Rock mass classification systems are the very important part for underground projects and rock mass rating(RMR) is one of the most commonly applied classification systems in numerous civil and mining projects. The typ...Rock mass classification systems are the very important part for underground projects and rock mass rating(RMR) is one of the most commonly applied classification systems in numerous civil and mining projects. The type of rock mass consisting of an interbedding of strong and weak layers poses difficulties and uncertainties for determining the RMR. For this, the present paper uses the concept of rock bolt supporting factor(RSF) for modification of RMR system to be used in such rock mass types. The proposed method also demonstrates the importance of rock bolting practice in such rock masses. The geological parameters of the Shemshak Formation of the Alborz Tunnel in Iran are used as case examples for development of the theoretical approach.展开更多
The significant difference between the mechanical properties of soft rock and hard rock results in the complexity of the failure mode of the anti-dip layered slope with soft and hard rock interbedding.In order to reve...The significant difference between the mechanical properties of soft rock and hard rock results in the complexity of the failure mode of the anti-dip layered slope with soft and hard rock interbedding.In order to reveal the landslide mechanism,taking the north slope of Fushun West Open-pit Mine as an example,this paper analyzed the failure mechanism of different landslides with monitoring and field surveys,and simulated the evolution of landslides.The study indicated that when the green mudstone(hard rock)of the anti-dip slope contains siltized intercalations(soft rock),the existence of weak layers not only aggravates the toppling deformation of anti-dip layered slope with high dip,but also causes the shear failure of anti-dip layered slope with stable low dip.The shear failure including subsidence induced sliding and wedge failure mainly exists in the unloading zone of the slope.Its failure depth and failure time were far less than that of toppling failure.In terms of the development characteristics of deformation,toppling deformation has the long-term and progressive characteristics,but shear failure deformation has the abrupt and transient characteristics.This study has deepened the understanding of such slope landslide mechanism,and can provide reference for similar engineering.展开更多
Dongyuemiao Member shale in the Sichuan Basin,China,is characterized by organic-rich shale intervals with different types of interbeds and accumulation modes.The aim of this study is to elucidate the impact of paleoen...Dongyuemiao Member shale in the Sichuan Basin,China,is characterized by organic-rich shale intervals with different types of interbeds and accumulation modes.The aim of this study is to elucidate the impact of paleoenvironmental indicators on interbed development.With this aim in mind,we established an interbed classification scheme and quantified the development of different types of interbeds and their frequencies.We categorized the shale interbeds into three types based on interbed type:silt interbeds(SIs),shell fragment interbeds(SFIs),and shell skeleton interbeds(SSIs).The SIs,SFIs,and SSIs are respectively the products of extrabasinal low-density turbidity currents,intrabasinal debris flow,and intrabasinal low-density turbidity currents.We propose that variations in paleoenvironmental conditions primarily influenced the types of interbeds that developed but had minimal impact on the frequency of their development.Models depicting the interbed development within the 1st Submember of Dongyuemiao Member indicate that during the early Dongyuemiao depositional period,under conditions of relatively aridity,weak weathering,high terrigenous input,and strong hydrodynamic activity,SSIs were well developed.In the middle depositional period,as the climate gradually transitioned to more humid conditions,and the weathering intensity and amount of terrestrial input increased,the development of SIs and SFIs significantly increased.During the late depositional period,with a continuous decrease in terrestrial inputs and sedimentation rates,the development of SIs decreased while that of SSIs increased.展开更多
China's shale oil and gas resources are widely distributed in shale-sandstone interbedded reservoirs,whose complex lithology and strong heterogeneity pose significant challenges to hydraulic fracturing design.To a...China's shale oil and gas resources are widely distributed in shale-sandstone interbedded reservoirs,whose complex lithology and strong heterogeneity pose significant challenges to hydraulic fracturing design.To address issues such as the difficulty in controlling fracture height and the challenge of forming an effective fracture network,this study utilizes synthetic rock samples that can represent the characteristics of interbedded reservoirs and investigates the initiation and propagation of hydraulic fractures under different viscosity,injection rate,and construction scheme.By combining real-time monitoring of injection pressure with acoustic emission,the temporal and spatial evolution characteristics of hydraulic fractures as well as the mechanisms of their vertical and horizontal extension are revealed.The results indicate that a higher fracturing fluid viscosity is essential for ensuring the vertical cross-layer propagation of hydraulic fractures,while a lower fluid viscosity facilitates the activation of weak interlayer surfaces,promoting sufficient horizontal propagation along these planes and forming branched fractures.Although a higher injection rate enhances the vertical cross-layer propagation of hydraulic fractures,it also causes greater diversion of the main fracture plane,resulting in simpler fracture morphology and limiting the stimulation effect.Additionally,an alternating injection of high and low viscosity fracturing fluids allows hydraulic fractures to both break through weak interlayer surfaces and achieve uniform horizontal propagation,resulting in a more complex fracture morphology.The findings are expected to provide a scientific basis and practical guidance for optimizing hydraulic fracturing designs in interbedded reservoir conditions.展开更多
In the frost-thaw region,prolonged freezethaw weathering can induce fracture and weaken rock masses,threatening engineering stability.While interbedded rock masses are common in such projects,their failure mechanisms ...In the frost-thaw region,prolonged freezethaw weathering can induce fracture and weaken rock masses,threatening engineering stability.While interbedded rock masses are common in such projects,their failure mechanisms remain insufficiently investigated in freezing and thawing environments.Therefore,this research establishes a particle flow code(PFC2D)model of interlayered rock masses with particular emphasis on the role of thickness variation.The analysis focuses on displacement,crack evolution,contact forces,and uniaxial compressive strength.The findings indicate that:(i)Completing 8 freeze-thaw cycles significantly increases displacement and contact forces,with crack growth accelerating markedly after 16 cycles.As the soft rock layer thickness ratio(Hs/H)increases,the peak contact force decreases by 18.3%,while the number of cracks rises by 48%.Once Hs/H exceeded 0.5,the rate of crack development decelerates.This reflects progressive bond degradation and damage accumulation:microscopic bonds weaken and rupture to form microcracks.Increased soft rock thickness promotes micro-damage accumulation,altering contact forces and intensifying degradation.(ii)Compressive cracks predominantly initiate in soft rock(limestone).After 20 cycles,cracking extends into the hard rock regions.As the Hs/H rises,compressive cracks first increase and then decline,with an overall reduction of 10.8%,while the compressive contact force exhibits a consistent downward trend.This trend indicates that freeze-thaw cycles cause severe microscopic degradation in soft rock,weakening its macroscopic strength and influencing compressive crack development.Increased soft rock thickness alters the stress state,thereby modifying crack propagation.(iii)Uniaxial compressive strength experiences a marked deterioration after 15 freeze-thaw cycles.It follows an exponential decay with increasing Hs/H,culminating in a total strength reduction of 76.9%.This demonstrates that freeze-thaw-induced microscopic damage deteriorates interparticle cohesion,reducing rock mass strength.A higher Hs/H ratio accelerates microscopic damage in the soft rock,causing cohesion to decay nonlinearly and macroscopic strength to drop exponentially.These results provide a theoretical basis for assessing the deformation and failure behaviors of rock masses under cyclic freeze-thaw action.展开更多
