Tempo-spatial Distribution Research Articles

Multi-phase metamorphism in the northern margin of the North China Craton: Records from metapelite in the Hongqiyingzi Complex

It is controversial about the tempo–spatial distribution and tectonic attributes of the Paleoproterozoic orogenic belts in the North China Craton (NCC). The Hongqiyingzi Complex in the northern margin of the NCC, comprising orthogneiss, supracrustal sequence and an ophiolitic mélange, was investigated to have experienced multiple tectonic evolution from Paleoproterozoic to Mesozoic. However, the depositional age and metamorphic P–T path of the supracrustal sequence have not been well addressed. Garnet mica schists are investigated on the basis of petrography, mineral chemistry, phase equilibria modelling and zircon and monazite dating, which record an extreme case with four phases of metamorphism. The first-phase is characterized by high pressure (HP) granulite facies with the peak conditions of 10–11 kbar/>780 °C, which occurred at ~1.95 Ga. It is considered to correspond to a collisional orogeny with crust thickening widespread in the Paleoproterozoic orogenic belts of the NCC, followed by an exhumation with heating at ~1.92 Ga. The second-phase is marked by the overprinting of staurolite-bearing assemblages with the peak conditions of 6–7 kbar/610–630 °C, which occurred at ~1.85 Ga. It may correlate a separate orogeny occurred along the northern margin of the NCC, following a ~1.90 Ga oceanic subduction. Phase modelling suggests this overprinting over the first-phase HP granulites is mainly controlled by water infiltration. The third-phase andalusite-type and the fourth-phase greenschist facies metamorphism are confined to local equilibrium domains and their ages have not been well constrained. With a comparison of regional geology, the third-phase metamorphism is inferred to be related with the 320–290 Ma extension in the northern part of the NCC during Late Paleozoic, and the fourth-phase metamorphism is correlated with the 250–230 Ma collision occurred along the Solonker Suture Zone in the Central Asia Orogenic Belt during Early Mesozoic. Moreover, detrital magmatic zircons yield ages of 2.0–2.1 Ga, providing a definite upper limit on the deposition of the Hongqiyingzi supracrustal sequence.

Mixed carbonate rocks lithofacies features and reservoirs controlling mechanisms in a saline lacustrine basin in Yingxi area, Qaidam Basin, NW China

Abstract Taking the mixed pre-salt carbonate rocks in the upper member of Eocene Xiaganchaigou Formation (E32) of Yingxi area in the Qaidam Basin as an example, the lithofacies and controlling mechanisms of reservoir formation are analyzed based on a large dataset of cores, thin sections and geochemical analysis. The reservoirs in E32 pre-salt layers have five types of lithofacies, of them, mixed granular calcareous dolostone, massive calcareous dolostone, plaque calcareous dolostone, and laminated dolomtic limestone are of sedimentary origin, and breccia calcareous dolostone is of tectonic origin. The four types of sedimentary lithofacies are divided into two types of saline sedimentary sequence lithofacies combinations, low-energy type in the sag area and low to high-energy type in the slope and paleo-uplift zone in the depression. Affected by high-frequency supply of continental clastic material, the two types of salty sedimentary sequences are mostly incomplete subtypes of lithofacies. Lithofacies have strong impacts on pre-salt reservoirs in E32: (1) Lithofacies type and sedimentary sequence controlled the formation and distribution of dolomite intercrystalline pores and dissolved pores during the pene-sedimentary period. (2) The structure of laminated dolomitic limestone controlled the formation of large-scale laminated fractures and high permeability channels during the diagenetic period. (3) Granular, massive, plaque calcareous dolostones have low mud content and strong brittleness, in the late tectonic reactivation period, the distribution of the three types of lithofacies, together with their distance from the top large slip faults and secondary faults, controlled the formation and distribution of high-efficiency fracture-cave brecciaed calcareous dolostone reservoirs. The above research led to the composite lithofacies-tectonic formation model of pre-salt reservoir in E32 of Yingxi area. The tempo-spatial distribution of tectonic breccia calcareous dolostone reservoirs, laminated dolomitic limestone shale oil reservoirs and granular, massive calcareous dolostone dissolved-intercrystalline pore tight reservoirs in various structural belts of the studied area have been figured out. These findings gave new insights into tight-shale oil accumulation theory in mixed carbonate successions from saline lacustrine basins, aiding in high efficient exploration and development of petroleum in the studied area.

