Ground Fissures Research Articles

Towards a complete understanding of the triggering mechanism of a large reactivated landslide in the Three Gorges Reservoir

The primary aim of this study is to research the characteristics of a slide motion and its relationships with environmental triggers, with reference to the Quchi landslide, which is a large, slow-moving, reactivated landslide in the Three Gorges Reservoir region. Since 2006, this instability has been involved in a slow-moving process with clearly visible signs (ground fissures, cracking of houses and road). The landslide consists of 18 Mm3 rock masses threatening Quchi Town and a road that is crucial for local transportation. For civil protection purposes, a continuous monitoring system has been put into use since 2009. Combining four years of meteorological and hydrological data with GPS displacement measurements and in situ observations, allows a detailed identification of the key processes involved. The deformation is thought to be closely related to precipitations and fluctuating reservoir levels: slope movements have a highly distinctive pattern that is characterized by high deformation starting in June and lasting into September, when the reservoir level drops and rainfall increases, followed by a rapid transition to constant deformation until the next wet season. In order to investigate in detail the influences of rainfall and fluctuating water levels on the hydromechanical behavior of the landslide, a series of two-dimensional numerical simulations are performed using the Universal Distinct Element Code (UDEC). The modeling reveals that precipitation mainly mobilizes the slope materials on the upper part of the slope, while the other trigger factor—fluctuating water levels—destabilizes the foot of the slope into a multistage failure with a remarkable retrogressive evolution. The slide is most likely to collapse in a complex pattern characterized by en masse sliding on the upper part of the slope and a retrogressive rupture at its foot.

Physical simulation and theoretical evolution for ground fissures triggered by underground coal mining.

Underground coal mining activities are prone to cause movement and breakage in geological strata and also lead to mining subsidence and even ground fissures. Along the direction working panel advancing, ground fissures may occur in roof in front and/or behind working panel. However, the investigations of previous similarity tests in lab only emphasize on the region behind working panel. By improving strata material property in construction and mounting artificial pressure devices, two physical simulation tests were conducted and successfully investigated the simulated results. Then, the mechanical model of “cantilever beam and elastic foundation beam” was proposed to calculate the stress distribution and the crack initiation angle in overlying strata and it well explains the mechanisms of ground fissures generation and propagation. Results show that, the maximum internal force in roof always occurred in front of working panel. However, because the void space in gob due to excavation is large enough to cause the bend and rotation of roof strata, compare to the triaxially compressed region in front of working panel, the roof always broke off at some positions above gob since the stress concentration resulting from such bend and rotation of strata could easily reach the limit strength of strata rocks. Also, the length of cantilever beam changed dynamically as respect to the panel advancing and the breakage intervals. Thus, the breakage position where the internal force first reached the limit tensile strength is not fixed and there will be two different kinds of relative positions between the crack initiation point and the working panel. The crack initiation direction is always perpendicular to the internal force, and the crack propagation direction is affected by the initiation angle, overburden-separation degree and the position of the hydraulic shields. If there is no overburden-separation or less, the roofs will break off as a composite beam and the propagation direction will be roughly along the central line between the initial broken point and the support position. Otherwise, the roof strata will bend with the support shields moving forward, then the fracture angle will be close to the initiation angle and the fault surface will be stepped.

Complex surface deformation monitoring and mechanism inversion over Qingxu-Jiaocheng, China with multi-sensor SAR images

Qingxu-Jiaocheng, China has been suffering severe land subsidence along with the development of ground fissure, which are controlled by local fault and triggered by groundwater withdrawal. With multi-sensor SAR images, we study the spatiotemporal evolution of ground deformation over Qingxu-Jiaocheng with an IPTA InSAR technique and assess the role of groundwater withdrawal to the observed deformation. Discrete GPS measurements are applied to verify the InSAR results. The RMSE of the differences between InSAR and GPS, i.e. ALOS and GPS and Envisat and GPS, are 5.7 mm and 6.3 mm in the LOS direction, respectively. The east-west and vertical components of the observed deformation from 2007 to 2010 are decomposed by using descending-track Envisat and ascending-track ALOS interferograms, indicating that the east-west component cannot be neglected when the deformation is large or the ground fissure is active. Four phases of land subsidence in the study region are successfully retrieved, and its spatiotemporal evolution is quantitatively analyzed. Lastly, a flat lying sill model with distributed contractions is implemented to model the InSAR deformation over Qingxu-Jiaocheng, which manifests that the ground deformation is mainly caused by groundwater withdrawal. This research provides new insights into the land subsidence monitoring and its mechanism inversion over Qingxu-Jiaocheng region.

