At present, the research on anti-dip seam is not enough. It is generally believed that its sliding along the approximate circular sliding surface will lead to tracking failure. With the increase of mining depth, anti-slope landslides also occur from time to time. Studying the stability of this kind of slope has become an urgent problem to be solved in production practice. In this section, taking the south slope of Haizhou Mine as an example, the slope stability is studied by the method of subsection along the whole length.
In the past, the treatment of Haizhou Mine was concentrated on the north side, but the south side has not been treated, which led to serious geological landslides, surface deformation, surface subsidence, ground fissures, spontaneous combustion of residual coal and other disasters, which seriously affected people's lives and production.
Figure 6- 10 shows the general situation of the open-air Nangang in Haizhou.
Fig. 6- 10 untreated south slope of Haizhou open pit mine
In order to comprehensively control the slope jointly mined by open-pit workers in the south of Haizhou Mine, factors such as three-dimensional scanning mapping of open-pit slope, mined-out area of underground workers, geological exploration stratum, total slope angle and slope height are comprehensively considered, and the main creep deformation and sliding direction of slope deformation or sliding body are taken as the cutting line, and the 12 calculation profile is determined, including W7, W5, W3 and E 1.
The stratigraphic structure characteristics of each profile are as follows: the 700m long slope of W3 ~ E4 profile is located in the north wing of anticline axis, and the bedding characteristics of coal seam are obviously transformed; E2 and E4 sections were cut by the middle Taiping 1 fault (reverse fault); E8 and E 10 were cut by No.3 fault (reverse fault) in the middle of Taiping. E 1 6 and E 18 sections are cut by the1fault (reverse fault) east of Taiping; E20 section was cut by Gaode 1 and No.2 faults (anterograde faults).
Based on the analysis of the whole slope height, the simulated total height is about 400 ~ 450 m; The horizontal range is intercepted according to the shape of each section: the coordinate at the south end is -600m, and the total length is 700 ~1100 m. In order to truly reflect the overall stability characteristics of the slope, according to the latest three-dimensional scanning topographic map, the mining data of small coal mines in the south slope are consulted to determine the topography, rock stratum, coal seam, fault, roadway, goaf, etc. of each calculated section.
According to the engineering geological survey results of Nanbang sections, the input physical and mechanical parameters are refined and the stability is analyzed. The Quaternary soil layer, coal seam, goaf, roadway and fault in the profile are all simulated according to the material parameters of the actual profile. The calculation results can truly reflect the safety factor index of each section of the south slope of the mine field.
(2) Analysis before reinforcement
The calculation model of the south side 12 profile of Haizhou mine is established, and the current slope safety factor of each profile is calculated. The results are shown in Figure 6- 1 1 and summarized in Table 6-5.
Figure 6- 1 1
Figure 6- 1 1
Figure 6- 1 1
Figure 6- 1 1 Part Status
Table 6-5 Current Slope Safety Factor 6-5 W7 ~ E25 Section
It can be seen from the calculation results that the safety factor of W3 ~ E 17 is between 1.0 ~ 1. 15, which is quite different from the safety factor limit. W3 ~ E 1 is the most dangerous area for landslide. It can be seen from the calculation results that the weak surface of the lower slope in this section has obvious bedding characteristics and is prone to local landslides. The upper part of the slope is the dense distribution area of on-site fire spots. Among them, the current safety factor of E 1 section is only Fs= 1.002, which is far less than 1.30, and it is easy to induce landslides under the influence of other factors.
(3) Analysis after reinforcement
Slope cutting and foot pressing method:
1) pit top: on the premise of satisfying the road and safe distance, the slope cutting line at the pit top should be as close as possible to the existing railway line and the factory area.
2) Bottom of the pit: the backfill elevation of the toe of the slope is set to -90m, and this elevation is also set to the elevation of the cutting point at the bottom of the pit, so that the width from the cutting slope to the top of the pit is gradually increased and pushed to the design cutting line at the top of the slope. If the current pit bottom elevation is higher than -90m, this elevation shall prevail.
3) Slope: the height of each level 10m, and the width of the slab is 3 ~ 5m. According to the calculation, the total slope angle of the central E 1 ~ E 17 danger zone after slope cutting is 34 ~ 37.
4) Goaf: Water-sand filling method is adopted for treatment.
According to the above principles, the slope cutting, foot pressing and goaf treatment schemes are designed, and the safety factor is calculated after modeling and inputting physical and mechanical parameters, as shown in Figure 6- 12. The results are shown in Table 6-6.
Table 6-6 Calculation Results of Safety Factor after Slope Cutting in W7 ~ E25 Section
Figure 6- 12
Figure 6- 12
Figure 6- 12
Figure 6- 12 Calculation Results of Section Stability
From the calculation results, it can be seen that the safety factor of each section is improved after reinforcement, which meets the minimum safety factor requirement.
(4) Conclusion
The results of limit equilibrium calculation of each profile show that the overall slope and local slope of the south side of Haizhou Mine can not meet the requirements of safety factor and must be treated. In the design of slope bottom treatment, we should grasp the principle of shallowest slope cutting and lowest cost, and draw up the reinforcement scheme; Check the stability of the existing slope and the slope after cutting, analyze the stability law of the whole length of the south slope, and put forward the design scheme of cutting the foot of the slope.
1) As can be seen from the three-dimensional slope numerical simulation nephogram, the maximum deformation is mainly concentrated in the area with the elevation of 0 ~- 150 m, and the analysis reason is that it is affected by the mining of middle and Taiping upper coal seams.
2) The safety factor of W3 ~ e17 is between 1.0 ~ 1. 15, which is far from the limit value of the safety factor and must be treated. Especially W3 ~ E 1 area is the most dangerous area of landslide.
3) The safety factors of 3)W7 ~ W5 and E23~E25 meet the requirements, and there is no need to cut the slope.
4) In W3 ~ E4 section, if the stripping amount is too large, the lower bedding area of coal seam fold will be exposed. It is suggested that the slope cutting and backfilling of this section should be combined to minimize the amount of slope cutting.
5) Slope must be cut in the range of W4 ~ E22 on the south side, and it is suggested to carry out proper slope shaping in the rest area with a total length of 2,600 m to realize smooth connection with the flat plate in W4 ~ E22 area.
6) During calculation, the backfill elevation at the bottom of the pit is set to -90m, which is also the location of the undercut point. In the design, the lowest elevation value of the bottom presser foot is -90m, and the elevation of the whole bottom backfill presser foot shall not be lower than this value.
7) Suggested design parameters for slope cutting: step height 10m, flat plate width 3 ~ 5m, and the inclination angle of each step is less than 46; The overall slope angle is less than 38, which basically conforms to the concept of 38 38' given at the beginning of Haizhou Mine construction.