Karst Fissure Research Articles

Failure mechanism analysis and treatment of tunnels built in karst fissure strata: A case study

With the rapid increase of tunnels built in karst fissure strata, much more problems appeared during the construction process. Based on the Liangwangshan Tunnel, this article presents a case of tunnel failure by karst fissure, and the failure mechanism and treatment were analyzed. Firstly, when the karst fissure was close to the excavation face, A large area of cavity appeared above the right spandrel, which was distributed diagonally with a narrow shape. However, the pressure on the left side was greater than it on the right side near the karst fissure by on-site monitoring. Secondly, laboratory tests were carried out to determine that the karst fissure weakened the strength of surroundings, especially in shear and tensile strength. The results of theoretical analysis and discrete element method considering the joints indicated that karst fissure will exacerbate the uneven stress distribution and prevent the transmission of stress. The failure mode can be manifested as bending fracture and shear fracture, and the tensile shear composite failure mainly occurred on tunnel near the fissure. Finally, the radial grouting and advanced pipes have been implemented on site, and the on-site monitoring showed that the treatment measures were effective to control the failure when tunnel was excavating. The research can provide guidance for the similar tunnel engineering built in karst fissure strata.

Effects of different karst fissures and rainfall distribution on the biomass, mineral nutrient elements, antioxidant substances, and photosynthesis of two coniferous seedlings

BackgroundStudying the physiological growth status of Pinus yunnanensis Franch and Pinus elliottii Engelm. seedlings under different karst fissure thicknesses and rainfall distributions is of great significance for the management, vegetation restoration, and tree species selection in karst rocky desertification areas. In this study, we used a two-factor block experiment and set different rainfall durations, namely reduced rainfall duration (I3d), natural rainfall duration (I6d), and extended rainfall duration (I9d); Different karst small habitats, i.e., stone-free soil (S0), less stone and more soil (S1/4), and half stone and half soil (S1/2), are simulated at these three levels. Analyze the changes in physiological growth and photosynthetic characteristics in two coniferous seedlings under different treatments with different karst thicknesses.ResultsThe results showed that with the increase of karst thickness, the growth volumes of height and diameter of P. yunnanensis seedlings, the biomass of various organs, and the accumulation of K+, Ca2+, Na+, and Mg2+ showed a significant change pattern of first increasing and then decreasing (P < 0.05); P. elliottii seedlings show a gradually decreasing trend (except for Ca2+). The biomass accumulation of each organ in two coniferous seedlings showed that leaves > stems > roots. The K+, Ca2+, and Mg2+ content in various organs of P. yunnanensis seedlings showed that leaves > roots > stems, while Na+ shows the order of roots > leaves > stems. The accumulation of mineral elements in various organs of P. elliottii seedlings is manifested as roots > stems > leaves and the accumulation of mineral elements in both coniferous seedlings is manifested as Ca2+ > Mg2+ > K+ > Na+. Root length, root volume, root surface area, root diameter, SOD, POD, SP, photosynthetic pigment content, fluorescence parameters, and gas exchange parameters of P. yunnanensis seedlings gradually increase with the increase of karst thickness (except for the 9-day rainfall duration), while those of P. elliottii seedlings gradually decrease. The light saturation point of P. yunnanensis seedlings is highest under the I6dS1/2 treatment, while that of P. elliottii is highest under the I3dS0 treatment.ConclusionsIn summary, prolonging rainfall duration has an inhibitory effect on the growth of two types of coniferous seedlings. Increasing karst thickness inhibits the growth of P. elliottii seedlings, and to some extent, promotes the growth and development of P. yunnanensis seedlings. I6dS1/4 and I3dS0 treatments have the best growth effects on P. yunnanensis and P. elliottii seedlings. Therefore, we give priority to P. yunnanensis as the tree species for vegetation restoration or rocky desertification management in karst areas. Our study reveals the role of limestone-filled different karst fissures in mitigating the effects of drought as “containers” for plant growth. These findings help us understand the response of plants to drought stress and provide valuable insights for vegetation restoration in karst environments affected by global climate change. Therefore, further experiments with various karst fissure sizes are necessary to test the universality of the reactions of various plants under different karst fissures.