Landslide Movement at Lokanthali during the 2015 Earthquake in Gorkha, Nepal

AbstractThe Gorkha earthquake (Mw=7.8) of April 25, 2015, caused widespread damage in the Kathmandu Valley. At a gently sloping site, known as Lokanthali, large ground fissures and tension cracks w...

Review: Water–rock interactions and related eco-environmental effects in typical land subsidence zones of China

Land subsidence is common in some regions of China. Various eco-environmental problems have arisen due to changes in water–rock interactions in these subsided areas, for which a comprehensive understanding of the hydrogeological setting is needed. This paper presents the general status of land subsidence in three typical subsided areas of China through the compilation of relevant data, and reviews some typical changes in the water–rock interactions in subsided areas along with related eco-environmental issues. It is found that the subsidence development and distribution are controlled by the groundwater-withdrawal intensity externally, and by the thickness and compressibility of unconsolidated sediments internally. The physical changes and related effects of water–rock interactions in subsided areas include: (1) the decreased ground elevation that caused floods, waterlogged farmland, etc.; (2) the differential subsidence that caused ground fissures; and (3) the change of seepage field that caused substantial reduction of the water resource. Chemically, the changes and related effects of water–rock interactions include: (1) the change to the chemical environment or processes due to the hydrogeologic structure alteration, which caused groundwater pollution; and (2) hydrologic mixing (seawater intrusion, artificial recharge; exchange with adjacent aquifers or aquitards), which degraded the groundwater quality. Further research on the subsided areas in China is suggested to reveal the mechanisms regarding biological and gaseous (meteorological) changes from the perspective of interacting systems among water, rocks, biological agents and gases.

Study on Geological Disaster Susceptibility in Nanyang and Xiangyang Basin

Nanyang and Xiangyang Basin is located in the east of Qinling Mountains and Daba Mountain, and the west of Dabie Mountain and Tongbai Mountain. Its north is the Funiu Mountain seated at the east end of Qinling Mountain, and the south is the east end of the Daba Mountains. The main geological environment problems in the area include collapse, landslides, ground fissure, high fluorine water, expansive soil etc. On the basis of collecting the data of geological environment in the basin area, the article regards Nanyang and Xiangyang Basin area and its surrounding area as research objects, and then builds the geological environment database of the study area through GIS platform. Based on the analysis of the factors that affect the geological disasters susceptibility in the study area, an evaluation index system of geological disaster susceptibility was established. The paper expounds the process and steps of applying analytic hierarchy process (AHP) to geological disaster susceptibility assessment, and uses this method (AHP) to establish the hierarchical analysis structural model and the judgment matrix of geological disaster susceptibility comprehensive evaluation, so as to determine the influence of geological disasters. The weight of degree factors establishes a mathematical model for the evaluation of susceptibility to catastrophic disasters in geological disasters and comprehensive evaluation of susceptibility to geology in regional geological disasters. Through using the evaluation module developed by MapGIS, the geological disaster susceptibility of the study area can be divided, and there are four zones: highly-prone area, mid-prone areas, low-prone areas, undeveloped area. This article analyzes the causes of geological disaster susceptibility in the study area, and the research results can provide the basis for geological environment management, planning and disaster prevention and reduction in the study area. At the same time, the reliability of the evaluation results is discussed by comparing the evaluation results with actual geological disasters.

基于高密度电法的地裂缝探测

基于高密度电法的地裂缝探测

Deformation at longyao ground fissure and its surroundings, north China plain, revealed by ALOS PALSAR PS-InSAR

The Longyao ground fissure (LGF) is the longest and most active among more than 1000 ground fissures on the North China Plain. There have been many studies on the formation mechanism of the LGF, due to its scientific importance and its potential for damage to the environment. These studies have been based on both regional tectonic analysis and numerical simulations. In order to provide a better understanding of the formation mechanism, the deformation of the crack and its surrounding environment should be taken into consideration. In this paper, PS-InSAR technology was employed to assess the ground deformation of LGF and its surrounding area, using L-band ALOS-1 PALSAR images from 2007 to 2011. The characteristics of ground deformation, relationships between fissure activity and surrounding faults and groundwater exploitation were analyzed. This study shows that the north side of Longyao fault (LF) is uplifting while the south side is subsiding. This provides the tectonic conditions responsible for the activity of the ground fissure. Local groundwater exploitation also plays an important role in the development of ground fissures. InSAR observations were modeled to infer the loading depth (-2.8 km) and the slip rate (31.1 mm/yr) of LF.

