Ground Fissures Research Articles

Determining the influencing factors of preferential flow in ground fissures for coal mine dump eco-engineering.

Ground fissures (GF), appearing in front of dumps, are one of the most obvious and harmful geological hazards in coal mining areas. Studying preferential flow and its influencing factors in the ground fissures of dumps may provide basic scientific support for understanding the rapid movement of water and vegetation restoration and reconstruction in mining areas. Based on field surveys of ground fissures, three typical ground fissures were selected in the studied dump. The morphological characteristics of preferential flow for ground fissures were determined through field dye tracing, laboratory experiments, and image processing technology. The results indicated that the lengths of the three ground fissures ranged from 104.84 cm to 120.83 cm, and the widths ranged from 2.86 cm to 9.85 cm. All of the ground fissure area densities were less than 10%, and the proportion of ground fissure surface area was small in the dump. The maximum fissure depth was 47 cm, and the minimum was 16 cm. The ground fissure widths ranged from 0 cm to 14.98 cm, and the fissure width and fissure width-to-depth ratios decreased with increasing soil depth. The stained area was greater than 90% in the 0–5 cm soil layers of the three fissures, and water movement was dominated by matrix flow. The stained width decreased from 90 cm to 20 cm with increasing soil depth. The preferential flow was mainly concentrated on both sides of the fissure, which was distributed as a “T” shape. The preferential flow stained area ratios were 27.23%, 31.97%, and 30.73%, respectively, and these values decreased with increasing soil depth. The maximum stained depths of the preferential flow among the three fissures were different, and the maximum stained depth of GF II was significantly larger than that of GF I and GF III (P < 0.05). The stained path numbers of the three fissures ranged from 0 to 49. With increasing soil depth, the stained path number first increased and then decreased. The stained path widths of the three fissures ranged from 0 cm to 90 cm. With the increase in soil depth, the stained path width decreased. The stained area ratio was significantly positively correlated with ground fissure width, the ground fissure width-to-depth ratio, soil saturated hydraulic conductivity, soil organic matter, and sand content and was significantly negatively correlated with soil water content and clay content. The stained path number was significantly positively correlated with ground fissure width, the ground fissure width-to-depth ratio, soil saturated hydraulic conductivity and soil organic matter. The stained path width was significantly positively correlated with the ground fissure width-to-depth ratio, soil saturated hydraulic conductivity, soil organic matter and sand content and was significantly negatively correlated with clay content. Plant roots could significantly increase the stained area ratio, stained path number, and width and promote the formation and development of preferential flow.

A study on energy distribution law of frame structure across ground fissure

In order to study the frame structure energy dissipation mechanism on the ground, a 3x3 span 5-story frame structure was used as the research background, and a shaking table test with a scale ratio of 1:15 was designed. Based on the prototype structure, a finite element model based on ABAQUS is established. The correctness of the finite element model is verified by experimental comparison. On this basis, the plastic energy dissipation and damping energy consumption of the structural beam and the plastic energy dissipation law of the column are analyzed. The weak part of the structure of the trans-ground fissure structure under energy conversion is found. This study provides a reference for the arrangement of energy-consuming devices in seismic design and disaster prevention and mitigation design for similar structural engineering.

Assessment of the temporal–spatial evolution of subsidence and its driving mechanism in the Beijing Plain (China) by using SAR interferometry and geological data

Based on the four types of SAR images from Envisat, Radarsat-2, and TerraSAR-X between 2007 and 2019, a linear time-series analysis of Coherence Targets method is employed to acquire the 13-year deformation velocity and cumulative deformation maps of the Beijing Plain. Such measurement firstly provides the annual subsidence rate and spatial evolution characteristics of the subsidence areas and the maximum subsidence rates in Laiguangying–Ciqu, which is the largest subsidence area of the Beijing Plain, were beyond 14 cm/year from 2009 to 2018. We correlate the observed subsidence with land use, Quaternary strata and pre-existing faults to assess the driving mechanisms of land subsidence. We find that large-scale land subsidence or patchy subsidence in the Beijing Plain takes on a similar variation to dry land and rural settlements/manufacturing enterprise land use. We also observe that the subsiding areas are mainly distributed in the edge of Alluvial–Proluval Fan or in the lacustrine or swampy sediments among Alluvial–Proluval Fans with much thicker compressible deposits, and the high subsidence gradients orientate along active faults. Therefore, this research could contribute to propose effective control measures for subsidence and ground fissure and achieve better hazard mitigation programme in Beijing.

