Cohesion variation during instability evolution of disaster medium in mud inrush of mountain tunnel

Mud inrush in mountain tunnel is an independent geological hazard type different from water inrush, landslide and debris flow. The intrinsic factor of mud inrush is the instability failure of disaster medium. Its essence is that when the cohesion decreases gradually with the increase of void ratio to the point where the movement of soil particles cannot be restricted, soil particles and groundwater form slurry and gush out. Thus, accurate calculation of cohesion with variable void ratios is crucial for analyzing the reliability of disaster medium. In this study, the disaster medium was regarded as graded soil and a structural model was established wherein soil particles were simplified as cubes and the interparticle pores were represented by the clearance between cubes. On the basis of the structure model of disaster medium, a function between the soil particle distance and void ratio was derived. Cohesion is equivalent to the resultant force between soil particles per unit area; thus, a cohesion function was derived in which the void ratio is the main variable. This function considers the influence of gradationcharacteristics on cohesion variation and is generally applicable to various types of disaster medium. A series of direct shear tests were carried out to determine the cohesion variation for different types of disaster medium with variable void ratios. By comparing the variation of cohesion obtained through direct shear tests with those deduced by the proposed cohesion function, we verified the validity and general applicability of the cohesion function. It is of great significance because the cohesion function can accurately predict the variation of cohesion by using the void ratio, and effectively evaluate the possibility of mud inrush according to the initial mechanical properties of disaster medium.     

示踪实验在湾潭隧道涌水突泥判别中的应用

以宜来高速湾潭隧道为研究对象, 通过现场调查、地下水示踪实验、地下水流量监测, 以及采用大气降雨入渗法计算隧道的平均涌水量和丰水期涌水量, 同时采用RFPA渗流软件对隧道涌突水的可能性进行判别。现场调查及示踪试验结果显示湾潭隧道岩溶管道为多支, 混合型岩溶管道, 水文地质条件复杂, 丰水期涌水量约为平均隧道涌水量的4.6倍。数值模拟结果表明, 隧道涌水突泥破坏要历经裂隙萌生、裂隙扩展、裂隙进一步扩展、贯通破坏阶段。同时当岩溶管道处的过水流量达到初始值(37 248 m3/d)约2.7~3.5倍之间时便可出现涌水突泥破坏, 也即出水口2流量达到10 000~13 000 m3/d时, 湾潭隧道具有极高的涌水突泥风险。      

Detection and treatment of water inflow in karst tunnel: A case study in Daba tunnel

In a karst tunnel, fissures or cracks that are filled with weathered materials are a type of potential water outlet as they are easily triggered and converted into groundwater outlets under the influence of high groundwater pressure. A terrible water inrush caused by potential water outlets can seriously hinder the project construction. Potential water outlets and water sources that surrounding the tunnel must be detected before water inflow can be treated. This paper provides a successful case of the detection and treatment of water inflow in a karst tunnel and proposes a potential water outlet detection (PWOD) method in which heavy rainfall (>50 mm/d) is considered a trigger for a potential water outlet. The Daba tunnel located in Hunan province, China, has been constructed in a karst stratum where the rock mass has been weathered intensely by the influence of two faults. Heavy rain triggered some potential water outlets, causing a serious water inrush. The PWOD method was applied in this project for the treatment of water inflow, and six potential water outlets in total were identified through three heavy rains. Meanwhile, a geophysical prospecting technique was also used to detect water sources. The connections between water outlets and water sources were identified with a 3-D graphic that included all of them. According to the distribution of water outlets and water sources, the detection area was divided into three sections and separately treated by curtain grouting.     