Quantifying the Cloud Water Resource: Methods Based on Observational Diagnosis and Cloud Model Simulation

Based on the concepts of cloud water resource (CWR) and related variables proposed in the first part of this study, this paper provides details of two methods to quantify the CWR. One is diagnostic quantification (CWR-DQ) based on satellite observations, precipitation products, and atmospheric reanalysis data; and the other is numerical quantification (CWR-NQ) based on a cloud resolving model developed at the Chinese Academy of Meteorological Sciences (CAMS). The two methods are applied to quantify the CWR in April and August 2017 over North China, and the results are evaluated against all available observations. Main results are as follows. (1) For the CWR-DQ approach, reference cloud profiles are firstly derived based on the CloudSat/CALIPSO joint satellite observations for 2007–2010. The NCEP/NCAR reanalysis data in 2000–2017 are then employed to produce three-dimensional cloud fields. The budget/balance equations of atmospheric water substance are lastly used, together with precipitation observations, to retrieve CWR and related variables. It is found that the distribution and vertical structure of clouds obtained by the diagnostic method are consistent with observations. (2) For the CWR-NQ approach, it assumes that the cloud resolving model is able to describe the cloud microphysical processes completely and precisely, from which four-dimensional distributions of atmospheric water vapor, hydrometeors, and wind fields can be obtained. The data are then employed to quantify the CWR and related terms/quantities. After one-month continuous integration, the mass of atmospheric water substance becomes conserved, and the tempospatial distributions of water vapor, hydrometeors/cloud water, and precipitation are consistent with observations. (3) Diagnostic values of the difference in the transition between hydrometeors and water vapor (Cvh − Chv) and the surface evaporation (Es) are well consistent with their numerical values. (4) Correlation and bias analyses show that the diagnostic CWR contributors are well correlated with observations, and match their numerical counterparts as well, indicating that the CWR-NQ and CWR-DQ methods are reasonable. (5) Underestimation of water vapor converted from hydrometeors (Chv) is a shortcoming of the CWR-DQ method, which may be rectified by numerical quantification results or by use of advanced observations on higher spatiotemporal resolutions.

Fossil dipterid fern Thaumatopteris in China: new insights of systematics, diversity and tempo-spatial distribution patterns

ABSTRACT Thaumatopteris (Goeppert) Nathorst is a typical dipterid fern in the early Mesozoic, showing global significances for palaeoclimate, phytogeography and biostratigraphy. However, the detailed understanding on the relationship between species diversity and the environmental background of this genus is still unclear. Here, we reinvestigated new collections and type specimens of Thaumatopteris contracta Li et Tsao collected from the Upper Triassic of Yunnan Province, and analysed the systematic, diversity variations and tempo-spatial distribution patterns of Thaumatopteris in China. An emendation was proposed for species diagnosis of Thaumatopteris contracta based on both sterile and fertile pinnae. Our analysis demonstrates that the genus Thaumatopteris reached a higher diversity and differentiation with 11 species during the Late Triassic in China and suffered a severe loss of species diversity across the Triassic-Jurassic transition. Changes in the spatial distribution pattern of Thaumatopteris demonstrate an ecological response to local environment degradation in the Upper Yangtze region. The destruction of habitat and the block of the transport channel of warm moist flow from the Tethys Ocean caused by the Indosinian tectonic movement, especially, the uplift of the Longmen Mountains may represent the potential environmental trigger.

