Designing of waste dumps vis a vis land use planning for marble quarries in southern Rajasthan (India)

Category Mine
Group GSI.IR
Location 20th WORLD MINING CONGRESS 2005
Author S.S. Rathore * S.C. Jain
Holding Date 14 January 2006
 
ABSTRACT
 
The study has been carried out in green marble (serpentine) mining area of Kherwara region in southern Rajasthan (India). In this region, production of saleable green marble is about 2.5 lakh tons and waste generation is about 7.5 lakh tons per annum. For disposal of this waste, seven common places have been identified. Out of these seven waste dump sites, the study for proper designing was conducted of one site. In designing waste dumps, geotechnical parameters have very crucial role. Stability of waste dumps is generally dependant on the height of the dump as well as overall slope angle. Shear strength is also the most important engineering property of soil or rock spoils. Moisture content & pore water pressure plays an important role in designing waste dump. Thus, these parameters have been determined in the laboratory to accommodate maximum waste generated at identified dump site with safety. The stability analysis has been carried out with the help of computer software. The concept of land use planning of the region is also taken into consideration while designing the waste dump.
Key words: Serpentine, Factor of safety, Waste dump, Block extraction, Geotechnical parameters
 
 

INTRODUCTION
 
Marble reserves in India are estimated at 1200 million tons with Rajasthan accounting for 91% of the reserves i.e. 1100 million tonnes (Rathore, 2000). In the state about 3475 mining leases of marble in 4215.57 hectares of land area are in operation and total production is about 6.8 million tons with an employment of 1,26,000 persons. In the study area 273 mining leases of green marble (serpentine) are situated in 305.15 hectares lease area. Marble is a rock, which has taken Southern Rajasthan on the world map and stands today gloriously as one of the wonders of the world.
 
The quarrying of marble deposit involves production of large sized blocks, which is different from those of the mining of other mineral deposits. Marble deposits are excavated with the help of following techniques:
 
1.  Feather and wedge method
2.  Drilling and controlled blasting technique
3.  Acconex method
4.  Wire/Chain/Belt saw cutting technique
5.  Water jet cutting
6.  Flame jet cutting technique
7.  Slot drilling technique
 
In southern Rajasthan, wire saw and chain saw cutting techniques are most commonly used and recovery of the saleable product has increased in recent years. Even though waste generation during the quarrying operation is about 70% and consisting mainly rock fragments in the form of overburden and khandas or bricks (small size uneven blocks generated during quarrying). Due to this, huge amount of waste generation and there is problem of its disposal. Earlier waste generated was dumped on roads, riverbeds, pasturelands and agriculture fields leading to wide spread environmental degradation. Therefore, designing of waste dumps vis a vis land use planning for marble quarries in southern Rajasthan, is a important aspect to accommodate maximum mining waste with safety in a limited area (Ramlu, 2003). At present lease area for marble quarrying operation is 100 m x 100 m size blocks, which is very small for systematic dumping of waste. Hence, district authority has identified seven common places for common dumping of waste. The production of marble and mine waste in study area (Kherwara region) has been given in the following Table 1
 
Year
Marble
Serpentine (Green Marble)
Mine Waste
1992-93
2056.26
82.20
3417.10
1993-94
1875.40
106.70
3125.67
1994-95
2324.24
171.91
3873.73
1995-96
2840.00
183.96
5041.27
1996-97
2912.58
201.40
5544.02
1997-98
3239.86
201.40
5735.00
1998-99
3284.19
289.45
5900.00
1999-2000
3653.33
625.31
6423.18
2000-2001
4059.40
705.65
7124.27
2001-2002
4929.52
757.04
8048.05
2002-2003
6150.75
703.27
8837.47
2003-2004
6657.98
964.42
9619.23
Table 1: Marble and mine waste production in Rajasthan (‘000 tonnes)
To determine factor of safety of any slip surface have important role in designing. The shape of potential slip surface and the mode of failure is governed basically by the behavior of the natural strata on which they are placed, nature of dumped materials, degree of compaction, dump height, slope angle, slope of floor, seepage of water from the dump to slope, change in cohesion of interface material, changes in stresses, ground vibration by blasting, dynamic impact due to plying of damper’s, dozers etc. (Das,2001).
 
