Rock excavation by drilling, charging and blasting is called drilling and blasting for short.
In the early days, this method developed from manual drilling and hammering, detonating individual explosive charges one by one, to drilling with a drill rig or dobby, and applied millisecond blasting, presplitting blasting, smooth blasting and other blasting technologies.
Before construction, according to geological conditions, section size, supporting methods, time limit for a project requirements, construction equipment, technology and other conditions, the excavation method is selected.
Construction process flow
(1) Before drilling, the center line of the section must be placed horizontally, and the contour line should be drawn on the excavation surface, and the hole position should be arranged according to the drilling and blasting parameter diagram.
(2) The depth, angle and spacing of holes shall be determined according to the requirements of drilling and blasting parameters.
The error between cut eye spacing and fundus spacing is not more than 5cm, the error between auxiliary eye spacing and row spacing is not more than 5cm, the error between peripheral eyes along the contour line of tunnel design section is not more than 5cm, the slope of peripheral eyes is not more than 5cm/m, the fundus is not more than the contour line of excavation section 10cm, and the maximum error is not more than 15cm.
The line spacing error from the inner eye to the peripheral eye should not be greater than 5 cm. When the hole depth exceeds 2.5m, the inner ring hole and the surrounding hole should adopt the same slope.
(3) Cut holes are arranged at the lower center of the excavation section to break the rocks at the bottom and reduce flying stones.
The peripheral blast holes should be arranged along the design excavation contour line, and the auxiliary holes should be staggered and evenly arranged between the peripheral holes and the cut holes, and drilled perpendicular to the excavation surface to ensure that the size of the blasted ballast blocks is suitable for the requirements of ballast loading.
At the two corners at the bottom of the excavation section, auxiliary eyes should be arranged reasonably, and the charge should be increased appropriately to eliminate the dead angle of blasting.
At the top of the section, the charge should be controlled to prevent overbreak.
(4) Before charging, the soil and stone chips in the hole should be blown clean.
After charging, the hole should be plugged with stemming in time.
The occlusion length of peripheral eyes should not be less than 20cm. When presplitting blasting is used, it should be blocked from the top of the cartridge, not just at the hole.
(5) Strictly control over-excavation and under-excavation in drilling and blasting construction.
When the rock stratum is complete, the compressive strength of the rock is greater than 30Mpa, and it is confirmed that the stability and strength of the lining structure will not be affected, it is allowed to underdig individual protruding parts of the rock, and the uplift amount shall not be greater than 5cm.
Underexcavation full-face excavation method is strictly prohibited above the arch foot1m.
1, full-face excavation method, one-time drilling and blasting of full-face excavation section, excavation and molding, and full propulsion.
When the tunnel is high, it can also be divided into upper and lower parts to form steps, synchronous blasting and parallel excavation.
When geological conditions and construction conditions permit, full-face tunneling method is preferred.
2, pilot tunnel method, first part of the excavation section as a pilot tunnel, and then gradually expand the excavation of full-face tunnel.
This is a construction method with small and medium-sized machinery as the mainstay when the tunnel section is large and it is difficult to adopt full-face excavation due to geological or construction conditions.
The pilot tunnel section should not be too large to meet the requirements of ballast machinery, ballast truck transportation, pipeline installation and construction safety.
The free surface can be increased when the pilot tunnel is excavated and blasted, which is beneficial to find out the geological and hydrogeological conditions of the tunnel and create conditions for tunnel ventilation and drainage.
According to geological conditions, groundwater conditions, tunnel length and construction conditions, determine the lower pilot tunnel, upper pilot tunnel or middle pilot tunnel.
After the pilot tunnel excavation, the expansion excavation can be carried out after the full length of the pilot tunnel excavation, or it can be operated in parallel with the pilot tunnel excavation.
3, the division excavation method, in the case of poor stability of surrounding rock, generally need support, excavation of large section of the tunnel, you can first dig a part of the section, timely support, and then gradually expand the excavation.
When excavating a tunnel by drilling and blasting, it is generally regarded as a tunnel excavation cycle from the first drilling sequence, through the processes of charging, blasting, ventilation, smoke dispersion, slag discharge and so on, to the end of the second drilling sequence.
Try to compress the operation cycle time and speed up the excavation.
In 1980s, some countries used the drilling and blasting method to excavate tunnels with a cross-sectional area of about1100m3 in medium-hard rocks, and the average tunneling speed was about 200m per month.
In the Lubuge Hydropower Project in China, a diversion tunnel with a diameter of 8.8m was excavated, with an average monthly footage of 23 1m and a maximum monthly footage of 373.7m
Survey information
A hydropower station located in the downstream mainstream is a low-head radial power station, which is a riverbed powerhouse with a designed installed capacity of 3× 65438+800,000 KW. In the flood season, there is a dam overflow problem in hydropower stations. The operation shows that the tailwater level of the workshop is higher than the designed original tailwater level, which seriously affects the output of the unit and the power generation benefit. After analysis and demonstration, it is planned to carry out tail water dredging transformation.