Source of high tsunamis along the southernmost Ryukyu trench inferred from tsunami stratigraphy

Four paleotsunamis deposits are exposed in a trench on the coastal lowland north of the southern Ryukyu subduction zone trench. Radiocarbon ages on coral and bivalve shells show that the four deposits record tsunamis date from the last 2000yrs., including a historical tsunami with a maximum run-up of 30m in 1771, for an average recurrence interval of approximately 600yrs. Ground fissures in a soil beneath the 1771 tsunami deposit may have been generated by stronger shaking than recorded by historical documents. The repeated occurrence of the paleotsunami deposits supports a tectonic source model on the plate boundary rather than a nontectonic source model, such as submarine landslides. Assuming a thrust model at the subduction zone, the seismic coupling ratio may be as low as 20%.

Recent ground fissures in the Hetao basin, Inner Mongolia, China

Ground fissures are a geological hazard with complex formation mechanisms. Increasing amounts of human activity have created more ground fissures, which can destroy buildings and threaten human security. Some ground fissures indicate potentially devastating earthquakes, so we must pay attention to these hazards. This paper documents recently discovered ground fissures in the Hetao basin. These ground fissures are located along the frontal margins of the terraces of the Sertengshan piedmont fault. These fissures are 600–1600m long, 5–50cm wide, and at most 1m deep. These ground fissures emerged after 2010 and ruptured newly constructed roads and field ridges. The deep geodynamic mechanisms within this extensional environment, which is dominated by NE-SW principal compressive shear, involve N-S tensile stress, which has produced continuous subsidence in the Hetao basin and continuous activity along the Sertengshan piedmont fault since the late Quaternary. Trenches across the ground fissures reveal that the fissures are the latest manifestation of the activity of preexisting faults and are the result of creep-slip movement along the faults. The groundwater level in the Hetao basin has been dropping since the 1960s because of overexploitation, resulting in subsidence. When the tensile stress exceeds the ultimate tensile strength of the strata, the strata rupture along preexisting faults, producing ground fissures. Thus, the Sertengshan piedmont fault planes are the structural foundation of the ground fissures, and groundwater extraction induces the development of ground fissures.

A large-scale landslide and related mechanism: a case study in the Qazvin–Rasht freeway, Iran

The Manjil landslide occurred after the slope cutting and the removal of the toe buttress (8 July 2013), between 41 + 400 and 42 + 200 km section of Manjil–Radbar in the Qazvin–Rasht freeway, Gilan Province, Iran. The occurrences of landslide led to blockage of the freeway. A cutting was designed with a width and height of 4 and 6 m, respectively, and a 5 to 6 m excavation depth within a 120 m line along the slope toe. Based on the site investigations, the landslide was characterized as a complex deep-seated landslide, displaying composite rotational-debris flow. Moreover, extensive field survey, subsurface investigation, laboratory and in situ tests show that although the landslide was triggered by an inappropriate cutting, geostructural, geological engineering properties and hydrology have also played a key role in its initiation and further aggravation. Therefore, the western and eastern boundaries of the landslide coincide with the two faults (F1 and F2). In addition, landslide sinisterly movement is controlled by a left lateral strike-slip fault (F2). It was observed that the scarp follows the N130°/75 direction of bedding rocks. The presence of marls and shale implies a high swelling under wet conditions, thus providing lubricating sliding surfaces. In addition, alteration and weathering of andesite, basalt, tuffite, and tuff have been reduced the shear strength of the slope. Engineering geological map (EGM) of the landslide was prepared on the basis of aerial interpretations, the orientation of ground cracks and fissures, geomaterial, geostructural and hydrology. Based on ground cracks and fissures, the displacement vectors are also determined and shown on the map. The relationship between the displacement vectors estimated from ground cracks and fissures with GPS observation and slickness slip surface is coherent.

