Shear mechanical properties and energy evolution of rock-like samples containing multiple combinations of non-persistent joints

Discontinuities are often considered as important factors responsible for the instability caused by shear failure in engineering rock mass,and energy-driven instability is the root cause of rock failure.However,few studies focus on the energy evolution during the failure process using a three-dimensional(3D)numerical model.In this study,a series of laboratory direct shear tests on rock-like samples is numer-ically simulated using bonded particle models(BPMs)with multiple combinations of discontinuous in the particle flow code(PFC3D),in which the location and size of the particles conform to the uniform distribution.The effects of joint row number and inclination on the stress-strain characteristics and failure mode of rock were studied from the perspective of microcrack growth and energy evolution.The results showed that,when the number of joint rows Nr>1,the shear failure region does not change with the increase of Nr for the type B(2-columnn multiple-row at center)and the type C(2-column multiple-row at edge)as compared to the type A(1-column multiple-row at center)joint models.Notably,joints significantly increase the post-peak energy dissipation but have little effect on the proportion of energy before the peak.Friction consumes most of the energy while kinetic energy accounts for less than 1%of total energy during the shear process.Peak elastic strain energy follows the variation trend of peak shear displacement.The development and accumulation of microcracks directly affect the energy dissipation,and there is a significant linear relationship between the cumulative number of critical microcracks and the critical dissipated energy at the failure,when the dip direction of joints is opposite to the shear direction,more microcracks will be accumulated at the peak time,resulting in more energy dissipation.The results contribute to deeply understanding the shear failure process of non-persistent jointed mass.

Changes in persistent and non-persistent extreme precipitation in Chinafrom 1961 to 2016

In this study, based on daily gage precipitation data of 2480 stations from 1961 to 2016, the summer （JuneeAugust） extreme precipitationevent was defined using the 95th percentile, and the changes in persistent （last for at least 2 d） and non-persistent （1 d） extreme precipitation inChina were analyzed. The results indicate that under global warming, the contribution of extreme precipitation to total summer precipitationincreased in most areas of China, but it decreased in the central part of Inner Mongolia and the Sichuan Basin. In North and Southwest China,both persistent and non-persistent extreme precipitation decreased; the decreasing trend of persistent extreme precipitation was more prominent;thus, extreme precipitation event occurred more as non-persistent event. Meanwhile, in the Yangtze River Basin and South China, both types ofextreme precipitation increased particularly the persistent extreme precipitation; persistent extreme precipitation occurred more compared withnon-persistent events.

Failure behavior around a circular opening in a rock mass with non-persistent joints:A parallel-bond stress corrosion approach

The stability of underground excavations is influenced by discontinuities interspaced in surrounding rock masses as well as the stress condition. In this work, a numerical study was undertaken on the failure behavior around a circular opening in a rock mass having non-persistent open joints using PFC software package. A parallel-bond stress corrosion(PSC) approach was incorporated to drive the failure of rock mass around the circular opening, such that the whole progressive failure process after excavation was reproduced. Based on the determined micro parameters for intact material and joint segments, the failure process around the circular opening agrees very well with that obtained through laboratory experiment. A subsequent parametric study was then carried out to look into the influence of lateral pressure coefficient, joint dip angle and joint persistency on the failure pattern and crack evolution of the rock mass around the circular opening. Three failure patterns identified are step path failure, planar failure and rotation failure depending on the lateral pressure coefficient. Moreover, the increment of joint dip angle and joint persistency aggravates the rock mass failure around the opening. This study offers guideline on stability estimation of underground excavations.

Strength behaviour of a model rock intersected by non-persistent joint

Several constructions in the field of civil engineering quite often need to deal with rocks.Strength behaviour of rock intersected by a discontinuity or a set of discontinuities has been a topic of keen interest for engineering community.The popular attributes of discontinuities that have been given due importance are their frequency,orientation and surface characteristics.Non-persistency,however,has been given little attention.This article presents an experimental study wherein focus has been made on the effect of non-persistency of the joint on the uniaxial compressive strength(UCS)of a model rock for various geometries such as orientation,discontinuity length ratio and number of joint segments.The applicability of single plane of weakness theory(SPWT)to assess the strength of jointed specimens has also been evaluated.It has been noticed that SPWT captures the strength behaviour only for a narrow range of discontinuity orientations.As an improvement,an approach is suggested by extending concepts of degree of persistence and joint factor to have a better understanding towards strength behaviour of rocks intersected by non-persistent joints.

