过刊目录

  • 2020年, 17卷, 第11期
    刊出日期:2024-06-19
      

  • 全选
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  • VIANI Cristina, CHIARLE Marta, PARANUNZIO Roberta, MERLONE Andrea, MUSACCHIO Chiara, COPPA Graziano, NIGRELLI Guido
    2020, 17(11): 2591-2610.
    Rockfalls are one of the most common instability processes in high mountains. They represent a relevant issue, both for the risks they represent for(infra) structures and frequentation, and for their potential role as terrestrial indicators of climate change. This study aims to contribute to the growing topic of the relationship between climate change and slope instability at the basin scale. The selected study area is the Bessanese glacial basin(Western Italian Alps) which, since 2016, has been specifically equipped, monitored and investigated for this purpose. In order to provide a broader context for the interpretation of the recent rockfall events and associated climate conditions, a cross-temporal and integrated approach has been adopted. For this purpose, geomorphological investigations(last 100 years), local climate(last 30 years) and near-surface rock/air temperatures analyses, have been carried out. First research outcomes show that rockfalls occurred in two different geomorphological positions: on rock slopes in permafrost condition, facing from NW to NE and/or along the glacier margins, on rock slopes uncovered by the ice in the last decades. Seasonal thaw of the active layer and/or glacier debutressing can be deemed responsible for slope failure preparation. With regard to timing, almost all dated rock falls occurred in summer. For the July events, initiation may have been caused by a combination of rapid snow melt and enhanced seasonal thaw of the active layer due to anomalous high temperatures, and rainfall. August events are, instead, associated with a significant positive temperature anomaly on the quarterly scale, and they can be ascribed to the rapid and/or in depth thaw of the permafrost active layer. According to our findings, we can expect that in the Bessanese glacierized basin, as in similar high mountain areas, climate change will cause an increase of slope instability in the future. To fasten knowledge deepening, we highlight the need for a growth of a network of high elevation experimental sites at the basin scale, and the definition of shared methodological and measurement standards, that would allow a more rapid and effective comparison of data.
  • Ali POLAT, Dursun ER?K
    2020, 17(11): 2611-2623.
    Turkey is highly prone to landslides because of the geological and geographic location. The study area, which is located in a tectonically active region, has been significantly affected by mass movements. Flow type landslides are frequently observed due to this location. This study aims at determining the source area and propagation of debris flows in the study area. We used the heuristic method to extract source areas of debris flow, and then used receiver operating characteristic(ROC) curve analysis to assess the performance of the method, and finally calculated the Area under curve(AUC) values being 83.64% and 80.39% for the success rate and prediction rate, respectively. We calculated potential propagation area and runout distance with Flow-R software. In conclusion, the obtained results(susceptibility map, propagation and runout distance) are very important for decisionmakers at the region located on an active fault zone, which is highly prone to natural disasters. The outputs of this study could be used in site selection studies, designing erosion prevention systems and protecting existing human-made structures.
  • Ayberk KAYA, ümit Murat M?D?LL?
    2020, 17(11): 2624-2635.
    Landslides are quite common natural hazards in the eastern Black Sea region of NE Turkey. Following the heavy rainfall in the K?prülü(Rize) village settlement area, located in this region where the slope debris overlies the agglomerates, a failure occurred. Due to the developed tension cracks and deformations on the ground, houses, tea gardens, and roads were damaged completely. To figure out the causes and mechanism of the sliding and to suggest the precautions, a detailed geotechnical study was carried out. Along the five survey lines, twelve boreholes were drilled with a total depth of 300 meters. Also, the geophysical surveys on ten profiles were conducted and the inclinometer measurements were taken in five boreholes. Undisturbed and disturbed samples were collected and laboratory experiments were performed. Inclinometer measurements indicated that the sliding started in the slope debris and then spread to the agglomeratic bedrock. The slope stability was examined using the limit equilibrium(LE) and finite element(FEM) analysis methods. The results of the slope stability analyses showed that the failure mode is talus slide with composite shape and outputs coincide with the inclinometer monitoring results. Based on the collected data, it is determined that there will be unavoidable engineering problems if no precautions are taken. Because of the negative reasons which make the application of supporting methods meaningless in the study area, it is considered that transferring the residences to a safer place without risk of natural hazards will be economical and reliable.
