**5. Geophysical measurements**

Monitoring of phenomena occurring in frozen rock mass is crucial for safety of the whole process of shaft sinking using ground freezing method. It is not an easy task, though. Number of geophysical measurements were conducted on Grzegorz shaft's construction plant in order to optimize process of ground freezing and monitoring of frozen rock mass. On a basis of gathered data, practical aspects of presented methods were analyzed.

Potential measuring methods assumed possible to use for Grzegorz shaft monitoring were [13]:


Surface waves analysis allows estimation of velocity of transverse wave behind the shaft lining, within few meters. Utilization of reflection seismology helps to anticipate geological faults and some of the parameters of rock mass. Especially prior recognition of faults plays critical role in safety of miners working in the shaft's heading, as well as for economic factors. Application of proposed methods has to be carefully considered and tested in real-life condition. Unfortunately, it was impossible, because of the small depth (20 meters) of Grzegorz shaft during measurement session. Initial assumptions involve utilization of geophones in short distance from shaft's heading [13].

An objective of tomography test is estimation of 2D wave velocity field between adjacent boreholes. Tests were carried out using vibration source of special construction, made especially for purpose of these tests. This device is presented on **Figure 4**. Two tests were made, first of them with utilization of probe consisting of

**7**

*Optimization Directions for Monitoring of Ground Freezing Process for Grzegorz Shaft Sinking*

four hydrophones with own frequency of 500 Hz and another one with using two probes equipped with three hydrophones with own frequency of 100 Hz [13]. The results obtained prove that monitoring of the frozen rock mass column using probes and vibration source is possible. High financial expenditures needed for vibration source construction (prototype used for tests is suited for use in control boreholes, final vibration source for use in freezing boreholes has to be constructed) and problematic technology of testing caused neglecting of further

Utilization of scattered waves allows monitoring of deformational phenomena occurring in rock mass. The appearance of cracks, rifts and microfractures affects velocity of wave propagation and its amplitude. What is even more important in case of ground freezing is high sensitivity of coda wave velocity for (even small)

Utilization of seismic interferometry was proposed for purpose of monitoring of phenomena occurring in frozen rock mass caused by temperature changes in the vicinity of the Grzegorz shaft. Sources of seismic noise, which is needed for such measurements, are operating freezing boreholes. This method of monitoring

Tests were conducted to prove correctness of initial assumptions. Measurements

were carried out using two probes consisting of three hydrophones with own frequency of 100 Hz each. **Figure 5** presents 5-minute record of seismic noise. Channels 0, 1 and 2 represent hydrophones located in control borehole T2, channels 3, 4 and 5 represent hydrophones used in borehole T1, located closer to freezing boreholes. High amplitude values about 13:02 are caused by tests of vibration source

From the practical point of view, the most relevant is the period of stationary seismic noise. It is probably an effect of freezing boreholes operation and its frequency varies between 10 and 200 Hz **Figure 6**. Presents record and spectrogram

On the basis of scattered wave interferometry correlation functions, representing estimated scattered wave propagation between hydrophones, were obtained. Further tests and analysis are required for purpose of utilization of this method for real life application, including tests covering long time period of measurement. To sum up, coda wave interferometry method can be used in practice, for monitoring of ground freezing process and become convenient and reliable monitoring method. High sensitivity for temperature changes can prevent potential unexpected failures, which are real threat for miners working in the shaft heading and for shaft

*DOI: http://dx.doi.org/10.5772/intechopen.95885*

development of such solution [13].

*A view of vibration source prototype.*

**Figure 4.**

temperature changes in rock mass [13–16].

provides near real-time information.

used in the tomography measurements.

of channel 0. Spectrogram's scale upper limit is 300 Hz.

*Optimization Directions for Monitoring of Ground Freezing Process for Grzegorz Shaft Sinking DOI: http://dx.doi.org/10.5772/intechopen.95885*

**Figure 4.** *A view of vibration source prototype.*

*Computational Optimization Techniques and Applications*

**5. Geophysical measurements**

presented methods were analyzed.

