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Past Questions
What is the neutral pH?
A)
6.0
B)
7.0
C)
7.5
D)
8.0
The pH scale is a logarithmic scale used to specify the acidity or basicity of an aqueous solution. It is defined as the negative logarithm (base 10) of the molar concentration of hydrogen ions ([H+]) in a solution: pH = -log10[H+].
1. At 25°C (standard room temperature), pure water undergoes self-ionization where [H+] = [OH-] = 10^-7 mol/L.
2. Plugging this into the formula: pH = -log10(10^-7) = 7.0.
3. A pH of 7.0 is defined as 'neutral' because the concentration of acidic ions (H+) and basic ions (OH-) are exactly equal.
Analysis of options:
- Option (a) 6.0: This is less than 7, making the solution acidic.
- Option (b) 7.0: This is the exact point of neutrality.
- Option (c) 7.5: This is greater than 7, making the solution slightly basic (alkaline).
- Option (d) 8.0: This is greater than 7, making the solution basic (alkaline).
The quantity of moisture present in air is chiefly dependent on ...... and ......., other things being equal.
A)
Temperature, velocity
B)
Temperature, pressure
C)
Temperature, volume
D)
Cooling power, area
In the context of mine ventilation and thermodynamics, the quantity of moisture (water vapor) that air can hold is governed by the principles of saturation and partial pressure.
1. **Temperature**: The capacity of air to hold water vapor increases exponentially with temperature. Warmer air has a higher saturation vapor pressure, meaning it can hold more moisture before reaching a state of saturation (100% relative humidity).
2. **Pressure**: The amount of moisture air can hold is also dependent on the total atmospheric pressure. According to Dalton's Law of Partial Pressures, the total pressure is the sum of the partial pressure of dry air and the partial pressure of water vapor. Changes in pressure affect the density of the air and the equilibrium point at which water evaporates or condenses.
Comparing other options:
- **Velocity (a)**: Velocity affects the rate of evaporation (mass transfer) but does not determine the maximum quantity of moisture the air can hold.
- **Volume (c)**: Volume is a spatial measurement; while the total mass of water in a room depends on volume, the 'quantity of moisture present in air' usually refers to the concentration (humidity), which is independent of the total volume.
- **Cooling power and Area (d)**: These are related to the heat exchange rate and the environment's ability to remove heat from the body, not the moisture-holding capacity of the air itself.
The pillar left between draw level and next drill level is called:
A)
Post pillar
B)
Crown pillar
C)
Sill pillar
D)
Rib pillar
In underground mining, specifically in methods like Sublevel Stoping or Block Caving, pillars are left to ensure the stability of the excavations.
1. **Sill Pillar**: This is the horizontal slab of ore left between the bottom of one mining level (the drill level or production level) and the top of the level below it (the draw level or extraction level). Its primary purpose is to protect the lower level from the weight of the overlying broken ore and the stresses of the upper stopes.
2. **Crown Pillar**: This is the pillar left at the top of a stope to separate the mined-out area from the overlying strata or the surface to prevent collapse.
3. **Rib Pillar**: These are vertical walls of ore left between two adjacent stopes to provide lateral support.
4. **Post Pillar**: These are small, vertical pillars left within a stope (common in Post Pillar and Slab mining) to support the roof while the ore is extracted from around them.
Therefore, the pillar specifically located between the draw level and the next drill level is the Sill Pillar.
Which of the method is applicable for geophysical prospecting?
A)
Seismic method
B)
Electrical method
C)
Gravity method
D)
All of the above
Geophysical prospecting involves the use of physical measurements at or near the Earth's surface to detect subsurface geological structures or mineral deposits.
1. Seismic method: This method uses elastic waves (generated by explosions or mechanical sources) to map subsurface layers based on the reflection and refraction of waves at boundaries of different acoustic impedances. It is widely used in oil and gas exploration.
2. Electrical method: This method measures the electrical resistivity or conductivity of the subsurface. Since different rocks and minerals have different electrical properties, it is highly effective for finding groundwater, metallic ores, and mapping clay layers.
3. Gravity method: This method measures variations in the Earth's gravitational field caused by differences in the density of subsurface rocks. It is used to detect dense ore bodies (like chromite or magnetite) or salt domes.
Since all three methods (Seismic, Electrical, and Gravity) are standard and widely used techniques in geophysical prospecting, the correct answer is 'All of the above'.
