Lecture 7 Rock Excavation

8/13/2019 Lecture 7 Rock Excavation

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BLDG 6831Construction Processes

Lecture 7Rock Excavation

1Dr C.J. Willis, CAPM, P.Eng

Learning ObjectivesLearners will be introduced to:

Rock characteristics and rock investigation Rock handling systems Rock drilling, drilling equipment, drilling

calculations

Rock ripping, ripping equipment, estimatingripping production and cost

References

Nunnally, S.W. 2011. Construction Methods and Management,8thEdition



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Rock Characteristics Rock may be classified according to its origin

as: igneous sedimentary metamorphic

Igneous rock formed when the Earths moltenmaterial cooled.

Very homogeneous and is the most difficult type ofrock to excavate.


Rock Characteristics Sedimentary rock formed by precipitation of

material from water and air Highly stratified and has many planes of weakness Most easily excavated type of rock Examples include sandstone, shale, limestone

Metamorphic rock originated as igneous orsedimentary rock but changed due to heat,pressure and chemical reaction Intermediate between igneous and sedimentary in its

difficulty of excavation

Examples: slate, marble and schist4Dr C.J. Willis, CAPM, P.Eng


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Rock Characteristics Difficulty involved in rock excavation depends

on: Rock type Extent of fractures and other planes of weaknessAmount of weathering that has occurred Predominant grain sizeWhether the rock has a crystalline structure Rock brittleness Rock hardness


Rock Investigation Relative hardness is measured on Mohs scale

from 1 (talc) to 10 (diamond).

As a rule, any rock that can be scratched by aknife blade (hardness about 5) can be easily

excavated by ripping or other mechanical

methods



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Rock Investigation Principle methods for investigating subsurface

conditions include:

Drilling Excavating test pits Seismic measurements


Rock Investigation Seismic Measurements

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FIGURE 6-1. Schematic representation of seismic refraction test.

Dr C.J. Willis, CAPM, P.Eng


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FIGURE 6-2. Graph of refractiontest data.



Used to determine the thickness of the upper layerwhen the sound velocity increases with layer depth(velocity in top layer < velocity in second layer)



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Rock-Handling Systems The process of rock moving may be considered

in four phases: Loosening Loading Hauling Compacting



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Rock-Handling Systems

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Table 6-1. Principal rock-handling systems


Rock-Handling Systems Traditional Method)

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Drill blast-holes

Load holes with explosives

Detonate explosives

Power shovels to load fractured rock into haul units

Haul rock away in trucks or wagons



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Rock-Handling Systems Newer alternatives in rock handling systems

include:

Tractor mounted rippers to loosen rockWheel loaders to load fractured rock into haul units Reinforced scrappers to load and haul fractured

rock


Drilling Drilling Equipment

Common types of drilling equipment include percussiondrills, rotary drills, and rotary-percussion drills.

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Table 6-2. Typical characteristics of rock drillingequipment



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Percussion Drills Penetrates rock by impact alone Drill bit rotates to assist in cleaning the hole

Rotation takes place on the upstroke No cutting is accomplished during rotation

Common types of percussion drills include: Hand held rock drill (jack-hammer)Wheel mounted wagon drill Crawler mounted track drill (hydraulically powered

boom for positioning the drill feed)


Percussion Drills

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FIGURE 6-6. Hydraulic track drill.(Courtesy of Atlas Copco)



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Rotary Drills and Rotary-Percussion Drills Rotary drills cut by turning the bit under

pressure against the rock face

Rotary-percussion drills combine rotary andpercussion cutting action

Penetrates rock several times faster in comparisonto percussion drill


Downhole Drills Utilize a percussion drilling device mounted

directly above the drill bit at the bottom of thehole.

Advantages of downhole drills include: Longer drill rod life Less air is required to clean the hole Noise level is lower Little loss of energy between drill and bit

Machine can function as a percussion drill, rotarydrill or rotary-percussion drill



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Drilling Rate Rate of Penetration) Rate of penetration depends on:

Rock hardness Drill type and energy Type of drill bit use

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Table 6-3. Representative drilling rates (carbide bit)Dr C.J. Willis, CAPM, P.Eng

Drilling Rate Increased air pressure at the drill results in

increased drill production (penetration/h)

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FIGURE 6-9. Drill penetrationversus air pressure.



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Drill Bits and Steel

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FIGURE 6-10. Major types of rock drill bits.Dr C.J. Willis, CAPM, P.Eng

Drill Bits and Steel Percussion Drill Bits

Include the cross-type bit, x-type bit and button bits. Points of an x-type bit are in an X rather than a cross X-type bits tend to drill straighter holes than do cross

type bits

X type and cross type bits are available with either solidsteel or tungsten carbide cutting edges. Tungsten carbide cuts faster and lasts longer then steel

Button-type bits have a higher penetration rate than Xor cross-type bits and are less likely to jam in the hole.