The Charging Characteristics of Large-Scale Electric Vehicle Group Considering Characteristics of Traffic Network

Electric vehicles, as a new generation of road transport, are primarily used for transportation. For this reason, the topological characteristics of traffic network may make great influence on the macroscopic characteristics of electric vehicle group. However, little attention is drawn to the study in this field. Therefore, typical approach to studying the impact of traffic network topological characteristics on the charging characteristics of large-scale electric vehicle group is presented by adopting the charging power distribution as analysis indicator. In this paper, a model of complex adaptive system is constructed including the electric vehicle group, traffic network and charging stations, where the tempo-spatial distribution of charging power can be obtained via the simulation with the multi-agent technique. The charging power of regional electric vehicles is found obedient to logarithmic normal distribution after analysis, while the mathematical expectation of probability density shows obvious cyclicity. Finally, the traffic networks of various cities in comparison testify to that improving the connectivity of traffic network and increasing the average clustering coefficient can effectively reduce the effect on power system brought by the charging load of large-scale electric vehicle group.

Evaluating grid-interactive electric bus operation and demand response with load management tariff

Electric Vehicles are expected to play a vital role in the transition of smart energy systems. Lots of recent research has explored numerous underlying mechanisms to achieve the synergetic interactions in the electricity balancing process. In this paper, the grid-interactive operation of electric buses is first time integrated within a dynamic market frame using the Distribution Locational Marginal Price algorithm for load congestion management. Since the defined problem correlates the opportunity charging flexibility with the bus mobility over a network, the tempo-spatial distribution of energy needs can be reflected in the dynamic of service planning. The interactions between bus operators and suppliers are quantitatively modelled by a bi-level optimisation process to represent the electric bus service planning and electricity market clearing separately. The effectiveness of the proposed load management has been demonstrated using data collected from an integrated real-world bus network. Experiments show that engagement of electric bus charging load in demand response is helpful to alleviate the network congestion and to reduce the power loss by 7.2% in the distribution network. However, alleviated charging loads have exhibited counter-intuitive capability for load shifting. The restricted electric bus operational requirements leads to a 8.17% loss of charging demand, while the reliance on large batteries has increased by 10.57%. However, the sensitivity analysis also shows that as the battery cost declines, the such discourage implications on grid-interactive electric bus operation will decrease once the battery cost below 190/kWh. The optimal grid-ebus integration have to consider the trade-off between range add-up, reduced battery cost and additional benefits.

Dynamics and diversity of bacteria associated with the disease vectors Aedes aegypti and Aedes albopictus

Aedes aegypti and Aedes albopictus develop in the same aquatic sites where they encounter microorganisms that influence their life history and capacity to transmit human arboviruses. Some bacteria such as Wolbachia are currently being considered for the control of Dengue, Chikungunya and Zika. Yet little is known about the dynamics and diversity of Aedes-associated bacteria, including larval habitat features that shape their tempo-spatial distribution. We applied large-scale 16S rRNA amplicon sequencing to 960 adults and larvae of both Ae. aegypti and Ae. albopictus mosquitoes from 59 sampling sites widely distributed across nine provinces of Panama. We find both species share a limited, yet highly variable core microbiota, reflecting high stochasticity within their oviposition habitats. Despite sharing a large proportion of microbiota, Ae. aegypti harbours higher bacterial diversity than Ae. albopictus, primarily due to rarer bacterial groups at the larval stage. We find significant differences between the bacterial communities of larvae and adult mosquitoes, and among samples from metal and ceramic containers. However, we find little support for geography, water temperature and pH as predictors of bacterial associates. We report a low incidence of natural Wolbachia infection for both Aedes and its geographical distribution. This baseline information provides a foundation for studies on the functions and interactions of Aedes-associated bacteria with consequences for bio-control within Panama.

