Stability Analysis and Engineering Measures of the Reclaimed Paddy Field in the Waste Dumping Site under Saturated Conditions

Abstract

The present invention discloses a method for stability analysis and engineering measures of a waste dump reclaimed into paddy fields under saturated conditions, belonging to the technical field of safety engineering. The steps are as follows: respectively construct a single-step waste dump and a multi-step vertical waste dump under natural conditions; construct a pile-slab retaining wall; conduct stability analysis of the single-step waste dump with a pile-slab retaining wall under natural conditions; respectively conduct stability analysis of the multi-step vertical waste dump with a pile-slab retaining wall under natural conditions; respectively construct a single-step waste dump and a multi-step vertical waste dump with a pile-slab retaining wall under saturated conditions; conduct stability analysis of the single-step waste dump and the multi-step vertical waste dump with a pile-slab retaining wall under saturated conditions to obtain the engineering measures for the single-step waste dump and the multi-step vertical waste dump under saturated conditions. The present invention solves the problems of stability analysis and engineering measures for the vertical slope waste dump of the reclaimed paddy fields.

Description

Technical Field

[0001] The present invention belongs to the technical field of safety engineering, and particularly relates to a method for stability analysis and engineering measures of a reclaimed paddy field after a waste dump under saturated conditions. Background Art

[0002] Cultivated land resources are resources related to the fate of all mankind and important production factors for the national economy and social development. Although China's land area ranks third in the world, cultivated land shows situations such as "non-grainification", "facilitation", and "marginalization". Due to China's large total population and social development, the actual situation of cultivated land in China is that the per capita cultivated land is scarce, the quality of cultivated land is not high, and the reserve resources of cultivated land are lacking. Temporary land generally cannot occupy permanent basic farmland. If a major construction project needs temporary land and it is truly difficult to avoid permanent basic farmland in the site selection, it can temporarily occupy permanent basic farmland with the approval of the natural resources department. After the expiration of the temporary land use, the original planting conditions need to be restored in a timely manner. According to the relevant contents of the Regulations on the Protection of Permanent Basic Farmland, the Administration of Temporary Land Use and Cultivated Land Balance, after a major construction project temporarily occupies permanent basic farmland with approval, it needs to be reclaimed in a timely manner and reclaimed according to the original site and original land type to ensure China's cultivated land resources.

[0003] If the temporary land is a waste dump generated by a key construction linear project, and due to inevitable reasons, it occupies permanent basic farmland and all of it is paddy field, then it is necessary to ensure that the original planting conditions are restored in a timely manner after the expiration of the temporary land use, and implement the principles of "one-for-one replacement, high-quality replacement, and paddy field replacement for paddy field occupation". The waste dump needs to be designed as a vertical slope waste dump; compared with gentle slopes and steep slopes, vertical slopes are less likely to be stable. Therefore, the stability of the vertical slope waste dump will be the key factor in whether the paddy field can be reclaimed; exploring the maximum stacking height and engineering support measures of single-step waste dumps and multi-step vertical waste dumps in this situation, and comprehensively analyzing single-step and multi-step vertical waste dumps is very necessary for restoring the protection of permanent basic farmland occupied by the waste dump. Summary of the Invention

[0004] Aiming at the above deficiencies in the prior art, the method for stability analysis and engineering measures of a reclaimed paddy field after a waste dump under saturated conditions provided by the present invention solves the problems of stability analysis and engineering measures for the vertical slope waste dump of the reclaimed paddy field.

[0005] In order to achieve the above invention purpose, the technical solution adopted by the present invention is as follows:

[0006] A method for stability analysis and engineering measures of a reclaimed paddy field after a waste dump under saturated conditions provided by the present invention includes the following steps:

[0007] S1. Respectively construct a single-step waste dump and a multi-step vertical waste dump under natural conditions;

[0008] S2. Construct a pile - slab retaining wall;

[0009] S3. Conduct a stability analysis of the single - step waste dump with a pile - slab retaining wall under natural conditions;

[0010] S4. Conduct a stability analysis of the multi - step vertical waste dump with a pile - slab retaining wall under natural conditions respectively;

[0011] S5. Based on the stability analysis results of the single - step waste dump under natural conditions, the stability analysis results of the multi - step vertical waste dump, and the saturated unit weight of the waste dump, construct a single - step waste dump, a multi - step vertical waste dump, and a pile - slab retaining wall under saturated conditions respectively;

[0012] S6. Use the same analysis method as the stability analysis under natural conditions to conduct a stability analysis of the single - step waste dump with a pile - slab retaining wall and the multi - step vertical waste dump under saturated conditions, and obtain the engineering measures for the single - step waste dump and the multi - step vertical waste dump under saturated conditions.

[0013] The beneficial effects of the present invention are as follows: A method for stability analysis and engineering measures after reclaiming paddy fields in waste dumps under saturated conditions provided by the present invention combines the research on paddy field reclamation, the stability analysis of waste dumps, theoretical analysis, physical experimental simulation analysis, and numerical simulation analysis to obtain a reference basis for constructing waste dumps and pile - slab retaining walls. By establishing models of single - step and multi - step waste dumps with different heights, combined with the stability analysis results of waste dumps, explore the maximum stacking height and the optimal pile - board wall size of single - step and multi - step waste dumps under natural conditions and saturated conditions, and conduct a comprehensive analysis of single - step and multi - step waste dumps, and the engineering measures for single - step waste dumps and multi - step vertical waste dumps under saturated conditions. Based on the simulation calculation results and comprehensive analysis conclusions, the present invention provides a high - value stability analysis and engineering measures method for the design of waste dumps occupying permanent basic farmland generated by linear projects.

[0014] Furthermore, the multi - step vertical waste dump includes a three - step waste dump, a five - step waste dump, and a seven - step waste dump, and the width of the step platform in both the single - step waste dump and the multi - step vertical waste dump is 10 m.

[0015] The beneficial effect of adopting the above - mentioned further scheme is as follows: In this scheme, the multi - step vertical waste dump provides a three - step waste dump, a five - step waste dump, and a seven - step waste dump according to the actual natural paddy field terrace environment.

[0016] Furthermore, the step S1 includes the following steps:

[0017] S11. Obtain the natural terrain slope according to the cultivated land terrain information along the linear project;

[0018] S12. Based on the natural slope of the terrain, single-step spoil banks with heights of 15m, 19m, 21m, and 23m are respectively constructed.

[0019] S13. Based on the natural slope of the terrain, three-step spoil banks with heights of 15m, 21m, 23m, 25m, 27m, and 30m are respectively constructed.

[0020] S14. Based on the natural slope of the terrain, five-step spoil banks with heights of 25m, 31m, 33m, 35m, and 37m are respectively constructed.

[0021] S15. Based on the natural slope of the terrain, seven-step spoil banks with heights of 35m, 36m, 38m, 40m, and 42m are respectively constructed.

[0022] The beneficial effects of adopting the above further scheme are: providing single-step spoil banks and multi-step vertical spoil banks with different suitable construction heights based on the natural slope conditions of the terrain.

[0023] Further, the step S2 includes the following steps:

[0024] S21. Use solid elements in FLAC3D to construct retaining plates, and use Pile elements to construct reinforced concrete square piles.

[0025] S22. Connect the retaining plates and the reinforced concrete square piles to construct a pile-sheet retaining wall.

