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过刊目录

  • 2021年, 18卷, 第05期
    刊出日期：2024-06-19
      
  • 全选
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  • Lithological and environmental controls on large tafoni along conglomerate cliffs in subtropic humid Danxiashan UNESCO Global Geopark
    CHEN Xin, CHEN Liu-qin, ZHANG Yan-hong, DU Ding-ding, HU Hai-ping, LIU Dong-xing, LI Wen-zhuo
    2021, 18(05): 1131-1143.
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    Tafoni are a type of cavernous weathering features widespread in different climate zones around the world, but their origin has not been fully understood. Little attention was paid on tafoni in conglomerates. Danxiashan UNESCO Global Geopark, located within the subtropic humid region of South China, has a landscape of large tafoni that occur on cliffs of red conglomerates. Both the Dinosaur Rock and Pagoda Peak of the geopark were selected to investigate the formation mechanisms of tafoni in conglomerates. During the field investigation, the size, rock hardness, and the external and internal meteorology of tafoni were measured and tested. The texture and composition of rock samples were observed, and the ion chromatography experiments were performed as well. Results show that tafoni have well ellipsoidal openings. Clasts of the conglomerates are largely sub-rounded and poorly sorted, and the cement is dominantly composed of calcite and iron oxide. The hardness of the lips is almost equal to that of the columns, and both are slightly higher than the backwalls. Compared with the external intense environmental changes, the interior of the tafoni is characterized by smaller temperature and relative humidity ranges and windless condition. Therefore, the porous and permeable conglomerates provide favorable lithology for tafoni development, and the micro-environment within the caverns is conducive to improving water utilization efficiency and enhancing salt weathering. The salts mainly consist of sulfates and nitrates, which might be derived from frequent raining, water evaporation and red beds as well. Consequently, tafoni are the result of the synergistic effects by multiple factors, rather than a single mechanism.
  • A 3-D morphological approach on spatial form and cultural identity of ethnic mountain settlements: Case from Guizhou, China
    JIA Zi-yu, MENG Cheng-yu, ZHOU Zheng-xu
    2021, 18(05): 1144-1158.
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    Ethnic mountain settlements are living heritage of varied vernacular cultures. The preservation of both the built form and the intangible socio-cultural associations with them are global concern in process of urbanization, and in the notion of sustainable development. However, there is a lack of multi-dimensional and cross-cultural quantitative research in settlement morphology, making it difficult to guide practice effectively. Therefore, this study focuses on exploring an automatic or semi-automatic quantification and classification method for the morphological identity of ethnic mountain settlements. We introduce and combine 3-D morphological indicators with existing 2-D indicators to build and test three different sets of indication systems for semi-automatic classification for the settlements' ethnic attribute basing on spatial morphology. Taking the Miao, Dong, and Tunpu(Han) ethnic settlements in Guizhou province, southwest China as research samples, we applied factor analysis and hierarchical clustering methods to compare the classification accuracy under the three systems using data from topographic map, field investigation map, satellite imageries, and ethnography or local chronicle. The results showed that, the 3-D indication system has succeeded in semi-automatic quantification and classification of settlement morphology and ethnic identity by greatly increasing the classification accuracy to 96.30%, which is a huge improvement compared with the basic 2-D indication system(42.59%) and the advanced 2-D indication system(61.11%). The settlement samples are further divided into two sub-types with significant morphological differences in each major ethnic category under the 3-D indication system. We then discussed the potential improvement and future large-scale application of this method with the help of machine learning and other smart techniques. We hope to provide a comprehensive quantitative perspective and a more scientific reference for the future preservation and sustainable development of the massive and diverse vernacular heritages across the world.
  • Influence of impulse waves generated by rocky landslides on the pressure exerted on bank slopes
    CAO Ting, WANG Ping-yi, QIU Zhen-feng, REN Jing-xuan
    2021, 18(05): 1159-1176.
