1.2 - Total Settlement Components
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Understanding Immediate Settlement
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Today, we will dive into total settlement, starting with immediate settlement. Does anyone know what immediate settlement means?
Is it the settlement that occurs right after the load is applied?
Exactly, Student_1! Immediate settlement happens very quickly, often due to changes in shape at constant volume. It mainly concerns less pervious soils. Who can tell me how we can visualize this?
Maybe by thinking of it like a sponge being pressed down?
Great analogy, Student_2! The sponge compresses immediately. Let's remember that with the acronym 'SI' for 'Settlement Immediately.'
So it’s mostly elastic deformation at this stage?
Yes! Good connection! Immediate settlement is all about elastic behavior.
Exploring Primary Consolidation Settlement
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Next, let’s talk about primary consolidation. Does anyone have an idea of what causes this type of settlement?
Is it because of the water leaving the soil pores?
That's correct! Primary consolidation involves the expulsion of pore water. This process is time-dependent, so it doesn't happen all at once. Can anyone explain how this impacts effective stress?
Like, as water leaves, the soil becomes denser, increasing effective stress?
Exactly! As pore water pressure diminishes, effective stress rises, leading to further consolidation. Think of it as 'PSC' for 'Primary Settlement Change.'
Understanding Secondary Consolidation Settlement
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We’ve covered immediate and primary consolidation settlements. Now, let’s tackle secondary consolidation, often called creep. What do you think happens here?
Is it the slow rearrangement of soil particles after primary consolidation?
You got it! This rearrangement occurs at constant effective stress and happens over longer periods. Remember the acronym 'SCS' for 'Secondary Creep Settlement.'
So it's like the soil continuing to settle, but at a much slower rate?
Exactly, Student_3! Secondary consolidation can affect structural stability over time. It's crucial for engineers to predict this behavior.
Introduction & Overview
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Quick Overview
Standard
The total settlement of soil in civil engineering consists of three main components: immediate settlement, primary consolidation settlement, and secondary consolidation settlement. Each component plays a vital role in understanding how soil beneath structures behaves under load, impacting design and construction processes.
Detailed
In civil engineering, understanding settlement is crucial for designing stable structures. Total settlement comprises three components:
- Immediate Settlement (Si): Occurs instantly when the load is applied, causing deformation without significant water flow.
- Primary Consolidation Settlement (Sc): Results from the expulsion of pore water in saturated soils, occurring over time as excess pore water pressure dissipates, leading to a gradual increase in effective stress.
- Secondary Consolidation Settlement (Ssc): Also known as creep, it is the volume change that occurs due to soil particle rearrangement after primary consolidation, taking place at constant effective stress.
Understanding these components is essential for engineers to predict settlement behaviors and design effective foundations.
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Overview of Total Settlement
Chapter 1 of 4
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Chapter Content
The total settlement consists of three components:
1. Immediate settlement.
2. Primary consolidation settlement
3. Secondary consolidation settlement (Creep settlement)
St = Si + Sc + Ssc
Detailed Explanation
Total settlement in soil engineering refers to the overall change in vertical position of the ground surface due to applied loads. It has three components:
1. Immediate Settlement (Si) - This happens right after the load is applied. It reflects the elasticity of the soil and requires little to no water movement in this stage.
2. Primary Consolidation Settlement (Sc) - This takes time and involves water being expelled from the soil's pores as pressure is applied. The soil rearranges itself over time as pore water pressure reduces.
3. Secondary Consolidation Settlement (Ssc) - Also known as creep, it continues after primary consolidation and involves gradual volume change due to rearrangement of soil particles under constant effective stress. These three components when summed give the total settlement (St).
Examples & Analogies
Imagine putting a heavy book on a sponge. Initially, the sponge squishes down (immediate settlement). Over time, if you keep the book on the sponge, some water might seep out of it, causing further squishing (primary consolidation). Even after you remove the book, the sponge continues to shrink a bit due to its internal structure rearranging (secondary consolidation).
Immediate Settlement
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Elastic Settlement or Immediate Settlement occurs immediately after the load is applied. This is due to distortion (change in shape) at constant volume. There is negligible flow of water in less pervious soils. In case of pervious soils, the flow of water is quick at constant volume. This is determined by elastic theory.