[0026] The beneficial effects of adopting the above further scheme are: FLAC3D has eleven constitutive models, which can meet the research of the vast majority of geotechnical engineering. Select solid elements to simulate the retaining plates and Pile elements to simulate anti-slide piles. The model nodes can be automatically established and assigned parameters to maximize the restoration of the interaction between the actual project, the soil body, and the retaining plates, avoiding the problems of excessive calculation amount or ineffective simulation of the forces and bending moments between pile-sheet retaining walls.

[0027] Further, the thickness of the retaining plate is 0.5m; the sizes of the reinforced concrete square piles include 1.2×1.5m, 1.5×1.5m, 1.5×2m, 2×2m, 2×3m, and 2×4m, and the pile spacing of the reinforced concrete square piles is 4m.

[0028] The beneficial effects of adopting the above further solution are as follows: The cross-sectional dimensions of the anti-slide pile are required to have a width of 1.5 - 2.5 m and a length of 2.0 - 4.0 m. The buried depth of the anchorage section of the reinforced concrete pile should be 1 / 3 of the pile length. The pile spacing should not be less than 2 times the short side dimension of the pile cross-section. The concrete grade of the piles in the pile-slab retaining wall should not be lower than C25, and when used for landslide support, the concrete strength grade of the pile body should not be lower than C30. In this solution, the pile spacing is determined to be 4 m, the thickness of the retaining plate is 0.5 m, the concrete strength grade of the square pile and the retaining plate is C30, and the buried depth is 1 / 3 of the total pile length. The sizes of the square piles are determined to be 1.2×1.5 m, 1.5×1.5 m, 1.5×2 m, 2×2 m, 2×3 m, and 2×4 m in order to explore the maximum height of the multi-step waste dump and the optimal size of each waste dump plan.

[0029] Further, the step S3 includes the following steps:

[0030] S31. Based on the elastoplastic solution method, establish the initial rock stress field of the single-step waste dump under natural conditions;

[0031] S32. Based on the initial rock stress field, successively set the pile-slab retaining walls with gradually increasing sizes of reinforced concrete square piles for the single-step waste dumps with increasing heights, and conduct stress analysis to obtain the stress nephograms in the ZZ direction, the minimum principal stress nephograms, the maximum shear strain increment nephograms, the horizontal displacement nephograms, the vertical displacement nephograms, and the total displacement vector nephograms of the single-step waste dumps corresponding to the heights;

[0032] S33. Respectively, according to the stress nephograms in the ZZ direction and the minimum principal stress nephograms, obtain the stress field law and the maximum shear strain increment of the single-step waste dump;

[0033] S34. According to the horizontal displacement nephograms, the vertical displacement nephograms, and the total displacement vector nephograms, obtain the displacement field of the single-step waste dump;

[0034] S35. Based on the stress field law, the maximum shear strain increment nephograms, and the displacement field of the single-step waste dump, use the strength reduction method to calculate the stability coefficient of the single-step waste dump with the corresponding size of the pile-slab retaining wall set at the corresponding height;

[0035] S36. Judge whether the stability coefficient is greater than or equal to the preset stability coefficient threshold. If so, enter step S37; otherwise, it is determined that the height of the single-step waste dump and the data settings of the pile-slab retaining wall size corresponding to this stability coefficient do not meet the stability requirements, and enter step S4;

[0036] S37. Take the corresponding height of the single-step waste dump and the corresponding size of the pile-slab retaining wall set for it as the preset stability analysis result;

[0037] S38. Take the preset stability analysis result corresponding to the stability coefficient closest to the preset stability coefficient threshold as the stability analysis result of the single-step spoil ground under natural conditions, and proceed to step S4.

[0038] The beneficial effects of adopting the above further solution are as follows: Provide a method for stability analysis of the spoil ground, analyze from stress, shear strain increment, displacement and stability coefficient. Through the analysis of the stress field law, the stress distribution of the spoil ground can be obtained. The shear strain increment generally can reflect the potential slip surface that may exist in the rock and soil mass, and the failure of the rock and soil mass generally occurs first at the position of the maximum shear strain increment. Through the analysis of displacement, the position where the maximum displacement occurs and the corresponding displacement amount can be obtained. The stability coefficient is a direct criterion for characterizing the stability of the spoil ground. This solution conducts stability analysis on the numerical simulation results of the spoil ground from the above aspects.

[0039] Further, the step S4 includes the following steps:

[0040] S41. Based on the elastoplastic solution method, establish the initial rock stress fields of the three-step spoil ground, five-step spoil ground, and seven-step spoil ground under natural conditions respectively;

[0041] S42. Based on the initial rock stress field of the three-step spoil ground, adopt the same analysis method as the stability analysis of the single-step spoil ground in step S3 to analyze and obtain the stability analysis result of the three-step spoil ground under natural conditions;

[0042] S43. Based on the initial rock stress field of the five-step spoil ground, adopt the same analysis method as the stability analysis of the single-step spoil ground in step S3 to analyze and obtain the stability analysis result of the five-step spoil ground under natural conditions;

[0043] S44. Based on the initial rock stress field of the seven-step spoil ground, adopt the same analysis method as the stability analysis of the single-step spoil ground in step S3 to analyze and obtain the stability analysis result of the seven-step spoil ground under natural conditions.

[0044] The beneficial effects of adopting the above further solution are as follows: Through the analysis of stress, shear strain increment, displacement and stability coefficient, obtain the stability analysis results of the multi-step vertical spoil ground under natural conditions, and obtain the maximum height of the multi-step spoil ground under natural conditions and the optimal dimensions of each spoil ground plan.

[0045] Further, the strength reduction method includes the following steps:

[0046] A1. Based on the stress field law, maximum shear strain increment and displacement field of the spoil ground, obtain the first model cohesion c and the first internal friction angle

[0047] A2. Define the upper limit K of the initial stability coefficient1 and the lower limit K of the initial stability coefficient 2 ;

[0048] A3. Based on the upper limit K of the initial stability coefficient 1 and the lower limit K of the initial stability coefficient 2 perform a binary calculation to obtain the first strength reduction coefficient K;

[0049] A4. Based on the first strength reduction coefficient K, reduce the cohesion c and the first internal friction angle φ of the first model respectively to obtain the cohesion c 1 of the second model and the second internal friction angle

[0050] A5. Based on the cohesion c 1 of the second model and the second internal friction angle perform a finite difference calculation;

[0051] A6. Judge whether the result of the finite difference calculation converges. If so, use the upper limit K 1 of the initial stability coefficient and the first strength reduction coefficient K as the upper limit and the lower limit of the second stability coefficient respectively, and perform a binary division. Use the binary division result as the second strength reduction coefficient K. Otherwise, use the first strength reduction coefficient K and the lower limit K 2 of the initial stability coefficient as the upper limit and the lower limit of the second stability coefficient respectively, and perform a binary division. Use the binary division result as the second strength reduction coefficient K';

[0052] A7. Repeat steps A4 to A6 until the calculated strength reduction coefficient is less than or equal to the preset accuracy, and then use this strength coefficient as the corresponding stability coefficient.

[0053] The beneficial effect of adopting the above further solution is: to provide a customized binary strength reduction method, and to calculate the stability coefficient of the corresponding spoil ground plan through the stress field law, the maximum shear strain increment and the displacement field of the spoil ground.

[0054] Furthermore, the calculation expression of the first strength reduction coefficient K is as follows:

[0055]

[0056] The beneficial effect of adopting the above further solution is: to provide a calculation method for performing binary division on the strength reduction coefficient, and to provide a calculation method for the stability coefficient when the calculated strength reduction coefficient is less than or equal to the preset accuracy.

