What is consolidation settlement in soil mechanics?
As noted previously, consolidation settlement is the time-dependent volume change that occurs as the excess pore water pressure, developed during load application, gradually dissipates and is transferred to the soil skeleton. The
What is the difference between immediate settlement and consolidation settlement?
Immediate settlement occurs in the soil upon load application and involves reduction in void space and rearrangements of the soil particles in response to that load. The consolidation settlement is induced due to volumetric change.
What is primary consolidation of soil?
Primary consolidation is a process of dissipation of increased pore water pressure due to the application of loads on the soil layer and increases in the effective stress in the soil skeleton. This results in a volumetric change in the soil skeleton.
What is the definition of consolidation in geography?
Some publications also use "consolidation" in the broad sense, to refer to any process by which soil changes volume due to a change in applied pressure. This broader definition encompasses the overall concept of soil compaction, subsidence, and heave.
What is consolidation settlement?
Some time is required for excess pore water pressed to dissipate and increase the stress to be transferred to the soil skeleton. This gradual increase in the effective stress in the clay layer will cause settlement over a period of time and is referred to as consolidation settlement.
What is meant by consolidation of soil?
The term consolidation describes the process by which a soil mass decreases in volume in response to either natural or man-made loadings. Natural loadings that induce consolidation result from geological processes such as sedimentation.
Is consolidation same as settlement?
Debt consolidation and debt settlement are strategies for making debt manageable, but they are different methods and bring different results. Debt consolidation reduces the number of creditors you'll owe. Debt settlement tries to reduce the amount of debt you owe.
Why is consolidation settlement important?
Consolidation plays an important role in stability analysis for the embankment, footings or a column constructed on clayey soils. The settlement behaviour of these structures and the pore pressure needs to be investigated for construction on these soils.
What is consolidation definition?
Definition of consolidation 1 : the act or process of consolidating : the state of being consolidated. 2 : the process of uniting : the quality or state of being united specifically : the unification of two or more corporations by dissolution of existing ones and creation of a single new corporation.
What is the process of consolidation?
Consolidation processes consist of the assembly of smaller objects into a single product in order to achieve a desired geometry, structure, or property. These processes rely on the application of mechanical, chemical, or thermal energy to effect consolidation and achieve bonding between objects.
What is the difference between settlement and consolidation in soil?
Different from immediate settlement, consolidation settlement occurs as the result of volumetric com- pression within the soil. For granular soils, the consolidation process is sufficiently rapid that consolida- tion settlement is generally included with immediate settlement.
What are the three different types of settlement of soil?
There are three main types of soil settlement in geotechnical engineering: Uniform settlement. Differential settlement. Curvature settlement.
What is the difference between compaction and consolidation?
Compaction is the compression of soil by the expulsion of air from the voids of the soil. Consolidation is the compression of soil by the expulsion of water from voids of the soil. It is a quick process.
What are the factors affecting consolidation?
The factors which affect the consolidation are: (e) Magnitude of the consolidating pressure and the manner of its distribution across the thickness of the layer. (a) Thickness of clay layer: If the thickness is more the consolidation of the layer will be more due to self overburden pressure.
How many types of consolidation are there?
Full consolidation, proportionate consolidation, and equity consolidation are the three consolidation methods.
What is the purpose of consolidation test?
Consolidation test is used to determine the rate and magnitude of soil consolidation when the soil is restrained laterally and loaded axially. The Consolidation test is also referred to as Standard Oedometer test or One-dimensional compression test.
What causes soil consolidation?
The increment of applied stress that causes consolidation may be due to either natural loads (e.g. sedimentation processes), or human-made loads (e.g. the construction of a building or an embankment above a soil mass) or even the decrease of the ground water table.
What is difference between consolidation and compaction?
Following are the differences between compaction and consolidation of soils. Compaction is the compression of soil by the expulsion of air from the voids of the soil. Consolidation is the compression of soil by the expulsion of water from voids of the soil. It is a quick process.
What are the two types of consolidation?