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    Rocky landslides on river banks can result in the generation of ultra-high waves, which may destroy structures on the opposite bank. Existing methods to calculate the pressure on bank slopes under the effect of impulse waves generated by landslides are, however, few and of low precision. Therefore, in this study, a three-dimensional physical model test was conducted by taking into account factors such as landslide geometry parameters and the bank slope angle. The model test section was generalized on the basis of a certain section of the Three Gorges reservoir area as a prototype, after which the wave parameters and wave pressure acting on the bank slope were measured. Subsequently, the magnitude, acting point, and distribution of the pressure of the impulse waves generated by the rocky landslide upon the bank slope were determined. The distribution curve of the impact pressure was similar to that calculated using the СНиПⅡ57-75 formula, and the experimental pulsating pressure value was close to the value calculated using the Subgrade formula. Based on the test results, a power function of the relative pulsating pressure steepness with respect to the reciprocal of the wave steepness, relative water depth, and slope ratio was proposed. The acting point of the maximum pulsating pressure was found to be located near the still water level. Finally, an empirical formula for calculating the envelope of the maximum pulsating pressure distribution curve was proposed. These formulas can serve as a theoretical basis for the prediction of impulse wave pressure generated owing to landslides on bank slopes.
  • Development of a region-partitioning method for debris flow susceptibility mapping
    QIAO Shuang-shuang, QIN Sheng-wu, SUN Jing-bo, CHE Wen-chao, YAO Jing-yu, SU Gang, CHEN Yang, NNANWUBA Uzodigwe Emmanuel
    2021, 18(05): 1177-1191.
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    Debris flow susceptibility mapping(DFSM) has been reported in many studies, however, the irrational use of the same conditioning factor system for DFSM in regional-scale has not been thoroughly resolved. In this paper, a region-partitioning method that is based on the topographic characteristics of watershed units was developed with the objective of establishing multiple conditioning factor systems for regional-scale DFSM. First, watershed units were selected as the mapping units and created throughout the entire research area. Four topographical factors, namely, elevation, slope, aspect and relative height difference, were selected as the basis for clustering watershed units. The k-means clustering analysis was used to cluster the watershed units according to their topographic characteristics to partition the study area into several parts. Then, the information gain ratio method was used to filter out superfluous factors to establish conditioning factor systems in each region for the subsequent debris flow susceptibility modeling. Last, a debris flow susceptibility map of the whole study area was acquired by merging the maps from all parts. DFSM of Yongji County in Jilin Province, China was selected as a case study, and the analytical hierarchy process method was used to conduct a comparative analysis to evaluate the performance of the region-partitioning method. The area under curve(AUC) values showed that the partitioning of the study area into two parts improved the prediction rate from 0.812 to 0.916. The results demonstrate that the region-partitioning method on the basis of topographic characteristics of watershed units can realize more reasonable regional-scale DFSM. Hence, the developed region-partitioning method can be used as a guide for regional-scale DFSM to mitigate the imminent debris flow risk.
  • Understanding how environmental heterogeneity and elevation drives the distribution of woody communities across vegetation types within the campo rupestre in South America
    Marcelo Leandro BUENO, Vanessa Leite REZENDE, Luiza Fonseca A.DE PAULA, Jo?o Augusto Alves MEIRA-NETO, José Roberto Rodrigues PINTO, reza Viana NERI, Vanessa PONTARA
    2021, 18(05): 1192-1207.
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    The campo rupestre sensu lato is a vegetation type that occurs in South American mountains, supports a distinctive flora characterized by high rates of endemism, high herbaceous species richness and often-neglected but also species-rich of the arboreal stratum. We aimed to investigate how environmental factors and elevation are associated with the distribution and diversity of woody species in different rupestrian vegetation types across South America. Using a database of 2,049 woody species from 185 sites across four vegetation types within the campo rupestre, we assessed how the vegetation types were grouped according to their floristic composition and number of shared indicator species, as well as by using different beta diversity indices. The most important variables from a set of 27 variables(e.g. altitude, geo-edaphic and climatic) explaining species distribution were identified using redundancy analysis(RDA) and variation partitioning methods. The distribution of vegetation types was related to both environmental and spatial fractions, with a set of 17 variables retained(e.g. rockiness, grass cover and temperature seasonality as the most important variables). There was an association between the floristic composition of each vegetation type and the elevation range. Although the identified vegetation types are floristically related, they are distinguished by exclusive and habitat-specialist woody species. This uniqueness of vegetation types should be considered in terms of complementarity for the conservation of campos rupestres.