• vertical seismic profiling,

• transmission tomography,

• seismic interferometry,

• surface wave analysis,

• reflection seismology.

toring were [13]:

**Figure 3.**

Monitoring of phenomena occurring in frozen rock mass is crucial for safety of the whole process of shaft sinking using ground freezing method. It is not an easy task, though. Number of geophysical measurements were conducted on Grzegorz shaft's construction plant in order to optimize process of ground freezing and monitoring of frozen rock mass. On a basis of gathered data, practical aspects of

*Arrangement of freezing and control boreholes and cross-section of Grzegorz shaft [1].*

Potential measuring methods assumed possible to use for Grzegorz shaft moni-

Surface waves analysis allows estimation of velocity of transverse wave behind the shaft lining, within few meters. Utilization of reflection seismology helps to anticipate geological faults and some of the parameters of rock mass. Especially prior recognition of faults plays critical role in safety of miners working in the shaft's heading, as well as for economic factors. Application of proposed methods has to be carefully considered and tested in real-life condition. Unfortunately, it was impossible, because of the small depth (20 meters) of Grzegorz shaft during measurement session. Initial assumptions

An objective of tomography test is estimation of 2D wave velocity field between adjacent boreholes. Tests were carried out using vibration source of special construction, made especially for purpose of these tests. This device is presented on **Figure 4**. Two tests were made, first of them with utilization of probe consisting of

involve utilization of geophones in short distance from shaft's heading [13].

**6**

four hydrophones with own frequency of 500 Hz and another one with using two probes equipped with three hydrophones with own frequency of 100 Hz [13].

The results obtained prove that monitoring of the frozen rock mass column using probes and vibration source is possible. High financial expenditures needed for vibration source construction (prototype used for tests is suited for use in control boreholes, final vibration source for use in freezing boreholes has to be constructed) and problematic technology of testing caused neglecting of further development of such solution [13].

Utilization of scattered waves allows monitoring of deformational phenomena occurring in rock mass. The appearance of cracks, rifts and microfractures affects velocity of wave propagation and its amplitude. What is even more important in case of ground freezing is high sensitivity of coda wave velocity for (even small) temperature changes in rock mass [13–16].

Utilization of seismic interferometry was proposed for purpose of monitoring of phenomena occurring in frozen rock mass caused by temperature changes in the vicinity of the Grzegorz shaft. Sources of seismic noise, which is needed for such measurements, are operating freezing boreholes. This method of monitoring provides near real-time information.

Tests were conducted to prove correctness of initial assumptions. Measurements were carried out using two probes consisting of three hydrophones with own frequency of 100 Hz each. **Figure 5** presents 5-minute record of seismic noise. Channels 0, 1 and 2 represent hydrophones located in control borehole T2, channels 3, 4 and 5 represent hydrophones used in borehole T1, located closer to freezing boreholes. High amplitude values about 13:02 are caused by tests of vibration source used in the tomography measurements.

From the practical point of view, the most relevant is the period of stationary seismic noise. It is probably an effect of freezing boreholes operation and its frequency varies between 10 and 200 Hz **Figure 6**. Presents record and spectrogram of channel 0. Spectrogram's scale upper limit is 300 Hz.

On the basis of scattered wave interferometry correlation functions, representing estimated scattered wave propagation between hydrophones, were obtained. Further tests and analysis are required for purpose of utilization of this method for real life application, including tests covering long time period of measurement.

To sum up, coda wave interferometry method can be used in practice, for monitoring of ground freezing process and become convenient and reliable monitoring method. High sensitivity for temperature changes can prevent potential unexpected failures, which are real threat for miners working in the shaft heading and for shaft

**Figure 5.** *Example of seismic noise record.*

**Figure 6.** *Record and spectrogram of channel 0.*

itself. However, this method has to be tested in long period tests, spanning for several days, as well as in situation of controlled stoppage of operation of freezing borehole, to check if the monitoring system work well in hazardous situation [13].

The most promising data was obtained in a test of vertical seismic profiling. Tests were conducted using device with parameters presented in **Table 2**. The source of seismic wave was generated on the surface in the near vicinity of a borehole by a 5 kg sledgehammer [13, 17, 18].

**9**

**Figure 7.**

*Optimization Directions for Monitoring of Ground Freezing Process for Grzegorz Shaft Sinking*

Probe 4 hydrophones with own frequency of 500 Hz

Amount of hits 1 for each probe position (each 0,6 m)

**Figure 7** presents results of seismic record initial analysis for single measurement in the borehole T1. Traces were filtered in frequency range between 150 and 800 Hz and normalized to common average. Regular amplitudes, effecting from

Basing on data obtained from profiling boreholes T1, T2 and T3, a collective map of wave velocity distribution was computed. It is limited to a depth where data obtained is characterized by high quality. Resulting map is shown in **Figure 8**.