The rock masses in the hydro-fluctuation zone of reservoir banks sustain wettingdrying cycles(WDC),thereby affecting the stability of the reservoir bank slope.In this paper,rock masses with argillaceous siltstone and ...The rock masses in the hydro-fluctuation zone of reservoir banks sustain wettingdrying cycles(WDC),thereby affecting the stability of the reservoir bank slope.In this paper,rock masses with argillaceous siltstone and silty mudstone interbedded in Badong Formation were taken as the research object to investigate the variation of strength parameters of soft and hard interbedded rock masses with WDC and dip angle through laboratory experiments and numerical experiments.Some attempts were made to reveal the mechanical properties deterioration mechanism of interbedded rock masses by quantitatively analyzing the contribution of strength parameters deterioration of hard rocks,soft rocks,and bedding planes to the strength parameters deterioration of rock masses.The results indicate that the logarithmic function could be used to describe the deterioration of each strength parameter of both argillaceous siltstone and silty mudstone and bedding plane with the number of WDC.The strength parameters of interbedded rock masses decrease as the number of WDC increases,with the largest decrease after the first cycle and then slowing down in the later cycles.The strength parameters initially decrease and then increase as the dip angles increase.The impact of deteriorated strength parameters of bedding planes and rocks on the deterioration of strength parameters of interbedded rock masses differs significantly with the dip angle,which can be divided into four typical ranges of different controlling factors.展开更多
The deformation and failure of mining slopes in layered rocks predominantly result from shear landslides.However,the instability process of the Pusa rock avalanche in Guizhou,China,revealed a unique damage phenomenon:...The deformation and failure of mining slopes in layered rocks predominantly result from shear landslides.However,the instability process of the Pusa rock avalanche in Guizhou,China,revealed a unique damage phenomenon:prominent breaking and toppling of rock blocks occurred in the central section of the mountain,with a lack of commonly observed shear landslide features.This paper aims to investigate the underlying reasons behind this distinctive damage pattern.The study employs various methods including geological survey,UAV aerial survey,physical simulation,and discrete element numerical simulation.The findings indicate that the geological conditions,characterized by a hard upper layer and a soft lower layer along with underground mining activities,play a significant role in triggering the landslide.Furthermore,the presence of a columnar structured rock mass emerges as the primary factor influencing the instability of the Pusa rock avalanche.To elucidate the mining failure mechanism of the rock mass with vertical joints,we propose a"subsidence-buckling"failure model.Following the subsidence and collapse of the roof rock mass in the goaf,the columnar rock mass in the upper and middle portions of the slope undergoes deflection and deformation,forming a three-hinged arch structure.This structural configuration converts the pressure exerted by the overlying rock mass into both vertical pressure and lateral thrust.Under the influence of external loads,the slope experiences buckling failure,ultimately leading to instability upon fragmentation.By shedding light on these findings,this study contributes to a better understanding of the spatiotemporal evolution of mining slope fractures and their impact on slope stability.展开更多
We present the first successful application of three-component seismic data to thin interbedded reservoir characterization in the Daqing placanticline of the LMD oilfield. The oilfield has reached the final high water...We present the first successful application of three-component seismic data to thin interbedded reservoir characterization in the Daqing placanticline of the LMD oilfield. The oilfield has reached the final high water cut stage and the principal problem is how to recognize the boundaries of sand layers that are thicker than 2 m. Conventional interpretation of single PP-wave seismic data results in multiple solutions, whereas the introduction of PS-wave enhances the reliability of interpretation. We analyze the gas reservoir characteristics by joint PP- and PS-waves, and use the amplitude and frequency decomposition attributes to delineate the gas reservoir boundaries because of the minimal effect of fl uids on S-wave. We perform joint inversion of PP- and PS-waves to obtain V P/V S, λρ, and μρ and map the lithology changes by using density, λρ, and μρ. The 3D–3C attribute λρ slices describe the sand layers distribution, while considering the well log data, and point to favorable region for tapping the remaining oil.展开更多
Whether hydraulic fractures could connect multiple gas zones in the vertical plane is the key to fracturing treatment to jointly exploit coalbed methane and tight sandstone gas through integrative hydraulic fracturing...Whether hydraulic fractures could connect multiple gas zones in the vertical plane is the key to fracturing treatment to jointly exploit coalbed methane and tight sandstone gas through integrative hydraulic fracturing in tight sandstone–coal interbedded formations. Laboratory true triaxial hydraulic fracturing experiments were conducted on layered specimens with di erent combination types of natural sandstone and coal to simulate the propagation behavior of hydraulic fractures. The effects of the fracture initiation position, fracturing fluid viscosity and injection rate were discussed. The results showed that di erent fracture morphologies could be found. When initiating from coal seams, three patterns of fracture initiation and propagation were obtained:(1) The main hydraulic fracture initiated and propagated along the natural fractures and then diverged due to the effects of in situ stress and formed secondary fractures.(2) The hydraulic fracture initiated and propagated in the direction of the maximum horizontal stress.(3) Multiple fractures initiated and propagated at the same time. With the same fracturing fluid viscosity and injection rate, the hydraulic fractures initiating in sandstones had greater chances than those in coal seams to penetrate interfaces and enter neighboring layers. Excessively small or large fracturing fluid viscosity and injection rate would do harm to the vertical extension height of the induced fracture and improvement of the stimulated reservoir volume. Compared with operation parameters(fracturing fluid viscosity and injection rate), the natural weak planes in coals were considered to be the key factor that a ected the fracture propagation path. The experimental results would make some contributions to the development of tight sandstone–coal interbedded reservoirs.展开更多
The distribution and intensity of tectonic fractures within geologic units are important to hydrocarbon exploration and development. Taken the Upper Triassic Yanchang Formation interbedded sandstone-mudstone in the Or...The distribution and intensity of tectonic fractures within geologic units are important to hydrocarbon exploration and development. Taken the Upper Triassic Yanchang Formation interbedded sandstone-mudstone in the Ordos Basin as an example, this study used the finite element method（FEM） based on geomechanical models to study the development of tectonic fractures. The results show that the sandstones tend to generate tectonic fractures more easily than mudstones with the same layer thickness, and the highest degree of tectonic fractures will be developed when the sandstone-mudstone thickness ratio is about 5.0. A possible explanation is proposed for the tectonic fracture development based on two important factors of rock brittleness and mechanical layer thickness. Generally, larger rock brittleness and thinner layer thickness will generate more tectonic fractures. In interbedded sandstone-mudstone formations, the rock brittleness increases with the increasing mechanical layer thickness, hence, these two factors will achieve a balance for the development of tectonic fractures when the sandstone-mudstone thickness ratio reaches a specific value, and the development degree of tectonic fractures is the highest at this value.展开更多