  • LIU Yang, YOU Yong, LIU Jin-feng, ZHAO Shu-xi, YANG Dong-xu, LIU Dao-chuan, LIU Lin, XIE Yan-fang, YANG Kai-cheng
    2020, 17(11): 2636-2651.
    The primary cracks in the rock block undergo series of steps and finally disintegrate, during this procession, the radius affects the impact force of rock block in clastic flow. Therefore, it is essential to figure out the evolution mechanism of crack propagation for the design of engineering protection. In this study, based on fracture mechanics and Hertz contact theory, collision happened between rock block and slope surface is assumed to be elastic contact. Based on the above assumption, the critical impact force of crack propagation is obtained, and a model used to calculate the crack propagation length in a single collision is established. Besides, a rock fall site in Jiuzhai Valley was used to verify the calculation model. According to the model, several key factors were identified to influence crack propagation length including falling height, initial equivalent radius, and recovery coefficient of slope surface. Moreover, as a result of the orthogonal experiment, the influence of those factors on the crack propagation length was ranked, normal recovery coefficient> initial radius >initial falling height. In addition, the kinetic energy of the rock block in the compression stage is transformed into elastic deformation energy, angular kinetic energy, and dissipated energy of crack propagation. Due to the increase of collisions, the kinetic energy is gradually transformed into angular kinetic energy, and the dissipated energy of crack propagation weights is reduced. In conclusion, the crack propagation in rock block is a complicated progress, which is affected by multiple factors, especially falling height, initial equivalent radius, and recovery coefficient of slope surface. Our study may provide guidance for the design of protective structure of clastic flows.
  • Susmita DHAKAL, CUI Peng, SU Li-jun, Olga MAVROULI, ZOU Qiang, ZHANG Jian-qiang, Lalu PAUDEL, Nirusha SHRESTHA
    2020, 17(11): 2652-2673.
    Kathmandu Kyirong Highway(KKH) is one of the most strategic Sino-Nepal highways. Lowcost mitigation measures are common in Nepalese highways, however, they are not even applied sufficiently to control slope instability since the major part of this highway falls still under the category of feeder road, and thus less resources are made available for its maintenance. It is subjected to frequent landslide events in an annual basis, especially during monsoon season. The Gorkha earthquake, 2015 further mobilized substantial hillslope materials and damaged the road in several locations. The aim of this research is to access the dynamic landslide susceptibility considering pre, co and post seismic mass failures. We mapped 5,349 multi-temporal landslides of 15 years(2004-2018), using high resolution satellite images and field data, and grouped them in aforementioned three time periods. Landslide susceptibility was assessed with the application of 'certainty factor'(CF). Seventy percent landslides were used for susceptibility modelling and 30% for validation. The obtained results were evaluated by plotting 'receiver operative characteristic'(ROC) curves. The CF performed well with the 'area under curve'(AUC) 0.820, 0.875 and 0.817 for the success rates, and 0.809, 0.890 and 0.760 for the prediction rates for respective pre, co and post seismic landslide susceptibility. The accuracy for seismic landslide susceptibility was better than pre and post-quake ones. It might be because of the differences on completeness of the landslide inventory, which might have been possibly done better for the single event based co-seismic landslide mapping in comparison with multitemporal inventories in pre and post-quake situations. The results obtained in this study provide insights on dynamic spatial probability of landslide occurrences in the changing condition of triggering agents. This work can be a good contribution to the methodologies for the evaluation of the dynamic landslide hazard and risk, which will further help to design the efficient mitigation measures along the mountain highways.
  • GUO Xiao-yi, ZHANG Hong-yan, WANG Ye-qiao, ZHAO Jian-jun, ZHANG Zheng-xiang
    2020, 17(11): 2674-2690.
