Evolution mechanism and treatment timing of penetrating fissures

The Inner Mongolia mining area in western China are characterized by the development of numerous penetrating fissures,resulting in severe land damage.It is significant to reveal the underlying evolution mechanism and identify treatment timing for restoring the ecological environment.The Guanbanwusu mining subsidence area in Inner Mongolia,China was selected as the research case for this study.The evolution mechanism of different penetrating fissures was revealed by field measurement,physical simulation and theoretical analysis.The treatment timing prediction model for the mining subsidence area was established based on the enhanced Weibull time function.The results show that the ground fissures are mainly step-type and collapse-type fissures.The breaking form of overlying strata determines their vertical opening and horizontal dislocation.The high mining intensity in the western mining area results in a shortened period of dynamic fissure expansion and reduced closure degree.The damage extent of the overlying strata exhibits zoning characteristics both vertically and horizontally.The relative standard deviation of the prediction model is only 3.7%.Concurrently,the prediction model is employed to determine the optimal timing for treatment in the study area,estimated to be 259 days.Subsequently,once this threshold is reached,the study area undergoes treatment and restoration of its e cological environment.This study addresses the knowledge gap in this field by highlighting the interconnectedness between rock strata structure and evolution mechanism of penetrating fissures,thereby providing a method for determining the treatment timing in mining subsidence areas.

Heat transfer and temperature evolution in underground mininginduced overburden fracture and ground fissures: Optimal time window of UAV infrared monitoring

Heat transfer and temperature evolution in overburden fracture and ground fissures are one of the essential topics for the identification of ground fissures via unmanned aerial vehicle(UAV) infrared imager. In this study, discrete element software UDEC was employed to investigate the overburden fracture field under different mining conditions. Multiphysics software COMSOL were employed to investigate heat transfer and temperature evolution of overburden fracture and ground fissures under the influence of mining condition, fissure depth, fissure width, and month alternation. The UAV infrared field measurements also provided a calibration for numerical simulation. The results showed that for ground fissures connected to underground goaf(Fissure Ⅰ), the temperature difference increased with larger mining height and shallow buried depth. In addition, Fissure Ⅰ located in the boundary of the goaf have a greater temperature difference and is easier to be identified than fissures located above the mining goaf. For ground fissures having no connection to underground goaf(Fissure Ⅱ), the heat transfer is affected by the internal resistance of the overlying strata fracture when the depth of Fissure Ⅱ is greater than10 m, the temperature of Fissure Ⅱ gradually equals to the ground temperature as the fissures’ depth increases, and the fissures are difficult to be identified. The identification effect is most obvious for fissures larger than 16 cm under the same depth. In spring and summer, UAV infrared identification of mining fissures should be carried out during nighttime. This study provides the basis for the optimal time and season for the UAV infrared identification of different types of mining ground fissures.

Crack mechanism of ground fissures in loess layer of Fenwei Basin, China

The Fenwei Basin, covered by loess, experiences severe ground fissure disasters. These disasters disrupt the continuity of the loess and pose significant threats to engineering construction safety along transportation routes. Nevertheless, the crack characteristics and the influence zone of ground fissures in the loess layer remain inadequately investigated. To effectively prevent and control ground fissure disasters, physical model tests and the PFC(particle flow code) numerical simulation method are used to investigate the crack mechanism of buried ground fissures in the loess layer. The results show that there are two main cracks in the layer profile, which have a Y-shape morphology. As the dip angle of the preset cracks increased from 60° to 90°, the main deformation zone at the surface gradually shifted towards the footwall. The process of crack propagation from depth to surface is divided into five stages. Additionally, the results confirm the accuracy of the width of the rupture zone d2in the footwall calculated by the cantilever beam theory. These findings can offer theoretical guidance for determining the avoidance distance of ground fissures in loess regions, as well as for implementing disaster prevention and corresponding control measures for various stages of buried ground fissure propagation.

