Collapsible Soils

1.Introduction

Collapsible soil is a type of soil that undergoes significant reduction in volume and strength when it is subjected to a change in moisture content or loading. This occurs when the soil particles are held together by a structure of cemented particles that are bound together by water-soluble minerals such as calcium carbonate or gypsum. When the water content of the soil is reduced, the cementing agents dissolve, causing the soil to collapse and lose its strength, leading to structural instability and potential damage to buildings and other structures built on it.

Collapsible soil is commonly found in arid and semi-arid regions, particularly in areas with a high concentration of clay minerals. In these areas, the soil is typically dry and stable during dry periods, but when rain or other moisture is introduced, the soil can rapidly change and lose its strength. This can lead to significant problems for construction projects and infrastructure development, as the soil may not provide a stable foundation for buildings or roads. Engineers and builders must take into account the potential for soil collapse when working with collapsible soil and use appropriate design and construction techniques to mitigate its effects.

2.Collapsible Soils

Collapsible soil is typically found in regions with a high concentration of clay minerals, particularly in arid and semi-arid regions. Some of the soil types that are known to be collapsible include:

  1. Loess: This is a wind-blown deposit of fine-grained, loosely compacted material that is common in many parts of the world. Loess soil is typically high in clay minerals and is prone to collapsing when it becomes saturated with water.

  2. Caliche: Caliche is a type of soil that is commonly found in arid regions and is formed when calcium carbonate cements together sand, silt, and clay particles. When caliche soil becomes saturated with water, the calcium carbonate dissolves, causing the soil to collapse.

  3. Limestone: Limestone is a sedimentary rock composed mainly of calcium carbonate. When limestone is exposed to water, it can dissolve, causing the soil to become unstable and collapse.

  4. Some types of clay soil: Certain types of clay soil, such as smectite and montmorillonite, are known to be collapsible. These soils are commonly found in arid and semi-arid regions and are prone to collapsing when they become saturated with water.

It’s important to note that not all soils with these mineral compositions are necessarily collapsible. The collapsibility of a soil depends on a variety of factors, including its mineral composition, moisture content, and other physical and chemical characteristics.

3.Identification

Collapsible soils can be identified in the field through a combination of visual observations, soil sampling, and laboratory testing. Here are some common methods for identifying collapsible soils:

  1. Visual observations: In the field, collapsible soils may have a characteristic appearance, such as deep cracks when dry, settling or sinking of the soil surface, and other signs of instability. A visual inspection of the soil can give an initial indication of whether it may be collapsible.

  2. Field tests: Field tests such as the pocket penetrometer test and the thumb penetration test can give an indication of the strength of the soil. Collapsible soils typically have low strength and can be easily penetrated by a thumb or pocket penetrometer.

  3. Soil sampling: Soil samples can be collected for laboratory testing to determine the soil’s properties and characteristics. A common test for collapsibility is the collapse potential test, which measures the change in volume and strength of a soil sample when it is subjected to changes in moisture content.

  4. Laboratory tests: In the laboratory, soil samples can be tested for various properties such as particle size distribution, mineralogy, and compressibility. These tests can help to identify the presence of minerals that are prone to collapsing, such as calcium carbonate and gypsum.

It’s important to note that identifying a soil as collapsible requires a combination of visual observations, field tests, soil sampling, and laboratory testing. A professional geotechnical engineer or soil scientist should be consulted for a thorough evaluation of the soil’s properties and potential for collapse.

3.1 Thumb Penetration Test

Thumb penetration is a simple field test used to determine the consistency and strength of soil. It involves using the thumb to press into the soil and observing the amount of force required to penetrate the surface. This test is also known as the thumb test or thumb penetration test.

In this test, a soil sample is compacted by hand into a small ball or clod, and then the thumb is pressed into the soil surface at a consistent rate of force. The amount of force required to penetrate the soil is then observed and recorded. The soil is classified based on the amount of force required to penetrate it. Soils that require little force to penetrate are considered to be soft or weak, while soils that require a significant amount of force to penetrate are considered to be hard or strong.

The thumb penetration test is a quick and simple method for evaluating the consistency and strength of soil in the field, but it is not as accurate or precise as laboratory testing. It is commonly used in construction and engineering projects to make initial assessments of the soil’s properties, and it can help to identify potential problems such as collapsibility. However, it should be used in conjunction with other tests and evaluations to fully assess the soil’s properties and characteristics.