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Construction of an Ash with Waste Recycled Product, and Locally Available Soil—A Case Study

IGC 2009, Guntur, INDIA

CONSTRUCTION OF AN ASH POND WITH WASTE RECYCLED PRODUCT, FLY ASH AND LOCALLY AVAILABLE SOIL—A CASE STUDY

A.K. Choudhary Department of Civil Engineering, National Institute of Technology, Jamshedpur, Jharkhand, India. E-mail: [email protected] J.N. Jha Department of Civil Engineering, Guru Nanak Dev Engineering College, Ludhiana, Punjab, India. E-mail:[email protected], B.P. Verma Director, Sangvi Innovative Academy, Indore, M.P, India. E-mail: [email protected]

ABSTRACT: The paper presents a case study for the construction of an ash pond dyke for a local thermal power plant (Tata Power) utilizing fly ash; being generated in the plant along with another industrial waste product generated after recycling of blast furnace slag from nearby Tata steel plant often called as Waste Recycled Product (WRP). The various geotechnical properties were evaluated by taking several trial mixes of these two waste products in different proportions so as to arrive at an optimum mix proportion. Further trials were carried out on this optimum mix by adding suitable admixtures such as cement or clayey soil in varying proportions. Based on the results of the study, two cross sections for the proposed ash pond dyke were suggested and one of the sections was finally adopted which is functioning quite satisfactorily for more than five years.

1. INTRODUCTION use of ash pond in which ash slurry is discharged is most widely used by thermal power plants. Fly ash along with Development of a nation is linked with its industrial growth is normally mixed with water to form slurry and and with rapid industrialization, the quantity of wastes being transported through pipes to be deposited in the ash , generated by the industries have been increasing immensely, which are usually located within few kilometers distance creating huge problems of their disposal and environmental from the power plant. After the ash particles settle in the ash degradation. In developing countries like India, the pond, clear decanted water from the top is either recycled or environmental protection measures are limited in comparison discharged in to a natural stream. Typically, an ash pond to the expected industrial growth and therefore it is necessary spreads over an area upto 10 km2 for a 500-MW power plant that the focus of the research should be towards utilization and is filled with ash upto 10 m in height within a period of 5 aspects of these wastes. Geotechnical characterization of years (Gandhi et. al. 1999). Construction of these ash ponds these industrial wastes along with their interaction behavior require huge quantity of soil and if good quality soil is not with the suitable admixtures like cement and natural soil is available at the nearby site, then the cost of construction of likely to provide an economical, viable and eco friendly such ash ponds becomes too high and even sometimes solution for the gainful utilization of these wastes and prohibitive also. When fly ash along with some other thereby solving the problem of their disposal to a great industrial wastes available in the vicinity of the plant are extent. Presently, about 75% of India’s energy supply is from mixed with some admixtures like cement or locally available coal based thermal power plants and is expected to remain soil and if found effective for the construction of ash ponds, same for the next few decades. There are about 90 thermal may solve the twin problems of the disposal as as power stations, in addition to several captive power plants in environmental degradation of these industrial wastes. But no our country using bituminous coal with ash content more well defined design procedure or codal provisions exist for than 30% that are producing approximately 100 million tones the ash pond construction and maintenance, though some of of fly ash annually (Gandhi 2005). In contrast to high the studies on specific use of industrial wastes along with utilization of fly ash in advanced countries, the utilization in India is far below satisfaction and disposal of this huge locally available soils for major geotechnical applications quantity of ash is a major problem facing the country today. have been reported by Gidley & Sack (1984), Chandrasekhar Out of various alternatives available for disposal of fly ash, et al. (1994), Mitsunari & Hanade (1996) and Sinha et al.

