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Examoogle • User • info@examoogle.com • EE-2024-8821
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Toughness index is defined as
IT=IFIP
IT=IPIF
IT=IFIC
IT=IPIC
IT=IFIP
The Toughness Index (IT) is a soil mechanics parameter that indicates the relationship between the consistency of a soil at the plastic limit and its ability to resist deformation. It is defined as the ratio of the plasticity index (IP) to the flow index (IF), representing the shear strength increment per unit change in water content.
The Toughness Index (IT) is a soil mechanics parameter that indicates the relationship between the consistency of a soil at the plastic limit and its ability to resist deformation. It is defined as the ratio of the plasticity index (IP) to the flow index (IF), representing the shear strength increment per unit change in water content.
IT=IFIP — Toughness Index formula
IP=wL−wP — Plasticity Index formula
IF=log10(N2/N1)w1−w2 — Flow Index formula
In the Atterberg limit classification, the flow index (IF) describes the slope of the flow curve (semi-log plot of water content vs. number of blows). A lower IF indicates a steeper slope, meaning the soil loses strength rapidly with moisture. The toughness index essentially normalizes this strength-moisture relationship; soils with higher IT are generally considered to be 'tougher' at the plastic limit.
The toughness index generally ranges between 0 and 3 for most soils.
A toughness index of 1 indicates that the soil's strength increases at the same rate as the change in water content near the plastic limit.
If IT<1, the soil is considered to be 'friable' or low in toughness.
The value helps in assessing the structural integrity of clayey soils in subgrades.
Provides a quantitative measure of soil workability.
Helps differentiate between clays of similar plasticity but different geological origins.
Value depends significantly on the accuracy of the flow curve test.
Limited utility for coarse-grained soils with low plasticity.
Earthwork construction quality control.
Subgrade strength evaluation in highway engineering.
Categorizing clay mineralogy types.
Standard testing involves the Casagrande cup apparatus to determine IF.
Option B represents the reciprocal, which is not the definition. Options C and D involve IC (Consistency Index), which is distinct from the Toughness Index.
A is correct — The toughness index is defined as the ratio of the plasticity index to the flow index, expressed as IT=IP/IF.
Remember that IP is the numerator because toughness is directly proportional to plasticity; a higher plastic range usually requires more energy to deform, leading to higher toughness.