A diversion method for open-pit mine parallel mining interval joint mining

Abstract

The present invention discloses a method for diverting open-pit and underground mining in parallel mining intervals of an open-pit mine, comprising the steps of lateral wall expansion, inverted L-shaped trench retention, pre-buried pipelines, layout of a dual-continuous transport system, underground interval mining and backfilling, advancement of a new mining area and trench backfilling, and the like; lateral wall expansion is carried out simultaneously with open-pit mining, which not only prepares for diversion in advance but also does not affect the normal production of the open-pit mine; the inverted L-shaped trench retention provides construction space for subsequent processes while avoiding a large amount of occupation of pit bottom space and does not affect the normal soil discharge of an internal dumping yard; the pre-buried pipelines leave road space for trucks running in the mining area, avoiding the cost of vehicle detours caused by the intersection of roads and belt conveyors; the layout of the dual-continuous transport system solves the problem of coal transportation in the underground mining stage and reduces the stripping and transportation cost of the new mining area, and after improvement, it can also reduce the trench backfilling cost; underground mining and backfilling ensure both mining efficiency and mining safety; seamless switching between new and old mining areas ensures the production capacity of the mine.

Description

Technical Field

[0001] The present invention relates to a steering method for parallel mining areas in an open-pit mine, and in particular to a steering method for combined open-pit and well mining between parallel mining areas in an open-pit mine. Background Art

[0002] Parallel open-pit mining refers to two adjacent open-pit mining areas, extending in the same direction or 180° apart. Currently, there are three common methods for diverting adjacent open-pit mining areas: re-trenching, double right-angle diversion, and 180° fan diversion. Re-trenching involves re-trenching and expanding the walls at the boundary of the new mining area after the old mining area has been mined to its limit, forming a new working face for the new mining area. This method requires significant infrastructure and is rarely used. Double right-angle diversion involves expanding the walls of the old mining area near the new mining area to form a first working face, which is then advanced toward the new mining area, achieving the first right-angle diversion. Once the working face has reached the boundary of the new mining area, the walls of the old mining area near the extension of the mining area are expanded to form a second working face, which is then advanced toward the extension of the new mining area, achieving the second right-angle diversion, thus completing the diversion task. This method is simple to operate, but it can pose issues such as uneven drainage space at different times. Sector-shaped diversion involves rotating the working line in the old mining area 180° around a certain center of rotation until the working face is perpendicular to the direction of advancement in the new mining area. This method provides a continuous working line and evenly distributes internal space, but the working line length fluctuates continuously, resulting in a limited effective working surface, complex construction management, and a significant impact on mine production capacity.

[0003] The above three existing methods of open-pit mine diversion in adjacent mining areas each have their own advantages and disadvantages. Therefore, studying how to give full play to the advantages of joint mining technology to achieve diversion between parallel mining areas in open-pit mines is currently an important and promising topic. Summary of the Invention

[0004] In response to the problems existing in the above-mentioned prior art, the present invention provides a method for steering open-pit mine parallel mining intervals and underground mining, which combines the dual advantages of open-pit mining and underground mining, ensures mine output with the high efficiency of open-pit mining, and realizes the mining of coal resources in deep or near corners with the flexibility of underground mining, thereby ensuring resource recovery rate.

[0005] To achieve the above-mentioned object, the present invention provides the following technical solution: a method for diverting open-pit mine parallel mining intervals, comprising six steps: horizontal wall expansion, inverted L-shaped trenching, pre-buried pipelines, dual continuous transportation system layout, underground mining and backfilling, and advancing the new mining area and backfilling the trench;

[0006] Horizontal expansion: The area two to three years from the bottom boundary of the old and new mining areas is divided into a turning area. When the stripping line of the old mining area is first advanced to the boundary of the turning area, on the one hand, the stripping line of the old mining area continues to advance in the old mining area while maintaining the same advancement direction. On the other hand, the stripping line of the old mining area is extended horizontally toward the side of the new mining area and expanded to the outer boundary of the new mining area to form the stripping line of the new mining area. At the same time, the mining working face of the old mining area is also extended to the new mining area along with the stripping line of the old mining area, forming the mining working face of the new mining area in the new mining area.