Distribution of green algae micro-propagules and their function in the formation of the green tides in the coast of Qinhuangdao, the Bohai Sea, China

Since 2015, a novel green tide has been recurring in the coastal areas of Qinhuangdao at the western coast of the Bohai Sea in China, threatening the environment and ecosystem of the Beidaihe seaside holiday resort along the coast. Micro-propagules of the green algae including gametes, spores, micro-germlings and micro-vegetative fragments play an important role in the formation of green tides. They serve as a “seed source” of green macroalgae, and their distributions could reflect and influence the “algae source” of green tides. In this study, monthly surveys in the inshore and offshore areas of the Qinhuangdao coast were conducted from April to September 2016 and in January 2017 to investigate the tempo-spatial distribution patterns and the biomass variations of the green algae micro-propagules. The obtained results show that micro-propagules were mainly distributed in the inshore areas with a significantly decreasing abundance towards offshore areas. Their biomass was highest in July and August, and lowest in winter. The areas that were affected by the green tides showed a remarkably higher abundance of micro-propagules compared to other areas. These micro-propagules could serve as the “seed” source of green tides. Their distribution patterns indicate that the green tide in the coastal areas of Qinhuangdao originated locally.

Influence of biomass burning on local air pollution in mainland Southeast Asia from 2001 to 2016

In this study, various remote sensing data, modeling data and emission inventories were integrated to analyze the tempo-spatial distribution of biomass burning in mainland Southeast Asia and its effects on the local ambient air quality from 2001 to 2016. Land cover changes have been considered in dividing the biomass burning into four types: forest fires, shrubland fires, crop residue burning and other fires. The results show that the monthly average number of fire spots peaked at 34,512 in March and that the monthly variation followed a seasonal pattern, which was closely related to precipitation and farming activities. The four types of biomass burning fires presented different tempo-spatial distributions. Moreover, the monthly Aerosol Optical Depth (AOD), concentration of particulate matter with a diameter less than 2.5 μm (PM2.5) and carbon monoxide (CO) total column also peaked in March with values of 0.62, 45 μg/m3 and 3.25 × 1018 molecules/cm2, respectively. There are significant correlations between the monthly means of AOD (r = 0.74, P < 0.001), PM2.5 concentration (r = 0.88, P < 0.001), and CO total column (r = 0.82, P < 0.001) and the number of fire spots in the fire season. We used Positive Matrix Factorization (PMF) model to resolve the sources of PM2.5 into 3 factors. The result indicated that the largest contribution (48%) to annual average concentration of PM2.5 was from Factor 1 (dominated by biomass burning), followed by 27% from Factor 3 (dominated by anthropogenic emission), and 25% from Factor 2 (long-range transport/local nature source). The annually anthropogenic emission of CO and PM2.5 from 2001 to 2012 and the monthly emission from the Emission Database for Global Atmosphere Research (EDGAR) were consistent with PMF analysis and further prove that biomass burning is the dominant cause of the variation in the local air quality in mainland Southeast Asia.

Stability evaluation of deep-buried TBM construction tunnel based on microseismic monitoring technology

During the construction of Duoxiongla tunnel in Tibet, China, instabilities of the surrounding rock such as rock spalling, rock collapses and rockbursts frequently occurred. An advanced microseismic (MS) monitoring system was built to monitor and evaluate the stability of the rock masses under tunnel boring machine (TBM) excavation. The monitoring results reveal the tempo-spatial distribution of the MS events in unstable areas and enable the relationship between the number and energy of MS events and TBM activity to be established. Furthermore, nonroutine methods such as magnitude–frequency analysis and double-difference tomography are used to assess the stability of the tunnel. These results show that: (1) The precursor of instability of surrounding rock is a concentration of MS events in space and time; (2) The temporal distribution of b-values is consistent with the actual situation of the tunnel, and an inverse relation between the b-values and depth can be observed. The smaller the b-value, the greater the risk of instability of the surrounding rock; (3) The distribution of the velocity field inverted by double-difference tomography can effectively reflect the influence of excavation disturbances. Based on the results of MS monitoring and analysis of Duoxiongla Tunnel, an integrated approach is proposed, which is promising for assessing the stability of similar deep-buried TBM construction tunnels.