Evaluation of the Efficacy of 99.9% Pure Silver Trilaminate Cups in the Prevention and Treatment of Nipple Pain and Fissures

Breastfeeding is drastically decreasing over time and nipple trauma constitutes one of the most significant reasons for its discontinuation. In this context, this study aimed at evaluating the effectiveness and tolerability of a topical treatment device, namely Silver Cap® (Depofarma S.P.A.), when used to prevent pain and nipple fissure formation. The medical device consists in a silver trilaminate cup to be placed on the nipple, providing physical protection and creating a moist environment. The study involved 187 women: 38 started to apply the device prior to lactation (PL group) and 149 during lactation (DL group). Aiming to collect safety and performance data, both groups were provided with questionnaires during 6 consecutive visits (120 days of follow-up). At last visit, absence of painful symptoms was reported by the 98.8% and the 100% of women in DL and PL groups, respectively. Moreover, no nipple fissures were observed and no adverse events directly correlated to use of the device were reported. According to these findings, it can be concluded that Silver Cap® is a safe and effective device for nipple pain and fissure prevention. .

Research on the feasibility of storage and estimation model of storage capacity of CO_(2)in fissures of coal mine old goaf

The concept of the carbon cycle in the old goaf of a coal mine based on CO_(2)utilization and storage was put forward adhering to the principle of low-carbon development,utilization of space resources in old goafs,and associated gas resources development.Firstly,the evolution characteristics of overburden fissures in the goaf of the case was studied using a two-dimensional physical similarity simulation test,the sealing performance of the caprocks after stabilization was analyzed,and the fissures were counted and classi-fied.Then,the process of gaseous CO_(2)injection in the connected fissure was simulated by Ansys Fluent software,and the migration law and distribution characteristics of CO_(2)under the condition of gaseous CO_(2)injection were analyzed.Finally,the estimation models of free CO_(2)storage capacity in the old goaf were constructed considering the proportion of connected fissure and the effectiveness of CO_(2)injection.The CO_(2)storage capacity in the old goaf of the case coal mine was estimated.The results showed that a caprock group of“hard-thickness low-permeability hard-thickness”was formed after the caprock-fissures system in the goaf of the case tended to be stable vertically.The connected fissure,occlude cracks,and micro-fractures in the goaf accounted for 85.5%,8.5%,and 6%of the total fissures,respectively.Gaseous CO_(2)first migrated to the bottom of the connected fissure after CO_(2)was injected into the goaf,then spread horizontally along the bottom of the connected fissure after reaching the bottom,and finally spread longitudinally after filling the bottom of the entire connected fissure.The theoretical and effective storage capacities of free CO_(2)at normal temperature and pressure in the old goaf of the case were 9757 and 7477 t,respectively.The effective storage capacity of free CO_(2)at normal temperature and pressure in the old goaf after all minefield mined was 193404 t.The research can provide some reference for the coal mining industry to help the goal of“carbon peaking and carbon neutrality”.

Microtremor-based analysis of the dynamic response characteristics of a site containing grouped earth fissures

In this study,the Beibu earth fissure site in the northeastern part of Weihe Basin,which contains four nearly parallel earth fissures,was studied.A long straight microtremor measuring line,containing 49 measuring points across four earth fissures,was established to investigate the dynamic response of this site using Fourier spectrum,response acceleration spectrum,Arias intensity,and HVSR analyses.The main results are as follows:(1)The fundamental frequencies of 44 measuring points obtained from HVSR analysis are concentrated within 1.67 Hz-2.25 Hz,and the existence of the earth fissures has little effect on the fundamental frequency changes.(2)There is an amplification effect near a single earth fissure.The dynamic responses are large at the measuring points near the earth fissure,and the values decrease with increasing distance from the earth fissure.In areas between two adjacent earth fissures,these values decrease and are even lower than those in sites without amplification effects.(3)In this earth fissure site,the general area(or less affected area)and affected areas were delineated based on the amplification effect.In engineering applications,construction design should avoid these affected areas and existing structures should be reinforced to satisfy the seismic fortification requirements.

