In this paper, we overview the historic evolution, present status of open-pit slope design methods in China, and present our opinions on their improvements. We divide the design methods of open-pit slopes into three stages, and analyze the features of each stage. In recent years, open-pit mining is facing more and more complicated circumstances: frequent rainstorms, great height and hanging ore mining, requiring modifications in the design method. On the other hand, modern investigation and monitoring techniques, such as BHTV, geophysical prospect, well logging, InSar, GPS etc., and various analysis techniques are well-developed, providing a sound basis for the modifications. The authors propose a modified open-pit mine slope design method that emphasizes key issue identifications, multiple analyses, feedbacks, managements and technical auditions, serving as a systematic framework for designing increasingly complex open-pit slopes. In addition, Fengshuxia Open-pit Project is outlined as a demonstration and verification for the modified method.
In China, metalliferous and non-metalliferous ores produced by open-pit mines amounts to 90% and 50% of the total output, respectively. There are more than 1500 open-pit mines, among which are 50 large-scale and ultra large-scale ones. As they are deepening at a speed of 12- 20m/a, their slopes become higher and higher, some of which have reached 300–500m in their heights.
Determination of an optimal slope angle is always one of the key points in open-pit mine designs. It has been well known that absolutely non-risky slope is not cost- effective; however, high-risk mining is certainly unacceptable. Therefore, the open-pit slope design is a practice to achieve the balance among operation safety, economy and sustainable development of open-pit mines.
The open-pit slope design method has evolved with the changes in technological and environmental constraints. With the open-pit slopes going higher and extreme rainfalls as a result of the climate change are more frequent; it is meaningful to consider the appropriate modifications of open-pit slope design methods.
This paper reviews the historical progress of open-pit slope design methods in China, recommends a modified method, and finally outlines the scheme of a demonstration project.
Although open-pit mining in China has a history of thousands of years, modern slope design method was introduced in 1950's when engineering analogy method was dominant. In 1970's-80's, rock mechanical test techniques and computational methods were widely applied for quantitative assessment of the slope stability, and the slope designs were to a great extent guided by Pit Slope Manual (Canada Centre for Mineral and Energy Technology 1977) and Rock slope engineering (Hoek & Bray 1981). Until 1991, China had its design guidelines- MINING HANDBOOK (Metallurgical Industry Press 1991) which has been followed widely so far. Based on the above-mentioned, the historical progress of open-pit slope design methods in China can be divided into3 stages, the features of which are outlined in Table1.
(Table in full paper)
First stage: in the early years of this stage, slope angle was determined solely according to economic stripping ratio and analogy method.