Water-rock interaction and groundwater mixing are important phenomena in understanding hydrogeological systems and the stability of rock slopes especially those consisting largely of moderately watersoluble minerals l...Water-rock interaction and groundwater mixing are important phenomena in understanding hydrogeological systems and the stability of rock slopes especially those consisting largely of moderately watersoluble minerals like calcite. In this study, the hydrogeological and geochemical evolutions of groundwater in a limestone quarry composed of three strata: limestone layer(covering), interbedded layer under the covering layer, and slaty greenstone layer(basement) were investigated. Water-rock interaction in the open-pit limestone quarry was evaluated using PHREEQC, while hierarchical cluster analysis(HCA)and principal component analysis(PCA) were used to classify and identify water sources responsible for possible groundwater mixing within rock layers. In addition, Geochemist's Workbench was applied to estimate the mixing fractions to clarify sensitive zones that may affect rock slope stability. The results showed that the changes in Ca2+and HCO3àconcentrations of several groundwater samples along the interbedded layer could be attributed to mixing groundwater from the limestone layer and that from slaty greenstone layer. Based on the HCA and PCA results, groundwaters were classified into several types depending on their origin:(1) groundwater from the limestone layer(LO),(2) mixed groundwater flowing along the interbedded layer(e.g., groundwater samples L-7, L-11, S-3 and S-4), and(3) groundwater originating from the slaty greenstone layer(SO). The mixing fractions of 41% LO: 59% SO, 64% LO: 36% SO, 43%LO: 57% SOand 25% LO: 75% SOon the normal days corresponded to groundwaters L-7, L-11, S-3 and S-4,respectively, while the mixing fractions of groundwaters L-7 and L-11(61% LO: 39% SOand 93% LO: 7% SO,respectively) on rainy days became the majority of groundwater originating from the limestone layer.These indicate that groundwater along the interbedded layer significantly affected the stability of rock slopes by enlarging multi-breaking zones in the layer through calcite dissolution and inducing high water pressure, tension cracks and potential sliding plane along this layer particularly during intense rainfall episodes.展开更多
Due to the effects of seismic wave field interference, the reflection events generated from interbedded and superposed sand and shale strata no longer have an explicit corresponding relationship with the geological in...Due to the effects of seismic wave field interference, the reflection events generated from interbedded and superposed sand and shale strata no longer have an explicit corresponding relationship with the geological interface. The absorption of the near-surface layer decreases the resolution of the seismic wavelet, intensifies the interference of seismic reflections from different sand bodies, and makes seismic data interpretation of thin interbedded strata more complex and difficult. In order to concretely investigate and analyze the effects of the near-surface absorption on seismic reflection characteristics of interbedded strata, and to make clear the ability of current technologies to compensate the near-surface absorption, a geological model of continental interbedded strata with near-surface absorption was designed, and the prestack seismic wave field was numerically simulated with wave equations. Then, the simulated wave field was processed by the prestack time migration, the effects of near-surface absorption on prestack and poststack reflection characteristics were analyzed, and the near-surface absorption was compensated for by inverse Q-filtering. The model test shows that: (1) the reliability of prediction and delineation of a continental reservoir with AVO inversion is degraded due to the lateral variation of the near-surface structure; (2) the corresponding relationships between seismic reflection events and geological interfaces are further weakened as a result of near-surface absorption; and (3) the current technology of absorption compensation probably results in false geological structure and anomaly. Based on the model experiment, the real seismic data of the Dagang Oil Field were analyzed and processed. The seismic reflection characteristics of continental interbedded strata were improved, and the reliability of geological interpretation from seismic data was enhanced.展开更多
The occurrence of interbeds in thick oil formations is one of the main reasons that cause the difference of remaining oil distribution. A quantitative method for predicting interbeds was proposed and the sedimentary o...The occurrence of interbeds in thick oil formations is one of the main reasons that cause the difference of remaining oil distribution. A quantitative method for predicting interbeds was proposed and the sedimentary origin and division criterion were demonstrated. The distribution of interbeds in different types of sedimentary sand bodies were predicted and analyzed by combining the theory of sedimentology and reservoir bed architectural-element analysis. The interbeds in a single well were recognized from high resolution well logs, and inter-well interbeds were predicted by using the methods of cyclothem correlation, physical properties trtmcation, and conditional simulation. Finally a 3-D model of interbed was built. Application to the Gudao Oilfield was successful.展开更多
The combination patterns and depositional characteristics of the carbonate banks are investigated based on outcrop sections, thin sections, and carbon isotopes of Ordovician in the western Tarim Basin, China. Four car...The combination patterns and depositional characteristics of the carbonate banks are investigated based on outcrop sections, thin sections, and carbon isotopes of Ordovician in the western Tarim Basin, China. Four carbonate bank combination patterns are deposited in the Ordovician, western Tarim Basin, including： Reef-Bank Complex （RBC）, Algae-Reef-Bank Interbed （ARBI）, Thick-Layer Cake Aggradation Bank （TLCAB）, and Thin-Layer Cake Retrogradation Bank （TLCRB）. All combination patterns show clear periods vertically. The RBC is mainly composed of reefs and bioclastic banks, and the dimension of the RBC depends on the scale of the reefs. Bioclastic banks deposits surround the reefs. The range of the ARBI is determined by the scale of algae-reefs, algae peloid dolomite microfacies and algal dolomite microfacies deposit alternating vertically. TLCAB and TLCRB are deposited as layer-cakes stacking in cycles and extending widely with cross bedding developed. The grains of TLCAB and TLCRB are diverse and multi-source. With the impacting of relative sea level change, biological development and geomorphology, the ARBI, TLCAB or TLCRB, RBC are successively developed from the Lower Ordovician Penglaiba Formation to the Middle Ordovician Yijianfang Formation. The depositional environment analysis of Ordovician indicates that the RBC and ARBI can form effective oil and gas reservoirs, and the TLCAB and TLCRB have the potential to form the huge scale oil and gas reservoirs and to be the crucial targets of exploration for the Ordovician carbonate banks in the future.展开更多
Three-dimensional(3D)printing technology is increasingly used in experimental research of geotechnical engineering.Compared to other materials,3D layer-by-layer printing specimens are extremely similar to the inherent...Three-dimensional(3D)printing technology is increasingly used in experimental research of geotechnical engineering.Compared to other materials,3D layer-by-layer printing specimens are extremely similar to the inherent properties of natural layered rock masses.In this paper,soft-hard interbedded rock masses with different dip angles were prepared based on 3D printing(3DP)sand core technology.Uniaxial compression creep tests were conducted to investigate its anisotropic creep behavior based on digital imaging correlation(DIC)technology.The results show that the anisotropic creep behavior of the 3DP soft-hard interbedded rock mass is mainly affected by the dip angles of the weak interlayer when the stress is at low levels.As the stress level increases,the effect of creep stress on its creep anisotropy increases significantly,and the dip angle is no longer the main factor.The minimum value of the long-term strength and creep failure strength always appears in the weak interlayer within 30°–60°,which explains why the failure of the layered rock mass is controlled by the weak interlayer and generally emerges at 45°.The tests results are verified by comparing with theoretical and other published studies.The feasibility of the 3DP soft-hard interbedded rock mass provides broad prospects and application values for 3DP technology in future experimental research.展开更多
