Weak rock tunnel design of blasting technology
Abstract: This paper mainly introduces the new forest economy highway tunnel Cheng Shao geological and hydro-geological conditions of the tunnel
sections in the soft rock blasting techniques, analysis of smooth blasting
design and construction safety measures, and the design of drilling and blasting method Construction of the organization provide a reference for similar projects.
Key words: weak rock; tunnel blasting; design; construction technology
1 Project Overview
The new tunnel is located WANGWU forest mountains, tunnels, split tunnel, length 670m. The tunnel is located in the new forest Wangwu Township Primary School near the end of an erosion of denuded mountain
hilly area (?). The tunnel axis through the Department, the maximum altitude of about 578 m, the maximum relative height difference of about 55m. Mountains to the north-south direction. Xin-Lin JOINTED rock tunnel
area general development, the tunnel area surrounding rock mainly
developed occurrence of 90 ? ? 88 ?, 60 ? ? 85 ?, 200 ? ? 28 ?,
183 ? ? 40 ? of the four sets of joints, joint-ping Straight-based,
multi-closed, joint density of 2 ~ 5 / m, local density of up to 7 / m. Rocks inside the tunnel section of sandstone, silty mudstone, less wind resistance capabilities. Into the east portal of the natural slope tilt, terrain slope from 200 to 400, in order to slope topography, surface Qel thinner, some missing, lithology for the sub-clay, is a V-class rock, the
underlying bedrock of the Triassic 2 Horse Camp Group sandstone, silty mudstone, strong weathering thickness of about 1.5m, poor stability of surrounding rock, BQ <250, belonging to grade ? rock.
The tunnel through the sandstone weathered, weak weathered layer,
buried shallow groundwater is not developed, mainly bedrock fissure water, water than the poor
Two weak rock tunnel blasting excavation plan was finalized
In the excavation process should be based on rock type (or level)
to adopt a reasonable form of blasting parameters and undercutting, blasting materials, detonating mode, charging structure and the plug material to minimize blasting of rock and neighboring cavern of the disturbance and destruction, and strictly control the under-excavation and
blasting vibration speed, the full protection of the self-supporting
ability of surrounding rock. The previous chamber blasting on adjacent chamber blasting vibration velocity should be controlled at 5cm / s within.
Three drill and blast design
3.1 Drilling and Blasting Design
The overall design idea is to use smooth blasting arch, side-wall
use of pre-split blasting, the core use of controlled blasting, undercutting the integrated use of throw blasting controlled blasting.
According to excavation methods were used two kinds of half-sections and
full-face blasting methods, using non-electric millisecond detonator
blasting network. Grade ? ? level and right semi-section of rock
blasting step approach, in order to reduce the disturbance of surrounding rock blasting, excavation cross-section multi-Dan non-electric blasting
caps to network design.
Characteristics of rock under this project, ? grade rock for the
weak siltstone, with parallel hole cut slot, strabismus undercutting mix. Used is less than 2m deep eyes askance undercutting.
In the weathered, broken more serious geological conditions, the appropriate use of smooth blasting or drilling eye contour method, or set aside smooth layer of smooth blasting excavation trimming.
3.2 Bottom eyes drilling and blasting requirements
? the floor is divided into paragraphs, separated from eye-
detonation, which can reduce the floor eye-detonation in the same
paragraph, the amount of explosives together and changed the bottom line of eye-resistance direction, would actually narrow the eye bottom line of resistance, which can be reduce the floor eye-bursting intensity generated
by an earthquake.
? initiation sequence: undercutting the inner eye ? boring eyes
? eyes ? eyes ? bottom peripheral eye.
? Select the paragraphs when the detonators are three: First, a reasonable interval between paragraphs; second, with a porthole of the loading dose should be less than the maximum permitted single-stage
loading dose; third, the bursting of the preceding paragraph as far as possible for the post-blasting to create a good overhead surfaces.
3.3 The selection of blasting parameters
By testing to determine if blasting blasting parameters, smooth blasting parameters
Blasting parameters on the selected Note:
? Soft Rock Tunnel smooth blasting the relative distance (E / W) should adopt the table minimum.
