2015 2nd International Conference on Material Engineering and Application (ICMEA 2015) ISBN: 978-1-60595-323-6
Experimental Study of Expansive Soil Improved by Ionic Soil
Stabilizer
Xuesong Lu Huanggang Normal University, Huanggang, Hubei 438000, P.R. China ABSTRACT: Based on expansive soil of Anyang district of Henan improved by Ionic Soil Stabi‐ lizer, expansive soil is tested in the free swelling ratio test and Shrinkage test. The results show that after mixing the ISS into expansive soil, free swelling ratio of expansive soil decreases, and performance of expansive soil is significantly weakened. When the ISS with the water volume ratio of 1: 250, a free expansion to minimize the expansive soil. And the ISS than without after adding ISS, expansive soils line shrinkage and shrinkage limit significantly reduced, indicating that the weak soil particles adsorbed on the surface of the part of bound water has been re‐ placed with off the coupling strength between soil particles to strengthen, soil shrinkage de‐ formation smaller. 1 INTRODUCTIONIonic soil stabilizer (ISS for short) is a water-soluble chemical substance composed by multiple strong ions, suitable for soil of different kinds with the clay particle content above 25%. Once it is put into the soil and interacts with soil, combination water of clay minerals can be removed based on electrochemical principle, transforming the soil from hydrophile to hydrophobe, reduc-ing the thickness of clay combination water film and improvreduc-ing the engineerreduc-ing properties of the soil effectively, which includes increased compactness and cut-resistant strength, decreased pore ration and water sensitivity, etc. Reinforcement of soil by ionic soil stabilizer (ISS) is short in circle, low in cost, environment-friendly and harm free to human and stock, avoiding the cost for expensive excavation and fetching materials from different places. Ionic soil stabilizer rein-forcement technology offers a method of civil engineering construction characteristic of low cost, convenient construction and material available on the spot, which is applied widely in road, airport, port, water conservancy engineering for soil mass reinforcement. In 1997, the Ministry of Water Conservancy listed ISS as major science and technology popularization pro-ject. However, there is few theoretical test research on expansive soil improved by ionic soil stabilizer. Expansive Soil is a special clay, according to ISS for cohesive soils mechanism of ac-tion, I try to use the ISS for expansive soil chemically modified, and improved soil were related to physical and mechanical properties test. Found by experiment, ISS can significantly reduce the swell - shrink capacity, improve performance and compressive strength of the soil.
2 TEST MATERIALS 2.1 Test soil
Experimental material is from expansive soil of Anyang. Expansive soil samples containing more tuberculosis matter, gray, hard plastic, soil samples to see more cracks. Expansive undis-turbed soil sampling depth of 3 ~ 5 m. The soil samples will be taken back in accordance with the "geotechnical engineering testing procedures" standard, the basic physical and mechanical tests were carried out to obtain test results are shown in Tables 1 and 2.
Table 1. Basic properties of expansive soil.
natural water content ω[%] Natural den-sity γ[g·cm-3] proportion △s liquid limit WL[%] plastic limit WP[%] plastic in-dex IP[%] free swelling ratio Fs[%] 13.25 2.06 2.81 44.22 15.36 28.86 58
Table 2. Granule composition of expansive soil. less than a particular size (mm) of the soil mass percentage [%]
<10 <5 <2 <1 <0.5 <0.25 <0.075 <0.05 <0.01 <0.005 <0.002 100 100 98.26 94.27 90.16 89.12 86.34 80.05 73.31 55.23 21.47 2.2 Curing materials
Ionic Soil Stabilizer (commonly known as "solid roadbed," "solid Lubao”), is a kind of mixed liquid that contains a number of strong ionic compounds, and it is brown-black water-soluble liquid. Dilute ISS into different concentrations as required. The amount of ISS admixture varies according to different kind of soil, generally the amount of ISS admixture is 0.15~1L per cubic meter of soil volume.
3 STUDY ON ISS-IMPROVED EXPANSIVE SOIL 3.1 The mix design of ISS- improved expansive soil
In road engineering, the mix rate design of ISS reinforcing soil use unconfined compression strength as its evaluation indicator. But I think, for expansive soils, the most essential character-istic is its expansion and contraction deformation outstanding. Thus, changing the hydrophilic expansive clay soil components, reducing its swelling potential, eliminate swelling - shrinkage ability to maximize overcome the swelling - shrinkage deformation damage caused to construc-tion, it is of importance, free expansion is one of the most direct measure of the index reflects
expansion characteristics of the soil. The air-dried soil samples retrieved over 0.5 mm grind fine sieve, sieve Soil samples after mixing evenly. The ISS dilute aqueous solution, the concentra-tion ratio was 1:50 to 1: 400, so that the soil samples with ISS soluconcentra-tion full role, place 24 h after the soil is baked at a temperature of 105 Ԩ, the ratio effects were taken after each 10 mL test soil samples free expansion, calculate the size of the free expansion, the test results shown in Table 3.
Table 3. Free swelling rations of expansive soil in different matches.
ISS: water free swelling ratio Fs [%] reducing the value of free swelling ratio △Fs [%] 0 58 0 1:50 33 25 1:100 22 36 1:150 24 34 1:200 25 33 1:250 19 39 1:300 21 37 1:350 26 32 1:400 29 29
The test results show that when ISS and water ratio of 1: 250, it is possible to make free long expansion rate to a minimum of expansive soils, compared with the ISS without soil, after join-ing ISS, free expansion of this soil the minimum can be controlled at around 19 percent, com-pared with free expansion without ISS can be reduced by 39%, and it can be seen, not ISS, the better, ISS solution in the ratio of high and low ratio of 1:50 1: 400, the expansive land reform of the effects are not ideal, but the ratio of expansive soil free expansion to other segments have significantly reduced the minimum control about 19%, that is the soil changed by the weak ex-pansive soil non-exex-pansive soil . In contrast, when a large concentration of ISS after free expan-sion have increased, increasing the cost of testing. At the same time it can be seen from the ta-ble, after joining ISS, under a variety of free expansion ratio of expansive soils were reduced,
indicating expansion ISS can impair performance. Therefore, the optimum mixture ratio ISS In-tegrated selected modified expansive soil is 1: 250.