There is a relationship between temperature (data collected at the beginning of ground freezing process), presented in **Figure 9**, and velocity distribution, shown in **Figure 10**. Data obtained from borehole T1 was chosen for presentation, because

Temperature and wave velocity were also compared on one graph, presented in

Consequently, graphical correlation of frozen rock mass column development,

*Example of seismic record in the borehole T1; vertical axis – Numbers of traces, horizontal axis – Time in ms.*

Non-linear, polynomial function with constant parameters was obtained. Function was suited with high correlation factor, equal 0,82. It is clear that there is a

temperature curve and map of velocity distribution was prepared. It is shown in **Figure 12**. Blue sections represent temperature and velocity drops, red color

indicates temperature and velocity rises. Relationship is clear [13].

*DOI: http://dx.doi.org/10.5772/intechopen.95885*

Distance between hydrophones 0,2 m Measuring step 0,6 m

Record time 0,5 s Frequency 4000 Hz Depth 0–200 m

*Parameters of seismic profiling record [13].*

**Table 2.**

**Seismograph Geode 24CH Geometrics**

wave propagation, can be observed in the figure.

of the shortest distance to freezing boreholes.

relationship between temperature and velocity.

**Figure 11**. Relationship between them was estimated.

*Optimization Directions for Monitoring of Ground Freezing Process for Grzegorz Shaft Sinking DOI: http://dx.doi.org/10.5772/intechopen.95885*


#### **Table 2.**

*Computational Optimization Techniques and Applications*

itself. However, this method has to be tested in long period tests, spanning for several days, as well as in situation of controlled stoppage of operation of freezing borehole, to check if the monitoring system work well in hazardous situation [13]. The most promising data was obtained in a test of vertical seismic profiling. Tests were conducted using device with parameters presented in **Table 2**. The source of seismic wave was generated on the surface in the near vicinity of a bore-

**8**

**Figure 6.**

**Figure 5.**

*Example of seismic noise record.*

hole by a 5 kg sledgehammer [13, 17, 18].

*Record and spectrogram of channel 0.*

*Parameters of seismic profiling record [13].*

**Figure 7** presents results of seismic record initial analysis for single measurement in the borehole T1. Traces were filtered in frequency range between 150 and 800 Hz and normalized to common average. Regular amplitudes, effecting from wave propagation, can be observed in the figure.

Basing on data obtained from profiling boreholes T1, T2 and T3, a collective map of wave velocity distribution was computed. It is limited to a depth where data obtained is characterized by high quality. Resulting map is shown in **Figure 8**.

There is a relationship between temperature (data collected at the beginning of ground freezing process), presented in **Figure 9**, and velocity distribution, shown in **Figure 10**. Data obtained from borehole T1 was chosen for presentation, because of the shortest distance to freezing boreholes.

Temperature and wave velocity were also compared on one graph, presented in **Figure 11**. Relationship between them was estimated.

Non-linear, polynomial function with constant parameters was obtained. Function was suited with high correlation factor, equal 0,82. It is clear that there is a relationship between temperature and velocity.

Consequently, graphical correlation of frozen rock mass column development, temperature curve and map of velocity distribution was prepared. It is shown in **Figure 12**. Blue sections represent temperature and velocity drops, red color indicates temperature and velocity rises. Relationship is clear [13].

**Figure 7.** *Example of seismic record in the borehole T1; vertical axis – Numbers of traces, horizontal axis – Time in ms.*

#### **Figure 8.**

*Map of wave velocity distribution.*

1,5 months after test described above, another measurements were carried out, within the stage II of the research. Another map of velocity distribution was made. This map, together with the previous one (**Figure 9**) are presented in the **Figure 13** [18].

On the basis of conducted research, conclusions were made [13, 18]:

• there is a clear relationship between frozen rock mass temperature changes and wave velocity measured. Ground-freezing process monitoring can be conducted using seismic methods.

**11**

**Figure 11.**

**Figure 10.**

*Velocity in the borehole T1.*

**Figure 9.**

*Temperature in the borehole T1.*

*Relationship between temperature and velocity.*

*Optimization Directions for Monitoring of Ground Freezing Process for Grzegorz Shaft Sinking*

*DOI: http://dx.doi.org/10.5772/intechopen.95885*

*Optimization Directions for Monitoring of Ground Freezing Process for Grzegorz Shaft Sinking DOI: http://dx.doi.org/10.5772/intechopen.95885*

**Figure 9.** *Temperature in the borehole T1.*

*Computational Optimization Techniques and Applications*

1,5 months after test described above, another measurements were carried out, within the stage II of the research. Another map of velocity distribution was made. This map, together with the previous one (**Figure 9**) are presented in the **Figure 13** [18]. On the basis of conducted research, conclusions were made [13, 18]:

• there is a clear relationship between frozen rock mass temperature changes and wave velocity measured. Ground-freezing process monitoring can be con-

**10**

**Figure 8.**

*Map of wave velocity distribution.*

ducted using seismic methods.