Geotechnical parameters such as height of the dump, overall slope angle, shear strength, moisture content, pore water pressure etc. have very important role in designing and stability of waste dumps in marble mining area of southern Rajasthan (Tripathy, 2003). Therefore, these properties have been determined and computer analysis has been carried out to accommodate maximum quantity of waste rock in available land area.
 
Land, the solid cover of the earth, is a finite non-renewable natural resource over which almost whole of the biotic community thrives. Greenery on the other hand helps protecting many environmental attributes like air quality, water resources and also food. The problem of land availability is more serious in India as it has 2.3% of the global land area and 16% of global population; as a result it’s having even less than 0.3 ha per capita land availability. The problem is being further aggravated due to rapid industrial development, which is demanding more and more land. Hence, during waste dump designing, land use planning of the area has great role for sustainable development of any area. Geographical Information System (GIS) tool is also used for land use planning (Sharma, 2003 & Singh, 2000).
 

STUDY AREA DESCRIPTION

 
The study area is situated near town Kherwara 70 kms away from Udaipur, India, as shown in geological map (Figure 1). The area is located in between latitude 730 40 to 730 45and longitude 240 05 to 240 0. Topography of the area is hilly terrain. The green marble deposit of this area is highly fractured and available in small lumps at upper level and large blocks at deeper level. Total reserves of green marble have been assessed about 42 million tons. There are number of leases where mining of green marble is carried out.
 
Figure 1: Geological map of the study area

EXISTING LAND USE PATTERN

 

Serpentine rocks are mostly occupied in this area. There is no agriculture land existing in the area. The green marble leased out land belongs to Forest and Devasthan departments of Rajasthan Government. The land use pattern of Kherwara area has been shown in Figure 2.

Figure 2: Land use pattern of the area

 
CLIMATE
 
The area is characterized by semi arid with an average annual rainfall of about 650 mm, which is mainly received during monsoon season from July to September. There is large variation of temperature in the area. The minimum temperature in winter goes minimum upto 20 C and maximum 250 C, while in summer it goes minimum 200C and maximum 420C. Relative humidity in the area is above 70% during monsoon months but is below 20% during the months of March-May. Wind velocity in the area is not very high in any of month to cause erosion.

 

MINERAL OCCURRENCE

 
Dolomite & phyllites banded gneissic complex are the only pre-dominant rock type in the area. Extensive ultramafic intrusions of Precambrian age have resulted the conversion of dolomites into green serpentine marble. This marble is commercially exploited and known as ‘Green Marble’. Green marble is hard, compact & massive in nature and found in various shades of green, olive green, grass green & light green in colour. It is mainly composed of pyroxine, olivine. Serpentine is hydrated magnesium silicate (Mg6 Si4 O10 (OH)8). In general calcite, quartz, iron, garnet etc. appears as an impurity and reduces the quality and cost of the green marble.
 
METHOD OF MINING PRACTICED IN MARBLE QUARRIES
 
The method of mining is opencast with semi-mechanization in this area. The lease area is fully exposed by serpentine rocks. The bench height is generally kept 6 m to 8 m and width more than 6 m. The following procedures are being adopted to extract the marble blocks from the quarries:
 
Over burden removal: Thickness of overburden having talus soil mixed small pieces of rock particles is 1 m to 1.5 m and marble is also found in outcrop. For removal of overburden, jack-hammer drilling of 32 mm diameter holes are done upto the depth of 0.5 m to 1.0 m leaving a partition of 0.5 m to 0.75 m from marble rock bed, with a spacing and burden of 1m and 1.2 m respectively. After drilling, controlled blasting is done with light explosives. Blasted muck is loaded with backhoe shovel of 1.1 m3 or 2 m3 capacities into 15 tonnes capacity tippers.
 
Block extraction: When blockable marble is exposed, a free face along the strike direction in weak zone strata is opened out by digging a trench box of 10m x 6m (called galli in local terminology). Compressed air operated drill machine is used to drill two holes of 80mm diameter in vertical and horizontal plane for co-planing to pass diamond wire for cutting. The diamond wire saw machine cut the marble directly from the face, with a long steel cable (30 m length) fitted with diamond bead (1000 beads for 30 m length) as cutting media. The continuous flow of water is maintained to cool the beads and clears the cuttings. The principle of wire sawing is to pull spinning the continuous loop of wire mounted with diamond beads through the marble rock to provide cutting action. Due grinding (abrasive action) by diamond, spinning of wire and constant pull on wire, a groove is cut on the rock. Cutting motion is given by motorized flywheel and pulling action is by D.C. motor. Cutting speed and life of beads depends on the hardness, abrasiveness and strength of material to be cut. Figure 3 shows the extraction of marble block with diamond wire saw cutting. For toppling the main block (phada in local language) from face, hydraulic jack/ water bag/ air bag / backhoe shovel or combination of these are used. The small blocks (saleable size) of 3 m x 1.5 m x 1.5 m are prepared from phada by feather & wedge technique after jackhammer drilling or by diamond wire saw cutting.
Figure 3: Extraction of marble block
 
