Exploring mechanism of hidden,steep obliquely inclined bedding landslides using a 3DEC model:A case study of the Shanyang landslide in Shaanxi Province,China

Catastrophic geological disasters frequently occur on slopes with obliquely inclined bedding structures(also referred to as obliquely inclined bedding slopes),where the apparent dip sliding is not readily visible.This phenomenon has become a focal point in landslide research.Yet,there is a lack of studies on the failure modes and mechanisms of hidden,steep obliquely inclined bedding slopes.This study investigated the Shanyang landslide in Shaanxi Province,China.Using field investigations,laboratory tests of geotechnical parameters,and the 3DEC software,this study developed a numerical model of the landslide to analyze the failure process of such slopes.The findings indicate that the Shanyang landslide primarily crept along a weak interlayer under the action of gravity.The landslide,initially following a dip angle with the support of a stable inclined rock mass,shifted direction under the influence of argillization in the weak interlayer,moving towards the apparent dip angle.The slide resistance effect of the karstic dissolution zone was increasingly significant during this process,with lateral friction being the primary resistance force.A reduction in the lateral friction due to karstic dissolution made the apparent dip sliding characteristics of the Shanyang landslide more pronounced.Notably,deformations such as bending and uplift at the slope’s foot suggest that the main slide resistance shifts from lateral friction within the karstic dissolution zone to the slope foot’s resistance force,leading to the eventual buckling failure of the landslide.This study unveils a novel failure mode of apparent dip creep-buckling in the Shanyang landslide,highlighting the critical role of lateral friction from the karstic dissolution zone in its failure mechanism.These insights offer a valuable reference for mitigating risks and preventing disasters related to obliquely inclined bedding landslides.

Mutual impact of true triaxial stress, borehole orientation and bedding inclination on laboratory hydraulic fracturing of Lushan shale

Unconventional resources like shale gas has been the focus of intense research and development for two decades. Apart from intrinsic geologic factors that control the gas shale productivity (e.g. organic matter content, bedding planes, natural fractures, porosity and stress regime among others), external factors like wellbore orientation and stimulation design play a role. In this study, we present a series of true triaxial hydraulic fracturing experiments conducted on Lushan shale to investigate the interplay of internal factors (bedding, natural fractures and in situ stress) and external factors (wellbore orientation) on the growth process of fracture networks in cubic specimens of 200 mm in length. We observe relatively low breakdown pressure and fracture propagation pressure as the wellbore orientation and/or the maximum in situ stress is subparallel to the shale bedding plane. The wellbore orientation has a more prominent effect on the breakdown pressure, but its effect is tapered with increasing angle of bedding inclination. The shale breakdown is followed by an abrupt response in sample displacement, which reflects the stimulated fracture volume. Based on fluid tracer analysis, the morphology of hydraulic fractures (HF) is divided into four categories. Among the categories, activation of bedding planes (bedding failure, BF) and natural fractures (NF) significantly increase bifurcation and fractured areas. Under the same stress regime, a horizontal wellbore is more favorable to enhance the complexity of hydraulic fracture networks. This is attributed to the relatively large surface area in contact with the bedding plane for the horizontal borehole compared to the case with a vertical wellbore. These findings provide important references for hydraulic fracturing design in shale reservoirs.

Experimental study on flow heterogeneity of shale bedding fractures based on full-diameter cores

A self-designed full-diameter core experimental facility was used to evaluate the flow heterogeneity of bedding fractures at four radial directions under different closure pressures and injection rates,using full-diameter cores retaining original natural bedding fractures.The distribution morphology of bedding surface affects the conductivity of bedding fractures,and the flow capacity of bedding fractures in four radial directions varies greatly with the closure pressure and injection rate.The rougher the fracture surface,the greater the flow capacity varies with the closure pressure.For unsupported bedding fractures,the mean percentage error(MPE)of the conductivity in four radial directions increase gradually with the increase of the closure pressure.This phenomenon is especially prominent in deep rock samples.It is indicated that the flow heterogeneity of bedding fractures tends to increase with the closure pressure.When proppant is placed in the fracture,at a low closure pressure,due to the combined effects of self-support of rough fracture surface,proppant instability and uneven proppant placement,the flow heterogeneity is greater than that when proppant is not placed at the same closure pressure;however,with the increase of the closure pressure,the proppant becomes compact and stable,and the flow heterogeneity is mitigated gradually.