基于地下水流系统理论的岩溶隧道涌突水来源及路径分析

双龙洞是国家重点风景名胜区，拟建金华山隧道位于浙江省金华市双龙洞景区北东向约12 km处，金华山隧道的开挖将可能导致双龙洞景区岩溶水的疏干，同时隧道也可能遭受岩溶涌突水的安全隐患。基于地下水流系统理论，结合研究区水文地质条件调查成果，岩溶地下水流系统的划分，隧道出口段关键岩溶分布区地质结构的分析，以及水文地球化学测试分析结果，对双龙洞与隧址区之间各岩溶地下水流系统间的水力联系及涌突水可能性进行了分析。结果表明，隧道出口段开挖若揭露至其所处岩溶含水层并进行排水，影响的只是周边有限的岩溶水及裂隙水，不会直接连通研究区西侧大规模岩溶地下水流系统；隧道施工和运行期间对双龙洞景区的岩溶水基本不会产生影响，同时双龙洞岩溶水也不会对隧道出口段形成直接的涌突水威胁。在岩溶区隧道涌突水来源的研究中，基于地下水流系统理论合理划分岩溶地下水流系统并分析各系统间水力联系，是分析涌突水来源及防范涌突水灾害的必要前提。      

Application of sedimentary pyrite in paleo-environment:a case study of Meihe Formation

The indices related to sedimentary pyrite are widely used in paleo-environmental studies;however its application principles and flaws have not been presented in detail so far , therefore it is necessary to review the controlling factors of them .In this study the authors described the application principles in detail , including py-rite morphology, C/S ratio, DOP, size distribution, sulfur isotope, and further discussed the C-S-Fe system in oil shale in Meihe Formation which indicates oxic or suboxic conditions during oil shale deposition .The concen-tration of TOC and S in the oil shale in Meihe Formation is more than that in background mudstone , and the py-rite formation is limited by sulfate .Therefore studying the indices related to pyrite proves to be of great impor-tance.     

The hydrodynamical characteristics of nearshore waters and the discharging process of mud flats— A case study of the mud flats near Lianyungang,China

It is apparent that there is a difference between mud coasts and sand coasts in such aspects as sediment components, hydrodynamics of nearshore waters, and the formative process in configuration, and profile. The intensity distribution of waves affecting the mud flats in Lianyungang, and the conditions determining tidal water levels, are discussed in this paper. A mathematical model which describes the erosion process of mud flats has been derived on the basis of the results of tests for the mud process in seawater. The model is satisfactory for the actual mud flat profile change in Lianyungang with artificial mud discharges.     

Geotechnical investigations and remediation design for failure of tunnel portal section: a case study in northern Turkey

Mass movements are very common problems in the eastern Black Sea region of Turkey due to its climate conditions, geological, and geomorphological characteristics. High slope angle, weathering, dense rainfalls, and anthropogenic impacts are generally reported as the most important triggering factors in the region. Following the portal slope excavations in the entrance section of Cankurtaran tunnel, located in the region, where the highly weathered andesitic tuff crops out, a circular toe failure occurred. The main target of the present study is to investigate the causes and occurrence mechanism of this failure and to determine the feasible remedial measures against it using finite element method (FEM) in four stages. These stages are slope stability analyses for pre- and postexcavation cases, and remediation design assessments for slope and tunnel. The results of the FEM-SSR analyses indicated that the insufficient initial support design and weathering of the andesitic tuffs are the main factors that caused the portal failure. After installing a rock retaining wall with jet grout columns and reinforced slope benching applications, the factor of safety increased from 0.83 to 2.80. In addition to slope stability evaluation, the Rock Mass Rating (RMR), Rock Mass Quality (Q) and New Austrian Tunneling Method (NATM) systems were also utilized as empirical methods to characterize the tunnel ground and to determine the tunnel support design. The performance of the suggested empirical support design, induced stress distributions and deformations were analyzed by means of numerical modelling. Finally, it was concluded that the recommended stabilization technique was essential for the dynamic long-term stability and prevents the effects of failure. Additionally, the FEM method gives useful and reasonably reliable results in evaluating the stability of cut slopes and tunnels excavated both in continuous and discontinuous rock masses.     

