Reclamation Design Research Articles

Design and Evaluation of Solar Photocatalytic Reclamation for Purification of Agricultural Wastewater

The study designed and assessed a solar-powered wastewater treatment system tailored for purifying agricultural wastewater in urban residential areas. Integrating advanced technologies, primarily solar energy-driven, the system aims to effectively remove pollutants to meet discharge standards. The detailed analysis included wastewater composition, sources and suitable treatment processes, with emphasis on comparative feasibility analysis and recommended quality assurance measures. The results of the study indicate that solar photocatalytic technology has great potential for degrading pollutants and reducing operating costs. The economic analysis showed that the technology is financially viable with a payback period of about 4.64 years. The photocatalytic system offers a higher level of efficiency and flexibility compared to existing methods. Emphasis is placed on implementing quality assurance to meet safety and environmental standards.

Strength characteristics and mix design of full-depth reclamation of asphalt pavement with cement

The research presents the strength characteristics and theoretical mix design of full-depth reclamation (FDR) with cement for road maintenance and rehabilitation. The reclaimed aggregates used in the study were pulverized and blended on the investigation site by the recycler machine. The FDR mix design covered the reclaimed asphalt pavement (RAP), reclaimed base, and reclaimed subbase courses. The unconfined compressive strength (UCS) was tested on the FDR with cement under different mix proportions, cement content, moisture content, and curing time. Two factors that affect the UCS of FDR, viz., moisture-induced packing density and moisture for cement hydration, were observed. The mix proportion with 40 % RAP required at least 6 % cement to stabilize the FDR for use as a bound base course as per the standard, while the effective limit of cement content for FDR was 9 %. The strength prediction model of FDR with cement was presented theoretically based on the modified soil-moisture/cement ratio concept. The verification of the proposed strength model was performed using 7 and 28-day UCS from another investigation site. The design recommendations for FDR with cement were summarized. This discovery could offer a cost-effective and precise method for the mix design of FDR with cement.

2D Model For Addu City Project - Wave Transformation Over Reef Flat

Van Oord DMC was awarded the Contract for the Reclamation by Dredging and Shore Protection works for land in Addu City by The Ministry of National Planning, Housing and Infrastructure of the Maldives. The Scope of Works consists of the Design and Construction of (among others) Reclamation and Shore Protection Works on various locations in the Addu City atoll. The project execution started in 2022 and has been finalized at the end of 2023. The design of the Shore Protection Works has been verified in 2022 by means of 2D physical model testing in the wave flume of DHI in Denmark. Cross-sections of shore protection works for three different reclamation areas have been tested, where this abstract will focus on 2 locations at the outside of the atoll: Maradhoo and Four Lane Link Road (4LLR). All dimensions given in this abstract are prototype values, unless otherwise specified. The length scale of the both models was selected at 1:30. The foreshore of the 2 tested cross-sections is very typical for atolls, consisting of a relatively shallow reef flat followed by a very steep slope to deep water. The modelled foreshores are presented in Figure 1. This figure also shows the locations of the wave gauges, which were placed both offshore (near the wave generator) and on top of the reef flat (in front of the structure). The tested seabed levels directly at the toe of the 4LLR and Maradhoo structures were MSL-0.70m and MSL-0.40m respectively. The target wave conditions were defined in deep water (in front of the wave generator), with design wave heights (Hm0) between 3.8m and 4.4m and 120% overload conditions. The tested peak wave periods (Tp) varied between 11.9s and 19.7s.

Targeting phosphorus transformation to hydroxyapatite through sewage sludge pyrolysis boosted by quicklime toward phosphorus fertilizer alternative with toxic metals compromised

