Numerical simulation of uneven settlement of municipal solid waste landfill by FLAC 3D

After the landfill site is sealed, the uneven settlement is related to the safety of reutilisation of the site, and it is critical to calculate the uneven settlement of the site without error. In this article, the soil parameter of garbage body was changed with biodegradation. Fast Lagrangian Analysis of Continua in three dimensions (FLAC 3D) numerical simulation was applied to the settlement of the landfill site closure. In calculating the settlement of landfill, the soil parameters of landfill with age were obtained by field drilling experiments. The parameters can reflect the characteristics of soil organic matter in different biodegradation stages. Finally, the uneven settlement within 20 years of the closure period was obtained by the numerical simulation taking Jinzhou Nanshan landfill as an example. The results show that the settlement with the age increases gradually, but the rate will be more and more moderate, and the maximum subsidence value in the sealing field after 20 years will be 9.11 m, 15.71% of the maximum elevation. Around the landfill slope position of uneven settlement rate is bigger, and the maximum angle of uneven settlement is up to 45°. But the middle position is small, which is close to 0°.

Mining-induced Land Subsidence Detected by Sentinel-1 SAR Images: An Example from the Historical Tadeusz Kościuszko Salt Mine at Wapno, Greater Poland Voivodeship, Poland

There are many mines in Poland that have been in operation for over 100 years, with theTadeusz Kościuszko mine being a large salt mine in Wapno, northern Poland. The mine was closed in1977 due to the greatest catastrophe in the history of Polish mining, but in the first days of 2021, a verylarge hole has been created in this area due to land subsidence. This article uses InSAR technology withSentinel-1 images to determine settlement and ongoing deformation in this mine. The study results areuseful for policymakers, managers, and authorities because land subsidence has caused serious anddangerous effects on people living in the area. The results processed by the Persistent Scatterer InSAR(PSInSAR) method with the Sentinel Application Platform and the Stanford Method for PersistentScatterers software packages show that deformation in the Wapno village area has been detected in bothresidential and non-residential areas, with maximum subsidence of up to −19 mm/yr. The subsidence inthe mine reaches −12 mm/yr, and that at surrounding area range from 0 to −18.8 mm/yr.

Experimental Study on the Fracture Distribution Characteristics of the Overlying Strata in an Abandoned Gob

A lot of gas resources remain in the abandoned gob. The overlying strata of the abandoned gob are the main places for gas storage and flow. The fracture distribution characteristics of the overlying strata have a significant impact on the gas migration. The mining similarity simulation test device of a plane stress was used to study the deformation and failure characteristics of overlying strata in an abandoned gob. The caved strata of the abandoned gob formed a trapezoidal distribution, and the caving range decreased gradually with an increase in distance from the coal seam. The strata collapsed in the caved zone, whereas the strata collapsed mainly on the bending subsidence in fractured zone. The subsidence curves of caved strata showed a lower concave shape, and the maximum subsidence existed in the middle of the abandoned gob. The caved strata subsidence decreased with an increase in distance from the coal seam. The horizontal fractures were dominant in the fractured zone. The abscission rate of the end mining position was greater than that of the start mining position. Large numbers of vertical fractures existed in the caved zone. The development degree of vertical fractures near the end mining position were larger than that of the start mining position, and the width of the gas-conducting fracture was more than three times that of the start mining position. The development degree, quantity and connectivity of the fracture in the end mining position were better than those in the start mining position.

Research and Application of an Innovative 110 Mining Method in Gob-Side Half Coal Rock Entry Retaining

In order to solve the problems of the high cost and time consumption of half coal rock entry driving, low coal recovery rate, and stress concentration on filling support body of retained entry along gob, the innovative 110 mining method based on pressure relief by roof cutting was adopted in 6302 thin coal seam working face of Baoshan Coal Mine. First the technical principle and key technology of this mining method was presented. Then, through theoretical analysis and calculation, engineering experience, and field test, the key parameters such as the length of constant resistance anchor cable, the cutting angle and height of presplitting blasting, the charge structure, and the blocking-gangue support structure were determined and conducted in the retained entry. The broken expanded coefficient varying law of caved gangue with time and space was obtained, which revealed roof movement characteristic. The displacement monitoring curve of the roof and floor indicated that the maximum subsidence of the roof was about 150 mm and the maximum amount of floor heaving was 100 mm, which were quite small. The field monitoring data indicated that the entry retaining effect is good, which indicated that the innovative 110 mining method can be an effective way for reducing the high cost and time consumption of half coal rock entry driving, enhancing the coal recovery rate and preventing the dynamic mine pressure disasters.

