Mining Handbook. Volume 3

Author: Chief Editor: Li Baoxiang
Publisher:
Publish Date: 1999-09-01
Features: The Mining Handbook is divided into 41 chapters and published in seven volumes:
Volume I: Mine Geology and Mine Surveying
Volume II: Blasting and Rock Support
Volume III: Open-Pit Mining
Volume IV: Underground Mining
Volume V: Mine Transport and Equipment
Volume VI: Mine Ventilation and Safety
Volume VII: Mine Management
This volume is the third part, covering five chapters: Open-Pit Mining, Open-Pit Slope Engineering, Open-Pit Mining of Sandstone Deposits, In-situ Leaching, Solution Mining, Hot Melting Mining, and Salt Lake Mining, as well as Marine Mining. This book is primarily intended for mine mining engineers, but it is also an important reference for researchers, designers, educators, and mine management personnel involved in mining.
Excerpt:
The depth of mining \( H = H_k - \frac{B}{\cot y + \cot \beta} \) (Equation 12-8)
Where:
\( H \) — Design depth of the open-pit mine, in meters;
\( H_k \) — Reasonable depth of open-pit mining with zero bottom width, in meters;
\( B \) — Design bottom width of the open-pit mine, in meters;
\( y \) — Final slope angle of the open-pit mine's top bench, in degrees;
\( \beta \) — Final slope angle of the open-pit mine's bottom bench, in degrees.
Figure 12-9b shows a schematic diagram of determining the reasonable mining depth on the cross-section of an inclined ore body using a graphical method. According to the selected final slope angle, determine the depth using the methods and steps shown in Figure 12-9a. First, draw the final slope lines for the boundary schemes AiBiOi, and select the upper bench surface boundary scheme DiCi (i = 1, 2, 3, ..., n) based on the same principle. Extend DiCi so that \( CiE_i = \frac{DiCi}{n \cdot H} \) (Equation 12-9)
Where:
\( DiCi \) — Rock segment on the final slope line of the lower bench of the i-th scheme, in meters;
\( CiE_i \) — Ore segment on the final slope line of the lower bench of the i-th scheme, in meters.
Connect the bottom points O1, O2, O3, ..., Om of the upper bench and the bottom points E1, E2, E3, ..., En, respectively, to obtain the curves O1O2O3...Om and E1E2E3...En. The intersection point Ok of these two curves is the reasonable mining depth with zero bottom width of the open-pit mine. Then, calculate the reasonable mining depth for the designed open-pit mine with bottom width B using Equation (12-8).
Determination of Mining Depth for Short Open-Pit Mining
Select several possible mining depth schemes. For each scheme, determine the bottom boundary of the mining area on the corresponding stratigraphic plan. Then, determine the surface boundary of the mining area (see Figure 12-5). Calculate the stripping ratio \( n_{j1}, n_{j2}, n_{j3}, ... \) for each depth scheme using the plan method. List the results and plot the \( n \)–\( H \) relationship curve. Identify the intersection point of \( n = f(H) \) and \( n = f(H) \). The abscissa corresponding to this point is the mining depth of the open-pit area.
Since determining the mining depth of a short open-pit area is essentially the design depth of the open-pit area, no further adjustments are needed on the longitudinal section.
12.2.3.4 Determining the Bottom Boundary of the Open-Pit Mining Area
A Adjusting the Longitudinal Bottom Elevation of the Open-Pit Mine
The bottom elevation of the open-pit mine determined by the plan method generally does not require additional adjustment. However, the longitudinal bottom elevation of long open-pit areas needs to be adjusted. The specific method is to project the reasonable mining depth determined on each geological section onto the longitudinal section (see Figure 12-10). Connect the points to obtain the theoretical longitudinal profile of the bottom of the open-pit mine. When the theoretical depths of the longitudinal sections differ little, the longitudinal section can be designed at the same elevation. When the burial depth of the ore body varies significantly along the strike, the bottom plane can be adjusted to a stepped shape. The adjusted lowest longitudinal length of the bottom plane should meet the requirements for setting up transport routes. The adjustment principle is that the stripping ratio of the entire mine after adjustment should be equal to or close to the economically reasonable stripping ratio. Approximately, the upper and lower areas of the adjusted bottom plane can be made equal in area.
B Defining the Perimeter of the Bottom Plane of the Open-Pit Mine
First, draw the geological stratigraphic plan of the level based on the adjusted mining depth. Correct the boundaries of each cross-section according to the adjusted mining depth, and project the positions of the bottom of each cross-section onto the aforementioned geological stratigraphic plan. Connect the bottom points of the upper bench and lower bench to obtain the theoretical perimeter of the bottom. The correction principle is that the bottom perimeter should be straight, with curved sections meeting the requirements for the radius of curvature of transport routes; the length of the bottom should meet the needs for setting up transport routes. The corrected perimeter is the design perimeter, as shown in Figure 12-11.
12.2.3.5 Drawing the Final Plan of the Open-Pit Mining Area
Based on the determined development and transport system, final bench components, and the perimeter of the bottom plane of the open-pit mine, draw the final plan of the open-pit mine. The steps are as follows:
(1) Draw the designed bottom perimeter on a transparent sheet.
(2) Cover the transparent sheet with the topographic map. Starting from the bottom perimeter, draw the slope bottom lines, slope top lines, and platform widths of each bench from inside to outside (with elevation from bottom to top) according to the final bench components (step height, slope angle, platform width), as shown in Figure 12-12.
(3) Layout the transport routes on the map. When drawing the routes, pay attention to the connection between inclined routes and each bench.
(4) Check and correct the above open-pit mining boundaries.
After drawing the final plan of the open-pit mining area, correct the boundaries of each cross-section based on this plan to ensure consistency between the plan and the cross-sections. In some cases, if the bench changes significantly after the layout of the development and transport routes, check the rationality of the final determination, i.e., whether the stripping ratio exceeds the economically reasonable stripping ratio, and make necessary corrections.