565 Construction of an Ash Pond with Waste Recycled Product, Fly Ash and Locally Available Soil—A Case Study

(1996). Keeping this in view, a systematic geotechnical From the grain size distribution curves and the subsequent laboratory investigation was carried out on a mix containing classification of the soil it is evident that both WRP and fly fly ash and another waste WRP mixed with small quantity of ash are poorly graded. Fly ash which predominantly consists admixtures and based on the study a suitable section of ash of silt size particles if mixed in certain appropriate pond was recommended which after construction is proportions with WRP containing mostly sand to gravel size functioning satisfactorily till date (Verma & Choudhary particles, then the resulting mix should have better gradation 2001). possessing higher stability and strength. Keeping this in view, four trials mixes (namely; M1, M2, M3 and M4) were 2. METHODOLOGY selected in which fly ash was mixed with varying proportions (20%, 30%, 40% and 50% of dry weight of WRP) and One of the thermal power stations of Tata Power (427.5 standard proctor compaction tests were carried out for all the MW) located in Jamshedpur, Jharkhand, is a pulverized coal four mixes. based power station in which a part of the ash produced in the plant is supplied in dry state through closed pipes to the neighboring cement plant of Lafarz India, Limited where as the remaining ash are to be pumped hydraulically (mixed with water) to a distant pond created by constructing the containment dykes of about 10 m height over an area extending up to about 250 acres. Earlier the dyke was proposed to be zoned with impervious core overlain by a relatively pervious casing on both upstream and downstream sides with imported soil wherever necessary. Due to the scarcity of good quality soil locally and the huge cost of transportation involved with the use of borrow materials, it was finally decided to design a suitable section of the dyke by utilizing fly ash coming out of the plant and Waste Recycled Product (WRP); a waste generated after recycling of blast furnace slag in the nearby steel plant of Tata Steel, Jamshedpur and being dumped in and around the proposed construction site. WRP consists mostly the particles in the Fig. 1: Grain Size Distribution for Materials size range of sand and gravel where as fly ash is having predominance of silt size particles. Laboratory trials were The Maximum Dry Density (MDD) and Optimum Moisture undertaken initially with trial mixes containing WRP and fly Content (OMC) values obtained from the above tests are ash in varying proportions in order to arrive at an optimum tabulated in Table 1. Observations during the proctor proportion of the mix so as to ensure better gradation and compaction tests indicated that for the first mix M1; fly ash hence closer packing of the grains within the compacted content was on lower side where as for the last mix M4, it mass of the dyke. However, both these materials are non appeared to be on the higher side and mix turned slushy at plastic in nature and highly permeable and therefore the mix higher moisture contents. Mix M2 and M3 were however could not meet the slope stability as well as permeability observed to be quite stable and therefore selected for further requirements. Further trials were undertaken by mixing trials. Unconsolidated undrained triaxial shear tests and admixtures such as cement or natural clay soil in varying falling head permeability tests were carried out for mix M2 proportions with the optimum mix of WRP and fly ash in and M3 with specimens prepared at MDD-OMC state. The order to improve the shear strength characteristics as well as shear strength parameters and the permeability values to meet the permeability requirements. Based on the results obtained from the above tests are also tabulated in Table-1. of the laboratory trials an appropriate mix of fly ash, WRP As can be seen from Table-1 that the permeability values for –5 and admixture was selected for use in the construction of the the mix M2 and M3 are in the range of 10 cm/sec where as ash pond dyke. the required range of permeability should be 10–7 cm/ sec. Therefore it was decided to undertake further trials by mixing admixtures such as cement or clay soil in varying 3. LABORATORY INVESTIGATION AND TEST proportions with one of these mixes in order to have a RESULTS resulting mix having permeability in the required range Grain size analysis was carried out for all the three materials (10–7 cm/sec). Two series of trials were undertaken in the i.e. WRP, fly ash and clayey soil to be used for the next phase. In the first series of trials, three trial mixes, construction of ash pond dyke. Figure 1 shows the grain size namely; M3C1, M3C2 and M3C3 were prepared by adding 3%, distribution curves for the same and the materials were 5% and 7% cement of dry weight of WRP and fly ash in the classified as ‘SP’,’ML’ and ‘CI’ respectively as per I.S 1498. mix M3. For the above mixes i.e. M3C1, M3C2 and M3C3,

