【文章內(nèi)容簡介】 the main mining level is elevated by 20 m, 1131 m of roadways are saved and the cost of the roadway construction and facilities is saved 165。2,760,000 ($336,600). The new system is shown in Fig. 5. 157 Fig. 5. Development system plans after optimization for Mine No. 5 in Youjiang. The second optimization measure is to change the layout of the pit bottom and openings to be parallel with the maximum principal stress as far as possible. The total length of roadways initially designed was 1481 m, and % of them were arranged to be perpendicular to the maximum principal stress. After amendment, the total length of roadways is 1191 m, which is a decrease of 290 m, and with only % of roadways that are perpendicular to the principal horizontal stress, roadways are easier to maintain. As shown in Fig. 6 and Fig. 7. Fig. 6. Layout of the pit bottom and chamber initially designed for Mine No. 5 in Youjiang. 158 Fig. 7. Layout of the pit bottom and chamber after the optimization for Mine No. 5 in Youjiang. The third optimization measure is to excavate the section of the roadway in a circular arch shape to reduce the stress concentrations. In order to increase the supporting ability of the surrounding rock itself, after the roadway has been excavated, rockbolts are installed as the first support. Considering the expansivity of the surrounding rock, guniting is not suitable. The secondary support is the use of precast concrete blocks. Between the support and the surrounding rock, the gaps should be filled with a pliable layer of mixed limepowder with sand. This produces the effect of distributing the stress and has a cushioning effect when the soft rock is deforming。 also, it inhibits the soft rock from absorbing water and expanding. This scheme is shown in Fig. 8 Fig. 8. Optimization design for the supporting structure of the main roadway for Mine No. 5 in Youjiang. The fourth optimization measure is to simplify the chamber layout so as to reduce the number of roadways. For example, in order to decrease the stress concentrations by the roadway, the number of passageways in the pumproom and the substation can 159 be reduced from three to one, and the roadway intersections connecting at rightangles can be reduced from 14 to nine. The fifth optimization measure is in accordance with the different stratigraphical lithologies which the roadways pass through, and for harder rock regions to change the roadway section into a structure with straightsided semicircular top arch and arc bottom arch, and another structure with a straightsided horseshoe arch, so that the investment of supporting structure can be saved when there are better rock masses with paratively few fractures. In construction, waterproofing and draining off the water should be implemented, and the catchment in the roadway bottom should be strictly prevented because it may cause the bottom rock to expand. When the opening groups are excavated, the construction sequence must be considered, enough rock pillar must be reserved, and the construction method of ‘shortdigging and shortbuilding’ must not be used, so that the interactions can be avoided. By the optimization described above, after the roadways have been constructed, the serviceable roadway is % of the total, % more than that of the adjacent mine No. 4. The length of the roadway was reduced, and 165。3,700,000 ($450,000) saved. In addition, 165。3,000,000 ($360,000) was saved in the maintenance costs of the roadways before the mine was put into production, so, the cost saving totals 165。6,700,000 ($810,000) in all. After the mine has been turned over to production, the main designed capacity was reached in that year, and added to the saved money for the maintenance cost of roadways in production, there was 165。8,700,000 ($1,050,000) saved. . The coal mine at Renziping, China The mine lies to the south of Qinzhou coalfield in Guangxi Zhuang Autonomous Region. It belongs to the new third Period and synclinal coal basin tectonics. There are two coal layers in it, the main seam thickness is 12–15 m. The roof and floor of the coal layers are arenaceous–argillaceous rocks, whose colour is greyish white, and whose essential minerals are quartz and kaolinite. The uniaxial pressive strength of the rock is from 10 to 15 MPa. Rock masses are quite integral with fractures only in it occasionally. It belongs to the class of soft rock that has weak expansio