[0007] Inverted L-shaped trench: While the stripping line in the old mining area is advancing normally and expanding horizontally, the inner dump follows suit. The bottom of the inner dump in the turning area is kept 50-100m away from the mining working face of the old mining area and the boundary between the old and new mining areas. As the stripping line in the old mining area continues to advance, an inverted L-shaped trench gradually forms at the bottom of the pit. The trench between the inner dump and the boundary between the old and new mining areas serves as the well construction working face.

[0008] Pre-buried pipelines: During the dumping process, transport pipelines are pre-buried inside the inner dumping yard in the turning area. The inlet of the transport pipeline is located at the bottom of the well construction working surface and at the inner boundary of the turning area. The outlet of the transport pipeline is located on the upper surface of the inner dumping yard and close to the outer boundary of the old mining area.

[0009] Double continuous transport system layout: As the mining working face of the old mining area gradually advances, a continuous coal mining belt conveyor and a continuous stripping belt conveyor are respectively set up on the underground construction working face, in the pre-buried pipeline and on the surface of the internal dumping ground;

[0010] Underground intermittent mining and backfilling: When the mining working face in the old mining area exceeds the boundary of the turning area by 50m, horizontal adits are excavated intermittently in the new mining area based on the underground construction working face. Coal in the horizontal adits is mined using underground mining methods, and the mined coal is directly transferred to the coal mining belt conveyor for transportation;

[0011] Advancement of new mining area and backfilling of trenches: On the one hand, the mining face of the old mining area is advanced to the end, and the stripping working line and mining working face of the new mining area are ready. At this time, the open-pit mining working face is transferred from the old mining area to the new mining area, and the stripping working line and mining working face of the new mining area are advanced along the extension direction of the new mining area to mine coal;

[0012] On the other hand, after all the coal on the side of the turning area close to the new mining area is mined through underground mining, all mining equipment, all stripping belt conveyors, and the coal mining belt conveyors in the pre-buried transport pipeline 13 are withdrawn, and the coal mining belt conveyors within the underground construction working face are retained. The inverted L-shaped trench in the old mining area is buried with the materials stripped from the new mining area.

[0013] The turnaround is now complete and the open-pit mine is operating normally in the new mining area.

[0014] Furthermore, the transport pipeline is formed by connecting several sections of prefabricated circular concrete pipes, and the inclination angle of the pre-buried transport pipeline is maintained within 14°.

[0015] Furthermore, the loading positions of the coal mining belt conveyor and the stripping belt conveyor in the dual continuous transportation system arrangement are both located on the underground construction working surface, the unloading point of the coal mining belt conveyor is located near the surface crushing station, and the unloading point of the stripping belt conveyor is located on the surface of the inner spoil dump in the old mining area and is connected to a continuous spoil dumping device.

[0016] Furthermore, the cross-section of the horizontal tunnel is rectangular, with a width of 20-30m and a height of 4-8m. The depth of the horizontal tunnel extends to the outer boundary of the new mining area. The width of the interval between two adjacent mining tunnels is 20-30m. The horizontal tunnel continues to advance as the mining working face of the old mining area advances. After the horizontal tunnel is mined, it is filled with open-pit mine stripping materials. After the two adjacent horizontal tunnels are filled, a new mining tunnel is arranged in the area between the two horizontal tunnels to mine the coal in the area. This reciprocating process is used to realize the complete mining of the coal on the side of the turning area close to the new mining area.

[0017] Furthermore, the horizontal tunnels can be arranged in multiple layers.

[0018] Furthermore, when the inverted L-shaped trench is buried, the loading point of the coal mining belt conveyor located within the underground construction working face is adjusted to the vicinity of the mining working face of the new mining area, and the unloading point is adjusted to the end of the underground construction working face close to the bottom boundary of the old and new mining areas, thereby converting it into a backfill belt conveyor. The materials stripped from the new mining area are transported to various positions in the inverted L-shaped trench via the backfill belt conveyor. As the inverted L-shaped trench is gradually buried, the backfill belt conveyor is also disassembled and shortened, and a reverse backfill method is adopted until the inverted L-shaped trench is filled.