566 Construction of an Ash Pond with Waste Recycled Product, Fly Ash and Locally Available Soil—A Case Study

cement was considered as the part of mix M3 and therefore possesses considerable shear strength. Therefore it is possible MDD-OMC values for each of these mixes were considered to design the dyke section using either of these mixes. same as that of mix M3. Unconsolidated undrained triaxial However, during triaxial compression tests on the specimens tests and the permeability tests were carried out for the of cement stabilized mixes i.e. M3C1, M3C2 and M3C3 it was specimens (at MDD-OMC state and damp cured for seven observed that the failure strain was in the range of 6–8% for days) of all the three mixes i.e. M3C1, M3C2 and M3C3 and almost all the cases and the specimens exhibited brittle the results are tabulated in Table 2. For the second series of behavior. Therefore; it is possible that the cement stabilized trial, two trial mixes, namely; M2C4 and M2C5 were prepared mix may either to the formation of interconnected by adding 10% and 15% of clay soil of dry weight of WRP cracks within the dyke section or in case the cement is not in the mix M2. Standard proctor compaction tests, properly mixed at the site it may lead to increased chances of unconsolidated undrained triaxial tests (with specimens of granulation in which hard compacted granules of WRP and MDD-OMC as well as saturated state) and the permeability fly ash may be formed throughout the dyke section thus tests (with specimens of MDD-OMC state) were carried out making it more vulnerable to internal erosion. In addition to for both the mixes i.e. M2C4 and M2C5 and the results of this, the cost of huge quantity of cement required for these tests are tabulated again in Table 2. stabilization of the mix can also affect the economic aspects of the project. Considering these aspects; possibility of using Table 1: Test Results for WRP and Flyash Mixes clay stabilized mixes i.e. M2C4 and M2C5 were also explored. Sr. Compaction Shear strength The clay stabilized specimens however exhibited ductile No. parameters parameters behavior during the triaxial tests and the range of failure strain was about 12–14%. In the light of these observations, ) 3 ) ° clay stabilized mix was finally preferred over the cement stabilized mix for the design of the section of ash pond dyke. (cm/sec) (cm/sec) However; keeping in view the fact that clay is to be Permeability OMC (%) Mix designation Friction ( Friction borrowed from far off distance from the site, mix M2C4 was MDD (kN/m Cohesion (kPa) Angle of Internal Internal Angle of finally selected for design of the dyke section considering the

1. M1 18.64 14.00 ------economy and maximum utilization of waste i.e. WRP and fly –5 2. M2 17.84 14.40 60 30 1.78 × 10 ash. Two sections for the construction of the ash pond dyke –5 were suggested as shown in Figure 2 and Figure 3 3. M3 16.66 15.60 85 25 1.75 × 10 respectively. As can be seen from Figure 2, that major 4. M4 16.09 17.20 ------portion of the dyke section consists of mixture of WRP, fly ash and clay while the right portion on the upstream side Table 2: Test Results for WRP, Fly ash and Cement (C)/Clay (CL) consists of local soil consisting of gravels, sand and silt. The Mixtures local soil is to be borrowed from within the ash pond itself Sr. Compaction Shear Shear Permeability thus ensuring that the construction is not only economically No. Parameters Strength Strength (cm/sec) viable but also has other advantages like saving in Parameter Parameters (MDD– (Saturation) construction time and creating an additional storage capacity OMC) in the ash pond. The section as shown in Figure 3 consists of a thin central impervious core of (an intimate mixture ) 3

) ) of stiff clay, sand and gravel and thoroughly tamped into the ° ° place) with upstream and downstream shells consisting of