Fracture evolution characteristics of sandstone containing double fissures and a single circular hole under uniaxial compression

The uniaxial compression experiments on the sandstone samples containing double fissures and a single circular hole were carried out by using electro-hydraulic servo universal testing machine to investigate the effect of rock bridge angle β and fissure angle α on mechanical properties and evolution characteristics of cracks.The results show that the peak strength,peak strain and elastic modulus of defected specimens decrease comparing with those for intact sample,and show a decreased trend firstly and then increase with β changing from 0° to 90°.The peak strength and elastic modulus achieve the minimum value as the rock bridge angle is 60°,while the peak strain reaches the minimum value with the rock bridge angle of 45°.The crack initiation of tested rock samples occurs firstly in stress concentration areas at tips of prefabricated fissures under uniaxial compression,and then propagates constantly and coalescences with the prefabricated hole.Some secondary cracks initiate and propagate as well until buckling failure happens.The rock bridge angle has a great influence on crack initiation,coalescence,final failure mode,crack initiation stress and transfixion stress.The peak strength varies significantly,while the elastic modulus and peak strain change slightly,and the failure modes are also different due to the influence of fissure angle.

Experimental and numerical study on loading rate effects of rock-like material specimens containing two unparallel fissures

A series of laboratory experiments and PFC numerical simulations for rock-like material specimens containing two unparallel fissures were carried out.On the basis of experimental and numerical results,the stress-strain curves,mechanical properties,AE events,cracking behavior and energy characteristics were analyzed to reveal the macro-mechanical behavior and meso-mechanism of pre-fissured specimens under different loading rates.Investigated results show that:1)When the loading rate is relatively low,the stress-strain curves show a brittle response.When the loading rate is relatively high,the curve shows a more ductile response.Both of the peak strength and elastic mudulus increase with the increase of loading rate,which can be expressed as power functions.2)Four crack types are identified,i.e.,tensile crack,shear crack,far-field crack and surface spalling.Moreover,the tensile crack,far-field crack and surface spalling are under tensile mechanism,while the shear crack is under shear mechanism.3)The drops of the stress-strain curves all correspond to the crack initiation or coalescence,which is also linked to a sudden increasing in the accumulated micro-crack curve.4)Both of the maximum bond force and energy have the similar trend with the increase of loading rate to peak strength,which indicates that the trend of peak strength can be explained by the meso-mechanics and energy.

Discrete element modeling on the crack evolution behavior of brittle sandstone containing three fissures under uniaxial compression

Based on experimental restilts of brittle, intact sandstone under uniaxial compression, the micro-parameters were firstly confirmed by adopting particle flow code （PFC2D）. Then, the validation of the simulated models were cross checked with the experimental results of brittle sandstone containing three parallel fissures under uniaxial compression. The simulated results agreed very well with the experimental results, including the peak strength, peak axial strain, and ultimate failure mode. Using the same micro- parameters, the numerical models containing a new geometry of three fissures are constructed to investigate the fissure angle on the fracture mechanical behavior of brittle sandstone under uniaxial compression. The strength and deformation parameters of brittle sandstone containing new three fissures are dependent to the fissure angle. With the increase of the fis- sure angle, the elastic modulus, the crack damage threshold, and the peak strength of brittle sandstone containing three fissures firstly increase and secondly decrease. But the peak axial strain is nonlinearly related to the fissure angle. In the entire process of deformation, the crack initiation and propagation behavior of brittle sandstone containing three fissures under uniaxial compression are investigated with respect to the fissure angle. Six different crack coalescence modes are identified for brittle sandstone containing three fissures under uniaxial compression. The influence of the fissure angle on the length of crack propagation and crack coalescence stress is evaluated. These investigated conclusions are very important for ensuring the stability and safety of rock engineering with intermittent structures.