Button bits do not normally require grinding orsharpening



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Drill Bits and Steel Rotary Drill bits

Include core bits and roller bits (cone bits) Coring bits are available as diamond drill bits and shot drill bits Diamond drill bits utilize diamonds set in a matrix on the bit body Shot drill coring bits utilize chilled steel shot fed into the hole

around the bit instead of diamond as the cutting agent

The lower end of the shot drill bit is slotted to help in retainingthe shot in between the bit and rock as the bit rotates

Rolling cutter bits use several cutters shaped like gears topenetrate the rock as the drill bit rotates


Drill Bits and SteelPercussion Drilling

Steel rod connecting a percussion drill and its bit isreferred to as drill steel

Drill steel is available in: diameters of 2.2cm to 5.1cm Lengths of 0.61m to 6.1m

Drill steel sections are fitted with threaded ends so thatsections may be added as the bit penetrates.

Sections are hollow allowing air to flow to the bit forcleaning



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Drill Bits and SteelRotary Drilling

Drill rod used for rotary drilling is called a drillpipe

Available in length increments of 1.5m startingwith 3m and is threaded on each end

Drill pipe is hollow to allow compressed air ordrilling fluid to the bottom of the hole


Drilling Patterns and Rock Yield Small holes closely spaced yield small rock

particles

Large holes widely spaced yield large rockparticles

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Table 6-4. Typical drill hole spacing (rectangular pattern) [ft (m)]Dr C.J. Willis, CAPM, P.Eng


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Drilling Patterns and Rock Yield

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FIGURE 6-11. Principal drillingpatterns.


Drilling Patterns and Rock YieldRectangular Pattern

Volume of blasted rock produced per hole is computed by:

S= pattern spacing (ft or m) H= effective hole depth (ft or m)

Effective depth of a blast hole is the average depth of the excavation areaafter the blast, not the original hole depth

Effective hole depth should be determined by trial blasting Effective depth has been found to average about 90% of original hole

depth



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Drilling Patterns and Rock Yield Rock produced per-hole is divided by the original hole

depth to yield rock volume per unit of hole drilled

The amount of drilling required to produce a unitvolume of blasted rock is calculated as the reciprocalof the volume per unit of drilled depth


Drilling Patterns and Rock YieldExample



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Rock Ripping Heavy duty tractor mounted rippers are used to

rip rock

Where ripping can be employed it is usuallycheaper than drilling and blasting

Ripping has the following advantages overdrilling and blasting

Increased production Fewer safety hazards Reduced insurance costs


Ripping Equipment

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FIGURE 6-15. Heavy-duty crawler-mounted ripper. (ReprintedCourtesy of Caterpillar Inc.)



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Ripping Equipment Most modern rippers are the adjustable

parallelogram type

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FIGURE 6-16.Adjustable parallelogram ripper.Dr C.J. Willis, CAPM, P.Eng

Ripping Equipment This type of ripper maintains a constant angle

with the ground as it is raised and lowered.

The upper hydraulic cylinder allows the tipangle to be varied as desired to obtain optimumresults

Tip angle that produces best surfacepenetration is usually different from the tipangle that produces optimum rock breakageafter penetration



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Ripping Equipment Impact Rippers

Uses a hydraulic mechanism to impart ahammering action to a single shank ripper

Able to effectively rip tougher rock thanconventional rippers


Ripper Production Seismic velocity of a rock formation provides a

good indication of the rocks rippability

There are charts that indicate the ripping abilityof a particular tractor/ripper combination in

various types of rock over a range of seismic

velocities



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Ripper Production

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FIGURE 6-17. Ripper performance vs. seismic velocity. (Reprinted Courtesy of Caterpillar Inc.Dr C.J. Willis, CAPM, P.Eng

Ripper Production



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Considerations in Ripping Ripping speed and depth, spacing of ripper passes,

and number of shanks depend on rock type andsoundness and tractor power

Rip downhill to take advantage of gravity Necessary to rip uphill when ripping laminated

material

Depth of ripping depends on number of shanksused and tractor power

Ripping speed should be kept low to reduce wearon ripper teeth and shanks43Dr C.J. Willis, CAPM, P.Eng

Estimating Production and CostExample

Estimate the hourly production and the unit cost of rockexcavation involved in preparing an industrial site by ripping.The site is 300ft (91.4m) by 400ft (121.9m) and must beexcavated to an average depth of 12ft (3.658m). Field testsindicate that a D7G dozer with ripper can obtain satisfactoryrock fracturing to a depth of 27in. (0.686m) with two passesof a single ripper shank at 3 ft (0.914m) intervals. Averagespeed, including turns, is estimated at 82ft/min (25m/min).Cost information: Labour (operator) = $20/h Equipment (D7G ripper, including ripper tips, shanks and shank

protectors) = $75/h



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Estimating Production and Cost


Estimating Production and Cost



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Lecture 7 Rock Excavation

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