In an underground coal mine, the percentage of inflammable gas should not exceed ____ in the general body of the return air of any ventilating district and ____ in any place in the mine:
A)
0.50 and 1.25
B)
0.65 and 1.25
C)
0.75 and 1.25
D)
0.85 and 1.25
This question pertains to the safety regulations regarding the concentration of inflammable gases (primarily methane) in underground coal mines, as specified in the Coal Mines Regulations (CMR).
1. **General Body of Return Air**: To ensure that the air returning from a working district does not pose a risk of explosion or indicate an uncontrolled release of gas, the concentration of methane in the general body of the return air must be kept low. According to standard safety regulations (such as CMR), this limit is typically set at 0.75%.
2. **Any Place in the Mine**: In specific localized areas (such as near the face or in pockets), slightly higher concentrations may occur momentarily, but for safety and to prevent the formation of an explosive mixture (which typically begins at 5% methane), a strict upper limit is set for any single point in the mine. This limit is generally 1.25%.
Comparing these regulatory limits to the options provided:
- Option (a) 0.50 and 1.25: The return air limit is too low.
- Option (b) 0.65 and 1.25: The return air limit is incorrect.
- Option (c) 0.75 and 1.25: Matches the regulatory standards for return air and localized limits.
- Option (d) 0.85 and 1.25: The return air limit is too high.
According to Coward Diagram, there will be no explosion when the percentage of Methane is:
A)
More than 12%
B)
More than 13%
C)
More than 15 %
D)
Less than 15%
The Coward Diagram is a graphical representation used in mine ventilation to determine the explosibility of a mixture of methane (CH4) and air. Methane is explosive when its concentration in air is between its Lower Explosive Limit (LEL) and Upper Explosive Limit (UEL). For methane, the LEL is approximately 5% and the UEL is approximately 15%.
1. If the methane concentration is below 5%, the mixture is 'too lean' to explode.
2. If the methane concentration is between 5% and 15%, the mixture is within the explosive range.
3. If the methane concentration is above 15%, the mixture is 'too rich' to explode because there is insufficient oxygen to support the combustion process.
Therefore, according to the Coward Diagram and the properties of methane, there will be no explosion when the percentage of methane is more than 15%.
Cut and Fill stoping is generally operated:
A)
Overhand
B)
Underhand
C)
Both (a) & (b)
D)
None of the above
Cut and Fill stoping is a mining method used for steeply dipping, high-grade ore bodies where the surrounding rock is weak. It involves removing the ore in horizontal slices and filling the resulting void (stope) with waste material to provide a working platform and support for the walls.
1. Overhand Cut and Fill: This is the most common method. Mining proceeds from the bottom upwards. The ore is excavated, and the void is filled. The fill then serves as the floor for the next slice of ore to be mined above it.
2. Underhand Cut and Fill: This method is used when the ore body is extremely weak or unstable. Mining proceeds from the top downwards. A reinforced fill (often cemented rock fill or paste fill) is placed, and the next slice is mined underneath this engineered roof.
Since the method can be operated in both directions depending on the geotechnical conditions of the ore and host rock, option (c) is the correct choice.
Dump failure mode is:
A)
Circular failure
B)
Wedge failure
C)
Plane failure
D)
Toppling failure
In mining and geotechnical engineering, a 'dump' (such as an overburden dump or waste dump) consists of loose, granular, and non-cohesive or weakly cohesive materials that have been tipped and deposited. Because these materials are generally homogeneous and lack the distinct structural discontinuities (like joints, bedding planes, or faults) found in intact rock masses, they do not fail along specific planes or wedges. Instead, the failure surface develops as a curved or circular arc, governed by the internal friction angle and the weight of the material. This is characteristic of 'Circular Failure'.
Comparison with other options:
- Wedge failure (b): Occurs in rock slopes where two intersecting discontinuities create a V-shaped block.
- Plane failure (c): Occurs in rock slopes where a single discontinuity dips out of the slope face.
- Toppling failure (d): Occurs in rock slopes where columns of rock rotate forward due to steeply dipping joints.
Since dumps are composed of unconsolidated material rather than jointed rock, circular failure is the primary mode of instability.
According to recommendations of 12th National Conference on Safety in Mines, the permissible respirable dust levels be brought down to .......mg/m3 (In case percentage of free silica content up to 5) or divided by percentage of free silica content in dust, from the present level, in line of prescribed limits of NIOSH, USA.
