Study on the Alleviation of Mining-Induced Surface Deformation via Goaf Solid Waste Backfill Mining in a Deep Coal Mine

Abstract

The deep mining of coal resources can lead to surface subsidence, thereby damaging the stability of buildings on the surface; however, this issue can be effectively mitigated through goaf backfilling with coal gangue and other solid wastes. In this study, the technical principles of goaf solid waste backfill mining are illustrated, and the surface movement and deformation patterns under different burial depths and compression rates are examined. Additionally, the monitoring and analysis of the roof subsidence and surface building conditions after goaf solid waste backfill mining are described. The results show that as the burial depth and compression rate increase, the maximum values of the surface subsidence and horizontal deformation gradually decrease. When the burial depth is between 800 and 1200 m, the design value of the compression rate for the goaf should be higher than 79%. The actual measurement results show that the maximum subsidence value of the roof after goaf backfilling is 635 mm, and the compression rate is about 80.8%, which is consistent with the theoretical design value. Hence, surface buildings are little affected by mining activities and are within the safe range for use.

1. Introduction

Coal serves as a fundamental and stabilizing component within the framework of energy strategic security [1,2,3,4]. However, due to the extensive and high-intensity extraction of shallow coal reserves and the ongoing depletion of coal resources in central and eastern regions of China, mining operations are progressively deepening, at an annual rate ranging from 10 to 25 m [5,6,7,8]. Consequently, there has been a surge in the number of deep mines, indicating a shift towards extracting coal from greater depths. Based on the statistical data, China possesses an impressive 2.86 trillion tons of coal reserves that are located at depths exceeding 1000 m, accounting for a remarkable 51.34% of the overall coal resources globally [9,10]. In addition, a large amount of excavation and washed gangue are generated in coal mines during the production process. The surface discharge of coal gangue not only introduces safety concerns such as spontaneous combustion, explosions, and landslides in waste heaps but also triggers a series of ecological issues such as air and water pollution [11,12,13,14,15]. At the same time, coal mining activities cause subsidence of the Earth’s surface, which in turn damages the stability of buildings on the surface and poses a threat to humans’ living environment and safety. There has been little coordinated development of coal mining and environmental protection in mining areas. Moreover, as the burial depth increases, the transportation lifting distance of the gangue also increases, which also causes problems such as increased mining costs and tight auxiliary transportation [16,17,18]. Goaf solid waste backfill mining is one of the key methods to realize the disposal of solid wastes and the control of surface deformation. China has successively issued policies such as the “14th Five-Year Plan for Industrial Green Development” and the “Guidelines for Coal Mine Backfill Mining Operations”, encouraging mining enterprises to actively adopt backfill mining techniques and promote sustainable development. Therefore, it is of great significance to study the impact of different burial depths and compression rates on the surface movement and deformation.