    Fire is an important disturbance in terms of forest management. A comprehensive understanding of the relationships between the spatial distribution of fire occurrence and its driving factors are critical for effective forest fire management. To reveal biogeoclimatic and anthropogenic influences, this study introduced a geographical detector model to quantitatively examine the effects of multiple individual factors and their combinations on spatial patterns of fire occurrence in the Greater Khingan Mountains between 1980 and 2009. The geographical detector computes the explanatory power(q value) to measure the connection between driving factors and spatial distributions of fire occurrence. Kernel density estimation revealed the spatial variability of fire occurrence which was impacted by bandwidth. 30 km might be the optimal bandwidth in this study. The biogeoclimatic and anthropogenic effects were explored using topography, climate, vegetation, and human activity factors as proxies. Our results indicated that solar radiation had the most influence on the spatial pattern of fire occurrence in the study area. Meanwhile, Normalized Difference Vegetation Index, temperature, wind speed, and vegetation type were determined as the major driving factors. For various groups of driving factors, climate variables were the dominant factors for the density of fire occurrence, while vegetation exerted a strong influence. The interactions between the driving factors had a more significant impact than a single factor. Individually, the factors in the topography and human activity groups exhibited weaker influences. However, their effects were enhanced when combined with climate and vegetation factors. This study improves our understanding of various driving factors and their combined influences on fire occurrences of the study area in a spatial context. The findings of this study verify that the geographical detector is applicable in revealing the driving factors of fire occurrence.
  • Magdalena TANONA, Pawe? CZARNOTA
    2020, 17(11): 2691-2706.
    The Index of Atmospheric Purity(IAP) is a popular tool used for the assessment of air quality in polluted urban areas, on the basis of phytosociological data of epiphytic lichen communities. We hypothesized that this indicator could also be used in less polluted forest areas to determine the quality of ecological conditions for lichens. The aim of the present study was to verify the use of IAP method in the assessment of environmental pollution, and alternatively for the assessment of general ecological conditions in protected mountain forests of Gorce National Park(Polish Western Carpathians) based on the epiphytic lichen biota associated with Picea abies. The spatial distribution of IAP values on monitored sites in GNP was compared with: 1) spatial distribution of accumulated sulfur, nitrogen, selected heavy metals, and total heavy metals in Hypogymnia physodes thalli in 1993 and 2018(30 sites), 2) mean ecological indicator values characterizing species requirements for light(L), substrate reaction(R) and nutrients(N), in 1993, 2013 and 2018(33 sites). Generalized linear model and redundancy analysis were performed for disclosing most influencing factors affecting lichen communities. The study revealed a few negligible relationships between IAP values and accumulation of such elements as Ni, Mn, Cd, and Cr in both monitoring periods.Simultaneously, IAP can be useful for the identification of forest areas with a high degree of naturalness.
  • ZHANG Mei-mei, ZHAO Hang, CHEN Fang, ZENG Jiang-yuan
    2020, 17(11): 2707-2723.
    Glacial lake mapping provides the most feasible way for investigating the water resources and monitoring the flood outburst hazards in High Mountain Region. However, various types of glacial lakes with different properties bring a constraint to the rapid and accurate glacial lake mapping over a large scale. Existing spectral features to map glacial lakes are diverse but some are generally limited to the specific glaciated regions or lake types, some have unclear applicability, which hamper their application for the large areas. To this end, this study provides a solution for evaluating the most effective spectral features in glacial lake mapping using Landsat-8 imagery. The 23 frequently-used lake mapping spectral features, including single band reflectance features, Water Index features and image transformation features were selected, then the insignificant features were filtered out based on scoring calculated from two classical feature selection methods-random forest and decision tree algorithm. The result shows that the three most prominent spectral features(SF) with high scores are NDWI1,EWI, and NDWI3(renamed as SF8, SF19 and SF12 respectively). Accuracy assessment of glacial lake mapping results in five different test sites demonstrate that the selected features performed well and robustly in classifying different types of glacial lakes without any influence from the mountain shadows. SF8 and SF19 are superior for the detection of large amount of small glacial lakes, while some lake areas extracted by SF12 are incomplete. Moreover, SF8 achieved better accuracy than the other two features in terms of both Kappa Coefficient(0.8812) and Prediction(0.9025), which further indicates that SF8 has great potential for large scale glacial lake mapping in high mountainous area.
  • YANG Yong, CHEN Ren-sheng, SONG Yao-xuan, HAN Chun-tan, LIU Zhang-wen, LIU Jun-feng
    2020, 17(11): 2724-2741.
