Blast-induced ground vibration may give serious impacts on wide range of surrounding environment, so it has to be paid much attention in the blasting process. Peak Particle Velocity PPV is one of the most important parameters related with blast-induced ground vibration. The prediction of PPV is very important in order to design an appropriate blasting standard and minimize its environmental impacts. Therefore, in this paper, indoor tests, field tests and numerical simulation were conducted for assessing the effect of fragment in the rock mass on propagation behavior of ground vibration. In order to enable versatile vibration prediction at different sites with different blasting and geological condition, we investigated the differences in vibration behaviors due to blasting design, and the difference in geological condition.
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Published28 May Abstract Drilling and blasting method as a common excavation method is widely used in the underground engineering construction. However, in the complicated geological conditions, the path of blasting excavation available has limitation, and then the larger blasting vibration is produced, which influence the stability and safety of the protected structure. To effectively reduce the blasting vibration by optimizing the blasting excavation method, firstly, the site test on blasting vibration is conducted to obtain the blasting vibration data; secondly, the LS-DYNA software is applied to simulate the vibration generated by blasting in site test, based on back analysis on the blasting vibration, the mechanical parameters of the rock mass are obtained, and they are used to simulate six different types of blasting excavation method.
According to the analysis on them, the reasonable blasting excavation method is proposed to reduce the blasting vibration which can satisfy the blasting safety regulation. Introduction In the process of blasting operation, the shock waves, stress waves, and earthquake waves subsequently develop.
Due to the existence of these waves, the internal structure of the rock mass is inevitably influenced. When the vibration velocity exceeds a critical value, it can induce the formation of internal cracks in the rock mass, thus causing potential harm to the structure protected [ 1 ]. In some complicated geological conditions, the path of blasting excavation has limitation, and then the blasting source is close to some special protective structures which have strict requirements for blasting vibration.
In such condition, to prevent the potential harm of internal crack formation resulting from the blasting vibration, the blasting excavation methods need to be optimized. Consequently, the optimized blasting method can be used to reduce blasting vibration in the complicated geological conditions, which provides reference for better application of the drilling and blasting method in the engineering construction.
To judge the potential damage of the blasting vibration to the structure of the rock mass, the reasonable blasting vibration safety criterion should be adopted according to the relationship between the inner structure failure of rock mass and vibration. The research shows that the inner structure failure of the rock mass is caused by the stress waves whose peak particle velocity PPV is related to the rock mass dynamic stress and dynamic strain [ 2 — 6 ].
Therefore, single PPV is widely used as the blasting vibration safety criterion in the early engineering practice [ 7 ]. However, it is found that when the blasting vibration amplitude is much higher than the control threshold, there is no damage to the protected object. While the blasting vibration amplitude is lower than the control threshold, the damage occurs.
This is because there is no consideration of blasting earthquake wave frequency and natural frequency of the protected object. When their frequencies are equal, there is resonance phenomenon in structure, causing the failure of rock mass.
Therefore, a relatively strict safety control criterion for blasting vibration has been developed, the bidirectional indicator of the PPV and blasting vibration frequency is used as blasting vibration safety criterion [ 6 ]. In order to study the influence of vibration caused by blasting excavation on rock mass structure, the methods of site test and numerical simulation are mainly used [ 8 — 12 ].
The site test can objectively reflect the influence of blasting vibration on the rock mass structure. However, due to the nonhomogeneity and the defects of the internal structure in the rock mass, the experimental conditions are difficult to control, so that less site tests are used to study the blasting vibration.
Compared with the site tests, the numerical calculation can simulate the dynamic response problem in the complicated geological conditions, thus the numerical simulation method is widely used to analyze the blasting vibration response. Zhao et al. Onederra et al. Chen et al. When the numerical simulation software is used to study the impact of explosive explosion on the rock mass structure, the correct explosive model and the loading method of the explosion load are the key to simulate the vibration response of rock mass.
According to the detonation reaction type after explosive explosion, it is clarified into ideal detonation and nonideal detonation [ 19 — 21 ], so that the shape of explosive load induced in rock mass is not the same.
In the numerical simulation software, the explosive explosion is regarded as the ideal detonation type, and the corresponding equation of state EOS is used to simulate the effect of the explosive explosion on the rock mass. However, in the process of numerical simulation, the large deformation and distortion of the finite elements at high pressure often cause the calculation process to be terminated when using JWL EOS.
In order to overcome this problem, fluid-solid coupling method and the method of applying pressure delay function are usually used [ 30 — 36 ]. The fluid-solid coupling method needs to refine the element grid of rock mass near the boreholes, since more unit grids are required in the numerical calculation of large-scale blasting engineering, which raises the numerical calculation difficulty.
Compared with the fluid-solid coupling method, the method of applying pressure delay attenuation function can reduce the number of element grids and is widely used in numerical simulation of large-scale blasting engineering.
To effectively reduce the blasting vibration by optimizing the blasting excavation method, firstly, the site test on blasting vibration is conducted to obtain the blasting vibration data.
The mechanical parameters of the rock mass are acquired by back analysis on the blasting vibration, and they are used to simulate six different types of blasting excavation method. According to the analysis on them, the reasonable blasting excavation method is proposed to reduce the blasting vibration.
Engineering Background Fengning pumped storage power station is a first-class large-scale Water Conservancy and Hydropower Engineering. Its construction is divided into two phases that the excavation in the phase I engineering construction has been completed, and the phase II engineering construction is in feasibility study phase.
According to the geological exploration results, there are many faults near the underground powerhouse in the phase II as shown in Figure 1. Due to such restriction of complicated geological conditions and limited watercourse system layout, combined arrangement scheme in phase II engineering construction has to be chosen, and their axial directions are consistent. Since the excavation in the phase I engineering construction has been completed, the internal structure in the phase I engineering construction will inevitably be influenced by blasting vibration in the phase II engineering construction.
In such condition, on account of the strict control requirement for blasting vibration, reasonable selection for blasting excavation method should be conducted, so as to ensure the safety of the internal structure in the phase I project along with the orderly construction of the entire project. It can be seen that it is of great significance to study the optimized blasting excavation method regarding this engineering as research background, which can provide reference for the application of drilling and blasting method in engineering construction.
Figure 1 Layout plan for underground powerhouses of two phases of construction. Site Experiment When the Fengning phase II engineering construction is conducted, taking the opportunity of excavating survey tunnel in underground powerhouse, the cutting holes are dilled to carry out the cut blasting tests in the appropriate position of the survey tunnel, and the design scheme of cutting blasting experiment is shown in Figure 2.
The vibration data in the cutting blasting test and the given mechanical parameters of the rock mass are used to conduct back analysis on the mechanical parameters of the rock mass in numerical calculation.
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