MATERIALS AND METHOLOGY
3.3 Methodology .1 Specific gravity
3.3.4 Atterberg limits
• Liquid limit
The atterberg limits such as liquid limit, plastic limit, volumetric shrinkage, linear shrinkage is calculated by following IS 2720 part 5, 6 (1985) and 20 (1992) respectively. Weight about 200 gm of air dried soil passing through 425 μ IS sieve have taken. Then distilled water is applied to it till it become paste. Almost 24 hours’ saturation period has adopted to allow the water permeate through the soil for every mix. After that that the paste placed on the cup of the
Chapter 3 Materials & Methodology
Casagrande apparatus. Using standard grooving tool, a groove has been made in the middle of the soil along the diameter of the cup. Then the handle of the liquid limit device turned at a rate of 2 revolutions per second, until the two parts of the soil join by 12 mm length. The number of blow and corresponding moisture content have recorded. Form the recorded value a semi- log graph has plotted with no of blow in x- axis and moisture content in y- axis. In the graph the moisture content corresponding to 25 numbers of blow have taken as the liquid limit of the mix.
• Plastic limit
A soil sample of 40 gm, passing through 425 μ IS sieve has taken. The distilled water is then mix with the soil until the mass become plastic enough to be easily mould. Almost 24 hours’
saturation period has adopted to allow the water permeate through the soil. About 8 gm of soil mass has taken and ball is formed. Then, rolling of the soil mass is performed. The rolling is continued until the thread becomes 3 mm in diameter. The process is continued until the thread crumbled with the diameter of 3 mm. Then the moisture content of the rolled specimen has determined and recorded. For each mix at least 3 numbers of samples are prepared for better identification of the plastic limit.
After calculating the liquid limit and plastic limit the plasticity index can be calculated by- Ip = WL - Wp
Where,
Ip = plasticity index in %, WL = liquid limit in %, WP = plastic limit in %
• Shrinkage limit
About 100 gm of soil sample passing through 425 μ IS sieve have taken. Distilled water is then added to the soil slightly more than the liquid limit and a creamy paste have made. Almost 24 hours’ saturation period has adopted to allow the water permeate through the soil. The shrinkage dish is coated with grease to prevent the soil stick to the dish. After that the soil paste is poured
Chapter 3 Materials & Methodology
in to the shrinkage dish by placing and tapping almost 1/3rd of the amount of wet soil. This process is repeated for 2 to 3 layers; then extra soil is trimmed with the help of spatula.
Immediate weight has taken and recorded. For each mix 3 samples are prepared. Then the wet soil pat is air dried in room temperature for several hours until the colour of the wet soil pat turns from dark to light. Then oven-dried the cake at 105 0C for about 12 to 16 hours. Then the oven dried pat weight and empty pat weight is recorded. After that with the help of mercury displacement method the volume of the wet soil pat and dry soil pat has calculated.
The shrinkage limit is calculated by following –
Shrinkage limit= (𝑊𝑊 −(𝑉𝑉 − 𝑉𝑉0)∗ 𝑌𝑌𝑌𝑌)∗100𝑊𝑊0 Where,
W= Moisture content, V= Volume of the wet soil pat, V0= Volume of the dry soil pat, Yw= Unit weight of water, W0= Oven dry soil pat.
• Linear shrinkage
About 150 gm oven dried 425 μ IS sieve have taken. Then distilled water is added to the soil specimen until it become smooth homogeneous mix, with a moisture content of 2 % above the liquid limit of the treated and untreated soil. Almost 24 hours’ saturation period has adopted to allow the water permeate through the soil. The thoroughly mixed and saturated soil paste is placed in the mould. The mould is gently jarred to remove the air pockets in the paste. Then with the help of a knife or spatula the top surface of the mould is levelled. For each mix 2 numbers of specimen has taken. Initially drying of the specimen is done at 60 to 65 0C until the colour changes from dark brown to light brown. Then it is placed in 105 to 110 0C for complete drying. The measurements have done by following-
Linear shrinkage=
�1 − �
Length of oven dry specimenInitial length of the specimen
�� ∗ 100
The liquid limit, plastic limit and the shrinkage limit of the virgin soil is tabulated in Table 5.
Chapter 3 Materials & Methodology
So from the values in Table. 3 and the plasticity chart shown in Fig. 8 it is concluded that the soil is high plastic inorganic clay (CH). Liquid limit and plastic limit test are conducted on immediate period and 28 days curing period for both xanthan gum treated and untreated soil samples. These tests are conducted in two phase, in first phase the atterberg limits of the virgin soil is calculated and in second phase, the soil is mixed with different quantity of xanthan gum such as 0, 0.2, 0.5, 0.8, 1.0% by the dry mass of the soil and then the atterberg limits of the different mix are calculated. In Fig. 9 apparatus are used to calculate the liquid limit and plastic limit of soil is given. The shrinkage limit and linear shrinkage are conducted on both treated and untreated soil samples at immediate case only.
Table 3 Atterberg limits of the virgin soil
Atterberg limits Value (%)
Liquid limit 86.76
Plastic limit 24.64 Volumetric shrinkage 13.32 Linear shrinkage 24.4 Plasticity index 62.12
Figure 9 Plasticity chart (IS soil classification system) (B.M.Das)
Chapter 3 Materials & Methodology
Figure 10apparatus for Liquid limit and plastic limit, volumetric and linear shrinkage test for soil