Goaf solid waste backfill mining has significant advantages such as a high compression rate, small surface movement and deformation, and a large disposal volume of solid wastes [19,20,21,22,23]. In recent years, there has been rapid progress in the development of this method, and much research has been conducted on goaf solid waste backfill mining. In [24], the authors analyzed the influence of solid backfilling on the surface settlement above the working face with a burial depth of 662 m through FLAC3D (v.5.00) simulation and obtained a maximum surface settlement of 50.4 mm, which was significantly lower than 281 mm and within the surface defense standard, thus ensuring the safety of the surface buildings. Zhu et al. [25] studied the influence of gangue cemented paste backfill (CPB) mining on the movement of the overlying strata and the surface deformation law during stratified mining with a burial depth of 351.45 m. The results showed that CPB mining can reduce the surface movement by 95%, effectively control the surface subsidence caused by the multi-layer mining of thick coal seams, and protect the surface buildings. Through numerical simulation and theoretical analysis methods, Li et al. [26] investigated the movement and deformation law of the overlying strata with a burial depth of 500 m in CPB mining. The results suggest that this method can effectively control the movement and deformation of overlying strata in the mining area, roof fracture is avoided, and the maximum settlement value is only 127 mm, which effectively reduces surface subsidence and improves the recovery rate of coal resources. By using the physical similarity simulation method, Jiřina et al. [27] explored the settlement characteristics of the surface after backfilling the goaf with a fly ash–cement mixture. The research results show that the use of this mixture to backfill the goaf can effectively reduce the impact of deep mining on surface buildings. Bai et al. [28] used ultra-high-water backfill mining technology to extract coal resources with a burial depth of 175 m under surface buildings. The measured results show that the horizontal deformation of surface buildings was 0.3 mm/m, and the deformation level was controlled within one level, ensuring the safety of surface buildings. To summarize, scholars have achieved many results; however, they mainly concentrated on the surface deformation control of coal mines with a burial depth ranging from 100 to 800 m. Compared with shallow coal mines, the stress environment of deep coal mines (Burial depth > 800 m) is more complex. The laws of surface deformation control by backfilling mining in shallow coal mines may not be applicable to deep coal mines. There are few studies focusing on the control of surface deformation by goaf solid waste backfill mining in deep coal mines.

The deep mining of coal resources may lead to surface subsidence and damage to surface buildings. Due to the different backfilling mining conditions in deep coal mines compared to those in shallow coal mines, the control effect of applying goaf solid waste backfill mining under different burial depths and compression rates on surface movement and deformation remains unclear. In response to the aforementioned issues, this research focuses on examining the ground surface deformation control effect of deep gangue solid waste backfilling in goafs. In this study, the technical principles of the goaf solid waste backfill mining are illustrated. According to the compression deformation characteristics of the gangue backfill materials, a surface subsidence prediction model based on the equivalent mining height theory is proposed, and the influence of different burial depths and compression rates on surface movement and deformation was studied. The prediction of the change in the surface of the mining area 930 in Tangkou Coal Mine was carried out, the roof subsidence and surface buildings’ condition after goaf solid waste backfill mining were monitored and analyzed, and the protective effect of goaf solid waste backfill mining on surface buildings was verified. The current research on backfilling mining mainly focuses on the issues of coal mines with a burial depth of less than 800 m. This research responds to the current policy requirements for green mine environmental construction and reveals the law of controlling surface deformation during the backfilling mining of gangue waste under different burial depths and compression rates in deep coal mines (Burial depth > 800 m). It lays the foundation for the study of coal mining under the same geological conditions.

2. Mine Study Area and Issues

Tangkou Coal Mine is located in Jining City, Shandong Province, China. The minefield area is about 72.2 km², the recoverable reserves are 104 million tons, and the approved production capacity is 5.0 Mt/a. The main coal seam is coal seam 3, which is relatively stable, its average thickness is 3.31 m, and the inclination angle is around 7–16°. Mining area 930 was the mining area of focus on this study, with an underground elevation of −1045 to −1186 m and a burial depth of 1082–1222 m. The length from north to south is about 0.3–0.9 km, the width from east to west is 1.0–1.3 km, and the mining area is about 0.85 km². Figure 1 shows the geographical location and mining area distribution of Tangkou Coal Mine. At present, the mine is currently in the phase of releasing coal resources under surface structures, with a reserve of 1.5668 million tons of compressed coal. The annual emissions of washed gangue and excavation gangue are approximately 1.3 million tons. A large area of gangue accumulation has been formed near the industrial square.

There are five villages (Fengtai, Sunjia, Limiao, Wujia, and Huangjing Villages) and Tangkou Coal Mine Industrial Square above the mining area of backfilling faces 9301–9309. In Fengtai Village, there is also a provincial-level protected cultural relic, the Fenghuangtai Site.

Table 1. Statistics of buildings in the mining area and surrounding villages.