ISS is a complex chemical formulation, since the ISS is a lignosulfonate resin charged with a high density, it is a water-soluble electrolyte, so that the water can dissociate the positively charged cation [X]n+ and negatively charged anion [Y]n-, soil colloids cations [M]n+ produce
ex-change effect, these originally adsorbed on the surface of soil particles, highly hydrophilic cati-onic away, and with the continuous aqueous ISS diffusive permeability, clay minerals gradually replaced between the outer edge and the crystal lattice layer hydration exchange cations, reduce adsorption water film thickness, changes in hydrophilic and expansive soil. When the ISS solu-tion ratio is too high, rapid dissociasolu-tion of a large number of casolu-tionic a small part in the ex-change interaction with the soil particle surface hydrophilic cations, and still wrapped in clay granules covering most of the surface of the grain interlayer Hydration cation exchange reaction is difficult; and when the ISS concentration is too low, the dissociation of [X]n+ cation
insuffi-cient amount so that the active cation exchange reaction is not thorough enough chemical soil; ISS solution ratio in the middle section, the dissociation The [X]n+ cation concentration in
mod-erate amounts, can be more thoroughly and inter-particle surface and mineral layer of hydrated cation exchange, which appeared not ISS, the better, improving expansive soil effect is getting better Happening.
3.2 The expansion and contraction effect of ISS-improved expansive soil
Determine the best prime soil and moisture curing mixture of soil and maximum dry density by compaction test. Test standard light compaction tester to a moisture content of the horizontal to the vertical axis dry density, water content and dry density plotted curve, thus optimum mois-ture content, maximum dry density. When mixed with ISS in the soil, and water by the ISS with the optimal volume ratio of 1: 250 ratio diluted with water, and according to the optimal com-paction test to determine the moisture content of 16.54%, shake and spill into the soil, mixing evenly, closed 24 hours after the removal, the moisture content was adjusted to limit state made cutting ring shrinkage test samples, and calculate the sample line shrinkage, volume shrinking, shrinking index and the shrinkage limit, the test results shown in Table 4. As it can be seen from Table 4, after addition of ISS-expandable wire shrinkage of soil shrinkage limit significantly re-duced. Line shrinkage and reduced shrinkage limit soil, explains in part the weak adsorption surface of soil particles bound water has been replaced with off the coupling strength between soil particles enhanced the ability of soil shrinkage smaller.
Table 4. Shrinkage test of expansive soil.
ISS：water
shrinkage
Line shrinkage [%] Shrinkage limit [%]
0 2.41 9.97
1：250 1.22 8.23
4 IMPROVING MECHANISM OF ISS
ISS is a sulfonated oil resin, and it is a combination of a number of strong ionic compounds. It can dissolve in water, and it can dissociate cations and anions. by adding ISS into red clay which primarily is clay, it can replace exchangeable cations adsorbed on the clay surface through physical and chemical functions. Double electrode layer in clay surface changes and thickness of water film reduces. The hydrophily of clay transform into hydrophobicity. Mean-time, ISS has a structure of polymer chain so that structure units can be linked to form large ag-gregates. Connection between particles becomes more tightly, therefor, strength of soil enhanc-es.
Expansive soil swelling, shrinkage of the underlying causes of loss of soil particles that interact with water, causing expansion and reduce the distance between the soil particles of soil particles of clay minerals in the soil combine lattice expansion and change water film thickness, thereby cause soil volume increase or decrease. Electric double layer theory that the contact surface of soil particles, especially when the interaction between soil and water on the surface of colloidal particles, due to lattice displacement electric double layer can be formed. Particles in an electric double layer adsorption capacity for water molecules in the surrounding clay mineral particles form a surface membrane hydration. Since the combination of a water film thick solid particles "wedge" open, so that the distance between the solid particles is increased, resulting in genera-tion of soil volume expansion. When the medium condigenera-tions change, so that the soil water film thinner or disappear, then reduce the distance between the particles, so that the soil volume con-traction.
5 CONCLUSIONS
ISS is a new material in China. In this paper, through a series study on expansive soil improved by ISS, conclusions are obtained as follows:
(1) Ionic soil stabilizer can reduce the free expansion expansive soil, impair expansion proper-ties of expansive soil. When the ISS and water ratio was 1: 250, enables free expansion
ex-pansive soil to minimize free expansion reduce the maximum value. Join dose should be controlled and the ratio of ISS, the high and low ratio under the modified results are not satisfactory, according to the free swelling index changes combined with the cost of the se-lected optimum ratio is 1: 250.
(2) after mixing the ISS into expansive soil, expansive soils line shrinkage and shrinkage limit significantly reduced, indicating that the weak soil particles adsorbed on the surface of the part of bound water has been replaced with off the coupling strength between soil particles enhanced the ability of soil shrinkage smaller. Expansive soil line shrinkage rate was sig-nificantly reduced.
ACKNOWLEDGEMENTS
This paper can be finished relying on the surface project of Hubei Province Natural Science Foundation (No.2014CFB401). I express my sincere thanks.
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