Stress tensor determination by modified hydraulic tests on pre-existing fractures:Method and stress constraints

The hydraulic testing of pre-existing fractures(HTPF)is one of the most promising in situ stress measurement methods,particularly for three-dimensional stress tensor determination.However,the stress tensor determination based on the HTPF method requires at least six tests or a minimum of 14-15 tests(under different conditions)for reliable results.In this study,we modified the HTPF method by considering the shear stress on each pre-existing fracture,which increased the number of equations for the stress tensor determination and decreased the number of tests required.Different shear stresses were attributed to different fractures by random sampling;therefore,the stress tensors were obtained by searching for the optimal solution using the least squares criterion based on the Monte Carlo method.Thereafter,we constrained the stress tensor based on the tensile strength criterion,compressive strength criterion,and vertical stress constraints.The inverted stress tensors were presented and analyzed based on the tensorial nature of the stress using the Euclidean mean stress tensor.Two stress-measurement campaigns in Weifang(Shandong Province,China)and Mercantour road tunnel(France)were implemented to highlight the validity and efficiency of the modified HTPF(M-HTPF)method.The results showed that the M-HTPF method can be applied for stress tensor inversion using only three to four tests on pre-existing fractures,neglecting the stress gradient.The inversion results were confined to relatively small distribution dispersions and were significantly reliable and stable due to the shear stresses on the fractures and the stress constraints employed.The M-HTPF method is highly feasible and efficient for complete stress tensor determination in a single borehole.

Influences of pre-existing fracture on ground deformation induced by normal faulting in mixed ground conditions

Physical model tests have been conducted by various researchers to investigate fault rupture propagation and ground deformation induced by bedrock faulting. However, the effects of pre-existing fracture on ground deformation are not fully understood. In this work, six centrifuge tests are reported to investigate the influence of pre-existing fracture on ground deformation induced by normal faulting in sand, clay and nine-layered soil with interbedded sand and clay layers. Shear box tests were conducted to develop a filter paper technique, which was adopted in soil model preparation to simulate the effects of pre-existing fracture in centrifuge tests. Centrifuge test results show that ground deformation mechanism in clay, sand and nine-layered soil strata is classified as a stationary zone, a shearing zone and a rigid body zone. Inclination of the strain localization is governed by the dilatancy of soil material. Moreover, the pre-existing fracture provides a preferential path for ground deformation and results in a scarp at the ground surface in sand. On the contrary, fault ruptures are observed at the ground surface in clay and nine-layered soil strata.

A method to model the effect of pre-existing cracks on P-wave velocity in rocks

Crack closure is one of the reasons inducing changes of P-wave velocity of rocks under compression.In this context,a method is proposed to investigate the relationships among P-wave velocity,pre-existing cracks,and confining pressure based on the discrete element method(DEM).Pre-existing open cracks inside the rocks are generated by the initial gap of the flat-joint model.The validity of the method is evaluated by comparing the P-wave velocity tested on a sandstone specimen with numerical result.As the crack size is determined by the diameter of particles,the effects of three factors,i.e.number,aspect ratio,and orientation of cracks on the P-wave velocity are discussed.The results show that P-wave velocity is controlled by the(i.e.number) of open micro-cracks,while the closure pressure is determined by the aspect ratio of crack.The reason accounting for the anisotropy of P-wave velocity is the difference in crack number in measurement paths.Both of the number and aspect ratio of cracks can affect the responses of P-wave velocity to the applied confining pressure.Under confining pressure,the number of open cracks inside rocks will dominate the lowest P-wave velocity,and the P-wave velocity of the rock containing narrower cracks is more sensitive to the confining pressure.In this sense,crack density is difficult to be back-calculated merely by P-wave velocity.The proposed method offers a means to analyze the effect of pre-existing cracks on P-wave velocity.

Damage and failure characteristics of rock similar materials with pre-existing cracks

In order to further study the damage and failure mechanism for rock similar materials,this study investigated the mechanical properties and failure characteristics,law of damage space development,and damage evolution characteristics for rock similar materials with pre-existing cracks of varying length under uniaxial compression load.The equipment used in this study is the self-developed YYW-Ⅱ strain controlled unconfined compression apparatus and the PCIE-8 acoustic emission monitoring system.Results show that,as the length of pre-existing crack increases:(1) the peak and residual strength reduces,and the peak axial strain and the strain during the initial compression phase increases;(2) the major failure mode is changed from shear failure to tensile failure along a vertical plane that passes the middle of the pre-existing crack;(3) The damage increases during the stable and accelerated development stage,and the effect of the pre-existing cracks is more during the accelerated development stage than the stable development stage.