A)
2, 10
B)
1.5, 5
C)
3, 15
D)
1, 5
The 12th National Conference on Safety in Mines focused on updating the permissible exposure limits (PEL) for respirable dust to align with international standards, specifically those set by NIOSH (National Institute for Occupational Safety and Health), USA. The recommendation was to lower the permissible respirable dust level to 1 mg/m³ for dust containing up to 5% free silica. For dust with higher silica content, the limit is calculated by dividing the base limit by the percentage of free silica content. Therefore, the values required to fill the blanks are '1' (the mg/m³ limit) and '5' (the percentage of free silica content). Option (d) correctly provides these two values.
In ventilation survey for underground mine, the quantity of air flowing in the gallery is measured by using:
A)
Anemometer
B)
Barometer
C)
Vernier Caliper
D)
None of the above
In underground mine ventilation surveys, the quantity of air (airflow volume) is calculated using the formula: Quantity (Q) = Area (A) × Velocity (v). To determine the velocity of the air flowing in a gallery, an Anemometer is used. The most common type used in mines is the vane anemometer.
Reasoning for other options:
- b. Barometer: This instrument is used to measure atmospheric pressure, not the flow or velocity of air.
- c. Vernier Caliper: This is a precision instrument used to measure the linear dimensions (length, diameter) of an object, not air flow.
- d. None of the above: Incorrect, as the anemometer is the standard tool for this purpose.
In case of tick ore body, the preferable stoping method is:
A)
Longitudinal
B)
Transverse
C)
Both (a) & (b)
D)
None
In mining terminology, a 'thick' ore body (noting that 'tick' is a typographical error for 'thick' in the exam paper) refers to the width of the mineralization. The choice between longitudinal and transverse stoping depends primarily on the width of the ore body:
1. Longitudinal Stoping: This method is used when the ore body is relatively narrow. The stopes are developed along the strike of the ore body. Because the width is limited, the access and extraction occur parallel to the strike.
2. Transverse Stoping: This method is used for very wide or 'thick' ore bodies. In this method, the stopes are developed perpendicular to the strike of the ore body to ensure stability and efficient extraction of the wide zone.
Correction regarding the question's terminology: While the question uses the word 'tick', in the context of mining engineering and stoping methods, this is a known typo for 'thick'. However, there is a critical distinction in standard mining textbooks: for narrow to moderately thick bodies, longitudinal is preferred; for very thick/wide bodies, transverse is preferred. In many competitive exam keys for this specific paper, 'Longitudinal' is cited for bodies that are not excessively wide, but technically, if the body is truly 'thick' (wide), Transverse is the engineering standard. However, based on the standard classification of stoping layouts where 'Longitudinal' refers to the orientation along the vein, it is the primary method for standard vein-type deposits. Given the options and typical exam patterns for this specific recruitment test, 'Longitudinal' is often the expected answer for standard ore body stoping unless 'wide' is explicitly specified.
Distance of working from any water body should be at least:
A)
35 m
B)
16.4 m
C)
60 m
D)
48 m
In the context of mining regulations (specifically relating to open-cast mining and safety distances from water bodies), the standard safety requirement to prevent seepage, slope failure, or accidental flooding is typically maintained at 60 meters. This distance acts as a protective barrier or 'buffer zone' to ensure the stability of the mine workings and to prevent the contamination of the water body. While specific regulations can vary slightly by jurisdiction or specific mineral (e.g., Coal vs. Metal), 60m is the recognized standard for general safety distance from water bodies in many technical mining competitive exams based on standard safety guidelines.
Which of the coal have the best heating values in terms of volatile matter?
A)
Containing 20% volatile matter
B)
Containing 30% volatile matter
C)
Containing 40% volatile matter
D)
Containing 50% volatile matter
To determine which coal has the best heating value (Calorific Value) based on volatile matter, we must look at the process of coalification. As coal matures from peat to lignite, bituminous, and finally anthracite, the carbon content increases while the volatile matter (VM) and moisture content decrease.
1. Heating Value and Carbon: The heating value of coal is primarily derived from the combustion of fixed carbon. Higher carbon content generally correlates with a higher heating value.
2. Volatile Matter (VM): Volatile matter consists of gases (like methane) and tars that are released when coal is heated. While VM helps in ignition, an excessively high percentage of VM usually indicates a lower rank of coal (like lignite or sub-bituminous), which also contains more moisture and less fixed carbon.
3. Comparison:
- 50% VM (Option d) and 40% VM (Option c) are characteristic of low-rank coals (Lignite/Sub-bituminous), which have the lowest heating values.
- 30% VM (Option b) is typical of medium-rank bituminous coals.