Advancing pyrolysis practice for phosphorus (P) recovery and recycling from sewage sludge arouses intensive research interests due to the forthcoming threat of global P sustainability. However, how to both in situ manipulate P targeted transformation to a designed form and accommodate downstream use while compromise adverse impacts of concomitant toxic metals (TMs) challenges the worldwide initiative of P reclamation from sewage sludge. Here, a P targeted transformation to hydroxyapatite (P2tHAP) technique to bridge the discrepancy of P recovery and subsequent use was developed. Through manipulating calcium-to-P molar ratio (Ca/P) of sludge feedstock by calcium oxide, the sludge P can be targetedly transformed to HAP during pyrolysis, a bioavailable form delivered as sewage sludge char-derived phosphorus fertilizer (SCPF). The P supply competency of the SCPF for Ca/P below or above 1.67 with a risk abatement of TMs was comparable to conventional P fertilizer, while the Ca/P = 1.67 was prone to the occurrence of sludge ash sintering, detrimental to the HAP formation. The lowered bioavailability of TMs was orchestrated by the root-secreted oxalic acid, due to the triggered phosphate starvation response. The random forest analysis indicated the driving force in the evolution of rhizobacterial communities, dominantly arising from those TMs after the SCPF soil application. Thermodynamic and kinetic calculations validated that HAP with the stable molar Gibbs energy gHAP (∼−7.23×103kJ/mol) underpinned the progress of P2tHAP during sludge pyrolysis. The outcome prospects to propel the integrative design of an innovative reclamation of P-rich wastes and simultaneous compromise of concomitant contaminants.

The role of microhabitat for bryophyte establishment in reclamation of boreal wetlands

Minerogenous peatlands that accumulate deep deposits of organic matter (fens) were an important part of the pre-disturbance landscape across Alberta’s oil sands mining area. Bryophytes occupy 80–100% of the ground layer in these site types and form an important part of the accumulated organic matter. Bryophytes are small plants that occur in microhabitats that are an integral part of the surrounding plant community. The objective of this paper is to evaluate the establishment of bryophytes at an experimental wetland (Sandhill Wetland-SHW) by assessing the changing vegetation and substrate regimes over eight years after wet-up. Included in this analysis is an account of the ground layer flora between 2014 and 2021 along with evaluation of associated environmental factors. At SHW, a number of peatland bryophytes initially established in numerous areas across the wetland. However, in subsequent years increasing water tables with expanding Typha-dominating areas, high sedge productivity along with increasing vascular plant cover, and increasing sodicity have reduced the microhabitats available for bryophytes, with the result being a much-diminished set of peatland bryophyte species. We suggest that future reclamation designs for fens should include microhabitats for bryophytes, as bryophytes are foundational species and integral to fen development. In comparison, reclamation designs for non-peat forming ecosystems that do not have abundant bryophytes, such as marshes and saline wetlands, do not require these microhabitat conditions. Installing a recently harvested peat substrate appears to provide suitable conditions for early establishment of bryophytes.

Hydrological sustainability of in-pit reclaimed oil sands landforms under climate change

Development of robust reclamation designs would require understanding the relative effects of climate change on the water budget of reclaimed Athabasca oil sands landforms (Alberta, Canada). A surplus water budget is critical to sustain pit lakes and periodically freshen localized surface water ponds within the closure landscape. In this study, four hypothetical future climate scenarios were developed from statistically downscaled RCP2.6 and RCP8.5 climate projections and used in a hydrological model to investigate the potential effects of climate change on the water budget of an in-pit reclaimed oil sands mine landform. The four scenarios allowed the assessment of climate change effects for endpoints that bracket a range of future climate conditions on the water balance of the landform. Surface water and groundwater flow and chloride transport were simulated for the 2024–2100 period using daily climate forcing and the results were compared with equivalent responses under historical climate (1944–2020). The results suggest that the hydrological behavior under historical and RCP2.6 scenarios is similar. The climatic water deficit (potential evapotranspiration exceeding precipitation) will rise significantly under the RCP8.5 scenario. However, the modeling suggests that the water budget of the landform will not be too different from the early 21st century prolonged dry climate period. The chloride released from the landform under the different projected and historical climate scenarios also remained similar. Although evapotranspiration increases and leads to relatively drier conditions, a modest increase in precipitation helps maintain a surplus water budget in most years. The results demonstrate that incorporating future climate projections into water balance analyses is crucial to understand the potential reductions in runoff depths.

Rekultivacija površinskog kopa "Garajevac Istok" kod Novog Bečeja

The surface exploitation of mineral raw materials is realized in the natural environment, causing the degradation of the narrower and wider space: the change of the physical appearance of the terrain and the degradation of the soil and autochthonous vegetation cover. The recultivation of the surface mine area, after the exploitation of mineral raw materials, is an important and mandatory measure in the function of environmental protection. In a biologically empty space, with damaged or destroyed natural content, in parallel with the slow and long-lasting process of spontaneous self-revitalization, technical and biological reclamation measures and procedures are applied to control and accelerate the revitalization process.The subject of this work is the design of reclamation on the surfaces affected by the exploitation of clay, on the example of the Garajevac Istok surface mine near Novi Bečej, with the aim of creating habitats for plant and animal life. The planned goals of the reclamation of the post-exploitation area of the Garajevac Istok surface mine will be realized by applying a combination of afforestation measures and spontaneous self-reclamation.