一类带Bedding反应函数的捕食模型在不同斑块环境中的扩散作用

研究了一类带Bedding类反应函数的捕食与被捕食扩散模型的整体及局部性态,证明了该模型在第一象限内存在一个吸引域,且它的一切正解是强持续生存的;得出系统的正平衡点是局部渐近稳定的充分条件;最后通过数值模拟仿真进一步验证了定理的准确性,补充和完善了前人的结果.

Rock Pressure on Tunnel with Shallow Depth in Geologically Inclined Bedding Strata

The method to calculate rock pressure to which the lining structure of tunnel with shallow depth is subjected in geologically inclined bedding strata is analyzed and put forward. Both the inclination angle of bedding strata as well as the internal friction angle of bedding plane and its cohesion all exert an influence upon the magnitude of the asymmetric rock pressure applied to tunnel. The feature that rock pressure applied to tunnel structure varies with the incUnation angle of bedding strata is discussed, At last, the safety factor, which is utilized to evaluate the working state of tunnel lining structure, is calculated for both symmetric and asymmetric lining structures. The calculation results elucidate that the asymmetric tunnel structure can be more superior to bear rock pressure in comparison with the symmetric one and should be adopted in engineering as far as possible.

具阶段结构和Bedding DeAngelis功能反应的食饵捕食系统(英文)

研究具阶段结构和Bedding-DeAngelis功能反应的食饵捕食系统.给出了一致持续生存和捕食者灭绝的条件.

A numerical simulation study on mechanical behaviour of coal with bedding planes under coupled static and dynamic load

To investigate the bedding influence on coal mechanical behaviour in underground environments such as coal or rock burst, simulations of dynamic SHPB tests of pre-stressed coal specimens with different bedding angles were carried out using a particle flow code 2-dimensional(PFC2D). Three impact velocities of 4, 8 and 12 m/s were selected to study dynamic behaviours of coal containing bedding planes under different dynamic loads. The simulation results showed that the existence of bedding planes leads to the degradation of the mechanical properties and their weakening effect significantly depends on the angle h between the bedding planes and load direction. With h increaseing from 0° to 90°, the strength first decreased and subsequently increased and specimens became most vulnerable when h was 30° or 45°.Five failure modes were observed in the specimens in the context of macro-cracks. Furthermore, energy characteristics combined with ultimate failure patterns revealed that maximum accumulated energy and failure intensity have a positive relation with the strength of specimen. When bedding planes were parallel or perpendicular to loading direction, specimens absorbed more energy and experienced more violent failure with increased number of cracks. In contrast, bedding planes with h of 30° or 45° reduced the specimens' ability of storing strain energy to the lowest with fewer cracks observed after failure.

Model test and numerical simulation on the dynamic stability of the bedding rock slope under frequent microseisms

Shake table testing was performed to investigate the dynamic stability of a mid-dip bedding rock slope under frequent earthquakes. Then, numerical modelling was established to further study the slope dynamic stability under purely microseisms and the influence of five factors, including seismic amplitude, slope height, slope angle, strata inclination and strata thickness, were considered. The experimental results show that the natural frequency of the slope decreases and damping ratio increases as the earthquake loading times increase. The dynamic strength reduction method is adopted for the stability evaluation of the bedding rock slope in numerical simulation, and the slope stability decreases with the increase of seismic amplitude, increase of slope height, reduction of strata thickness and increase of slope angle. The failure mode of a mid-dip bedding rock slope in the shaking table test is integral slipping along the bedding surface with dipping tensile cracks at the slope rear edge going through the bedding surfaces. In the numerical simulation, the long-term stability of a mid-dip bedding slope is worst under frequent microseisms and the slope is at risk of integral sliding instability, whereas the slope rock mass is more broken than shown in the shaking table test. The research results are of practical significance to better understand the formation mechanism of reservoir landslides and prevent future landslide disasters.

