Application of blasting technology in rock-socketed construction of manual digging piles?

How about the application of blasting technology in the rock-socketed construction of manual digging piles? The following Zhong Da consults the bidding teacher to answer your questions for your reference.

Shenzhen Xufei Huada Garden plans to build five frame-shear structures with 22-28 floors and one underground floor. The foundation is hand-dug pile, with pile diameter Ф1.3-2.3m, a small number of pile ends are weathered into soil 1.2m, and the rest are weathered by 0.8m. * * * There are 280 piles with design pile length 12-35m, and the retaining wall is made of C25 reinforced concrete with wall thickness/kloc. Because many piles can't meet the design requirements of pile length, and the moderately weathered rock layer is thin, the pile end of the foundation pile of this project must enter the slightly weathered rock layer.

Engineering geological data show that the construction must pass through cultivated soil, slope deposit, eluvial layer, strongly weathered, moderately weathered and slightly weathered granite (a small amount of gneiss), and the groundwater level is relatively high (within 2m below the foundation pit bottom), without external precipitation design. The depth of foundation pit in this project is 3.9-6.6m. The east, south and north sides are multi-storey and high-rise buildings, and the west side is Cuizhu North Road. The shortest distance between the building and the foundation pit is 2m.

Combined with the above engineering examples, this paper discusses the blasting technology, construction organization and safety technical measures of pile tip blasting engineering encountered in the construction of manual digging piles in Shenzhen in recent years.

A, blasting technology design

Due to the narrow free face and deep working face of manual digging pile during blasting construction, the retaining wall in some sections is of poor quality and low seismic capacity when the hole is formed in the section above the moderately weathered layer. Therefore, small-diameter shallow-hole millisecond blasting should be adopted for hole pile blasting.

1, blasting parameters

The blasting parameters of pile foundation into rock are different from those of large free face tunnel, but some blasting parameters of vertical shaft development can be used for reference. The actual value should be determined according to the diameter of hole pile, physical and mechanical properties of rock, weathering degree of rock, structural composition, cohesion, cracks, especially the deformation ability and dynamic characteristics of rock, and the performance of explosives used.

(1) unit dose coefficient

The rock blasted by hole pile is moderately weathered, and the diameter of hole pile is Ф1.3-2.3m, so the surrounding area has great binding force on the blasted rock. According to the analogy and correction of blasting parameters of several high-rise buildings in Shenzhen.

(2) Hole spacing

The hand-held pneumatic rock drill is used to drill the hole pile into the rock, and the hole diameter d=32-42mm, that is, a=( 15-20)d and a = 500-800 mm.

(3) Drilling depth and circulating footage

In the blasting of small diameter hole pile into rock, the clamping force around rock is large and the utilization rate of blast hole is low. Generally, the hole depth L is 0.6-0.8 times of the hole pile diameter D, that is, L = (0.6-0.8) D. The cutting hole should be deeper than the surrounding hole100-200mm.

The hole utilization ratio η of hole pile blasting can generally reach 85-95%, so the circulating footage L ˊ = η L = (0.85-0.95) L L.

2, the hole layout

In small-diameter hole pile blasting, there are usually 3-4 cut holes and 7- 13 peripheral holes in the working face. Among them, the cut holes are conically arranged with an inclination of10-15; Most of the peripheral eyes are vertical eyes, which are evenly arranged at a distance of 100-200mm from the hole pile retaining wall. However, for the hole pile with enlarged head, its peripheral inclination angle should be 5-10 smaller than that of the enlarged head, so as to ensure the stability of surrounding rock of the enlarged head and avoid over-excavation.

3. Cost calculation

(1) Dose Q required for each circulating footage

Where: q—— the consumption of footage per cycle (g)

K-unit dose coefficient, as shown in table 1(g/m3).

D—— Driving diameter of bored pile, (m)

L- the average depth of the hole, (m)

(2) theoretical charge q of a single hole

Q—— footage consumption per cycle (g)

N—— number of holes in the working face, (pieces)

4, the distribution of charge

Generally speaking, the dose qt of the cut eye is 20-25% more than that of the peripheral eye qb.

qt=( 1.2- 1.25)q

qb=(0.85-0.95)q

Where: Qt-the charge of the cut hole, (g)

Qb-peripheral eye dose, (g)

Second, the selection of blasting equipment

1, explosive

When manual digging piles enter the blasting construction of rock section, cracks will always appear in the rock stratum, and the hole-forming wall will drip, so it is best to use explosives with good waterproof performance. In addition, in order to ensure the stability of the hole-forming wall in blasting construction, explosives with moderate explosive force should be selected. Rock emulsion explosive can be used, which has good water resistance, easy separation of cartridge and moderate power; If 2# rock ammonium ladder is selected, it is necessary to waterproof the explosive itself.