[0057] Further, the construction heights of the single-step spoil disposal site under the saturation condition are 15m, 17m, 19m, and 21m respectively; the construction heights of the three-step spoil disposal site under the saturation condition are 17m, 19m, 21m, and 23m respectively; the construction heights of the five-step spoil disposal site under the saturation condition are 20m, 23m, 25m, and 27m respectively; the construction heights of the seven-step spoil disposal site under the saturation condition are 25m, 27m, 29m, and 31m respectively.

[0058] The beneficial effects of adopting the above further scheme are as follows: According to the stability analysis results of the single-step spoil disposal site and the multi-step vertical spoil disposal site under natural conditions, after removing the schemes with excessive heights that result in the instability and insecurity of the spoil disposal site scheme, single-step spoil disposal sites and multi-step vertical spoil disposal sites with different construction heights under the saturation condition are set up, so as to narrow the range for exploring the stability of the single-step spoil disposal site and the multi-step vertical spoil disposal site under the saturation condition, and provide a basis for obtaining the engineering measures for reclaiming paddy fields from the spoil disposal site under the saturation condition according to the stability analysis results. Description of the Drawings

[0059] Figure 1 It is a step flow chart of the stability analysis and engineering measure method for reclaiming paddy fields from the spoil disposal site under the saturation condition in the embodiment of the present invention.

[0060] Figure 2 It is a schematic diagram of the single-step spoil disposal site in the embodiment of the present invention.

[0061] Figure 3 It is a schematic diagram of the three-step spoil disposal site in the embodiment of the present invention.

[0062] Figure 4 It is a schematic diagram of appropriately densifying the grid in the contact area between the spoil disposal site and the bedrock in the embodiment of the present invention.

[0063] Figure 5 It is the ZZ stress nephogram of the 15m single-step spoil disposal site under the support of a 1.2×15m pile-slab wall in the embodiment of the present invention;

[0064] Figure 6 It is the minimum principal stress nephogram of the 15m single-step spoil disposal site under the support of a 1.2×15m pile-slab wall in the embodiment of the present invention;

[0065] Figure 7 It is the maximum shear strain increment nephogram of the 15m single-step spoil disposal site under the support of a 1.2×15m pile-slab wall in the embodiment of the present invention;

[0066] Figure 8 It is the horizontal displacement diagram of the 15m single-step spoil disposal site under the support of a 1.2×15m pile-slab wall in the embodiment of the present invention.

[0067] Figure 9This is the vertical displacement diagram of the 15m waste dump at the bench in the embodiment of the present invention under the support of a 1.2×15m pile-plank wall.

[0068] Figure 10 This is the total displacement vector nephogram of the 15m waste dump at the bench in the embodiment of the present invention under the support of a 1.2×15m pile-plank wall.

[0069] Figure 11 This is the curve graph of the displacement and stability coefficient change corresponding to the 19m single-bench waste dump in the embodiment of the present invention. Specific embodiments

[0070] The following describes the specific embodiments of the present invention to facilitate those skilled in the art of the present technology to understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art of the present technology, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions and creations using the concept of the present invention are within the scope of protection.

[0071] As Figure 1 shown, in an embodiment of the present invention, the present invention provides a method for analyzing the stability and engineering measures of a waste dump after reclaiming paddy fields under saturated conditions, including the following steps:

[0072] S1. Respectively construct a single-bench waste dump and a multi-bench vertical waste dump under natural conditions;

[0073] The multi-bench vertical waste dump includes a three-bench waste dump, a five-bench waste dump, and a seven-bench waste dump, and the width of the bench platform in both the single-bench waste dump and the multi-bench vertical waste dump is 10m;

[0074] The step S1 includes the following steps:

[0075] S11. Obtain the natural terrain slope according to the cultivated land terrain information along the linear project; there are many cultivated lands along the linear project, the terrain is relatively flat, and the natural slope is mostly 5-15°. Therefore, in this scheme, the natural terrain slope is designed to be 5-15°, and the stability calculation and analysis of the waste dump generated by stacking under such terrain conditions are carried out;

[0076] As Figure 2 shown, S12. Based on the natural terrain slope, respectively construct single-bench waste dumps with heights of 15m, 19m, 21m, and 23m;

[0077] As Figure 3 shown, S13. Based on the natural terrain slope, respectively construct three-bench waste dumps with heights of 15m, 21m, 23m, 25m, 27m, and 30m;

[0078] S14. Based on the natural slope of the terrain, construct five-step waste dumps with heights of 25m, 31m, 33m, 35m, and 37m respectively;

[0079] S15. Based on the natural slope of the terrain, construct seven-step waste dumps with heights of 35m, 36m, 38m, 40m, and 42m respectively;

[0080] As Figure 4 shown, since the thickness of the Quaternary bedrock layer in contact with the waste dump is too small, it is ignored when establishing the model. At the same time, in order to ensure accurate and reliable calculations, the grids of the waste dump and the area in contact with the bedrock are appropriately refined;

[0081] S2. Construct a pile-slab retaining wall;

[0082] The step S2 includes the following steps:

[0083] S21. Use solid elements in FLAC3D to construct retaining plates and Pile elements to construct reinforced concrete square piles;

[0084] S22. Connect the retaining plates and reinforced concrete square piles to construct a pile-slab retaining wall;

[0085] The thickness of the retaining plate is 0.5m; the dimensions of the reinforced concrete square piles include 1.2×1.5m, 1.5×1.5m, 1.5×2m, 2×2m, 2×3m, and 2×4m, and the pile spacing of the reinforced concrete square piles is 4m;

[0086] In this scheme, the pile spacing is determined to be 4m, the thickness of the retaining plate is 0.5m, the concrete strength of the square piles and retaining plates is C30 grade, the burial depth is 1 / 3 of the total pile length, and the dimensions of the square piles are determined to be 1.2×1.5m, 1.5×1.5m, 1.5×2m, 2×2m, 2×3m, and 2×4m in order to explore the maximum height of the multi-step waste dump and the optimal dimensions of each waste dump scheme; the design value of the axial compressive strength FC of the C30 concrete strength grade is 14.3N / mm 2 and the design value of the tensile strength ft is 1.43N / mm 2 and the elastic modulus EC of the concrete is 3.00×10 4 Nmm 2 ,

[0087] S3. Conduct a stability analysis of the single-step waste dump with a pile-slab retaining wall under natural conditions;

[0088] The step S3 includes the following steps:

[0089] S31. Based on the elastoplastic solution method, establish the initial stress field of the bedrock of the single-step waste dump under natural conditions;

[0090] S32. Based on the initial in-situ stress field of bedrock, successively set retaining walls with pile plates of gradually increasing reinforced concrete square pile sizes for single-step spoil grounds with increasing heights, and conduct stress analysis to obtain the stress nephograms in the ZZ direction, minimum principal stress nephograms, maximum shear strain increment nephograms, horizontal displacement nephograms, vertical displacement nephograms, and total displacement vector nephograms for single-step spoil grounds at corresponding heights respectively;

[0091] S33. Respectively obtain the stress field law and maximum shear strain increment of the single-step spoil ground according to the stress nephograms in the ZZ direction and the minimum principal stress nephograms; As Figure 5 shown, from the ZZ stress nephogram of the spoil ground, it can be seen that only considering the self-weight effect in the stress field of the spoil ground, the initial stress is roughly distributed in layers along the slope inclination direction, and the positions with the maximum stress are all at the bottom of the bedrock. The maximum stress value reaches 2.645 Mpa, which is consistent with the theoretical calculation results and gradually increases with depth, conforming to the general distribution law of the initial in-situ stress field;