The Formation Mechanism of Surface Landslide Disasters in the Mining Area under Different Slope Angles

Slope stability analysis is important for the safe mining of mineral resources. The collapse of goafs in loess gullies can lead to natural disasters such as surface landslides. In this context, this study analyzes monitoring data obtained from surface observation in the Shendong mining area of the Hanjiawan coal mine based on the geological conditions therein. The monitoring results show that the working face experiences a starting period, an active period, and a declining period, from the start of mining to the end of the working face. At the initial mining stage, there is no evident surface movement or deformation in the mining area. When the advance distance of the 12106 working face is between 13 m and 109 m, the surface movement and deformation vary significantly, and the maximum subsidence reaches 1963 mm, which is enough to cause landslides. We select the physical and mechanical parameters of the rock and soil in the mine and then simulate the formation mechanism of surface landslides under different slope angles of the mining area using FLAC3D software. Because of the collapse of the mined‐out area, the overlying strata structure is destroyed, the subsidence basin is shifted to the center as a whole, and the slope mass is subjected to tensile and compression deformation, resulting in plastic damage, which develops downward along the crack and leads to a collapse because of the discontinuous movement and deformation of the surface; moreover, step‐type ground fissures are produced. The results also show that when the slope angle is greater than 60°, the displacement of the slope mass is not uniform, and the rock stratum in a position with large displacement loses its support, leading to landslides; when the slope angle is less than 30°, the bedrock surface forms a sliding surface and develops to the surface, thus decreasing the possibility of landslides. Based on the stability analysis of the collapsed slope in the goaf of the loess gully, a scientific basis is provided for the effective prevention and control of geological disasters in the Shendong mining area.

Factors Influencing Activity of Xiwang Road Ground Fissure Based on Time-series Interferometric Synthetic Aperture Radar and Detection of Land Cover Changes Using Optical Imaging

Factors Influencing Activity of Xiwang Road Ground Fissure Based on Time-series Interferometric Synthetic Aperture Radar and Detection of Land Cover Changes Using Optical Imaging

Impacts of soft soil compaction and groundwater extraction on subsidence in the Yellow River Delta

Recently, many of the world’s major river deltas have been sinking, making them increasingly vulnerable to floods and storm surges, salinization and permanent inundation. For the Yellow River delta, annual subsidence rates of several to dozens of centimeters have been reported in the past few years. The extraction of a considerable amount of groundwater due to continuous pumping is suggested as the main driver of the groundwater depression cone. Despite its scale and severity, methods to quantify subsidence are scarce. We introduce a soil mechanics approach to quantify subsidence due to the compaction of soft soil. The largest reduction in soft soil thickness, which is more than 2.6 m, occurred in the salt field area to the north of the Yellow River. Furthermore, by estimating the primary consolidation of soft soil, the subsidence caused by groundwater exploitation is quantified. In the coastal area of the delta, due to excessive exploitation of shallow underground brine resources, the maximum accumulated subsidence is as high as 2 m. Since the natural consolidation of these deltaic sediments has ended, if the current groundwater exploitation intensity is maintained, major subsidence disasters, such as subsidence depressions and ground fissures, will occur.