Directivity effect of unloading bedding coal induced fracture evolution and its application

In the coal mining process, the gas contained in the coalbed is one source of the most serious accident hazards. Stress releasing from the coal deposit is the main controlling factor that leads to such accidents.Based on the bedding of coal samples, the gas permeability well describes the evolution of fracture, so the paper carries out research on the permeability properties of coal under different unloading directions.The research obtains that when the stress unloading direction is perpendicular to bedding, more penetrating fractures and bedding fractures occur, and the permeability significantly increases. Although the axial stress reduced, the confining pressure makes the permeability of the bedding plane fracture exist under constant. The permeability obtained when the unloading direction was perpendicular to the bedding is 52 times larger than that when it is parallel to the bedding. The results show that the efficiency of gas drainage is impacted by the relative direction of gas drainage drilling in relation to the bedding orientations. The maximum amount of gas extraction when drilling is perpendicular to the bedding is 1.3 times than that when drilling is oblique to the bedding, and 1.75 times than that when drilling is parallel to the bedding.

Experimental study on seismic response and progressive failure characteristics of bedding rock slopes

Bedding rock slopes are common geological features in nature that are prone to failure under strong earthquakes. Their failures induce catastrophic landslides and form barrier lakes, posing severe threats to people’s lives and property. Based on the similarity criteria, a bedding rock slope model with a length of3 m, a width of 0.8 m, and a height of 1.6 m was constructed to facilitate large-scale shaking table tests.The results showed that with the increase of vibration time, the natural frequency of the model slope decreased, but the damping ratio increased. Damage to the rock mass structure altered the dynamic characteristics of the slope;therefore, amplification of the acceleration was found to be nonlinear and uneven. Furthermore, the acceleration was amplified nonlinearly with the increase of slope elevation along the slope surface and the vertical section, and the maximum acceleration amplification factor(AAF) occurred at the slope crest. Before visible deformation, the AAF increased with increasing shaking intensity;however, it decreased with increasing shaking intensity after obvious deformation. The slope was likely to slide along the bedding planes at a shallow depth below the slope surface. The upper part of the slope mainly experienced a tensile-shear effect, whereas the lower part suffered a compressive-shear force. The progressive failure process of the model slope can be divided into four stages, and the dislocated rock mass can be summarized into three zones. The testing data provide a good explanation of the dynamic behavior of the rock slope when subjected to an earthquake and may serve as a helpful reference in implementing antiseismic measures for earthquake-induced landslides.

Modeling shale with consideration of bedding planes by cohesive finite element method

Shale contains distributed directional bedding planes,which make the shale transverse isotropic.To model shale with consideration of the bedding planes,a cohesive finite element method(CFEM)is developed based on the randomized triangular mesh.The interface orientation generated from such mesh tends to be uniformly distributed with the element number increasing.To represent the bedding plane,the interfaces aligned with the bedding plane are assigned the cohesive law that characterizes the bedding plane while the other interfaces are assigned the cohesive law that characterizes the matrix.By this means,the anisotropy characteristics of the stiffness and the strength of shale are well represented.The simulation examples demonstrate that the bedding plane has a significant influence on the fracture trajectory,which is consistent with the observation in the experiment.It is suggested that this modeling method of shale is feasible.It provides an alternative approach to fracture simulation in shale.

Influence of bedding structure on stress-induced elastic wave anisotropy in tight sandstones