  • Cryostructures and ground ice content in ice-rich permafrost area of the Qinghai-Tibet Plateau with Computed Tomography Scanning
    FAN Xing-wen, LIN Zhan-ju, GAO Ze-yong, MENG Xiang-lian, NIU Fu-jun, LUO Jing, YIN Guo-an, ZHOU Fu-jun, LAN Ai-yu
    2021, 18(05): 1208-1221.
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    Permafrost is an important part of the cryosphere, playing an integral role in the hydrologic cycle, ecology, and influencing human activity. Melting of ground ice can drastically change landscapes and associated thaw subsidence may induce instability of infrastructure. The terrain conditions on the Qinghai-Tibet Plateau are complex, and the spatial distribution of ground ice is highly variable, so knowledge of its abundance and variability is required for impact assessments relating to the degradation of permafrost. This study examined 55 permafrost samples from warm, ice-rich permafrost region in Beiluhe Basin, Qinghai-Tibet Plateau. The samples were examined using Computed Tomography scanning, and the ice content and cryostructure were determined. The results indicated that: 1) variation in volumetric ice content was considerable(0%-70%), with a mean value of 17%; 2) seven cryostructures were identified, including crustal, vein, lenticular, ataxitic, reticulate and layered cryostructure; 3) volumetric ice content varied by cryostructure, with the highest associated with layered and ataxitic cryostructures. Volumetric ice contents were lowest for samples with pore and lenticular cryostructures. This work provides detailed ground ice content and will be helpful for assessing thaw subsidence and infrastructure stability on Qinghai-Tibet Plateau.
  • Effects of soil conservation practices on soil erosion and the size selectivity of eroded sediment on cultivated slopes
    XU Lu, ZHANG Dan, PROSHAD Ram, CHEN Yu-lan, HUANG Tian-fang, UGURLU Aysenur
    2021, 18(05): 1222-1234.
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    Soil conservation practices can greatly affect the soil erosion process, but limited information is available about its influence on the particle size distribution(PSD) of eroded sediment, especially under natural rainfall. In this study, the runoff, sediment yields, and effective/ultimate PSD were measured under two conventional tillage practices, downhill ridge tillage(DT) and plat tillage(PT) and three soil conservation practices, contour ridge tillage(CT), mulching with downhill ridge tillage(MDT), and mulching with contour ridge tillage(MCT) during 21 natural rainfall events in the lower Jinsha River. The results showed that(1) soil conservation practices had a significant effect on soil erosion. The conventional tillage of DT caused highest runoff depth(0.58 to 29.13 mm) and sediment yield(0.01 to 3.19 t hm-2). Compared with DT, the annual runoff depths and sediment yields of CT, MDT and MCT decreased by 12.24%-49.75% and 40.79%-88.30%, respectively.(2) Soil conservation practices can reduce the decomposition of aggregates in sediments. The ratios of effective and ultimate particle size(E/U) of siltand sand-sized particles of DT and PT plots were close to 1, indicating that they were transported as primary particles, however, values lower/greater than 1 subject to CT, MDT and MCT plots indicated they were transported as aggregates. The ratios of E/U of claysized particles were all less than 1 independently of tillage practices.(3) The sediments of soil conservation practices were more selective than those of conventional tillage practices. For CT, MDT and MCT plots, the average enrichment ratios(ERs) of clay, silt and sand were 1.99, 1.93 and 0.42, respectively, with enrichment of clay and silt and depletion of sand in sediments. However, the compositions of the eroded sediments of DT and PT plots were similar to that of the original soil. These findings support the use of both effective and ultimate particle size distributions for studying the size selectivity of eroded sediment, and provide a scientific basis for revealing the erosion mechanism in the purple soil area of China.
  • Predicting the impacts of climate change on the distribution of Moringa peregrina(Forssk.) Fiori-A conservation approach
    Emad A.FARAHAT, Aliaa M.REFAAT
    2021, 18(05): 1235-1245.