Effects of pre-existing cracks and infillings on strength of natural rocks--Cases of sandstone, argillite and basalt

This study aims to examine the influence of pre-existing discontinuities on the strengths of four natural rocks of different origins.A series of unconfined compression tests was performed on specimens of two types of sandstones,argillite and basalt that contain open and filled cracks.It was found that the presence of cracks tends to decrease the overall strength for all studied rocks;however,the magnitude of strength reduction is related to the property of rock.The larger strength decrease was observed for the relatively harder argillite and basalt,compared to the softer sandstone.It was also found that the infill material could increase the strength of rock specimens,while the obtained strength depended on the characteristics of the fill material.

Seismic stability analysis of slopes with pre-existing slip surfaces

In analyzing seismic stability of a slope with upper bound limit analysis method, the slip surface is often assumed as a log-spiral or plane slip surface. However, due to the presence of a weak layer and unfavorable geological structural surface or a bedrock interface with overlying soft strata, the preexisting slip surface of the slope may be irregular and composed of a series of planes rather than strictly logspiral or plane shape. A computational model is developed for analyzing the seismic stability of slopes with pre-existing slip surfaces. This model is based on the upper bound limit analysis method and can consider the effect of anchor bolts. The soil or rock is deemed to follow the Mohr-Coulomb yield criterion. The slope is divided into multiple block elements along the slip surface. According to the displacement compatibility and the associated flow rule, a kinematic velocity field of the slope can be obtained computationally. The proposed model allows not only calculation of the rate of external work owing to the combined effect of self-weight and seismic loading, but also that of the energy dissipation rate caused by the slip surface, interfaces of block elements and anchorage effect of the anchors. Considering a direct relationship between the rate of external work and the energy dissipation rate, the expressions of yield acceleration and permanent displacement of anchored slopes can be derived. Finally, the validity of this proposed model is illustrated by analysis on three typical slopes. The results showed that the proposed model is more easily formulated and does not need to solve complex equations or time consuming iterations compared with previous methods based on the conditions of force equilibrium.

Relationship of Pre-Existing Maternal/Caregiver Acute Respiratory Infection in the Pattern and Risk of Acute Respiratory Infection among Infants in Rivers State, Nigeria

History of upper respiratory tract infection in the mother or siblings was associated with higher risk of acute lower respiratory tract infection in cases. Most upper respiratory tract infections were caused by viral pathogens and likely to occur in many members of the family. The study aimed to determine the existence and pattern of relationship between risk of acute respiratory infection (ARI) among infants and exposure to pre-existing maternal/caregiver acute respiratory tract infection. The study was designed as a community-based Nested case-control study of 1100 infants randomly selected from 12 communities out of 6 Local Government Areas of the 3 senatorial districts of Rivers State. A multistage random sampling technique was used in selecting the subjects up to the community level. Descriptive method was used to represent the characteristics of the subjects and the differences in ARI between exposed and unexposed infants were tested in a bivariate logistics regression at 5% level of significance. Odds ratio (OR) was used to interpret the size effect measures of ARI on exposure to pre-existing maternal/caregiver ARI differences. A total of 275 Cases of ARI and 825 controls were included in the study. Among exposed infants (N = 104), ARI cases were found to be higher n = 80 (76.9%) than in control n = 24 (23.1%). Whereas, among unexposed infants N = 991, ARI cases were found to be lower n = 195 (19.7%) than in control n = 796 (80.3%). For the exposed infants, the odds for ARI were 13.5 times significantly higher compared to those of their unexposed counterparts (OR-Unadjusted = 13.52, (p < 0.0001, 95% CI = 0.047 - 0.121)). The findings will widen the horizon in the etiological consideration of ARI among infants vis-à-vis exposure potential to pre-existing maternal/caregiver ARI via nursing care. Therefore, community-based sensitization programme on barrier nursing care techniques and personal hygiene practices should be on focus.

