Experimental Study on Effect of Gypsum and NaCl in Improvement of Engineering Properties of ClayeySoil

--Soil stabilization is a process generally which improves the engineering properties of weak soil such as compaction characteristics, bearing capacity etc. and this can be achieved by controlled compaction or addition of suitable stabilizers like cement, lime fly ash etc. But the cost of these additives has also become expensive in recent years which opened the door widely for introducing the other kinds of soil admixtures like gypsum and Sodium Chloride (NaCl). The objective of this research paper is to investigate the effect of gypsum and NaCl on the engineering properties of clay soil with high compressibility (CH).Gypsum is a source of calcium which has major mechanism that binds soil organic matter to clay in soil which gives stabilizes the weak soil. This study involves the investigation of the effect of gypsum and NaCl on clayey soil for which a series of Compaction tests and California Bearing Ratio (CBR) tests performed on both virgin soil and reinforced soil with varying percentages of gypsum and NaCl (3%, 8% and 13%). The results reflect that with increase in the percentages of both gypsum and NaCl, engineering properties of soil such as Maximum Dry Density (MDD) and CBR value are also increased significantly comparing with the properties of natural soil.


LITERATURE REVIEW
studied the effect of the gypsum as an stabilizer for treatment of the expansive clay soils by means of swell potential and strength. Maximum dry density and optimum moisture content for bentonite soils was determined by standard compaction test. Different quantities of gypsum such as 2.5%, 5%, 7.5%, and 10% by mass are added to bentonite. A series of compaction tests, Atterberg limit tests are performed to see the changes in the plasticity, swell percent and strength parameters of treated and untreated samples. Results indicated that gypsum can be used as a stabilizing agent for expansive clay soils effectively. Aly Ahmed, Usama H.Issa (2014) has studied the stability of soft clay soil stabilized with recycled gypsum in a wet environment. The recycled gypsum was mixed with cement and lime in different ratios in the dry state, and different amounts of admixtures were mixed with the tested soil to explore the effect of the wet environment on the stability and durability of the stabilized gypsum clay soil. The results show that increasing the content of both types of admixtures had a positive effect on the improvement of stability and durability for the tested soil in a wet environment, while the increase in the admixture ratio had a slightly negative effect on both the stability and the durability of the samples subjected to soaking.
Dina Kuttah, Kenichi Sato (2015) reviewed on the effect of gypsum content on soil behavior. They added the varying percentages of gypsum to the soil. Form the results, it is reviewed that addition of gypsum content to the soil, the properties of soil are also increased significantly. Tamadher et.al (2007) investigated the stabilization of soft soils like silty clay using salts of chloride like NaCl, MgCl 2 and CaCl 2 .Three amount percentage of salt (2%, 4% and 8%) were added to the soil to study the effect of salts on the compaction characteristics, Atterberg limits, and unconfined compressive strength. The results showed that the increase in the percentage of each of the chloride salts increased the maximum dry density and decreased the optimum water content. The liquid limit, plastic limit, and plasticity index decreased with increasing salt content. Also the results showed that the unconfined compressive strength increased when the salt content increased too.
Swarna Kolaventi et.al (2016) studied the stabilization of black cotton soil using salts and their comparative analysis. To investigate the effect of adding different chloride compounds including (NaCl, CaCl 2 ) on the engineering properties of black cotton soil. Various amount of salt (2%, 4%, 6%and 8%) were added to the soil to study the effect of salts on the compaction characteristics, consistency limits and compressive. The main findings of this study were that the increase in the percentage of each of the chloride compounds increase the maximum dry density and decrease the optimum moisture content. The liquid limit, plastic limit and plasticity index decreased with the increase in salt content. The strength increases as the salt content increases.

III. SCOPE OF THE STUDY
The scope of work includes addition of gypsum and NaCl to the given locally available weak clay soils to see the effect on the engineering properties. The work presented in this paper aims to investigate the improvement of soil properties such maximum dry density (MDD) and CBR values by adding gypsum and NaCl. A series of laboratory tests are conducted on both virgin soils as well as on reinforced soil with gypsum and NaCl to compare the improvement of soil properties. List of experiments conducted in laboratory as per IS Codes are given in Table 1.

IV. MATERIALS AND METHODOLOGY 4.1 Natural Soil
In this section, the results for various tests such as specific gravity test, grain size analysis, liquid and plastic limit tests, standard proctor test and CBR test are performed on natural soil. The results for properties of natural soil obtained from these experiments are shown in Table 2.Natural soil used in this study is collected from the plain of Hyderabad (TS) near CMR College of Engineering & Technology (CMRCET).  Dry sieve analysis is performed on dry soil to determine the percentages of coarse grained soil and hydrometer analysis is conducted on the soil sample to determine the percentages of silt and clay. From Table 2, it is observed that the percentage of soil passing through 0.075mm is more than 50%, so soil is classified as fine grained soil. As per IS 1498-1970 soil classification if LL>50% and PI >17%, then the soil is classified as Clay with high compressibility. From Table 2 it is observed that liquid limit and plasticity index are found to be 53% and 26% respectively. Based on this the given soil is classified as Clay with High Compressibility (CH).To find Maximum Dry Density and Optimum moisture content of given soil, Standard Proctor compaction test is adopted. As per IS standards, Maximum Dry Density (MDD) and Optimum Moisture Content (OMC) of fine grained soils are less than 19g/cc and greater than 15% respectively. From the Table 2, it is noticed that MDD and OMC are within the limits for clayey soil as per standards (MDD=1.25g/cc, OMC=18.4%). Un-soaked CBR test was conducted on given natural soil and the CBR value is found to be 3.28% and is within the limits as per IS code for fine grained soils.

