1、翻译部分英语原文COAL MINING UNDER SPECIAL CONDITIONSSECTION1 LONGWALL MINING TECHNIQUESFOR MINIMIZING SURFACE STRUCTURAL DAMAGESLongwall mining is a relatively new mining method in the United States. Early trials in the eastern and central coal fields were not successful, mainly because, among others, the f
2、ace supports did not have sufficient capacity. It was not until in the late 1960s , when the highcapacity self-advancing powered supports became available,that longwall mining was successfully reintroduced. Since then the number of mines employing the longwall method has been steadily increasing. It
3、 has reached approximately 7.5 in 1981.One of the major concerns for longwall mining is the extent of surface subsidence and its induced surface structural damages. The experiences have been that room and pillar mining with low recovery ,e.g. no pillar mining can be implemented such that no measurab
4、le surface subsidence occurs during the period of underground mining, although subsidence may occur long after (say 4050 years)mining. In contrast, the general concept about longwall mining is that since there is a complete extraction of coal in a longwall panel, there will be much large surface sub
5、sidence and thus structural damages. This is to some extent justifiable because past research has demonstrated that surface subsidence due to longwall mining occurred even when the seam depth was close to 1000 ft. and that minor ctackings could occur in a residential house depending on the type and
6、location of the residential house within the panel. In other words under longwall mining there could be some damage to some surface structures such as houses. But it can be protected such that the damages are so minor that except minor crackings, the houses are practically the same before and after
7、mining.Therefore in dealing with the protective measures for surface structural damages due to underground longwall mining it must be recognized that mearly all surface structures can be completely protected if the cost is not the subject. But this is not necessary . Instead, there should be a compr
8、omise between the cost to be expended and the degree of damages the structures will be sustained. In anticipation of the development of longwall mining, the authors have been studying the subsidence problems that have occurred in major coal producing countries in the world. In this paper various min
9、ing techniques that have been successfully employed for reducing surface structural damages are reviewed and presented. Protective Measures for Surface Structures It is well known that underground mining will induce movements and deformation of the overburden strata and surface. As a result, surface
10、 structures within the movement basin will be subjected to deformation. In general it is uncommon to adopt measures that will completely eliminate structural deformations because its extremely costly and difficult to accomplish . The technical methods that are normally employed can be divided into t
11、wo categories : Methods for protecting the structural elements of the structures and protective mining methods for reducing surface movements. The basic principle is that a small amount of deformation is allowed to occur. Within this limit, the structure maintains its normal functions as well as it
12、did before mining. The objective of any methods employed for protection of the structural elements is that the structures can tolerate the deformation induced by longwall mining. The repair cost for those protected structures will be much less than those unprotected ones. The normal practice is to p
13、redict the potential amount of surface deformation, followed by evaluating the intensity of damage based on the allowable amount of deformation for the structures. Finally, the proper protective measures are adopted. The protective mining methods should be such that they reduce the amount of deforma
14、tion occurred on the surface and the structures. These include partial and backfill mining and any other mining methods that achieve high percentage of recovery by making use of the deformational characteristics of surface movements. Under normal conditions, mining under a group of surface structure
15、s should consider the protective mining methods and the corresponding methods for protecting the structural elements of the surface structures. Experiences in foreign countries have demonstrated that such considerations are economically reasonable and technically feasible. As the characteristics of
16、surface movements become better known, the preferential mining techniques for surface structural protection changes from strip mining or room and pillar mining to full face longwall mining; and later from longwall backfilling to longwall caving method. In many cases, the longwall caving with proper designs and procedures, coupled with the protective measures for structural elements has achieved satisfactory results.