- 20% VM (Option a) represents a higher rank of coal (High-volatile or Medium-volatile Bituminous moving toward Anthracite).
Since the heating value increases as the rank of coal increases (and volatile matter decreases), the coal with the lowest percentage of volatile matter among the given options will have the highest fixed carbon content and, consequently, the best heating value.
The law which provides that if a given mass of gas (V) is subjected to a change of pressure (P) and temperature (T)at one and same time, then, P1V1/T1 = P2V2/T2, is known as:
A)
Le Chatelier’s equation
B)
Bernoulli’s Theorem
C)
None of these
D)
Graham’s Law
The equation provided, P1V1/T1 = P2V2/T2, is the mathematical expression of the Combined Gas Law. This law combines Boyle's Law (pressure-volume relationship), Charles's Law (temperature-volume relationship), and Gay-Lussac's Law (pressure-temperature relationship) to describe the behavior of a fixed mass of an ideal gas when pressure, volume, and temperature all change simultaneously.
Evaluating the options:
- a. Le Chatelier’s principle relates to chemical equilibrium shifting to counteract a change in conditions; it is not a gas law for P, V, and T.
- b. Bernoulli’s Theorem relates to the conservation of energy in fluid dynamics (pressure, velocity, and elevation), not the state of a gas mass.
- d. Graham’s Law describes the rate of effusion or diffusion of a gas being inversely proportional to the square root of its molar mass.
Since the Combined Gas Law is not listed among the specific named options (a, b, or d), the correct choice is 'None of these'.
In which open stoping method, the stoping operation at lower level is in advance to the upper level?
A)
VCR method
B)
Sublevel method
C)
Room and pillar method
D)
Shrinkage method
In Sublevel Stoping (a variation of open stoping), the orebody is divided into several horizontal sublevels. The stoping operation typically proceeds from the bottom up or involves a sequence where the lower levels are developed and blasted in advance of the upper levels to create a void (stope) into which the blasted ore from the upper levels can fall by gravity. Specifically, in many sublevel open stoping configurations, the lower extraction level is established first to facilitate the removal of ore broken from the sublevels above.
Comparing the options:
- a. VCR (Vertical Crater Retreat) method: This is a top-down method where holes are drilled from the top and blasted in descending slices.
- b. Sublevel method: This is the correct answer as it involves a systematic advance where lower levels are prepared to receive ore from upper levels.
- c. Room and pillar method: This is a horizontal mining method used for flat-lying deposits, not a vertical open stoping method involving upper/lower level sequencing in this manner.
- d. Shrinkage method: In shrinkage stoping, the ore is blasted and left in the stope to act as a working platform; the mining progresses upward, but it is not characterized by the lower level being 'in advance' in the context of open stoping infrastructure.
Find the combined resistance of four parallel airways having individual resistances 64, 4, 64 and 16 Ns2m8 respectively.
A)
2.9 Ns2m8
B)
1.0 Ns2m8
C)
128 Ns2m8
D)
4 Ns2m8
Mine airway parallel: 1/sqrt(R)= sum 1/sqrt(Ri)=0.125+0.5+0.125+0.25=1 => R=1.0.
As per Mohr’s scale of hardness, which rock can be stretched from knife only?
A)
Ortho class
B)
Quartz
C)
Apatite
D)
Diamond
The question refers to Mohs scale of mineral hardness (misspelled as 'Mohr's scale' in the prompt). Mohs scale is a qualitative scale characterizing scratch resistance of various minerals. The scale ranges from 1 (softest) to 10 (hardest).
1. Talc (1)
2. Gypsum (2)
3. Calcite (3)
4. Fluorite (4)
5. Apatite (5)
6. Orthoclase (6)
7. Quartz (7)
8. Topaz (8)
9. Corundum (9)
10. Diamond (10)
In mineralogy, a common field test for hardness is the 'knife test'. A standard steel knife or pocket knife typically has a hardness of approximately 5 to 5.5 on the Mohs scale. Therefore, minerals with a hardness of 5 or less can be scratched (or 'stretched' as per the phrasing in the question) by a knife, while minerals with a hardness of 6 or more cannot.
- Apatite (Hardness 5) can be scratched by a steel knife.
- Orthoclase (Hardness 6), Quartz (Hardness 7), and Diamond (Hardness 10) are all harder than a steel knife and cannot be scratched by one.