Handling & transportation: The block is lifted by electric operated derrick crane (20 tonnes capacity and 40 m boom length) and loaded into the truck. The truck takes the block from mine site to processing unit for further processing.
 
DETERMINATION OF GEOTECHNICAL PARAMETERS
 
The four samples, labeled as SS1, SS2 &SS3 of spoil material from a depth of 0.5 m were collected from a dump of study area. The quantity of each sample collected was about 20 to 30 kilogram with maximum size of 20 mm and packed in air tight polythene bags to preserve moisture. One sample (SS4) collected by the core cutter method for determination of the insitu unit weight and dry & wet densities by making a 15 cm x 15 cm rectangular opening for a depth of 20 cm. The samples were collected on grid pattern with 75 m distance from various places. Then the samples were transported from mine site to laboratory.Several laboratory tests has been performed for the determination of moisture content, insitu unit weight, compaction, shear strength parameters and slake durability index for the designing of waste dumps.
 
INSITU MOISTURE
 
The moisture content of waste dump samples was determined by oven drying method at 1050 C to 1100C and it is 5.26%.
 
INSITU UNIT WEIGHT
 
The sample (SS4) collected for insitu unit weight determination was first weighed and it was 9640 grams. Therefore, the unit weight of the insitu sample = Weight / volume
                 = 9640 / (15 x 15 x 20)
= 2.14 gm/cm3 or 20.97 kN/m3
The unit weight of dry spoil material can be found by following formula:
 
G­­d = Gs/ 1+w
 
Where Gd = unit weight of dry sample
Gs = unit weight of wet sample
w = moisture percentage
Therefore, Gd = 20.97 / (1+ 0.05) = 19.97 kN/m3
 
COMPACTION
 
It is the process by which the soil particles are artificially rearranged and packed together into a closer state of contact by mechanical means in order to decrease the porosity (or void ratio) of the soil and thus increase its dry density. The dry density goes on increasing as the water content is increased, till maximum density is reached. The water content corresponding to the maximum density is called optimum moisture content. The testing results of dry density and optimum moisture content are given in Table 3.
 
Sample no.
Dry density kN/m3
Optimum moisture content %
SS1
23.40
10.90
SS2
22.70
10.40
SS3
23.50
10.90
Table 3: Optimum moisture content
 
SHEAR STRENGTH PARAMETER
 
The shear strength of soil is the resistance to deformation by continuous shear displacement of soil particles or on masses upon the action of shear stress. At different moisture content percentage, cohesion and frictional angle have been determined in the laboratory by using direct shear test apparatus. The results are given in Table 4.
 
Sample no.
Moisture
Shear strength
Friction angle (deg.)
Cohesion kN/m3
SS1
4.76
33.0
0.0
 
8.16
32.5
0.0
 
12.20
28.5
0.0
SS2
4.66
33.5
0.0
 
7.84
31.0
0.0
 
13.45
27.5
0.0
SS3
3.46
32.0
0.0
 
7.48
29.0
0.0
 
12.30
26.5
0.0
Table 4: Test result of standard shear box
SLAKE DURABILITY TEST
 
This test is carried out on samples of highwall. The weathering effect on spoil dump can be easily detected by slake durability test. The result of slake durability tests are summarized in Table 5 and it is clear that the dump material is a rock spoil.
 
Sample no.
Slake durability index
Classification
SS1
97.00
Rock
SS2
97.40
Rock
SS3
89.90
Rock of bad quality
Table 5: Test results of slake durability test
 
LIQUID LIMIT AND PLASTIC LIMIT
 
Liquid limit is the water content corresponding to the arbitrary limit between liquid and plastic state of consistency of a soil. It is defined as the minimum water content at which the soil is still in the liquid state but has a small shearing against flowing which can be measured by standard available means. Plastic limit is the water content corresponding to an arbitrary limit between the plastic and the semi-solid states of consistency of a soil. It is defined as the minimum water content at which a soil will just begin to crumble when rolled into a thread approximately 3 mm in diameter.
 