[0019] Compared with the existing technology, the horizontal expansion of the present invention is carried out simultaneously with open-pit mining, which can prepare for the turning in advance without affecting the normal production of the open-pit mine; the inverted L-shaped ditch provides construction space for subsequent processes while avoiding occupying a large amount of pit bottom space and does not affect the normal discharge of soil in the inner spoil yard; the pre-buried pipeline leaves road space for trucks in the mining area, avoiding the cost of vehicle detours caused by the intersection of roads and belt conveyors, and at the same time can provide protection for the belt conveyor to prevent the influence of weather and falling rocks in the spoil yard; the double continuous transportation system layout solves the coal transportation problem in the underground mining stage and reduces the stripping of new mining areas. The improvement can also reduce the transportation cost and trench backfill cost; the parallel deployment of dual systems reduces construction cost and the difficulty of operating and maintaining pipelines; underground mining and backfilling ensure the mining efficiency and improve the safety of underground mining; seamless switching between old and new mining areas ensures the production capacity of the mine; the plan is implemented in parts and areas, with little interference between each other, which is convenient for organization and management; the whole plan combines the dual advantages of open-pit mining and underground mining, using the high efficiency of open-pit mining to ensure mine output, and using the flexibility of underground mining to realize the mining of coal resources in the turning area, and in the process of realizing the turning, the resource recovery rate is guaranteed to the greatest extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the initial stage of the present invention;

[0021] Figure 2 This is a schematic diagram of the present invention turning to the mid-term stage;

[0022] Figure 3 This is a schematic diagram of the final stage of the transition;

[0023] In the figure: 1-bottom boundary of the new and old mining areas; 2-turning area; 3-old mining area; 4-stripping working line of the old mining area; 5-inner boundary of the turning area; 6-new mining area; 7-external boundary of the new mining area; 8-mining working face of the old mining area; 9-mining working face of the new mining area; 10-inner dump; 11-pit bottom; 12-underground construction working face; 13-transport pipeline; 14-external boundary of the old mining area; 15-coal mining belt conveyor; 16-stripping belt conveyor; 17-crushing station; 18-continuous dumping device; 19-ground surface; 20-horizontal adit; 21-backfill belt conveyor; 22-stripping working line of the new mining area. DETAILED DESCRIPTION

[0024] The present invention will be further described below with reference to the accompanying drawings.

[0025] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0026] like Figures 1 to 3 As shown, the present invention provides a technical solution, including six steps: horizontal wall expansion, inverted L-shaped trench, pre-buried pipelines, double continuous transportation system layout, well mining and backfilling, and new mining area advancement and trench backfilling.

[0027] Horizontal expansion: The range of two to three years of advancement from the bottom boundary 1 of the old and new mining areas, generally 600-1000m, is divided into the turning area 2. When the old mining area stripping work line 4 is first advanced to the boundary 5 of the turning area, on the one hand, the old mining area stripping work line 4 maintains the same advancement direction in the old mining area 3 and continues to advance the mining of coal in the old mining area 3. On the other hand, the old mining area stripping work line 4 is laterally extended toward the side of the new mining area 6 and expanded to the outer boundary 7 of the new mining area, forming a new mining area stripping work line 22. At the same time, the old mining area mining face 8 also extends to the new mining area 6 along with the old mining area stripping work line 4, forming a new mining area mining face 9 in the new mining area 6. At this stage, the stripping work line construction within the new mining area 6 is mainly to prepare for the formation of the new mining area mining face 9. Therefore, the new mining area stripping work line 22 does not need to be advanced synchronously with the old mining area stripping work line 4.

[0028] Inverted L-shaped ditch: While the stripping work line 4 in the old mining area is advancing normally and expanding laterally, the inner spoil dump 10 follows the advancement, and the bottom of the inner spoil dump 10 located in the turning area 2 is kept 50-100m wide from the mining working face 8 of the old mining area and the boundary line between the old and new mining areas. As the stripping work line 4 in the old mining area continues to advance, an inverted L-shaped ditch gradually forms at the bottom of the pit 11, and the ditch between the inner spoil dump 10 and the boundary line between the old and new mining areas is the well construction working face 12; the purpose of the inverted L-shaped ditch is to provide construction space for subsequent processes while not occupying too much space at the bottom of the pit 11, and try not to affect the normal soil discharge of the inner spoil dump 10, because in the previous step of horizontal expansion, the inner spoil dump in the new mining area 6 has not yet been formed, so the materials stripped during the horizontal expansion process also need to be transported to the inner spoil dump 10 in the old mining area 3.