Reclaiming Wetlands after Oil Sands Mining in Alberta, Canada: The Changing Vegetation Regime at an Experimental Wetland

Surface mining for oil sand results in the formation of large pits that must be reclaimed. Some of these pits are backfilled with a myriad of substrates, including tailings rich in cations and anions, to form a solid surface. Experimental reclamation of the East in-pit located on the Syncrude Canada Ltd. mine lease was initiated in 2011 with Sandhill Wetland. Here, we report on monitoring (between 2015 and 2021) of Sandhill Wetland plant communities and significant environmental features, including base cations and water tables. Multivariate analyses demonstrated that the three dominant plant communities established in 2013 have continued to be dominated by the same species nine years after reclamation was initiated, but with reduced species richness. Plant communities have shifted across the wetland in response to water table changes and increases in sodium concentrations. The stoichiometry of base cations is unlike the natural wetlands of the region, and the surficial water chemistry of the wetland is unique. In response to variability in precipitation events coupled with wetland design, water tables have been highly variable, creating shifting water regimes across the wetland. Plant community responses to these shifting conditions, along with increases in base cation concentrations, especially sodium, provide background data for future in-pit reclamation designs. The plant responses underscore the need to develop reclamation designs for landscapes disturbed by mining that alleviate extreme water table fluctuation events and decrease cation concentrations to levels that approach natural wetlands.

Marine environment numerical simulation of morphological planning of land reclamation

Based on the evaluation criteria of the impact of different types of reclamation design on the natural environment of coastal waters, the environmental fluid dynamics model was used to simulate the seawater environment in 13 scenarios from three aspects: the shape of the artificial island, the size of inner lake outlet and the layout of the artificial island. The hydrodynamic force and water exchange capacity of these islands were quantitatively compared, and the effects of different artificial islands on the Marine environment were summarized. The planning morphology design guidelines are summarized in four aspects: (1) reduce the serrated steep slope shoreline, avoid forming semi-closed water, and increase the simple and smooth shoreline; (2) reduce the width of the lake mouth to increase the length of the lake; (3) choose a simple alignment parallel to the shore; (4) the design mainly focuses on the morphology of shoreline, followed by consideration of the lake mouth and artificial island arrangement.

Wastewater reclamation design from sewerage system for gardening activity in Universitas Pertamina

Wastewater recycling is one of the criteria for continuous innovation at the campus level. Reclamation of water from the sewage system for gardening activities is one way to achieve this target at Universitas Pertamina. The aim of this study is to design and verify a water treatment unit from sewage to ready-to-use water for gardening activities. The units needed for the wastewater treatment system are a tank, Horizontal Roughing Filter (HRF), Rapid Sand Filtration (RSF), reservoir, and disinfection. The expected quality of effluent from processing is TDS 278 mg/L; TSS 1.3 mg/L; Turbidity 0.17 NTU; BOD5 0.63 mg/L; COD 6.12 mg/L; Total phosphate 0.95 mg/L; Nitrate 0.07 mg/L; detergent 0.7 mg/L; and total coliform MPN/100mL. The most important parameter in the sewerage water treatment process is the total coliform which must achieve an efficiency of 99%. This conventional method of water treatment is used because the availability of land is still sufficient, if it is not sufficient then further processing that is efficient, environmentally friendly, and has economic value is required.

Influence of Atmospheric Pressure Surges on the Level of Suprapermafrost Waters and the Flow of Small Rivers (Anadyr Lowland, Chukotka)