Project and scope of work: this dredging project consists of two parts: the concrete guide wall on the right side of the tailrace channel is removed, with a length of about 45m, a top elevation of _52.0m and a thickness of 1.5m, and it is divided into two sections, each of which is about 22.5m long. Demolition of the downstream section of expansion joint to the elevation of _ 45.0m: Dredge the channel bottom in the guide wall and the riverbed in the range of about 100m downstream of the guide wall. The dredging width is 45 ~ 70 m from top to bottom, and the elevation of the bottom after dredging is about _ 43.0 ~ 42.5m, but not higher than _ 43.0m.. ..
Most of the dredged riverbeds in this section are slate, and some are sandy pebbles.
Construction requirements of blasting dredging project: During the construction period of this project, due to the overhaul of Unit 2 in Zheng Zhi Power Plant, water was not injected into the runner of the unit. Therefore, the possible influence of underwater blasting construction on the maintenance gate of the unit should be considered in the design.
Improving blasting efficiency and reducing the destructive influence of blasting vibration and flying stones on nearby buildings during construction are the keys to affect the construction progress and safety.
Underwater blasting construction
According to the viewpoint of information theory, the experience of similar projects in the past and the strength of underwater drilling and blasting machinery and equipment put into this project, the drilling and blasting method is selected for underwater blasting construction.
The construction process flow is as follows: blasting design → anchoring the drilling platform → moving the machine to position → determining the hole depth → protecting the hole → drilling → washing the hole → measuring and checking the hole → charging → connecting → platform evacuation → initiating signal → initiating and vibration monitoring → checking the blasting effect → demolition.
This paper introduces several main technical measures in construction: the design of drilling platform; Buoy simple lifting drilling and blasting platform ship (16m×6m).
The working platform adopts steel floating box structure, and the distance between two floating boxes is 5m.
The inner diameter of the buoy is φ 1 100 mm, and the single length is 12m. After deducting the weight of buoy and platform steel structure, the buoyancy is about 15t.
The two pontoons are welded by channel steel and I-beam to form a hull bearing the drilling rig and auxiliary equipment.
Down-the-hole drilling rig is hinged and fixed on the platform through scaffolding steel pipes to form a drilling platform.
Both sides of the pontoon bridge protrude outward by 0.5m, and two small platforms are welded, which can be used by four KQ- 100 DTH rigs.
In order to speed up the positioning of the drilling rig, the drilling rig platform can slide and shift along the groove rail.
After investigation and positioning, eight iron anchors and anchor cables with the height exceeding 100m were used, which were towed to the blasting area by a small motorized barge, and then accurately positioned with the help of manually shrinking anchor cables on board.
Manually control 5t chain block to sink four columns (240mm) into the river bottom, so that the drilling platform basically emerges from the water. At this time, the load on the whole drilling platform is completely supported on four steel pipe strings.
During drilling construction, it is not affected by wave fluctuation to ensure drilling quality.
When the drilling platform is displaced, the column should be retracted to make the drilling platform float on the water. At this time, the platform should be moved to the next drilling position by pulling the anchor cable.
Drilling equipment and its selection
(1) Selection of drilling equipment
Due to underwater drilling and blasting, as well as the water surface, KQ- 100 DTH drilling rig was selected for drilling, with a diameter of 90 mm.
(2) Drilling subsidiary bodies
Vertical drilling is used in underwater blasting.
KQ- 100 DTH drilling rig is selected as the drilling tool, and the cartridge is 70mm, and the cartridge with good waterproof performance is selected.
In order to ensure the charging and hole cleaning after drilling, drill through the overburden (silty soil layer) and drill into the bedrock to a certain depth before drilling, then lower the drill pipe in the casing and drill holes in the bedrock. The lower end of the casing is an annular 1 hollow casing (drilling diameter φ 1 17 mm).
In order to ensure that the excavation reaches the design depth, the drilling hole should have a certain over-drilling depth, which is 1.0 ~ 1.5m, that is, the actual drilling depth is1.5m ~ 4.5m. ..
(3) Variety selection.
Select the one with good waterproof performance and put it into 80mmPVC pipe.
"Double height" for non-power use.
The detonation network adopts a millisecond delay composite detonation network with high in-hole and low in-hole to ensure the accuracy of detonation transmission.
To ensure safety, fill the blasting hole with coarse sand to prevent blasting.
The orifice of each blast hole is sealed and covered with sandbags, which are floating balls exposed to the water. Its functions are as follows: (1) is used as the mark of the position of the blast hole, which is convenient for centralized charging; (2) After charging, it is convenient to connect the detonating needle wires and form a detonating network.
(4) Place nonel tube.
Put the floating tire into the water to make it float on the water surface, tie the nonel tubes in the same row on each boat to a tire, and connect the nonel tubes on the tire to the same section in order from back to front. In order not to make other nonel tubes burst by booster, we should put the nonel tube on the floating tire and wrap it tightly with foam box to avoid floating on the water and drifting with the waves.
safety detector
The hazards caused by underwater blasting include blasting earthquake effect, underwater shock wave effect, air shock wave effect and water surface wave effect.
Blasting effect
After blasting, the rock is broken perfectly, and the underwater slag removal is smooth. After inspection, it has no influence on the gate and surrounding buildings.