QUARRY OPERATIONS
1) INTRODUCTION
Roads network, as a means of communication, plays a very important role in the life of a nation. The building activities of roads need various naturally available construction materials like stone, sand, shingle, etc. which are quarried. The proper selection and operation of quarries for quality material will go a long way not only in economy/efficiency in consumption but will also increase the quality/ life of roads constructed.
2) Background
The existing Technical Instruction TI No.-15 on "Maintenance of Quarrying Charts" was issued during 1964, based on technical data available at that time.
With the additional inputs now available and improvement in blasting technology, a need is felt to revise the T.I. based on experience gained on the ground in the last many years in BRO, Accordingly, the old TI has been revised and redesigned as "Technical Instruction No. 15 (Revision-1994) - Quarry Operations in BRO".
3. NECESSITY
1). The road construction activity needs various natural materials like soil, sand, chips, metal, shingle, and stones apart from other materials like steel, cement, bitumen, etc.
The former are quarried from natural sources like exposed rock faces, pit quarries, river / nallah bed, etc.
2). The road materials need a certain degree of quality, as per Codes/Standards, depending on their use for a particular purpose.
Similarly, the source (quarry) must be easily accessible from the road by heavy transport.
Thus basic parameters for selection of the quarry are easy accessibility, the economy in operation, and availability of adequate materials of requisite standards.
Fig.2) Open Loop in line Pattern
Fig.3) Staggered Pattern for an open Face.
The normal terms used in quarry operation are given below:
1) Quarry:-
A place from where construction material is extracted
2) Sand:-
A road material having sizes passing through a 4.75 mm sieve and retained on 75-micron sieve and could be extracted from river/nallah bed or pits or stone dust from the crusher.
3) Gravel:-
Road materials having a size between 80 mm to 4.75 mm and will include other termed materials like chips, metal, shingle. pebble etc.
4) Cobble:
This material will have sizes between 300 mm to 80 mm.
5) Boulder:-
Stones having size more than 300 mm.
LOCATION OF QUARRIES
1.) The locations of quarries should be marked on a plan during the recce and survey stage, where new roads are to be constructed.
In the case of old roads, the same should be surveyed on the ground and marked on the plan of road.
Finally, these should be transferred on the road plan in the road register maintained by Task Force/Road Construction Company.
2.) A separate chart, as per proforma in Appendix 'A' must be prepared and kept in Road Register.
The test results of quarry materials should be recorded on the quarry chart in a tabular form for ready reference.
2.a) The quarries will be operated every year and hence there is a need to update the yield of each quarry at least once in a year, as per column 6 of Appendix 'A,'preferably in April and written in pencil.
3. The various criteria for selecting a quarry are summarised as follows:-
(A) The quarry should have good quality material required for a particular purpose. Quarries having soft/elongated/rounded materials are normally rejected.
(B) it should be approachable from road by heavy vehicles without much difficulty and should not be very far from road.
(C) Quarry operation on road side, though possible and most economical, should not lead to formation of slides or cause damage to road or road Structure/ Building/ fileds or any other property.
(D) there should be least amount of disturbance to local ecology.
(E) it should have sufficient yield.
(F) in case blasting is required, the quarry site should be away from in ed places, bridges etc. to avoid during blasting.
PRECAUTIONS DURING QUARRYING OPERATION
1). The precautions mentioned in succeeding paras must be taken during quarrying operation.
2.) A supervisor must be positioned at the site to oversee all safety precautions as well as supervision of work and accounting of quarried material.
3) Materials must be stocked at safe places.
4). The consistency and quality of quarried materials must be checked frequently, as laid down in Codes/Standards For ready reference, some of the important tests with their limiting values for various Items of road work are given In Appendix 'B'. In case any other information Is required, refer "Ministry of Surface Transport (Roads Wing) Specifications for Road and Bridge Works", IRC Special Publication No 11 "Handbook of Quality control for Construction of Roads and Runways" and BIS: 383- 1970 "Specifications for Coarse and Fine Aggregates from Natural Sources for Concrete." The limiting values are given in Appendix B'are based on the current specifications given in MOST/IRC/BIS.
Future changes, as and when made by MOST/IRC/BIS in their codes, may be made accordingly,
5.) All precautions, as laid down in 15:4081-1986 on 'Safety code for Blasting and Related Drilling Operations' must be taken. BROO No 1/93 may also be referred to.
6) While undertaking roadside quarrying on a sloped surface, care must be taken to maintain, as far as possible, the natural angle of repose to avoid slides in the future.
Similarly, when a roadside quarry is abandoned/not likely to be used in the future, afforestation must be done on the quarry face where the soil is mixed with boulders.
This step will avoid future erosion leading to slides.