Karst fissures mitigate the negative effects of drought on plant growth and photosynthetic physiology.

Hard limestone substrates, which are extensively distributed, are believed to exacerbate drought and increase the difficulty of restoration in vulnerable karst regions. Fissures in such substrates may alleviate the negative effect of drought on plants, but the underlying mechanisms remain poorly understood. In a two-way factorial block design, the growth and photosynthesis of 2-year-old Phoebe zhennan seedlings were investigated in two water availabilities (high versus low) and three stimulated fissure habitat groups (soil, soil-filled fissure and non-soil-filled fissure). Moreover, the fissure treatments included both small and big fissures. Compared to the soil group, the non-soil-filled fissure group had decreased the total biomass, root biomass, total root length, and the root length of fine roots in the soil layer at both water availabilities, but increased net photosynthetic rate (Pn) and retained stable water use efficiency (WUE) at low water availability. However, there were no significant differences between the soil-filled fissure group and soil group in the biomass accumulation and allocation as well as Pn. Nevertheless, the SF group decreased the root distribution in total and in the soil layer, and also increased WUE at low water availability. Across all treatments, fissure size had no effect on plant growth or photosynthesis. Karst fissures filled with soil can alleviate drought impacts on plant root growth, which involves adjusting root distribution strategies and increasing water use efficiency. These results suggest that rock fissures can be involved in long-term plant responses to drought stress and vegetation restoration in rocky mountain environments under global climate change.

Unraveling soil filling and transport in fissures on karst slopes using multiple tracers

The fragile ecological environment and unique surface–subsurface geological duality of karst regions have led to complex processes and rates of underground soil loss, which is subject to much controversy. However, to ensure the ecological sustainability of karst areas, it is imperative to address this issue systematically using innovative study methods. With focuses on ten fissures and fivecross-sections in a typical karst area in southwestern China, this study applied unmanned aerial vehicles for field surveys and indoor modeling techniques to investigate the distribution density of fissures in typical karst areas, which is crucial for calculating underground soil loss. By measuring magnetic susceptibility, organic carbon content, and particle size of fissure soils, the primary sources of soil in the fissures were identified. Additionally, the rate of soil loss passing through karst fissure was calculated using 137Cs tracing and 14C dating techniques. Results indicate that (1) the proportion of fissure area per square kilometer of land is 1.59 %; (2) the soil in the fissures is mainly filled with the topsoil outside the fissures, and (3) the average rate of soil filling into the fissures is 16.13 t km−2 yr−1, account for only 5.8 % of the total soil erosion modulus. The study shows that soil filling into fissures is the main process of underground soil loss on karst slopes, and the rate of soil loss through fissures is very small. This study offers valuable insights into soil movement processes and quantification of soil erosion in karst regions, thus aiding in the preservation and sustainable management of these unique ecosystems.

Mid-Miocene onset of the NE Bohemian Massif (SW Poland, Europe) growth, landscape evolution, and paleoenvironmental changes unraveled using paleokarst sediment palynology

Newly discovered paleokarst sediments with an abundant Miocene palynological record in the Eastern Sudetes bridge the gap in reconstructing the landscape and tectonic history of the NE Bohemian Massif during the Neogene. Palynological analysis performed for seven samples derived from the karst fissure allowed the examination of the sporomorph distribution (pollen grains and spores of plants) and nonpollen palynomorph content (algal and fungal microremains) in each layer. The results revealed the presence of numerous pre-Quaternary taxa, including “paleotropical” species, within the analyzed sediments. The pollen analysis results indicate a warm-temperate and humid climate during sedimentation of the Nowy Waliszów karst infill, along with the development of wetland vegetation (swamp forests, riparian forests, and shrub bogs) and mesophytic forests. Recorded taxa are typical for flat and hilly landscapes, predating growth of the present >1000-m relief mountainous topography and formation of the primary European triple drainage divide in the Śnieżnik Massif area. Paleokarst palynology strongly supports a mid-Miocene (∼15 ± 1.5 Ma) onset of environmental change in the Sudetes due to accelerated tectonic uplift of the Eastern Boundary Fault bounding the Upper Nysa Kłodzka Graben and Orlica–Śnieżnik Dome tectonic block. The data presented enhance our understanding of the pre-Pleistocene development of the NE Bohemian Massif, with a particular focus on the orogen-scale landscape evolution from flat, inland wetlands to hilly, mountainous topography.

