foundation system of burj al arab

What is the allowable settlement of foundation?

Allowable settlement:

The settlement of a foundation that is acceptable both structural and esthetic point of view is called allowable settlement which generally includes a rational factor of safety. As esthetic issue is considered to set acceptable settlement, architect often take part in determining allowable settlement. The structural engineer and architect should consult with foundation engineer about expected

• Loading conditions
• Allowable settlement of building
• Primary selection of foundation type

If above information is not available, geotechnical engineer has to calculate allowable settlement of building to determine proper type of foundation. Many studies has been conducted to determine settlement of buildings and it is ascertained that allowable total settlement and differential settlement depends on

• Complexity and flexibility of buildings

• Construction materials

• Construction type.

According to Coduto (1994) the factor affecting allowable settlement are follows:

Construction type:

Different types of construction have different level of tolerance against settlement. For example, buildings having wood frame including wood siding will have more tolerance than unreinforced masonry buildings.


In dwelling house, even a tiny crack is considered unacceptable; on the other hand, in a structure used as warehouse, storage or industrial purposes, a large crack may be even not noticed.

Type of finishing:

When sensitive finishing is provided into a building, like tile, a small cracks or movement will provided visual disturbance.

Structural integrity:

When a structure is designed as rigid body, a settlement of a particular footing under any portion of it relative to other footings, will not result significant affect as some load will be transferred to nearby footing. In case of flexible structure, settlement of any footing is significant as movement occur before any considerable transfer of load to nearby footings, which indicates that a rigid structure will not subjected to significant differential settlement relative to flexible one.

Coduto also interestingly concluded settlement that in most case structures, particularly buildings, settlement is governed by serviceability and aesthetic requirements not by structural. Visual hazard like jamming doors-windows, cracks and other identical problems appears first long before structural integrity is hampered.

Determination of allowable settlement:

Evaluation of allowable settlement of a building is very complex. Engineers often try to correlate settlement with observed behavior of buildings. The relation between performance of structures and settlement of foundation that may cause damage has been present by Skempton & Macdonald in 1956 based on study on 98 buildings. In this study, it has been found that 40 buildings had been subjected to different degree of damage