Influence of intermediate principal stress on failure mechanism of hard rock with a pre-existing circular opening

Based on particle flow theory, the influences of the magnitude and direction of the intermediate principal stress on failure mechanism of hard rock with a pre-existing circular opening were studied by carrying out true triaxial tests on siltstone specimen. It is shown that peak strength of siltstone specimen increases firstly and subsequently decreases with the increase of the intermediate principal stress. And its turning point is related to the minimum principal stress and the direction of the intermediate principal stress. Failure characteristic(brittleness or ductility) of siltstone is determined by the minimum principal stress and the difference between the intermediate and minimum principal stress. The intermediate principal stress has a significant effect on the types and distributions of microcracks. The failure modes of the specimen are determined by the magnitude and direction of the intermediate principal stress, and related to weakening effect of the opening and inhibition effect of confining pressure in essence: when weakening effect of the opening is greater than inhibition effect of confining pressure, the failure surface is parallel to the x axis(such as σ2=σ3=0 MPa); conversely, the failure surface is parallel to the z axis(such as σ2=20 MPa, σ3=0 MPa).

Oblique extension of pre-existing structures and its control on oil accumulation in eastern Bohai Sea

Based on 3D seismic data, the evolution mechanism and characteristics of faults were investigated to reveal the structural origin and its control on differential hydrocarbon accumulation through comprehensive analyses, including structure style analysis, fault activity analysis, analogue modelling and comparison among the wells. The complex fault system with differently trending faults resulted from strike-slip and rifting in Paleogene was partly activated, developed successively and stretched obliquely by the near-NS extensional stress field in Neogene. In the area little affected by pre-existing faults, new faults nearly perpendicular to the extension direction developed. The structural development in the study area was not caused by transpressional strike slip. Under the oblique extension effect of pre-existing faults, if the angle between the strike of pre-existing fault and the extensional direction is different, the strike-slip and extensional stresses are different in ratio. The larger the angle between the two is, the stronger the extensional component, the poorer the sealing ability of the fault, and the stronger the oil and gas migration capacity will be. Conversely, the smaller the angle between the two is, the stronger the strike-slip component, the better the sealing ability of the fault, and the poorer the oil and gas migration capacity will be. The accumulation condition analysis results considering the fault trend are in good agreement with the oil and gas shows in wells drilled in this area.

On the Reactivation of the Pre-Existing Normal Fault

The reactivation of pre-existing faults is a common phenomenon in a basin. This paper discusses the relationship between the pre-existing faults and the newly formed Coulomb shear fractures regarding pore fluid pressures. Based on the Coulomb fracture criterion and Byerlee frictional sliding criterion, an equation relating pore pressure coefficient (&lambda;e), minimum dip angle (αe) of the reactive pre-existing fault and the intersection point depth (z) between the pre-existing fault and a newly formed Coulomb shear fault in an extensional basin, is established in this paper. This equation enhanced the understanding on the reactivation of pre-existing faults and can be used to calculate paleo-pore fluid pressures. The bigger the pore fluid pressure in a pre-existing fault is, the less the minimum dip angle for a reactive pre-existing fault will be. The minimum dip angle is less in shallow area than that in deep area. This will be of significance in petroleum exploration and development.

On the Orientation of Fractures with Transpressional and Transtensional Wrenches in Pre-Existing Faults

The orientation of fractures with transpressional and transtensional wrenches in pre-existing faults has not been quantitatively determined. Based on Coulomb failure criterion and Byerlee’s frictional sliding criterion, this paper has indicated quantitative geometric relationships between the pre-existing fault and the local induced principal stress axes caused by the rejuvenation of the pre-existing fault. For a hidden pre-existing fault with some cohesion, the angles between the local induced principal stress axes and the pre-existing fault quantitatively vary with the applied stress and the cohesion coefficient, the ratio of the thickness of the cover layer to the thickness of the whole wrench body, whether transpressional or transtensional wrenches occur. For a surface pre-existing fault with zero cohesion, the angles between the pre-existing fault and the local induced principal stress axes are related to the rock inner frictional angle regardless of both the applied stress and the cohesion coefficient where transpressional wrenches occur, and the local induced maximum principal stress axis is identical with the applied maximum principal stress axis where transtensional wrenches occur. Therefore, the geometric relationships between the pre-existing faults and their related fractures are defined, because the local induced principal stress axes determine the directions of the related fractures. The results can be applied to pre-existing weak fabrics. They can help to understand and analyze wrench structures in outcrops or subsurface areas. They are of significance in petroleum exploration.