Rockburst mechanism and prediction based on microseismic monitoring

In this study, the rockburst definition is comprehensively described and several main rockburst theories (the strength theory, the energy theory, the bursting liability theory, the rigidity theory and the instability theory) are analyzed. The two-body interaction theory based on the Newton's law can explain the rockburst mechanism most reasonably. The rockburst development process is a static process and the rockburst occurrence process is within the scope of dynamics. In addition, some precursors exist before rockburst occurrence, reflected by the consistency between acoustic emissions and damage variables in rock mass, which can be summarised as three seismogenic models according to the tempo-spatial distribution. By utilizing the 3S (Stress buildup, Stress shadow and Stress transfer) principle in seismology, three rockburst criteria are proposed in this paper (namely, the stress tempo-spatial evolution, the magnitude, energy and concentration degree of microseismic events, sudden change of apparent volume). Finally, by comparing the results obtained by microseismic monitoring and landsonar positioning, it is shown that the root cause of rockburst occurrence is rock heterogeneity, and the existence of joints and fractures. The fracture intersection points are the locations for rockburst initiation. It is proven that the two-body interaction principle can perfectly explain the rockburst mechanism.

Stability Assessment of the Excavated Rock Slope at the Dagangshan Hydropower Station in China Based on Microseismic Monitoring

A high-resolution microseismic (MS) monitoring system was implemented at the right bank slope of the Dagangshan hydropower station in May 2010 to analyse the slope stability subjected to continuous excavation. The MS monitoring system could real-time capture a large number of seismic events occurring inside the rock slope. The identification and delineation of rock mass damage subject to excavation and consolidation grouting can be conducted based on the analysis of tempospatial distribution of MS events. However, how to qualitatively evaluate the stability of the rock slope by utilizing these MS data remains challenging. A damage model based on MS data was proposed to analyse the rock mass damage, and a 3D finite element method model of the rock slope was also established. The deteriorated mechanical parameters of rock mass were determined according to the model elements considering the effect of MS damage. With this method, we can explore the effect of MS activities, which are caused by rock mass damage subjected to excavation and strength degradation to the dynamic instability of the slope. When the MS damage effect was taken into account, the safety factor of the rock slope was reduced by 0.18 compared to the original rock slope model without considering the effect. The simulated results show that MS activities, which are subjected to excavation unloading, have only a limited effect on the stability of the right bank slope. The proposed method is proven to be a better approach for the dynamical assessment of rock slope stability and will provide valuable references for other similar rock slopes.

Investigation into the tempo-spatial distribution of recent fire hazards in China

Fire hazards are considered to be one of the most dangerous hazards in the world, which could lead to significant casualties and economic losses. This paper summarizes the fire hazards in China during the period from 2000 to 2016 in daily life, transportation, storages, industrial production, etc. In this research, the tempo-spatial distribution of fire hazards that result in fatalities, injuries and direct economic losses was studied. The place distribution of fire hazards was analyzed, and the primary causes of fire hazards were also discussed. In addition, an extensive fire hazard induced by an explosion incident at Tianjin harbor was studied and discussed. Linear regression relationships between the four indicators of fire hazard and the average gross domestic product were developed and analyzed. Based on the analyzed results, recommended mitigation measures against fire hazards were recommended.

Turing Instability-Driven Biofabrication of Branching Tissue Structures: A Dynamic Simulation and Analysis Based on the Reaction⁻Diffusion Mechanism †.

Four-dimensional (4D) biofabrication techniques aim to dynamically produce and control three-dimensional (3D) biological structures that would transform their shapes or functionalities with time, when a stimulus is imposed or cell post-printing self-assembly occurs. The evolution of 3D branching patterns via self-assembly of cells is critical for the 4D biofabrication of artificial organs or tissues with branched geometry. However, it is still unclear how the formation and evolution of these branching patterns are biologically encoded. Here, we study the biofabrication of lung branching structures utilizing a simulation model based on Turing instability that raises a dynamic reaction–diffusion (RD) process of the biomolecules and cells. The simulation model incorporates partial differential equations of four variables, describing the tempo-spatial distribution of the variables in 3D over time. The simulation results present the formation and evolution process of 3D branching patterns over time and also interpret both the behaviors of side-branching and tip-splitting as the stalk grows and the fabrication style under an external concentration gradient of morphogen, through 3D visualization. This provides a theoretical framework for rationally guiding the 4D biofabrication of lung airway grafts via cellular self-organization, which would potentially reduce the complexity of future experimental research and number of trials.