Geochemical Characteristics and Controlling Factors of Groundwater Chemical Composition in the Zihe River Source Area, Shandong, China

The geochemical characterization and evolution of shallow groundwater in the Zihe River source area is a key issue that needs to be addressed. In this study, a combination of traditional geochemical techniques and geochemical modeling was used to explain the geochemical processes and major ion sources in the chemical evolution of shallow groundwater in the Zihe River source area, Northeast China. Fifty-seven water samples were collected in June 2020 for chemical analysis, and the results showed that the main groundwater chemistry types in the three major aquifers are HCO3·SO4-Ca·Mg-type pore water from loose quaternary rocks, HCO3·SO4-Ca·Mg-type karstic fissure water from carbonate rocks, and HCO3·SO4-Ca-type weathered fissure water from massive rocks. Water–rock interactions in alkaline environments were the main causes of changes in groundwater chemistry. Rock weathering dominated the geochemical evolution of each aquifer. The analysis of ion concentration ratios and modeling revealed that the aquifer’s chemical components are mainly derived from the dissolution of dolomite and calcite and partly from the infiltration of pollutants containing Cl− and NO3−, as well as from the dissolution of quartz. Mg2+ is derived from the dissolution of dolomite. HCO3− is primarily derived from the co-dissolution of calcite and dolomite, and to a lesser extent, its content is also influenced by the recharge of rainfall. SO42− has two sources: it mainly originates from the dissolution of gypsum and the anhydrite layer, followed by atmospheric precipitation. The synthesis showed that the groundwater quality in the source area of Zihe River is good, all the indices reached the standard of class III groundwater quality, and the overall degree of human pollution is low. The results of this research will provide a scientific basis for the local authorities to delineate karst groundwater protection zones in the Zihe River source area and to formulate resource management strategies for the development, utilization, and protection of karst groundwater.

Natural and anthropogenic factors regulating fluoride enrichment in groundwater of the Nansi Lake Basin, Northern China

Excess fluoride (F−) in groundwater can be hazardous to human health of local residents who rely upon it. Beside natural sources, anthropogenic input may be an additional source to be considered. Twenty surface water and 396 groundwater samples were collected from the Nansi Lake Basin, with hydrogeochemical and isotope techniques employed to clarify the spatial variability, source, and the natural and anthropogenic factors regulating the occurrence of high F− groundwater. The factors responsible for elevated F− levels in surface water and deep confined aquifers are discussed based on their hydraulic relationship. Also a conceptual model of F− enrichment with different aquifer systems is put forward based on the geomorphic units of the basin. The results show that F− concentration is between 0.1 and 6.9 mg/L in the west of Lake, while ranged from 0.03 to 1.74 mg/L in the east of Lake. The hydrogeological setting and lithology are the primary factor determining the provenance of high-fluoride groundwater in the basin. Fluoride mainly originated from the dissolution of fluorine-bearing minerals, and is affected by the alkaline groundwater environment, cation exchange, adsorption, and evaporation. The landforms on the east side of Nansi Lake are low hills and piedmont sedimentary plains, where the aquifers consist of karst fissure water and overlying porewater. High F− groundwater is not observed in this area due to its rapid flow and Ca2+-enriched hydrochemical characteristics. The anthropogenic input (such as fertilizer application on farms and illegal industrial pollutant discharge), contribute F− to groundwater in varying degrees, especially in the shallow aquifers east of the lake and in some parts west of the lake. This work is a clear example of how natural processes together with human activities can affect the chemical quality of groundwater, which is essential to safeguard the sustainable management of water resources in semi-arid areas.