Bearing capacity of foundations on rock slopes intersected by non-persistent discontinuity

Rocks encountered in foundations of heavy structures are invariably intersected by discontinuities(joints).In the past,several studies have been performed by researchers to incorporate the effect of fully persistent joints in the assessment of the load-carrying capacity of rocks.However,in the field,the joints are non-persistent,and an assumption of full persistency will underestimate the capacity.Recently,Shaunik&Singh have studied the influence of non-persistency,number of joint segments and discontinuity orientation on the strength behaviour of rock specimens(Shaunik and Singh,2019).Bell’s approach can be used to obtain the bearing capacity of shallow foundations placed in jointed rocks.In the present study,results of the experimental work(Shaunik and Singh,2019)conducted by Shaunik&Singh have been used to suggest expressions by extending Bell’s approach for computing bearing capacity of the foundation placed near the crown of a rock slope.Easy to use design charts are also presented for field application.Finally,a real-life problem from Indian Garhwal Himalayas is considered,and the approach suggested in this study is utilised to obtain the bearing capacity of a bridge foundation as a function of uniaxial compressive strength(UCS)of intact rock,joint friction,spacing and orientation of joint,nonpersistency and number of joint segments.

RB-DEM Modeling and Simulation of Non-Persisting Rough Open Joints Based on the IFS-Enhanced Method

When the geological environment of rock masses is disturbed,numerous non-persisting open joints can appear within it.It is crucial to investigate the effect of open joints on the mechanical properties of rock mass.However,it has been challenging to generate realistic open joints in traditional experimental tests and numerical simulations.This paper presents a novel solution to solve the problem.By utilizing the stochastic distribution of joints and an enhanced-fractal interpolation system(IFS)method,rough curves with any orientation can be generated.The Douglas-Peucker algorithm is then applied to simplify these curves by removing unnecessary points while preserving their fundamental shape.Subsequently,open joints are created by connecting points that move to both sides of rough curves based on the aperture distribution.Mesh modeling is performed to construct the final mesh model.Finally,the RB-DEM method is applied to transform the mesh model into a discrete element model containing geometric information about these open joints.Furthermore,this study explores the impacts of rough open joint orientation,aperture,and number on rock fracture mechanics.This method provides a realistic and effective approach for modeling and simulating these non-persisting open joints.

Changes in Persistent and Non-Persistent Flood SeasoPrecipitation over South China During 1961–2010

The characteristics and possible causes of changes in persistent precipitation（PP） and non-persistent precipitation（NPP） over South China during flood season are investigated using daily precipitation data from 63 stations in South China and NCEP/NCAR reanalysis data from 1961 to 2010. This investigation is performed using the Kendall＇s tau linear trend analysis, correlation analysis, abrupt climate change analysis, wavelet analysis, and composite analysis techniques. The results indicate that PP dominates total precipitation over South China throughout the year. The amounts of PP and NPP during flood season vary primarily on a 2–5-yr oscillation. This oscillation is more prominent during the early flood season（EFS; April–June）. NPP has increased significantly over the past 50 years while PP has increased slightly during the whole flood season. These trends are mainly due to a significant increase in NPP during the EFS and a weak increase in PP during the late flood season（LFS; July–September）. The contribution of EFS NPP to total flood season precipitation has increased significantly while the contribution of EFS PP has declined. The relative contributions of both types of precipitation during LFS have not changed significantly. The increase in EFS NPP over South China is likely related to the combined efects of a stronger supply of cold air from the north and a weaker supply of warm, moist air from the south. The increase in NPP amount may also be partially attributable to a reduction in the stability of the atmosphere over South China.