2. detonator

Electric detonator network should be used in hole pile excavation blasting, and fuse and fire detonator initiation network are strictly prohibited. The joint of electric detonator initiation network must be well insulated, and the contact should leave the mud surface. At the same time, in order to obtain better blasting effect and protect the stability of retaining wall, the second delay detonator used in millisecond blasting should be selected, and the peripheral hole lags behind the cut hole by more than 0.1s.

3. Sponsor

MFJ- 100 domestic capacitor detonator can be selected, and the series initiation capacity can reach 100 rounds, the charging time is 7- 10s, the power supply time is 3-6ms, and the power supply is 1# battery.

The number of detonators detonated by hole pile blasting is about 20 rounds. Detonators are required to be small in size, easy to carry and simple in structure. MFJ- 100 or JZDF-300-B domestic capacitor detonators can be selected.

Third, the construction management and organization

In the process of manual digging pile construction, there are many workers and overlapping processes. In order to ensure the safety and smooth progress of rock blasting, the following procedures should be adopted for organization and management:

1, construction management

(1) under the guidance of the project department, the blasting operation headquarters is established, which is composed of blasting director, technical director, safety officer and team leader, and each professional type of work holds relevant certificates.

(2) Establish a centralized sending and receiving system for blasting equipment, and distribute materials according to workload. After the completion of the construction on duty, the surplus blasting materials should be handed over to the distributing personnel for recycling in time, so as to achieve centralized distribution, unified production, unified recycling and centralized storage, and strict registration procedures to prevent the blasting materials from flowing into the society.

(3) Arrange the operation time and blasting time, and announce the blasting time to the surrounding residents.

(4) The general manager of blasting is responsible for the construction organization, personnel deployment and production arrangement, and is fully responsible for safety and production.

(5) The technical director shall be responsible for the technical work in the construction process, supervise the safety and quality, and comprehensively guide the implementation of blasting work.

(6) The safety officer is responsible for on-site safety inspection, arrangement and inspection of blasting alert.

(7) The blaster is responsible for initiation.

2, the construction organization

Mixed operation method and professional operation method are usually used in hole pile blasting, and professional operation method is often used in Shenzhen area. That is, the professional team is engaged in blasting work, responsible for drilling, hole cleaning, charging, connection, blasting, ventilation, and handling misfires and squibs; During drilling, other operation groups are responsible for slag removal, slag discharge, hole formation and wall protection.

Fourth, safety technical measures

1, blasting earthquake control measures

Blasting the hole pile into the rock may affect the temporary support of the pile and its adjacent hole piles and the poured pile core concrete. In Shenzhen area, C25 reinforced concrete is generally used for hole pile retaining wall, which has high early strength and good shape. Generally, after 5 days of concrete pouring for the retaining wall, blasting construction can be carried out without destroying the retaining wall. At the same time, the hole pile blasting operation shall not be carried out within 20m of the hole pile whose core concrete has been poured, but the core concrete has not reached the age, so as not to crack the core concrete that has not reached the design strength.

2. Control measures for blasting slungshot

The blasting faces of hole piles are all below the surface 10m, the hole pile mouth is covered with bamboo basketry or wooden formwork, and sandbags are pressurized to prevent the blasting flying stones from flying out of the ground.

3, blasting gun smoke elimination measures

The gun smoke produced by explosive blasting is toxic and harmful gas, so it must be exhausted by mechanical forced ventilation. At the construction site, blower can be used for forced ventilation and smoke exhaust at the wellhead, and air compressor conduit can also be used for ventilation and smoke exhaust at the bottom of the well. Ventilation and smoke exhaust time shall be subject to the blasting smoke exhaust time of the working face.

4, blasting leakage prevention measures

Special attention should be paid to leakage prevention when charging the hole pile into the rock, and all electrical equipment in the hole pile should be hoisted to the ground before charging. When charging, the detonator crural line should be short-circuited. When connecting the blasting bus, the joint should be well insulated. It is forbidden to mop the floor and contact mud. Blasting operation should be stopped in thunderstorm weather.

5. Handling of fire

After the hole pile blasting operation is completed and the gun smoke in the hole pile is removed, the inspectors should go down to the working face to check the misfire and deal with it in time according to the blasting regulations. In addition, if misfire is found during slag cleaning, it should be reported to the project department in time, and professionals should be arranged to deal with it. Non-professionals are forbidden to deal with it privately.

6, blasting equipment safety management measures

Blasting equipment belongs to dangerous goods and should be strictly managed.

(1) Strict collection, distribution, use and recycling system of blasting equipment;

(2) The on-site blasting equipment shall be clearly classified, packed in wooden cases, locked and kept by special personnel, and mixed loading is strictly prohibited. Handle with care when using and transporting, and collision is strictly prohibited; The detonator should be short-circuited before connecting the bus to avoid contact with the charged body.

Verb (abbreviation of verb) construction effect

In Hua Dayuan, the manual digging pile was blasted into the rock section, and the rock penetrated 2.0-5.3m, which achieved high safety, fast progress, small overbreak of retaining wall and nearly 100% blast hole utilization rate. 280 piles were constructed in 5 buildings, and all blasting workload was completed in 25 days.

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