[0029] Pre-buried pipelines: During the dumping process of the inner dumping yard 10 in the turning area 2, a transport pipeline 13 is pre-buried inside the inner dumping yard 10. The entrance of the transport pipeline 13 is located on the pit bottom 11 of the well construction working face 12 and is located on the inner boundary 5 of the turning area. The outlet of the transport pipeline 13 is located on the upper surface of the inner dumping yard 10 and is close to the outer boundary 14 of the old mining area; the transport pipeline 13 is connected by several sections of prefabricated circular concrete pipes, and the inclination angle of the pre-buried transport pipeline 13 is maintained within 14° to ensure the stability of transportation; the transport pipeline 13 is pre-buried in the inner dumping yard 10 to reserve space for trucks to operate in the mining area, avoid the vehicle detour cost caused by the intersection of the road and the belt conveyor in the transport pipeline 13, and at the same time provide protection for the belt conveyor to prevent the influence of weather and falling rocks in the dumping yard.

[0030] Layout of the dual continuous transportation system: As the mining working face 8 of the old mining area gradually advances, a continuous coal mining belt conveyor 15 and a continuous stripping belt conveyor 16 are respectively set on the underground construction working face 12, in the pre-buried pipeline 13 and on the surface of the inner spoil dump 10; the loading positions of the coal mining belt conveyor 15 and the stripping belt conveyor 16 are both located on the underground construction working face 12, and the two conveyors can be continuously connected and lengthened as the underground construction working face 12 extends. The unloading point of the coal mining belt conveyor 15 is located near the surface crushing station 17, and the unloading point of the stripping belt conveyor 16 is located on the surface of the inner spoil dump 10 in the old mining area 3, and is connected to the continuous soil discharge device 18 for subsequent process soil discharge. The stripping materials from the steps close to the ground surface 19 can be transported to the inner spoil yard 10 by truck. When the lateral expansion step is carried out to the later stage, the stripping belt conveyor 16 has been laid out. At this time, during the stripping process of the lateral expansion step, the stripping materials near the bottom of the pit 11 are transported to the inner spoil yard 10 by the stripping belt conveyor 16 for disposal, which greatly reduces the stripping transportation cost.

[0031] Underground intermittent mining and backfilling: When the distance between the mining working face 8 in the old mining area and the boundary 5 in the turning area reaches 50m, a horizontal tunnel 20 is excavated in an intermittent jumping manner toward the interior of the new mining area 6 based on the underground construction working face 12. The coal in the horizontal tunnel 20 is mined using the underground mining method, and the mined coal is directly transferred to the coal mining belt conveyor 15. The coal is then transported in sequence through the underground construction working face 12, the transportation pipeline 13, the internal spoil dump 10 to the crushing station 17, and the coal is crushed and loaded onto trucks. The horizontal tunnel 20 has a rectangular cross-section, a width of 20-30m, and a height of 4-8m. The depth of the horizontal tunnel 20 reaches the outer boundary 7 of the new mining area, and the width of the interval between adjacent mining tunnels is 20-30m. The horizontal tunnel 20 continues to advance as the mining working face 8 of the old mining area advances. After the horizontal tunnel 20 is mined, the mining equipment is withdrawn and the open-pit mine stripping material is used for filling. After the two adjacent horizontal tunnels 20 are filled, a new mining tunnel is laid in the area between the two horizontal tunnels 20 to mine the coal in this area. This reciprocating process is carried out to achieve the complete mining of the coal on the side of the turning area 2 close to the new mining area 6. When the coal seam thickness is too large, the horizontal tunnel 20 can be laid out in multiple layers. When using multiple layers, the upper and lower mining tunnels at the same location should be mined alternately, that is, the upper mining tunnel is mined first, and after the upper mining tunnel is filled, the lower mining tunnel is mined. It is not necessary to mine the entire upper layer before mining the lower layer.

