1、PDF外文：http:/ 152 Optimization of soft rock engineering with particular reference to coal mining Abstract Soft rock engineering is a difficult topic which has received much attention in the field of rock mechanics and engineering. Research and practical work have been carried out, but muc
2、h of the work has been limited to solving problems from the surface. For overcoming the difficulties of large deformations, long duration time-dependent effects, and difficulties in stabilizing the soft rock, the problem should be tackled more radically, leading to a more effective method of achievi
3、ng optimization of the engineering system in soft rock. A summary of the optimization procedure is made based on engineering practice. 1. Introduction There are many soft rock engineering problems around the world, involving engineering for mines, highways, railways, bridges, tunnels, ci
4、vil subways, buildings, etc. Engineering losses have occurred because of volumetric expansion, loss of stability of the soft rock, etc. This has been an important question to which much attention has been paid in engineering circles, and in the field of academic rock mechanics. Since the 1970s, cons
5、iderable research and practical efforts have been made in the field of soft rock engineering in various countries, but the major efforts were concentrated on such aspects as the method of construction, the design and reinforcing of the supporting structures, measurement and analysis of the rocks phy
6、sical and mechanical properties, its constitutive relations and engineering measurement. It has been found that the soft rock engineering problem involves complex systematic engineering including such subsystems as classification of soft rocks, judgement concerning the properties of soft rock,
7、 project design and construction. Only by considering the integral optimization of the system can we obtain an improved solution to the problem. Hopefully, a radical approach can lead to engineering feasibility, lower costs and engineering stability in order to achieve the engineering objectives. &n
8、bsp;1.1. Mechanical properties of soft rock and associated engineering 153 Soft rock is an uneven and discontinuous medium. Its strength is low, with a uniaxial compressive strength usually lower than 30 MPa. Some soft rocks expand when they are wet. Cracks in some soft rocks will propagate e
9、asily which makes them exhibit volumetric expansion. Large deformation and creep can occur in soft rocks. Many soft rocks are compound ones which have composite properties formed from two or more sets of constituent properties. Soft rock can be graded into divisions according to its properties. Afte
10、r engineering has occurred, soft rock can deform rapidly and by time-dependent deformation, owing to its low strength and sensitivity to the stress field. With the effect of water, the expansive minerals in soft rocks volumetrically expand, which causes large convergent deformations, which leads to
11、damage of the surrounding rock. The mechanical properties of soft rocks appear so various and different that it is difficult to express them with mathematical formula, which is the technological challenge for soft rock engineering. 1.2. Engineering in soft rock and its optimization
12、;Because soft rock engineering can induce large deformations, the maintenance of the engineering can be difficult. Moreover, volumetric expansion and loss of stabilization of the surrounding rock often causes damage to supporting structures. If we use strong supports to control the deformation of th
13、e surrounding rock, the engineering cost will be high, and the construction time will be increased by repeated installation of support, sometimes the support itself has to be repaired. In order to obtain the benefits of easier construction and lower cost, the integral optimization of the system must
14、 be carried out and managed in a systematic and comprehensive way. Design and construction are the two important steps in soft rock engineering. These must begin by understanding the physical and mechanical properties of soft rock, in the context of the stress field, hydrogeology and engineeri
15、ng geology. The engineering design plan is conceived as a whole according to the theory of rock mechanics and combining practical data from adjacent or similar projects, including integrating the many factors. The establishment of the correct soft rock engineering system should come from practice, b
16、asing on a full mastery of the factors. The scheme is shown in Fig. 1. 154 Fig. 1. Engineering system for soft rock. Optimization of soft rock engineering is achieved by making the surrounding rock interface with the supporting structure such that the engineering wi
17、ll be stable. The key technological strategy is to avoid a high stress field and enhance the supporting ability of the surrounding rock. Feasible measures are as follows: reducing the external load； optimizing the engineering structures size and shape, improving planar and cubic layouts of engineeri
18、ng； choosing better strata, and structure orientation, etc., as shown in Fig. 2. Fig. 2. The principle of the optimization process. According to these ideas, take the development of a coal mine in soft rock as an example. Integrated optimization of the development system of the mi
19、ne should take the relevant factors into account: existing information； an overall arrangement for optimal development and production； eliminate adverse factors； and deal with the problems of soft rock by a simple construction method. The content of the first part of the optimization includes: choosing the mine development method； deciding on the mining level； and determining layers in which the main roadways are to be located. Also important is arranging a reasonable layout of the pit bottom and