It is known that atmospheric pressure surges affect the discharge of underground water sources in large artesian basins. In southern latitudes, the groundwater tables change insignificantly following the diurnal variations of atmospheric pressure. There is no information on the influence of rapid changes in atmospheric pressure on the position of the surface of the suprapermafrost waters and river flow in the Arctic region. The study of the diurnal course of the level of underground suprapermafrost and surface waters was carried out to identify the links of river flow with atmospheric phenomena and cryogenic processes. It was found that the daily atmospheric pressure drop with an amplitude of 1.2 kPa in the area of the small Ugolnaya-Dionisia river, located in the Anadyr lowland in Chukotka, led to a simultaneous decrease and then an increase in the level of suprapermafrost underground and surface river basin waters by 2.5-7.8 cm. This corresponds to a short-term decrease and then an increase in the river water discharge by more than 3.5 times. To clarify the factors that determine the mechanism of the influence of atmospheric pressure on the water level and river flow, a consideration of the hydrophysical properties of aquifer-containing peat soils was carried out. Compression tests revealed that the elasticity of the peat soils horizon remains within the range of 0-15 kPa, which contributes to a dynamic change in porosity even with a slight change in the external load. This means that the atmospheric pressure changes during weather development are sufficient to modify the water capacity of peat soils and deposit them, and then discharge a part of the suprapermafrost flow. The discovered pressure impact in the tundra soils of the permafrost zone is a unique mechanism for providing plants with moisture during droughts and reducing the risk of tundra fires. As part of the further study of the pressure impact, it is planned to conduct laboratory experiments to determine the quantitative parameters of the change in the peat soils moisture capacity under pressure drops in the atmosphere. Mathematical modeling of the capillary moisture capacity of peat soils will be performed under conditions of ambient load changes. The results of experiments and theoretical studies are assumed to be useful for predicting the flow of bogged-up river basins, design of reclamation, and irrigation of areas of peat soils distribution.

Состояние и перспективы развития мелиорации в Амурской области

The reclamation complex of the region, after a long period of uncertainty, is among the priorities of agricultural development. The article deals with the problems of land reclamation, which acts as a means of ensuring the sustainable development of the agro-industrial complex of the region, since land reclamation plays a crucial role in increasing the fertility of developed lands and crop yields. However, reclamation systems need constant maintenance. It is noted that forest reclamation is insufficiently developed in the region. The purpose of the study is to analyze the current state of land reclamation in the Amur region. The study was conducted in 2018 – 2021 in the Amur region. It has been established that the majority of reclamation systems are in unsatisfactory condition due to a long service life, lack of repair and maintenance, as well as great wear and tear. As a result of the conducted research, the necessity of restoration and reconstruction of the reclamation systems of the region was established. The ways of development of land reclamation on the basis of restoration, repair, reconstruction and construction of new land reclamation systems are outlined. An example of the reconstruction of the reclamation Gilchinsk drainage system and the results of this reconstruction are given, which are expressed in the fact that agricultural work began to be carried out in optimal agrotechnical terms, regardless of weather conditions, and farmers receive stable high yields of agricultural crops. It was noted that it became necessary to pay attention to the design and construction of land reclamation. The modern approach to the survey of reclamation systems, the main directions of repair of concrete structures of reclamation structures are considered. The subject methods of economics, ecology, principles: diversity of forms are used. To conduct this study, information data from websites and other open sources were used.

How Should Mine Reclamation Design Effectively Respond to Climate Change? A Mini Review Opinion

Climate change is a growing concern with each of the last three decades being successively warmer than preceding decades. Mine wastes are mandatory required to be reclaimed after mine operation due to their high risks of contaminating environment and huge volumes occupying large useable land resources. However, most traditional mine reclamation plans are designed with an assumption of unchanged, consistent conditions of environment, climate and hydrology conditions, which may not work properly under the global climate change. This paper discussed the previously ignored problem that is how mine reclamation design should effectively respond to climate change. Through reviewing the current responding strategy to the climate change during mine reclamation and closure, this mini review was structured, and the opinion is concluded that the more active the designers consider the factors of climate change, the more manageable, predictable and sustainable the reclaimed ecosystem and landscape are. Nature-based solutions can act as the general guidelines when considering climate change with mine reclamation, and the six-step framework aims more specifically on mine reclamation. The two methods can work together to help designers and regulators to effectively respond to climate change when planning mine reclamation and closure.

Assessment of reclamation-induced consolidation settlement considering stratigraphic uncertainty and spatial variability of soil properties

Consolidation analysis is a key task for reclamation design. Although consolidation is a long-term process, acceleration of consolidation is often preferred for speeding up the reclamations. Before proposing measures to accelerate the consolidation and reclamation process, it is imperative to have an accurate prediction of consolidation settlement for fine-grained materials, which is greatly affected by spatial distribution of subsurface zones with different soil types (i.e., stratigraphic heterogeneities and uncertainty) and spatial variability of soil properties. In current practice, calculation of consolidation settlement often uses simplified stratigraphic boundaries and deterministic consolidation parameters without considering stratigraphic uncertainty or soil property spatial variability. The oversimplified practice might result in unconservative estimations of consolidation settlement and pose threats to safety and serviceability of constructed facilities on reclaimed lands. In this study, a stochastic framework is proposed for consolidation settlement assessment with explicit modeling of stratigraphic uncertainty and spatial variability of soil properties by machine learning and random field simulation from limited site investigation data. Performance of the proposed framework is demonstrated using an illustrative example. Results indicate that the proposed method effectively generates multiple realizations of geological cross section and random field samples of geotechnical properties from limited measurements and offers valuable insights into spatial distribution of the estimated total primary consolidation settlement curves and angular distortion.

