## 5 Discussion
After the roadway was controlled by high-preload bolt + deep and shallow crack filling, the displacement amount and rate of the roadway further decreased. This technology effectively restrains the rheology of the deep surrounding rock and ensures the long-term stability of the roadway. Different parts of the roadway completed the main deformation on around the 50 th day. The deformation adjustment period was from the 50 th day to the 150 th day, and the stabilized deformation period started after the 150 th day. The roadway deformation was limited, and no severe deformation trend was found on the 300 th day. As can be observed from Figure 16, in the initial stage, only a few shear cracks caused by instantaneous deformation appeared in the roadway surrounding rock. On the 300 th day, the anchor bolts at the shoulder corners and the bottom corners of the ribs bent slightly without breakage. The ribs shared consistent damage characteristics, and only a few cracks were distributed on the roadway surface, while almost no cracks appeared in the deep surrounding rock. On the roadway floor, there were merely tensile cracks on the surface; the central block of the roof no longer moved, and the surrounding rock of the roof was relatively integrated. As can be observed form Figure 17, on the 300 th day, the total number of cracks in the surrounding rock was 1073, including 976 shear cracks (accounting for 91%) and 97 tensile cracks (accounting for 9%). Compared with those in the original support method, the total number of cracks decreased by 46.4%; the number of shear cracks fell by 44.7%; and the number of tensile cracks declined by 37%. In the primary deformation stage, the cumulative number of shear cracks was 950, accounting for 97% of the total number of shear cracks. In the secondary deformation stage, 26 new shear cracks appeared, accounting for 3% of  
Figure 16: Crack distribution of the improved support. (**a**) 5 th d; (**b**) 300 th d.  
Figure 15: Average displacement of two ribs, roof, and floor of the roadway. (**a**) ribs; (**b**) roof and floor. the total number of shear cracks. The cumulative number of tensile cracks in the primary deformation stage was 86, accounting for 89% of the total number of tensile cracks, and 11 new tensile cracks occurred in the secondary deformation stage, accounting for 11% of the total number of tensile cracks. Both shear and tensile cracks mainly appeared in the primary deformation stage. According to the overall roadway damage characteristics, after the support optimization, the shear cracks exerted smaller damage to the roadway surrounding rock, while the tensile cracks did not cause bolt breakage or floor bulge due to their small number. In the primary deformation stage, the total damage was 31.5%, and it increased to 32.9% in the secondary deformation stage. It can be seen that the control technology of high-preload bolt + deep and shallow crack filling could well inhibit the shallow crack propagation and the rheological deformation of the deep surrounding rock and prevent secondary damage to the roadway. Based on the reinforcement idea of this control technology, the following support scheme was adopted on site: the arch roof bolts were \(\Phi\)22 mm \(\times\) 2800 mm thread steel anchor bolts with a row spacing of 700 mm \(\times\) 800 mm between arches; the high preload applied by the anchor bolts was no less than 90 kN; the reinforcing anchor cables were \(\Phi\)22 mm \(\times\) 6300 mm with a row spacing 2450 mm \(\times\) 1600 mm; the rib bolts adopted were \(\Phi\)22 mm \(\times\) 2800 mm thread steel anchor bolts, three bolts for each rib, with a row spacing of 600 mm \(\times\) 800 mm; the high preload applied by the anchor bolts was no less than 90 kN; and the floor bolts were \(\Phi\)22 mm \(\times\) 2200 mm ordinary thread steel anchor bolts with a row spacing of 1000 mm \(\times\) 800 mm. Six grouted anchor cables were arranged in the full section with a spacing of 1250 mm \(\times\) 2400 mm.