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    Climate change will affect the geographic distribution and richness of species at different spatial and temporal scales. We applied Maximum entropy(MaxEnt) modeling to predict the potential influence of climatic change on the current and future distribution of the important mountainous tree species Moringa peregrina(Forssk.) Fiori. The Maxent model performed better than random models for the species with the training and test AUC(Area Under the receiver-operating characteristic Curve) values of 0.96 and 0.90, respectively. Jackknife test and response curves showed that the distribution of the species negatively correlates with higher altitudes and precipitation in October and November. Moreover, it positively correlates with the total annual precipitation and precipitation in January. Under current and future climatic conditions, our model predicted habitat gains for M. peregrina towards the coastal northern and southern limits of its distribution. The potentially suitable habitats, under future climate projections, are currently characterized by elevations of <1000 m a.s.l. and total annual precipitation of 80-225 mm/year. Moderate and high potential habitat suitability will increase by 5.6%-6% and 2.1%-2.3%, under RCP2.6 and RCP4.5 scenario, respectively. The results indicated that the habitat suitability of M. peregrina would increase with increasing climate warming, particularly under RCP2.6 scenario. We recommend sustainable conservation and cultivation of Moringa peregrina in its current habitats along the Red Sea mountains.
  • Vegetation dynamics and climate variability over the past 2000 years inferred from Son Kul marsh in the western Tianshan Mountains
    ZHANG Dong-liang, LI Yao-ming, LI Kai-hui, MA Xue-xi, YANG Yun-peng
    2021, 18(05): 1246-1255.
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    A pollen study was conducted on an alpine marsh sediment in the Son Kul Basin and was allowed to reconstruct changes in vegetation dynamics and climatic information in the western Tianshan Mountains during the past 2000 years. Pollen diagram reveals that regional vegetation is dominated by alpine meadow in the past 2000 years, being similar with modern vegetation components in the basin. The Artemisia/Chenopodiaceae-indicated moisture exhibits a warm-dry Roman Warm Period(RWP, ～0-～500 AD), a cold-dry Dark Ages Cold Period(DACP, ～500-～800 AD), a warm-wet Medieval Warm Period(MWP, ～800-～1350 AD), a cold-dry Little Ice Age(LIA, ～1350-～1850 AD) and a warm-dry Current Warm Period(CWP, since ～1850 AD). Our pollen-based moisture reconstructions are supported by other nearby moisture records. Combined with other pollen data in the western Tianshan Mountains, we found that the vegetation was relatively stable before ～1650-～1750 AD and the anthropogenic activities obviously intensified afterwards(especially at the middle-elevation sites). Further work involving more and higher-resolution palaeovegetation records would contribute to fully understand the information on the complex links between environmental, climatic and anthropogenic changes in the western Tianshan Mountains.
  • A remote sensing based analysis of climate change in Sikkim supported by evidence from the field
    Rumia BASU, Gourav MISRA, Dipto SARKAR
    2021, 18(05): 1256-1267.
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    The Himalayas hailed as the ‘water towers of the world' feed many perennial rivers which form the lifeline of the Indian sub-continent. Climate change induced rising global temperatures and changing rainfall patterns are currently threatening the glaciers that feed the rivers. The combination of these factors is causing water stresses to a part of the world which is usually considered water abundant. Though there are some large-scale studies done in the Himalayas, regional analysis of changing rainfall patterns and their impacts on vegetation and agriculture is lacking. Here we focus on the Indian state of Sikkim located in the Eastern Himalayas to evaluate these issues using mixed methods. We use satellite data from PERSIANN and MODIS to characterise the regional rainfall, vegetation, and surface temperature trends between 2001 and 2019. While the analysis shows overall declining rainfall trends across most land cover classes, the trends in temperature are mostly positive for the period of study, with winter Land Surface Temperature(LST) values showing the largest area with marginally significant(p<0.1) positive trends. In contrast, such patterns are not observed for agriculture. However, the interviews corroborate that even agriculture is impacted, implying that the trends continue at finer spatial scales too. The lack of government support for adaptation and mitigation is also lamented placing the communities at a precarious position to continuing climate change.
  • Geomorphological responses of rivers to active tectonics along the Siwalik Hills, Midwestern Nepalese Himalaya
    Indu BHATTARAI, Nahid D.GANI, Liang XUE
    2021, 18(05): 1268-1294.
