1477 3. STUDY AREA AND RESEARCH METHODOLOGY The investigations were conducted in a roadway with a total length of 1,970 m. Due to a change in the driving direction resulting from the proximity of a fault, this paper presents the results of analyses for the section between 230 m and 1,040 m. The roadway was developed within a coal seam of 2.5 m thickness, with claystone roof and floor, locally sandy, and locally interbedded with a sandstone layer. During roadway development, the rock strength was continuously monitored using a penetrometer, and the Rock Quality Designation (RQD) of drill cores was also locally assessed. The results indicate (Table 1) that the in situ uniaxial compressive strength of the roof rocks to a depth of 10 m ranged from 32 MPa at the 1,003 m chainage, through approximately 37 MPa at the 299 m chainage, to approximately 41 MPa at the 365 m chainage. Table 1 – Mechanical properties of roof rocks obtained from in situ investigations Roadway length [m] c [MPa] t [MPa] RQD [%] 299 37.39 2.06 17.4 365 41.47 2.28 25.0 1003 32.06 1.76 29.4 Prior to the commencement of roadway development with a self-supporting rock bolt system, in situ stress measurements were carried out. The measurements were performed at a depth of 865 m using the CSIRO overcoring method, which is applied to determine the three-dimensional stress state. A CSIRO probe was bonded into a Ø38 mm pilot borehole. During subsequent overcoring, stress measurements were recorded. The measurement results were as follows: Ø Mean orientation of the maximum horizontal stress: 345°. Ø Mean value of the maximum horizontal stress: 23 MPa. Ø Mean value of the minimum horizontal stress: 10 MPa. Ø Mean value of the vertical stress: 22.3 MPa. The orientation of the maximum horizontal stress direction relative to the roadway axis, as well as a typical lithological profile of the rocks surrounding the roadway, are presented in Fig. 1. a) b) Figure 1 - Roadway location: (a) orientation of the maximum horizontal stress direction relative to the roadway axis; (b) lithological profile of the surrounding rock mass (chainage 399 m)
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