Simulation Study on Seepage Patterns of Geothermal Reinjection in Carbonate Thermal Reservoir and Geothermal Doublet Well Patterns in Xiong’an New Area

The karst fissures of the carbonate thermal reservoir in Xiong’an New Area have developed, and they have the advantages of a concentrated distribution, shallow burial, large water volume, and easy recharge, which are conducive to the development and utilization of geothermal resources. This paper took the carbonate thermal reservoir in Xiong’an New Area as the research object and studied the characteristics of the seepage patterns and temperature distribution in thermal storage with different well arrangements and recharge methods by laser etching the micromodel of the carbonate thermal reservoir and simulating the recharge methods. The paper established a numerical model of the resettlement area of Xiong’an New Area based on the production data and the current recharge well pattern, and it proposed a plan for a geothermal doublet well arrangement. The results showed that the injection speed and angle significantly influenced the seepage of injected water in the fractured reservoir. The injection speed correlated with the breakthrough time and swept area. The breakthrough time plummeted as the injection speed increased, and the swept area crept up as the injection-fracture dip increased. The well arrangements also impacted the seepage patterns. The well pattern of two injectors and three producers was relatively suitable for geothermal reinjection, and it was more appropriate to choose the maximum injection-fracture dip because of the largest swept area. Factors that affected the sustainable development and utilization of geothermal fields included the well pattern arrangement, well spacing, injection and production volumes, and the temperature of the injected water. Based on the modeling, it is recommended that the well spacing be greater than 500 m, and the injection and production volumes less than 110 m3/h in the resettlement area of Xiong’an New Area. Moreover, a vertical fracture well is recommended to reduce thermal breakthroughs.

Locating geothermal resources using seismic exploration in Xian county, China

The seismic exploration was used to explore the potential geothermal resource and geological structure in Xian County, N China. Micro-logging was used to conduct surveys on the velocity structure near the surface, the static correction models and the observation system was determined by this method. By testing different borehole depths and different quantities of explosives, the best experimental parameters were obtained in a series of test locations and in two test sections. The surface differences were eliminated by the static correction, and an interference wave survey was conducted to improve the data signal to noise ratio (SNR). The post-stack wave equation for the PR splitting finite difference was used for migration imagery, and post-stack, underground imaging profiles were obtained. The corrected seismic signals were then interpreted, and converted into geological information. The results showed that the burial depths and morphology in each layer had been successfully obtained. The areas favorable for heat storage in karst fissures were mainly in the Jixian Formation and the Cambrian–Ordovician. Our investigation allowed us to predict and calibrate favorable locations for two geothermal energy exploration holes.

Migration of dissolved carbon on bare karst slopes in soil in response to natural rainfall events

Soil carbon in karst critical zones is an essential part of the global carbon pool, and the migration of dissolved carbon is a vital component of the carbon cycle in such regions. The unique “dual hydrological structure” makes the path and process of migration of soil dissolved carbon driven by rainfall unclear in karst slopes, which ultimately hinders the accurate evaluation of the carbon sink effect in such regions. Therefore, based on field monitoring of natural rainfall, this study evaluated the process and characteristics of the spatial migration of soil dissolved carbon in bare karst slopes and its response to natural rainfall (rainfall duration and amount). The results showed that the concentration of dissolved carbon transported in surface runoff was significantly lower than that transported within the soil layer; however, carbon loss displayed the opposite trend. Rainfall factors (rainfall amount and duration) and runoff volume significantly affected soil dissolved carbon, contributing 46.91% to soil dissolved carbon. Rainfall factors significantly affect soil dissolved carbon migration by influencing runoff. In addition, the hydrological path is an important factor affecting soil dissolved carbon transport. Our study shows that the soil and bedrock interface (SBI) and shallow karst fissures (SKF) are the main routes of dissolved carbon migration in soils in bare karst slopes. Dissolved carbon migrating along SKF is a vital contributor to the “missing carbon sink” in karst regions, and dissolved carbon migrating along the SBI is potentially an important contributor to the “missing carbon sink.” This study provides primary data and is expected to serve as a reference for revealing the mechanism of karst carbon migration and transformation and accurately evaluating the carbon sink effect in karst areas.

