New Blast Damage Criterion for Damage Prediction

There are several underground mines in India which operate in close proximity to an operating surface mine.Under such scenario,the blast induced stress waves generated due to surface blasting may be a potential source to cause instability of adjoining underground mine structures.Using seismographs,54 blast induced vibration data were recorded at various locations in the roof,floor and pillars of the underground mine at Hingir Rampur mine of Coal India Limited by synchronizing the timing of surface blasting carried at an adjacent Samleshwari opencast mine.Results of this study show that Artificial Neural Network(ANN)has better prediction potential of peak particle velocity(PPV)and damage to adjacent underground structures due to surface blasting as compared to conventional regression methods.In order to assess and predict the impact of surface blasts on underground workings,Blast Damage Factor(BDF)has been evolved.The study shows that site specific charts can predict the blast damage class at an underground location due to surface blasting for known distances and explosive charge per delay.The severe damage in case study mine site took place when peak particle velocity exceeded 162 mm/s and PPV less than 51 mm/s had no probability of damage to underground structures due to surface blasting.

Modelling of blast-induced damage in tunnels using a hybrid finite-discrete numerical approach

This paper presents the application of a hybrid finite-discrete element method to study blast-induceddamage in circular tunnels. An extensive database of field tests of underground explosions above tunnelsis used for calibrating and validating the proposed numerical method; the numerical results areshown to be in good agreement with published data for large-scale physical experiments. The method isthen used to investigate the influence of rock strength properties on tunnel durability to withstand blastloads. The presented analysis considers blast damage in tunnels excavated through relatively weak（sandstone） and strong （granite） rock materials. It was found that higher rock strength will increase thetunnel resistance to the load on one hand, but decrease attenuation on the other hand. Thus, undercertain conditions, results for weak and strong rock masses are similar. 2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.

Analysis of blasting damage in adjacent mining excavations

Following a small-scale wedge failure at Yukon Zinc＇s Wolverine Mine in Yukon, Canada, a vibration monitoring program was added to the existing rockbolt pull testing regime. The failure in the 1150 drift occurred after numerous successive blasts in an adjacent tunnel had loosened friction bolts passing through an unmapped fault. Analysis of blasting vibration revealed that support integrity is not compromised unless there is a geological structure to act as a failure plane. The peak particle velocity（PPV） rarely exceeded 250 mm/s with a frequency larger than 50 Hz. As expected, blasting more competent rock resulted in higher PPVs. In such cases, reducing the round length from 3.5 m to 2.0 m was an effective means of limiting potential rock mass and support damage.

Blast Induced Damage to Surrounding Rock Mass in an Underground Excavation

Authors have conducted experiments to measure blast induced rock mass damage at L＆T-（Singoli-Bhatwari Hydro-Power Project SBHP） Rudraprayag. Repetitive NX size rock core up to 5.0 m depth were taken from side wall and face with triple tube core barrel drill. CR （core recovery） and RQD （rock quality designation） of the rock cores is computed to evaluate effect of blasting on the surrounding rock mass. RQD and CR values for the initial one meter from the line of excavation in each case reflect maximum damage due to blast. RQD for initial one meter reduced to as high as 40% of the average RQD. The rock samples were also tested using ultrasonic techniques. Ultrasonic tests on NX size core reveal that the 2.0 m of the zone surrounding the opening are adversely affected by the tunnel excavation blasting process. The ultrasonic velocities reduce to approx. 80% of the average values in the initial 0.5 m from the excavation line.

Impact of spatially varying rock disturbance on rock slope stability

Degradation of rock mass produced by rock blasting,stress relief,and other causes is an important factor in the assessment of rock strength.Quantified as a disturbance factor,such degradation varies depending on blasting control,stress state and stress relief,and rock mass quality.This study focuses on the impact of disturbance on the safety of slopes.The disturbance in the rock mass is characterized by the geometry of the disturbed zone,its size,the magnitude,and the decaying rate with the distance away from the slope surface.A method accounting for decay of rock disturbance is presented.A study of the impact of rock disturbance characteristics on the quantitative stability measures of slopes was carried out.These characteristics included disturbed zone geometry,its thickness,the maximum magnitude of the disturbance factor,and the rate of disturbance decaying.The thickness of the disturbed zone and the maximum factor of disturbance were found to have the greatest impact.For example,the factor of safety for a 45slope in low-quality rock mass can decrease from 1.96 to 1.09 as the thickness of the disturbed zone increases from 1/4 of slope height H to the double of H and the maximum disturbance factor increases from 0.5 to 1.Uniform thickness of a disturbed zone was found to yield more conservative outcomes than the triangular zones did.The critical failure surfaces were found to be shallow for high rates of disturbance decay,and they were the deepest for spatially uniform disturbance factors.

Simultaneous investigation of blast induced ground vibration and airblast effects on safety level of structures and human in surface blasting

The significance of studying, monitoring and predicting blast induced vibration and noise level in mining and civil activities is justified in the capability of imposing damages, sense of uncertainty due to negative psychological impacts on involved personnel and also judicial complaints of local inhabitants in the nearby area. This paper presents achieved results during an investigation carried out at Sungun Copper Mine, lran. Besides, the research also studied the significance of blast induced ground vibration and air- blast on safety aspects of nearby structures, potential risks, frequency analysis, and human response. According to the United States Bureau of Mines （USBM） standard, the attenuation equations were devel- oped using field records. A general frequency analysis and risk evaluation revealed that： 94% of generated frequencies are less than 14 Hz which is within the natural frequency of structures that increases risk of damage. At the end, studies of human response showed destructive effects of the phenomena by ranging between 2.54 and 25.40 mm/s for ground vibrations and by the average value of 110 dB for noise levels which could increase sense of uncertainty among involved employees.