Large Deformation Characteristics and Reinforcement Measures for a Rock Pillar in the Houziyan Underground Powerhouse

The underground powerhouse of the Houziyan Hydropower Station is under the conditions of high geo-stress and a low strength/stress ratio, which leads to significant rock deformation and failures, especially for rock pillars due to bidirectional unloading during the excavation process. Damages occurred in thinner rock pillars after excavation due to unloading and stress concentration, which will reduce the surrounding rock integrity and threaten the safety of the underground powerhouse. By using field investigations and multi-source monitoring data, the deformation and failure characteristics of a rock pillar are analyzed from the tempo-spatial distribution features. These results indicate that significant deformation occurred in the rock pillar when the powerhouse was excavated to the fourth layer, and the maximum displacement reached 107.57 mm, which occurred on the main transformer chamber upstream sidewall at an elevation of 1721.20 m. The rock deformation surrounding the rock pillar is closely related to the excavation process and has significant time-related characteristics. To control large deformation of the rock pillar, thru-anchor cables were used to reinforce the rock pillar to ensure the stability of the powerhouse. The rock deformation surrounding the rock pillar decreases gradually and forms a convergent trend after reinforcement measures are installed based on the analysis of the temporal characteristics and the rock pillar deformation rate.

Pattern analysis of tempo-spatial distribution of schistosomiasis in marshland epidemic areas in stage of transmission control

To investigate the tempo-spatial patterns of schistosomiasis in Jiangling County, Hubei Province, so as to identify the risk areas and provide the scientific evidence in following intervention plans for marshland epidemic areas in the stage of transmission control. The schistosomiasis epidemiological data in Jiangling County from 2009 to 2013 together with the related geographical information were collected and analyzed. The tempo-spatial distribution patterns were analyzed by the spatial autocorrelation analysis and spatial clustering analysis. The human infection rate was decreased from 2.15% in 2009 to 0.63% in 2013, which was the historically low level. The results of tempo-spatial analysis showed that there were spatial clustering effects in human schistosomiasis infection for each of the years. The values of spatial autocorrelation index Moran's I were statistically significant. Eighteen and thirty-five clusters were detected by using SatScan and FlexScan software, respectively. From 2009 to 2013, the schistosomiasis endemic situation in Jiangling County presented a decline trend and reached the historical low level. The identified spatial clustering areas should be targeted as the prioritized areas for schistosomiasis control.

Performance evaluation of a miniature plate Electrostatic Aerosol Analyzer (mini-plate EAA)

To enable the tempo-spatial distribution monitoring/measurement of ultrafine particles, a cost-effective and miniature plate Electrostatic Aerosol Analyzer (mini-plate EAA) has been designed and characterized in this study for the use in electrical-mobility-based aerosol sizers. The prototype consists of two metal plates, installed in parallel in an insulation block, to establish the zone for particle classification. To minimize the effect of side wall in the classification zone, the length of aerosol entrance slit opening is half of the width of the classification zone. The performance of the mini-plate EAA, i.e., its transmission efficiency and transfer function, were experimentally evaluated for particles with the sizes ranging from 20 to 120nm. It is shown that the transmission efficiency of singly charged particles was nearly 100% in the sizes larger than 60nm and was dependent on the aerosol-to-sheath flow rate ratio for particles with the sizes less than 60nm when operated at the total flow rate of 3.0lpm. The particle penetration curves as a function of applied voltages were obtained for various combinations of aerosol and sheath flow rates. A modified 2-D model was further proposed to better calculate the cutoff voltage at the 50% penetration. The experimental transfer functions of the mini-plate EAA under the conditions of various aerosol-to-sheath flow rate ratios and at 3.0lpm sheath flow were given in this study.

