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Delayed Compaction Effects on the Behaviour of Stabilized Soils

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DELAYED COMPACTION EFFECTS ON THE BEHAVIOUR OF

STABILIZED SOILS

S. Sahaya Vincy P.G Student, Division of Soil Mechanics and Foundation Engineering, Department of Civil Engineering, Anna University Chennai, Chennai–600 025, India. E-mail: [email protected] M. Muttharam Assistant Professor, Division of Soil Mechanics and Foundation Engineering, Department of Civil Engineering, Anna University Chennai, Chennai–600 025, India. E-mail:[email protected]

ABSTRACT: Fly ash is the most abundant of all residues and its disposal not only needs enormous land, water and power resources, but it also causes serious environmental hazards. In India there are about 82 thermal plants producing more than 95 millions tonnes of fly ash every year and the figure is likely to soar. The disposal of fly ash in ecologically suitable manners has lately become a global concern. Standard Proctor tests were conducted on the soil-fly ash-lime mix (10% 20%, 30% fly ash and 2%, 4%, 6% lime), the maximum dry density decreased linearly and optimum moisture content increased linearly with the increase of fly ash and lime content. Various UCC tests were conducted on the soil-fly ash-lime mix, for the variation of lime 2%, 4% and 6%, fly ash 10%, 20% and 30% with the time delays (time delay between mixing the contents with water and compaction) of 0, 3, 6 and 24 hrs. The prepared samples were tested to find out the effect of delayed compaction on strength. The addition of 2% lime reduced the strength with time, 4% lime decreased the strength up to 6 hrs after that it is increased, and 6% lime addition increased the strength with delayed compaction. Some of the samples were curd for 7, 14 and 28 days in order to find out the strength with the age of curing. Curing periods increased the strength considerably. 1% ammonium chloride was added with 2% lime and 10% fly ash and the UCC tests were conducted on the specimens prepared with time delay. It is concluded that, ammonium chloride didn’t affect the strength much with time delay. CBR tests were conducted on the soil-fly ash-lime mix (2%, 4%, 6% lime and 10% fly ash) by delaying the compaction time for 0, 1, 2 and 3 hrs. It is observed that time delay and the increasing percentage of lime and fly ash decreased the CBR values. 1. INTRODUCTION

Soil can be used as a load bearing material or construction material. When used for these purposes soil should posses engineering properties to meet the requirements such as high strength, low settlement etc. In many situations the soil present in the field may be a problematic one such as expansive soil. Expansive soils undergo volumetric changes due to changes in water content. The swelling characteristics of these soils depend on various factors such as the initial water content and suction. However shrinkage occurs on evaporation of water in dry seasons. This dual problem of swelling and shrinkage causes damage to many lightly loaded structures. In order to proceed with construction under engineering conditions, some techniques are needed to improve such properties of the soil. Soil Stabilization of expansive soils with various additives is one of the techniques to mitigate the problems possessed by expansive soils (Sharma 2007). Chemical stabilization of expansive soils involves additives such as cement, lime, bitumen, calcium chloride, fly ash etc (Osinubi 2006). Soil stabilization has been used in the buildings of roads & air-craft runways,

earth dams and embankments in erosion control (Osinubi 2006).

The strength and durability properties of expansive soils can be improved by chemical stabilization. One of the ways of attempting chemical stabilization is, mixing thoroughly the stabilizers with soil at required moisture content and then compacting the soil stabilization mix to the required density. A delay between mixing the stabilizers with soil and compaction of the soil-stabilizers mix leads to a decrease in both density and strength for a fixed compactive effort. Most of the time, the time delay is unavoidable one because of any of the followings, sudden raining, delaying of compaction equipments after mixing, insufficient workers, poor transportations etc. These make the compaction process as a delayed one. These delaying hours considerably affects the strength of stabilized soils. Among the various chemicals used for stabilizing the expansive soils, lime is very popular. In addition, fly-ash which is a waste product from thermal power station is also used for stabilizing expansive soil. Hence study of compaction delay effects is needed, to find the compaction effects of compaction delay between the

IGC 2009, Guntur, INDIA


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mixing and compaction on the engineering properties of expansive soil stabilized with lime and fly ash. The primary aim of this study is to find out the nature of compaction delay effects on the properties of stabilized soil.

2. MATERIALS

Locally available expansive soil was to be used for the experimental investigation. Soil sample was collected from the local area at a depth of 0.5 m to 1.0 m. To characterize the soil various experiments were conducted as per BIS procedure. Laboratory grade hydrated lime and fly ash collected from Ennore Thermal power plant, were used in present study.