This paper discusses the effect of influencing factors on the distribution of incremental oil displaced by a polymer flood （extra-displaced oil） using numerical reservoir simulation. These factors include the locati...This paper discusses the effect of influencing factors on the distribution of incremental oil displaced by a polymer flood （extra-displaced oil） using numerical reservoir simulation. These factors include the location, area and permeability of a thin low-permeability interbed, and the perforation location relative to the interbed. Simulation results show the locations from where the incremental oil was displaced by the polymer solution. The interbed position from the oil formation top affects the location of extra-displaced oil. The interbed area has a slight influence on the whole shape of extra-displaced oil. Larger interbed area leads to higher partition extent of extra-displaced oil. Higher vertical permeability of interbeds contributes to worse partition extent of extra-displaced oil and the partition effect disappears if the ratio of vertical to horizontal permeability is more than 0.05. The perforation location relative to the interbed affects polymer displacement efficiency, and also has a significant effect on the distribution of extra-displaced oil in polymer flooding.展开更多
Water-and-mud inrush disasters have become a major challenge in underground engineering for the construction of tunnels in sandstone and slate interbedded Presinian strata.Disaster prediction and prevention rely in pa...Water-and-mud inrush disasters have become a major challenge in underground engineering for the construction of tunnels in sandstone and slate interbedded Presinian strata.Disaster prediction and prevention rely in part on realistic modeling and observation of the disaster process,as well as the identification and examination of the underlying mechanisms.Based on the geological conditions and the historical records of the Xinping Tunnel on the China–Laos Railway,an engineering geological model of the water-and-mud inrush was established.A physical model test that accurately reproduced water-and-mud inrush during tunnel excavation in sandstone and slate interbedded strata was also carried out.Then,testing was conducted that examined the stress and strain,seepage pressure,and high-leakage flow of the surrounding rock.The results indicated that the water-and-mud inrush proceeded through three stages:seepage stage,high-leakage flow stage,and attenuation stage.In essence,the disaster was a catastrophic process,during which the water-resistant stratum was reduced to a critical safety thickness,a water-inrush channel formed,and the water-resistant stratum gradually failed under the influence of excavation unloading and in situ stress–seepage coupling.Parameters such as the stress and strain,seepage pressure,and flow of the surrounding rock had evident stage-related features during water-and-mud inrush,and their variation indicated the formation,development,and evolution of the disaster.As the tunnel face advanced,the trend of the stress–strain curve of the surrounding rock shifted from sluggish to rapid in its speed of increase.The characteristics of strain energy density revealed the erosion and weakening effect of groundwater on the surrounding rock.The seepage pressure and the thickness of the water-resistant stratum had a positive linear relationship,and the flow and thickness a negative linear relationship.There was a pivotal point at which the seepage pressure changed from high to low and the flow shifted from low to high.The thickness of the water-resistant stratum corresponding to the pivotal point was deemed the critical safety thickness.展开更多
Hydrocarbon-producing lacustrine basins are widely developed in the world, and China has a large number of lacustrine basins that have developed since the early Permian. The organic-rich shale-dominated heterogeneous ...Hydrocarbon-producing lacustrine basins are widely developed in the world, and China has a large number of lacustrine basins that have developed since the early Permian. The organic-rich shale-dominated heterogeneous source rock intervals in Chinese lacustrine basins generally contain frequent thin interbeds of stratigraphically associated sandstone, siltstone, marl, dolomite, and limestone. The concept of ‘‘Hybrid Plays＇ ＇ as put forth in this article recognizes this pattern of alternating organicrich shale and organic-lean interbeds and existence of mixed unconventional and conventional plays. Hybrid Plays in lacustrine source rock intervals present a unique closed petroleum system hosting continuous hydrocarbons.The interbedded organic-lean siliciclastic and/or carbonateplays are efficiently charged with hydrocarbons via short migration pathways from the adjacent organic-rich shale that is often also a self-sourced play. We assert ‘‘Hybrid Plays＇ ＇ provide the most realistic exploration model for targeting multiple-stacked and genetically related very tight shale, tight and conventional plays together in the entire source rock interval rather than individual plays only. The Hybrid Play model has been proven and works for a wide variety of lacustrine rift, sag and foreland basins in China.展开更多
Block-flexure toppling failure is frequently encountered in interbedded anti-inclined rock(IAR)slopes,and seriously threatens the construction of hydropower infrastructure.In this study,we first investigated the Lean ...Block-flexure toppling failure is frequently encountered in interbedded anti-inclined rock(IAR)slopes,and seriously threatens the construction of hydropower infrastructure.In this study,we first investigated the Lean Reservoir area’s geological setting and the Linda landslide’s characteristics.Then,uniform design and random design were used to design 110 training datasets and 31 testing datasets,respectively.Afterwards,the toppling response was obtained by using the discrete element code.Finally,support vector regression was used to obtain the influence weights of 21 impact factors.The results show that the influence weight of the slope angle and rock formation dip angle on the toppling deformation among tertiary impact factors is 25.96%and 17.28%,respectively,which are much greater than the other 19 impact factors within the research range.For the primary impact factors,the influence weight is sorted from large to small as slope geometry parameters,joints parameters,and rock mechanics parameters.Joints parameters,especially the geometric parameters,cannot be ignored when evaluating the stability of IAR slopes.Through numerical simulation,it was qualitatively determined that failure surfaces of slopes were controlled by cross joints and that the rocks in the slope toe play a role in preventing slope deformation.展开更多
Soft and hard interbedded bedding rock slopes,which is prone to failure,are widely distributed in the Three Gorges Reservoir,China.Limit equilibrium method(LEM)is commonly used to analyze the stability of bedding rock...Soft and hard interbedded bedding rock slopes,which is prone to failure,are widely distributed in the Three Gorges Reservoir,China.Limit equilibrium method(LEM)is commonly used to analyze the stability of bedding rock slopes that have a single failure plane.However,this method cannot accurately estimate the stability of soft and hard interbedded bedding reservoir slopes because the strength parameters of a soft and hard interbedded rock mass vary spatially along the bedding plane and deteriorate with time due to periodic fluctuations of reservoir level.A modified LEM is proposed to evaluate the stability evolution of soft and hard interbedded bedding reservoir slopes considering the spatial variation and temporal deterioration of shear strength parameters of rock masses and bedding planes.In the modified LEM,the S-curve model is used to define the spatial variation of shear strength parameters,and general deterioration equations of shear strength parameters with the increasing number of wettingdrying cycles(WDC)are proposed to describe the temporal deterioration.Also,this method is applied to evaluate the stability evolution of a soft and hard interbedded bedding reservoir slope,located at the Three Gorges Reservoir.The results show that neglecting the spatial variation and temporal deterioration of shear strength parameters may overestimate slope stability.Finally,the modified LEM provides useful guidance to reasonably evaluate the long-term stability of soft and hard interbedded bedding reservoir slopes in reservoir area.展开更多
文摘Rock mass classification systems are the very important part for underground projects and rock mass rating(RMR) is one of the most commonly applied classification systems in numerous civil and mining projects. The type of rock mass consisting of an interbedding of strong and weak layers poses difficulties and uncertainties for determining the RMR. For this, the present paper uses the concept of rock bolt supporting factor(RSF) for modification of RMR system to be used in such rock mass types. The proposed method also demonstrates the importance of rock bolting practice in such rock masses. The geological parameters of the Shemshak Formation of the Alborz Tunnel in Iran are used as case examples for development of the theoretical approach.
