differential Settlement 4
What is Differential Settlement? - Civil & Geotechnical Engineering

3. What is Differential Settlement? - Civil & Geotechnical Engineering
The stability of any building structure is based on the stability of
the foundation underneath the structure. Any variation in the strength or bearing
capacity of the soil over which the foundation is constructed can result in sinking of the
wholestructure. This sinking is called a settlement of thestructure.
The settlement occurred can be uniform throughout the plan of the building. This uniform
process is called as a uniform settlement.This settlement is an expected process during the
service life of any building structure. This can occur after 2 to 3 years from the completion
of thebuilding. Uniform settlement does not bring any severeissueto thebuilding.
If the settlement caused is non-uniform in nature, we call the settlement as the
differential settlement. And this settlement is an undesirable process for a building which
will requirestudy, analysis, and rehabilitation.
Fig.1.Differential Settlement of theBuilding
What is Differential Settlement? - Civil & Geotechnical Engineering

4. What is Differential Settlement? - Civil & Geotechnical Engineering
De ne Differential Settlement of Structures?
Thedifferenceof elevation/settlement of two adjacent columns in a structurewill givethe
value of the differential settlement. The difference of elevation across the boundary of the
structure can also give a value for differential settlement if there exists any non-
uniformity.
Suppose, we have a plan to add a structure to an existing one. The differential settlement
herecan becalculated as
=Settlement after addition of structure- Settlement of theexisting structure
Theaccepted levels of thesettlement are:
For Institutional or commercial building = 25 mm
Industrial Buildings = 40 mm
Ware Houses = 50 mm
Machine Foundations < 0.05 mm
What Causes Differential Settlement?
The main cause of differential settlement is the expansion and contraction of the soil
beneath thefoundation. Themain reasons for this movement are:
Frost Actions
Vibrations from Nearby Construction work
Improper compaction of the soil
Floods
Root penetration of the matured tree
Hydraulic pressure exerted from groundwater or broken water lines
What is Differential Settlement? - Civil & Geotechnical Engineering

5. What is Differential Settlement? - Civil & Geotechnical Engineering
Fig.2.Causes of Differential Settlement
Note: A well-known example of differential settlement is the Lean Tower of Pisa. This
leaning was dueto theinsuf cient bearing capacity of thesoil below thestructure.
Signs of Differential Settlement
Thefollowing signs observed in thebuilding re ects differential settlement:
1. Leaking of theroof and thebasement
2. Cracking of bricks or thewalls
3. Drywall Separation
4. Windows and Door Sticking
5. Leaning of Garage
6. Wall bulging or leaning
7. Tilting of Chimney
8. Cracks in steps - masonry mortar joints
What is Differential Settlement? - Civil & Geotechnical Engineering

6. What is Differential Settlement? - Civil & Geotechnical Engineering
Prevention of Differential Settlement
Following preventive measures will help in avoiding the chances of differential
settlement:
1. Careful Inspection of thesiteprior to theconstruction process
2. Checkfor thecloseness of thesiteto earthquake-pronefaults
3. Its not necessary that the differential settlement will leave behind a symptom. So its
necessary to evaluatethesitewith utmost accuracy and care.
4. If the site is made of clayey or expansive or contracting soils, a resistance or helical
pier system will bethebest choice.
What is Differential Settlement? - Civil & Geotechnical Engineering

7. What is Differential
Settlement? - Civil &
Geotechnical Engineering
Dr. Costas Sachpazis