**Figure 10.** *Velocity in the borehole T1.*

**Figure 11.** *Relationship between temperature and velocity.*

**Figure 12.** *Graphical correlation between velocity distribution, temperature and frozen rock mass cylinder shape.*

**13**

*Optimization Directions for Monitoring of Ground Freezing Process for Grzegorz Shaft Sinking*

• development of frozen rock mass column is correlated with velocity. It is in stronger relationship with velocity than just temperature, because temperature value only does not give complete information about geomechanical state of rock mass.

• relative temperature and velocity changes are complementary. Their correla-

Number of seismic methods can be used for measurements of frozen rock mass parameters, such as frozen ground cylinder shape and size during shaft sinking. However, some of them might be too expensive or problematic in use, not effective

Different methods were proposed for the purpose of frozen rock mass column monitoring during Grzegorz shaft sinking. Scattered waves interferometry and

Seismic interferometry method is favorable because of possibility of conducting near real-time monitoring. High sensitivity for temperature changes can provide accurate indication of failures in freezing installation operation. However, technology of such measurements needs further research, spanning for a long time and covering controlled stoppage of freezing installation operation. Financial aspect of

Vertical seismic profiling provides information about shape and size of frozen ground column. Constant measure is impossible, but periodic measurements might find application, because of possibility of determination of shape of frozen rock mass cylinder for tens of meters forward the shaft heading. Therefore, it helps to forecast potential hazards before the beginning of successive sinking stages. Similar to seismic interferometry method, vertical seismic profiling needs further development and analysis of economic factors. However, this method is considered prospective. To sum up, geophysical methods of frozen ground column monitoring are prospective direction of research. Technological aspects of these methods should be

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

tion might have an impact on rock mass imaging state.

enough, etc. Important factor is also time needed for measurements.

vertical seismic profiling were assumed the most convenient.

analyzed and developed to make them economically reasonable.

this kind of technology is also an issue to consider.

This research received no external funding.

The author declares no conflict of interests.

provided the original work is properly cited.

*DOI: http://dx.doi.org/10.5772/intechopen.95885*

**6. Summary**

**Acknowledgements**

**Conflict of interest**

**Figure 13.** *Maps of velocity distribution.*

*Optimization Directions for Monitoring of Ground Freezing Process for Grzegorz Shaft Sinking DOI: http://dx.doi.org/10.5772/intechopen.95885*


#### **6. Summary**

*Computational Optimization Techniques and Applications*

*Graphical correlation between velocity distribution, temperature and frozen rock mass cylinder shape.*

**12**

**Figure 13.**

**Figure 12.**

*Maps of velocity distribution.*

Number of seismic methods can be used for measurements of frozen rock mass parameters, such as frozen ground cylinder shape and size during shaft sinking. However, some of them might be too expensive or problematic in use, not effective enough, etc. Important factor is also time needed for measurements.

Different methods were proposed for the purpose of frozen rock mass column monitoring during Grzegorz shaft sinking. Scattered waves interferometry and vertical seismic profiling were assumed the most convenient.

Seismic interferometry method is favorable because of possibility of conducting near real-time monitoring. High sensitivity for temperature changes can provide accurate indication of failures in freezing installation operation. However, technology of such measurements needs further research, spanning for a long time and covering controlled stoppage of freezing installation operation. Financial aspect of this kind of technology is also an issue to consider.

Vertical seismic profiling provides information about shape and size of frozen ground column. Constant measure is impossible, but periodic measurements might find application, because of possibility of determination of shape of frozen rock mass cylinder for tens of meters forward the shaft heading. Therefore, it helps to forecast potential hazards before the beginning of successive sinking stages. Similar to seismic interferometry method, vertical seismic profiling needs further development and analysis of economic factors. However, this method is considered prospective.

To sum up, geophysical methods of frozen ground column monitoring are prospective direction of research. Technological aspects of these methods should be analyzed and developed to make them economically reasonable.

#### **Acknowledgements**

This research received no external funding.

#### **Conflict of interest**

The author declares no conflict of interests.

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Computational Optimization Techniques and Applications*
