Table of Contents
8.5 Calculation of the plasticity index and its significance On the basis of the liquid limit and the plastic limit, the plasticity index (PI) can be defined as the numerical difference between them: PI = LL – PL. The plasticity index is expressed in percent of the dry weight of the soil sample.
What does a high plasticity index mean?
The plasticity index (PI) is a measure of the plasticity of a soil. Soils with a high PI tend to be clay, those with a lower PI tend to be silt, and those with a PI of 0 (non-plastic) tend to have little or no silt or clay.
What does a plasticity index of 0 mean?
The Plasticity Index (PI) is the difference between the Liquid Limit (LL) and the plastic limit (PL), so: Soils with a PI of zero or less are considered non-plastic and usually have little or no clay or silt.
How important is Atterberg limits?
Atterberg limits of soils are very important in construction. Water content drastically influences properties of fine-grained soils. The soil will remain in this plastic state until its liquid limit is exceeded, which causes it to transform into a viscous liquid that flows when jarred.
Is plasticity a chart?
A plasticity chart , based on the values of liquid limit (WL) and plasticity index (IP), is provided in ISSCS to aid classification. The ‘A’ line in this chart is expressed as IP = 0.73 (WL – 20). Depending on the point in the chart, fine soils are divided into clays (C), silts (M), or organic soils (O).
Which soil has more plasticity index?
Soils with a high PI tend to be clay, Those with a lower PI tend to be silt, and.
How can plasticity index be reduced?
Based on the previous studies: – Lime can be utilized as the additional material of clay soil’s stabilization in order to reduce its plasticity index and enlarge CBR rate by 10%; LL rate by 49.33%; PI by 31.47%; swelling by 27.67%; and CBR by 16.3%.
What is liquid limit of soil?
Liquid limit is the water content where the soil starts to behave as a liquid. Liquid limit is measured by placing a clay sample in a standard cup and making a separation (groove) using a spatula. The cup is dropped till the separation vanishes. The water content of the soil is obtained from this sample.
Why do we use plasticity chart?
The Casagrande plasticity chart has been used for more than 70 years to classify fine-grained soils in accordance with the USCS. The majority are classified in the field as SILT, whereas these same soils are classified by the plasticity chart as CLAY.
What is Liquidity Index?
The liquidity index calculates the days required to convert a company’s trade receivables and inventory into cash. The index is used to estimate the ability of a business to generate the cash needed to meet its current liabilities. It is commonly used by credit analysts to evaluate the creditworthiness of customers.
Can liquid limit be more than 100%?
For Attapulgite, the liquid limit varies from 150 to 250, which are greater than 100 and the shrinkage limit varies from 100 to 125 which are also greater than 100. Therefore, the Atterberg’s limits can be greater than 100.
How do you calculate toughness index?
TOUGHNESS INDEX:- (P.L) As a shearing resistance od soil is directly proportional to the number of blorosin Casagrande’s device. Np= No. of blow at plastics limit when shear strength is Sp.
How do you find plasticity index?
Calculate the plastic limit wp by dividing the “weight of moisture” by the “dry weight of sample” and multiply by 100. Plasticity Index (Ip) of a soil is the numerical difference between its Liquid Limit and its Plastic Limit.
Is code for Atterberg limits?
STANDARD • IS: 2720 (Part 5) 1985. DEFINITION • Liquid Limit is defined as the water content at which the soil changes from liquid state to plastic state. APPARATUS • Casagrande apparatus confirming to IS: 9259-1979. Grooving tool.
What is plasticity index for soil?
1.1 The plasticity index of a soil is the numerical difference between its liquid limit and its plastic limit, and is a dimensionless number. Both the liquid and plastic limits are moisture contents.
What does plasticity in clay mean?
Plasticity is the outstanding property of clay–water systems. It is the property a substance has when deformed continuously under a finite force. When the force is removed or reduced, the shape is maintained.
What is weighted plasticity index?
The Weighted Plasticity Index (WPI) is defined as the value of the plasticity index (PI) times the % passing the 425 micron sieve. The Contractor must provide the calculations to verify the WPI.
What is hardness and toughness?
Toughness is a bulk property whereas hardness is a surface property. Hardness is related to scratches, abrasion and erosion whereas toughness is related to fracture, compression strength or elongation strength. A tough material can be hard as well but its not true the other way round.
What is soil index properties?
Soil index properties are properties which facilitate identification and classification of soils for engineering purposes. Plastic soils (clays) are normally described as cohesive as a distinction from non-plastic soils (sands and gravels) which are often called granular or non-cohesive.
What are the three 3 Atterberg limits?
7.3. 3 Atterberg Limits. There are three important Atterberg limits: shrinkage limit (SL), plastic limit (PL), and liquid limit (LL). The shrinkage limit is the water content at which the volume of the soil starts to increase.
Is high plasticity index good?
A high PI indicates an excess of clay or colloids in the soil. Its value is zero whenever the PL is greater or equal to the LL. The plasticity index also gives a good indication of compressibility (see Section 10.3). The greater the PI, the greater the soil compressibility.
What is a toughness index?
Toughness index is defined as the ratio of plasticity index (IP) of the soil to the flow index (IF) of the soil. Toughness index varies between 0 to 3. This gives us an idea of shear strength of soil at its plastic limit.
What is plasticity limit?
Plastic limit is defined as the water moisture content at which a thread of soil with 3.2mm diameter begins to crumble.
Can you have a negative plasticity index?
Can you have a negative plasticity index? Yes ? it can have have a negative value. A negative liquidity index means that the soil is drier that the plastic limit.
Which kind of soil holds the most water?
The clay soil had the highest water holding capacity and the sand soil had the least; clay>silt>sand. Clay particles are so tiny and have many small pore spaces that make water move slower (the highest water holding capacity). Sandy soils have good drainage but low water and nutrient holding capacities.