Calculation of the Vertical Strata Load of Utility Tunnel Crossing Ground Fissure Zone

A ground fissure is a geological disaster in which the vertical dislocation of strata causes surface rupture. Ground fissures can cause extreme harm to the surface and underground buildings. Ground fissure activity can result in different settlement on the two sides of the strata, which will generate additional stress (pressure) that differs from the stress of the general stratum on underground structures across the ground fissure zone. It is essential to assess the effective stress of strata in the design of underground engineering structures across a ground fissure zone. The Xi’an ground fissure through a utility tunnel was focus of the research, and a physical model and data for oblique crossing of the 45° ground fissure were analyzed. A model of the utility tunnel structure was established, including the surrounding soil load as an active ground fissure environment. This model was used to calculate the vertical formation pressure of the overlying soil on the utility tunnel. A method to calculate the overlying load on the utility tunnel caused by ground fissure activity was proposed and compared with the calculation based on the A. Marston principle. The results showed that the ground fissure load calculation method based on the strata-holding effect can effectively calculate the earth pressure of the surrounding soil layer of the utility tunnel in the cross-ground fissure section. The results of this work provide guidance and reference value for the design of a utility tunnel in an area with the potential for a ground fissure.

Intelligent identification method for near-surface ground fissures based on seismic data

Intelligent identification method for near-surface ground fissures based on seismic data

Spatial-Temporal Evolution of Land Subsidence and Rebound over Xi’an in Western China Revealed by SBAS-InSAR Analysis

Land subsidence is one of the major urban geological hazards, which seriously restricts the development of many cities in the world. As one of the major cities in China, Xi’an has also been experiencing a large area of land subsidence due to excessive exploitation of groundwater. Since the Heihe Water Transfer Project (HWTP) became fully operational in late 2003, the problem of subsidence has been restrained, but other issues, such as ground rebounds, have appeared, and the effect of the underground space utilization on land subsidence remains unsolved. The spatial-temporal pattern of land subsidence and rebound in Xi’an after HWTP and their possible cause have so far not been well understood. In this study, the evolutionary characteristics of land subsidence and rebound in Xi’an city from 2007–2019 was investigated using Small Baseline Subset Interferometric Synthetic Aperture Radar (SBAS-SAR) technology to process the Advanced Land Observing Satellite (ALOS) and Sentinel-1A SAR datasets, and their cause and the correlation with groundwater level changes and the underground space utilization were discussed. We found that the land subsidence rate in the study area slowed from 2007–2019, and the subsidence area shrank and gradually developed into three relatively independent and isolated subsidence areas primarily. Significant local rebound deformation up to 22 mm/y commenced in the groundwater recharge region during 2015–2019. The magnitude of local rebound was dominated by the rise in groundwater level due to HWTP, whereas tectonic faults and ground fissures control the range of subsidence and the uplift area. The influence of building load on surface deformation became increasingly evident and primarily manifested by slowing the subsidence reduction trend. Additionally, land subsidence caused by the disturbances during the subway construction period was stronger than that in the operational stage. Future land subsidence in Xi’an is predicted to be alleviated overall, and the areas of rebound deformation will continue increasing for a limited time. However, uneven settlement range may extend to the Qujiang and Xixian New District due to the rapid urban construction. Our results could provide a scientific basis for land subsidence hazard mitigation, underground space planning, and groundwater management in Xi’an or similar regions where severe ground subsidence was induced by rapid urbanization.

The impact of groundwater drawdown and vacuum pressure on sinkhole development. Physical laboratory models

A considerable proportion of the damaging sinkholes worldwide correspond to human-induced subsidence events related to groundwater withdrawal and the associated water-table decline (e.g. aquifer overexploitation, dewatering for mining). Buoyancy loss in pre-existing cavity roofs is generally claimed to be the main underlying physical mechanism. It has been also postulated that rapid water-table drawdowns may create a vacuum effect in the subsurface and contribute to enhance sinkhole activity in karstic terrains with a low effective porosity cover. Our laboratory physical model explores the role played by vacuum pressure induced water-table drops with different magnitudes and rates on sinkhole development, simulating an invariable mantled karst comprising cavernous bedrock and a low-permeability cover. The multiple tests performed include real-time monitoring of the water level drawdown (magnitude, duration, rate), the negative air pressures in the bedrock cavity and the cover, and several features of the subsidence phenomena (deformation style, size, magnitude, rate). The main findings derived from the test results include: (1) Vacuum pressure may trigger the development of cover collapse sinkholes in areas with low-permeability covers. (2) Different water-table decline patterns (magnitude, duration, rate) may result in different subsidence styles or rheological behaviours: sagging versus collapse. (3) Ground fissuring, frequently related to extension at the margin of sagging depressions, may cancel or significantly diminish the vacuum effect. (4) An overall direct relationship between the water-table decline rate and the subsidence rate. Some possible strategies are proposed to ameliorate the adverse effect of the negative air pressure on sinkhole hazard, which most probably has a local impact restricted by the concurrence of rapid water drawdowns and low-permeability covers.

