**4. Conclusions**

The increasing interest in the use of rock bolt support systems has its economic background. This system of prevention is less time and material consuming as well as technically more feasible. In strong rocks the use of rock bolt systems is prevailing. In Polish coal mines where rock strata are weaker, the interest in the usage of rock bolt support system is much lower but recently marked changes may be observed in this area. At the same time there is no satisfactory nondestructive method for testing rock bolt installation [6]. It was the reason for undertaking the research on the method for identification of grouting discontinuity for rock bolts. The invented method uses modal analysis procedures and is based on an impact excitation and reconciliation of experimental and theoretical modal models.

In laboratory conditions a cause-effect relation was found between excitation of a rock bolt to transverse vibration and response characteristic of the examined structure. To enable in situ measurement a portable measurement system was invented and constructed. The LabVIEW environment was used as a programming tool. Simultaneously, import of recorded data and derivation of modal parameters were performed utilizing modal analysis software LMS TestLab.

Dynamic parameters of a tested structure (installed rock bolt) are determined by its border conditions, which are directly connected with a grouting discontinuity length. That fact enabled us to diagnose the discontinuity length.

It was necessary to build a theoretical modal model of an installed rock bolt where different cases of grouting discontinuity were encountered. The results of theoretical modal analysis performed on validated FE model constituted a reference base for unknown cases (correlation and comparison techniques were used to validate the model). The reference to the base of validated theoretical models was found reasonable (the discontinuities of verification tests were determined a priori). The reference base may be used for different types of rocks.

Based on the prototype construction the final version fulfilling ATEX requirements was constructed.

The transverse excitation was found as more adequate to identify the discontinuity length of the resin layer of the installed rock bolts.

A mass of a response transducer has influence on the results [26], hence it is desired to minimize it.

The measurement system was verified in real coal mine conditions.

On the basis of the carried out research and calculations of finite element models of the system under test, rock bolt - resin - rock mass, it can be concluded that the developed method and analytical application actually classifies the measured natural frequencies group and enables to identify cases of discontinuity (regions of lack of bonding, which is seen as crucial here).

At present a diagnosis is completed after analytical phase performed in laboratory conditions, so results are not accessible in situ. Its usage is restricted to steel rock bolts up to 2.5 m long (longer rock bolts were not investigated), though not only in mining but also in building engineering.

### **Acknowledgements**

The realized research was financed by Polish Ministry of Science and High Education, project no 11060317.

*Quality Assessment of Installed Rock Bolts DOI: http://dx.doi.org/10.5772/intechopen.101125*