基金supported by the National Key Research and Development Program of China(Nos.2022YFC2903902 and 2022YFC2903903)the National Natural Science Foundation of China(Nos.U1903216 and 52174070).
文摘The significant difference between the mechanical properties of soft rock and hard rock results in the complexity of the failure mode of the anti-dip layered slope with soft and hard rock interbedding.In order to reveal the landslide mechanism,taking the north slope of Fushun West Open-pit Mine as an example,this paper analyzed the failure mechanism of different landslides with monitoring and field surveys,and simulated the evolution of landslides.The study indicated that when the green mudstone(hard rock)of the anti-dip slope contains siltized intercalations(soft rock),the existence of weak layers not only aggravates the toppling deformation of anti-dip layered slope with high dip,but also causes the shear failure of anti-dip layered slope with stable low dip.The shear failure including subsidence induced sliding and wedge failure mainly exists in the unloading zone of the slope.Its failure depth and failure time were far less than that of toppling failure.In terms of the development characteristics of deformation,toppling deformation has the long-term and progressive characteristics,but shear failure deformation has the abrupt and transient characteristics.This study has deepened the understanding of such slope landslide mechanism,and can provide reference for similar engineering.
基金sponsored by the National Natural Science Foundation of China,China(No.42272171)National Science and Technology Major Project of China,China(No.2017ZX05036).
文摘Dongyuemiao Member shale in the Sichuan Basin,China,is characterized by organic-rich shale intervals with different types of interbeds and accumulation modes.The aim of this study is to elucidate the impact of paleoenvironmental indicators on interbed development.With this aim in mind,we established an interbed classification scheme and quantified the development of different types of interbeds and their frequencies.We categorized the shale interbeds into three types based on interbed type:silt interbeds(SIs),shell fragment interbeds(SFIs),and shell skeleton interbeds(SSIs).The SIs,SFIs,and SSIs are respectively the products of extrabasinal low-density turbidity currents,intrabasinal debris flow,and intrabasinal low-density turbidity currents.We propose that variations in paleoenvironmental conditions primarily influenced the types of interbeds that developed but had minimal impact on the frequency of their development.Models depicting the interbed development within the 1st Submember of Dongyuemiao Member indicate that during the early Dongyuemiao depositional period,under conditions of relatively aridity,weak weathering,high terrigenous input,and strong hydrodynamic activity,SSIs were well developed.In the middle depositional period,as the climate gradually transitioned to more humid conditions,and the weathering intensity and amount of terrestrial input increased,the development of SIs and SFIs significantly increased.During the late depositional period,with a continuous decrease in terrestrial inputs and sedimentation rates,the development of SIs decreased while that of SSIs increased.
基金supported by the National Key Research and Development Program of China(Grant Nos.2023YFF0614102 and 2023YFE0110900)the National Natural Science Foundation of China(Grant Nos.52374004,52204005,and 52304003)the Natural Science Foundation of Sichuan Province(Grant Nos.2024NSFSC0961 and 2023NSFSC0940).
文摘China's shale oil and gas resources are widely distributed in shale-sandstone interbedded reservoirs,whose complex lithology and strong heterogeneity pose significant challenges to hydraulic fracturing design.To address issues such as the difficulty in controlling fracture height and the challenge of forming an effective fracture network,this study utilizes synthetic rock samples that can represent the characteristics of interbedded reservoirs and investigates the initiation and propagation of hydraulic fractures under different viscosity,injection rate,and construction scheme.By combining real-time monitoring of injection pressure with acoustic emission,the temporal and spatial evolution characteristics of hydraulic fractures as well as the mechanisms of their vertical and horizontal extension are revealed.The results indicate that a higher fracturing fluid viscosity is essential for ensuring the vertical cross-layer propagation of hydraulic fractures,while a lower fluid viscosity facilitates the activation of weak interlayer surfaces,promoting sufficient horizontal propagation along these planes and forming branched fractures.Although a higher injection rate enhances the vertical cross-layer propagation of hydraulic fractures,it also causes greater diversion of the main fracture plane,resulting in simpler fracture morphology and limiting the stimulation effect.Additionally,an alternating injection of high and low viscosity fracturing fluids allows hydraulic fractures to both break through weak interlayer surfaces and achieve uniform horizontal propagation,resulting in a more complex fracture morphology.The findings are expected to provide a scientific basis and practical guidance for optimizing hydraulic fracturing designs in interbedded reservoir conditions.
基金supported by the National Natural Science Foundation of China(Grant Nos.52379100 and 42462030)。
文摘In the frost-thaw region,prolonged freezethaw weathering can induce fracture and weaken rock masses,threatening engineering stability.While interbedded rock masses are common in such projects,their failure mechanisms remain insufficiently investigated in freezing and thawing environments.Therefore,this research establishes a particle flow code(PFC2D)model of interlayered rock masses with particular emphasis on the role of thickness variation.The analysis focuses on displacement,crack evolution,contact forces,and uniaxial compressive strength.The findings indicate that:(i)Completing 8 freeze-thaw cycles significantly increases displacement and contact forces,with crack growth accelerating markedly after 16 cycles.As the soft rock layer thickness ratio(Hs/H)increases,the peak contact force decreases by 18.3%,while the number of cracks rises by 48%.Once Hs/H exceeded 0.5,the rate of crack development decelerates.This reflects progressive bond degradation and damage accumulation:microscopic bonds weaken and rupture to form microcracks.Increased soft rock thickness promotes micro-damage accumulation,altering contact forces and intensifying degradation.(ii)Compressive cracks predominantly initiate in soft rock(limestone).After 20 cycles,cracking extends into the hard rock regions.As the Hs/H rises,compressive cracks first increase and then decline,with an overall reduction of 10.8%,while the compressive contact force exhibits a consistent downward trend.This trend indicates that freeze-thaw cycles cause severe microscopic degradation in soft rock,weakening its macroscopic strength and influencing compressive crack development.Increased soft rock thickness alters the stress state,thereby modifying crack propagation.(iii)Uniaxial compressive strength experiences a marked deterioration after 15 freeze-thaw cycles.It follows an exponential decay with increasing Hs/H,culminating in a total strength reduction of 76.9%.This demonstrates that freeze-thaw-induced microscopic damage deteriorates interparticle cohesion,reducing rock mass strength.A higher Hs/H ratio accelerates microscopic damage in the soft rock,causing cohesion to decay nonlinearly and macroscopic strength to drop exponentially.These results provide a theoretical basis for assessing the deformation and failure behaviors of rock masses under cyclic freeze-thaw action.
