Comparison of approximate assessments of the harmfulness of mining shocks using ground and building foundation vibrations

3.1. Brief presentation of the mining intensity scales applied in the USC area

GSI-GZW_KW-2012 scale (denoted No. 1) is an empirical-measurement scale. This scale was used in the USC region up to 2017 year for monitoring and assessing the influence of mining- related ground vibrations both for structures and human percebility of vibrations [11, 13]. The scale refers to buildings and very important underground structures (e.g. water, gas, sewage network) whose failure-free functioning provide the safety of residents. Scale No. 1 consists of two versions. The basic is a velocity version. Acceleration version of the scale is treated as auxiliary. The scale No. 1 associates values of the ground parameters with macro-seismic effects in structures. Impact assessment of surface mining-related vibrations is made using the maximum value of the resultant of ground velocity $PG{V}_H$ – (velocity version of the scale) and the maximum value of the resultant ground acceleration calculated using the filtered components of the horizontal vibration in the band to 10Hz ($PG{A}_{H10}$) in auxiliary version of the scale. The second parameter used in impact assessment is duration of the intensive phase of vibrations $t_{Hv}$ and $t_{Ha}$ for the velocity and acceleration, respectively [11, 13, 14]. Two versions of GSI-GZW_KW-2012 scale (No. 1) are shown in Fig. 2.

Fig. 2The GSI-GZWKW-2012 scale in: a) velocity, b) acceleration versions

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Scale No. 1 allows to assess the influence of mining-related ground vibrations from not noticeable with no effect on buildings (level 0 of vibration intensity) up to the level IV in which structural damages in buildings may occur. The scale No. 1 introduces five levels of vibration intensity listed in Table 1. Given levels of vibration intensity are attributed to damage that may occur in structures. The scale No.1 refers to new buildings (in good technical condition) and old ones referring to building usually in poor condition.

The GSIS-2017 scale (denoted No. 2) is another version based on the previous GSI-GZW_KW-2012 scale. The results of registration and observation of several strongest shocks occurring in the USC area in the years 2015-2016, with seismic energies exceeding 10⁸ J and the maximum values of vibration velocity $PGV$ > 0.05 m/s, and acceleration with $PGA$ > 1.0 m/s², were additionally included in the scale. In the scale, the technical condition and type of the building structure for its dynamic resistance were taken into account.

On the GSIS-2017 scale (No. 2), the impact of the shock is also expressed by measuring the level of seismic intensity. These levels are classified based on the recorded and/or predicted free-field vibration parameters. These parameters are correlated with macroseismic observations in buildings described by levels of vibration harmfulness. The parameters of the classification are the same as parameters used in the case of GSI-GZW_KW-2012 scale (No. 1).

The GSIS-2017 scale distinguishes 7 levels of seismic intensity (from 0 to VI), which were assigned the effects of free-field vibrations on buildings and linear underground infrastructure and human percebility on vibrations and the inconvenience of using buildings, in correlation with parameters of free-field vibration (see Fig. 3). The GSIS-2017 scale gives the level of vibration intensity (IV-VI) at which structural damage to buildings may occur together with a description of damage to buildings and the level of harmfulness of vibrations – comp. Table 2. It should be emphasized that VI level has not been verified by measurement.

Fig. 3The GSIS-2017 scale in: a) velocity, b) acceleration versions

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The GSIS-2017 scale includes the following types of buildings with: traditional and traditional-improved construction, i.e. buildings made of brick or other small-size elements, having wall bearing systems; concrete and/or reinforced concrete bearing structure; frame buildings of reinforced concrete or steel construction.

In addition, the scale includes: effects of vibrations on buildings in poor technical condition and subjected to the influence of continuous deformations characteristic of the III–V category of mining area [15]; effects of vibrations on sensitive historic buildings of historical significance; criteria for empirical assessment of dynamic resilience of buildings subject to seismic effects of mining, developed using the GSIS-2017 scale.

3.2. Vibration harmfulness assessments based on GSI-GZW_KW-2012 and GSIS-2017 scales

Results of approximate evaluations of considered rockbursts harmfulness using GSI-GZW_KW-2012 and GSIS-2017 scales, are shown in Figs. 4 and 5 in the cases of velocity and acceleration versions of scales, respectively. All analysed mining shocks are taken into consideration in these figures, and moreover, the mining tremor intensity levels obtained using both the ground and building foundation vibrations measured at the same time, are visible in Figs. 4 and 5.