Civil and Environmental Engineering, West Virginia University, Morgantown, WV 26506

Abstract. A coal refuse pile located in Greenbrier County, West Virginia was studied to restrict generation of acid mine drainage through the use of a cap and cover system. This paper presents results of a finite element method seepage analysis on a proposed reclamation design. The proposed reclamation incorporates a cap and cover system with a 0.3-m thick surface vegetation cap layer over a 0.6-m thick low permeability layer. The low permeability layer is directly above the coal refuse. Unsaturated soil mechanics was utilized, adopting the Fredlund and Xing equation for soil-water characteristic curve (SWCC) estimation. SWCC fitting parameters were calculated using the Zapata and the Hernandez estimation techniques. Different precipitation events were used to evaluate seepage throughout the reclamation area and assess the effectiveness of the cap and cover system. A steep area (>4H:1V) and a flat area were considered. The water balance analysis showed a 50% to 88% reduction in water volume at the coal refuse layer and a reduction in the time for the refuse to return to initial water content due to the cap and cover system implementation. Moisture detainment was observed in the growth layer and is important for supporting vegetation persistence.

Assessing the potential of integrating distribution and structure of permanent open-water wetlandscapes in reclamation design: a case study of Alberta, Canada

Wetlands are multi-functional systems that provide a disproportionatenumber of ecosystem services given the spatial extent they occupy bothnationally and globally. The ecological functioning of these wetlands isdependent on the structure of the landscape, which poses unique challenges whenreclaiming wetlands in areas where resource extraction is occurring. Resource extraction mega-projects requirethat entire wetlandscapes be reclaimed and often involve timelines thatnecessitate the consideration of climate projections to create self-sustaining,naturally appearing wetlandscapes that meet policy objectives. To understandwetlandscape structure and guide reclamation planning and closure permittingevaluation, a random sample of 13,676 1-km2 landscapes weresubselected to identify 1684 permanent open-water wetlandscapes. A parsimoniousset of landscape metrics were applied and compared across levels ofanthropogenic disturbance and across natural regions (i.e., Grassland, Parklandand Boreal). Results demonstrated that permanent open-water wetlands arerelatively rare (12.3% of our total random sample) and typically occupy lessthan 8% of wetlandscapes when present. The majority of wetlands in the study area are lesspermanent and more variable in nature than the permanent open waterwetlandscapes created by megaproject reclamation, which has the potential to alter thedistribution and size of open-water wetlands beyond their natural occurrence.Comparison across disturbance levels and natural regions yield statisticaldifferences among landscape structure. General wetland landscapes representinga combination of disturbance level and natural region can be created for eachmetric to guide reclamation design and closure planning approval.

Reactive transport modeling of the geochemical behavior of highly reactive tailings in different environmental conditions

The hydrogeochemical behavior of highly reactive tailings with no or very low neutralizing capacity and their hydrogeochemical response when covered by a cover with capillary barrier effects (CCBE) were evaluated in laboratory columns. The hydrogeochemical response of highly reactive tailings under wetting-drying cycles and saturated conditions was also simulated using the MIN3P code, a finite volume model for coupled groundwater flow, oxygen diffusion and multi-component reactive transport. Laboratory tests were conducted for approximately 18 wetting and drying cycles, over a period of one and a half years. A numerical simulation model was validated using laboratory results of uncovered highly reactive tailings under wetting and drying cycles conditions. The acceptable agreement between the geochemical observations in the laboratory and the numerical simulations shows that MIN3P can simulate the hydrogeochemical response of highly reactive tailings (initially very acidic) under laboratory experimental conditions and can make realistic predictions. The laboratory hydrogeochemical response of highly reactive tailings covered by a CCBE and the numerical modeling results of highly reactive tailings under saturated conditions (an equivalent CCBE oxygen barrier) indicated a decrease in the concentration of sulfate and most metals in the leachate compared to uncovered highly reactive tailings, indicating that both scenarios decreased sulfide oxidation. The simplified approach for geochemical modeling of saturated reactive tailings evaluated in this paper could be used to determine the required oxygen barrier efficiency to reach the target effluent geochemistry as a preliminary stage of reclamation design.