7) In case the earth/soil is required to be quarried along the roadside, instructions given in IRC: 10-1961, must be followed strictly to avoid sinking/erosion of road berms. While abandoning a quarry, its surface is dressed-up to merge with the adjoining area before afforestation.
OVERBREAK:-
In a conventional primary blast, when the highly concentrated energy of an explosive is released, it can destroy or reduce the structural strength of the rock alongside the blasted face, New fractures, and planes of weakness are created and joints, bedding planes, etc, are opened up.
This is manifested as "overbreak".
Failures of bench slopes create hazards to men and machines and can result in appreciable and costly delays to operating schedules.
1) The overbreak can be controlled by lowering the energy density in the ground adjacent to the blast.
This can be achieved by following the guidelines are given below:-
1.(a) Use decoupled charges, particularly in back rows when continuous charge column is used.
2.) Drill blast holes in a staggered formation/pattern.
3.) The effective burden should not be greater than 25 times the blast hole diameter, particularly in back rows, to facilitate progressive relief of burden in forwarding direction.
4.) The best spacing between back row blast holes is the largest spacing that gives a straight face of the cut. Adopt spacing as 30 to 40 times the blast hole diameter.
5.) Because of the need to prevent surface overbreak due to the cratering effect, it may be necessary:-
a) To reduce the stemming column and
b) To use an upper decoupled charge in the back-row holes.
Fig.1 Upper decoupled charge in back row holes for reduced overbreak.
Select initiation sequence such that:-
a) there are minimum number of blast holes firing on the same delay, and
b) the blast holes along the back row and sides of the shot are detonation in a delayed sequence.
The staggerd'V'pattern,as Illustrated in Fig 3. has been found to be the best avallable pattern from the point of view of overbreak control as all the holes in the back row and the end holes fire at different delays.
A). The inter-row delays should be such that each blast hole in sub- sequent row should 'see' an effective vertical free face to break for ensuring progressive relief of burden.
B). The shape of the blasting round should be so designed that the length is at least 1.5 times or preferably 3 to 4 times the width of the cut.
C). Overbreak may also be caused due to geological conditions, in particular,the angle of dip of the rock formation with respect to the bench face. The best solution is to suitably orient the bench face at the planning stage itself.
FLYROCK :-
Flyrock in blasting usually means flying of the unex- pected/undesired projection of rock mass during blasting.
It should not be mixed in 'throw'. Flyrock poses a serious problem to the users of explosives, as not only the "Mine Equipments" are at risk, but also the personal safety and adjacent property are endangered.
Control of Flyrock :-
It should be possible to control the flyrock formation to acceptable levels with an appropriate blast design followed by adequate supervision during charging.
Major factors include:-
Blast hole location :-
To avoid the irregularities in the front row bur- den, it is important to ensure that the holes are correctly collared with respect to the back break/inclination of the face and also digging alongside the inclination face is controlled.
Charge configuration :-
It is misunderstood to assume that under- charging the front row holes results in control of flyrock.
Charging of the front row holes should be critically determined with some tolerance for forward throw to avoid harmful flyrock from the back.
Where permanent geological planes of weakness, particularly the bedding planes are encountered,deck charging should be used to reduce the concentration of charge located directly adjacent to these planes of weaknesses.
Stemming medium :-
The stemming length should not be less than the hole burden.
To prevent premature venting of explosion gases Through the stemming column, effective stemming materials like crushed angular rock should be used.
4) Initiation Pattern/Sequence:-
The forward fly rock can be fairly controlled by adopting the 'V'pattern of initiation with adequate Inter-row delay intervals as compared to the commonly used 'in-line open Loop' pattern.
Both patterns are given in Fig. 3 and Fig. 2.
5) Blast Pattern experience has shown that blasts designed with face length to width ratio in the range of 3 to 4 produce minimum fly rock,
6) To reduce drastically the incidence of fly rock, the protective covering of blast with blasting mats, conveyor belting or truck tires, etc. can be used. However, in view of their bulkiness, these will be limited to small blasts only.
8. DOCUMENTATION
A separate work diary will be maintained for quarry operation as per BRDB Form W-8.
All relevant details of input, output, transportation of materials, and stock in hand should be entered in the work diary on day to day basis.
The work diary should be checked and authenticated by the officer-in-charge of the Sector daily.
WATER POINTS
1). The requirement of water, though not forming part of quarrying is an essential component for road construction and hence mentioned in this Technical Instruction.
2). The water points along the alignment of the road must also be mentioned in Road Register and indicated on the plan.
This will help in the planning works in the future, whenever needed. While indicating water points, their nature like perennial, rainfed, snowed, etc. must also be indicated suitably. 3).Whenever required/possible, masonry/static storage tanks with discharge spouts for gravity feed into the water trucks should be constructed to obviate the need for pumping.
