METHODOLOGY FOR EXCAVATION OF HARD ROCK

 EXCAVATION OF HARD ROCK

1.  Scope:

 This work shall consist of excavation by mechanical means in all types of strata, in rock by controlled blasting to final line, level, grades, cross slopes as shown in drawings for roadway, drains, shoulders, median and foundation for structures, including hauling suitable excavated materials to site/crusher for embankment, sub grade or GSB construction and also disposal of unsuitable cut materials in specified manner.

2.  References:

Technical specification of contract document-schedule D and MoRT&H Specifications.

Safety Requirements: As per relevant clauses of the project^·s Safety Manual.

 Plant /Machinery and Equipment:

		Make /Model No /
S No.	Plant / Equipment	Features	Nos.
1	Jack hammers	-	according to type and quantum of work
2	Wires, charges etc for blasting	-
3	Excavator	Bucket capacity 0.9 m3, (with 3 tippers, lead 2 kms)	@90 m3/hr
4	Dumpers	10 m3
5	Motor Grader		@75 m3 /hr
6	Vibratory Roller	8-10 T Static weight	@80 m3 /hr
7	Water Tanker	10 KL capacity	@ 1/ 5kms stretch
8	Level Machine	Suitable capacity and numbers, to be decided according to type and quantum of work
9	Sand Replacement Method Apparatus/NDG

 

2. Procedure:

a. Rock excavation:

Unsuitable shales, large boulders and loose pieces of rock those move when pierced by a crow bar which cause differential settlement shall be removed to the extent of 500mm below the level prescribed in the drawings and shall brought up to the required level by filling and compacting with granular sub-base. In all cases at no point on cut formation the rock shall protrude above specified levels. Records shall be maintained in formats A/F1 & A/F5

b. Rock excavation by blasting:

 In rock excavation where ever blasting is required it shall be of controlled/open blasting with least disturbance to the adjacent materials and to the required lines as indicated in drawings and the method of blasting consistent with safety and job requirements. The blasting operations shall be prepared or made by the competent and experienced personnel and workmen who are thoroughly equinted with details of handling explosives and blasting operations. 

c. CHARGE HOLES

The charge holes shall be drilled by using jack hammer drill to a diameter and depth depending upon the quantity of rock to be excavated ranging from 750mm to 1500mm in such a pattern of burden and spacing are at 500mm to 750mm. All over burden soil and weathered rock along the top of the excavation for a distance of 5to 15m beyond drilling limits or to the end of excavation shall be removed. The drilled holes shall be not less than 60mm and not more than 75mm in dia no hole shall deviate more than 300mm from the plane of the planned slope nor deviate by more than 2/3rd of the horizontal spacing between holes in being parallel to an adjacent hole, length of any individual lift shall not exceed 9m and the center to center distance between holes shall not exceed 900mm. A working bench at the bottom of each lift for use in drilling the next pattern shall not exceed 600m

d. STEMMING

After the charge securely placed in the drill hole, a space of 200mm immediately above the charge shall be filled with dry clay and the rest with any convenient material, gently packed with a wooden rammer.

e. MUFFLING

 This shall be done to control the fly rock. MS plates of 3 sqm to 5 sqm in size of 6mm/8mm thickness/rubber pads shall be used for this purpose. The plates/pads shall be kept on the top face of rock to cover the charge holes, in such a manner that the edge of the plate/pads exceeds the extreme charge hole at least by 500mm. Over the muffling plates/pads a load of 150kg/sqm to 200kg/sqm shall be placed by means of sand bags.

f. SITE CLEARANCE & FIRING

Blasting shall be carried out in fixed hours as ordered in writing by the Engineer and kept known to the people, public and authorities in the vicinity sufficiently in advance with the help of Safety Department. Red flags shall be displayed in all directions during blasting operations. People except those who actually light the fuse shall be prohibited from the area and all persons including workmen shall be excluded from the flagged area at least 10 minutes before firing, a warning alarm or siren sounded for this purpose. The man in charge shall satisfy himself that all charges are exploded before allowing workmen or people around the blasted area. The firing of charge hole shall be done by electric detonators, by using sufficiently long fuse wire (at least 100m) fired with zero delay at pre – split row and with a delay of 50 milliseconds to the farthest row and all charge holes shall be blasted at one instance.

g. MISFIRE

 In case of misfire, sufficient time shall be allowed for delayed blast. The Man in charge shall inspect all the charges and determine miss-charge. In case of blasting powder charge it shall be completely flooded with water and a new hole at a distance of 300mm from the old hole shall be drilled and fired to blast the old charge. In cases of charges like gelatin, dynamite, etc the Man in-charge shall gently remove the primer with the detonator by tamping. The hole may be cleaned by tamping and a new hole at a distance of 300mm then be drilled , a fresh detonator and primer then be filled to blast the charge alternatively and fired to blast both at the same time. The man in-charge shall report Engineer all cases of miss-fire. If a miss-fire is due to a defective detonator or dynamite the whole quantity or box from the defective article was taken must be thoroughly inspected.

3. Important Safety Precautions:

·  The area shall be restricted from public entrance.

·   All truck shall be provided with reverse horns.

·  Only experienced and licensed operators / drivers shall be engaged for excavation and hauling.

·       Flagmen shall be provided at all exit points of the trucks /tippers near the job to be done.

·       All persons including the workmen shall be excluded from the blasting area at least 10 minutes before the blasting.

·       If night work is to be carried out the area shall be sufficiently provided with lighting.

·    The pit, which exceeds 1200mm in depth, shall be barricaded.

·    Proper access shall be provided to go down to pit excavated for structures.

·       Before going for the blasting the necessary checklist (blasting permit) needs to be verified.