Geomechanical Response Induced by Multiphase (Gas/Water) Flow in the Mallik Hydrate Reservoir of Canada

Summary Natural gas hydrate (NGH) is regarded as an important alternative future energy resource. In recent years, a few short-term production tests have been successfully conducted with both permafrost and marine sediments. However, long-term hydrate production performance and the potential geomechanical problems are not very clear. According to the available geological data at the Mallik site, a more realistic hydrate reservoir model that considers the heterogeneity of porosity, permeability, and hydrate saturation was developed and validated by reproducing the field depressurization test. The coupled multiphase and heat flow and geomechanical response induced by depressurization were fully investigated for long-term gas production from the validated hydrate reservoir model. The results indicate that long-term gas production through depressurization from a vertically heterogeneous hydrate reservoir is technically feasible, but the production efficiency is generally modest, with the low average gas production rate of 4.93 × 103 ST m3/d (ST represents the standard conditions) over a 1-year period. The hydrate dissociation region is significantly affected by the reservoir heterogeneity and reveals a heterogeneous dissociation front in the reservoir. The depressurization production results in significant increase of shear stress and vertical compaction in the hydrate reservoir. The response of shear stress indicates that the potential region of sand migration is mainly in the sand-dominant layer during gas production from the hydraulically heterogeneous hydrate reservoir (e.g., sand layers interbedded with clay layers). The maximum subsidence is approximately 78 mm and occurred at the 72nd day, whereas the final subsidence is slowly dropped to 63 mm after 1-year of depressurization production. The vertical subsidence is greatly dependent on the elastic properties and the permeability anisotropy. In particular, the maximum subsidence increased by approximately 81% when the ratio of permeability anisotropy was set at 5:1. Furthermore, the potential shear failure in the hydrate reservoir is strongly correlated to the in-situ stress state. For the normal fault stress regime, the greater the initial horizontal stress is, the less likely the hydrate reservoir is to undergo shear failure during depressurization production.

Ground Subsidence Prediction Model and Parameter Analysis for Underground Gas Storage in Horizontal Salt Caverns

Due to a great demand of natural gas or oil storage in these years, horizontal caverns were proposed to fully use bedded salt formations of China. Under the same geological and operating conditions, the horizontal cavern would shrink more than traditional pear-shaped cavern, which might bring larger ground subsidence and affect the safety of storage facilities. A new prediction model was proposed in this paper for the time-dependent ground subsidence above horizontal caverns. The proposed model considered the impurity of bedded salt formations and simplified the horizontal cavern to an ideal cylinder. The shape of the subsidence trough was determined by the probabilistic integration method, and corresponding calculation formulas for the tilt, curvature, horizontal displacement, and horizontal strain were derived. Based on the assumption that the subsidence volume at the ground was proportional to the reduced volume of horizontal cavern, a formula for the reduced volume over time was established. FLAC3D was introduced to simulate the ground subsidence, and the results show that the proposed prediction model agreed well with the simulation results. Finally, the proposed prediction model was used to analyze the impacts of different stratigraphic parameters and design parameters. The results mainly show that, as the draw angle increases, the subsidence trough becomes deeper and narrower; as the depth of the cavern increases, the maximum subsidence first increases and then decreases, and the subsidence trough gradually becomes round; with the increase of the purity, the subsidence gradually decreases; with the increase of the creep properties and the stress exponential constant, the maximum subsidence first increases rapidly and then slowly approaches the limit; increasing the brine extraction velocity can shorten the cavern construction period and then reduce excessive ground subsidence; the subsidence decreases nonlinearly with the increase of internal pressure; with the increase of the cross section diameter and length of the horizontal cavern, the subsidence presents a significant nonlinear increase. In addition, unlike the traditional pear-shaped cavern, under the same conditions, the ground subsidence above the horizontal cavern according to this newly proposed model is much larger, and the ground subsidence contour line is no longer a standard circle. The findings of this study can help for better understanding of the prediction of ground subsidence above salt caverns and also provide a reference for the design and construction. However, the proposed prediction method is ideal and theoretical and should be further improved by engineering practice in the future.

The Detection of Active Sinkholes by Airborne Differential LiDAR DEMs and InSAR Cloud Computing Tools

InSAR (Interferometric Synthetic Aperture Radar) cloud computing and the subtraction of LiDAR (Light Detection and Ranging) DEMs (Digital Elevation Models) are innovative approaches to detect subsidence in karst areas. InSAR cloud computing allows for analyzing C-band Envisat and Sentinel S1 SAR images through web platforms to produce displacement maps of the Earth’s surface in an easy manner. The subtraction of serial LiDAR DEMs results in the same product but with a different level of accuracy and precision than InSAR maps. Here, we analyze the capability of these products to detect active sinkholes in the mantled evaporite karst of the Ebro Valley (NE Spain). We found that the capability of the displacement maps produced with open access, high-resolution airborne LiDAR DEMs was up to four times higher than InSAR displacement maps generated by the Geohazard Exploitation Platform (GEP). Differential LiDAR maps provide accurate information about the location, active sectors, maximum subsidence rate and growing trend of the most rapid and damaging sinkholes. Unfortunately, artifacts and the subsidence detection limit established at −4 cm/yr entailed important limitations in the precise mapping of the sinkhole edges and the detection of slow-moving sinkholes and small collapses. Although InSAR maps provided by GEP show a worse performance when identifying active sinkholes, in some cases they can serve as a complementary technique to overcome LiDAR limitations in urban areas.