    As an important soil property, saturated hydraulic conductivity(K_s) controls many hydrological processes, such as runoff generation types, soil moisture storage and water movement. Because of the extremely harsh natural environmental conditions and soil containing a significant fraction of gravel fragments in high-elevation mountainous catchments, the measurement data of K_s and other soil properties are seriously lacking, which leads to poor understanding on its hydrological processes and water cycle. In this study, the vertical variation(0-150 cm) of K_s and other soil properties from 38 soil profiles were measured under five different land cover types(alpine barren, forest, marshy meadow, alpine shrub and alpine meadow) in a small catchment in Qilian Mountains, northwestern China. A typical characteristic of soil in mountainous areas is widespread presence of rock and gravel, and the results showed that the more rock and gravel in the soil, the higher K_s and bulk density and the lower the soil capillary porosity, field water capacity and total porosity. The K_s of the lower layer with rock and gravel(18.49 ± 10.22 mm·min~(-1)) was significantly higher than that of the upper layer with relatively fine textured soil(0.18 ± 0.18 mm·min~(-1)). The order of values of the K_s in different land cover types was alpine barren, forest, alpine shrub, marshy meadow and alpine meadow, and the values of the K_s in the alpine barren were significantly higher than those of other land covers. Most rainfall events in the research catchment had low rain intensity(<0.04 mm·min~(-1)), and deep percolation(DP) was the dominant runoff generation type. When the rainfall intensity increased(0.11 mm·min~(-1)), subsurface stormflow(SSF) appeared in the alpine meadow. Infiltration excess overland flow(IOF), SSF and DP existed simultaneously only when the rainfall intensity was extremely high(1.91 mm·min~(-1)). IOF and SSF were almost never appeared in the alpine barren because of high K_s. The alpine barren was the main runoffcontributed area in the mountainous catchment because of high K_s and low water-holding capacity, and the alpine shrub and meadow showed more ecological functions such as natural water storage and replenishment pool than contribution of runoff.
  • HAN Fang, WAN Li, WU Hong-zhi, ZHANG Bai-ping, GAO Lan, SONG Ge
    2020, 17(11): 2742-2749.
    The mass elevation effect(MEE) of the Tibetan Plateau(TP) has attracted the attention of geographers because of its significant influence on the Asian climate, snow line, timberline, and other important climate-ecological boundaries of the plateau and on global ecological patterns. In recent years, much progress has been made in quantifying the MEE of TP. However, factors that affect the size of MEE have not been examined in depth, and the key factors still remain unclear. Based on quantification of MEE for each mountain basal elevation plot, this study identifies the factors that contribute significantly to MEE of the plateau. Seven factors are considered, including mountain basal elevation, distance from the core zone of MEE, thermal continentality, maximum elevation, height difference, area, and difference of underlying surface(with the yearly max "Normalized Difference Vegetation Index"(NDVI) serving as a quantitative indicator). We also used these seven factors as independent variables to develop a multiple linear regression model for MEE of the plateau. Results show that:(1) the determination coefficient(R2) of the model reaches as high as 0.877, and the contributions of mountain basal elevation, distance from the core zone of MEE, thermal continentality, maximum elevation, topographical height difference, area, and NDVI are 39.77%, 23.02%, 14.48%, 5.78%, 11.41%, 2.92%, and 2.62%, respectively, with mountain basal elevation and the distance from the core of MEE as the most important factors;(2) thermal continentality and MEE are significantly correlated, and maximum elevation only has a coupling relationship with MEE, with height difference and NDVI contributing little to MEE. This study deepens our understanding of MEE and its forming factors in the Tibetan Plateau.
  • ZHANG Ji, WANG Yuan-zhong, GAO Hong-kai, ZUO Zhi-tian, YANG Shao-bing, CAI Chuan-tao
    2020, 17(11): 2750-2757.