Detailed Explanation
Immediate settlement is the part of total settlement that occurs right after a load is applied to the soil. It involves the soil temporarily deforming under load without any significant water movement. In less permeable soils, like clay, the change happens fast in terms of shape but doesn’t involve much water displacement. On the other hand, in more permeable soils, like sand, immediate water movement might occur but still within a short time frame. This phenomenon is described by elastic theory, which considers how materials deform under load.
Examples & Analogies
Think of it like using a rubber band. When you stretch it quickly, it deforms (immediate settlement) but returns to its original shape after the load is removed, showing that the change was temporary.
Primary Consolidation Settlement
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Chapter Content
Primary consolidation settlement occurs due to expulsion of pore water from the voids of a saturated soil. In case of saturated fine grained soils, the deformation is due to squeezing of water from the pores leading to rearrangement of soil particles. The movement of pore water depends on the permeability and dissipation of pore water pressure, ultimately leading to effective stress increase.
Detailed Explanation
Primary consolidation occurs after the immediate response to a load, as excess pore water pressure is reduced over time. In saturated fine-grained soils, when a load is applied, the water trapped in soil pores is gradually pushed out. As this excess pore water is expelled, the soil particles start to reorganize and settle into a denser formation due to the increase in effective stress (the stress carried by soil particles after accounting for pore water pressure). This process can take a significant amount of time depending on the soil's permeability.
Examples & Analogies
Consider a sponge soaked in water. When you apply pressure, the water starts to squeeze out. Initially, the sponge doesn't change much in shape, but over time, as you keep pressing, the water escapes, and the sponge slowly becomes denser and settles down into a smaller form. This illustrates primary consolidation.
Secondary Consolidation Settlement
Chapter 4 of 4
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Chapter Content
Secondary Consolidation Settlement (Creep) is defined as the change in volume of a fine-grained soil due to rearrangement of soil particles (fabric) at constant effective stress. The rate of secondary consolidation is very slow when compared with primary consolidation.
Detailed Explanation
Secondary consolidation is the gradual, long-term settlement that occurs in saturated fine-grained soils after primary consolidation has concluded. Unlike primary consolidation, where pore water is expelled, secondary consolidation involves the slow rearrangement of soil particles that occurs even when the effective stress remains constant. This process is typically much slower and can continue for years after the initial loading.
Examples & Analogies
Think of secondary consolidation like a bowl of jello settling at room temperature. Even after you remove any force that was applied to it (like shaking it), the jello continues to settle and reshape itself very slowly over time, reflecting the slow and gradual changes that occur in the soil.
Key Concepts
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Immediate Settlement: Occurs right after a load is applied, due to elastic deformation.
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Primary Consolidation: Settlement caused by slow expulsion of water from soil pores, increasing effective stress.
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Secondary Consolidation: Long-term rearrangement of soil particles at constant effective stress.
Examples & Applications
An example of immediate settlement would be a newly placed concrete slab that deforms slightly under its own weight.
A practical illustration of primary consolidation can be seen in clay soils, which take time to settle as pore water escapes.
Secondary consolidation can be observed in buildings over time as they slightly sink into their foundations due to rearranging soil particles.
Memory Aids
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Rhymes
When load is applied, immediate's the way, the soil's shape will change, not much of a delay.
Stories
Imagine a sponge under a weight, it squishes down right away, but over time, water leaves, and the sponge settles into place.
Memory Tools
Remember 'IPC' - Immediate, Primary, and Creep for the types of settlements.
Acronyms
Use 'SICS' - Settlement, Immediate, Consolidation (Primary), Settlement (Secondary) to recall the components.
Flash Cards
Glossary
- Immediate Settlement
Settlement that occurs instantly when a load is applied due to elastic deformation at constant volume.
- Primary Consolidation Settlement
Settlement that occurs from the expulsion of pore water over time, leading to an increase in effective stress.
- Secondary Consolidation Settlement
Slow volume change of soil due to particle rearrangement at constant effective stress, also known as creep.
- Effective Stress
The stress carried by the soil skeleton, which increases as pore water pressure decreases.
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