[0032] Advancement of the new mining area and backfilling of the trench: On the one hand, after the mining working face 8 of the old mining area is advanced to the end, that is, after the mining of the old mining area 3 is completed, the stripping working line 22 of the new mining area and the mining working face 9 of the new mining area are ready. At this time, the open-pit mining working face is transferred from the old mining area to the new mining area, and the stripping working line 22 of the new mining area and the mining working face 9 of the new mining area are advanced along the extension direction of the new mining area 6 to mine coal; this process can keep the open-pit mining continuous and ensure that the output is not reduced. On the other hand, after the coal on the side of the turning area 2 close to the new mining area 6 is fully mined through underground mining, all mining equipment is withdrawn, all stripping belt conveyors 16 are withdrawn, and the coal mining belt conveyors in the pre-buried transport pipeline 13 are withdrawn. The coal mining belt conveyors 15 within the scope of the underground construction working face 12 are retained, and the materials stripped from the new mining area 6 are used to bury the inverted L-shaped trench of the old mining area 3, which not only prevents the water in the trench from affecting the stability of the inner spoil dump 10, but also makes full use of the mine space. When burying the inverted L-shaped trench, the loading point of the coal mining belt conveyor 15 located within the underground construction working face 12 is adjusted to the vicinity of the mining working face 9 of the new mining area, and the unloading point is adjusted to the end of the underground construction working face 12 near the bottom boundary 1 of the new and old mining areas, thereby converting it into a backfill belt conveyor 21. The materials stripped from the new mining area 6 are transported to various positions in the inverted L-shaped trench via the backfill belt conveyor 21. As the inverted L-shaped trench is gradually buried, the backfill belt conveyor 21 is also disassembled and shortened, and a reverse backfill method is adopted until the inverted L-shaped trench is filled.

[0033] After completing the above steps, the parallel mining area open-pit mine and underground mining are all completed, and the open-pit mine is operating normally in the new mining area 6.

[0034] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

[0035] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any minor modifications, equivalent replacements, and improvements made to the above embodiments based on the technical essence of the present invention shall be included in the scope of protection of the technical solution of the present invention.

Claims

1. A method for diverting open-pit mine parallel mining intervals between open-pit mines, characterized in that: It includes six steps: horizontal wall expansion, inverted L-shaped trench, pre-buried pipelines, dual continuous transportation system layout, underground mining and backfilling, and new mining area advancement and trench backfilling. Horizontal expansion: The area of ​​two to three years of advancement from the bottom boundary of the old and new mining areas (1) is divided into a turning area (2). When the stripping working line (4) of the old mining area is first advanced to the boundary (5) of the turning area, on the one hand, the stripping working line (4) of the old mining area continues to advance in the old mining area (3) while maintaining the same advancement direction. On the other hand, the stripping working line (4) of the old mining area is laterally extended and expanded to the outer boundary (7) of the new mining area to form the stripping working line (22) of the new mining area. At the same time, the mining working face (8) of the old mining area is also extended to the new mining area (6) along with the stripping working line (4) of the old mining area, forming the mining working face (9) of the new mining area (6). Inverted L-shaped trench: while the old mining area stripping line (4) is advancing normally and expanding horizontally, the inner dump (10) is advancing accordingly, and the bottom of the inner dump (10) located in the turning area (2) is kept 50-100m away from the old mining area mining working face (8) and the boundary line between the new and old mining areas. As the old mining area stripping line (4) continues to advance, an inverted L-shaped trench is gradually formed at the pit bottom (11). The trench between the inner dump (10) and the boundary line between the new and old mining areas is the well construction working face (12); Pre-buried pipelines: During the dumping process of the inner dumping field (10) in the turning area (2), a transport pipeline (13) is pre-buried inside the inner dumping field (10). The inlet of the transport pipeline (13) is located on the pit bottom (11) of the well construction working surface (12) and is located on the inner boundary (5) of the turning area. The outlet of the transport pipeline (13) is located on the upper surface of the inner dumping field (10) and is close to the outer boundary (14) of the old mining area. Dual continuous transport system arrangement: as the mining working face (8) of the old mining area gradually advances, a continuous coal mining belt conveyor (15) and a continuous stripping belt conveyor (16) are respectively set on the underground construction working face (12), in the transport pipeline (13) and on the surface of the inner spoil dump (10); Underground intermittent mining and backfilling: When the distance between the mining working face (8) of the old mining area and the boundary (5) of the turning area reaches 50m, a horizontal tunnel (20) is excavated intermittently from the underground construction working face (12) to the interior of the new mining area (6). The coal in the horizontal tunnel (20) is mined using the underground mining method, and the mined coal is directly transferred to the coal mining belt conveyor (15) for transportation; Advancement of the new mining area and backfilling of the trench: On the one hand, the mining face (8) of the old mining area is advanced to the end, and the stripping line (22) and the mining face (9) of the new mining area are ready. At this time, the open-pit mining face is transferred from the old mining area to the new mining area, and the stripping line (22) and the mining face (9) of the new mining area are advanced along the extension direction of the new mining area (6) to mine coal; On the other hand, after all the coal on the side of the turning area (2) close to the new mining area (6) is mined through underground mining, all mining equipment is withdrawn, all stripping belt conveyors (16) are withdrawn, and the coal mining belt conveyors in the pre-buried transport pipeline (13) are withdrawn, and the coal mining belt conveyors (15) within the scope of the underground construction working face (12) are retained, and the inverted L-shaped trench of the old mining area (3) is buried with the materials stripped from the new mining area (6); At this point, the turnaround is complete and the open-pit mine is operating normally in the new mining area (6).