There are two major processes that lead to the final consolidation. These are synaptic consolidation which takes place within immediate hours of learning and encoding while the other is system consolidation where hippocampal memories are independent of hippocampus storage after a certain period of time.
What is difference between compression and consolidation?
In compaction process, soil volume is reduced by removing air void from the saturated and dry soil. In consolidation process, soil volume is reduced by squeezing out pore water from the saturated soil.
What is the consolidation settlement?
For fine-grained soils, the consolidation settlement often is the major component of the total settlement. As noted previously, consolidation settlement is the time-dependent volume change that occurs as the excess pore water pressure, developed during load application, gradually dissipates and is transferred to the soil skeleton. The consolidation settlement is given by
What is secondary settlement?
Secondary settlement continues after consolidation settlement is complete, as the soil structure gradually readjusts to the new level of effective stress. This process continues indefinitely. The prediction of secondary settlement is of considerable importance with clays of high plasticity and with micaceous and organic soils, but it typically is of minor concern with coarse-grained soils and overconsolidated, low plasticity, inorganic clays. Secondary settlement often is computed from the relation
What was the pressure of the airtight sheet during the consolidation settlement?
Vacuum pressure measured under the airtight sheet was maintained constantly at about 80 kPa along to the consolidation settlement between October 2008 and December 2009. The water discharge at the beginning of vacuum pumping was about 400 m 3 /day and gradually decreased during consolidation settlement to about 200 m 3 /day.
What are the phases of settlement?
As stated above, when a load is applied to the foundation, three distinct phases of settlement occur: immediate or elastic (ρ e ), consolidation (ρ c ), and secondary settlement (ρ s ):
How to determine the settlement of a foundation?
The elastic settlement of a foundation is determined by assuming that the soil behaves as an elastic material. The basic approach employed is to use the traditional Boussinesq solution for stress changes in an isotropic, elastic medium subjected to a point load applied normal to the surface of a half-space (the ground is a half-space because it does not exist above the ground surface). The elastic settlement of the foundation is given by
What is the estimated average degree of consolidation in 2024?
The estimated average degree of consolidation in 2024, according to non-Darcian flow, becomes 84%, corresponding to a settlement of 2.1 m.
Fig. 9.7 Void ratio to effective pressure curves
curve, primary compression being made up of (i) a reversible part and (ii) an irreversible part. Once the consolidation pressure is extended beyond the original consolidation pressure value (the preconsolidation pressure ), the e p curve follows the trend of the original compression curve.
Typical values of mv are given in Table 9.3
In the laboratory consolidation test the compression of the sample is one-dimensional as there is lateral confinement, the initial excess pore water pressure induced in a saturated clay on loading being equal to the magnitude
What is soil consolidation?
Soil consolidation refers to the mechanical process by which soil changes volume gradually in response to a change in pressure. This happens because soil is a two-phase material, comprising soil grains and pore fluid, usually groundwater.
How long does it take for a soil to consolidate?
The time for consolidation to occur can be predicted. Sometimes consolidation can take years. This is especially true in saturated clays because their hydraulic conductivity is extremely low, and this causes the water to take an exceptionally long time to drain out of the soil. While drainage is occurring, the pore water pressure is greater than normal because it is carrying part of the applied stress (as opposed to the soil particles).
What is overconsolidated soil?
The soil which had its load removed is considered to be "overconsolidated". This is the case for soils that have previously had glaciers on them. The highest stress that it has been subjected to is termed the " preconsolidation stress ". The "over-consolidation ratio" (OCR) is defined as the highest stress experienced divided by the current stress. A soil that is currently experiencing its highest stress is said to be "normally consolidated" and has an OCR of one. A soil could be considered "underconsolidated" or "unconsolidated" immediately after a new load is applied but before the excess pore water pressure has dissipated. Occasionally, soil strata form by natural deposition in rivers and seas may exist in an exceptionally low density that is impossible to achieve in an oedometer; this process is known as "intrinsic consolidation".
What happens when stress is removed from a soil?