[0092] As Figure 6 shown, from the minimum principal stress nephogram of the spoil ground, it can be seen that the distribution form of the stress nephogram shows a gradually increasing phenomenon from top to bottom, and the whole stress nephogram is distributed in a quasi-layered form. This is because the state of the spoil ground is mainly the stress field under self-weight. Under the action of gravity, stress concentration occurs at the lower part of the retaining wall. In some areas of this position, the value is greater than 0, indicating that this area is in a tensile state. It can be seen from the stress nephogram that the landslide thrust of the spoil ground acts on the middle part of the pile plate wall, and tensile areas will appear at the upper and lower parts of the retaining wall;

[0093] As Figure 7 shown, from the maximum shear strain increment nephogram, it can be seen that under the support of the pile plate wall, the shear strain increment of the spoil ground mainly appears behind the retaining wall, which is the weakest and most easily damaged area of the spoil ground. However, looking at the overall maximum shear strain increment of the spoil ground, it can be found that its order of magnitude is small and is not sufficient to affect the stability of the spoil ground;

[0094] S34. Obtain the displacement field of the single-step spoil ground according to the horizontal displacement nephogram, vertical displacement nephogram, and total displacement vector nephogram;

[0095] As Figure 8 、 Figure 9 and Figure 10As shown, it can be seen from the displacement nephogram that the deformation area of the waste dump mainly occurs in the waste body behind the pile-plank wall. The maximum horizontal displacement during the reclamation of the paddy field in the waste dump is 2.91 cm, and the direction is outward. The maximum vertical displacement is 2.87 cm, and the direction is downward. It can be seen that under the action of gravity, the single-step waste dump not only has vertical deformation but also horizontal deformation. This is because the waste dump is a vertical slope, and there will also be a pressure difference in the horizontal direction at some parts. Generally speaking, the overall displacement of the waste dump is 3.99 cm. The front end of the waste dump has a tendency to tilt outward, but the overall displacement is small. The pile-plank wall effectively prevents the horizontal deformation of the waste dump, and the vertical deformation mainly comes from the natural settlement of the waste soil;

[0096] S35. Based on the stress field law, the maximum shear strain increment nephogram and the displacement field of the single-step waste dump, the stability coefficient of the single-step waste dump with the corresponding height and the corresponding size of the pile-plank retaining wall is calculated by using the strength reduction method;

[0097] S36. Determine whether the stability coefficient is greater than or equal to the preset stability coefficient threshold. If so, go to step S37; otherwise, it is determined that the data settings of the height of the single-step waste dump and the size of the pile-plank retaining wall corresponding to this stability coefficient do not meet the stability requirements, and go to step S4;

[0098] S37. Take the corresponding height of the single-step waste dump and the corresponding size of the pile-plank retaining wall set as the preset stability analysis result;

[0099] S38. Take the preset stability analysis result corresponding to the stability coefficient closest to the preset stability coefficient threshold as the stability analysis result of the single-step waste dump under natural conditions, and go to step S4;

[0100] For the 15m-high single-step waste dump, the stability coefficient of the waste dump calculated by the strength reduction method is 1.36, which meets the set safety conditions, and the waste dump is in a stable state. Therefore, a 1.5×1.5m pile-plank wall can be selected for the support of the 15m-high single-step waste dump. Under the support of this size pile-plank wall, the waste dump is in a stable state;

[0101] For the 19m-high single-step waste dump, the stability calculations were carried out for different sizes of pile-plank walls with dimensions of 1.2×1.5m, 1.5×1.5m, 1.5×2m, 2×2m, and 2×3m. The corresponding displacement and stability coefficient changes were plotted into a change curve graph, as Figure 11As shown in the figure, as the size of the pile-plank wall increases, the overall displacement of the waste dump decreases, and at the same time, the stability coefficient increases. When the size of the pile-plank wall is 2×2m, the stability coefficient of the waste dump meets the set safety conditions. And when the waste dump reaches stability, the rate of decrease in the displacement of the waste dump significantly drops, indicating that even if the size of the pile-plank wall is further increased, it cannot prevent the minor deformation of the waste dump. If only considering safety, the larger the size of the pile-plank wall, the better the stability. However, in actual engineering, safety and economic factors need to be considered for resource optimization. In the same waste dump model, the larger the selected size of the pile-plank wall, the higher the corresponding project cost. To sum up, the comprehensive effect of selecting a 2×2m pile-plank wall for this waste dump is the best;

[0102] For the single-step waste dump with a height of 19m, in order to show the influence of pile-plank walls of different sizes on the displacement and stability of the waste dump, a waste dump in an under-stable state after being supported by a 1.2×1.5m pile-plank wall and a waste dump in a stable state after being supported by a 2×2m pile-plank wall are selected for comparative analysis. When a 1.2×1.5m pile-plank wall is selected for the waste dump, the maximum horizontal displacement is 48.88cm, the maximum vertical displacement is 47.15cm, and the overall maximum displacement is 66.49cm. Combining with the displacement vector cloud diagram, it can be seen that the waste dump has an obvious tendency to tilt outwards. At this time, the deformation of the waste dump is large, and the waste dump is very likely to become unstable; the stability coefficient of the waste dump calculated by the strength reduction method is 1.05, which does not meet the set safety condition of Fs>1.25, and the waste dump is in an unstable state; when a 2×2m pile-plank wall is selected for the waste dump, the maximum horizontal displacement is 6.38cm, the maximum vertical displacement is 6.25cm, and the overall maximum displacement is 8.77cm. At this time, the deformation of the waste dump is small. The stability coefficient of the waste dump calculated by the strength reduction method is 1.27, which meets the set safety condition of Fs>1.25, and the waste dump is in a stable state; through comparison, it can be found that the maximum displacement of the waste dump after being supported by pile-plank walls of the two sizes occurs at the top of the soil behind the retaining wall, but after the waste dump with an increased size becomes stable, the displacement value significantly decreases, and the stability coefficient increases by 0.23, indicating that increasing the size of the pile-plank wall can block the horizontal deformation of the waste dump and improve the stability of the waste dump, which is also consistent with the trend of the displacement curve graph at the same time;

[0103] Similarly, for the stability analysis result of the single-step waste dump with a height of 21m, it can be known that the minimum size of the pile-plank wall to make it reach a stable state is 2×2m. Therefore, for the single-step waste dump with a height of 21m, pile-plank walls with sizes of 2×2m, 2×3m, and 2×4m are selected for stability calculation. Continuing to use a 2×2m pile-plank wall cannot meet the set safety conditions for the single-step waste dump with a height of 21m, and at this time the waste dump is in an unstable state; when the pile-plank wall is 2×3m, the safety factor of the waste dump meets the set safety conditions, and the waste dump is in a stable state; also considering safety and economic factors, the comprehensive effect of selecting a 2×3m pile-plank wall for this waste dump is the best;

[0104] For the stability analysis of the single-step spoil ground with a height of 23m, it can be seen from the stability analysis results of the single-step spoil ground with a height of 21m that when using a 2×3m pile-plank wall, the stability coefficient of the spoil ground just meets the safety condition of Fs>1.25. However, if the 2×3m pile-plank wall is still selected for the spoil ground with a height of 23m, it will surely not reach stability. Therefore, for the single-step spoil ground with a height of 23m, the maximum-sized 2×4m pile-plank wall determined this time is selected for stability calculation. The maximum displacement of the spoil ground is 11.6cm. Combining with the displacement vector nephogram, the front end of the spoil ground has a tendency to tilt outwards. The failure form of the spoil ground is that the pile-plank wall is very likely to be damaged under the continuous and extremely large thrust of the spoil ground landslide and cannot prevent the deformation of the spoil ground, and the spoil ground may collapse; the stability coefficient of the spoil ground calculated by the strength reduction method is 1.14, which does not meet the set safety condition of Fs>1.25, and the spoil ground is in an unstable state; in summary, the single-step spoil ground with a height of 25m cannot reach a stable state even when using the maximum-sized 2×4m pile-plank wall; therefore, this stacking height scheme needs to be abandoned;