To understand the evolution of stress-induced elastic wave anisotropy,three triaxial experiments were performed on sandstone specimens with bedding orientations parallel,perpendicular,and oblique to the maximum principal stress.P-wave velocities along 64 different directions on each specimen were monitored frequently to understand the anisotropy change at various stress levels by fitting Thomsen’s anisotropy equation.The results show that the elastic wave anisotropy is very sensitive to mechanical loading.Under hydrostatic loading,the magnitude of anisotropy is reduced in all three specimens.However,under deviatoric stress loading,the evolution of anisotropic characteristics(magnitude and orientation of the symmetry axis)is bedding orientation dependent.Anisotropy reversal occurs in specimens with bedding normal/oblique to the maximum principal stress.P-wave anisotropyε0 is linearly related to volumetric strain Sv and dilatancy,indicating that stress-induced redistribution of microcracks has a significant effect on P-wave velocity anisotropy.The closure of initial cracks and pores aligned in the bedding direction contributes to the decrease of the anisotropy.However,opening of new cracks,aligned in the maximum principal direction,accounts for the increase of the anisotropy.The experimental results provide some insights into the microstructural behavior under loading and provide an experimental basis for seismic data interpretation and parameter selection in engineering applications.

Influence of Bedding and Mineral Composition on Mechanical Properties and Its Implication for Hydraulic Fracturing of Shale Oil Reservoirs

The premise of hydraulic fracturing is to have an accurate and detailed understanding of the rock mechanical properties and fracture propagation law of shale reservoirs. In this paper,a comprehensive evaluation of the mechanical properties of the shale oil reservoir in the south of Songliao Basin is carried out. Based on the experiments and the in-situ stress analysis, the fracture propagation law of three types of shale reservoirs is obtained,and the suggestions for fracturing are put forward. The results have shown that the fracture propagation of pure shale and low mature reservoir is easy to open along the bedding plane under compression loading,which is greatly influenced by the bedding. Sand-bearing shale is slightly better,the fractures of which are not easy to open along the bedding plane. The mechanical experimental results show that all the samples have the characteristics of low compressive strength,low Young’s modulus and strong anisotropy,indicating that the shale oil reservoir is certain plastic,which is related to its high clay mineral content and controlled by the bedding development. Compared with pure shale and low mature shale,the sandbearing shale has less clay content and less developed bedding,which maybe the main reason for its slightly better brittleness. Overall,the expansion of hydraulic fracture is controlled by in-situ stress and bedding. Because of the development of bedding,it is easy to form horizontal fractures. Thus it is not suitable for horizontal well fracturing.Because of the high content of clay minerals,the applicability of conventional slick hydraulic fracturing fluid is poor. It is suggested to use vertical well or directional well to carry out volume fracturing. In this way,the effect of bedding can be effectively used to open and connect the bedding and form a larger fracture network.

Influence of varying bedding thickness of underclay on floor stability

The variation in bedding thickness of the weak immediate floor has long been a challenge in the Illinois basin coal mines when it comes to floor stability. The vertical thickness of the immediate floor is not constant throughout the mines and can vary over short horizontal distances. The biggest misconception from a design standpoint is to use the maximum or average thickness found from core logs taken from various locations on the mine property. The result of this practice is oversized pillars in the areas where the weak immediate floor has thinned vertically. This over-design leaves coal in situ which could have otherwise been extracted. This paper presents a plane strain numerical model to illustrate the effect of a change in bedding thickness of a weak immediate floor across one or two coal pillars. The floor bearing capacity of the variable floor below each pillar where then compared to the consistent floor. The results show that the varying bedding thickness of weak underclay has an impact on the bearing capacity of the floor.Geometrically with the decrease in bedding thickness for constant pillar width, the B/H ratio increases exponentially. The influence of varying bedding thickness on the floor bearing capacity is apparent at higher B/H ratios. The floor bearing capacity under a single pillar is in variable floor model if the average thickness remains constant. For single pillar, the average of the bedding thickness can be considered and for pillars in a panel, and a safety factor has been proposed to take into account this change in bedding thickness.