Effects of vegetation restoration types on soil erosion reduction of a shallow karst fissure soil system in the degraded karst areas of Southwestern China

AbstractShallow karst fissures are the main hydrological paths, underground loss channels, and one of the most critical root habitats in fragile karst rocky desertification areas. Revegetation may alter the type of vegetation cover in fissures, resulting in changes to soil properties and erosion reduction. In this study, we evaluate the influence of revegetation on the soil erosion reduction of fissure‐soil–plant systems (FSPS) for three vegetation types (herbs, shrubs, and trees) in FSPS and use bare FSPS without vegetation as a control in a karst rocky desertification area. The results show that the soil physicochemical properties of FSFS degraded first and then improved after abandonment, resulting in the order of soil erosion reduction of FSPS with vegetation succession being: shrub &lt; herb &lt; bare &lt; tree. Vegetation restoration can significantly improve the soil erosion resistance of the 10–20 cm soil layer in the fissure zone, making it stronger than that in the non‐fissure zone, thus reducing the risk of underground leakage on the slope. The results obtained in this study deepen our knowledge of the impact of vegetation restoration type on soil erosion reduction and has significant implications for guiding vegetation restoration and preventing underground leakage in karst areas.

An extended ITL-VIKOR model using triangular fuzzy numbers for applications to water-richness evaluation

Jiaozuo coalfield is the most typical in Northern China type coalfield. When it mined the Permian coal seams, it was threatened by water inrush from the confined aquifer of thin karst fissure limestone in the lower Carboniferous. How to scientifically evaluate and predict the water-richness of thin karst fissure limestone in Carboniferous system has become the most important work in mine water control and prevention. Taking the mining of coal seam No. 21 of Shanxi Formation in Guhanshan coal mine as an example, this paper analyzed the water-richness main controlling factors of L8 Limestone Aquifer of Taiyuan Formation, and selected four evaluation indexes, i.e. water inflow of drilling, the thickness of L8 Limestone Aquifer, the water level of L8 Limestone Aquifer and fault fractal dimension. The 2-tuple linguistic weights of all factors were obtained by the use of interval 2-tuple linguistic method extended by triangular fuzzy numbers. Following the above outlines, the mathematical model for the 2-tuple linguistic evaluation of water-richness was established based on ITL-VIKOR method extended by triangular fuzzy numbers. The data of geophysical exploration were collected to test the accuracy of the model. In addition, the results of 2-tuple linguistic assessment of water-richness and geophysical exploration were used to evaluate the water-richness of L8 Limestone Aquifer, which extends the evaluation and prediction of water abundance for karst fractured aquifers to dyadic array. These results have been applied to guide the safe mining in Guhanshan coal mine, and will be further extended to the mines with similar geological conditions. It is our goal to establish an intelligent application system to ensure safe production in coal mines, which is great beneficial to the technical personnel engaged in mine water prevention and control.

Chronological context, species occurrence, and environmental remarks on the Gelasian site Pedrera del Corral d’en Bruach (Barcelona, Spain) based on the small-mammal associations

ABSTRACT Here we present the results of a study of the small mammal assemblage recovered from a now disappeared karstic fissure located in a quarry called ‘Pedrera del Corral d’en Bruach’. The site was located at 330 m a.s.l. in the Garraf Massif, ca. 20 km south of Barcelona. An archaeological rescue excavation was conducted in 2006 by the Grup de Recerca del Quaternari, focusing on sieving the sediments that had accumulated at the foot of the quarry face. Fortunately, some faunal remains and sediment were recovered, which were later processed and sorted. Two hundred and seventy small mammal remains were identified at genus or species level, bringing to light 15 taxa. The assemblage is typical of the Mammal Neogene 17 (MN17) biozone, placing this site in the Gelasian stage of the Early Pleistocene. It is noteworthy that the first record of the glirid Glirulus pusillus in Iberia is documented. Based on the small mammals identified, the surrounding environment of the Garraf Massif is judged to have been characterised by open forest landscape and more humid environmental conditions than nowadays. Finally, the site provides a remarkable contribution to what is known of the Iberian small mammals of this time period.