[0105] When conducting the stability analysis of the single-step spoil ground, different-sized pile-plank walls are selected for the single-step spoil grounds with different heights for support to explore the maximum stacking height of the single-step spoil ground and the optimal size of the pile-plank wall. It is found that the stability coefficients of the single-step spoil grounds with heights of 15m, 19m, and 21m can meet the stable condition of Fs>1.25 after selecting the pile-plank wall for support. The maximum-sized pile-plank wall set for the single-step spoil ground with a height of 23m fails to reach stability. Therefore, the maximum stacking height of the single-step spoil ground is 21m;

[0106] After selecting different-sized pile-plank walls for the single-step spoil grounds with heights of 15m, 19m, and 21m for support, the stability coefficients of the spoil grounds can all meet the stable condition of Fs>1.25; when the pile-plank wall is selected for the support of the spoil ground, the maximum displacement of the spoil ground all appears at the front end of the spoil ground. Increasing the size of the pile-plank wall can improve the stability of the spoil ground and reduce the displacement at the top of the spoil ground; when a 1.2×1.5m pile-plank wall is selected for the single-step spoil ground with a height of 15m, the stable condition of Fs>1.25 can be met. Considering safety and economic factors, a larger pile-plank wall is no longer selected for the support of this spoil ground. At this time, the maximum displacement at the front end of the spoil ground is 2.91cm, and the safety factor of the spoil ground is 1.36; similarly, when a 2×2m pile-plank wall is selected for the single-step spoil ground with a height of 19m, the stable condition of Fs>1.25 can be met. At this time, the maximum displacement at the front end of the spoil ground is 6.38cm, and the stability coefficient of the spoil ground is 1.27; when a 2×3m pile-plank wall is preferably selected for the single-step spoil ground with a height of 21m, the stable condition of Fs>1.25 can be met. At this time, the maximum displacement at the front end of the spoil ground is 6.10cm, and the stability coefficient of the spoil ground is 1.29;

[0107] S4. Respectively conduct the stability analysis of the multi-step vertical spoil ground with pile-plank retaining walls under natural conditions;

[0108] Step S4 includes the following steps:

[0109] S41. Based on the elastoplastic solution method, establish the initial rock stress fields of the three-step spoil ground, five-step spoil ground, and seven-step spoil ground under natural conditions respectively;

[0110] S42. Based on the initial rock stress field of the three-step spoil ground, use the same analysis method as the stability analysis of the single-step spoil ground in step S3 to analyze and obtain the stability analysis results of the three-step spoil ground under natural conditions;

[0111] For the three-step 15m-high spoil ground, a 1.2×1.5m pile-plank wall can be selected for support, and the spoil ground is in a stable state under the support of this size pile-plank wall; for the three-step 21m-high spoil ground, when a 1.2×1.5m pile-plank wall is selected for the spoil ground, the maximum horizontal displacement of the spoil ground is 9.14cm, the maximum vertical displacement is 6.89cm, and the overall maximum displacement is 10.51cm. Using the strength reduction method, the stability coefficient of the spoil ground is calculated to be 1.17, which does not meet the set safety condition of Fs>1.25. When a 1.5×1.5m pile-plank wall is selected, the maximum horizontal displacement is 3.58cm, the maximum vertical displacement is 3.02cm, and the overall maximum displacement is 4.16m. At this time, the deformation of the spoil ground is small. Using the strength reduction method, the stability coefficient of the spoil ground is calculated to be 1.26, which meets the set safety condition of Fs>1.25, and the spoil ground is in a stable state; the best pile-plank wall size scheme for the three-step 23m-high spoil ground is 1.5×2m; the best pile-plank wall size scheme for the three-step 25m-high spoil ground is 2×2m; the best pile-plank wall size scheme for the three-step 27m-high spoil ground is 2×3m; for the three-step 30m-high spoil ground, even if the largest size 2×4m pile-plank wall is selected, stability cannot be achieved. Therefore, the maximum stacking height of the three-step spoil ground is 27m;

[0112] S43. Based on the initial rock stress field of the five-step spoil ground, use the same analysis method as the stability analysis of the single-step spoil ground in step S3 to analyze and obtain the stability analysis results of the five-step spoil ground under natural conditions;

[0113] For the five-step 25m-high spoil ground, a 1.2×1.5m pile-plank retaining wall can be used to keep it in a stable state; for the five-step 31m-high spoil ground, the overall effect is the best when a 2×2m pile-plank wall is selected; increasing the pile-plank wall can effectively block the horizontal deformation of the spoil ground, and the vertical deformation mainly comes from the natural settlement of the spoil; the best pile-plank wall size scheme for the five-step 33m-high spoil ground is 2×3m; the best pile-plank wall size scheme for the five-step 35m-high spoil ground is 2×4m; for the five-step 37m-high spoil ground, even if the largest size 2×4m pile-plank wall is selected, stability cannot be achieved. Therefore, the maximum stacking height of the five-step spoil ground is 35m;

[0114] S44. Based on the initial in-situ stress field of the seven-step spoil ground, using the same analysis method as in the stability analysis of the single-step spoil ground in step S3, the stability analysis results of the seven-step spoil ground under natural conditions are obtained;

[0115] For the 27m-high seven-step spoil ground, a 1.2×1.5m pile-plank wall is selected for support. Through numerical simulation and strength reduction method calculation, the stability coefficient of the spoil ground is 1.54, meeting the set safety condition of Fs>1.25, and the spoil ground is in a stable state; for the 36m-high seven-step spoil ground, the 2×2m pile-plank wall has the best comprehensive effect; for the 38m-high seven-step spoil ground, the best pile-plank wall size plan is 2×3m; for the 40m-high seven-step spoil ground, a 2×4m pile-plank retaining wall can be used to make it in a stable state; for the 42m-high seven-step spoil ground, even the largest-size 2×4m pile-plank wall cannot achieve stability. Therefore, the maximum stacking height of the seven-step spoil ground is 40m;

[0116] When conducting stability analysis on multi-step spoil grounds, different-sized pile-plank walls are selected for support for the three-step, five-step, and seven-step spoil grounds. Among them, the three-step spoil ground is divided into spoil grounds with heights of 15m, 21m, 23m, 25m, 27m, and 30m; the five-step spoil ground is divided into spoil grounds with heights of 25m, 31m, 33m, 35m, and 37m; the seven-step spoil ground is divided into spoil grounds with heights of 27m, 36m, 38m, 40m, and 42m; different-sized pile-plank walls are selected for different multi-step spoil grounds to explore the height limits and the best pile-plank wall sizes of the three-step, five-step, and seven-step spoil grounds; it is found that for the 15m, 21m, 23m, 23m, 25m, and 27m-high spoil grounds of the three-step spoil ground, pile-plank walls can be selected for support, and the stability coefficient of the spoil ground reaches the stable condition of Fs>1.25. For the 30m-high three-step spoil ground, the stability cannot be achieved by selecting the set maximum pile-plank wall size. Therefore, the maximum stacking height of the three-step spoil ground should be designed as 27m; for the 25m, 31m, 33m, and 35m-high spoil grounds of the five-step spoil ground, pile-plank walls can be selected for support, and the stability coefficient of the spoil ground reaches the stable condition of Fs>1.25. For the 37m-high five-step spoil ground, the stability cannot be achieved by selecting the set maximum pile-plank wall size. Therefore, the maximum stacking height of the five-step spoil ground should be designed as 35m; for the 27m, 36m, 38m, 40m, and 42m-high spoil grounds of the seven-step spoil ground, pile-plank walls can be selected for support, and the stability coefficient of the spoil ground reaches the stable condition of Fs>1.25. For the 42m-high seven-step spoil ground, the stability cannot be achieved by selecting the set maximum pile-plank wall size. Therefore, the maximum stacking height of the seven-step spoil ground is 40m;

[0117] The strength reduction method includes the following steps:

[0118] A1. Based on the stress field law, maximum shear strain increment, and displacement field of the waste dump, the cohesion c and the first internal friction angle of the first model are obtained.