An experimental investigation of failure mechanical behavior in cylindrical granite specimens containing two non-coplanar open fissures under different confining pressures

Fissures play a significant role in predicting the unstable failure of rock mass engineering.For deep rock underground engineering,rock mass containing pre-existing fissures is usually located in triaxial stress state.Therefore,not only pre-existing fissure but also confining pressure affects the failure mechanical behavior of rock material.In this research,the granite specimens containing two non-coplanar open fissures were investigated by a series of conventional triaxial compression tests.First,the effect of bridge angle and confining pressure on strength and deformation characteristics of granite specimens was evaluated.Results show that the triaxial compressive strength,failure axial strain,and crack damage threshold increased nonlinearly with confining pressure.Under high confining pressures,elastic modulus was insensitive to bridge angle.Then,an X-ray micro-CT scanning technique was used to analyze the internal fracture characteristics of granite specimens with respect to various bridge angles and confining pressures.Five typical crack coalescence modes were identified,namely,indirect coalescence,shear coalescence and three types of tensile coalescence.The reconstructed 3-D CT images indicated that under uniaxial or low confining pressures,the bridge angle had a significant effect on crack evolution behavior,while under high confining pressures,shear-dominated failures occurred with the development of anti-wing cracks.

Mechanical behaviours of sandstone containing intersecting fissures under uniaxial compression

Predicting rock cracking is important for assessing the stability of underground engineering.The effects of the intersecting angle a and the distribution orientation angleβof intersecting fissures on the uniaxial compressive strength and the failure characteristics of sandstone containing intersecting fissures are investigated through laboratory experiments and two-dimensional particle flow code(PFC2D).The relationship between the mechanical properties of sandstone and the intersecting angle a and the distribution orientation angleβis analysed.Crack initiation forms and the final failure modes are then categorised and determined via empirical methods.In addition,the cracking processes of intersecting fissures with different a andβvalues are discussed.The results show that variations in the peak stress,peak strain,average modulus,and crack initiation stress of sandstone containing intersecting fissures show a“moth”shape in the space of the a-β-mechanical parameters.Two crack initiation forms are identified:inner tip cracking(usually accompanied by one outer tip cracking)and only outer tips cracking.Two failure modes are observed:(1)the main fracture planes are created at the inner tip and one outer tip,and(2)the main fracture planes are formed at the two outer tips.Two main crack evolution processes of sandstone containing intersecting fissures under uniaxial compression are found.Approaches for quickly determining the crack initiation form and the failure mode are proposed.The combination of the determination equations for the crack initiation form and the failure mode can be used to predict the crack evolution.The approach for determining the crack evolution processes is hence proposed with acceptable precision.

An experimental study on fracture mechanical behavior of rock-like materials containing two unparallel fissures under uniaxial compression

Strength and deformability characteristics of rock with pre-existing fissures are governed by cracking behavior. To further research the effects of pre-existing fissures on the mechanical properties and crack coalescence process, a series of uniaxial compression tests were carried out for rock-like material with two unparallel fissures.In the present study, cement, quartz sand, and water were used to fabricate a kind of brittle rock-like material cylindrical model specimen. The mechanical properties of rock-like material specimen used in this research were all in good agreement with the brittle rock materials. Two unparallel fissures（a horizontal fissure and an inclined fissure） were created by inserting steel during molding the model specimen.Then all the pre-fissured rock-like specimens were tested under uniaxial compression by a rock mechanics servocontrolled testing system. The peak strength and Young＇s modulus of pre-fissured specimen all first decreased and then increased when the fissure angle increased from 0？to 75？.In order to investigate the crack initiation, propagation and coalescence process, photographic monitoring was adopted to capture images during the entire deformation process.Moreover, acoustic emission（AE） monitoring technique was also used to obtain the AE evolution characteristic of prefissured specimen. The relationship between axial stress, AE events, and the crack coalescence process was set up： when a new crack was initiated or a crack coalescence occurred, thecorresponding axial stress dropped in the axial stress–time curve and a big AE event could be observed simultaneously.Finally, the mechanism of crack propagation under microscopic observation was discussed. These experimental results are expected to increase the understanding of the strength failure behavior and the cracking mechanism of rock containing unparallel fissures.