Gypsum and NaCl
The various percentages of gypsum and NaCl are added to the given clayey natural soil and the laboratory tests are performed. While mixing gypsum and NaCl in soil, care should be taken such that all ingredients mixed throughout the soil sample uniformly by making soil sample partially wet. Quantity of Gypsum and NaCl ( gn W ) to be added to a given amount of natural soil is obtained using the following formula given in Eq. n (1) Where a = 3%, 8% and 13% of Gypsum and NaCl d W = Quantity of Dry Natural Soil (gm.)

Experimental Procedure
A series of laboratory tests are conducted on both virgin soils as well as on reinforced soil with gypsum and nacl. List of experiments conducted in laboratory with IS codes and equivalent ASTM codes are given in Table  1.The results and discussions for natural soil are discussed in the following sections. In this section, procedures for conducting the tests on both natural soil and reinforced soil with gypsum and NaCl are discussed.

Compaction Test
From compaction test, water content-dry density relationship of soil with varying percentages (3%, 8% and 15%) of gypsum and NaCl is obtained. A series of Standard Proctor Tests are conducted on reinforced soil with gypsum and NaCl as per (IS-2720 Part-VII) Procedure. First, the amount of gypsum and NaCl ( gn W ) needed to be mixed with given natural soil ( d W =2500gm) is calculated for particular percentage of gypsum and NaCl ( a ) as given by the Eq. (1).Gypsum and NaCl thus obtained are added to natural soil after making dry soil into partially wet soil by adding sufficient amount of water to ensure soil sample uniform and paste could be formed. Gypsum, NaCl and soil are mixed thoroughly until mix becomes uniform and homogeneous. As per Standard Proctor Test procedure, reinforced soil sample is filled in the mould by three equal layers and each layer is being given with 25 blows of 2.6 kg hammer from height of 30 cm. Water contents and dry densities are evaluated from the test data and are shown in Table 3 in Results and Discussion section. The test is performed for all soil specimens containing different percentage of gypsum and NaCl.

California Bearing Ratio (CBR) Test
A series of un-soaked California Bearing Ratio Tests are performed on reinforced soil with varying percentages of gypsum and NaCl (3%, 8% and 15%) as per IS-2720 Part 16 procedure for light static compaction. At first, required amount of gypsum and NaCl calculated from Eq. (1) and are blended with 5kg of dry soil, and then mixed thoroughly until homogeneous mix is obtained. After reinforced soil sample is prepared, sample is filled in the mould with three equal layers and each layer is being given by 56 numbers of blows by a 2.6kg rammer for light static compaction. Load required for penetrating through the reinforced soil sample up to 10mm penetration depths is noted. From the loads obtained, CBR values for all reinforced soil samples are evaluated and the results are shown in Table 3 in Results and Discussion section.

V. RESULTS AND DISCUSSIONS
In this section, detailed results for reinforced soil with varying percentages of gypsum and NaCl (3%, 8% and 15%) are presented. A series of standard proctor tests and California bearing ratio tests are performed on soil with varying percentages of gypsum and NaCl and the corresponding results are shown in Table 3.   Table 3 il is found to r increased to ural soil. If th to 16.8% wi and NaCl in so reduced. The ment. Increase e in the soil s  Fig.6 shows the CBR vs. Pavement thickness curve for design of flexible pavements. From the Fig.6, it is observed that sub grade thickness for natural soil is found to be around 52 cm for heavy traffic condition (55 kN wheel load) for CBR value of 3.28% and it reduces to 28 cm for the same traffic condition for 3% gypsum and NaCl having CBR value of 10.4%. For 8% gypsum and NaCl pavement thickness is found to be around 24 cm having CBR value of 14.6% and finally for 13% gypsum and NaCl, pavement thickness is found to be around 21 cm having CBR value of 16.85.It implies that reduction in pavement thickness from 52 cm to 21 cm, quantity of aggregate materials and soil (borrowed) used in sub-grade thickness and quantity of bitumen used in base thickness is considerably decreased. Therefore, the construction cost is reduced by a considerable amount as well as the time for construction of pavements and also the improvement in soil as CBR value is increased considerably compared to natural soil.

CONCLUSIONS
As per data and results obtained from the experimental work on stabilization of clayey soil with varying percentages of gypsum and NaCl (3%, 8% and 13, the following conclusions can be drawn regarding the aspect of strength improvement of soil due application of Gypsum and NaCl as a mean of soil reinforcement.
Based on results and discussions from compaction test, it is observed that with increase in percentage of gypsum and NaCl, the compaction properties are also increased. The maximum dry densities are found to be 1.33 g/cc for 3%, 1.49 g/cc for 8% and 1.72 g/cc for 13% of gypsum and NaCl and it shows an increasing trend in MDD value. it is also observed that there is an decreasing trend in optimum moisture content with increase of gypsum and NaCl and this is due to the fact that, gypsum and NaCl absorbs more water during compaction process. It can be concluded that for effective soil stabilization, increase in gypsum and NaCl will give better results.
Based on CBR test results it is observed that addition of Sodium Chloride and Gypsum as stabilizing agent produces a marked increase in CBR value. It can be concluded that, with increase in gypsum and NaCl, the CBR values are also increased considerably as CBR is found to be 16.8% for 13% Gypsum and NaCl compared to natural soil.
From the discussions, it can be concluded that addition of gypsum and NaCl to the natural soil (clay) shows the considerable effect on the compaction properties and bearing capacity of soil.It is also concluded that, expensive methods like cement, lime etc. for soil stabilization can be replaced with gypsum and NaCl as an alternative to improve the weak soil properties. Gypsum and NaCl can be used for stabilization of embankments, pavement sub-grade and other fields of civil engineering as per needs for clayey type of soil.