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    The Nepalese Himalaya is well known for ongoing collisional tectonics, witnessed by major historical and recent earthquakes. The Siwalik Hills in Midwestern Nepalese Himalaya are bounded by eastwest trending Main Frontal Thrust(MFT) to the south and the Main Boundary Thrust(MBT) to the north. The area is dissected by numerous southwest to south-flowing bedrock rivers. This study investigates geomorphic metrics of these rivers to unravel landscape evolution and active tectonics of the Siwalik Hills. Digital Elevation Model(DEM) analysis was conducted to extract structural lineaments and longitudinal river profile and their metrics(knickpoints, Normalized Steepness Index(ksn), concavity index, and chi integral) using steam powerlaw approaches. Most of the lineaments trend eastwest like MFT. River profiles exhibit convex to double-concave shapes with upstream-propagating tectonic knickpoints that separate upstream and downstream reaches, indicating different phases of river incision. The spatial distribution of ksn shows high values along with low concavity values at the eastern part of the study area, reflecting disequilibrium conditions that are likely responding to a high uplift rate. Chi integral distribution shows a variation in drainage divide migration between the eastern and western parts of the study area. This study suggests that the rivers in the Siwalik Hills are undergoing active incision likely related to the ongoing uplift and active deformation associated with the Himalayan tectonics. The above findings can bring fresh perspectives to comprehend the neotectonic deformation and lateral variability along the Siwalik Hills landscapes within the Himalaya.
  • Characteristics of soil erosion and sediment size distribution for different land uses in the Chinese Mollisol region
    SHEN Hai-ou, FENG Jun, WANG Dong-li, LI Hong-li, WANG Yu
    2021, 18(05): 1295-1306.
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    Soil erosion is currently a major contributor to the degradation of global soil resources. The characteristics of sediment size distribution affect soil erosion processes. However, few studies have quantitatively explored soil erosion processes and sediment size distributions on natural hillslopes for different land uses, especially in the Chinese Mollisol region. The objective of this study was to investigate the impacts of land uses(corn, fallow, buffer strip and bare hillslopes) under 5° and 10° slope gradients on total runoff, runoff rates, soil losses, sediment concentration processes, and sediment size distributions. Natural runoff plots(20 m long and 5 m wide) were subjected to inflow scour experiments(1 L min~(–1) m~(–2), lasting 40 min). The results showed that the total runoff varied from 2.62 to 6.40 L m~(–2) and from 8.36 to 20.39 L m~(–2) on hillslopes at 5° and 10°, respectively. The changes in runoff rates versus run time exhibited gradual increasing trends at 5°, but exhibited initial rapidly increasing trends and then relatively stable trends at 10°. Fallow hillslopes produced the lowest soil losses, which were 45.34%-45.92%, 2.74%-6.72% and 1.68%-3.44% for the corn, buffer strip and bare hillslopes, respectively. Most sediment concentrations were very small and stabilized between 0.5-2.0 g L~(–1) on the fallow hillslopes and 1.5-3.0 g L~(–1) on the corn hillslopes at 5°, but the changing trends in sediment concentration versus run time for the four land uses generally decreased at 10°. Furthermore, it was demonstrated that the proportion of sediment <0.25 mm was the largest in comparison with the other sediment size fractions, and <0.25 mm soil particles and aggregates played a dominant role in soil aggregate loss under different land uses. Thus, protecting these precious soil particles and aggregates by applying proper soil conservation measures especially for the relatively gentle hillslopes was particularly important. Additionally, the fallow hillslope with greater soil and water conservation capacities was very suitable for the Mollisol hillslopes.
  • Influences of pika and simulated grazing disturbances on bare patches of alpine meadow in the Yellow River Source Zone
    LI Jie-xia, LI Xi-lai, GAO Jay, SHI Yan, MA Ge-liang, Ka-zhao-cai-rang
    2021, 18(05): 1307-1320.