Table 1: Chemical Properties of Ennore Fly Ash Chemical properties

Fly ash F Chemical properties % by mass ASTM C618

class-F SiO2 63.60 - CaO 1.57 < 10 Al2O3 28.20 - Fe2O3 2.99 - MgO 0.54 5 (max) Na2O 0.05 - K2O 0.003 - SO3 0.26 - MnO 0.03 - Loss on ignition 0.85 Soluble residue - Al2O3/Fe2O3 - SiO2+Al2O3+Fe2O3 94.78 70 (min)

Table 2: Physical Properties of Ennore Fly Ash Physical properties

Fineness (m2/kg) 252 Specific gravity 2.09

Table 3: Index Properties of Clay Sl. No

Parameter Symbol or percentage

Values

1. Specific Gravity Gs 2.43 2. Clay % 76 3. Silt % 18 4. Sand % 6 5. Liquid Limit % 86 6. Plastic Limit % 29 7. Plasticity Index Ip 57 8. IS Classification CH High Plasticity

Clay 9. MDD g/cc 1.48

10. OMC % 24

3. EXPERIMENTAL PROCEDURES

The expansive soil passing through 425µ is mixed in dry state with various percentages of lime and fly ash on weight basis. The required amount of water was added to the soil-lime-fly ash mix to carryout Standard Proctor Compaction test. Immediately after addition of water, the compaction is carried out without any delay to get the compaction characteristics of soil-lime-fly ash mix for the given percentages of admixtures. After getting the compaction curve, maximum dry density and corresponding optimum moisture content is obtained for the given soil-lime-fly ash mix. To find the effect of compaction delay on the various properties of stabilized soil, the soil was mixed with the required percentage of lime and fly ash in dry state. The predetermined amount of water was added to the mix to achieve the water content of the mix equal to the optimum moisture content for the mix. Then this wet mix was left undisturbed for a period of 0hr (no delay), 1hr, 3hrs, 6hrs, 12hrs and 24hrs. During the period of time delay, care is taken to avoid the evaporation loss of water.

After the required period of time delay the specimens for UCC test and CBR test were prepared, by applying Standard Proctor Compactive energy. The UCC samples thus prepared were cured at a relative humidity of 100% for various curing periods before testing. For selected percentages of lime and fly ash the UCC tests were conducted by adding the chemical ammonium chloride, to find out whether it retards the effect of delay between mixing and compaction on strength.

4. EXPERIMENTAL PROGRAMME

1. Three different percentage of lime addition 2%, 4% and 6% was selected such that one percentage is less than lime fixation point, another percentage is at lime fixation point and the next percentage of lime is above lime fixation point.

2. Three different percentage of fly ash addition was proposed by taking into consideration the bulk utilization of fly ash. At the same time due consideration is given not to use very high fly ash, which is mere a replacement not a stabilization. Hence the percentage of fly ash addition was varied from 10% to 30%.

3. The time delay considered was selected to replicate the practical situation. Few hours of time delay is normally expected. Hence, the time delay of 0hrs, 1hr, 3hrs, 6hrs and 24hrs are selected. In this 0hr time delay means, immediately after mixing the soil-lime-fly ash mix with water, the samples are compacted to the required dimensions for various tests. This is included to have the reference.

4. The compacted specimens were cured for 0days, 7days, 14days, and 28days before testing, since as per the standards for lime stabilized soil, the strength should be obtained for these curing periods.


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5. Some of the UCC tests were conducted by adding 1% ammonium chloride salt, to check whether this salt can help in maintaining the strength of soil even there is some time delay between mixing and compaction.

5. RESULTS AND DISCUSSIONS

Figure 1 presents the variation of maximum dry density of soil-fly ash-lime mix with lime content. It can be seen from Figure 1 that for the given fly ash content the addition of lime decreased the Standard Proctor maximum dry density. It can also be seen that for the given lime content, the effect of increasing the fly ash content is to decrease the maximum dry density. The reduction in the dry density with increase in lime content is almost linear expect for fly ash addition of 20%. The reduction in dry density upon increase in lime content may be due to the reduction between lime and soil which makes the soil to reduce its plasticity. Further,the dispersed structure of the soil is modified to flocculated due to the soil-lime reaction, which inturn offers more resistance against compactive energy. The effect of reduction in dry density upon increase in fly ash content may be attributed to the lower specfic gravity of fly ash compared to the soil.