Hydrogeological Study in Tongchuan City Using the Audio-Frequency Magnetotelluric Method

Tongchuan City, located in Shaanxi Province, northwest China, has limited groundwater resources. Rational planning and exploitation of groundwater are crucial to the sustainable development of the city, for which investigating the distribution of groundwater is the premise. Traditional resistivity sounding methods are often used to detect groundwater; however, these methods are not applicable in the study area where thick Quaternary loess is extensively distributed. In this study, we arranged five audio-frequency magnetotelluric (AMT) profiles to detect the deep clastic rock groundwater and carbonate karst fissure groundwater in Tongchuan. Firstly, we analyzed the electromagnetic interference (EMI) noises in Tongchuan City, revealing that the main EMI is power frequency interference (PFI). We used the dictionary learning processing technology to suppress the PFI. Secondly, the two-dimensional (2D) nonlinear conjugate gradient method was employed to invert a 2D electrical structure model for the area shallower than 1 km. We analyzed the characteristics of the electrical structure and its geological significance. Lastly, the three-dimensional (3D) electrical structure model of the study area was inverted using the 3D nonlinear conjugate gradient method, and the spatial distribution characteristics of the water-bearing strata were further analyzed. The results show that the PFI in urban environment can be suppressed by the dictionary learning processing technology. In Tongchuan city, the distribution of clastic rock fissure water is controlled by folds and faults, as well as the thickness of sandstone layers, and that of the carbonate karst fissure water is mainly controlled by faults. On this basis, we infer that the water-bearing areas are in the middle east and south of the study area.

Mercury migration to surface water from remediated mine waste and impacts of rainfall in a karst area – Evidence from Hg isotopes

Mine waste (MW) in historical mercury (Hg) mining areas continuously emits Hg into local environment, including aquatic ecosystems. Tracing Hg migration process from MW and determining its relative contribution to Hg pollution is critical for understanding the environmental impact of MW remediation. In this study, we combined data of Hg concentration, speciation, and isotope to address this issue in the Wanshan Hg mining area in southwest China. We found that rainfall can elevate Hg concentrations in river water and control the partitioning and transport of Hg in karst fissure zones through changing the hydrological conditions. A consistently large offset of δ202Hg (1.24‰) was observed between dissolved Hg (DHg) and particulate Hg (PHg) in surface water during the low-flow period (LFP), which may have been related to the relatively stable hydrologic conditions and unique geological background (karst fissure zones) of the karst region (KR). Results from the ternary Hg isotopic mixing model showed that, despite an order of magnitude reduction in Hg concentration and flux in river water after remediation, the remediated MW is still a significant source of Hg pollution to local aquatic ecosystems, accounting for 49.3 ± 11.9% and 37.8 ± 11.8% of river DHg in high flow period (HFP) and LFP, respectively. This study provides new insights into Hg migration and transportation in aquatic ecosystem and pollution source apportionment in Hg polluted area, which can be used for making polices for future remediation actions.