Mechanism investigation of pre-existing void-induced multi-modal electro-migration behavior

A multi-modal time-to-failure distribution for an electro-migration(EM) structure has been observed and studied from long duration in-situ EM experiment, for which the failure mechanism has been investigated and discussed comprehensively. The mixed EM failure behavior strongly suggest that the fatal voids induced EM failure appear at various locations along the EM structure. This phenomenon is believed to be highly related to the existence of pre-existing voids before EM stress. Meanwhile, the number and location of the pre-existing voids can influence the EM failure mode significantly. Based on our research, a potential direction to improve the EM lifetime of Cu interconnect is presented.

Pre-existing cirrhosis is associated with increased mortality of traumatic patients: Analysis of cases from a trauma center in East China

AIM:To determine the impact of cirrhosis on trauma patients and define the factors predicting death.METHODS:The data on patients admitted to the trauma center from January 2000-2005 were studied retrospectively.The clinical variables were recorded and compared to identify the factors differentiating cirrhotic trauma survivors from non survivors.Child's classification criteria were derived from the reviewed charts of cirrhotic trauma patients to evaluate their predictive value in cirrhotic trauma.Trauma registry was also used to generate a trauma control group by matching for age,sex,abbreviated injury score(AIS)over the same period of time.The outcome variables compared were mortality rate,time of ICU and hospital stay.Results were expressed as mean ± SD.These data were analyzed by SPSS.11.0 statistical software.Univariate analysis was performed to identify significant medical factors for survivor and non survivors subjected to chi-square test.Fisher's exact test and Student's t test were performed to determine the statistical difference between cirrhotic and control groups.P < 0.05 was considered statistically significant.RESULTS:Poor prognosis of traum patients was associated with one or more of the following findings:ascitcs,hyperbilirubinemia(more than 2 mg/dL),hypoalbuminemia(less than 3.5 mg/dL),and prolonged prothrombin time(more than 12.5 seconds).Although Child's classification was used to predict the outcome in cirrhotic patients undergoing portacaval shunt procedures,no significant difference was found in mortality rate as a function of Child's classification.CONCLUSION:Cirrhosis is associated with a highermortality,a longer time of ICU and hospital stay of trauma patients.It seems that treatment of trauma patients with pre-existing severe liver disease is a challenge to surgeons.

Numerical simulation of rock progressive failure on samples with a pre-existed weak zone during brittle failure

Considering the heterogeneity of geomechanical materials, seismicity during brittle rock failure under compressive loading on the sample with an original weak zone is simulated by using rock failure process analysis code (RFPA2D). The run-through process of weak zone, the forming of new fault and associated micro-seismicities are studied. The modeling demonstrates the total process of source development of earthquake from deformation, micro-failure to collapse and the behavior of temporal-spatial distribution of micro-seismicities. The stress, strain and the temporal-spatial distribution of micro-seismicities life-likely portrayed the phenomena of localization and temporal-spatial transitions, which is similar to those observed in our real crust. Also, the results obtained in simulations are in agreement with or similar to the reported experimental observations.

Relationship between the Pre-existing Active Kunlun Fault and Co-seismic Surface Ruptures Produced by the 2001 Mw 7.8 Central Kunlun Earthquake, China

Field investigations allow to constrain the co-seismic surface rupture zone of ～400 km with a strike-slip up to 16.3 m associated with the 2001 Mw 7.8 Central Kunlun earthquake that occurred along the western segmentof the Kunlun fault, northern Tibet. The co-seismic rupture structures are almost duplicated on the pre-existing fault traces of the Kunlun fault. The deformational characteristics of the co-seismic surface ruptures reveal that the earthquake had a nearly pure strike-slip mechanism. The geologic and topographic evidence clearly shows that spatialdistributions of the co-seismic surface ruptures are restricted by the pre-existing geological structures of the Kunlun fault.

