RU2052119C1 - Method for preparation of permafrost placers for dredging - Google Patents

Abstract

FIELD: mining. SUBSTANCE: method for preparation of permafrost placers for dredging includes stripping of peats, natural thawing of sands, removal and disposing of a part of sands within transition district. Novelty consists in that after natural thawing of sands, in autumn, trench is formed along the entire transition district, and depth at the beginning of transition district equalling thickness of sands of sands and linearly decreasing to zero at the end of transition district. Sands removed in trench formation are located within limits of dragline run along trench flank into pile with height equal to depth of seasonal freezing of incoherent dewatered sands. In spring, when natural thawing begins, frozen sands in pile are loosened by layers and periodically returned to trench onto completely thawed sands. Front of work for returning sands from pile is successively advanced from beginning of trench to its end as sands become fully thawed on trench bottom. EFFECT: higher efficiency. 4 dwg

Description

 The invention relates to mining and can be used in the development of shallow permafrost placers, specifically those deposits in which it is not possible to retain water in flooded areas in order to protect the sands from seasonal freezing.

 The preparation of such placers for dredging is based on various methods of thawing seasonal or perennial permafrost and preventing seasonal freezing of thawed rock mass, which is transferred for dredging at the beginning of the next washing season. Drag operation in such conditions has two periods. In the first period (1-2 months), the dredge develops a site thawed in the previous year and protected for the winter from seasonal freezing. This site is called rolling. In the second period, the dredge fulfills the site, thawed already in the current year and called the site of the current preparation. Therefore, the preparation problem boils down to the reliable protection of the transitional area and the rapid thawing of the current preparation area.

On shallow perennially frozen placers and on thawed placers with a large depth of seasonal freezing, thawing of permafrost both in the transitional area and in the current preparation area is carried out by the heat of solar radiation, and protection from seasonal freezing by flooding [1]
Flooding has two drawbacks. Due to the multiple reduction of water inflow in the winter time or its complete cessation, the water level in the flooded area decreases rapidly and reliable protection of the entire transitional area becomes impossible. In addition, in order to increase the reliability of flooding, the water is raised in the autumn in the transitional area with a reserve, taking into account its withdrawal from the reservoir in the winter. An increased level of water rise leads to a complete or partial flooding of the current preparation area, and subsequently to its freezing in a state of maximum moisture capacity. For the summer, for this reason, the current preparation site thaws slowly, and the dredge after working out the transitional area (provided that it is reliably protected) does not have thawed reserves over the entire depth. This leads to losses of the richest lower part of the reservoir and to a decrease in dredge productivity.

There is a method of preparing frozen placers for dredging, which consists in giving the placer section planned for mining this year stepwise with a rise in the direction of dredge movement by layer-by-layer removal of the upper part of the rocks to be dredged beyond the bounds. After thawing of the first stage, the thickness of the rocks, at which at least the depth of 2-3-day thawing is left, the removed rocks are returned and begin to dredge, continuing to return the rocks to subsequent stages as they thaw. Return rocks are placed along the sides of the dragee course [2]
The disadvantage of this method is its low efficiency due to the length of time for preparatory work, because giving the dragee move a stepped form and thawing the steps are carried out in the warm period, and dredging of this move is carried out in the same year.

 The disadvantage of this method is also the significant cost of preparing the sands for dredging, associated with large distances of transportation of the sands in the preparation of the transition section, because the sands are removed beyond the dredged course with the rise of a peat dump.

 There is also a method of developing a placer in conditions of repeated dredging, which is adopted as a prototype, as the closest technical solution to the claimed invention.

 The known method includes overburden peat, natural thawing of sand, removal and placement of part of the sand within the transient area.

 The disadvantage of this method is its low efficiency when used on dragees, in which the slope of the valley is close to or exceeds the limit value, because the flooding of the deepened areas of the transition section on large longitudinal slopes does not provide their reliable protection against freezing due to the rapid withdrawal of water even in conditions of lowering its level. This subsequently leads to additional costs for removing ice and delaying the launch of the dredge, as Natural thawing of frozen sands in a state of maximum moisture capacity is slow.

 The task to which the claimed invention is directed is to increase the efficiency of the development of permafrost placers of those deposits where it is not possible to retain water in the flooded areas due to the large longitudinal slopes of the valley of the pellet landfill, the high permeability of rocks and the lack of water flow in winter.

 The task can be solved by achieving a technical result, which consists in reducing the time and cost of providing dredges with reserves ready for excavation for the entire washing season and accelerating the launch of dredges in the spring.

 The specified technical result is achieved by the fact that in the known method, including overburden peat, natural thawing of the sands, removal and placement of part of the sands within the transit section, according to the invention, after the natural thawing of the sand in autumn along its transition section, a trench is formed with a depth at the beginning of the transition section equal to power of the sands and linearly decreasing to zero at its end, place the sands removed during the formation of the trench within the dredging course along its side into a shoulder equal to the height the season of freezing of dry dehydrated sands, with the onset of natural thawing in spring, the sands frozen in the pile are loosened in layers and periodically returned to completely thawed sands at the bottom of the trench for complete thawing, while the front of the work to return the sands from the pile is progressively moved from the beginning of the trench to its end along the end as the sand completely thaws in the bottom of the trench.

 Comparative analysis shows that the claimed method differs from the prototype, which allows us to conclude that the claimed invention meets the criterion of "novelty."

 Each distinguishing feature is essential because the absence of any of them will not allow to achieve the specified technical result.

 The formation in the autumn time after natural thawing of the sands of a trench with a depth at the beginning of the transitional section of equal sand power and linearly decreasing to zero at its end can reduce the time and cost of giving part of the transitional section variable power, since work is carried out not by layer-by-layer thawing, but on completely thawed sand, and also to accelerate the launch of the dredge, as it does not require the time of the warm period in the year of dredging for layer-by-layer thawing of the sands to give the transition section a variable power.