Fig. 1: Variation of Maximum Dry Density with Lime

Content

Table 4: MDD and OMC for Various Soil-Fly Ash-Lime Mix

% of lime & % fly ash

MDD in g/cc

OMC in %

0% & 0% 1.48 24 2% & 10% 1.45 26 4% & 10% 1.40 28 6% & 10% 1.35 30 2% & 20% 1.43 27 4% & 20% 1.39 29 6% & 20% 1.32 31 2% & 30% 1.40 28 4% & 30% 1.34 30 6% & 30% 1.30 32

From Table 4 it is observed that addition of 10% of fly ash and 2%, 4% and 6% of lime with soil decreases the

maximum dry density from 1.48 g/cc to 1.45 g/cc,1.4 g/cc and 1.35g/cc and increses the optimum moisture content from 24% to 26%, 28% and 30% respectively. Similarly addition of 20% fly ash and 2%, 4% and 6% of lime with soil decreases the maximum dry density from 1.48 g/cc to 1.43 g/cc, 1.39 g/cc, 1.32g/cc and increses the optimum moisture content from 24% to 27%, 29% and 31% respectively. Further addition of 30% fly ash and 2% ,4% and 6% of lime with soil decreases the maximum dry density from 1.48 g/cc to 1.4 g/cc, 1.34 g/cc, 1.3g/cc and increses the optimum moisture content from 24% to 28%, 30% and 32% respectively.

Fig. 2: Variation of UCC Strength with Time Delay and

Lime Content with 30%FA

Figure 2 shows the variation of UCC strength with the variation of time delay and lime content, it has been observed that, for 2% lime the strength has been decreased with time delay. The delaying time above three hours increased the strength after 6 hrs in the case of 4% lime. For 6% lime there is little variation in strength


Percentage of Lime Content with 20% FA

Figure 3 shows the variation of UCC strength with time delay and lime content. For the addition of 2% lime there is a no major difference in strength between the without delay and to the 24 hrs delay. 24 hrs delays with the addition of 4% lime have attained the strength almost equal to the strength of undelayed strength. In the case of 6% lime, the strength is not much affected by time delay.


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Percentage of Lime Content with 10% FA

Figure 4 shows the variation of UCC strength with the variation of time delay and lime content, it has been observed that, for 2% lime the strength has been decreased with time delay. The delaying time above three hours increased the strength after 6 hrs in the case of 4% lime. For 6% lime there is a little increase in strength with time delay.


Percentage of Lime Content

Figure 5 shows the difference in strength between the soil-fly ash-lime-ammonium chloride mix to the soil-fly ash –lime mix. Fig shows that the strength was increased with the addition of ammonium chloride.

Fig. 6: Variation of CBR with Time Delay and Lime Content

CBR test was conducted on the soil-fly ash- lime mix by delaying the time, varying the percentages of lime content

(2%, 4%, and 6%) and the percentage of fly ash was to be maintained as constant 10% is shown in Figure 6.

6. CONCLUSIONS

1. The maximum dry density decreased with increasing fly ash content and lime content.

2. The optimum moisture content increased with increasing fly ash and lime content.

3. Compaction delay affects the strength of soil-lime-fly ash mix, if the lime content is less than lime fixation point and the effect is to reduce the strength.

4. For the lime addition equal to lime fixation point, the effect of compaction delay is to reduce the strength initially for shorter compaction delay and slightly increases the strength upon further delay.

5. If the addition of lime is above the lime fixation point, the compaction delay does not have any detrimental effect on strength.

6. The addition just 1% of ammonium to soil-lime-flyash mix increased the strength considerably. Further the compaction delay has not affected the strength and for various periods of time delay, the strength remained unchanged.

7. Compaction delay affects the CBR value for all the percentages of lime addition. The CBR value reduces with increase in time delay. However, the rate of reduction in CBR value decreases as the lime content increases.

REFERENCES

Kolawole J. Osinubi (1998). “Influence of Compactive Effort and Compaction Delays on Lime-Treated Soil”, Journal of Transportation Engineering, ASCE, Vol. 124, No. 2, pp. 149–155.

Kolawole J. Osinubi and Charles M.O. Nwaiwu (2006). “Compaction Delay Effects on Properties of Lime-Treated Soil”, Journal of Materials in Civil Engineering, ASCE, Vol. 18, No. 2, pp. 250–258.

Sanjeev Kumar and Vijay K. Puri (2001). “Geotechnical Properties of Fly Ash and Lime-fly Ash Stabilized Coal Mine Refuse”, Environmental Geotechniques, Vol. 2, pp. 785–789.

Scott M. Mackiewicz and Glen Ferguson E. (2005). “Stabilization of Soil with Self-Cementing Coal Ashes”, Kleinfelder, 7802 Barton, Lenexa, Kansas 66214.

Sunil S. Pusadkar and Ramasamy, G. (2005). “Collapse Behaviour of Compacted Coal Ash Fills”, Geotechnical Testing Journal, ASTM, Vol. 28, No. 3, pp. 297–303.

Tuncer B. Edil, Hector A. Acosta and Craig H. Benson (2006). “Stabilizating Soft Fine-Grained Soils with Fly Ash”, Journal of Materials in Civil Engineering in Civil Engineering, Vol. 18, No. 2, pp. 283–294.


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