No.	Village Name	Building Area/10,000 m2	Building Structure/Set
			Adobe Bungalow	Brick Bungalow	Buildings
1	Fengtai Village	5.77	36	326	36
2	Sunjia Village	3.42	21	194	21
3	Limiao Village	9.24	57	522	57
4	Wujia Village	2.12	13	120	13
5	Huangjing Village	1.86	15	102	10
6	District office buildings	0.33	--	--	--
7	Dormitory building 1	0.34	--	--	--
8	Dormitory building 2	0.49	--	--	--
9	Substation	0.12	--	--	--
10	Canteen	0.34	--	--	--
	Total	24.03	142	1264	137

shows the surface buildings above Tangkou Coal Mine. Based on the regulations for coal mining under buildings and the dense buildings on the surface above mining area 930, the fortification indicators for surface movement and deformation were determined as follows: the subsidence value was ≤500 mm, the horizontal deformation value was ≤1.5 mm/m, the tilt deformation value was ≤2 mm/m, and the curvature value was ≤0.2 mm/m². The application of caving mining in this mining area would inevitably have a serious impact on the stability of the surface buildings [29,30]. To effectively protect the surface buildings and maximize the recovery of coal resources, goaf solid waste backfill mining was used in mining area 930 to achieve the dual purpose of controlling the surface movement and deformation and the large-scale disposal of gangue solid wastes.

3. Goaf Solid Waste Backfill Mining

Goaf solid waste backfill mining is developed on the basis of a fully mechanized coal mining method, which enables the simultaneous operation of coal mining and solid waste backfilling, with backfill mining hydraulic support. Compared with traditional fully mechanized mining, the goaf solid waste backfill mining incorporates a vertical feeding system for the safe and efficient transport of ground waste to the working face’s goaf. Additionally, there is a compaction system located at the back of the backfill mining hydraulic support, as depicted in Figure 2.

The raw materials used in goaf solid waste backfill mining come from two sources. On one hand, solid wastes such as gangue, fly ash, and slag from the ground are transferred to the vertical feeding well through the ground transfer machine and then to the underground storage bin. Transportation equipment such as underground belt conveyors and transfer machines are used to transport gangue and other solid wastes to the backfilling working surface. On the other hand, the gangue sorted out by the underground intelligent sorting chamber is directly transferred to the underground storage warehouse after crushing and screening and then transported to the backfilling working surface through a belt conveyor. This method allows for the prevention of gangue lifting and effectively mitigates the lifting pressure of the wellbore. After reaching the backfilling face, the backfill material is transported to the goaf area by means of a bottom-loading scraper conveyor suspended on the rear roof beam of the backfill mining hydraulic support. Subsequently, the backfill material is compacted by a tamping mechanism behind the hydraulic support until it is fully in contact with the roof. In this way, the roof of the goaf can be supported to reduce and control the rock formation movement and surface deformation.

4. Influence Mechanism of Goaf Solid Waste Backfill Mining on Surface Deformation in Deep Coal Mines

4.1. Equivalent Mining Height Theory for Goaf Solid Waste Backfill Mining

For goaf solid waste backfill mining, the key to controlling the surface subsidence is to control the actual effective thickness of the backfill material after compaction under the load of the overlying strata [31,32]. After the backfill material is backfilled into the goaf, it serves as the main support body, bearing most of the load of the overlying strata. The backfill material is compacted and deformed (Figure 3a). The theory of equivalent mining height was put forward in order to study the surface subsidence law after the application of goaf solid waste backfill mining [33]. The equivalent mining height is the actual mining height of the backfilling face minus the height after compaction of the backfill material in the goaf, as shown in Figure 3b. The calculation function is as follows [34]:

$$M_e=h_t+(1-\eta )(M-h_t),$$

(1)

where M is the actual mining height; M_e is the equivalent mining height; η is the compaction degree of the backfill material; h_t is the advance subsidence amount of the roof.