    Patterns of biomass allocation among organs in plants are important because they influence many growth processes. The Yunnan-Guizhou Plateau(YGP) is considered to be one of the most sensitive areas in China to climate changes, but we know little about how current climatic gradients on the plateau influence plant biomass allocation. Gentiana rigescens and G. rhodantha, on the YGP, are important species because they are used in traditional Chinese medicines. We therefore analyzed the biomass allocation patterns of the two species across an elevation gradient(1000–2810 m a.s.l.) on the YGP to understand and predict the impact of climate change on these plant species. We found that the total biomass, reproductive biomass, vegetative biomass, aboveground biomass, and belowground biomass in G. rigescens were all significantly larger than those in G. rhodantha(p<0.05). However, for both species the aboveground biomass was nearly isometrically related to belowground biomass, regardless of elevation, mean annual temperature(MAT) ranging from 8.4℃t to 18.8℃t, and mean annual precipitation(MAP) ranging from 681 to 1327 mm, while the reproductive biomass was allometrically related to vegetative biomass. Intriguingly, there was a significant positive relationship(p<0.05) between the slope of the allometric scaling of reproductive and vegetative biomass and elevation among G. rigescens populations, i.e. plants growing at high elevationsallocate proportionately more biomass to reproduction at larger sizes and less at smaller sizes than plants growing at lower elevations. However, for G. rhodantha the reproductive allocation was negatively correlated with latitude. The results suggested different strategies in reproductive allocation in the two Gentiana plants on the YGP. Further studies are needed to investigate other environmental factors, such as nutrients and light, and genetic factors, in order to understand the trend of reproductive allometry along the environmental gradients. Our study has implications for the management and conservation practices of the two Gentiana species.
  • TONG Hua-li, SHI Pei-ji
    2020, 17(11): 2758-2773.
    The construction of an ecological security pattern(ESP) is an important way to ensure regional ecological security and to achieve sustainable regional development. It is also one of the hotspot topics of landscape ecology research. This paper identifies the ecological source through the evaluation of the ecosystem service and ecosystem sensitivity of the Lanzhou-Xining(Lan-Xi) urban agglomeration. The minimum cumulative resistance(MCR) model modified by night light data NPP/VIIRS(National Polar-orbiting Operational Environmental Satellite System Preparatory Project/Visible Infrared Imaging Radiometer Suite) was used to measure the relative resistance of the materials and energy circulation between the source areas, and to establish the resistance surface of the ecological source area expansion. Then ecological corridors were identified based on ecological sources and resistance surface. The ecological strategic node is the ecological fragile point in the ecological corridors. The ecological strategic node is identified with hydrological module by superimposing the "ridge line" of cumulative ecological resistance with the ecological corridor. Combined with ecological sources, corridors and strategic nodes, the ESP of the Lan-Xi urban agglomeration can be constructed. The ecological source of the Lan-Xi urban agglomeration accounts for 28.42% of the total area, most of which is distributed within Qinghai Province. The nature reserves in the area are all located within the ecological source area. A total of 41 potential ecological corridors have been identified in the study area. The total length of the potential corridors is 1201.03 km, comprising 23 source corridors and 18 radiation corridors. There are 30 strategic nodes identified in the Lan-Xi urban agglomeration. These locations are the most vulnerable areas of the ecological corridors. Ecological engineering should be applied in the construction of corridors. Affected by the ecological source, the potential ecological corridor extends from the northwest to the southeast, which is basically consistent with the direction trend of the mountains in the region.
  • LIU Ying, DENG Wei, PENG Li
    2020, 17(11): 2774-2783.