Differences in Meteorological Conditions between Days with Persistent and Non-Persistent Pollution in Beijing, China

We compared the regional synoptic patterns and local meteorological conditions during persistent and non-persistent pollution events in Beijing using US NCEP–Department of Energy reanalysis outputs and observations from meteorological stations. The analysis focused on the impacts of high-frequency（period 〈 90 days） variations in meteorological conditions on persistent pollution events（those lasting for at least 3 days）. Persistent pollution events tended to occur in association with slow-moving weather systems producing stagnant weather conditions, whereas rapidly moving weather systems caused a dramatic change in the local weather conditions so that the pollution event was short-lived. Although Beijing was under the influence of anomalous southerly winds in all four seasons during pollution events, notable differences were identified in the regional patterns of sea-level pressure and local anomalies in relative humidity among persistent pollution events in different seasons. A region of lower pressure was present to the north of Beijing in spring, fall, and winter, whereas regions of lower and higher pressures were observed northwest and southeast of Beijing, respectively, in summer. The relative humidity near Beijing was higher in fall and winter, but lower in spring and summer. These differences may explain the seasonal dependence of the relationship between air pollution and the local meteorological variables. Our analysis showed that the temperature inversion in the lower troposphere played an important part in the occurrence of air pollution under stagnant weather conditions.Some results from this study are based on a limited number of events and thus require validation using more data.

The molecular mechanism of efficient transmission of plant viruses in variable virus-vector-plant interactions

Plant viruses are mainly transmitted by insect vectors in the non-persistent,semi-persistent,or persistent modes.In the non-persistent mode,plant viruses are retained in the stylets of their insect vectors.In the semi-persistent mode,plant viruses are carried to vector foreguts or salivary glands,but they cannot spread to salivary glands.In the persistent mode,plant viruses are retained in vector guts and can spread to salivary glands.In the non-persistent and semi-persistent modes,plant viruses are retained for a short time and cannot enter the hemolymph of insect vectors,whereas in the persistent mode,plant viruses are retained for a relatively long time and can be found in the hemolymph.Here,we reviewed recent studies that uncovered molecular mechanisms of how plant viruses manipulate host traits for efficient transmission by insect vectors.Normally,plants that are infected with viruses,regardless of the transmission mode,tend to release more attractive volatiles to vectors.However,plant defensive systems are regulated differently by viruses in these three modes.In the non-persistent mode,virus infections significantly induce plant defense responses,which probably trigger vectors(e.g.,winged aphids)to disperse and transmit viruses in a short time.In the semi-persistent mode,virus infections frequently suppress plant defense responses,resulting in an increase of vector population and facilitating viral transmissions during vector outbreaks.In the persistent mode,virus infections reduce plant defense responses and manipulate plant traits to become suitable feeding sites in a relatively long period of time.Understanding the underlying mechanisms of virus–vector–plant interactions will lay a foundation for preventing virus transmission.

Recursive Least Squares Identification With Variable-Direction Forgetting via Oblique Projection Decomposition

In this paper,a new recursive least squares(RLS)identification algorithm with variable-direction forgetting(VDF)is proposed for multi-output systems.The objective is to enhance parameter estimation performance under non-persistent excitation.The proposed algorithm performs oblique projection decomposition of the information matrix,such that forgetting is applied only to directions where new information is received.Theoretical proofs show that even without persistent excitation,the information matrix remains lower and upper bounded,and the estimation error variance converges to be within a finite bound.Moreover,detailed analysis is made to compare with a recently reported VDF algorithm that exploits eigenvalue decomposition(VDF-ED).It is revealed that under non-persistent excitation,part of the forgotten subspace in the VDF-ED algorithm could discount old information without receiving new data,which could produce a more ill-conditioned information matrix than our proposed algorithm.Numerical simulation results demonstrate the efficacy and advantage of our proposed algorithm over this recent VDF-ED algorithm.