The compaction degree refers to the compression degree of the backfill material under the load of the overlying strata. It is defined as the ratio of the compression height of the backfill material to the original height. This parameter can be obtained from the mechanical compaction test of the backfill material; the amount of advanced roof subsidence can be measured on site.

4.2. Prediction of Surface Deformation After Goaf Solid Waste Backfill Mining

Based on the surface subsidence control principle of the equivalent mining height theory, the probability integration method was used to predict the surface movement and deformation. The specific parameters used in the prediction model cannot be directly derived from the predicted parameters of the caving mining method. They require adjustment based on the movement patterns of the overlying strata and surface subsidence laws associated with solid backfill mining. The mining height is the equivalent mining height calculated through the equivalent mining height theory.

The surface movement deformation in this model is calculated by Equation (2) [34]:

$$\begin{array}{l}W(x)={\displaystyle \frac{W_0}{2}}[erf({\displaystyle \frac{\sqrt{\pi }}{r}}x)+1]\\ i(x)={\displaystyle \frac{\mathrm{d}W(x)}{\mathrm{d}x}}={\displaystyle \frac{W_0}{r}}{e}^{-\pi {\displaystyle \frac{x^2}{r^2}}}\\ k(x)={\displaystyle \frac{{\mathrm{d}}^{2}W(x)}{{\mathrm{d}}^{2}x}}=-2\pi {\displaystyle \frac{W_0}{r^3}}x{e}^{-\pi {\displaystyle \frac{x^2}{r^2}}}\\ U(x)=bri(x)=\mathrm{b}{W}_0{e}^{-{\displaystyle \frac{\pi x^2}{r^2}}}\\ \epsilon (x)=brk(x)=-2\pi \mathrm{b}{\displaystyle \frac{W_0}{r^2}}x{e}^{-\pi {\displaystyle \frac{x^2}{r^2}}}\end{array},$$

(2)

where W₀ = M_eq cosα, r = H/tgβ; M_e is the equivalent mining height; q is the surface subsidence coefficient, which is closely related to the goaf compression rate and equivalent mining height; b is the horizontal movement coefficient; tgβ is the tangent of the major influence angle; and α is the inclination angle of the mining seam.

Thus, the function for calculating the maximum surface movement deformation after backfill mining (maximum subsidence value w_o, maximum tilt deformation i_o, maximum curvature deformation k_o, and maximum horizontal deformation ε_o) is obtained as follows [34]:

$$\left\{\begin{array}{ll}{w}_o& =q{M}_e\cos \alpha \begin{array}{}\end{array}\\ i_o& =w_o/r\begin{array}{}\end{array}\\ k_0& =\pm 1.52{\displaystyle \frac{W_0}{r^2}}\begin{array}{}\end{array}\\ {\epsilon }_0& =\pm 1.52b{W}_0/r.\end{array}\right.$$

(3)

The key to ensuring the accuracy of the surface movement and deformation prediction is to scientifically and reasonably determine the subsidence prediction parameters in the probability integration model [35,36]. Different from the movement and deformation of rock formations and surface caused by caving mining, the movement of rock formations and surface subsidence after goaf solid waste backfill mining are gradually transmitted upwards with the compaction of backfill materials, with significant subsidence characteristics. Therefore, the parameters of the probability integration model based on equivalent mining heights cannot be directly selected based on the parameters of the probability integration model for thin-seam mining with similar mining heights, and the predicted parameters need to be modified.

Table 2. The modified predicted parameters for surface subsidence.

Parameter	Subsidence Coefficient	Tangent of Major Influence Angle	Deviation of Inflection Point	Horizontal Movement Coefficient	Mining-Affected Propagation Angle
Caving mining	q	tgβ	S	b	θ0
Goaf solid waste backfill mining	1.05q	tgβ − 0.2 to 0.3	S + 0.05 to 0.1H	≈b	≈θ0

shows the modified predicted parameters of surface subsidence for goaf solid waste backfill mining.