Shaking table test and numerical analysis of a new method for disaster control and reinforcement of frame structure crossing ground fissures

In order to seek suitable reinforcement measures for disaster control of structures spanning the ground cracks in high-intensity areas, a shaking table test of a five-story frame structure model spanning the ground cracks and being supported was designed according to the scale of 1:15. ABAQUS software was used to establish the calculation model of the frame structure before and after reinforcement, and the results were compared with the results of the shaking table test. The reinforcement model was analyzed from the dynamic characteristics, acceleration, displacement and strain of the structure. Therefore, the proposed disaster control and reinforcement method is feasible. The results of this study can provide a reference for the reinforcement of this kind of straddle-crack structure.

Characteristics and genesis mechanism of ground fissures in Taiyuan Basin, northern China

Since the 1980s, ground fissures in the Taiyuan Basin have experienced blowouts, resulting in a significant but hidden danger to cities in the Basin. This paper describes the plane and damage characteristics of the ground fissures based on the findings of field investigations and mapping. Most ground fissures in the Basin were determined as linear with pinch-out reappearances on the surface. They were characterized by both horizontal tension with maximum widths and vertical offsets of up to 40 and 15 cm, respectively. The ground fissure strikes in the Basin were observed to be consistent with those of nearby active faults and the long-axis direction of the groundwater depression funnel. The roads and houses that lie across the fissures were determined to be the most affected by ground-fissure disasters in the Basin. The primary damage modes for the roads were vertical offset and surface collapse, whereas buildings experienced foundation failure and tensile damage. Profiles obtained through geological drilling and trench exploration further revealed obvious tension and synsedimentary characteristics of the ground fissures correlated with existing faults. Correlation analysis shows that the formation of ground fissures in Taiyuan Basin is mainly related to faults and excessive groundwater extraction. Theoretical analysis revealed that the size and activity of ground fissures in the Basin were positively correlated with four factors—the dip of faults in an area, regional tensile stress, difference between the thicknesses of aquifers on either side of a fault, and groundwater exploitation. The significant increase in ground fissure activity since the 1980s mainly reflects uncontrolled groundwater discharge. Hence, prevention of excessive groundwater exploitation in the Basin would mitigate the destructive effects of the ground fissures.

The study of road deformation induced by ground fissure in Xi’an, Central China

Tremendous losses and threaten traffic safety were caused by ground fissures as it covers over half of the area of Xi’an, in China. This study summarizes the formation of ground fissures and found that variations in the dip angles and cross angles influence road deformation and cracking. Based on survey data, numerical simulation using MSC.MARC finite element software was conducted to analyze the impact of ground fissures on roads. The results show that the cross angle has a negative correlation with the deformation range and a positive correlation with the tensile and compressive stresses, plastic strain and shear stress. The dip angle has a negative correlation with the maximum tensile stress and plastic strain and a positive correlation with the vertical displacement of pavement, but it has little effect on the maximum compressive stress. It is recommended to take some engineering measures for prevention and treatment when road projects cross a ground fissure, such as avoiding ground fissures, changing the road structure, and establishing a monitoring system. These conclusions can serve as a reference for structural design and preventative measures for roads passing through active ground fissure zones.