Experimental study of a segmented metro tunnel in a ground fissure area

This paper studies the seismic response of a segmented metro tunnel with flexible joints passing through active ground fissures in Xi’an by shaking table model test. A coupling dynamic ground motion was generated in the test model. The tunnel acceleration, earth pressure and tunnel structure strain were monitored and compared. It was observed that each part of the tunnel has an independent movement with flexible joints. The tunnel located in the hanging wall has 3.17 times peak acceleration than that in the foot wall. Higher magnitudes of earth pressures were recorded close to the areas of the ground fissures. The earth pressure in the hanging wall was greater than that in the foot wall. The coupling loads increase the earth pressure. The strain in the middle of the tunnel arch was the largest. The strain at the bottom of the floor was the secondary. The one on the top of the arch was the smallest. The strain increased less in each section because the tunnel is divided into four parts by flexible joints, and no sharp strain increase close to the ground fissure was observed. The results indicate that the flexible joints can decrease the stress concentration. The tunnel with flexible joints can adjust to large deformations in the ground fissure areas.

Spatio-temporal distribution and gas conductivity of overburden fissures in the mining of shallow thick coal seams

The spatio-temporal distribution and gas conductivity of overburden fissures in the mining of shallow thick coal seams are investigated to understand the correlation between the dynamic growth of overburden fissures in the mining of shallow thick coal seams and their gas conductivity. Theoretical analysis, numerical simulation and on-site measurements were combined for the mining of shallow thick coal seams in the Chuancao Gedan Mine. The results revealed that ground fissures with dynamic changes were observed periodically as the coalface moved forward. Dynamic changes of the horizontal fissure opening and vertical deformation related to the instability motion of the loading key stratum in the overburden were observed. The coalface mined-out area was divided into the fissure initiation, fissure propagation and fissure closure zones based on the changes in the horizontal opening and the vertical deformation of adjacent rocks in the overburden.

Soft-sediment deformation structures related to volcanic earthquakes of the Lower Cretaceous Qingshan Group in Lingshan Island, Shandong Province, East China

The study on soft-sediment deformation structures (SSDS) of Lingshan Island has been one of the hot topics of sedimentology researches in China in recent years, and SSDS developed in turbidite system in the Laiyang Group are widely known by domestic researchers. However, few studies were conducted on the SSDS in fan delta system in the Qingshan Group, Lingshan Island.This study analyzes the classification and characteristics of SSDS especially their lithofacies association and lithologic characteristics through field outcrops investigation and thin section analysis as well. A conclusion was acquired that the paleoenvironment was a fan delta system with occurrence of several volcanic eruptions, where the water became gradually shallower.The SSDS types in the Qingshan Group includes load and flame structure, ball and pillow structure, water-escape structure, hydroplastic deformation structure, plastic sandstone breccia structure, volcanic drop stone and V-shaped ground fissure mainly caused by volcanic earthquakes of three types: (1) seismic waves, (2) gravity and inertia effect of pyroclastic flows, (3) instant differential air pressure; which is different from slumping and tectonic earthquakes occurred in the Laiyang Group. In addition, with the lithofacies association analysis between pyroclastic flow and SSDS beds, a distribution model of SSDS related to volcanic earthquakes can be established: SSDS types changed gradually with their distance further away from the volcanic activity core. Brittle deformation which was common in the proximal zone disappeared gradually; liquefied and plastic SSDS continued to dominate in the medial zone; and slightly liquefied SSDS were developed in the distal zone. Meanwhile, the scale and size of SSDS is negatively correlated with the distance of SSDS depositional locations from the volcanic vent.

Variations in spatial patterns of soil–vegetation properties over subsidence-related ground fissures at an arid ecotone in northeastern Iran

This study examines variations in the spatial patterns of soil–vegetation properties in the vicinity of subsidence-related ground fissures caused by groundwater over-pumping over an arid ecotone situated in northeastern Iran. It was assumed that subsidence-related fissures have a possible effect on the soil–vegetation structures. Vegetation metrics (mean canopy area, mean volume, vegetation cover percentage) and soil properties (EC, pH, CaCO3, particle size distribution) were measured for locations with differing spatial expanses of ground fissures, including surface ground fissures, deeper ground fissures, as well as those exhibiting no signs of ground fissure. Statistical analyses indicated significant differences (P < 0.05) in the spatial patterns of vegetation and soil properties for locations with different expanses of ground fissures. Greater degradation of soil–vegetation, presenting as mortality of plants and the formation of impermeable layers on the soil surface, was observed around deep fissures linked to groundwater over-pumping, in comparison with other locations. These findings confirm the relationship between heterogeneities in patterns of vegetation and soil properties and variations in structure and extent of ground fissures, as well as indicating that the expansion of groundwater over-pumping-induced surface ground fissures can promote soil–vegetation degradation over time, leading ultimately to barren soils.