4.3. Surface Deformation Prediction Plan and Predicted Parameter Determination

4.3.1. Surface Deformation Prediction Plan

To study the surface movement and deformation rules of goaf solid waste backfill mining in a deep coal mine, the Tangkou Coal Mine in Shandong Province, China, was taken as the research object, and the effects of different burial depths (800–1200 m) and compression rates (60–90%) on the surface movement and deformation were studied. The prediction plan of the surface deformation is shown in

Table 3. Surface deformation prediction plan.

Plan	Burial Depth/m	Compression Rate/%
1	800	60/70/80/90
2	900	60/70/80/90
3	1000	60/70/80/90
4	1100	60/70/80/90
5	1200	60/70/80/90

.

4.3.2. Predicted Parameters for Surface Deformation

According to the geological data of the mine, the average coal thickness in the mining area 930 was 3310 mm, and the average inclination angle was 6°. The compression rate was estimated at 60%, 70%, 80%, and 90%, and the equivalent mining heights of the backfilling face were 1324 mm, 993 mm, 662 mm, and 331 mm, respectively. Based on the specific geological conditions of mining area 930 and the measured parameters of the mine, the predicted parameters of the surface deformation were determined, as listed in

Table 4. Predicted parameters of mining area 930.

Coal Seam Inclination Angle/°	Subsidence Coefficient q	Tangent of Major Influence Angle/tanβ	Horizontal Movement Coefficient b	Mining-Affected Propagation Angle θ/°
6	0.82	2.15	0.35	87°

. The performance of the backfilling material directly determines the effect of surface deformation control. Through the test of the bearing capacity of loose gangue material, it can be known that the stress–strain relationship during the bearing process of loose gangue is: ε = 0.0899ln(8.3273σ + 1.06509), the Poisson’s ratio of the gangue blocks is 0.19, the density is 2530 kg/m³, and the shear modulus is 15 GPa.

4.4. The Influence of Burial Depth and Compression Rate on Surface Deformation

From the analysis of Figure 4, we can determine the following:

(1) When the compression rate is fixed, as the burial depth increases, the maximum values of the surface subsidence, horizontal deformation, tilt deformation, and curvature deformation gradually decrease. When the compression rate is 80%, and the burial depth is 1200 m, the maximum values of the surface movement deformation are the lowest. Compared with those at the compression rate of 80% and the burial depth of 800 m, the maximum values of the surface subsidence, horizontal deformation, tilt deformation, and curvature deformation are reduced by 26.95%, 24.50%, 43.48%, and 49.61%, respectively. This can be explained as follows: as the burial depth increases, the number of key layers above the mining area increases; the key layers have a controlling effect on surface deformation, and the displacement amount decreases through the sequential layer transmission, resulting in a decrease in surface subsidence [37,38].

(2) When the burial depth is fixed, as the compression rate increases, the maximum values of the surface subsidence, horizontal deformation, tilt deformation, and curvature deformation gradually decrease. When the burial depth is 1000 m, and the compression rate is 90%, the maximum values of the surface subsidence, horizontal deformation, tilt deformation, and curvature deformation are 224.08 mm, 0.66 mm/m, 0.63 mm/m, and 0.0044 mm², respectively. Compared with those at the compression rate of 60%, these values are reduced by 75.46%, 76.54%, 75.12%, and 74.97%, respectively. This is because as the compression rate rises, there is a decrease in the equivalent mining height, leading to an enhancement in the supporting effect of the backfill body. This enhancement effectively restricts the movement deformation of the overlying strata and minimizes the breakage of key layers, resulting in a reduction in surface subsidence [39,40].