Molecular dynamics study on mechanical behaviors of Ti/Ni nanolaminate with a pre-existing void

Metallic nanolaminated materials possess excellent mechanical properties due to their unique modulation structures and interfacial properties.However,how microdefects affect their mechanical properties is still uncertain.To evaluate the influences of void location(in the crystalline layer and the Ti/Ni interface),void diameter(d)and thickness of the intermediate layer(h)on overall tensile behaviors,various types of defective Ti/Ni nanolaminates with pre-existing void are established by the molecular dynamics method in this work.The results indicate that the strength and plastic deformation mechanisms are strongly dependent on those determinants.Yield stresses of Ti/Ni nanolaminates decrease distinctly with increasing void diameter,while peak stresses with a void in the crystalline layer decrease with increasing d/h.Different void locations lead eventually to disparate initial plastic deformation carriers around the void,and various evolutions in the microstructure of the defective Ti/Ni nanolaminates.The Ti/Ni interface plays a significant role in the tensile process.The semi-coherent interface impedes new grains and lattice dislocations from passing across the interface,while the incoherent interface facilitates dislocations generating and sliding along the interface,and absorbs the dislocations moving to the interface.The results also indicate that the strain rate significantly affects the evolution of the microstructure and the tensile properties of defective Ti/Ni nanolaminates.

中国式现代化视域下中国财政收入目标制演变研究

财政收入目标作为财政预算收入编制的基础,是财政政策相机调控的政策工具,亦是有为政府动员部署和调配资源的重要途径。中国财政收入目标制的发展阶段可划分为新中国成立初期财政收入目标考核确立前阶段(1949—1977年)、改革开放后财政收入目标考核萌发阶段(1978—1993年)、分税制后财政收入目标考核发展阶段(1994—1999年)、新世纪财政收入目标与预算绩效融合阶段(2000—2012年)及新时代财政融入国家治理体系阶段(2013年以来)等五个阶段,具有历史演进特征。根据1998—2020年相关数据,全国、省级和地市级三个层面的财政收入目标具有时空格局演变特征:就整体而言,中国财政收入目标具有很强的引导作用,体现了财政的主动性和目标意识;从区域来看,东部发达地区因为自身较大的经济体量,财政收入增速呈现正常的趋缓现象,财政收入目标总体上小于其他欠发达省份;而在区域内部,城市间财政收入目标差异分化较大,中部和西部地区城市所制定目标的水平会更高,目标的增长压力也更大,大部分城市的财政收入目标小于其实际经济增速,目标存在留有余地的空间;各省份和城市之间的收入目标差距均存在收敛效应。

行政规范性文件备案审查中比例原则的适用

行政规范性文件备案审查是一种事后的合法性监督制度。作为方法论意义上的比例原则引入行政规范性文件备案审查,旨在改善行政规范性文件备案审查的方法,提升行政规范性文件备案审查的实效。适当性原则审查的核心是手段与目的关联性。关联性是指手段能够正向推进目的得以实现的单向关系。必要性原则审查的核心是手段与结果的关联性,最小损害是确定关联性的基本要素。均衡性原则审查的核心是手段与结果的合比例性,利益衡量是确定合比例性的基本方法。在行政规范性文件备案审查中,事实审查有助于提升行政规范性文件的“科学性”。对因紧急状态而制定的行政规范性文件进行备案审查,可以适度降低比例原则的要求。

事实转向与理由基础

英美知识论近期出现一种所谓“事实转向”的思想趋向,它反对的主要目标是内在主义的思想。事实转向的出现曾被归结为来自三个方面的影响:麦克道尔的析取论;威廉姆森的《知识及其限度》,其核心主张“知识优先”意味着诉诸事实性;丹西的只有事实才能够是行动或信念的好的理由的“实践的实在论”。不过,事实转向存在如下的问题:一是在当今科学创造的时代,突出想象的、构造性的认识方式,应当更符合时代的需要。二是威廉姆森的“只相信你所知道的”说法,是一种理想化的说法。实际上在面临所知不足的状况下,我们往往只能先相信,然后进一步去寻找证据来确证。三是就认识与事实的关系而言,单有事实是不够的,事实是需要解读与把握的。四是威廉姆森的“证据等于知识(E=K)”说可能会遇到问题。

《堡垒》:事实逻辑与信仰诗意相交融的视听景观建构

为纪念毛泽东同志诞辰130周年而拍摄的红色电影《堡垒》于2023年12月16日在毛主席的家乡韶山首映。电影《堡垒》坚持以“红色人物”为依托进行主角形象塑造,遵循以“红色史实”为基础的事实叙事逻辑,践行以“红色信仰”为底色的诗意主题表达,在视听景观的建构上将独特的叙事方式和创新性的表现手段融于一体,成功实现了事实逻辑与信仰诗意相交融的视听景观建构,它既为新时代党员重温入党初心和使命提供了新的渠道和思考,又为新主流电影在新时代如何做好传承红色基因、赓续红色血脉的工作展开了有益探索,是一部电影佳作。