    Some settlements were located in unsuitable regions due to limited land resources in mountainous areas, some settlements were even even constructed in areas prone to geological hazards in Southwest China. Therefore, it was important to evaluate the spatial appropriateness of a region and determine the areas that were unsuitable for settlements, and then find out the settlements located in unsuitable regions. It will assist in decision making associated with the relocation of settlements. Furthermore, it will be the key to ensure the safety of inhabitants and promoting sustainable development in mountainous areas. This study explored the coupling mechanism between suitable space and rural settlements in the upper Minjiang River basin, which is an ecologically fragile area with high-frequency of natural hazards. Firstly, we identified relief degree of land surface(RDLS), elevation, and disaster risk as the limiting factors. Then, by determining the thresholds of these limiting factors, we recognized the suitable areas for inhabitation in the upper Minjiang River basin with GIS. Finally, using the distribution map of rural settlements and that of suitable space,the distribution of rural settlements located at unsuitable area was obtained by coupling relationship analysis. Consequently, an in-depth understanding of this relationship was achieved as follows:(1) The suitable space of the upper Minjiang River basin is 13.7 thousand km~2, accounting for 54.9% of the total land space;(2) There were 196 settlements located in the unsuitable area, the total area of these settlements was 125.27 km~2, and there were 68000 people in these settlements, accounting for 17.65% of the total population;(3) There were 65 settlements located near mountain hazard areas, accounting for 4.9% of the total. These findings suggest that it was necessary to carefully investigate settlements with risks and develop targeted relocation policies to help find the most effective way of using land safely and to good effect. The details are as follows:(1) Fully consider the safety of residents: For the 196 settlements distributed in the unsuitable region, the government should undertake a point-by-point survey and classify these settlements into different categories for relocation;(2) For the 65 settlements closely related with mountain hazards, professional geological prospecting teams should be organized to conduct a field survey at each point;(3) Besides considering the safety of residents during the relocation process, it is necessary to pay more attention to the cultural customs of inhabitants and livelihood sustainability
  • SU Li-jun, HU Bing-li, XIE Qi-jun, YU Fang-wei, ZHANG Chong-lei
    2020, 17(11): 2784-2795.
    Plant roots mechanically enhance the strength of soil and improve slope stability through anchoring. Given the popularization of ecological slope-protection technology, a quantitative study of how roots help to anchor soil is highly pertinent. The object of the present study is thus to investigate how roots and soil combine to affect the mechanical properties of the root-soil interface. Toward this end, pullout experiments of cedar roots of different diameters in soils of different density were conducted. The experimental results show that the maximum pullout force increases significantly with increasing root diameter, but only slightly increases with increasing soil density, which indicates that the root diameter has a greater impact on the maximum pullout force than soil density. Next, based on studies of fiber-reinforced composites, a root-soil pull-out model was proposed to study the evolution of shear stress on root-soil interface. This approach ensures that the model accurately reflects the dynamic stress distribution evolution at the root-soil interface and can calculate the pullout process of embedded root from soil. The accuracy of the model is verified by comparing the calculated results with experimental results. Finally, how soil density and root diameter affect the anchoring force was analyzed. The results indicate that the maximum anchoring force increases linearly with increasing root diameter, but nonlinearly with increasing soil density until reaching a fixed value. These results show that the root soil pull-out model has significant practical value in slope protection.
  • ZHANG Ze-lin, WANG Tao
    2020, 17(11): 2796-2815.
    The mechanical behavior of the joints inside a loess layer is greatly important in weak intercalation studies owing to its involvement in a wide range of landslides in the loess region in China. The shear behavior of the joints in the loess stratum during direct shear and cyclic loadings was investigated using the PFC2D discrete element software. Loess mudstone and mudstone with weak intercalated layer materials were subjected to direct testing, and cyclic shear tests were conducted with consideration to the influence of normal stress and shear velocity. The macroscopic properties and damage patterns were obtained for six numerical configurations; namely, loess-weathered mudstone with 0°, 10°, and -10° joints and weathered mudstone with 0°, 10°, and -10° weak intercalated layers. The numerical test results revealed that, in the direct shear tests, the shear stress and shear displacement of the samples increased with the normal stress. In the cyclic shear tests with a total cycle number N=20, the shear stress-shear strain curve of the six different configurations exhibited a hysteresis loop. The numerical tests also revealed that, under cyclic shear, the normal stress and shear velocity affected the shear strength. The degree of damage increased as the shear velocity decreased from 0.1 mm/s to 0.005 mm/s for all six numerical configurations. Compared with the damage pattern of the direct shear tests, the damage of the cyclic shear tests mainly comprised shear cracks and fractures, some shaking consolidation settlement and fewer shear strain occurred around the joints. In the direct shear tests, more compression cracks and fractures occurred in the samples. The damage mainly developed along the joints, and shearing-off damage occurred. The results obtained by this study further elucidate the failure mechanism and microscopic damage response of the joints in the loess stratum in Northwest China.