(3) As the compression rate increases, the change amplitude of the surface movement and deformation amount gradually decreases as the burial depth increases. When the compression rate is 60%, and the burial depth increases from 800 m to 1200 m, the maximum values of the surface subsidence, horizontal deformation, tilt deformation, and curvature deformation are reduced by 277.25 mm, 0.73 mm/m and 1.39 mm/m, 0.0113 mm/m², respectively. However, when the compression rate is 90%, they are reduced by 69.32 mm, 0.18 mm/m, 0.35 mm/m, and 0.0028 mm/², respectively.

4.5. Design of the Compression Rate for the Goaf

From Figure 5, the influence of the burial depth and compression rate on the maximum values of the surface subsidence, horizontal deformation, tilt deformation, and curvature deformation can be comprehensively analyzed. As shown in Figure 5a, when the burial depth is within 800 m to 1200 m, and the compression rate is greater than 79%, the maximum value of the surface subsidence is less than 500 mm, which meets the surface building fortification index. As shown in Figure 5b, when the burial depth ranges from 800 m to 1200 m, and the compression rate is greater than 73%, the maximum value of horizontal deformation is less than 1.5 mm/m, meeting the surface building fortification index. As illustrated in Figure 5c, when the burial depth is between 800 m and 1200 m, and the compression rate is greater than 63%, the maximum value of the tilt deformation of the ground surface is less than 2 mm/m, meeting the surface building protection index. As revealed in Figure 5d, when the burial depth is from 800 m to 1200 m, and the compression rate is greater than 64%, the maximum value of the tilt deformation of the ground surface is less than 0.2 mm/m². At this time, the surface building fortification indicators are met.

In summary, surface buildings can be safeguarded to the greatest extent when the compression rate is greater than 79%, and the burial depth ranges from 800 to 1200 m, as all maximum values of surface deformation meet the fortification indicators.

5. Analysis of the Surface Deformation Prediction and Monitoring Results in Tangkou Coal Mine

5.1. Prediction Results of Surface Deformation

Based on the analysis in Section 4.5, a burial depth of 1000 m and a compression rate of 80% were employed as the actual mining conditions in Tangkou Coal Mine.

Table 5. Maximum values of the building movement and deformation after backfill mining in mining area 930.

Villages	Subsidence (mm)	Extreme Value of Horizontal Deformation/(mm/m)	Extreme Value of Tilt Deformation/(mm/m)	Extreme Value of Curvature Deformation/(mm/m2)
Limiao and Fengtai Villages	230	0.23	0.65	0.0021
Sunjia and Wujia Villages	110	0.07	0.35	0.0008
Fenghuangtai Site	200	0.23	0.25	0
New District in Limiao Village	110	0.14	0.42	0
Limiao Primary School	20	0.12	0.25	0
Huangjing Village	0	0.03	0	0
District office buildings	0	0	0	0
Dormitory 1#	0	0	0	0
Dormitory 2#	0	0	0	0
Substation	0	0	0	0
Canteen	0	0	0	0

shows the maximum values of the regional movement and deformation of surface buildings after goaf solid waste backfill mining in mining area 930. Figure 6, Figure 7, Figure 8 and Figure 9 show the surface movement and deformation contour maps of each working face in the study area after backfill mining.

As shown in Table 5 and Figure 6, Figure 7, Figure 8 and Figure 9, after backfill mining in mining area 930, the highest value of the surface subsidence (448 mm) occurs in the middle of the working face. The highest values of the surface horizontal movement deformation, horizontal movement deformation, and curvature deformation are 1.43 mm/m, 1.25 mm/m, and 0.0088 mm/m², respectively. The deformations of the villages and main buildings above the backfilling area are within the fortification range, ensuring their safe utilization.

5.2. Roof Subsidence Monitoring and Surface Building Condition Analysis

5.2.1. Arrangement of the Monitoring Equipment in the Goaf

To monitor the roof displacement of the backfilling face 9301, a total of 12 measuring points were set up, and 12 roof dynamic detectors were installed in the backfill body [41]. The instruments were arranged in three rows, with four in each row. Figure 10 shows the specific installation positions.