桢楠幼苗适应喀斯特岩溶裂隙生境及降雨时间格局变化的方式

PDF HTML阅读 XML下载 导出引用 引用提醒 桢楠幼苗适应喀斯特岩溶裂隙生境及降雨时间格局变化的方式 DOI: 10.5846/stxb202112183590 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 重庆市自然科学基金面上项目（cstc2020jcyj-msxmX0244）；中央高校基本科研业务费专项（XDJK2020B037）；国家自然科学基金项目（31500399） Phoebe zhennan S. Lee seedlings adjust the biomass allocation and root distribution to adapt to the karst fissure habitat and rainfall temporal pattern Author: Affiliation: Fund Project: General Project of Chongqing Natural Science Foundation(cstc2020jcyj-msxmX0244);Special Funds for Fundamental Scientific Research Operation of Central Universities(XDJK2020B037);National Natural Science Foundation of China(31500399) 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:喀斯特生态系统是全球陆地生态系统的重要组成部分，生态环境极为脆弱。由于碳酸盐岩长期强烈的化学溶蚀作用，其基本特征体现为地表土壤和地下岩溶裂隙及洞穴的二元结构。近年来，在全球气候变化下，我国西南地区降雨格局呈现降雨频次减少且单次降雨量增加的趋势。因此，岩溶裂隙和区域降雨时间格局改变将对喀斯特地区的植物生长产生重要影响。通过模拟不同岩溶裂隙生境（S0：24 cm土壤；S1/2：12 cm土壤层+12 cm裂隙层；S3/4：6 cm土壤层+18 cm裂隙层）和不同降雨时间格局（I2d：2 d降雨间隔；I19d：19 d降雨间隔），探究二年生桢楠（Phoebe zhennan S.Lee）幼苗是否通过生物量分配及根系分布的调整来适应变化环境。结果显示：（1）短时间降雨格局下，相比全土生境，少量岩溶裂隙存在并不影响桢楠幼苗生物量的积累，然而随着岩溶裂隙层进一步增厚和降雨时间间隔延长，桢楠降低了总生物量，减少了茎且增大了根和叶的生物量分配。（2）桢楠幼苗的根系垂直分布随着深度增加而下降，且无论在何种降雨时间格局下，两种岩溶裂隙生境下桢楠均增加了岩溶裂隙之上土壤层的根系生物量分配比例。研究表明：赋存有土壤的岩溶裂隙能成为植物幼苗赖以生存的生境，但这种提供生境的能力随岩溶裂隙层增厚以及降雨时间间隔延长而减弱。桢楠幼苗以牺牲对茎生物量的分配投资为代价，提高对根系或者叶片的生物量投资，同时增大界面土层中的根系分布，来保证最大化地利用有限的土壤资源，从而适应喀斯特的岩溶裂隙（及干旱）生境。 Abstract:Karst is one of the most important fragile ecological environments in globally terrestrial ecosystems. It is basically characterized by the dual structure of surface soil and underground karst fissures and caves, due to the long-term strong chemical dissolution of carbonate rocks. In recent years, under global climate change, the rainfall pattern in southwestern China has shown a trend of decreasing rainfall frequency and greater sub-rainfall. The karst region in southwestern China, which belongs to the subtropical monsoon climate, often suffers from more obvious alternating wet and dry conditions. The underground karst fissures and variation in the temporal pattern of regional rainfall will have a significant impact on plant growth and development in this region. In this study, in order to explore whether the seedlings of Phoebe zhennan S. Lee adjust biomass allocation and root distribution to adapt to the changing environment, we simulated different karst fissure habitats (S0:24 cm soil; S1/2:12 cm soil layer+12 cm karst fractured layer; S3/4:6 cm soil layer+18 cm karst fractured layer) and different rainfall temporal patterns (I2d:rainfall interval of 2 days; I19d:rainfall interval of 19 days), and checked the plants biomass accumulation and allocation, root vertical distribution. The results showed that:(1) under the short-term rainfall pattern, compared with the whole soil habitat, the habitat with a small proportion of karst fissures did not affect the biomass accumulation of P. zhennan seedlings. With the thickening of karst fractured layer and the extension of the rainfall interval, P. zhennan reduced the total biomass, allocating less biomass to stems and more to roots and leaves. (2) The vertical distribution of root system of P. zhennan seedlings decreased with the deepen of soil layer, but increased the root biomass allocation ratio in the soil layer above the karst fissures, regardless of the rainfall temporal pattern. The results show that the fissures hosted soil can be a certain habitat for plants. However, with the thickening of fractured layer and extension of the rainfall interval, the fissures weaken the ability of the habitat. P. zhennan seedlings increase investment to root and leaf at the expense of stem biomass, and increase the root distribution in the interface soil layer above the fissures to ensure the maximum use of limited soil resources so as to adapt to the fissure (and arid) habitat in karst. 参考文献 相似文献 引证文献

Discrete element analysis of deformation features of slope controlled by karst fissures under the mining effect: a case study of Pusa landslide, China

Karst landforms are widely distributed in the southwestern mountain areas of China, and the continuous underground mining activities lead to frequent occurrence of catastrophic collapses and landslides. Revealing the relationship between the development characteristics of the controlling karst fissures and the slope deformation process is crucial to understand the collapse and landslide phenomena. The Pusa landslide is selected as the geological prototype of discrete element analysis, and the universal distinct element code (UDEC) is applied to simulate the overall deformation response of the mountain containing extensive karst fissure during the mining process. The results show that under the action of mining, the roof above the goaf bends and subsides, and the middle of the roof even breaks and collapses. The separation fractures effectively block the upward transmission of the collapse state of the rock stratum. The bottom of the karst fissure is susceptible to cracking first in the process of coal seam mining due to stress concentration, and the area of severe deformation in the slope coincides with the mining pressurization area. The morphology of the karst fissure controls and determines the deformation characteristics of the rock mass at the slope top, and only the karst fissure located within the mining influence range is the object to be considered in the slope stability analysis. The limit karst fracture depth, about 1/3 of the slope height, is the limit value to determine whether the rock mass at the slope top is toppled or slipped. The relationship between the karst fissure and the free surface gradually changes from the directional or co-directional to the reverse, the motion state of the rock mass at the slope top changes from slipping to toppling, and the role of karst fissure changes from a potential slip surface to the cracking boundary. Although the deformation damage of the reverse structural slope is not very serious, the influence of the karst fissure on the stability of the slope still cannot be ignored. This study aims to provide basic theoretical support for the subsequent research on the failure mechanism of karst mountains under the combined action of multi-structural planes.

