• Tunnel and Underground Space
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• v.29 no.6
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• pp.523-531
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• 2019

In the applications of rock mechanics or rock engineering including drill and blast, drilling and mechanical excavation, the fracture toughness is an important factor. Several methods have been proposed to measure the fracture toughness of rocks. In this study, wedge splitting test specimen which is prepared with ease and tested under compression loading was used to obtain mode I fracture toughness of rocks. The equation of stress intensity factor through numerical analysis is proposed from the stress state of crack tip considering both vertical and horizontal loads due to the vertical load acting on the wedge. The validity of the wedge splitting test method was confirmed by comparing the mode I fracture toughness values obtained by the GD and SENB test specimens.

• Explosives and Blasting
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• v.31 no.2
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• pp.14-24
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• 2013

The most effective way of the rock removing works in the downtown area is to removing rocks by splitting the rock by blasting with small amount of explosives in the hole. However environmental factors not only limit the applications but also increase the forbidden area. As this is a distributed multi-stage blasting method and to reduce vibration by applying the optimized precisioncontrol-blasting method, it is applicable in all situations. The process is to fix the stemming-help plastic sheet to the hole entrance when stemming explosives and insert detonator and explosive primer with same delay time, two or three sets. This method is more efficient in the downtown area where claims and dispute from vibration are expected. This method is easily usable by designing blast pattern even in the area where delay time blasting is difficult after multi-stage explosive stemming due to short length of blast hole (1.2~3.0m) and there is no detonator wire shortage or dead-pressure.

• Tunnel and Underground Space
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• v.10 no.4
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• pp.516-525
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• 2000

Recently, the demand for pollution-free demolition work of old reinforced concrete and steel structure has rapidly increased as the redevelopment of urban area has been accelerated. This study deals with linear shape charges for explosive jet cutting on steel structure. We have tested material and shape of steel structure, characteristics of thickness and strength, shape of linear shape charges, type of shape charges, cumulative charges, type of liner, stand-off distance, detonation method. effect of sound and vibration by air blast in explosive jet cutting method. So, We developed linear shape charges in order to take advantage of optimum explosive jet cutting condition. Shape charges were made of PETN explosives. We obtained the experimental formula to decide the amount of explosive needed for thickness of steel structure plate. There are prospects for application of the explosion curving technology under the open space conditions for dismantling the steel structure and steel bridge, scrapped old boats, which are going out of service.

• Explosives and Blasting
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• v.8 no.1
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• pp.3-16
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• 1990

The cautious blasting works had been used with emulsion explosion electric M/S delay caps. Drill depth was from 3m to 6m with Crawler Drill $\varphi{70mm}$ on the calcalious sand stone(sort-moderate-semi hard Rock). The total numbers of feet blast were 88. Scale distance were induces 15.52-60.32. It was applied to propagation Law in blasting vibration as follows. Propagtion Law in Blasting Vibration $V=K(\frac{D}{W^b})^n$ where V : Peak partical velocity(cm/sec) D : Distance between explosion and recording sites (m) W : Maximum Charge per delay-period of eighit milliseconds or more(Kg) K : Ground transmission constant, empirically determind on th Rocks, Explosive and drilling pattern ets. b : Charge exponents n : Reduced exponents Where the quantity $D/W^b$ is known as the Scale distance. Above equation is worked by the U.S Bureau of Mines to determine peak particle velocity. The propagation Law can be catagrorized in three graups. Cabic root Scaling charge per delay Square root Scaling of charge per delay Site-specific Scaling of charge per delay Charge and reduction exponents carried out by multiple regressional analysis. It's divided into under loom and over loom distance because the frequency is verified by the distance from blast site. Empirical equation of cautious blasting vibration is as follows. Over 30m----under l00m----- $V=41(D/3\sqrt{W})^{-1.41}$ -----A Over l00m-----$V= 121(D/3\sqrt{W})^{-1.66}$-----B K value on the above equation has to be more specified for furthur understang about the effect of explosives, Rock strength. And Drilling pattern on the vibration levels, it is necessary to carry out more tests.

• Tunnel and Underground Space
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• v.28 no.5
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• pp.457-475
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• 2018

For increase of reality in numerical analysis, a blasting vibration waveform obtained from field blast operations has been directly used for input parameters of dynamic analysis in the form of vibration velocity. A numerical model was built considering the geological characteristics of underground limestone opening as well as the mining stages in this opening, and the effect of blast operations on stability of underground limestone opening was investigated by dynamic numerical analysis. The adequacy of applying the real vibration waveform to dynamic analysis has been approved from the preliminary analysis, and the dynamic numerical analysis results show that the continuous mining operation can cause the collapse of roof in openings and the active yield zone around openings. Therefore, the additional reinforcements should be applied for ensuring the stability of underground limestone openings.