Unsymmetrical load effect of geologically inclined bedding strata on tunnels of passenger dedicated lines

In order to study the unsymmetrical load effect in geological bedding strata for the Muzhailing tunnel on the Lanzhou-Chongqing passenger dedicated line in China, we investigated the deformation, mechanical response and pressure of the surrounding rock and the mechanical characteristics of bolts of the tunnel. The results suggest that open zones appear at arch and invert where joints open up, when layered stratum is horizontal, or when the dip angle of in- clined bedding is small. Open zones occur perpendicular to a joint. The failure mode is bending disjunction at the arch tain shear displacement, and lead to obvious geological bedding unsymmetrical load. The failure mode is shear damage. For the joint dip angle in the range of 75-90°, the failure mode is flexural crushing at the wall and vertical shear rup- ture above the arch. The restraining effect of two sides weakens for vertical dip. On the whole, shear failure instabilitytrend would occur and the tunnel collapses evenly. When the angle between the bolt and structure plane is greater than 23°, bolts can enhance the shearing stiffness of joint plane. Unfortunately, in the general purpose graph of tunnel for 250 km/h of passenger dedicated lines, the bolts have equal length and spacing. The rationale behind this is worthy offurther study. For inclined bedding, the surrounding rock pressure at the left wall is more than that at the right wall. In addition, lining is likely to be damaged at left shoulder and side wall. With the dip angle increasing, the unsymmetrical load gradually achieves symmetry. Asymmetry design for support is recommended to reduce the unsymmetrical load on lining disturbed by excavation.

Bedding parallel fractures in fine-grained sedimentary rocks:Recognition,formation mechanisms,and prediction using well log

Core,thin section,conventional and image logs are used to provide insights into distribution of fractures in fine grained sedimentary rocks of Permian Lucaogou Formation in Jimusar Sag.Bedding parallel fractures are common in fine grained sedimentary rocks which are characterized by layered structures.Core and thin section analysis reveal that fractures in Lucaogou Formation include tectonic inclined fracture,bedding parallel fracture,and abnormal high pressure fracture.Bedding parallel fractures are abundant,but only minor amounts of them remain open,and most of them are partly to fully sealed by carbonate minerals(calcite)and bitumen.Bedding parallel fractures result in a rapid decrease in resistivity,and they are recognized on image logs to extend along bedding planes and have discontinuous surfaces due to partly-fully filled resistive carbonate minerals as well as late stage dissolution.A comprehensive interpretation of distribution of bedding parallel fractures is performed with green line,red line,yellow line and blue line representing bedding planes,induced fractures,resistive fractures,and open(bedding and inclined)fractures,respectively.The strike of bedding parallel fractures is coinciding with bedding planes.Bedding parallel fractures are closely associated with the amounts of bedding planes,and high density of bedding planes favor the formation of bedding parallel fractures.Alternating dark and bright layers have the most abundant bedding parallel fractures on the image logs,and the bedding parallel fractures are always associated with low resistivity zones.The results above may help optimize sweet spots in fine grained sedimentary rocks,and improve future fracturing design and optimize well spacing.

Lower temperature hydrothermal pretreatment improves the anaerobic digestion performance of spent cow bedding

The anaerobic digestion(AD)performance of spent cow bedding was investigated with different hydrothermal pretreatment(HP)conditions.Spent cow bedding was pretreated with low temperatures(50,70,and 90℃)and different pretreatment times(2-72 h)with ammonia and without ammonia.The results showed that spent cow bedding was a good raw material for AD.After pretreatment,the concentration of volatile fatty acids(VFAs)in the group of hydrothermal pretreatments with ammonia(HPA)was higher than that in the HP group at the same pretreatment temperature and time.The optimal pretreatment condition was achieved with an HPA of 50℃ holding for 72 h.At the optimal condition,the highest concentration of VFAs was 1.58-10.85 times higher than that of the other pretreated groups.The highest hemicellulose and lignin removal rates were 58.07%and 10.32%,respectively.The highest methane yield was 163.0 ml(g· VS)^(-1),which was 48.9%higher than that of the untreated group.The VFAs,pH,and reducing sugars showed positive relationships with the methane yield.Therefore,HP at low temperature can enhance the AD performance of spent cow bedding.