基金supported by the Chinese National Key R&D Program(No.2022YFC3080200)the Chinese National Natural Science Foundation(No.42090054)。
文摘The rock masses in the hydro-fluctuation zone of reservoir banks sustain wettingdrying cycles(WDC),thereby affecting the stability of the reservoir bank slope.In this paper,rock masses with argillaceous siltstone and silty mudstone interbedded in Badong Formation were taken as the research object to investigate the variation of strength parameters of soft and hard interbedded rock masses with WDC and dip angle through laboratory experiments and numerical experiments.Some attempts were made to reveal the mechanical properties deterioration mechanism of interbedded rock masses by quantitatively analyzing the contribution of strength parameters deterioration of hard rocks,soft rocks,and bedding planes to the strength parameters deterioration of rock masses.The results indicate that the logarithmic function could be used to describe the deterioration of each strength parameter of both argillaceous siltstone and silty mudstone and bedding plane with the number of WDC.The strength parameters of interbedded rock masses decrease as the number of WDC increases,with the largest decrease after the first cycle and then slowing down in the later cycles.The strength parameters initially decrease and then increase as the dip angles increase.The impact of deteriorated strength parameters of bedding planes and rocks on the deterioration of strength parameters of interbedded rock masses differs significantly with the dip angle,which can be divided into four typical ranges of different controlling factors.
基金funded by the State Key Laboratory of Geohazard Prevention and Geoenvironment Protection Independent Research Project(SKLGP2022Z001)National Natural Science Foundation of China(Grant No.41877273)+3 种基金Science and Technology Plan Project of Sichuan Province(Grant No.2021YJ0053)Sichuan Natural Science Foundation(Grant No.2022NSFSC1176)Innovative Research Groups of the National Natural Science Foundation of China(Grant No.41521002)POWERCHINA Science and technology project(Grant No.DJ-ZDXM-2020-03)。
文摘The deformation and failure of mining slopes in layered rocks predominantly result from shear landslides.However,the instability process of the Pusa rock avalanche in Guizhou,China,revealed a unique damage phenomenon:prominent breaking and toppling of rock blocks occurred in the central section of the mountain,with a lack of commonly observed shear landslide features.This paper aims to investigate the underlying reasons behind this distinctive damage pattern.The study employs various methods including geological survey,UAV aerial survey,physical simulation,and discrete element numerical simulation.The findings indicate that the geological conditions,characterized by a hard upper layer and a soft lower layer along with underground mining activities,play a significant role in triggering the landslide.Furthermore,the presence of a columnar structured rock mass emerges as the primary factor influencing the instability of the Pusa rock avalanche.To elucidate the mining failure mechanism of the rock mass with vertical joints,we propose a"subsidence-buckling"failure model.Following the subsidence and collapse of the roof rock mass in the goaf,the columnar rock mass in the upper and middle portions of the slope undergoes deflection and deformation,forming a three-hinged arch structure.This structural configuration converts the pressure exerted by the overlying rock mass into both vertical pressure and lateral thrust.Under the influence of external loads,the slope experiences buckling failure,ultimately leading to instability upon fragmentation.By shedding light on these findings,this study contributes to a better understanding of the spatiotemporal evolution of mining slope fractures and their impact on slope stability.
基金sponsored by the China Postdoctoral Science Foundation Projects(2014M550779)
文摘We present the first successful application of three-component seismic data to thin interbedded reservoir characterization in the Daqing placanticline of the LMD oilfield. The oilfield has reached the final high water cut stage and the principal problem is how to recognize the boundaries of sand layers that are thicker than 2 m. Conventional interpretation of single PP-wave seismic data results in multiple solutions, whereas the introduction of PS-wave enhances the reliability of interpretation. We analyze the gas reservoir characteristics by joint PP- and PS-waves, and use the amplitude and frequency decomposition attributes to delineate the gas reservoir boundaries because of the minimal effect of fl uids on S-wave. We perform joint inversion of PP- and PS-waves to obtain V P/V S, λρ, and μρ and map the lithology changes by using density, λρ, and μρ. The 3D–3C attribute λρ slices describe the sand layers distribution, while considering the well log data, and point to favorable region for tapping the remaining oil.
基金the support from the National Science and Technology Major Projects of China(Grant No.2016ZX05066)Major Program of National Natural Science Foundation of China(Grant No.51490650)PetroChina Innovation Foundation(No.2018D-5007-0307)
文摘Whether hydraulic fractures could connect multiple gas zones in the vertical plane is the key to fracturing treatment to jointly exploit coalbed methane and tight sandstone gas through integrative hydraulic fracturing in tight sandstone–coal interbedded formations. Laboratory true triaxial hydraulic fracturing experiments were conducted on layered specimens with di erent combination types of natural sandstone and coal to simulate the propagation behavior of hydraulic fractures. The effects of the fracture initiation position, fracturing fluid viscosity and injection rate were discussed. The results showed that di erent fracture morphologies could be found. When initiating from coal seams, three patterns of fracture initiation and propagation were obtained:(1) The main hydraulic fracture initiated and propagated along the natural fractures and then diverged due to the effects of in situ stress and formed secondary fractures.(2) The hydraulic fracture initiated and propagated in the direction of the maximum horizontal stress.(3) Multiple fractures initiated and propagated at the same time. With the same fracturing fluid viscosity and injection rate, the hydraulic fractures initiating in sandstones had greater chances than those in coal seams to penetrate interfaces and enter neighboring layers. Excessively small or large fracturing fluid viscosity and injection rate would do harm to the vertical extension height of the induced fracture and improvement of the stimulated reservoir volume. Compared with operation parameters(fracturing fluid viscosity and injection rate), the natural weak planes in coals were considered to be the key factor that a ected the fracture propagation path. The experimental results would make some contributions to the development of tight sandstone–coal interbedded reservoirs.
基金financially supported by the Fundamental Research Funds for the Central Universities(No.2015QNA69)the State Key Laboratory of Continental Tectonics and Dynamics(No.K201406)the PetroChina Major Science and Technology Project(No.2011E-2602)
文摘The distribution and intensity of tectonic fractures within geologic units are important to hydrocarbon exploration and development. Taken the Upper Triassic Yanchang Formation interbedded sandstone-mudstone in the Ordos Basin as an example, this study used the finite element method（FEM） based on geomechanical models to study the development of tectonic fractures. The results show that the sandstones tend to generate tectonic fractures more easily than mudstones with the same layer thickness, and the highest degree of tectonic fractures will be developed when the sandstone-mudstone thickness ratio is about 5.0. A possible explanation is proposed for the tectonic fracture development based on two important factors of rock brittleness and mechanical layer thickness. Generally, larger rock brittleness and thinner layer thickness will generate more tectonic fractures. In interbedded sandstone-mudstone formations, the rock brittleness increases with the increasing mechanical layer thickness, hence, these two factors will achieve a balance for the development of tectonic fractures when the sandstone-mudstone thickness ratio reaches a specific value, and the development degree of tectonic fractures is the highest at this value.