Since the roof dynamic detector was located in the goaf, its data transmission line was easily damaged. Therefore, the data transmission lines were placed in a special pipeline (rubber hose or steel pipe) and buried in the backfill body in the goaf, located in the trough. The pipelines located in the haulage gate were also buried in the backfill body.

5.2.2. Roof Dynamic Monitoring Results and Surface Building Conditions

The roof subsidence monitor was used to monitor the roof subsidence in the goaf after backfill mining. The monitor was installed in the goaf during the mining period, and the monitoring data were transmitted by wired connection. The 3# measuring point located 28 m away from coal wall near the haulage gate was selected to monitor and analyze the dynamic subsidence of the roof. Figure 11 displays the monitoring results of the dynamic subsidence of the roof.

As shown in Figure 11, the dynamic subsidence of the roof in the goaf first increased and then stabilized with the advancement of the working face. After reaching a distance of 188 m from the working surface, the deformation of the surrounding rock entered the stable stage. As the working face advances, the backfill body was gradually compacted and became the main body bearing the load of the overlying strata. The roof subsidence also tended to be stable. The maximum subsidence value of the 3# measuring point was 635 mm; it can be concluded that the compression rate at the measuring point 3# is 80.6%.

Figure 12 shows the situation of the surface buildings after the goaf backfilling.

As illustrated in Figure 12, after goaf solid waste backfill mining, the buildings in Fengtai Village, Wujia Village, and Fenghuangtai Site above the mining area did not suffer damage and deformation, the subsidence and deformation of the surface were effectively controlled, and the surface buildings were protected to the greatest extent.

6. Conclusions

This study focused on deep coal mines, in response to the fact that the control laws for surface movement and deformation in shallow coal mines do not apply to deep coal mining backfilling operations. The influence of different burial depths and compression rates on the surface deformation after the backfilling of solid waste in the mined area was explored. The surface deformation of the 930 mining area in Tangkou Coal Mine after backfilling mining was predicted, and the roof subsidence and surface building conditions after the backfilling of solid waste in the mined area were monitored and analyzed. Thus, the control laws of surface deformation during the backfilling mining of gangue waste under different burial depths and compression rates in deep coal mines were verified and clarified. The main conclusions are as follows:

(1) The technical principles of goaf solid waste backfill mining were introduced. Based on the movement characteristics of rock formations in goaf solid waste backfill mining, the theory of the equivalent mining height was proposed, and a prediction model of the surface subsidence using the probability integral method based on the equivalent mining height was established. Additionally, the effects of different burial depths (800–1200 m) and compression rates (60–90%) on the surface movement and deformation were predicted.

(2) The surface deformation data were predicted using the surface subsidence prediction model. As the burial depth and compression rate increased, the maximum values of the surface subsidence, horizontal deformation, tilt deformation, and curvature deformation gradually decreased, and the method of backfilling goaf with deep coal waste also showed better control effects on surface movement and deformation. When the burial depth was 800 m, and the compression rate was 60%, their maximum values were 1025.51 mm, 3.23 mm/m, 2.23 mm/m, and 0.02 mm/m², respectively.

(3) Based on the predicted results of surface subsidence, the extreme deformation cloud map of the surface was obtained through analysis. When the compression rate was greater than 79%, and when the burial depth ranged from 800 to 1200 m, the maximum values of the surface movement and deformation were lower than the maximum fortification index. The compression rate of 80% was designed as the backfill mining condition for Tangkou Coal Mine. The estimated values were below the critical value for building damage, indicating that buildings can be utilized without safety concerns.

(4) The roof subsidence and surface deformation of the backfilling face 9301 were measured after backfill mining. The maximum roof subsidence value was 635 mm, and the compression rate was 80.8%; the surface buildings were little affected by mining, without obvious cracks. This indicates that all buildings remained within the safe range of use, and the protective effect of goaf solid waste backfill mining on surface building was verified.