The spatial distribution characteristics of shallow fissures of a landslide in the Wenchuan earthquake area

Shallow fissures, being the main infiltration paths of fluid on the surface of a slope, played an important role in the whole process of a landslide. However, the spatial distribution characteristics of fissures in the slope are difficult to be determined. In this study, we attempted to characterize the variation pattern of slope fissures along depth in the Wenchuan earthquake area in Sichuan Province by combining engineering geological investigation, geomorphologic analysis and geophysical investigation. The geophysical methods that were used in this study include Multichannel Analysis of Surface Wave(MASW), Ground Penetrating Radar(GPR) and Electrical Resistivity Tomography(ERT). The results suggested that geophysical parameters(shear wave velocity, electromagnetic signals attenuation and resistivity) could provide valuable information for the spatial network of shallow fissures. Through the verification by engineering geological survey and geophysical sensitivity analysis, this work highlighted that MASW was the most appropriate technique to delineate the propagation of shallow fissures in a gravel soil slope.

Study on Ground Fissures and Land Subsidence Induced by Seepage Deformation in Xi'an

There are lots of theories about the causation of ground fissures in Xi’an,such as the tectonics theory,the excessive groundwater exploitation theory and the compositive theory. Based on the construction of the geologic environment monitoring network in Guanzhong urban agglomeration,the latest survey of ground fissures and land subsidence in Yuhuazhai in Xi’an shows that the extensive piping and quicksand in self-supply wells is a factor to induce ground fissures and land subsidence. It is suggested that the seepage deformation caused by high hydraulic gradient leads to sand gushing and changes some aquifers into the composite aquifer,which is the main factor to induce ground fissures and land subsidence. The development characteristics of ground fissures and land subsidence caused by seepage deformation were summarized. The results will supply new schemes and methods for the causation of land subsidence and ground fissures in Xi’an and lay out a clear road map of measures to control land subsidence and ground fissures.

Failure characteristics and its influencing factors of rock-like material with multi-fissures under uniaxial compression

The compression test on rock-like specimens with prefabricated closed multi-fissures made by pulling out the embedded metal inserts in the precured period was done on the servo control uniaxial loading instrument. The influence of fissure inclination angle and distribution density on the failure characteristics of fissure bodies was researched. It was found that, the fissure inclination angle was the major influencing factor on the failure modes of fissure bodies. The different developmental states of micro-cracks would appear on specimens under different fissure inclination angles. However, the influence of fissure distribution density on the failure mode of fissure bodies was achieved by influencing the transfixion pattern of fissures. It was shown by the sliding crack model that, the effective shear, which drove the relative sliding of the fissure, was a function of fissure inclination angle and friction coefficient of the fissure surface. The strain-softening model of fissure bodies was established based on the mechanical parameters that were obtained by the test of rock-like materials under the same experimental condition. And the reliability of experimental results was identified by using this model.

Mechanical properties and cracking behaviors of limestone-like samples with two parallel fissures before and after grouting

In the present work,uniaxial compressive tests were carried out on limestone-like samples containing two parallel open fissures or cement-infilled fissures with different geometries.Mechanical property and crack behavior of limestone-like samples with two parallel open fissures or cement-infilled fissures were affected by bridge inclination angle and fissure inclination angle.Four types of coalescence of rock bridge for samples containing open fissures or cement-infilled fissures were summarized and classified.The closure of tensile crack was observed in the samples with small fissure inclination angle.This is a new phenomenon which is not mentioned in previous studies.Test results show that the peak strength,crack initiation stress,and coalescence type are different between open fissures and cement infilled fissures.The reason for this phenomenon is that grouting of cement can transfer stress and reduce stress concentration at the flaw tip and rock bridge area.