Similar Physical Modeling of Roof Stress and Subsidence in Room and Pillar Mining of a Gently Inclined Medium-Thick Phosphate Rock

Gently inclined medium-thick orebodies are generally recognized as the most difficult type of orebody to mine, using current available strategies (i.e., the room and pillar method). In the present study, a similar physical model was used to investigate the roof stress and subsidence for mining gently inclined medium-thick phosphate rock from the Jinning Phosphate Mine, Yunnan Province, China. The stress field, displacement field, and roof failure evolution characteristics of the surrounding rock with stope structures of 3 m, 5 m, or 8 m ore pillars were considered. The results showed that, after mining stopped, obvious pressure relief areas formed above the three stope structures, and pressure-bearing areas formed at the front of the roof. With extending the mining in the working face, the stress relief boundary also gradually increased, and the top of the roof tended to sink with a maximum subsidence of –14.58 mm, –4.67 mm, and –3.48 mm. Due to the mining activity, the overlying strata bent and subsided from top to bottom, creating bending subsidence, fracture, and caving zones.

Subsidence of the lava flow formed during 2012-2013 Tolbachik fissure eruption: SAR data and thermal model

<p>During the Tolbachik fissure eruption which took place from November 27, 2012 to September 15, 2013 a lava flow of area about 45.8 km<sup>2</sup> and total lava volume ~0.6 km<sup>3</sup> was formed. We applied method of persistent scatterers to the satellite Sentinel-1A SAR images and estimated the rates of displacement of the lava field surface for 2017–2019. The surface mainly subsides along the satellite’s line-of-sight, with the exception of the periphery of the Toludski and Leningradski lava flows, where small uplifts are observed. Assuming that the displacements occur mainly along the vertical, the maximum average displacement rates for the snowless period of 2017–2019 were 285, 249, and 261 mm/year, respectively. On the Leningradski and Toludski lava flows the maximum subsidence was registered in areas with the maximum lava thickness.</p><p>To estimate the thermal subsidence of the lava surface we constructed a thermal model of lava cooling. It provides subsidence rate which are generally close to the real one over a significant part of the lava field, but in a number of areas of its central part, the real subsidence values are much higher than the thermal estimates. According to the thermal model when lava thickness exceeds 40 meters, even 5 years after eruption under the solidified surface there can be a hot, ductile layer, which temperature exceeds 2/3 of the melting one. Since on the Leningradski flow, the maximum subsidence is observed in the area of the fissure along which the eruption took place, one could assume that the retreat of lava down the fissure could contribute to the observed displacements of the flow surface. Subsidence can also be associated with compaction of rocks under the weight of the overlying strata. Migration of non-solidified lava under the solidified cover, also can contribute to the observed distribution of displacements - subsidence of the surface of the lava field in the upper part of the slope and a slight uplift at its periphery.</p><p>The work was supported partly by the mega-grant program of the Russian Federation Ministry of Science and Education under the project no. 14.W03.31.0033 and partly by the Interdisciplinary Scientific and Educational School of Moscow University «Fundamental and Applied Space Research».</p>

Co-Seismic Inversion and Post-Seismic Deformation Mechanism Analysis of 2019 California Earthquake

In July 2019, a series of seismic events, including a magnitude (Mw) 7.1 mainshock and Mw 6.4 foreshock, occurred in Eastern California. Studying these seismic events can significantly improve our understanding of the Eastern California tectonic environment. Sentinel-1A and ALOS-2 PALSAR images were utilized to obtain co-seismic deformation fields, including mainshock and foreshock deformation. The Okada elastic dislocation model and ascending and descending orbit results were used to invert the co-seismic slip distribution and obtain a co-seismic focal mechanism solution. Using ascending Sentinel-1A images, a time-series deformation was obtained for 402 d after the earthquake, and the deformation evolution mechanism was analyzed. The maximum uplift caused by the co-seismic mechanism reached 1.5 m in the line of sight (LOS), and the maximum subsidence reached 1 m in the LOS. For 402 d after the earthquake, the area remained active, and its deformation was dominated by after-slip. The co-seismic inversion results illustrated that California earthquakes were mainly strike-slip. The co-seismic inversion magnitude was approximately Mw 7.08. The Coulomb stress change illustrated that the seismic moment caused by the co-seismic slip was 4.24 × 1026 N × m, which is approximately Mw 7.06. This finding is consistent with the co-seismic slip distribution inversion results.