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    Bare patches in alpine meadow are the main manifestation of its degradation. The change of bare patches in an alpine meadow in the Yellow River Source Zone during 2018-2019 was studied in relation to the disturbances caused by plateau pika(Ochotona curzoniae) population and simulated grazing via artificial mowing both independently and interactively. The disturbance was set at three levels of high, medium and no disturbance(control group). Bare patches were mapped by from unmanned aerial vehicle(UAV) images with fine resolution of 1 cm obtained in August 2018 and August 2019 in ArcGIS. The results showed that the total area of bare patches decreased by 112.05 m~2 in sub-plots devoid of pika disturbance but increased by 126.37 m~2 in other subplots. The highest rate of increase is 89.02%. The individual effect of pika exceeds the joint effect of pika and mowing disturbances. The sole effect of mowing is lower than the joint effect of pika disturbance and intensive mowing, but higher than the joint influence of pika disturbance and moderate mowing. Strong pika disturbance(14 per sub-plot) caused the influence of mowing from moderate to intensive to increase by five-fold. The area of bare patches treated with moderate mowing and no pika disturbance decreased at the highest pace(-37.22%). Intensive mowing and medium density pikas(100 pikas/ha) are considered the thresholds at which the bare patches start to expand. Even if the meadow is mowed at the medium and high intensity, the area of bare patches can be significantly reduced if plateau pika population is controlled to a low level. ANOVA analysis and longterm macro-scale satellite-derived results reveal that pika disturbance is more important in causing the bare patches to change than simulated grazing. Therefore, it is more important to control the number of pikas than to reduce grazing intensity to prevent the expansion of bare patches in the degraded alpine meadow in the study area.
  • Intercontinental response to variations in the Arabia-Eurasia Plate convergence, calcite e-twin evidence of the Kuhbanan Fault system, Central Iran
    Sara ESMAEILIAN, Saeed MADANIPOUR, Shahram SHAAFIEIBAFTI, Yasamin EBRAHIMI
    2021, 18(05): 1321-1339.
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    Variations in the plate convergence direction have generally reflected on the kinematics of the major fault zones developed in the intercontinental parts of the collision zones. The Kuhbanan Fault system is one of the most important intercontinental faults in the Arabia-Eurasia collision zone with a dextral strike slip mechanism. This fault system is composed of three fault strands including Kuhbanan, Bazargan, and Kerman Faults. Here we used calcite e-twin analysis of the vein samples developed in these fault zones to reconstruct deformation condition and the paleodifferential stress direction and magnitude at the Kuhbanan Fault system. Our results represent 190°C-200°C of the deformation temperature and related 5–6 ± 1 km of deformation depth at the Kuhbanan Fault system. Calculated paleodifferential stress magnitude in the Kuhbanan Fault system using e-twin parameters ranges from 169-196 MPa similar to the inner parts of the orogenic systems. Comparing the data set of the Kuhbanan Fault system with previous studies at the Zagros orogen represents an increase of deformation depth and paleodifferential stress magnitudes from the foreland of the Zagros orogen to its hinterland and finally northward around the Kuhbanan Fault system in the central Iranian blocks. We have also proposed a shift of the stress direction from paleo NE to recent N directed by comparing paleostress direction deduced from the calcite e-twin and recent stress direction calculated from GPS and earthquake data analysis around the Kuhbanan Fault system. This kinematics change due to plate reorganization is in agreement with the observed regional variation in convergence direction all in the Arabia-Eurasia collision zone.
  • Wind-sand movement characteristics and erosion mechanism of a solar photovoltaic array in the middle of the Hobq Desert, Northwestern China
    TANG Guo-dong, MENG Zhong-ju, GAO Yong, DANG Xiao-hong
    2021, 18(05): 1340-1351.
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    The operation and power generation of utility-scale solar energy infrastructure in desert areas are affected by changes in surface erosion processes resulting from the construction of solar photovoltaic(PV) power stations. However, few studies have addressed the interactions between solar PV arrays and aeolian erosion processes. In this study, wind flow field characteristics and the vertical distribution of sediments were investigated in the near-surface transport layer at three different locations with respect to the solar PV arrays in a 200 WM-p PV power station in the central Hobq Desert, northwestern China. The results indicate that the sediment transport varied around the panels, with the greatest transport occurring between the panels, followed by behind and in front of the panels. The sediment fluxes of all of the observation sites obey an exponential function. The secondary flow field zones formed around the PV panels: the conflux accelerating zone between the panels, the resistance decelerating zone of the under panels, and the transition zone of the rapid velocity increase in front of and behind the panels. This resulted in a greater shear force in front of the panels under the downward flow diversion effect of PV panels, and the wind erosion depressions were finally formed here. The results of this study provide information for planning better technical schemes for wind-sand hazards at solar PV power stations, which would ensure operational stability and safety in desert areas.