Diversity variation and tempo-spatial distributions of the Dipteridaceae ferns in the Mesozoic of China

The extant family Dipteridaceae is a remarkable leptosporangiate fern because it includes only one genus with a restricted distribution to tropical regions. The fossil record of this family has been widely reported from the Mesozoic strata in Eurasia, America, Australia, and Greenland. In China, numerous fossils of the Dipteridaceae have been documented, in total, about 74 species of 6 genera. Geographically, they are distributed both in the Southern and Northern Floristic Provinces, and were particularly well developed in the Southern Floristic Province during the Late Triassic and the Early Jurassic intervals. Fossil diversity of Dipteridaceae varies in the different episodes of the Mesozoic in China. It is shown that Dipteridaceae has undergone a diversity development process and a distinct turnover during the Mesozoic. They appear to have diversified in the warm and humid Late Triassic–Early Jurassic, but declined sharply as aridity developed in the Middle Jurassic, and became extinct at the end of the Early Cretaceous. The diversity variation and tempo-spatial distribution pattern is suggested to be linked with paleoclimatic variations during the Mesozoic.

Microseismic monitoring and numerical simulation on the stability of high-steep rock slopes in hydropower engineering

For high-steep slopes in hydropower engineering, damage can be induced or accumulated due to a series of human or natural activities, including excavation, dam construction, earthquake, rainstorm, rapid rise or drop of water level in the service lifetime of slopes. According to the concept that the progressive damage (microseismicity) of rock slope is the essence of the precursor of slope instability, a microseismic monitoring system for high-steep rock slopes is established. Positioning accuracy of the monitoring system is tested by fixed-position blasting method. Based on waveform and cluster analyses of microseismic events recorded during test, the tempo-spatial distribution of microseismic events is analyzed. The deformation zone in the deep rock masses induced by the microseismic events is preliminarily delimited. Based on the physical information measured by in situ microseismic monitoring, an evaluation method for the dynamic stability of rock slopes is proposed and preliminarily implemented by combining microseismic monitoring and numerical modeling. Based on the rock mass damage model obtained by back analysis of microseismic information, the rock mass elements within the microseismic damage zone are automatically searched by finite element program. Then the stiffness and strength reductions are performed on these damaged elements accordingly. Attempts are made to establish the correlation between microseismic event, strength deterioration and slope dynamic instability, so as to quantitatively evaluate the dynamic stability of slope. The case studies about two practical slopes indicate that the proposed method can reflect the factor of safety of rock slope more objectively. Numerical analysis can help to understand the characteristics and modes of the monitored microseismic events in rock slopes. Microseismic monitoring data and simulation results can be used to mutually modify the sensitive rock parameters and calibrate the model. Combination of microseismic monitoring and numerical simulation provides a more objective basis for the numerical model and parameters and a solid mechanical foundation for the microseismic monitoring.

Microseismic monitoring and stability evaluation for the large scale underground caverns at the Houziyan hydropower station in Southwest China

The stability of underground caverns and the excavatability of rock masses are important for geotechnical engineering practices during the design and construction stages. The risks associated with underground caverns at the Houziyan hydropower station in Southwest China are growing due to excavation-induced unloading. To assess the instability of underground caverns and resolve the complex subsurface conditions of the highly fractured rock mass, a high-resolution microseismic monitoring system was established in deep underground caverns. This system was used to determine the relationship between the measured microseismic activities and the excavation damage zones of the surrounding rock mass. The excavation damage zones and potential risk regions in the underground caverns were identified by analyzing the tempo-spatial distribution of microseismic activities. In addition, the correlation between microseismic activities and pre-existing geological structures was determined, and traditional monitoring results were analyzed. To validate the correlation between seismicity and the excavation damaged zones of the underground caverns, a numerical model was employed to further evaluate the deformation and stability of the surrounding rock mass. The monitoring results demonstrate that microseismic events mainly occurred in high-stress-concentration regions, corresponding with the results obtained from the numerical analysis. Therefore, this comprehensive method, which incorporates microseismic monitoring, numerical analysis, traditional monitoring and field observations, is promising for predicting the deformation and instability of surrounding rock masses in the underground caverns subjected to excavation.