Mix designation mixture of WRP, fly ash and clayey soil. The top width of the dyke was kept as 5.0 m in order to accommodate a single OMC (%) Friction ( Friction Friction ( Friction MDD (kN/m Cohesion (kPa) Cohesion (kPa) lane WBM road for inspection and maintenance of the dyke. Angle of Internal Internal Angle of Angle of Internal Internal Angle of Suitable side slopes for downstream and upstream as –6 1. M3C1 - - 25 36 - - 2.39 × 10 indicated in Figures 2 and 3 were arrived at based on slope –7 2. M3C2 - - 100 33 - - 3.30 × 10 stability analysis (Bishop’s simplified method). Horizontal –7 3. M3C3 - - 120 30 - - 2.38 × 10 sand filter and a rock toe were provided for internal drainage. 4. M C 17.82 15.80 60 35 25 29 2.36 × 10–7 The downstream slope will be protected against gully 2 4 –7 5. M2C5 18.04 16.40 80 30 30 25 2.04 × 10 formation due to surface water flowing during rain either with riprap placed over a bed of gravel or by maintaining grass turfing. A suitable free board was also provided. Out of 4. SECTION OF THE ASH POND DYKE the two sections suggested; finally the first proposed section From the results of the laboratory investigation as indicated as shown in Figure 2 was selected for implementation and in Table 2, it is observed that the mixes M3C2, M3C3, M2C4 the dyke was constructed like a rolled fill dam with proper and M2C5 conform the permeability requirements and also quality control measures.

567 Construction of an Ash Pond with Waste Recycled Product, Fly Ash and Locally Available Soil—A Case Study

ProposedProposed DykeDyke SectionSection Forfor Ash Pond helped in saving the construction time, saving of natural NearPond Jemco, Near Jemco, Jamshedpur. Jamshedpur resources (earth) and also in creating additional storage capacity by use of local soil. The ash pond dyke has already 5m been constructed and is functioning well since last so many F.B. years. Sodding 1 :2 :2 :5 or rip rap 1 ACKNOWLEDGEMENT WRP+FA+C Facility extended by NIT Jamshedpur is duly acknowledged. Rock Local :2 Toe 1 soil H.Filter REFERENCES Bureau of Indian Standards (BIS), (1970). “Classification Section-I and Identification of Soils for General Engineering Purposes”, IS:1498 (First Revision). Fig. 2: First Proposed Section Chandra Sekhar, Vasudevan, C. and Jagannadham, S. (1994). “Use of Coal Ash for the Construction of Dyke for ProposedProposed Dyke Section Forfor AshAsh Pond Containing Ash”, Proceeding, Indian Geotechnical PondNear NearJemco, Jemco, Jamshedpur. Jamshedpur Conference, pp. 225–228. Pitching Gandhi, S.R. (2005). “Design and Maintenance of Ash Pond 5m for Fly Ash Disposal”, Proceeding, Indian Geotechnical F.B. Conference, Vol. 1, pp. 85–90. Sodding 1 8 Core : 2 Gandhi, S.R., Dey, K.A. and Salven, S. (1999). “Densification :2 n Sodding

or rip rap i 1 of of Pond Ash by Blasting”, Journal of Geotechnical and 1 or rip rap puddle Geoenvironmental Engineering, ASCE, 125(10), pp. 889– Rock Gravel :2 WRP+FA+C 1 899. Toe H.Filter WRP+FA+C Gidley, S.J. and Sack, W.A. (1984). “Environmental Aspects of Waste Utilization in Construction”, Journal of Nomial C- Clay soil Environmental Engineering, ASCE, 110(6), pp. 1117– Section-II 1131.

Mitsunari, T. and Hanada M. (1996). “Studies on Reclamation Fig. 3: Second Proposed Section using Slag-Red mud Mixture”, Environmental Geotechnics, Kamon (ed.), Balkema, Rotterdam, pp. 821–826. 5. CONCLUSIONS Sinha, U.N., Ghosh, A., Bhargava, S.N. and Kumar, D. (1996). “Geotechnical Investigation of Earth-Flyash Two industrial wastes viz. WRP and fly ash which are Embankment of a Flyash Pond”, Proceeding, Workshop creating lot of environmental problems apart from occupying on Tailing Dams, IGS, N. Delhi, pp. 13–20 vast tracts of valuable land space in the vicinity of the plant were advantageously used as fill material for the construction Verma B.P and Choudhary, A.K. (2001). “Report on of the ash pond dyke. The proposed solution and Construction of Proposed Dykes for Ash Pond near Jamco methodology adopted for design of the section was found to Area, Jamshedpur”, Project report submitted to Tata be techno-economically viable at the site. It has further Power, Jamshedpur.

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