Assessment of blasting operations effects during highway tunnel construction

Blasting operations are one of the fundamental parts of daily civil engineering. Drilling and blasting still remain the only possible ways of tunnelling in very adverse geological conditions. However, this method is a source of various disadvantages, the main one being tremors propagating through the geological environment which not only affect buildings, but also disturb the comfort of living in the vicinity of the source. Designing this procedure is mostly done using standardized empirical relations. This article shows the possibility of using a FEM technique in predicting blast effects. This approach is demonstrated in a simple case study on the impact of blasting operations on steel pipes

Quantification of potential macroseismic effects of the induced seismicity that might result from hydraulic fracturing for shale gas exploitation in the UK

The furore that has arisen in the UK over induced microseismicity from ‘fracking’ for shale gas development, which has resulted in ground vibrations strong enough to be felt, requires the urgent development of an appropriate regulatory framework. We suggest that the existing regulatory limits applicable to quarry blasting (i.e. peak ground velocities (PGV) in the seismic wavefield incident on any residential property of 10 mm s<sup>−1</sup> during the working day, 2 mm s<sup>−1</sup> at night, and 4.5 mm s<sup>−1</sup>1 at other times) can be readily applied to cover such induced seismicity. Levels of vibration of this order do not constitute a hazard: they are similar in magnitude to the ‘nuisance’ vibrations that may be caused by activities such as walking on wooden floors, or by large vehicles passing on a road outside a building. Using a simple technique based on analysis of the spectra of seismic S-waves, we show that this proposed daytime regulatory limit for PGV is likely to be satisfied directly above the source of a magnitude 3 induced earthquake at a depth of 2.5 km, and illustrate how the proposed limits scale in terms of magnitudes of induced earthquakes at other distances. Previous experience indicates that the length of the fracture networks that are produced by ‘fracking’ cannot exceed 600 m; the development of a fracture network of this size in one single rupture would correspond to an induced earthquake c. magnitude 3.6. Events of that magnitude would result in PGV above our proposed regulatory limit and might be sufficient to cause minor damage to property, such as cracked plaster; we propose that any such rare occurrences could readily be covered by a system of compensation similar to that used over many decades for damage caused by coal mining. However, it is highly unlikely that future ‘fracking’ in the UK would cause even this minor damage, because the amount of ‘force’ applied in ‘fracking’ tends to be strictly limited by operators: this is because there is an inherent disincentive to fracture sterile overburden, especially where this may contain groundwater that could flood-out the underlying gas-producing zones just developed. For the same reason, seismic monitoring of ‘fracking’ is routine; the data that it generates could be used directly to police compliance with any regulatory framework. Although inspired by UK conditions and debates, our proposals might also be useful for other regulatory jurisdictions

Dynamic Response and Safety Control of Newly Poured Secondary Lining Concrete under Large Section Tunnel Blasting-A Case Study of Longnan Tunnel of Ganshen High-speed Railway

The age of newly poured concrete is short, the cementation between aggregates is weak. At this time, the vibration will affect its performance. The secondary lining concrete newly poured in the tunnel is close to the work face and is susceptible to blasting vibration during construction. In order to study the safety threshold of blasting vibration velocity of newly poured secondary lining concrete in tunnels, the finite element model is established in ANSYS with the large-section Longnan tunnel project as an example. The attenuation law of vibration velocity in three directions of secondary lining under blasting load was analyzed by combining field blasting monitoring with numerical simulation, and the reliability of numerical simulation was verified. Through the numerical simulation results, the vibration velocity and von mises stress distribution of the newly poured secondary lining concrete of the tunnel are analyzed; combined with the dynamic tensile strength theory of concrete, the safety threshold of vibration velocity of newly poured secondary lining concrete of tunnel based on numerical calculation is established; through the indoor vibration test, taking the compressive strength and acoustic velocity of concrete as the indexes, the safety threshold of blasting vibration velocity of newly poured secondary lining concrete of tunnel based on shaking table test is obtained. Combined with the results of numerical simulation and vibration test, the safety threshold of blasting vibration velocity of newly poured secondary lining concrete in large-section tunnels is obtained, and the standard in this field is improved

Dynamic response and limit analysis of buried high-pressure gas pipeline under blasting load based on the Hamilton principle