  • Cracking behaviors and strength of rock-like samples with steps of different geometries under shear stress
    LE Hui-lin, WEI Ji-hong, SUN Shao-rui, ZHANG Chu-chu
    2021, 18(05): 1352-1370.
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    Steps are distinctive features for estimating the movement of the upper and lower block of faults. However, studies about the influence of steps as a special type of discontinuity on cracking behaviors and strength of rock masses are limited. In this research, rock-like samples with steps and preexisting flaws were fabricated. Step height h and the inclination angle of gentle slope of the step α were set to different values. Direct shear tests were conducted on these samples under different normal stresses. The experimental results reveal that the inclination angle of the gentle slope of the step α, step height h, and normal stress have an influence on the strength, crack initiation, and crack propagation of the samples. The experimental results show that crack behaviors and shear strength were affected by step inclination angles α and step height h. As the normal stress increases, the improvement of the strength of samples with a large step height is larger than that of samples with a small step height, the improvement of the strength of samples with α of 10° is larger than that of samples with α of 0° and-10°. The discrete element method was used to simulate the shear test. Numerical results show five different types of displacement vectors, which can be used to determine whether the cracks are tensile cracks or shear cracks. The above conclusions can provide help for estimating mechanical properties and failure modes of rock masses with steps of different geometries.
  • Time-dependent squeezing deformation mechanism of tunnels in layered soft-rock stratum under high geo-stress
    CHEN Zi-quan, HE Chuan, WANG Jun, MA Chun-chi
    2021, 18(05): 1371-1390.
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    Large squeezing deformation of layered soft rock tunnel under high geo-stress has a significant time-dependent deformation behavior. In this paper, we studied the deformation mechanism during the construction period of deep-buried softrock tunnel by means of a combination of field observations and a numerical method. First, a new classification criterion for large deformations based on the power exponent variation law between the deformation and the strength-stress ratio is proposed. Then, the initial damage tensor reflecting the bedding plane(joint) distribution and an equivalent damage evolution equation derived from the viscoplastic strain are introduced based on the geometric research method, i.e., a new rheological damage model(RDL model) of layered soft rock is established consisting of elastic, viscous, viscoelastic, viscoplastic and plastic elements. A field test was conducted on the Maoxian tunnel in Sichuan province, southwestern China, which is in broken phyllite(layered soft rock) under high geo-stress. The tunnel has experienced large deformation due to serious squeezing pressure, thus we adopted double primary support method to overcome the supporting structure failure problems. The rheological parameters of phyllite in the Maoxian tunnel were recognized by using SA-PSO optimization, and the RDL model does a good job in describing the time-dependent deformation behavior of a layered soft-rock tunnel under high geo-stress. Thus, the RDL model was used to investigate the supporting effect and bearing mechanism of the double primary support method. Compared with the single primary support method, the surrounding rock pressure, secondary lining force, surrounding rock deformation, and the depth of the damage to the rock mass was reduced by 40%-60% after the double primary support method was used.
  • The collision experiment between rolling stones of different shapes and protective cushion in open-pit mines
    ZHU Chun, HE Man-chao, KARAKUS Murat, ZHANG Xiao-hu, GUO Zhen
    2021, 18(05): 1391-1403.
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    Though gravel cushions are used worldwide in open-pit mines and railway slopes to control the impact of rolling stones, no universal technical standards have been put in place to guide engineers in their correct design, and few laboratory test results are available with which to characterize collisions between rolling stones and a gravel cushion. We carried out a large number of experiments in which rolling stones made of the same material but differently shaped were dropped from various heights onto cushions with various particle sizes and thicknesses. We investigated the characteristics of the resulting collisions, and the relationships between coefficients of restitution(CORs) of blocks with different shape and release height H, cushion thickness h and particle diameter d are obtained through linear fitting method. Orthogonal testing reveals the relative influence of block shape, release height, and the particle size and thickness of the cushion on the collision characteristics, which can assist engineers in designing a gravel cushion suitable to the distribution and weathering characteristics of rolling stones in a specific area.