Failure Mechanism of Anti-Inclined Karst Slope Induced by Underground Multiseam Mining

There occurred a lot of catastrophic landslides in Southwest China karst areas in recent years. This study numerically simulated the failure process of Pusa landslide by distinct element method (UDEC). The Voronoi diagram algorithm was used to discretize the rock blocks in the upper part of the mining area, and the erosion in sliding source area caused by heavy rainfall was simulated by increasing the block density and reducing the joint strength. Results obtained using UDEC matched the failure process recorded by UAV, and the subsidence of monitoring points on the slope surface was well coincident with the InSAR results. The DEM results are as follows: firstly, under the action of underground coal mining, the overlying strata of the mountain deform toward the goaf and the deformation of the stratum increase significantly with the caving of the roof stratum; and the deep karst fissures in the overlying stratum have an important influence on the deformation of the mountain; the upper strata form a subsidence zone along the fissures, expanding the range of tensile fissures. Secondly, due to the excavation and unloading of the rock masses at the leading edge of the sliding area, the extrusion deformation occurs to the outside of the slope, resulting in the critical instability of sliding area. Finally, with the strength decreasing of rock masses and structural planes by heavy rainfall, the stability of the mountain continues to decrease until the sliding area collapses.

A Joint Method Based on Geochemistry and Magnetotelluric Sounding for Exploring Geothermal Resources in Sedimentary Basins and Its Application

The precise exploration of the characteristics of geothermal fields in sedimentary basins, such as the temperature and burial depth of their deep geothermal reservoirs, is of great significance for improving the probability of penetration and reducing exploration risks and development costs. This study proposed a joint exploration method combining magnetotelluric (MT) sounding and geothermometers. Using this method, this study estimated the geothermal reservoirs’ temperature and the circulation depth of geothermal water in the Xianxian geothermal field, a typical geothermal field in a large sedimentary basin in northern China, and prepared the temperature and depth maps of the geothermal reservoirs. The main results are as follows. First, the bedrock’s geothermal reservoirs with karst fissures in the Xianxian geothermal field have great potential for development. Among them, geothermal reservoirs in the Jixianian Wumishan formation have a top depth of 1100–1500 m and a thickness of 700–1700 m, and the geothermal reservoirs in the Jixianian Gaoyuzhuang formation have a top depth of 3700–4000 m and a maximum drilled thickness of 400 m. The geothermal reservoirs of the Xianxian geothermal field mainly have medium and low temperatures of 138–160 °C and the circulation depth of the geothermal water is 5873 m.

Seismic Geothermal Resource Exploration based on CPU/GPU Collaborative Parallel Prestack Time Migration

AbstractGeothermal resources exist in complex and comprehensive geological settings. In the current study, we proposed a CPU/GPU collaborative parallel prestack time migration methodology for geothermal resource exploration. First, seismic geological conditions in Xian County were obtained based on an analysis of drill cores for further seismic evaluation. Then, combined with the analysis of two‐dimensional seismic data in the adjacent area, a test section with three seismic survey lines were designed to explore the geological structure of the study area. In the study area, the seismic data were derived through the multiple coverage reflection wave exploration method with explosive ignition in deep wells and high coverage frequency observations. Finally, we employed CPU/GPU collaborative parallel prestack time migration technology to analyze the obtained seismic data for geothermal resource evaluation. The favorable areas of karst fissure heat storage in Middle–Upper Proterozoic Jixianian and Paleozoic Cambrian–Ordovician rocks were inferred together with two preferred recommended exploration holes.