文摘Water-rock interaction and groundwater mixing are important phenomena in understanding hydrogeological systems and the stability of rock slopes especially those consisting largely of moderately watersoluble minerals like calcite. In this study, the hydrogeological and geochemical evolutions of groundwater in a limestone quarry composed of three strata: limestone layer(covering), interbedded layer under the covering layer, and slaty greenstone layer(basement) were investigated. Water-rock interaction in the open-pit limestone quarry was evaluated using PHREEQC, while hierarchical cluster analysis(HCA)and principal component analysis(PCA) were used to classify and identify water sources responsible for possible groundwater mixing within rock layers. In addition, Geochemist's Workbench was applied to estimate the mixing fractions to clarify sensitive zones that may affect rock slope stability. The results showed that the changes in Ca2+and HCO3àconcentrations of several groundwater samples along the interbedded layer could be attributed to mixing groundwater from the limestone layer and that from slaty greenstone layer. Based on the HCA and PCA results, groundwaters were classified into several types depending on their origin:(1) groundwater from the limestone layer(LO),(2) mixed groundwater flowing along the interbedded layer(e.g., groundwater samples L-7, L-11, S-3 and S-4), and(3) groundwater originating from the slaty greenstone layer(SO). The mixing fractions of 41% LO: 59% SO, 64% LO: 36% SO, 43%LO: 57% SOand 25% LO: 75% SOon the normal days corresponded to groundwaters L-7, L-11, S-3 and S-4,respectively, while the mixing fractions of groundwaters L-7 and L-11(61% LO: 39% SOand 93% LO: 7% SO,respectively) on rainy days became the majority of groundwater originating from the limestone layer.These indicate that groundwater along the interbedded layer significantly affected the stability of rock slopes by enlarging multi-breaking zones in the layer through calcite dissolution and inducing high water pressure, tension cracks and potential sliding plane along this layer particularly during intense rainfall episodes.
基金supported by the National 973 Key Basic Research Development Program(No. 2007CB209608)National 863 High Technology Research Development Program(No.2007AA06Z218)
文摘Due to the effects of seismic wave field interference, the reflection events generated from interbedded and superposed sand and shale strata no longer have an explicit corresponding relationship with the geological interface. The absorption of the near-surface layer decreases the resolution of the seismic wavelet, intensifies the interference of seismic reflections from different sand bodies, and makes seismic data interpretation of thin interbedded strata more complex and difficult. In order to concretely investigate and analyze the effects of the near-surface absorption on seismic reflection characteristics of interbedded strata, and to make clear the ability of current technologies to compensate the near-surface absorption, a geological model of continental interbedded strata with near-surface absorption was designed, and the prestack seismic wave field was numerically simulated with wave equations. Then, the simulated wave field was processed by the prestack time migration, the effects of near-surface absorption on prestack and poststack reflection characteristics were analyzed, and the near-surface absorption was compensated for by inverse Q-filtering. The model test shows that: (1) the reliability of prediction and delineation of a continental reservoir with AVO inversion is degraded due to the lateral variation of the near-surface structure; (2) the corresponding relationships between seismic reflection events and geological interfaces are further weakened as a result of near-surface absorption; and (3) the current technology of absorption compensation probably results in false geological structure and anomaly. Based on the model experiment, the real seismic data of the Dagang Oil Field were analyzed and processed. The seismic reflection characteristics of continental interbedded strata were improved, and the reliability of geological interpretation from seismic data was enhanced.
文摘The occurrence of interbeds in thick oil formations is one of the main reasons that cause the difference of remaining oil distribution. A quantitative method for predicting interbeds was proposed and the sedimentary origin and division criterion were demonstrated. The distribution of interbeds in different types of sedimentary sand bodies were predicted and analyzed by combining the theory of sedimentology and reservoir bed architectural-element analysis. The interbeds in a single well were recognized from high resolution well logs, and inter-well interbeds were predicted by using the methods of cyclothem correlation, physical properties trtmcation, and conditional simulation. Finally a 3-D model of interbed was built. Application to the Gudao Oilfield was successful.
基金financially supported by the National Natural Science Foundation of China grant(41102087)the Key Project of the National Science & Technology grant(2011ZX05005-002-010HZ,2011ZX05009-002)+1 种基金National Basic Research Program of China grant (2012CB214802)the Special Foundation for Doctoral Subjects in China University of Geosciences(Beijing) grant(2011PY0199)
文摘The combination patterns and depositional characteristics of the carbonate banks are investigated based on outcrop sections, thin sections, and carbon isotopes of Ordovician in the western Tarim Basin, China. Four carbonate bank combination patterns are deposited in the Ordovician, western Tarim Basin, including： Reef-Bank Complex （RBC）, Algae-Reef-Bank Interbed （ARBI）, Thick-Layer Cake Aggradation Bank （TLCAB）, and Thin-Layer Cake Retrogradation Bank （TLCRB）. All combination patterns show clear periods vertically. The RBC is mainly composed of reefs and bioclastic banks, and the dimension of the RBC depends on the scale of the reefs. Bioclastic banks deposits surround the reefs. The range of the ARBI is determined by the scale of algae-reefs, algae peloid dolomite microfacies and algal dolomite microfacies deposit alternating vertically. TLCAB and TLCRB are deposited as layer-cakes stacking in cycles and extending widely with cross bedding developed. The grains of TLCAB and TLCRB are diverse and multi-source. With the impacting of relative sea level change, biological development and geomorphology, the ARBI, TLCAB or TLCRB, RBC are successively developed from the Lower Ordovician Penglaiba Formation to the Middle Ordovician Yijianfang Formation. The depositional environment analysis of Ordovician indicates that the RBC and ARBI can form effective oil and gas reservoirs, and the TLCAB and TLCRB have the potential to form the huge scale oil and gas reservoirs and to be the crucial targets of exploration for the Ordovician carbonate banks in the future.
基金the support of the National Natural Science Foundation of China(Grant Nos.42207199,52179113,42272333)Zhejiang Postdoctoral Scientific Research Project(Grant Nos.ZJ2022155,ZJ2022156)。
文摘Three-dimensional(3D)printing technology is increasingly used in experimental research of geotechnical engineering.Compared to other materials,3D layer-by-layer printing specimens are extremely similar to the inherent properties of natural layered rock masses.In this paper,soft-hard interbedded rock masses with different dip angles were prepared based on 3D printing(3DP)sand core technology.Uniaxial compression creep tests were conducted to investigate its anisotropic creep behavior based on digital imaging correlation(DIC)technology.The results show that the anisotropic creep behavior of the 3DP soft-hard interbedded rock mass is mainly affected by the dip angles of the weak interlayer when the stress is at low levels.As the stress level increases,the effect of creep stress on its creep anisotropy increases significantly,and the dip angle is no longer the main factor.The minimum value of the long-term strength and creep failure strength always appears in the weak interlayer within 30°–60°,which explains why the failure of the layered rock mass is controlled by the weak interlayer and generally emerges at 45°.The tests results are verified by comparing with theoretical and other published studies.The feasibility of the 3DP soft-hard interbedded rock mass provides broad prospects and application values for 3DP technology in future experimental research.