[0119] A2. Define the upper limit K of the initial stability coefficient 1 and the lower limit K of the initial stability coefficient 2 ;

[0120] A3. Based on the upper limit K of the initial stability coefficient 1 and the lower limit K of the initial stability coefficient 2 perform binary calculation to obtain the first strength reduction coefficient K;

[0121] The calculation expression of the first strength reduction coefficient K is as follows:

[0122]

[0123] A4. Based on the first strength reduction coefficient K, reduce the cohesion c and the first internal friction angle φ of the first model respectively to obtain the cohesion c of the second model 1 and the second internal friction angle

[0124] A5. Based on the cohesion c of the second model 1 and the second internal friction angle perform finite difference calculation;

[0125] A6. Judge whether the finite difference calculation result converges. If so, take the upper limit K of the initial stability coefficient 1 and the first strength reduction coefficient K as the upper limit and lower limit of the second stability coefficient respectively, and perform binary division. Take the binary division result as the second strength reduction coefficient K. Otherwise, take the first strength reduction coefficient K and the lower limit K of the initial stability coefficient 2 as the upper limit and lower limit of the second stability coefficient respectively, and perform binary division. Take the binary division result as the second strength reduction coefficient K';

[0126] A7. Repeat steps A4 to A6 until the calculated strength reduction coefficient is less than or equal to the preset accuracy, then take this strength coefficient as the corresponding stability coefficient;

[0127] S5. Based on the stability analysis results of the single-step waste dump under natural conditions, the stability analysis results of the multi-step vertical waste dump, and the saturated unit weight of the waste dump, construct the single-step waste dump, multi-step vertical waste dump, and pile-slab retaining wall under saturated conditions respectively;

[0128] Under natural conditions, the upper limit of the height of a single-step waste dump is 21 m. On this basis, a calculation model of a single-step waste dump under saturated conditions is designed. When designing the waste dump, the slag volumes of the single-step waste dump and the multi-step waste dump are also corresponding. Then, the construction heights of the single-step waste dump under the saturated conditions are designed to be 15 m, 17 m, 19 m, and 21 m respectively; the construction heights of the three-step waste dump under the saturated conditions are 17 m, 19 m, 21 m, and 23 m respectively; the construction heights of the five-step waste dump under the saturated conditions are 20 m, 23 m, 25 m, and 27 m respectively; the construction heights of the seven-step waste dump under the saturated conditions are 25 m, 27 m, 29 m, and 31 m respectively;

[0129] S6. Use the same analysis method as the stability analysis under natural conditions to conduct stability analysis on the single-step waste dump with a pile-plank retaining wall and the multi-step vertical waste dump under saturated conditions, and obtain the engineering measures for the single-step waste dump and the multi-step vertical waste dump under saturated conditions;

[0130] The engineering measures for the single-step waste dump and the multi-step vertical waste dump under saturated conditions are as follows:

[0131] For the 15-m-high single-step waste dump under saturated conditions, when the size of the pile-plank wall is selected as 1.5×2 m, the stability coefficient of the waste dump meets the set safety conditions at this time. And when the waste dump reaches stability, the displacement reduction rate of the waste dump decreases significantly, indicating that even if the size of the pile-plank wall is continued to be increased, it cannot prevent the small deformation of the waste dump; if only considering safety, the larger the size of the pile-plank wall, the better the stability. However, in actual engineering, safety and economic factors need to be considered for resource optimization; and in the same waste dump model, the larger the selected size of the pile-plank wall, the higher the corresponding project cost; in summary, the comprehensive effect of selecting a 1.5×2 pile-plank wall for this waste dump is the best; the best pile-plank wall size scheme for this 17-m-high single-step waste dump is 2×2 m; the minimum size of the pile-plank wall for the 19-m-high single-step waste dump to reach a stable state is 2×4 m, and the stability coefficient is 1.27, just meeting the 1.25 stability condition. Due to the increase in the height of the slag yard, the stability will decrease accordingly. If the pile-plank wall of this size is continued to be selected, the waste dump is very likely not to reach a stable state. Using the strength reduction method, it is calculated that the stability coefficient of the 21-m-high single-step waste dump with a pile-plank wall size of 2×4 m is 1.21, which does not meet the set safety condition of Fs>1.25. The pile-plank wall is very likely to be damaged under the continuous great thrust of the landslide of the waste dump and cannot prevent the deformation of the waste dump, and the waste dump may collapse;

[0132] When analyzing the stability of a single-step waste dump under saturated conditions, retaining walls with different sizes were selected for supporting single-step waste dumps of different heights to explore the maximum stacking height of the single-step waste dump and the optimal size of the retaining wall. The analysis found that for single-step waste dumps with heights of 15m, 17m, and 19m, retaining walls can be selected for support, and the stability coefficient of the waste dump meets the stability condition of Fs>1.25. For the 21m-high single-step waste dump, the maximum size of the retaining wall set could not achieve stability. Therefore, the maximum stacking height of the single-step waste dump is 19m;

[0133] The stability of the three-step waste dump will be analyzed one by one for waste dumps with heights of 17m, 19m, 21m, and 23m at the three steps when selecting retaining walls of different sizes; for the 17m-high three-step waste dump, the stability coefficient of the waste dump was calculated to be 1.29 using the strength reduction method, meeting the set safety condition of Fs>1.25, and the waste dump is in a stable state; for the 19m-high three-step waste dump, stability calculations were carried out for different sizes of 1.2×1.5m, 1.5×1.5m, 1.5×2m, 2×2m, 2×3m, and 2×4m. When the size of the retaining wall is 1.5×2m, the stability coefficient of the waste dump meets the set safety condition. Therefore, the 1.5×2m retaining wall has the best comprehensive effect for the 19m-high three-step waste dump; for the 21m-high three-step waste dump, it is unstable when the retaining wall sizes are 1.5×2m and 2×2m, and it is in a stable state until the retaining wall size is 2×3m; for the 23m-high three-step waste dump, it is still unstable when supported by the largest size 2×4m retaining wall;