Response analysis of shale bedding structure to ultrasonic characteristics and its application

Based on the wave theory, different bedding structure models for shales in Lower Silurian Longmaxi Formation of southeastern Chongqing area were established, numerical simulations of responses of different bedding structures of shale to ultrasonic wave were carried out by using the second order in time and fourth order in space grid finite difference method, based on the grey system theory, sensitive factors of acoustic parameters of bedding structure were selected, and the dynamic mechanical parameter model of bedded shale was established, which was verified by the ultrasonic transmission experiment results on core down Well ZY1 and YY1 and the logging data of Well ZY2. The results show that:(1) The correlation coefficient between analog and experimental waveforms is greater than 80%, indicating that the numerical simulation method can effectively simulate ultrasonic transmission experiment.(2) Acoustic velocity is a conventional sensitive factor used to characterize shale bedding structure, whereas the attenuation coefficient is sensitive to the change of bedding thickness, with correlation coefficient of 0.89, therefore, using the normalized results of attenuation coefficient to comprehensively describe the shale bedding can make the results more accurate.(3) The correlation between the dynamic and static parameters calculated by the model is better than that of the traditional model; and the predicted values of rock mechanics obtained by using the model and logging data inversion are in good agreement with the experimental values. The research results lay the foundation for further accurate prediction of rock mechanic parameters using sonic logging data.

Assessing the microbiota of recycled bedding sand on a Wisconsin dairy farm

Background:Sand is often considered the preferred bedding material for dairy cows as it is thought to have lower bacterial counts than organic bedding materials and cows bedded on sand experience fewer cases of lameness and disease.Sand can also be efficiently recycled and reused,making it cost-effective.However,some studies have suggested that the residual organic material present in recycled sand can serve as a reservoir for commensal and pathogenic bacteria,although no studies have yet characterized the total bacterial community composition.Here we sought to characterize the bacterial community composition of a Wisconsin dairy farm bedding sand recycling system and its dynamics across several stages of the recycling process during both summer and winter using 16S rRNA gene amplicon sequencing.Results:Bacterial community compositions of the sand recycling system differed by both seasons and stage.Summer samples had higher richness and distinct community compositions,relative to winter samples.In both summer and winter samples,the diversity of recycled sand decreased with time drying in the recycling room.Compositionally,summer sand 14 d post-recycling was enriched in operational taxonomic units(OTUs)belonging to the genera Acinetobacter and Pseudomonas,relative to freshly washed sand and sand from cow pens.In contrast,no OTUs were found to be enriched in winter sand.The sand recycling system contained an overall core microbiota of 141 OTUs representing 68.45%±10.33%SD of the total bacterial relative abundance at each sampled stage.The 4 most abundant genera in this core microbiota included Acinetobacter,Psychrobacter,Corynebacterium,and Pseudomonas.Acinetobacter was present in greater abundance in summer samples,whereas Psychrobacter and Corynebacterium had higher relative abundances in winter samples.Pseudomonas had consistent relative abundances across both seasons.Conclusions:These findings highlight the potential of recycled bedding sand as a bacterial reservoir that warrants further study.

Calculation of reverse-fault-related parameters using topographic profiles and fault bedding

Fault-related parameters are critical for studying tectonic evolution, deformation character- istics, active tectonism, and seismic hazards. A new method of calculating reverse-fault- related parameters has been developed, which uses systematic analysis of the geometrical characteristics of normal and reverse scarps of reverse faults together with measurements of topographic profiles and fault bedding. The results show that the most suitable method of calculating fault parameters heavily relies on the specific type of fault scarp. For a reverse scarp, the size of the vertical displacement （VD） of the fault, the vertical separation （VS） of the hanging wall and the footwall, and the fault scarp height （SH）how the relationship VD ≥VS ≥ SH; conversely, for normal scarps, VD ≤ VS ≤ SH. The theoretical equations were used to study fault deformation in the Southwest Tianshan Mountain foreland basin. The results showed that, for every fault, VD ≥ VS ≥SH, which is consistent with our predicted relationship. This finding demonstrates that this method is suitable to explore structural information of reverse faults. In the study area, the vertical displacement is 1.4 times the horizontal displacement, suggesting that fiexural-slip faults may play an important role in transferring local deformation from horizontal shortening to vertical uplift. Therefore, one of the most important steps in correct calculation of reverse-fault-related parameters is selection of the proper equations by identifying the specific type of fault scarp and the corresponding calculation method.