• Journal of the Korean Professional Engineers Association
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• v.24 no.6
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• pp.97-105
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• 1991

The cautious blasting works had been used with emulsion explosion electric M/S delay caps. Drill depth was from 3m to 6m with Crawler Drill ø70mm on the calcalious sand stone (soft-moderate-semi hard Rock). The total numbers of fire blast were 88 round. Scale distance were induces 15.52-60.32. It was applied to propagation Law in blasting vibration as follows. Propagation Law in Blasting Vibration (Equation omitted) where V : Peak partical velocity(cm/sec) D : Distance between explosion and recording sites(m) W : Maximum Charge per delay-period of eighit milliseconds o. more(kg) K : Ground transmission constant, empirically determind on the Rocks, Explosive and drilling pattern ets. b : Charge exponents n : Reduced exponents Where the quantity D / W$^n$ is known as the Scale distance. Above equation is worked by the U.S Bureau of Mines to determine peak particle velocity. The propagation Law can be catagrorized in three graups. Cubic root Scaling charge per delay Square root Scaling of charge per delay Site-specific Scaling of charge per delay Charge and reduction exponents carried out by multiple regressional analysis. It's divided into under loom and over 100m distance because the frequency is verified by the distance from blast site. Empirical equation of cautious blasting vibration is as follows. Over 30 ‥‥‥under 100m ‥‥‥V=41(D/$^3$√W)$\^$-1.41/ ‥‥‥A Over 100 ‥‥‥‥under 100m ‥‥‥V=121(D/$^3$√W)$\^$-1.56/ ‥‥‥B K value on the above equation has to be more specified for furthur understang about the effect of explosives, Rock strength. And Drilling pattern on the vibration levels, it is necessary to carry out more tests.

• Tunnel and Underground Space
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• v.25 no.1
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• pp.46-55
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• 2015

A water tube with detonating cord was devised to control the blast dust. Water diffusion experiments with different detonating cord positions were conducted during the series of experiments to optimize the design parameters of the tube. Images from high speed camera were analyzed to evaluate the results. AUTODYN program was adopted to simulate the diffusion process of water and compared with the images. Diffusion of water shows cross flow in case of external charge while the internal case shows radial flow. A bubble ring was formed during the numerical analysis of internal charge case as occurred in underwater blast. An additional bubble ring was formed by the reflection pressure from the ground. And the Weber number was determined as sufficient for spray atomization performance of the water tube.

• Tunnel and Underground Space
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• v.24 no.1
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• pp.97-109
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• 2014

In order to identify the characteristics of the propagation depending on delay time (20, 25 ms) and priming location (top priming, middle priming, bottom priming), test blasts were carried out a total of 4 times using different spacing, burden, drilling length, charge per delay and was derived the formula to predict blast vibration. This study investigated the characteristics of vibration by analysis of the nomogram and prediction of Peak Particle Velocity (PPV) from delay time and priming location by the formula to predict ground vibration. And it analyzed the trends of vibration increase by standards charge 0.5, 1.6, 5, 15 kg. Standards charge is "Blasting design and construction guidelines to road construction" by the Ministry of Land, Infrastructure and Transport. Depending on the charge in favor of vibration control method is proposed. Thus, when the design was to be used as a variable.

• Explosives and Blasting
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• v.9 no.4
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• pp.3-12
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• 1991

The cautious blasting works had been used with emulsion explosion electric M /S delay caps. Drill depth was from 3m to 6m with Crawler Drill 70mm on the calcalious sand stone (soft-moderate-semi hard Rock) . The total numbers of feet blast were 88. Scale distance were induces 15.52-60.32. It was applied to Propagation Law in blasting vibration as follows .Propagtion Law in Blasting Vibration V=k(D/W/sup b/)/sup n/ where V : Peak partical velocity(cm/sec) D : Distance between explosion and recording sites(m) W ; Maximum Charge per delay -period of eight milliseconds or more(Kg) K : Ground transmission constant, empirically determind on the Rocks, Explosive and drilling pattern ets. b : Charge exponents n : Reduced exponents Where the quantity D/W/sup b/ is known as the Scale distance. Above equation is worked by the U.S Bureau of Mines to determine peak particle velocity. The propagation Law can be catagrorized in three groups. Cabic root Scaling charge per delay Square root Scaling of charge per delay Site-specific Scaling of charge delay Charge and reduction exponents carried out by multiple regressional analysis. It's divided into under loom and over loom distance because the frequency is varified by the distance from blast site. Empirical equation of cautious blasting vibration is as follows. Over 30m--under 100m----V=41(D/ W)/sup -1.41/-----A Over l00m---------V=121(D/ W)/sup -1.56/-----B K value on the above equation has to be more specified for furthur understand about the effect of explosives. Rock strength, And Drilling pattern on the vibration levels, it is necessary to carry out more tests.

• Tunnel and Underground Space
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• v.31 no.1
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• pp.1-9
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• 2021

Recently, the development of underground space has been accelerated with rapid urbanization, and it is significantly important for safe construction to accurately understand the geological conditions of the section when excavating rocks. In this paper, a boring alignment tracking and geological exploration system have been developed to identify the geological conditions beyond the excavation face by utilizing a MSP method that bores a large empty hole to reduce blast-induced vibration. The major advantage of the proposed exploration system is that we can obtain the ground condition of 50 m ahead of the excavation face through exploration along blast cut-holes drilled for the NATM tunnel construction. In addition, we introduce several case histories regarding the assessment of the geological conditions beyond the tunnel face by monitoring the inside of large empty holes using the proposed hole exploration system.