What is Geotechnical Investigation Test?

Table of Contents

What are the Geotechnical Properties? 

What is the Specific Gravity Test of Soil? 

Liquid limit Test of Soil 

Proctor Test of Soil 

What is Permeability and How to Measure it?

Explain the Consolidation and details to Perform the Experiment

What is Swelling Pressure and Its Measurement Techniques 

What are the Geotechnical Properties? 

There are many geotechnical properties of soils such as specific gravity, density index, consistency limits, particle size analysis, compaction, consolidation, permeability, swelling and shear strength. 

What is the Specific Gravity Test of Soil? 

To verify the density of soil solids using a Pycnometer bottle.

When measured at a certain temperature, the specific gravity is the variation between the mass of a unit volume of soil and the mass of the same volume of gas-free distilled water at the same temperature.

This test is specified in IS: 2720 (Part 4) – 1985. A soil’s specific gravity mainly depends on the density of the mineral deposits of the soil particles.

A high-level thumb rule is:

• The specific gravity of the solid ingredient of most inorganic soils differs between 2.60 and 2.80.
• Tropical iron-rich laterite, lateritic soils, normally have a specific gravity of between 2.75 and 3.0, sometime could be higher.
• Sand particles comprised of quartz have a specific gravity varying from 2.65 to 2.67.
• Inorganic clays normally range from 2.70 to 2.80.
• Soils with large quantities of porous particles or organic matter have specific gravities below 2.60.

Liquid limit Test of Soil 

The point at which soil begins to act like a liquid is identified as the liquid limit. Clay samples are placed in a standard cup and a separation (groove) is made using a spatula to define the liquid limit. Dropping the cup till the separation disappears.

The soil's liquid limit serves as a barometer for its compressibility. The soil's compressibility rises in tandem with the liquid limit. Increasing the amount of clay-size fraction in the soil increases the shrinkage index. It is a good indication of clay.

Clay samples are placed in a standard cup and a separation (groove) is made using a spatula to establish the liquid limit. Dropping the cup till the separation disappears. This sample provides information on the soil's water content. The experiment is repeated with a higher concentration of water. More blows would be generated by soil with low water content and fewer blows would be generated by soil with high water content.

Read More:

• What is ground contamination? Causes and Impacts

• Ground Improvement Techniques

Proctor Test of Soil 

In compaction, the soil is exposed to mechanical stress and becomes denser. Particles of solid matter and spaces filled with water or air make up the bulk of soil. Soil as a three-phase system provides a more in-depth explanation of the three-phase nature of soils.

Densification occurs when soil elements are redistributed inside the mass and the void volume decreases as a result of stress. It is feasible to apply mechanical stress through kneading, as well as by dynamic or static means. The change in a dry unit mass of the soil, d, is used to calculate the degree of compaction.

Compaction is very beneficial in engineering applications since it leads in:

• Strengthening of the soil
• Soil shrinkage is a common occurrence.
• Soil impermeability is decreasing.
• Structures and engineering applications such as earth dams, embankments, pavement support, and foundation support all depend on these variables.

Several factors influence how much soil is compacted, including the kind and quantity of energy used during the compaction process, the water substance of the soil, and the density of the soil. When the soil has enough moisture in it, it may compress to its full extent. Alternatively, a soil's extreme dry unit weight (d, max) is reached at an optimal water content level for a particular compact effort.

When water is added to dry soil, its compressibility rises. In other words, waterworks as a lubricant to allow soil particles to glide past each other, resulting in a denser structure when the water content is below the optimum. An increase in soil pore pressure occurs when water substance in the soil exceeds the wet-of-optimal threshold, which causes the soil particles to separate. Dry unit weight and water content are typically linked.

What is Permeability and How to Measure it?

There's a big variance between the permeability of one fluid and the flow of two or more fluids.

Poiseuille's equation, which is a simplified version of Navier-Stokes' equation for laminar flow and incompressible fluids in a cylindrical tube, describes the flow of fluid through the tube.

Explain the Consolidation and details to Perform the Experiment

When soil is confined laterally and forced axially, a consolidation test can be performed to measure the pace and amount of soil consolidation.

For this test, soil specimens must be completely soaked, especially in cohesion-rich soils. Consolidation settlement and time are calculated for a particular loading condition using the test's consolidation parameters (i.e. given the height of the embankment). "Ground Improvement measures" are also utilised in the planning of embankment construction on soft soils.

What is Swelling Pressure and Its Measurement Techniques 

When exposed to water, the surface characteristics of the expansive clays cause them to expand in volume. Expansive soil applies swelling pressure of soil if it is not permitted to swell or if the volume change of the soil is prevented.

There are several factors that influence the swelling pressure, including the type and quantity of clay present in the soil, the nature of clay minerals present, water content, pore fluid composition, dry density, and drying and wetting cycles.

If the sub-soil has high swell pressure, then ground improvement procedures" may be required before building embankment over such soil, which is regarded to be unsuitable.

A CNS (non-swelling clay) layer can be used to isolate the subsoil from moisture (mostly rainwater) flowing in vertically downwards while building embankments on expansive soils. CNS (non-swelling clay) is defined as having a swell pressure that is less than or equal to the stated value (often 0.5 kg/m2).

Both intact and remoulded soils in the partly saturated condition are tested in the laboratory using either fixed or floating rings. The consolidometer method and constant volume method are used to measure soil volume changes, respectively.

I hope this post provides you a good understanding of Ground Investigation Testing, and associate features. Please feel free to like, comment and share it.  

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