Fig. 4Assessments of the surface vibrations intensity using velocity version of the scales: a) GSI-GZWKW-2012-V, b) GSIS-2017-V

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Some differences in the harmfulness classifications of the rockbursts from the same analysed set, but carried out on the basis of ground vibrations or on the basis of building foundation vibrations simultaneously measured, can be noticed. Table 3 presents summary of rockbursts with the same intensity levels obtained on the basis of free-field ($IG$) and foundation ($IF$) vibrations in the case of using the velocity, basic versions of scales, whereas in Fig. 6 the comparisons of the intensity levels of ground and building foundation vibrations in the cases of their inconsistencies are shown. Table 4 and Fig. 7 contain the analogous data, but corresponding to acceleration versions of the Mining Intensity Scales.

It is worth mentioning that because of the same boundaries of the zones corresponding to 0-III intensity level valid in the case of GSI-GZW_KW-2012 scale, as well as in the case of GSIS-2017 scale, of course the results obtained for these intensity levels are identical for the both scales. Thus, it is clear that the differences in the vibration intensity assessments obtained using GSI-GZW_KW-2012 or GSIS-2017 scales can occur only in the ranges of the higher intensity levels – IV level in the case of GSI-GZW_KW-2012 or IV, V, and VI levels in the case of GSIS-2017 scale. This note applies to both versions of scales: velocity and acceleration.

Fig. 5Assessments of the surface vibrations intensity using acceleration version of the scales: a) GSI-GZWKW-2012-A, b) GSIS-2017-A

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It is visible that for about 80 % of all (156) rockbursts, the same vibration intensity levels were determined on the basis of the simultaneously recorded ground and foundation vibrations, using the velocity versions of both of scales: GSI-GZW_KW-2012-V scale (80.1 %), as well as GSIS-2017-V (79.5 %). Slightly better and also similar conformity of vibration harmfulness assessments based on the ground and building foundation vibrations was achieved in the cases of acceleration versions of also both of the considered scales: GSI-GZW_KW-2012-A scale – 84.6 %, GSIS-2017-A – 84.0 %. The most of incompatible levels of vibration intensity appeared in the cases of the mine-induced shocks classifying to 0 and I levels of free-field vibration intensity. This applies to the GSI-GZW_KW-2012, as well as GSIS-2017 scales, in their both versions (velocity and acceleration), cf. Figs. 6, 7. However, as it is visible on Figs. 6, 7, different free-field and building foundation vibration harmfulness assessments could appear also in the case of the most intensive rockbursts.

Fig. 6Levels of the ground and building foundation vibrations intensity in the cases of their inconsistencies – velocity versions of scales

Fig. 7Levels of the ground and building foundation vibrations intensity in the cases of their inconsistencies – acceleration versions of scales

Additionally, apart from the analysis of the impact of the vibration measurement place (free-field or building foundation) on the compatibility of the level of vibration intensity according to the velocity as well as acceleration versions of the considered mining scales, the compatibility of the vibration intensity levels determined on the basis scale in the velocity version, with the assessments obtained using GSI-GZW_KW-2012 scale in the acceleration version, as well as GSIS-2017 scale, was also investigated, cf. Table 5. It can be concluded that the number of mining tremors with the same intensity levels obtained from velocity and acceleration versions of the both scales (GSI-GZW_KW-2012 and GSIS-2017), is similar, despite of the vibration measurement site: 74.3 %-76.2 % of the all (156) cases of shocks, $cf$. Table 5. It is worth noting that unfortunately, the different assessments of rockburst harmfulness using velocity and acceleration versions of GSIS-2017 concern also the strongest shocks. For instance, using the free-field vibrations, the rockburst with $t_{Hv}=$ 1.3 s, $PG{V}_H=$ 0.056 m/s and $t_{Ha}=$ 1.54 s, $PG{A}_{H10}=$ 1.69 m/s², should be classified to IV intensity level according to GSIS-2017-V, whereas to V intensity level according to GSIS-2017-A. Similarly, based on the foundation vibrations, the mining tremor with $t_{Hv}=$ 1.68 s, $PG{V}_H=$ 0.091 m/s and $t_{Ha}=$ 1.51s, $PG{A}_{H10}=$ 2.29 m/s², should be classified to V intensity level according to GSIS-2017-V, whereas to VI intensity level according to GSIS-2017-A. But due to the fact that the number of rockbursts with high level of intensity, is very small in the analysed set of cases, these observations could not be simply generalised.