Sample no.
Liquid limit %
Plastic limit %
SS1
33.78
30.03
SS2
22.75
22.50
SS3
37.00
33.50
Table 6:0 Liquid limit and plastic limit of dump soil
 
DESIGN OF WASTE DUMP
 
In the Kherwara marble mining area, the procedure of dumping is end dumping from a height of about 20 meters. Therefore large size boulders are deposited at the base of the dump by their gravitational force and small size of particles fill the voids of the boulders. For proper designing of waste dump, following parameters were analyzed (Rathore, 1994):
 
1.  Type of dump material and its geotechnical parameters
2.  Effect of moisture and height on angle of internal friction
3.  Effect of pore water pressure
4.  Computer programme for analysis using Bishop’s method
 
TYPE OF DUMP MATERIAL AND ITS GEOTECHNICAL PARAMETERS
 
As discussed in Para 3, the type of material is rock spoil (Table 4). It is not possible to determine the actual shear strength of dump material due to presence of large fragments. However, the angle of internal friction of rock spoil material varies from 37 to 55 degree (Gulhati, 1985).
 
The value of angle of internal friction of fine portion (-1.0 mm) of dump material determined in this study is 320. The proportion of fine material in the dump material is not likely to exceed 5%. Therefore, the angle of internal friction of this dry dump material is not likely to be less than 370 and this value is taken for the design of dump in this study. The value of cohesion of this dump material determined for fine portion is zero and hence cohesion is considered zero for design. The condition of foundation for this dump material has been taken as competent.
EFFECT OF MOISTURE AND HEIGHT ON ANGLE OF INTERNAL FRICTION
 
The insitu moisture of the soil material is 5.26 % and the decrease in angle of internal friction with increase of moisture from 0 to 6 % will not be more than one degree (Khandelwal, 1988). The angle of internal friction of dry dump material is 370, therefore, it will be 360 for wet dump material. The effect of increase in height on the angle of internal friction for this rock waste dump will be very less. The maximum decrease of internal friction for the height of 65.0 m of waste dump will be one degree (Campbell 1986). After taking account both the parameters i.e moisture and height, the minimum possible value of angle of internal friction will be 350.
 
EFFECT OF PORE WATER PRESSURE
 
In the end dumping process, the large boulders at the base of waste dump will provide a good drainage. Due to this, the effect of pore water pressure on the stability of waste dump will be negligible. Hence, the piezometric line in the design of waste dump has been considered to concide with the base of the waste dump.
 
FACTOR OF SAFETY FOR WASTE DUMP
 
Waste dumps having factor of safety 1.10 to 1.15, have less risk of failure. Waste dumps designed for a factor of safety less than 1.10 may be prone to failure even with accurate data. The height of waste dump, strength of waste material and underclay effect the factor of safety and the fluctuation may be about 10%. Table 7 gives the minimum factor of safety recommended by some agencies.
 
Assumption
Factor of safety
Reference
Using peak shear strength parameters
1.3
Federal surface mining regulations
---do----
1.3
Coates and Yu 1977
--- do----
1.3
Baliga, 1987
Using residual shear strength parameters
1.1 to 1.15
Miller, 1979
Table 7: Factor of safety given by some agencies
 
COMPUTER PROGRAMME FOR STABILITY ANALYSIS
 
Bishop’s method of stability analysis has given due consideration to interslice forces and pore water pressure developed in the slopes. Bromhead (1986) developed a short computer programme for simple stability calculation using Bishop’s method. The authors have modified this programme in C-language in the department. On the basis of experimental results obtained, the factor of safety at different internal friction has been determined and given in Table 8.
 