A seismological overview of the April 25, 2015 Mw7.8 Nepal earthquake

This paper aims to determine the damage distribution and to analyze the available strong motion records of the April 25, 2015 Nepal earthquake and its eight aftershocks. For this purpose, an earthquake investigation team was dispatched to Nepal from May 6 to 11, 2015 to evaluate the damages of the epicentral region and the four affected cities containing Kathmandu, Bhaktapur, Gorkha, and Pokhara. Based on the observations from the damages to the built environment, an iso-intensity map is prepared on the EMS-98 intensity scale in which the maximum intensity in the epicentral region is estimated to be about VIII. However, based on the geological and geotechnical evidences such as landslide volumes and ground fissures, the maximum intensity can be inferred about IX or X on the International Union for Quaternary Research (INQUA) intensity scale. In addition, the available strong motion data of the 2015 Nepal mainshock and its eight large aftershocks recorded at the KATNP accelerometric station in Kathmandu were processed and analyzed. In order to investigate the probable site effects, the Fourier amplitude spectra (FAS) of the horizontal north-south (N) and east-west (E) components and the average of them (H avg) were divided to the FAS of the vertical (Z) component and thus, the $$ \raisebox{1ex}{$ N$}\!\left/ \!\raisebox{-1ex}{$ Z$}\right. $$ , $$ \raisebox{1ex}{$ E$}\!\left/ \!\raisebox{-1ex}{$ Z$}\right. $$ , $$ \raisebox{1ex}{${H}_{\mathrm{avg}}$}\!\left/ \!\raisebox{-1ex}{$ Z$}\right. $$ spectral ratios were calculated. Based on these horizontal to vertical spectral ratios, a low-frequency peak at about 0.2–0.3 Hz (3.5–5-s period) is observed clearly in all the records. Accordingly, the repeated results might imply site amplification due to the thick alluvial deposits and the high groundwater level at the KATNP accelerometric station within the Kathmandu basin. It should be noted that all the horizontal to vertical spectral ratios of the aftershocks show a high peak at around 1.5–3 Hz, which is missed in the horizontal to vertical spectral ratio of the mainshock. On the other hand, considering the low angle of the causative fault plane, a near-source directivity effect on the fault normal direction (here, the vertical component) of the April 25, 2015 mainshock rupture may exist. Therefore, vertical to horizontal spectral ratios ( $$ \raisebox{1ex}{$ Z$}\!\left/ \!\raisebox{-1ex}{$ N$}\right. $$ and $$ \raisebox{1ex}{$ Z$}\!\left/ \!\raisebox{-1ex}{$ E$}\right. $$ ) were also calculated to find the vertical peak more clearly. The figures confirmed a peak at the frequency of 1.5–3 Hz in the mainshock spectra which is not repeated on the aftershock spectra and thus can probably be attributed as the pulse of directivity effect toward Kathmandu. This inferred directivity pulse can be also well distinguished on the velocity and displacement time histories of the mainshock.

Late Quaternary Activity of the Huashan Piedmont Fault and Associated Hazards in the Southeastern Weihe Graben, Central China