When stress is removed from a consolidated soil, the soil will rebound, regaining some of the volume it had lost in the consolidation process. If the stress is reapplied, the soil will consolidate again along a recompression curve, defined by the recompression index.
What is creep in soil?
This process of creep is sometimes known as "secondary consolidation" or "secondary compression" because it also involves gradual change of soil volume in response to an application of load ; the designation "secondary" distinguishes it from "primary consolidation", which refers to volume change due to dissipation of excess pore water pressure. Creep typically takes place over a longer time-scale than (primary) consolidation, such that even after the restoration of hydrostatic pressure some compression of soil takes place at slow rate.
What is the process of a soil change volume?
According to the "father of soil mechanics ", Karl von Terzaghi, consolidation is "any process which involves a decrease in water content of saturated soil without replacement of water by air". More generally, consolidation refers to the process by which soils change volume in response to a change in pressure, encompassing both compaction and swelling.
Why does soil creep?
However, in soils with a high amount of organic material such as peat, the phenomenon of creep also occurs, whereby the soil changes volume gradually at constant effective stress. Soil creep is typically caused by viscous behavior of the clay-water system and compression of organic matter.
What is the process of a soil being packed more closely together under static load?
Consolidation is the process by which soil particles are packed more closely together under the action of static load. It is a natural process and its take a long time. It is a two-stage process.
Is reducing the volume voids due to plastic readjustment of soil solids time dependent?
It is a time-dependent process of reducing the volume f voids due to plastic readjustment of soil solids.
What is the term for the movement of soil in the vertical direction?
Settlements refer to the soil’s movement in the vertical direction typically induced by stress changes. The total settlement of the ground consists of 3 components: immediate settlement (commonly referred to as elastic settlement, although this is a misnomer), consolidation settlement (or primary settlement) and creep settlement (or secondary settlement).
How long does creep settlement last?
The settlement process may be completed almost immediately or may last for a significant amount of time (even decades) depending on the soil’s permeability and water drainage paths.
What is the difference between creep and immediate settlement?
Since soil particles are practically incompressible, consolidation settlements is caused by a reduction in voids due to gradual squeezing out of water. Finally, creep settlement occurs under a constant load and is depended on the stress history, the type of soil and the anisotropy of the soil.
Which soil has higher permeability?
In particular, cohesionless soils have higher permeability than cohesive soils that have small voids blocking the water movement. In geotechnical design, the total settlement of the soil has to be properly predicted and must meet the requirements of the project. If the soil’s characteristics are not adequate to meet the aforementioned requirements ...
What type of settlement occurs when the increase in vertical effective stress causes the individual particles of the soil to rearrange into?
” The type of settlement in which the increase in vertical effective stress causes the individual particles of the soil to rearrange into a tighter packing, is known as consolidation settlement.”
What causes a decrease in the volume of voids in soil?
This process causes a decrease in volume of voids. If the soil is 100% saturated then the reduction in volume of voids can occur only if some of the water squeezed out of the soil.
What is secondary consolidation?
Secondary consolidation may be the larger component if settlement in some soils, particularly in soils with a large organic component. Secondary consolidation is associated with both immediate & consolidation type settlements, although it is usually not of much significance with immediate settlements.
What is the final settlement of a foundation?
Generally, the final settlement of a foundation is of interest and U is considered equal to 1 (i.e. 100% consolidation) 1. Immediate Settlement. Immediate settlement takes place as the load is applied or within a time period of about 7 days. Predominates in cohesion less soils and unsaturated clay.
Why is the leaning tower of Pisa undergoing consolidation settlement?
The lean is caused by consolidation settlement being greater on one side. This, however, is an extreme case. The principal settlements for most projects occur in 3 to 10 years.
What is the difference between total settlement and differential settlement?
Total settlement is the magnitude of downward movement. Differential settlement is non-uniform settlement. It is "the difference of settlement between various locations of the structure. Angular distortion between two points under a structure is equal, to the differential settlement between the points divided by the distance between them.