Experimental study on pumping-induced land subsidence and earth fissures: a case study in the Su-Xi-Chang region, China

Land subsidence and earth fissures caused by excessive groundwater exploitation severely damage the surrounding property and environment. To examine changes caused by land subsidence and earth fissures, a large-scale physical-geological model was designed to simulate groundwater exploitation and the conditions of bedrock ridges. This model enables real-time monitoring of the groundwater level, soil strain, and changes to subsidence and fissures. It is based on a case study conducted on the ground surface of Guangming Village in the Su-Xi-Chang region, China. The results revealed the following: (1) the land subsidence lagged behind the decline in water level during the pumping process; (2) a strong agreement between the shape and location of the bedrock ridge and settlement was reached, and the region with the most severe subsidence corresponded to the distribution of the fissures; (3) the tensile-stress concentration of the soil mass was essentially the same as that during the stage when the fissures developed, (which is an important means of determining the fissure development); and (4) the rose diagram illustrating the fissures indicated the fissures in the area of the bedrock ridge propagated parallel to the contour lines of the bedrock ridge. These results are consistent with the changes in the earth fissures examined in the case study and, therefore, provide support for the use of the physical-geological model in future research on ground fissures.

Detection of shallow underground fissures by time-frequency analysis of Rayleigh waves based on wavelet transform

Ground fissure is a geological hazard that poses a great threat to human life and, property and the environment. Therefore, it is necessary to detect shallow underground fissures effectively. In this paper, a time-frequency analysis of Rayleigh waves based on the wavelet transform is proposed to detect shallow underground fissures. The arrival time of the directed Rayleigh waves and the diffracted Rayleigh waves from the underground fissure is extracted from the time-frequency spectrum of any two traces. Furthermore, the locations of the underground fissures are calculated according to the time difference relation. Four sets of fracture models and one set of field data were used to test the effectiveness of the wavelet transform of Rayleigh waves. Moreover, the detection results of the actual data are compared with that of the high-density electrical method to further prove its detection effect. The field investigation shows that using the wavelet transform of Rayleigh waves to detect shallow underground fissures is feasible and effective.

Prediction and prevention of spontaneous combustion of coal from goafs in workface: A case study

Aiming at forecasting and preventing remnant coal spontaneous combustion in goaf, this thesis conducts determination on the spontaneous combustion tendency of coal seam, simultaneous thermogravimetry and differential scanning calorimetry(TG-DSC) analysis on coal samples, optimization on index gas of spontaneous combustion, and division of spontaneous combustion “three zones” with O2 concentration as the indicator. The conclusions are as follows: the spontaneous combustion period of remnant coal is 1–3 months, so the coal seam is easy to spontaneous combustion. CO and C2H4 are selected as the index gas for forecasting spontaneous combustion in No.12 coal seam and No.12-up coal seam because of their regular evolution tendency in concentration changing with coal temperature and easiness in detecting. As to the spontaneous combustion “three zones” divided by O2 concentration, the depth and width of both heat dissipation zone and left side oxidation zone in the goaf is slightly increased when the “Y” type ventilation is adopted, comparing with the “U” type ventilation, and the asphyxiation zone is extended to about 200 m behind the workface. Pressure balance method and ground fissure sealing are proposed for spontaneous combustion prevention and extinction, which offers some practical experiences for adjacent mine or similar coal seam.

Ground deformation and fissure activity of the Yuncheng Basin (China) revealed by multiband time series InSAR

The Yuncheng Basin (China) is affected by severe land subsidence and ground fissure hazards, which have caused serious land damage and economic losses to the local inhabitants. Due to the lack of long-term continuous monitoring in the region, the trend of land subsidence and fissure activities is unknown, which cannot meet requirements for disaster reduction and disaster prevention. In this study, Envisat ASAR, ALOS PALSAR, and TerraSAR-X are employed to monitor these hazards using time series InSAR methodology. The results showed that there were two obvious subsidence centers occurred in Yuncheng. Compared to the period from 2007 to 2011, the land subsidence rate in the Yuncheng Basin from 2012 to 2015 decreased significantly. Analysis of the differential deformation rate observed by InSAR between the two sides of the ground fissure indicates that fissure activity has weakened in recent years at the cross-section. To explain the phenomena observed by InSAR, FLAC3D was used to study the effect of pumping on ground fissure activity under the condition of pre-existing faults, and the results show that pumping promotes differential activities between two sides of the fault and has a positive impact on the occurrence and the activity of ground fissures. Horizontal rectangular sill with uniform opening model is used to simulate the land subsidence and invert the pumping depth. The results are basically consistent with the local situation.