? Charge concentration (q) in accordance with No. 2 rock ammonium nitrate explosives to consider, when the change should be carried out using other explosives, filling, conversion targets mainly Brisance and burst strength (average). Reposted elsewhere in the paper for free
? The smooth blasting, the blasting vibration velocity should be controlled in: the hard rock 15 cm / s, soft rock 5 cm / s. Require blasting vibration velocity is based on face to leave the dug-hole inter-1
~ 2 times that obtained at the measured, it can be obtained with the speed sensor signal amplification by seismometers, in the light oscilloscope records are. After the smooth blasting, excavation of rock surface should not have significant knock cracks.
3.4 Smooth soft rock blasting equipment, the choice of
? undercutting eyes, boring eye use emulsion explosive.
? around the eyes use a low detonation velocity, low-density,
high-explosive strength, small diameter, light and good booster
? initiation of non-electric detonators selected sub-millisecond
3.5 Parameter selection and drilling around the eyes eye required
Selection of parameters around eye
Experience around the eye-parameter formula:
Pitch: E = (8 ~ 12) d (d is borehole diameter), cm;
Resistance line: W = (1.0 ~ 1.5) E, cm
Charge concentration: q = 0.04 ~ 0.19Kg / m.
3.6 Design and Construction Blast Hole
? hole layout. First layout undercutting eyes, around the eyes, and then arranged bottom eye, inner eye, two sets of eyes, the final layout of tunneling eyes, boring eye evenly arranged around the inner eye to eye spacing interval of 1.5 times the resistance line spacing 0.7-fold.
According to experience, does not cause the higher the floor the more explosive, backplane design the next interpolation point of view Eye; two sets eyes, eyes boring than the bottom eye is also an appropriate encryption, to ensure that, taking into account the first part of the eye blasting stone ballast pile on top, reduce the blast load.
? blast-hole depth L. Weak rock tunnel loop footage as the eyes are usually deep undercutting eyes with 10 ~ 20%. In weak rock, according
to experience, usually in the 1.0 ~ 1.5m should be considered within the scope of the new forest and blasting the tunnel under the effect of the progress, select borehole depth of 1.5m.
? The number of blast-hole N. In the small-diameter (35cm ~
42cm) borehole, excavation-off area of 5 ~ 50m2 conditions, the number of eyes drilling unit area is 1.5 ~ 4.5 / m2. In the calculation Note: soft rock tunnel blast-hole charge an average coefficient of n about 0.2 to 0.4 within the framework; unit consumption of explosives, blasting in the large section and small guide hole blasting is different from the use of a
smooth blasting, blast-hole number should increase by 20 % or so.
? smooth blasting hole loading dose calculations.
- Single-hole loading dose, g;
- Smooth blasting borehole filling coefficient;
- Borehole depth;
- Explosive density, g/cm3;
- Explosives diameter, cm;
Burst assembly dose calculation of: (Kg)
- Excavation basal area, m2;
- Perforation depth, m.
Drilling operations and charge structure and the way to plug the implementation in accordance with relevant construction standards.
4 blasting effect
Soft rock tunnel in the new forest (?, ? grade) construction
blasting, to optimize the drilling and blasting design, from the straight groove hole cut into the cross-eye cross-eye undercutting undercutting
method and combination of methods to optimize the blasting results are
obvious, linear average overbreak 13.2cm, embrasure utilization reaches 90% ~ 95%, side-wall of smooth blasting borehole preservation rate 62%, using pre-splitting blasting up to 80% (? grade rock), almost every crop
footage shot each contributed 1.5 m (hole depth 1.7m). This effect is great economic value. Reposted elsewhere in the paper for free download http://
? weak rock tunnel blasting construction, the construction step method should be adopted on the explosion drill design, the first field test, and then sum up constantly, constantly perfect.
? For the level of parallel-shaped rock with a good pre-
splitting blasting results in the tilt-like layered rock in the
implementation of smooth blasting effect is good.
? For the weak rock tunnel drilling and blasting method of construction is a long-term development of the construction method can be used engineering analogy method and field test the Combination of options blasting parameters, we must constantly be summed up.
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 Wang Meng-shu. SHALLOW TUNNEL EXCAVATION METHOD Design - Construction
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 Qi prison. Tunnel of modern blasting technology [M]. Beijing: China Railway Publishing House, 1995.
 JTJ042-94, highway tunnel construction technical specifications [S]. Reposted elsewhere in the paper for free download http://