How much settlement is acceptable for a road embankment?
A fixed-end arch would suffer greatly if the abutments settle or rotate. For road embankments, storage silos and tanks a settlement of 300mm - 600mm may be acceptable, but for machine foundations the settlement may be limited to 5mm 30mm. Different types of construction materials can withstand different degrees of distortion. For example, sheet metal wall panels do not show distress as readily as brick masonry.
What happens if soil shears fail?
A soil shear failure can result in excessive building distortion and even collapse. Excessive settlements can result in structural damage to a building frame nuisances such as sticking doors and windows, cracks in tile and plaster, and excessive wear or equipment failure from misalignment resulting from foundation settlements.
What happens after primary consolidation?
After primary consolidation the soil structure continues to adjust to the load for some additional time. This settlement is termed secondary consolidation/secondary compression. At the end of secondary consolidation the soil has reached a new K o -state (at-rest state).
Consolidation
- When the construction of the foundation is done(application of additional load), pore water pressure in the saturated clay increases as the hydraulic conductivity of the clay is very small. Some time is required for excess pore water pressed to dissipate and increase the stress to be t…
Primary Consolidation
- The definition of primary consolidation is discussed above under the terminology. Let’s the method of primary Consolidation settlement calculation There are two different stages of soil. 1. Normally Consolidated Soil 2. Over Consolidated Soil It is required to assess the consolidation of soil is done based on the above states. In simple terms, the normally consolidated soil is experiencing …
Secondary Consolidation
- Secondary consolidation settlement occurs after the completion of dissipation of the excess pore water pressure developed immediately after the application of load. The settlement caused due to the plastic adjustment of the soil fabrics at the end of the primary consolidation is called secondary consolidation. Secondary Consolidation also can be explained as slippage and reorientation of s…
Types of Tests to Find Consolidation Settlement
- One dimensional consolidation test
- Oedometer Test
- Incremental Loading Oedometer
Overview
Soil consolidation refers to the mechanical process by which soil changes volume gradually in response to a change in pressure. This happens because soil is a two-phase material, comprising soil grains and pore fluid, usually groundwater. When soil saturated with water is subjected to an increase in pressure, the high volumetric stiffness of water compared to the soil matrix means that the water i…
History and terminology
According to the "father of soil mechanics", Karl von Terzaghi, consolidation is "any process which involves a decrease in water content of saturated soil without replacement of water by air". More generally, consolidation refers to the process by which soils change volume in response to a change in pressure, encompassing both compaction and swelling.
Magnitude of volume change
Consolidation is the process in which reduction in volume takes place by the gradual expulsion or absorption of water under long-term static loads.
When stress is applied to a soil, it causes the soil particles to pack together more tightly. When this occurs in a soil that is saturated with water, water will be squeezed out of the soil. The magnitude of consolidation can be predicted by …
Time dependency
The process of consolidation is often explained with an idealized system composed of a spring, a container with a hole in its cover, and water. In this system, the spring represents the compressibility or the structure of the soil itself, and the water which fills the container represents the pore water in the soil.
1. The container is completely filled with water, and the hole is closed. (Fully saturated soil)
Creep
The theoretical formulation above assumes that time-dependent volume change of a soil unit only depends on changes in effective stress due to the gradual restoration of steady-state pore water pressure. This is the case for most types of sand and clay with low amounts of organic material. However, in soils with a high amount of organic material such as peat, the phenomenon of creep also occurs, whereby the soil changes volume gradually at constant effective stress. Soil creep i…
See also
• Compaction (geology)
• Soil mechanics
• Vacuum consolidation
• Settlement (structural)
Bibliography
• Coduto, Donald (2001), Foundation Design, Prentice-Hall, ISBN 0-13-589706-8
• Kim, Myung-mo (2000), Soil Mechanics (in Korean) (4 ed.), Seoul: Munundang, ISBN 89-7393-053-2
• Terzaghi, Karl (1943), Theoretical soil mechanics, John Wiley&Sons, Inc., p. 265