S.No.
Angle of internal friction
Factor of safety
1
370
1.27
2
360
1.23
3
350
1.18
4
340
1.14
Table 8: Factor of safety for waste dump
 
LAND USE PLANNING
 
Geographical Information System is a powerful tool for environmental data analysis and planning. GIS stores spatial information (data) in a digital mapping environment. A digital basemap can be overlaid with data or other layers of information onto a map in order to view spatial information and relationships. GIS allows better viewing and understanding physical features and the relationships that influence in a given critical environmental condition. Factors, such as steepness of slopes, aspects, and vegetation, can be viewed and overlaid to determine various environmental parameters and impact analysis. GIS can also display and analyze aerial photos. Digital information can be overlaid on photographs to provide environmental data analysts with more familiar views of landscapes and associated data (Sharma et al 2003)
 
Keeping in mind the land use planning of the area, the waste dump site has been selected. The barren land has been decided in the manner so that it will not affect the cultivated area, land and water environment of surrounding.
 
PROPOSED CONFIGURATION FOR WASTE DUMP
 
The base area of waste dump site is about 11250 m2 (250 m x 450 m). The general profile of the ground is flat. It can accommodate the waste generation for a period of 2-2.5 yrs. The most suitable configuration is to accommodate the waste material in three slices. The first two slices are of 20 m in height and third slice is 15 m in height. The berm for each bench is 10 m wide. The overall slope angle is 300. The factor of safety for this configuration varies from 1.18 to 1.27 for angle of internal friction from 350 to 370 respectively. Therefore, the proposed configuration is the ideal design for waste dump as shown in Figure 4.
Figure 4: Proposed design of waste dump
 
CONCLUSIONS
 
The following specific conclusions have been arrived from this study:
 
1)       With the help of computer programme developed by Bromhead, a stable waste dump to accommodate 56 million cubic meters of marble waste material in the available land has been designed.
 
2) The material of waste dump has been classified as rock spoil on the basis of slake durability index and shear strength parameters.
 
3) Waste dump material indicates negligible cohesion and with increase of moisture content from 0 to 6 percent, the angle of internal friction & shear strength decreases. Hence, with increase in moisture content of waste material for a slope angle, the safe dump height decreases for a desired factor of safety.
 
4) The angle of slope of any overburden dumps shall be less then the angle of repose of the material being dumped but in no case exceed 37.50 from the horizontal.
 
5) The dumping operation shall be carried out in such a way that the operations do not cause accumulation of water in, under or near the dump, which may make the dump insecure.
 
6) Land use planning of the area with GIS tool has important role in waste dump site selection.
 
REFERENCES
 
1.        Bromhead, E.N., 1986, The stability of slopes. Surrey university press, USA, pp.105-112, 167-173.
 
2.        Campbell, D.B., 1986, Stability and performance of waste dumps on steeply sloping terrain. Proc.Int.Symp. on Geotech. Stability in Surfce Mining, Calgary, pp.317-326.
 
3.        Coates, D.F., Yu, Y.S., 1977, Waste embankments pit slope manual. Canmet report 77-1, p.137.
 
4.        Das (Dr.), S.K., 2001, Problems of high wall and spoil stability and various preventive measures in highly mechanised opencast mines, The Indian Mining & Engineering Journal, October, pp. 63-68
 
5.        Gulahati, S.K., 1985, Engineering properties of soils. Tata McGraw Hill publishing company limited, New Delhi, pp 147-148.
 
6.        Khandelwal, M., and Singh, T.N., 2004, A computational approach to failure analysis of a compound slope, Mining Engineers Journal, Aug. pp. 11-15.
 
7.        Miller et al 1979. Surface mine spoil stability evaluation. Interior coal province, v.1 & 2, USBM – DFR 77 (1) & (2) – 80.
 
8.        Rahtore, S.S., & Jain, S.C., 1994, Geotechnical considerations for designing a waste dump – A case study. Proceeding of Mine Planning and Equipment Selection, Istanbul, Turkey, Oct.18-20. pp. 865-870.
 
9.        Rathore, S.S. et al, 2000, Dimensional Stone Technology, Himanshu Publication, New Delhi, pp 10-20.
 
10.     Ramlu (Prof.) M.A. 2003, Mining wastes, Mining Engineers Journal, Oct. pp. 9-15.
 
11.     Sharma, (Dr.) V.N., et al 2003. GIS in Environmental Studies - An overview. InfoTech Enterprises Limited, Hyderabad, INDIA.
 
12.     Singh, B. et al., 2000, Technologies for mineral waste land reclamation through plantation, The Indian Mining & Engineering Journal, May, pp. 18-20.
 
13.     Tripathy, D.P., 2003, Stability analysis of spoil dumps: a computational approach. Mining Engineering Journal, Feb., pp. 13-18.
 

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