  • ZHANG Chao-bo, LIU Ya-ting, LI Dong-rong, JIANG Jing
    2020, 17(11): 2816-2826.
    Plant root system plays an important role in preventing soil erosion and improving slope stability. However, its performance is significantly affected by soil moisture content, and the role of soil moisture in root reinforcement is not fully understood. In this study, the influence of soil moisture on root pullout properties was studied by experiments. Vertical in-situ pullout tests under four different levels of soil matric suction(12 kPa, 18 kPa, 24 kPa, 30 kPa) were carried out on roots of sea buckthorn plants(Hippophae rhamnoides Linn.) which were artificially cultivated for 7 months. Diameter and length of the root system of sea buckthorn were investigated. The results showed that a very significant correlation was observed between root diameter(D) and root length(L)(P<0.01), and root diameter decreased with soil depth. When soil bulk density was constant, peak pullout force(F) and friction coefficient of root-soil interface(μ) decreased with increasing gravimetric soil moisture content in power functions. Soil moisture content significantly affected root pullout resistance because the increase of soil moisture content decreased the friction coefficient between the roots and soil. Root diameter at breakage point(D_b) and length of root segment left in soil(L_b) were increased with soil moisture content.In addition, peak pullout force of the roots increased in a power function with root diameter at the soil surface(D_0) and in a linear function with total root length(L). The results provided an experimental basis for quantifying the effects of soil moisture content on soil reinforcement by plant roots.
  • GAO Fang-fang, TIAN Wei
    2020, 17(11): 2827-2839.
    In order to reduce the damage of ordinary gravity dam impacted by boulders in debris flow, a blocks-combined dam based practical project is proposed. The dynamic response of the proposed dam under impact load is investigated by using ABAQUS finite element software. Considering the impact velocity and impact height, the anti-impact performance of blocks-combined dam is discussed in terms of deformation, displacement, impact force, acceleration, and energy, and is compared with that of ordinary dam. Results show that the displacement, impact force and acceleration of dam increase with the increase of impact velocity and height. The impact energy of blocks-combined dam is mainly absorbed and consumed by the friction between the component interfaces, which is related to the location of impact point. Compared with the ordinary gravity dam, the blocks-combined dam has better impact resistance to boulders in debris flow.
  • REN Xiu-ling, YU Qi-hao, ZHANG Gui-ke, YUE Pan, LIU En-long, ZHANG Zhen-yu, YOU Yan-hui
    2020, 17(11): 2840-2852.
    The construction of water conservancy projects in cold regions experiences freezing-thawing cycles, which can greatly change the engineering properties of soil and have a significant impact on the construction of projects. Lianghekou Hydropower Station(LHS), is a controlling station with the largest installed capacity among the 7 middle reach projects in the Yalong River, the secondary tributary of the Yangtze River. LHS is located in a seasonally frozen soil area. Based on the measured data of air and ground temperature in winter in the dam core wall, the freezing-thawing variation of gravelly soil and contact clay during the filling process of the core wall are compared and analyzed, then the main impact factors of the freezing-thawing variation of soils are discussed. The results show that under the influence of air temperature, soil freezes unidirectionally from ground surface downward and deepens gradually, and the thawing processes are different at the aspects of thawing direction and rate. Air temperature and physical properties of soil including soil type, moisture content and dry density affect the freezingthawing processes of soils. And the impact of engineering construction is more remarkable than natural factors. The engineering construction affects soil temperature and freezing-thawing process by controlling the initial temperature of soil, the speed and duration of the technological conversion of paving, compaction, and the length of placed duration at night. Due to the long placed duration of soil with the slow construction method, the initial temperature of soil gradually reduces, the heat transfer process inside soil is fast. Then the internal heat of soil releases, the decreasing rate of ground temperature of soil at different depths is fast and the frozen depth deepens. While due to the short placed duration of soil with the rapid construction process, the initial temperature of soil is high, high internal heat of soil is supplied every day, and the heat transfer process inside soil is slow. Then the decreasing rate of temperature of soil at different depths is slow, and the variation amplitude of frozen depth is small. This study provides useful guidance for the freezingthawing prevention during the construction process of core wall dams located at high altitude region in winter.