基金support from the National Natural Science Foundation of China (NO.10772200,10972237)the Important National Science & Technology Specific Projects of China(No.2011ZX05011)
文摘This paper discusses the effect of influencing factors on the distribution of incremental oil displaced by a polymer flood （extra-displaced oil） using numerical reservoir simulation. These factors include the location, area and permeability of a thin low-permeability interbed, and the perforation location relative to the interbed. Simulation results show the locations from where the incremental oil was displaced by the polymer solution. The interbed position from the oil formation top affects the location of extra-displaced oil. The interbed area has a slight influence on the whole shape of extra-displaced oil. Larger interbed area leads to higher partition extent of extra-displaced oil. Higher vertical permeability of interbeds contributes to worse partition extent of extra-displaced oil and the partition effect disappears if the ratio of vertical to horizontal permeability is more than 0.05. The perforation location relative to the interbed affects polymer displacement efficiency, and also has a significant effect on the distribution of extra-displaced oil in polymer flooding.
基金the National High-Speed Rail United Foundation of China(No.U1934213)。
文摘Water-and-mud inrush disasters have become a major challenge in underground engineering for the construction of tunnels in sandstone and slate interbedded Presinian strata.Disaster prediction and prevention rely in part on realistic modeling and observation of the disaster process,as well as the identification and examination of the underlying mechanisms.Based on the geological conditions and the historical records of the Xinping Tunnel on the China–Laos Railway,an engineering geological model of the water-and-mud inrush was established.A physical model test that accurately reproduced water-and-mud inrush during tunnel excavation in sandstone and slate interbedded strata was also carried out.Then,testing was conducted that examined the stress and strain,seepage pressure,and high-leakage flow of the surrounding rock.The results indicated that the water-and-mud inrush proceeded through three stages:seepage stage,high-leakage flow stage,and attenuation stage.In essence,the disaster was a catastrophic process,during which the water-resistant stratum was reduced to a critical safety thickness,a water-inrush channel formed,and the water-resistant stratum gradually failed under the influence of excavation unloading and in situ stress–seepage coupling.Parameters such as the stress and strain,seepage pressure,and flow of the surrounding rock had evident stage-related features during water-and-mud inrush,and their variation indicated the formation,development,and evolution of the disaster.As the tunnel face advanced,the trend of the stress–strain curve of the surrounding rock shifted from sluggish to rapid in its speed of increase.The characteristics of strain energy density revealed the erosion and weakening effect of groundwater on the surrounding rock.The seepage pressure and the thickness of the water-resistant stratum had a positive linear relationship,and the flow and thickness a negative linear relationship.There was a pivotal point at which the seepage pressure changed from high to low and the flow shifted from low to high.The thickness of the water-resistant stratum corresponding to the pivotal point was deemed the critical safety thickness.
基金National Natural Science Foundation of China (Grant Numbers 40872077 and 41272122)China National Key Technology Research and Development Program (Grant Number 2001BA605A09-1)+1 种基金Sinopec’s Petroleum Exploration and Production Research Institute (Grant No. G5800-15-ZS-WX038)EGI’s China Shale Gas and Shale Oil Plays Consortia (100980) sponsored by 20 multi-national oil companies
文摘Hydrocarbon-producing lacustrine basins are widely developed in the world, and China has a large number of lacustrine basins that have developed since the early Permian. The organic-rich shale-dominated heterogeneous source rock intervals in Chinese lacustrine basins generally contain frequent thin interbeds of stratigraphically associated sandstone, siltstone, marl, dolomite, and limestone. The concept of ‘‘Hybrid Plays＇ ＇ as put forth in this article recognizes this pattern of alternating organicrich shale and organic-lean interbeds and existence of mixed unconventional and conventional plays. Hybrid Plays in lacustrine source rock intervals present a unique closed petroleum system hosting continuous hydrocarbons.The interbedded organic-lean siliciclastic and/or carbonateplays are efficiently charged with hydrocarbons via short migration pathways from the adjacent organic-rich shale that is often also a self-sourced play. We assert ‘‘Hybrid Plays＇ ＇ provide the most realistic exploration model for targeting multiple-stacked and genetically related very tight shale, tight and conventional plays together in the entire source rock interval rather than individual plays only. The Hybrid Play model has been proven and works for a wide variety of lacustrine rift, sag and foreland basins in China.
基金supported by the National Key Scientific Instrument and Equipment Development Projects of China(No.41827808)the Major Program of the National Natural Science Foundation of China(No.42090055).
文摘Block-flexure toppling failure is frequently encountered in interbedded anti-inclined rock(IAR)slopes,and seriously threatens the construction of hydropower infrastructure.In this study,we first investigated the Lean Reservoir area’s geological setting and the Linda landslide’s characteristics.Then,uniform design and random design were used to design 110 training datasets and 31 testing datasets,respectively.Afterwards,the toppling response was obtained by using the discrete element code.Finally,support vector regression was used to obtain the influence weights of 21 impact factors.The results show that the influence weight of the slope angle and rock formation dip angle on the toppling deformation among tertiary impact factors is 25.96%and 17.28%,respectively,which are much greater than the other 19 impact factors within the research range.For the primary impact factors,the influence weight is sorted from large to small as slope geometry parameters,joints parameters,and rock mechanics parameters.Joints parameters,especially the geometric parameters,cannot be ignored when evaluating the stability of IAR slopes.Through numerical simulation,it was qualitatively determined that failure surfaces of slopes were controlled by cross joints and that the rocks in the slope toe play a role in preventing slope deformation.
基金supported by the National Natural Science Foundation of China(Project No.42377182 and 42090054)the National Key R&D Program of China(No.2022YFC3080200)。
文摘Soft and hard interbedded bedding rock slopes,which is prone to failure,are widely distributed in the Three Gorges Reservoir,China.Limit equilibrium method(LEM)is commonly used to analyze the stability of bedding rock slopes that have a single failure plane.However,this method cannot accurately estimate the stability of soft and hard interbedded bedding reservoir slopes because the strength parameters of a soft and hard interbedded rock mass vary spatially along the bedding plane and deteriorate with time due to periodic fluctuations of reservoir level.A modified LEM is proposed to evaluate the stability evolution of soft and hard interbedded bedding reservoir slopes considering the spatial variation and temporal deterioration of shear strength parameters of rock masses and bedding planes.In the modified LEM,the S-curve model is used to define the spatial variation of shear strength parameters,and general deterioration equations of shear strength parameters with the increasing number of wettingdrying cycles(WDC)are proposed to describe the temporal deterioration.Also,this method is applied to evaluate the stability evolution of a soft and hard interbedded bedding reservoir slope,located at the Three Gorges Reservoir.The results show that neglecting the spatial variation and temporal deterioration of shear strength parameters may overestimate slope stability.Finally,the modified LEM provides useful guidance to reasonably evaluate the long-term stability of soft and hard interbedded bedding reservoir slopes in reservoir area.