Use of Remote Sensing Tools to Measure a Fluvial Geomorphic Design-Input Parameter for Land Reclamation

Fluvial geomorphic approaches for reclamation landform design have been applied since 2000, mostly in mined lands, as an alternative to conventional landform design methods. Those approaches aim to reconstruct mature landforms and drainage networks that would develop within a natural catchment, after thousands of years of work performed by geomorphic processes. Some fluvial geomorphic design methods take specific measurements from natural and stable reference areas for initial input values for reclamation design. Valid reference areas can be difficult to find, can be in highly anthropized environments, or may be difficult to access. This paper evaluates the use of remote sensing tools to measure morphometric parameters in upper sections of agricultural land catchments considered for use as reference areas. The ridge to head of channel distance (Xrh) was the parameter of interest. We used land surface profiles developed from LiDAR (Laser Imaging Detection and Ranging) data and planimetric measurements from orthoimages to estimate Xrh. The results obtained by the two methods were encouraging but showed a significant difference. Ground truthing showed that ploughing obliterated between 19.5 and 22.4 m (on average) of the headwater section of first-order channels, reducing the channel length by 15.1 to 32.4%. Using a greater Xrh value than appropriate for near steady-state conditions as a design input for a geomorphic reclamation project would be expected to result in active erosion processes in the constructed reclamation to regain their missing channel length. We recognize the advantages and limitations of remote sensing methods for measuring the morphometric parameters of the landform relief design inputs. We show how these tools may be used to help select and prioritize reference areas, and warn about the use of disturbed landscapes as reference areas to assure the geomorphic stability of the constructed reclamation designs.

Consolidation behavior of dredged ultra-soft soil improved with prefabricated vertical drain at the Mae Moh mine, Thailand

The effectiveness of the prefabricated vertical drains (PVDs) in the consolidation of ultra-soft dredged soil with various soil water contents (W) in Mae Moh mine, Lampang, Thailand was researched via a series of large-scale model tests and numerical analysis. Large settlements with the delay of excess pore pressures is a distinct behavior of ultra-soft soil. The PVD dimensions were found to have a significant effect on the rate of consolidation and the delay of excess pore pressure at low total vertical stress (σv). The smaller PVD dimension resulted in the smaller rate of consolidation and longer delay of excess pore pressure. The undrained shear strength (Su) of ultra-soft clay at various degrees of consolidation could be approximated by the vertical effective stress (σ′v) based on the SHANSEP where the σ′v was determined from the Asaoka's observational method. The finite element analysis with axisymmetric and plane strain models showed that the axisymmetric model produced an excellent settlement prediction. However, the excess pore pressures were not well predicted by the axisymmetric model, due to the delay of excess pore pressures at the early stages of consolidation. In practice, the plane strain models proposed by Chai et al. and Indraratna and Redana's methods are suggested to predict the consolidation settlement of the Mae Moh dredged soil improved with PVD. The outcome of this research will facilitate the geotechnical design of reclamation of ultra-soft dredged soil in Mae Moh mine and other similar soils.

Calculation of Residual Surface Subsidence Above Abandoned Longwall Coal Mining

Exhausted or abandoned underground longwall mining may lead to long-term residual subsidence on surface land, which can cause some problems when the mined-out land is used for construction, land reclamation and ecological reconstruction. Thus, it is important to assess the stability and suitability of the land with a consideration of residual surface subsidence. Assuming a linear monotonic decrease in the annual residual surface subsidence, the limit of the sum of the annual residual subsidence factor, and continuity between surface subsidence in the last year of the weakening period and the residual surface subsidence in the first year, we establish a model to calculate the duration of residual subsidence and the annual residual surface subsidence factor caused by abandoned longwall coal mining. The duration of residual surface subsidence increases with the increase in mining thickness as well as the factor of extreme residual subsidence. The proposed method can quantitatively calculate the annual residual subsidence, the accumulative residual subsidence, and the potential future accumulative residual subsidence. This approach can be used to reasonably evaluate the stability and suitability of old mining subsidence areas and will be beneficial for the design of mining subsidence land reclamation and ecological reconstruction.