[0134] The stability of the five-step waste dump will be analyzed one by one for waste dumps with heights of 20m, 23m, 25m, and 27m at the five steps when selecting retaining walls of different sizes; for the 20m-high five-step waste dump, a 1.2×1.5m retaining wall can be selected for support, and the waste dump is in a stable state under the support of this size of retaining wall; for the 23m-high five-step waste dump, when the size of the retaining wall is 1.5×1.5m, the stability coefficient of the waste dump meets the set safety condition, and when the waste dump reaches stability, the rate of decrease in the displacement of the waste dump significantly decreases, and even if the size of the retaining wall is continued to be increased, it cannot prevent the small deformation of the waste dump; for the 25m-high five-step waste dump, simulations were carried out for retaining walls of 1.2×1.5m, 1.5×1.5m, 1.5×2m, 2×2m, and 2×3m. When the size of the retaining wall is 2×2m, the stability coefficient of the waste dump calculated using the strength reduction method is 1.27, meeting the set safety condition of Fs>1.25, and the waste dump is in a stable state; for the 27m-high five-step waste dump, the stability coefficient of the waste dump calculated by selecting a 2×4m retaining wall for stability is 1.08, not meeting the set safety condition of Fs>1.25;

[0135] For the seven-step waste dump, the stability of waste dumps with heights of 25m, 27m, 29m, and 31m at the seven steps was analyzed one by one when different-sized pile-plank walls were selected. For the 25m-high waste dump at the seven steps, a 1.2×1.5m pile-plank wall was selected for support, and the waste dump was in a stable state under the support of this-sized pile-plank wall; for the 27m-high waste dump at the seven steps, 1.2×1.5m, 1.5×1.5m, 1.5×2m, and 2×2m pile-plank walls were selected for simulation calculation. When the size of the pile-plank wall was 1.2×1.5, the stability coefficient of the waste dump was 1.14, which did not meet the set safety condition of Fs>1.25. When the size of the pile-plank wall was 2×2m, the field stability coefficient was 1.28, and the waste dump was in a stable state; for the 29m-high waste dump at the seven steps, 2×2m, 2×3m, and 2×4m pile-plank walls were selected for simulation calculation. Under saturated conditions, when a 2×2m pile-plank wall was selected for the waste dump, the stability coefficient was less than 1.25, and a 2×4m pile-plank wall needed to be selected to reach 1.25;

[0136] When a 2×4m pile-plank wall was selected for the 29m-high waste dump at the seven steps, the stability coefficient was 1.29. For the 31m-high waste dump at the seven steps, the largest-sized 2×4m pile-plank wall was selected for simulation calculation. The maximum horizontal displacement occurred inside the waste body, which was 3.29cm, and the maximum vertical displacement was 3.3cm. There was also an upward vertical displacement of 1.66cm at the bottom platform. Combining with the displacement vector cloud diagram, it can be found that although the displacement amount was small, the overall displacement of the waste dump occurred inside the waste dump. There was a tendency for the upper platform to displace outward, and an upward displacement tendency at the lower platform. It was very likely that internal sliding of the waste body occurred in the waste dump. Using the strength reduction method, the stability coefficient of the waste dump was calculated to be 1.06, which did not meet the set safety condition of Fs>1.25 in this article;

[0137] When conducting a stability analysis of a multi-step waste dump under saturated conditions, different-sized pile-plank walls are selected for supporting the three-step, five-step, and seven-step waste dumps. Among them, the three-step waste dump is divided into waste dumps with heights of 17m, 19m, 21m, and 23m; the five-step waste dump is divided into waste dumps with heights of 21m, 23m, 25m, and 27m; the seven-step waste dump is divided into waste dumps with heights of 25m, 27m, 29m, and 31m. Different-sized pile-plank walls are selected for different multi-step waste dumps to explore the height limits of the three-step, five-step, and seven-step waste dumps and the optimal sizes of the pile-plank walls. The analysis finds that for the three-step waste dumps with heights of 17m, 19m, and 21m, the stability coefficient of the waste dump reaches the stable condition of Fs>1.25 after selecting the pile-plank wall for support. The three-step waste dump with a height of 23m fails to reach stability when selecting the maximum pile-plank wall size determined in this paper. Therefore, the maximum stacking height of the three-step waste dump is 21m; for the five-step waste dumps with heights of 21m, 23m, and 25m, the stability coefficient of the waste dump reaches the stable condition of Fs>1.25 after selecting the pile-plank wall for support. The five-step waste dump with a height of 27m fails to reach stability when selecting the maximum pile-plank wall size determined in this paper. Therefore, the maximum stacking height of the five-step waste dump is 27m; for the seven-step waste dumps with heights of 25m, 27m, and 29m, the stability coefficient of the waste dump reaches the stable condition of Fs>1.25 after selecting the pile-plank wall for support. The seven-step waste dump with a height of 31m fails to reach stability when selecting the maximum pile-plank wall size determined in this paper. Therefore, the maximum stacking height of the seven-step waste dump is 29m.

[0138] Under saturated conditions, due to the poor water permeability of the waste body, the overall strength of the waste dump is relatively low. After the height of the waste dump increases, the internal stress in the waste dump body is prone to imbalance, and the waste dump will not be able to reach the maximum stacking height of the multi-step waste dump under natural conditions;

[0139] Calculate the floor area, slag storage volume and the engineering quantity of the pile-slab wall measures for each waste dump plan. When calculating the floor area and slag storage volume of the waste dump, the floor area = the designed model length of the waste dump × the model depth, the slag volume = the designed cross-sectional area of the waste dump × the model depth, and the model depth is 10m. The engineering quantity of the pile-slab wall measures is estimated by the volume of the pile-slab wall. Under saturated conditions, on the premise of ensuring stability, the maximum slag volume of a single-step waste dump is 13,050 m³; the slag storage volume of a three-step waste dump with a maximum stacking height of 21m corresponds to a single-step waste dump with a height of 19m, that is, the slag storage volume is 13,050 m³; the slag storage volume of a five-step waste dump with a maximum stacking height of 25m corresponds to a single-step waste dump with a height of 21m, that is, the slag storage volume is 15,700 m³; the slag storage volume of a seven-step waste dump with a maximum stacking height of 29m corresponds to a single-step waste dump with a height of 23m, that is, the slag storage volume is 17,820 m³. By analyzing the data, it can be obtained that as the number of steps of the waste dump increases, the maximum slag storage volume of the waste dump also increases. However, when the slag volume is equal, as the number of steps increases, the floor area of the waste dump and the engineering quantity of the pile-slab wall measures will increase. When designing a waste dump in actual engineering, considering safety and economic factors for resource optimization, it is preferred to design the waste dump as a single-step waste dump. If the single-step waste dump cannot be stable, the waste dump can be designed as a multi-step waste dump, and the waste dump with fewer steps should be considered first.

[0140] Under saturated conditions, the maximum slag volume reduction of a single-step waste dump is 0.155; the maximum slag volume reduction of a three-step waste dump is 0.369; the maximum slag volume reduction of a five-step waste dump is 0.463; the maximum slag volume reduction of a seven-step waste dump is 0.465. Analyzing the values, it can be obtained that compared with the maximum slag volume of the waste dump under natural conditions, the maximum slag volume of waste dumps with different numbers of steps under saturated conditions has decreased; as the number of steps increases, the maximum slag volume reduction of the waste dump increases, and the slag volume reduction of the seven-step waste dump is the largest.