Placing the sands removed during the formation of the trench within the dredging along the side in the pile equal to the depth of the seasonal freezing of loose dehydrated rocks allows reducing the amount of sand removal to give the transition site a variable thickness, because sands are not removed from the entire width of the dragee course, but only from its part and to reduce the cost of removing 1 m ^{3 of} sand, because they are placed within the dragee course with a shorter transportation distance.

 Periodic return of frozen sands from the pile using loosening in layers into the trench allows to increase the area of thawing of frozen sands, thereby reducing the time to thaw the pile and accelerate the launch of the dredge. Thus, all of the above signs make it possible to reduce the time and cost of preparatory work, accelerate the launch of dredge in the spring, and thereby increase the efficiency of the development of permafrost placers.

 To prove compliance of the claimed invention with the criterion of "inventive step", a comparison was made with other technical solutions known from sources included in the "prior art".

 The inventive method of preparing permafrost placers for dredging meets the requirements of an inventive step, because the combination of its essential features provides a reduction in time and cost of preparatory work, accelerating the launch of dredge in the spring, i.e. provides improved development of permafrost placers, which does not follow explicitly from the prior art.

 To prove the criterion of "industrial use" it is enough to say that the issue of using the proposed technical solution at the Chaldonka MP (Ksenyevsky mine, Chita region) in 1993 is being worked out

 In FIG. 1 shows a longitudinal section of the transition section along the trench at the time of completion of preparatory work in the autumn period; in FIG. 2 plan of the transitional site by the time of winter sludge dredge; in FIG. 3 cross-section along aa in figure 2 (at the time of completion of preparatory work in the autumn); in FIG. 4 the same, after thawing the sand in the pile by moving them into the trench in the spring.

где В_х ширина дражного хода, м;
Н_пр глубина промерзания рыхлых обезвоженных песков, м;
К_р коэф. разрыхления песков;
h_п мощность песков, м.The method is as follows. In autumn, after thawing the sands at full capacity, the place where the dredge stops at winter sludge is determined, the beginning and end of the transition section 1. The dimensions of the transition section depend on the capacity of the dredge and the existing fleet of earthmoving equipment and determine their minimum cost for processing 1 m ^{3 of} rock mass. Before the dredge approaches the transition area and is flooded with water from the dragee section, trench 2 and collar 3 are formed. In the event of groundwater, they are diverted by drainage ditches using the natural slope of the valley, or pumped out. With a dredging width of 60-70 m, one collar is formed, and with a larger width, two on both sides. Sands are moved from the trench to the pile with bulldozers or bulldozers in combination with dragline excavators. In the process of dumping the shoulder, they maintain a slope angle of 4 that is extremely possible for the existing type of earthmoving equipment and avoid moving equipment along it to prevent sand compaction. Since the depth of the trench towards the end of the transition section reaches zero, and the height of the shoulder must be constant and equal to the depth of the seasonal freezing of loosened dehydrated sands, the shoulder 3 in plan has a triangle shape with an apex at the end of the transition section. Width B _b collar 3 is calculated from the expression:
B _b =

where B _{x the} width of the dragee, m;
N _{pr the} depth of freezing of loose dehydrated sand, m;
To _r coefficient. loosening of sand;
h _{p the} power of the sand, m

 When the dredge approaches the beginning of the transitional section, the dredge is installed over a previously prepared “pillow”, water is released from the cut, and the dredge is lowered onto the “pillow”. In this position, the winter sludge dredges. In spring, at the end of the period with negative air temperatures, the freezing boundary 5 passes as shown in FIG. 3, and with the onset of positive air temperatures, the front of complete natural thawing of the sand left in the bottom of trench 2 gradually moves with the increase in the number of positive degree days from the beginning of trench 2 to its end. After thawing the sands at the beginning of trench 2 at a distance of 20-30 m along its length, they begin to return the sands from pile 3 to the thawed part of trench 2. To accelerate the preparation (thawing) of frozen sand from pile 3, they are returned with bulldozers using loosening. At the same time, the area of sand thawing and the rate of preparation of frozen sand in pile 3 increases. As the front of full natural thawing of sand in the bottom of trench 2 advances, the front of the return of sand from pile 3 to trench 2 is frozen. The frozen sands from pile 3 into trench 2 are returned layer by layer from the time interval necessary for the natural thawing of a layer of frozen sand laid in a trench. Upon the return of the sands, a recess 6 is formed at the border of the shoulder 3 and trench 2 to ensure thawing of the whole sands located at this boundary. After preparing the sands at the beginning of the transitional area in a volume sufficient for 5-7 days of dredging, the dredged section is flooded and dredging is started. Work on the preparation of the transition section 1 while continuing in the same sequence.

 The sequence of operations during the implementation of the method does not depend on the order of mining the placer dredge: from top to bottom or from bottom to top.

Claims (1)

 METHOD FOR PREPARING PERMANENT FROZEN SPRAYS FOR DRAGING, including peat overburden, natural thawing of sand, removal and placement of part of the sand within the transition section, characterized in that after natural thawing of the sand in the fall along the entire transition section, a trench is formed with depth at the beginning of the transition thickness, the depth of sand at the beginning of the transition section and linearly decreasing to zero at its end, place the sands removed during the formation of the trench within the dredging course along its side in a pile of high, equal depth seasonal freezing of loose dehydrated sands, with the onset of natural thawing in spring, the sands frozen in the pile are loosened in layers and periodically returned to completely thawed sands at the bottom of the trench for complete thawing, while the front of work on returning sand from the pile is progressively moved from the beginning of the trench to its end as full thawing of sand in the bottom of the trench.

Images