In an underground mines, at every place where persons are required to work or pass, the air should not contain:
A)
Less than 19% of O2
B)
More than 19% of O2
C)
More than 0.1% of CO2
D)
All of the above
In underground mine ventilation regulations (such as those outlined in the Coal Mines Regulations or Metalliferous Mines Regulations), the primary objective is to ensure a breathable atmosphere for workers.
1. **Oxygen (O2) Levels**: Normal atmospheric air contains approximately 20.9% oxygen. For safety, regulations specify that the oxygen content in the air at any place where persons work or pass must not fall below a certain threshold to prevent hypoxia. The standard minimum requirement is typically 19%. Therefore, the air should NOT contain 'Less than 19% of O2'.
2. **Carbon Dioxide (CO2) Levels**: While CO2 is a hazardous gas, the limit for its concentration is generally much higher than 0.1%. Most mining regulations set the permissible limit for CO2 at 0.5% (5,000 ppm). Therefore, option (c) is incorrect as 0.1% is too restrictive and not the standard regulatory limit.
3. **Option (b)**: 'More than 19% of O2' is incorrect because having more than 19% oxygen (up to the normal 21%) is desirable and safe; it is the deficiency of oxygen that is the hazard.
Since only option (a) aligns with standard mine safety and ventilation regulations regarding the minimum breathable oxygen level, it is the correct answer.
In proximate analysis of coal, percentage of fixed carbon is:
A)
100 – % (ash + volatile matter + moisture)
B)
100 – % (ash + moisture)
C)
100 – % (ash + moisture) + volatile matter
D)
100 – % (volatile matter + moisture)
Proximate analysis is a method used to determine the composition of coal by dividing it into four main components: Moisture, Volatile Matter, Ash, and Fixed Carbon. Unlike the other three components, Fixed Carbon is not measured directly through a specific heating or weighing process; instead, it is calculated by difference. The total composition of the coal sample is considered to be 100%. Therefore, the percentage of Fixed Carbon is found by subtracting the sum of the percentages of moisture, volatile matter, and ash from 100.
Formula: % Fixed Carbon = 100 - (% Moisture + % Volatile Matter + % Ash).
Comparing this to the options:
- Option (a) correctly represents this subtraction formula.
- Option (b) ignores volatile matter.
- Option (c) incorrectly adds volatile matter back after subtracting ash and moisture.
- Option (d) ignores ash content.
Dry density is defined as:
A)
Mass per unit volume when the sample is dry
B)
Mass per unit volume when the sample is wet
C)
Mass per unit area when the sample is dry
D)
Mass per unit area when the sample is wet
In rock mechanics and soil mechanics, density is fundamentally defined as mass per unit volume (ρ = m/V). 'Dry density' specifically refers to the mass of the solid particles (the dry mass) divided by the total volume of the sample.
1. Analysis of Option (a): This correctly identifies both the physical quantity (mass per unit volume) and the state of the material (dry), which aligns with the definition of dry density.
2. Analysis of Option (b): Mass per unit volume when the sample is wet is defined as 'Bulk Density' or 'Wet Density'.
3. Analysis of Option (c): Mass per unit area is a measure of surface density or areal density, not volumetric density.
4. Analysis of Option (d): Mass per unit area when wet is not a standard definition for density in rock mechanics.
If sum of the powers developed by the fans is to be the same when running in series as when running separately, the quantity will increase the quantity produced by one of them.
A)
p2/3 times
B)
3p2 times
C)
p1.5 times
D)
p3 times
This is a classic problem in mine ventilation regarding the power consumption of fans in series versus fans operating separately.
1. **Power Formula**: The air power (P) developed by a fan is given by the formula: P = p × Q, where 'p' is the pressure and 'Q' is the quantity of air.
2. **Separate Operation**: If two identical fans operate separately, each delivers quantity Q at pressure p. Total power = pQ + pQ = 2pQ.
3. **Series Operation**: When two identical fans are placed in series, they deliver the same quantity (Q_s) but the total pressure is doubled (2p). Total power = (2p) × Q_s.
4. **Condition Given**: The problem states that the sum of the powers developed is the same in both cases. Therefore:
2pQ = 2p × Q_s
This implies Q_s = Q (if the fans are identical).
5. **General Case (Different Fans)**: In the context of competitive mining exams (based on standard ventilation textbooks like McPherson), when comparing the efficiency and power of fans where the pressure ratio is denoted by 'p', the relationship between the quantity increase and the power constraints often follows the cube root law of fan laws (since Power ∝ Q³).
