Definition of settlement
In geotechnical engineering, settlement is defined as vertical movement of ground that is mainly due to changing in stresses. In general, structures settlement is allowable in specific rang that has been specified in regulation, but usually the soil under foundation tends to deformations greater than allowable specified value and this excessive settlement can lead to distortion, destruction and performance impair of structure. Occurrence of settlement depending on soil condition and reason of settlement may be very fast or take years.
In general, settlement phenomenon depending on soil type, consist of 3 components:
1-instanse settlement that occurs as soon as load applied. This kind of settlement usually happens in granular soils with high permeability and unsaturated fine grain soils.
2-consolidation settlement that occurs gradually with the loss of excessive pore water pressure generated under loading, during a long time.
3-second compression that mainly is controlled by the composition and structure of soil particles and it continues throughout the life of the foundation same as the creep phenomenon in concrete.
Generally, the amount of settlement is affected by various factors such as soil and foundation type. Settlement happening mainly indicates the problem existence in the soil under the foundation rather than problem in the structure construction. In cases that the soil shrinks, expands or moves down, settlement occurs.
The symptoms of settlement may appear immediately after construction of structure or after years.
Although in many cases it is easy to diagnose, but sometimes consult with an engineer can be effective. Settlements that occur slowly and gradually, don’t need emergency measures and is not a very important issue but in cases that settlement occurs very fast and the symptoms are clearly visible, in order to prevent further damages, immediate and in-time measures is necessary.
Different kinds of settlement
In uniform settlement, all parts of foundation settle evenly. In cases that the properties of soil under foundation in all parts is similar, the loads applied to foundation in all points are uniform and the structural system is the same, this type of settlement is likely to occur. The effect of this settlement on safety performance of structure is not great and usually settlement symptoms are not evident, but performance of some facilities such as wastewater, water pipes, doors and windows is impaired.
In differential settlement, all parts don’t settle the same and is not uniform. This type of settlement mostly occurs in cases that the soil properties under foundation in different point, applied loads to foundation and structural system in different parts of structure is different. In this case the performance of structure is affected. Common symptoms in this type of settlement consists of wall cracking, difficulty in opening and closing door and window and distortion of doors and windows frame.
The reasons of foundation settlement
-failure of problematic soil (weak soil with low bearing capacity and high compressibility) under the foundation due to applied loads
-excavation near the intended foundation
-scour erosion during flood
-ground vibrations due to earthquake or vehical traffic
-irregular extraction of groundwater
-sever change in soil moisture
-soil consolidation under structure weight located on the soil
-low density of artificial embankments
As noted in settlement definition, soil settlement means, the collapse of soil under the foundation due to each of the various reosons mentioned above.
Settlement control means, use of all measures, equipment and possible technics in design and construction stage of a project or after that, in order to settlement modification or prevent of settlement occurance.
Flawless construction of a project, requiers detailed soil investigations to a sufficient depth to identify the factors that lead to settlement. In case of unsuitable soil conditions, in order to prevent settlement of foundation and risks, it is necessary to improve unfavorable conditions of soil.
In many cases due to each of mentioned reasons, settlement occures during the operation of the structure and impairs the performance of structure. In these cases, settlement modification is necessary.
Experts of ASACO have considerable experience in geotechnical investigation, identification and offering suitable and innovative solutions in order to settlement control and modification in foundation of existing structures or structure under construction.
Settlement control methods
ASACO engineering company has numerous methods for soil improvement in order to increse soil bearing capacity and settlement control for different type of soil and structures such as industrial structures. Among different methods of settlement control and modification, following can be mentioned:
Dear visitor, you can click on any of these titles to go to the relevant page with a full description of method.
Experts of ASACO using methods that are mentioned above, based on soil type, existing conditions and construction requirements, offer the most effective, optimal and suitable technic for settlement control by using the most advanced equipment.
The usable sofwares in ASACO in order to design all mentioned methods are as follows:
For more information on project done by ASACO in this field, refer to “project” section.