Modeling rock failure using the numerical manifold method followed bythe discontinuous deformation analysis

A complete rock failure process usually involves opening/sliding of preexisting discontinuities as well as frac- turing in intact rock bridges to form persistent failure sur- faces and subsequent motions of the generated rock blocks. The recently developed numerical manifold method （NMM） has potential for modelling such a complete failure process. However, the NMM suffers one limitation, i.e., unexpected material domain area change occurs in rotation modelling. This problem can not be easily solved because the rigid body rotation is not represented explicitly in the NMM. The discontinuous deformation analysis （DDA） is specially de- veloped for modelling discrete block systems. The rotation- induced material area change in the DDA modelling can be avoided conveniently because the rigid body rotation is represented in an explicit form. In this paper, a transition technique is proposed and implemented to convert a NMMmodelling to a DDA modelling so as to simulate a complete rock failure process entirely by means of the two methods, in which the NMM is adopted to model the early fracturing as well as the transition from continua to discontinua, while the DDA is adopted to model the subsequent motion of the generated rock blocks. Such a numerical approach also im- proves the simulation efficiency greatly as compared with a complete NMM modelling approach. The fracturing of a rock slab with pre-existing non-persistent joints located on a slope crest and the induced rockfall process are simulated. The validity of the modelling transition from the NMM to the DDA is verified and the applicability of the proposed nu- merical approach is investigated.

Influence of degree of interlock on confined strength of jointed hard rock masses

The strength of jointed rock mass is strongly controlled by the degree of interlock between its constituent rock blocks.The degree of interlock constrains the kinematic freedom of individual rock blocks to rotate and slide along the block forming joints.The HoekeBrown(HB)failure criterion and the geological strength index(GSI)were developed based on experiences from mine slopes and tunneling projects in moderately to poorly interlocked jointed rock masses.It has since then been demonstrated that the approach to estimate the HB strength parameters based on the GSI strength scaling equations(called the‘GSI strength equations’)tends to underestimate the confined peak strength of highly interlocked jointed rock masses(i.e.GSI>65),where the rock mass is often non-persistently jointed,and the intact rock blocks are strong and brittle.The estimation of the confined strength of such rock masses is relevant when designing mine pillars and abutments at great depths,where the confining pressure is high enough to prevent block rotation and free sliding on block boundaries.In this article,a grain-based distinct element modeling approach is used to simulate jointed rock masses of various degrees of interlock and to investigate the influences of block shape,joint persistence and joint surface condition on the confined peak strengths.The focus is on non-persistently jointed and blocky(persistently jointed)rock masses,consisting of hard and homogeneous rock blocks devoid of any strength degrading defects such as veins.The results from this investigation confirm that the GSI strength equations underestimate the confined strength of highly interlocked and non-persistently jointed rock masses.Moreover,the GSI strength equations are found to be valid to estimate the confined strength of persistently jointed rock masses with smooth and non-dilatant joint surfaces.

RT-PCR and CP gene based molecular characterization of a cucumber mosaic cucumovirus from Aligarh, U.P., India

A virus disease of garden sage (Salvia splendens Ker-Gawl.) was observed and characterized showing symptoms of severe mosaic, mottling and distortion of leaves being remain shortened and growth retarded. The virus was transmitted to the healthy plants of Salvia spp. as well as many other hosts by mechanical inoculation, Myzus persicae Sulzer and Aphis gossypii Glover transmit the virus in non-persistent manner. Purified sample in EM showed spherical particles c.28 nm in diameter. DAC- ELISA [1] was performed with crude sap, specific polyclonal anti-serum (PVAS 242a, ATCC, USA) and alkaline phosphatase-linked secondary antibodies (Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH or DSMZ, Germany). The mean absorbance at 405 nm for negative and positive controls were 0.061 ± 0.008 and 0.349 ± 0.003 respectively, while infected samples were recorded four-times more than the value of negative controls with values that ranged between 0.289 ± 0.005 and 0.325 ± 0.003. RT-PCR was performed using total RNA as templates and CMV Coat Protein (CP) gene specific reverse and forward primers, gel was electrophoresed on 1% agarose, an amplification of expected size 650 bp fragment was obtained only in the infected sample which proved that the present virus is a strain of CMV, the type member of the genus cucumovirus belonging to the family Bromoviridae.