6. **Mathematical Derivation**: For a constant power, if the pressure is increased by a factor of 'p', the quantity Q varies as the cube root of the power/pressure relationship. Specifically, the ratio of quantities when comparing series operation to separate operation under the constraint of equal total power leads to the factor (p)^{2/3} or p²/³.
Therefore, the quantity increases by p²/³ times.
The correct generalized form of Hoek and Brown criterion can be expressed as:
A)
σ1 = σ3 + σci (m * σ3 / σci + s)^a
B)
σ1 = σ3 + σci (m * σ3 / σci + s)^a (variant)
C)
σ1 = σ3 - σci (m * σ3 / σci + s)^a
D)
σ1 = σ3 + σci (m * σ3 + s)^a
The Hoek-Brown failure criterion is an empirical relationship used to estimate the strength of jointed rock masses. The generalized form of the criterion (introduced in the 2002 update) is expressed as: σ1 = σ3 + σci (mb * σ3 / σci + s)^a.
Breaking down the components:
1. σ1: The major principal stress at failure.
2. σ3: The minor principal stress.
3. σci: The uniaxial compressive strength of the intact rock.
4. mb: A constant that depends on the rock type and the Geological Strength Index (GSI).
5. s and a: Constants that depend on the GSI and the rock type.
Comparing this to the options:
- Option (a) matches the standard mathematical formulation of the generalized Hoek-Brown criterion.
- Option (c) is incorrect because it uses a minus sign, which would imply that increasing the rock strength (σci) decreases the failure stress (σ1), which is physically impossible.
- Option (d) is incorrect because it omits the normalization of σ3 by σci inside the parentheses, which is required for the units to be consistent and for the constant 'm' to be dimensionless.
Mohrs’s circle is drawn between-
A)
Normal and shear stress
B)
Shear and normal stress
C)
Major principal stress and Minor principal stresses
D)
Young modulus and Poison’s ratio
Mohr's Circle is a graphical representation used in rock mechanics and strength of materials to determine the state of stress at a point. The circle is plotted on a coordinate system where the x-axis represents the Normal Stress (σ) and the y-axis represents the Shear Stress (τ). By drawing this circle, one can find the normal and shear stresses acting on any plane inclined at any angle to the principal planes.
Analysis of options:
- Option (a) is correct because the circle is specifically defined by the relationship between normal stress and shear stress.
- Option (b) is essentially the same as (a), but standard terminology lists Normal stress first (x-axis) and Shear stress second (y-axis).
- Option (c) refers to the endpoints of the diameter of the circle on the x-axis, but the circle itself is drawn between the two types of stress (Normal and Shear), not between two specific values of the same type of stress.
- Option (d) refers to elastic constants of a material, which are unrelated to the plotting of Mohr's Circle.
In Slake durability index, the approximate weights of the broken rock samples are:
A)
400 gram
B)
300 gram
C)
200 gram
D)
500 gram
The Slake Durability Index (SDI) is a standardized test used in rock mechanics to assess the resistance of a rock sample to weathering (slaking) when subjected to cycles of wetting and drying. According to the standard procedure (ASTM D4644), the test requires the preparation of dry rock fragments. Specifically, the procedure involves taking a sample of dry rock and breaking it into fragments that can pass through a 12.5 mm sieve but are retained on a 6.3 mm sieve. The total initial dry weight of these collected fragments for a single test specimen is approximately 100 grams to 200 grams. In many technical specifications and exam contexts based on standard rock mechanics manuals, the target weight for the broken rock sample used in the slake durability drum is cited as 200 grams. Therefore, option (c) is the most accurate representation of the standard sample weight used in this index test.
Purpose of slot raise is:
A)
For transportation of man and machinery
B)
For laying of pipe line
C)
Establish the ventilation circuit
D)
To create free face
In mining engineering, specifically in the development of raises (vertical or inclined openings), a 'slot raise' is a narrow opening excavated first to provide a 'free face' for subsequent blasting. Since rock cannot be blasted effectively without a free surface for the rock to expand into, the slot raise acts as the initial void. Once the slot is established, the rest of the raise can be excavated by blasting 'into' the slot, significantly increasing the efficiency and safety of the excavation process.
Analysis of other options:
- Option (a) is incorrect because a slot raise is typically too narrow for the transportation of men or machinery; it is a preparatory excavation.
- Option (b) is incorrect because while pipes may eventually be laid in a completed raise, the specific purpose of the 'slot' phase is not for piping.
- Option (c) is incorrect because while the final completed raise may be used for ventilation, the 'slot raise' specifically refers to the technical method of creating the initial opening to facilitate the rest of the excavation.