Relationship of Resistivity with Water Content and Fissures of Unsaturated Expansive Soils

The development of fissures in expansive soils has a great effect on the stability of slope. Of the three phases of soils,the gas phase and solid phase are relatively insulated,so the average resistivity of soils can be calculated from the resistivity of the liquid phase. On this basis,the two-part model of resistivity changing with the water saturation of the expansive soil can be deduced. A 2-D resistance grid model is established based on simulating the resistance of ver-tically developed fissures. Variation in measured resistance of vertically developed fissures at different positions can be calculated from this model. Fissure development can be inversely determined from the variation in the measured resis-tance. Finally,the model is verified by an indoor resistivity test for remolded soil samples,indicating that the test result agrees well with that of the model established.

Application of Seismic Anisotropy Caused by Fissures in Coal Seams to the Detection of Coal-bed Methane Reservoirs

Coal-bed methane is accumulated in micro-fissures and cracks in coal seams. The coal seam is the source terrace and reservoir bed of the coal-bed methane (Qian et al., 1996). Anisotropy of coal seams is caused by the existence of fissures. Based on the theory of S wave splitting: an S wave will be divided into two S waves with nearly orthogonal polarization directions when passing through anisotropic media, i.e. the fast S wave with its direction of propagation parallel to that of the fissure and slow S wave with the direction of propagation perpendicular to that of the fissure.

Model test study on the formation and development of underground erosion ground fissures in the Kenya Rift Valley

The Kenya Rift Valley is relatively prone to underground erosion ground fissures and associated disasters,which gravely hinder local engineering construction and economic development.In this research,we performed field and experimental studies on ground fissures in the Kenya Rift Valley area,and determined the structural characteristics of underground erosion fissures.Based on a geological survey of the area,we generalized a geological model for typical ground fissures and reproduced the intermediate process of ground fissure propagation using a large-scale physical model test.Further,the development process of underground erosion fissures were categorized into four stages:uniform infiltration,preferential infiltration,cavity expansion,and collapse formation stages.During the development of underground erosion fissures,water content was distributed symmetrically along the fissures,and these fissures acted as the primary infiltration paths of water.When the ground collapsed,the increase in negative pore water pressure was greater,whereas the increase in positive pore water pressure was less in the shallow soil;moreover,in the deep soil,the increase in positive pore water pressure was greater than that of negative pore water pressure.Additionally,the earth pressure increment initially increased and then decreased with the development of erosion.During underground erosion collapse,the water content and pore water pressure appeared to increase and decrease rapidly.These results can be employed to predict the occurrence of underground erosion ground fissures and the resulting soil collapse.

Characteristics of fissures and pores of anthracite in Jincheng by SEM

Anthracite in Jincheng is a highly metamorphic coal and its system of fissures and pores is differentfrom that of low and medium ranked coal.In order to discover their characteristics,69 samples were collected from 18 CBM wells in Zhengzhuang in Jincheng and their fissures and pores were observed by a Scanning Electron Microscope(SEM).To the naked eyes and by SEM,the pores in the Jincheng anthracite are seen to have abundant mold pores with isolated,shallow and poor connectivity(diameters between 1～50 μm) and few plant tissue pores,gas pores,and solution pores.Most of the fissures are filled with clay minerals or closed;while open fissures are not often visible in the Jincheng coal(aperture between 3～10 μm).These characteristics are determined by the high rank and high vitrinite content of the coal.The existence of too many mold pores and filled fissures does not allow the migration of methane,hence hydraulic fracture stimulation will be required and is an effective method of adding and connecting fissures to enhance CBM production.