A study of the symbiotic relationship between tectonic fissures and faults in the Fenwei Graben System, China

The Fenwei Graben System is an important extensional fault-depression zone, which is the tectonic boundary between the Ordos Block and the South China Block and the North China Block. The graben system presents an “S” shape, with a total length of 1200 km and a width of 30–60 km and an overall strike of NNE. Due to complex tectonic background and active faults, nearly 612 ground fissures develop in these basins, and more than 90% of these ground fissures are tectonic fissures, which are closely associated with fault activities. To reveal the plane symbiotic phenomena, profile symbiotic modes and symbiotic mechanism between tectonic fissures and faults in the Fenwei Graben System, the developmental characteristics were investigated in detail by surveying, mapping, trenching and drilling in the study area. The main conclusions are as follows. (1) The tectonic fissures of the Fenwei Graben System are mainly distributed along the margin faults of basins, the boundary faults between blocks and the hidden faults within blocks, causing serious damages to farmlands, houses and roads. The symbiosis between these fissures and faults is obvious on the surface. (2) The profile symbiotic morphology includes vertical extension type, syncline and anticline “y” type, and stepped type. (3) The symbiotic mechanisms include vertical growth, lateral rupture and clustery derivation. (4) The activities of underlying faults give impetus to the formation and expansion of tectonic fissures. The exposure of the fissures makes underlying faults continue to develop in the form of surface fractures.

Ongoing research on the pumping-induced land deformation in the Aguascalientes Valley: an analysis of the recent data of vertical deformation, groundwater level variations and local seismicity

Abstract. In the Aguascalientes valley, middle Mexico, the demand of groundwater from the local aquifer system was suddenly increased after the late 1970s. Since then, several related problems have been occurring or become critical such as land subsidence, ground fissuring, and low-magnitude earthquakes. The most recent data of vertical deformation from PSInSAR, groundwater levels, and earthquakes, has provided critical information regarding the relationship amongst all these processes. In particular, that related to land subsidence, earth fissuring and seismicity. Regarding this, more satellite imagery and data from GPS stations are being revised as a possibility of a more generalized vertical deformation derived with low-magnitude seismicity. A particular seismic event recorded on 6 April 2019 has revealed critical information on the close association between vertical displacements occurred in active faults and low-magnitude seismic events.

Reconstruction of earth fissures 3-D from videos

Abstract. Earth fissures are pervasive cracks that develop on valley floors as a consequence of land subsidence associated with extensive groundwater withdrawal. To capture geometrical, geological and geotechnical information of ground fissures is of paramount importance for their characterization. Recent advances in remote sensing techniques and the accessibility to remotely piloted aircraft systems (RPAS) as well as the evolution of onboard digital cameras enable the capture of digital photos and videos. Using digital photos along with the Structure from Motion (SfM) technique and following certain strategies, we can reconstruct a 3-D model of the earth fissures under study. This technique requires digital photos, but when a digital video is available, we can convert it into a set of frames and equally apply the procedure. Besides, the extraction of frames from a video assures a key condition for the SfM technique: the overlap between photos. The resulting 3-D model should be scaled and oriented using a rigid transformation matrix or even better including ground control points (GCP) into the captured photos or frames. The latter enables the geo-referencing of the point cloud and the correction of linear and non-linear deformations. In this work, the proposed methodology is illustrated through the application of SfM technique to a high-resolution video downloaded from YouTube (i.e. https://youtu.be/9xdAnftBKvY, last access: 20 February 2020). The video shows a mile-long earth fissure that appeared sometime between March 2014 and December 2014 near the Tator Hills (Arizona, USA) over Quaternary sediments. The Arizona Geological Survey captured these videos using an RPAS. The frames of the video were downloaded and extracted using a simple Matlab code. Then, we sub-sampled the frames and processed them using the software Agisoft Metashape Professional. Finally, we got metric data from Google Earth and generated a 3-D model. The quality of the 3-D model strongly depends on the quality of the photos and the GCP. However, this study shows the potential of this technique, instrumentation and data available on Internet for the development of 3-D point clouds and 3-D models for the detailed analysis of earth fissures.