Claims

1. A method for stability analysis and engineering measures of a waste dump reclaimed into paddy fields under saturated conditions, characterized in that, it includes the following steps: S1. Respectively construct a single-step waste dump and a multi-step vertical waste dump under natural conditions; S2. Construct a pile-slab retaining wall; S3. Conduct a stability analysis of the single-step waste dump with a pile-slab retaining wall under natural conditions; S4. Respectively conduct a stability analysis of the multi-step vertical waste dump with a pile-slab retaining wall under natural conditions; S5. Based on the stability analysis results of the single-step waste dump under natural conditions, the stability analysis results of the multi-step vertical waste dump, and the saturated unit weight of the waste dump, respectively construct a single-step waste dump and a multi-step vertical waste dump with a pile-slab retaining wall under saturated conditions; S6. Use the same analysis method as the stability analysis under natural conditions to conduct a stability analysis of the single-step waste dump and the multi-step vertical waste dump with a pile-slab retaining wall under saturated conditions, and obtain the engineering measures for the single-step waste dump and the multi-step vertical waste dump under saturated conditions; The step S3 includes the following steps: S31. Based on the elastoplastic solution method, establish the initial rock stress field of the single-step waste dump under natural conditions; S32. Based on the initial rock stress field, successively set pile-slab retaining walls with gradually increasing reinforced concrete square pile sizes for the single-step waste dump with heights from low to high, and conduct stress analysis to obtain the ZZ-direction stress nephogram, minimum principal stress nephogram, maximum shear strain increment nephogram, horizontal displacement nephogram, vertical displacement nephogram, and total displacement vector nephogram of the single-step waste dump corresponding to the height; S33. Respectively obtain the stress field law and the maximum shear strain increment of the single-step waste dump according to the ZZ-direction stress nephogram and the minimum principal stress nephogram; S34. Obtain the displacement field of the single-step waste dump according to the horizontal displacement nephogram, vertical displacement nephogram, and total displacement vector nephogram; S35. Based on the stress field law, maximum shear strain increment nephogram, and displacement field of the single-step waste dump, use the strength reduction method to calculate the stability coefficient of the single-step waste dump corresponding to the height with the corresponding size of the pile-slab retaining wall set; S36. Judge whether the stability coefficient is greater than or equal to the preset stability coefficient threshold. If so, enter step S37; otherwise, it is determined that the height of the single-step waste dump corresponding to the stability coefficient and the data of the pile-slab retaining wall size setting do not meet the stability requirements, and enter step S4; S37. Take the height of the single-step waste dump corresponding to the height and the corresponding size of the pile-slab retaining wall set as the preset stability analysis result; S38. Take the preset stability analysis result corresponding to the stability coefficient closest to the preset stability coefficient threshold as the stability analysis result of the single-step waste dump under natural conditions, and enter step S4.

2. The method for stability analysis and engineering measures of a waste dump reclaimed into paddy fields under saturated conditions according to claim 1, characterized in that, the multi-step vertical waste dump includes a three-step waste dump, a five-step waste dump, and a seven-step waste dump, and the width of the step platform in both the single-step waste dump and the multi-step vertical waste dump is 10m.

3. The method for analyzing the stability and engineering measures after reclaiming paddy fields in the spoil ground under saturated conditions according to claim 2, characterized in that, the step S1 includes the following steps: S11. Obtain the natural terrain slope according to the cultivated land terrain information along the linear project; S12. Based on the natural terrain slope, construct single-step spoil grounds with heights of 15m, 19m, 21m, and 23m respectively; S13. Based on the natural terrain slope, construct three-step spoil grounds with heights of 15m, 21m, 23m, 25m, 27m, and 30m respectively; S14. Based on the natural terrain slope, construct five-step spoil grounds with heights of 25m, 31m, 33m, 35m, and 37m respectively; S15. Based on the natural terrain slope, construct seven-step spoil grounds with heights of 35m, 36m, 38m, 40m, and 42m respectively.

4. The method for analyzing the stability and engineering measures after reclaiming paddy fields in the spoil ground under saturated conditions according to claim 3, characterized in that, the step S2 includes the following steps: S21. Use solid elements in FLAC3D to construct retaining plates, and use Pile elements to construct reinforced concrete square piles; S22. Connect the retaining plates and the reinforced concrete square piles to construct a pile-sheet retaining wall.

5. The method for analyzing the stability and engineering measures after reclaiming paddy fields in the spoil ground under saturated conditions according to claim 4, characterized in that, the thickness of the retaining plate is 0.5m; the dimensions of the reinforced concrete square piles include 1.2×1.5m, 1.5×1.5m, 1.5×2m, 2×2m, 2×3m, and 2×4m, and the pile spacing of the reinforced concrete square piles is 4m.

6. The method for analyzing the stability and engineering measures after reclaiming paddy fields in the spoil ground under saturated conditions according to claim 5, characterized in that, the step S4 includes the following steps: S41. Based on the elastoplastic solution method, establish the initial in-situ stress field of the bedrock for the three-step spoil ground, five-step spoil ground, and seven-step spoil ground under natural conditions respectively; S42. Based on the initial in-situ stress field of the three-step spoil ground, use the same analysis method as the stability analysis of the single-step spoil ground in step S3 to analyze and obtain the stability analysis result of the three-step spoil ground under natural conditions; S43. Based on the initial in-situ stress field of the five-step spoil ground, use the same analysis method as the stability analysis of the single-step spoil ground in step S3 to analyze and obtain the stability analysis result of the five-step spoil ground under natural conditions; S44. Based on the initial in-situ stress field of the seven-step spoil ground, use the same analysis method as the stability analysis of the single-step spoil ground in step S3 to analyze and obtain the stability analysis result of the seven-step spoil ground under natural conditions.

7. The method for analyzing the stability and engineering measures after reclaiming paddy fields in the spoil ground under saturated conditions according to claim 6, characterized in that, the strength reduction method includes the following steps: A1. Based on the stress field law, maximum shear strain increment, and displacement field of the spoil ground, the cohesion c and the first internal friction angle of the first model are obtained A2. Define the upper limit K of the initial stability coefficient 1 and the lower limit K of the initial stability coefficient 2 ; A3. Based on the upper limit K of the initial stability coefficient 1 and the lower limit K of the initial stability coefficient 2 perform binary calculation to obtain the first strength reduction coefficient K; A4. Reducing the cohesion c and the first internal friction angle of the first model based on the first strength reduction factor K respectively to obtain the cohesion c 1 and the second internal friction angle A5. Perform finite difference calculations based on the cohesion c of the second model 1 and the second internal friction angle . A6. Determine whether the finite difference calculation result converges. If so, use the initial upper limit of the stability coefficient K 1 and the first strength reduction coefficient K as the second upper limit of the stability coefficient and the second lower limit of the stability coefficient respectively, and perform bisection. Take the bisection result as the second strength reduction coefficient K. Otherwise, use the first strength reduction coefficient K and the initial lower limit of the stability coefficient K 2 as the second upper limit of the stability coefficient and the second lower limit of the stability coefficient respectively, and perform bisection. Take the bisection result as the second strength reduction coefficient K′; A7. Repeat steps A4 to A6 until the calculated strength reduction factor is less than or equal to the preset accuracy, then use this strength reduction factor as the corresponding stability coefficient.

8. The stability analysis and engineering measure method for the paddy field reclaimed from the waste dump under saturated conditions according to claim 7, characterized in that, the calculation expression of the first strength reduction coefficient K is as follows:

9. The stability analysis and engineering measure method for the paddy field reclaimed from the waste dump under saturated conditions according to claim 8, characterized in that, the construction heights of the single-step waste dump under saturated conditions are 15m, 17m, 19m and 21m respectively; the construction heights of the three-step waste dump under saturated conditions are 17m, 19m, 21m and 23m respectively; the construction heights of the five-step waste dump under saturated conditions are 20m, 23m, 25m and 27m respectively; the construction heights of the seven-step waste dump under saturated conditions are 25m, 27m, 29m and 31m respectively.

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