The Weihe Graben is not only an important Cenozoic fault basin in China but also a significant active seismic zone. The Huashan piedmont fault is an important active fault on the southeast side of the Weihe Graben and has been highly active since the Cenozoic. The well–known Great Huaxian County Earthquake of 1556 occurred on the Huashan piedmont fault. This earthquake, which claimed the lives of approximately 830000 people, is one of the few large earthquakes known to have occurred on a high–angle normal fault. The Huashan piedmont fault is a typical active normal fault that can be used to study tectonic activity and the associated hazards. In this study, the types and characteristics of late Quaternary deformation along this fault are discussed from geological investigations, historical research and comprehensive analysis. On the basis of its characteristics and activity, the fault can be divided into three sections, namely eastern, central and western. The eastern and western sections display normal slip. Intense deformation has occurred along the two sections during the Quaternary; however, no deformation has occurred during the Holocene. The central section has experienced significant high–angle normal fault activity during the Quaternary, including the Holocene. Holocene alluvial fans and loess cut by the fault have been identified at the mouths of many stream valleys of the Huashan Mountains along the central section of the Huashan piedmont fault zone. Of the three sections of the Huashan piedmont fault, the central section is the most active and was very active during the late Quaternary. The rate of normal dip–slip was 1.67–2.71±0.11 mm/a in the Holocene and 0.61±0.15 mm/a during the Mid–Late Pleistocene. As is typical of normal faults, the late Quaternary activity of the Huashan piedmont fault has produced a set of disasters, which include frequent earthquakes, collapses, landslides, mudslides and ground fissures. Ground fissures mainly occur on the hanging–wall of the Huashan piedmont fault, with landslides, collapses and mudslides occurring on the footwall.

Application of Distributed Optical Fiber Sensing Technique in Monitoring the Ground Deformation

The monitoring of ground deformation is important for the prevention and control of geological disaster including land subsidence, ground fissure, surface collapse, and landslides. In this study, a distributed optical fiber sensing technique based on Brillouin Optical Time-Domain Analysis (BOTDA) was used to monitor the ground deformation. The principle behind the BOTDA is first introduced, and then laboratory calibration test and physical model test were carried out. Finally, BOTDA-based monitoring of ground fissure was carried out in a test site. Experimental results show that the distributed optical fiber can measure the soil strain during ground deformation process, and the strain curve responded to the soil compression and tension region clearly. During field test in Wuxi City, China, the ground fissures deformation area was monitored accurately and the trend of deformation can also be achieved to forecast and warn against the ground fissure hazards.

Future groundwater extraction scenarios based on COMSOL multiphysics for the confined aquifer at Linfen basin, Shanxi Province, China

As one of the six largest river basins in Shanxi Province, China, Linfen basin has been in severe groundwater level declining status caused by over-extraction of groundwater since 1976, along with dense distribution of land subsidence and ground fissures. Future Groundwater drawdown analysis due to over-extraction is a major concern for not only water resource management, but also preventive and controlling measures of land subsidence and ground fissures. Consequently, in this paper groundwater extraction dynamic process for the confined aquifer at Linfen basin was simulated based on COMSOL Multiphysics. Then future groundwater extraction scenarios, namely, groundwater drawdown values within a period of consecutive 20 years and their consequent impacts on confined aquifer discharge amount to the Yellow River were predicted. The results demonstrated that the groundwater drawdown value and lateral discharge to the Yellow River would reach 7.07 m/a and 0.56 × 108 m3/a respectively in 10 years, while these two numbers drop to 3.44 m/a and 0.25 × 108 m3/a in 20 years. In order to provide valuable information for local government and policy makers, the paper would finally quantify a sustainable groundwater extraction value—20% of current groundwater extraction amount.

Formation Mechanism and Reduction Technology of Mining-Induced Fissures in Shallow Thick Coal Seam Mining

Surface mining-induced fissures formed in shallow coal seam mining have serious impact on safety mining and water resources protection. This paper proposes a novel approach to study the formation mechanism and dynamic development of surface mining-induced fissures in shallow coal seam mining. This approach combines field tests, theoretical analysis, and numerical simulations based on the geological condition of shallow coal seam mining in Chuancao Gedan Coal Mine. Two typical surface mining-induced fissures, step-type fissures and collapse-type fissures, are generated in shallow coal seam mining. The fissures with large vertical throw or horizontal opening severely impact water resource protection and surface ecological environment. Surface mining-induced fissures are generated periodically and changed dynamically with the advancing of working face. The vertical throw and horizontal opening of surface fissures are changed dynamically with the movement of loading key strata. The movement forms of loading key strata determine the morphological development of surface fissures. Downward sliding movement of broken rocks causes step-type fissures, while downward rotation movement leads to collapse-type fissures. The degree of the downward sliding and rotation of broken rocks determines the vertical throw and horizontal opening of surface fissures. This paper proposes mining technologies to reduce damaging ground fissures in shallow coal seam mining and analyzes their control effects.