2. The method for diverting open-pit mine parallel mining intervals according to claim 1, characterized in that: The transport pipeline (13) is formed by connecting a plurality of sections of prefabricated circular concrete pipes, and the inclination angle of the pre-buried transport pipeline (13) is maintained within 14°.

3. The method for diverting open-pit mine parallel mining intervals according to claim 1, characterized in that: The loading positions of the coal mining belt conveyor (15) and the stripping belt conveyor (16) in the dual continuous transport system arrangement are both located on the well construction working surface (12), the unloading point of the coal mining belt conveyor (15) is located near the surface crushing station (17), and the unloading point of the stripping belt conveyor (16) is located on the surface of the inner dumping yard (10) in the old mining area (3) and is connected to the continuous dumping device (18).

4. The method for diverting open-pit mine parallel mining intervals according to claim 1, characterized in that: The cross section of the horizontal tunnel (20) is rectangular, with a width of 20-30m and a height of 4-8m. The depth of the horizontal tunnel (20) reaches the outer boundary (7) of the new mining area, and the width of the interval between two adjacent mining tunnels is 20-30m. The horizontal tunnel (20) is continuously advanced as the mining working face (8) of the old mining area is advanced. After the horizontal tunnel (20) is mined, it is filled with open-pit mine stripping materials. After the two adjacent horizontal tunnels (20) are filled, a new mining tunnel is arranged in the area between the two horizontal tunnels (20) to mine the coal in the area. This reciprocating process is used to realize the complete mining of the coal on the side of the turning area (2) close to the new mining area (6).

5. The method for diverting open-pit mine parallel mining intervals according to claim 4, characterized in that: The horizontal tunnel (20) is arranged in multiple layers.

6. The method for diverting open-pit mine parallel mining intervals according to claim 1, characterized in that: When the inverted L-shaped trench is buried, the loading point of the coal mining belt conveyor (15) located within the scope of the underground construction working face (12) is adjusted to the vicinity of the mining working face (9) of the new mining area, and the unloading point is adjusted to the end of the underground construction working face (12) close to the bottom boundary (1) of the new and old mining areas, thereby being converted into a backfill belt conveyor (21). The materials stripped from the new mining area (6) are transported to various positions in the inverted L-shaped trench via the backfill belt conveyor (21). As the inverted L-shaped trench is gradually buried, the backfill belt conveyor (21) is also disassembled and shortened, and a backward backfilling method is adopted until the inverted L-shaped trench is filled.

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