What is compression index and recompression index?
1. The slope of the straight-line portion of the virgin part of the compression curve on a semi-logarithmic plot is the compression index (Cc) and the slope of the recompression or swelling curve is the recompression index (Cr) as shown in Fig. 1.
What is the use of compression index?
The compression index is used to find the settlement in the normally consolidated clay. The total stress applied is larger than the stress in the field, to which the soil sample has been undergone in the past.
What is the compression index?
Compression index (Cc) is used to predict the compressibility of soil and estimate how much settlement which is occurred due to loads of different engineering structures.
What is secondary compression index?
Secondary compression index: This definition is analogous, of course, to the primary compression index Cc. To determine the magnitude of secondary settlement under the final vertical effective stress. where t = time of interest; tp = time of end of primary consolidation.
How do you get recompression index?
The recompression index is usually obtained from one- dimensional consolidation tests. The consolidation tests are relatively lengthy process and expensive. An undisturbed soil sample need to be obtained during subsurface investigations, carefully handled, and prepared for testing.
How do you find compression index?
Mechanical property, namely Compression Index (Cc) are determined by conducting One-dimensional Consolidation Test (Oedometer Test). The Oedometer test is the method to determine consolidation characteristic of low-permeability soils when subjected to vertical load.
How do you find the compressive index?
compression index – YouTube
What is the difference between compression and compaction?
Compression is a process of compressing, or increase in density or lessening in the bulk volume of granules or powder. While Compaction is the process of alteration of powders into a coherent specimen or compacting powder or granules.
What is the difference between primary and secondary compression?
One-dimensional compression of a saturated soil, subjected to an increment of total vertical stress, consists of a primary compression that takes place during the increase in effective vertical stress and a secondary compression that follows at constant effective vertical stress.
How do you calculate compression index?
The Compression Index (Cc) is equal to the slope of the graph of pressure versus void ratio (log scale) [7]. Compression Index (Cc) for clay is in the range 0.258 to 0.968, while for laterite soil was in the range 0.101 to 0.940. Value of Compression Index (Cc) is different between each type of soil.
What is the coefficient of consolidation?
Coefficient of consolidation is the rate at which saturated soil undergoes consolidation. It can be only measured in laboratory. Time factor is given by T v = C v t d 2 . From this equation, the unit of coefficient of consolidation comes out to be cm2/sec.
What is over consolidation ratio?
The overconsolidation ratio (OCR) is a qualitative indicator of this densification or stiffening of the soil, and it is defined as the ratio of the maximum overburden stress ever experienced by the soil (i.e., with the ice sheet on top) to the present overburden stress (i.e., without the ice sheet).
What is consolidation index?
A consolidation phase is one in which a stock or an index moves within a specific range, between the ‘support’ and ‘resistance’ levels.
What do you mean by Free Swell Index?
DEFINITION • Free Swell Index is the increase in volume of a soil, without any external constraints, on submergence in water.
What do you mean by void ratio?
The void ratio of a mixture is the ratio of the volume of voids to volume of solids.
What does 95% compaction mean?
95 percent compaction means that the soil has been compacted to 95 percent of the possible density of the soil through compactive efforts. Maximum dry density, along with optimum moisture content, is determined in the laboratory and provides the target for field compaction.
What are the factors affecting compaction?
Factors affecting compaction
Nature and type of soil, i.e. sand or clay, grading, plasticity. Water content at the time of compaction. Site conditions, e.g. weather, type of site, layer thickness. Compactive effort: type of plant (weight, vibration, number of passes)
What is initial primary and secondary consolidation?
To distinguish between the two mechanisms, “primary consolidation” refers to consolidation due to dissipation of excess water pressure, while “secondary consolidation” refers to the creep process.
What is 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 does higher coefficient of consolidation mean?
The coefficient of consolidation is the parameter used to describe the rate at which saturated clay or other soil undergoes consolidation, or compaction, when subjected to an increase in pressure. It is measure in square centimeters per second or square inches per minute.
Why is the coefficient of consolidation important?
Coefficient of consolidation (Cv) is a measure of compressibility of soil. This coefficient is an important parameter which is used in the design of foundation of civil engineering structures and also in the slope stability analysis.
What is normal consolidation and over consolidation?
If the current effective stress, s’, is equal (note that it cannot be greater than) to the preconsolidation stress, then the deposit is said to be normally consolidated (NC). If the current effective stress is less than the preconsolidation stress, then the soil is said to be over-consolidated (OC).
Can over consolidation ratio be less than 1?
The overconsolidation ratio, OCR, is the ratio of σp to σ o, and nu- merically represents the state of consolidation: an OCR equal to 1 is a normally consolidated sediment, an OCR greater than 1 shows over- consolidation, and an OCR less than 1 shows underconsolidation.
Why is coefficient of consolidation important?
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.