For non-conservative systems consisting of elastic-plastic material, dissipative damping of a system in a dynamic environment involves two parts: (1) the dissipative energy related to the velocity of the mass point and (2) the dissipative energy associated with the strain rate. In this paper, the dynamic response of buried high-pressure gas pipeline under blasting load is studied, where, dissipation of energy is explicitly considered. The dissipative work was introduced into the Lagrange function. According to the Hamilton principle and finite element theory, a non-conservative explosion model composed of elastic and plastic materials was established to identify the dynamic response and the propagation characteristics of a detonation wave in the earth medium, where the explosion cavity with a triangle pressure time history on internal wall was used to describe the explosive stress from blasting buried gas pipeline. In the scheme of modeling, 15 cases of different explosive payloads, different distances from the explosion center and different wall thicknesses of the pipe were regarded as the generalized load were carried out. Then the specific dynamic responses of pipeline under blasting load were shown in the post processing, as well as the relationship between peak particle vibration velocity and explosion distance and payload. Using three types of limit analysis methods, the critical explosive loading, critical blasting center distance and critical wall thickness of a buried high-pressure gas pipeline under blasting loading were determined. The computational method and results in this paper could be referenced for security operation of a buried pipeline and blasting construction scheme

The stability analysis of blasting excavation in short distance on water diversion tunnel underpassing Jinduicheng Molybdenum Mine

To investigate effect induced by blasting in Jinduicheng molybdenum mine on the Dongchuan river diversion tunnel, the tunnel vibration has been monitored. According to the actual conditions, the corresponding numerical simulation is performed in FLAC3D, and dynamic response of the lining and surrounding rock of the diversion tunnel caused by blasting load is analyzed. The variation of vibration velocity in the later stage of tunnel under the action of existing blasting scale is predicted, when the vertical distance between blasting source and diversion tunnel is 50 m, the velocity of tunnel vibration reaches the critical value. The blasting scheme of mine production can be modified according to the practical distance between the explosion source and the diversion tunnel

EFFECT OF BLASTING ON THE STABILITY OF LINING DURING EXCAVATION OF NEW TUNNEL NEAR THE EXISTING TUNNEL

In recent years, experimental and numerical researches on the effect of blasting pressure on the stability of existing tunnels was widely obtained. However, the effect of the blasting pressure during excavation a new tunnel or expansion old tunnels on an existing tunnel has disadvantages and still unclear. Some researches were carried out to study the relationship of the observed Peak Particle Velocity (PPV) on the lining areas along the existing tunnel direction, due to either the lack of in situ test data or the difficulty in conducting field tests, particularly for tunnels that are usually old and vulnerable after several decades of service. This paper introduces using numerical methods with the field data investigations on the effect of the blasting in a new tunnel on the surrounding rock mass and on the existing tunnel. The research results show that not only predicting the tunnel lining damage zone under the impact of blast loads but also determination peak maximum of explosion at the same time at the surface of tunnel working

An investigation of stress wave propagation through rock joints and rock masses

Tese de doutoramento. Engenharia Civil. Faculdade de Engenharia. Universidade do Porto, Laboratório Nacional de Engenharia Civil. 201

DISPLACEMENT DISTRIBUTION MODEL OF ANDESITE ROCK MASS DUE TO BLASTING ACTIVITY USING FINITE ELEMENT METHOD

In mining operation, blasting is the most common method to disperse rocks. Blasting process does not only minimize rock fraction, but also produce less favourable energy for its surroundings. One of less favourable energies is ground vibration. The ground vibration will affect slope stability, because it will increase the driving force of the slope to collapse. Thereby, a research is needed to understand the influence of ground vibration in the slope stability. From the level of ground vibration influence on slope stability, it can be set the limit of the blasting process to keep the slope stable. Numerical method that used in this research is finite element method. One of its advantages is to accomodate time element in its calculations. Analysis results of this method are the displacements distribution model of the rock mass in static and dynamic conditions. On the track of A-A’, rock mass displacement took place at the crest of 6.6 mm (static condition) to 8.5 mm (dynamic condition). Likewise, the track of B-B’ line of 0.4 mm to 2.5 mm and line C-C’ from 0.6 mm to 2.0 mm. The safety factor value on the floor of the lines B-B ‘and C-C’ in the dynamic conditions is 1.3. This value is quite prone, so it needs a treatment at the mine slope in order not endanger workers’ safety, mining equipment and the surrounding buildings