Formation of an anticyclonic eddy and the mechanism involved: a case study using cruise data from the northern South China Sea

Data from satellite altimetry and in situ observations together with the Hybrid Coordinate Ocean Model(HYCOM)reanalysis data were used to investigate the mechanism and formation of an anticyclonic eddy in the northeastern South China Sea(SCS).Analysis of water mass using cruise data indicated that the water captured in the eddy differs from those in the SCS,the Kuroshio intrusion,and the eddy-forming region.Data from sea surface height(SSH)and sea level anomaly(SLA)indicate that the eddy formed due both to the Kuroshio intrusion and the local circulation in the SCS.The Kuroshio intrusion is present at the start of the eddy growth(March 5-9)before Kuroshio leaps the Luzon Strait.The eddy then becomes larger and stronger in the absence of the Kuroshio intrusion.From the eddy budget of the HYCOM reanalysis data,the formation of the eddy goes in three steps.By the third step,the eddy had become affected by variations of local SCS circulation,which is more strongly than in the first step in which it is affected more by the Kuroshio intrusion.The variability of the temperature and salinity inside the eddy provide a support to this conclusion.The water in the SCS intruded into the eddy from the southeast,which decrease the salinity gradually in the southern part of the eddy during the growth period.     

Evaluating mountain water scarcity on the county scale: a case study of Dongchuan District,Kunming, China

Mountain water, which contributes 50% to 90% to the lower reaches of the watershed, has a considerably low utility efficiency. The water accessibility could be a quantitative measure of water scarcity in the mountains. It can be used effectively for emergency water shortage planning and water resource management. In the present study, Dongchuan District, a typical county in the Hengduan Mountains in Yunnan province of Southwest China, was selected as the study area, and the minimal cumulative resistance(MCR) model was used to simulate the least-cost path(LCP) from 1255 point features of natural villages, as well as 12,368 dryfield centroids, to their respective surrounding river systems, which serve as a source for emergency drinking water and irrigation during droughts. The average length of the LCP for each administrative village was calculated to represent the accessibility to water sources for agricultural production and daily life in these mountain villages. The distribution of population and dryfields, as well as other geographic elements, were analyzed to classify the degree of water scarcity in these villages. The results indicate that the area facing the highest risk of water shortage for agricultural irrigation is located in northern Dongchuan, in particular along the two sides of the Xiaojiang Valley, and that the area with the highest risk of water shortage for daily life needs is located along the Xiaojiang Valley.     

峡口隧道间歇性岩溶涌突水过程及来源解析

岩溶涌突水问题勘察与防治一直是隧道工程建设面临的难题。峡口隧道有着较长的岩溶涌突水历史,为了查明间歇性涌突水来源,探究岩溶水系统结构对涌突水过程的控制作用,综合利用水文地质调查、水文学和水文地球化学等方法对涌突水来源和过程进行了识别与分析。结果表明:在研究区孟家陵一带存在地下水分水岭,北部和南部的地下水分别向响龙洞和峡口洞排泄。在集中涌水事件中,次涌水总量与次降雨量具有显著的线性正相关关系,集中涌水与4条盲沟排水在水文地球化学特征上具有同源性,均来自于隧道北部的岩溶水;在隧道稳定排水期间,右洞北侧盲沟主要排泄隧道北部的岩溶水,其他3处盲沟排水则主要来源于碎屑岩裂隙水;集中涌水点位于峡口岩溶水系统的饱水带附近,强降雨导致隧道上方整体处于充水状态,涌水点截断了岩溶通道的快速流而发生涌突水,并且混合了小比例的基流。在岩溶涌突水问题研究中,综合利用多技术方法和多信息渠道验证可提高涌突水来源分析的准确性。      

基于成像测井的泥页岩裂缝研究:以焦石坝区块为例

富有机质泥页岩裂缝类型及其发育分布特征是影响页岩气聚集与散失的重要因素。基于岩心观测和高分辨微电阻率成像测井（FMI）,对焦石坝区块2口关键井（JYA井和JYB井）裂缝发育特征进行了精细标定与定量解释,并在此基础上联合含气性资料简要探讨了裂缝对页岩含气性的影响。研究结果表明,JYA井和JYB井主力层段及下伏地层裂缝差异较小,均以层理缝为主,但上覆盖层具有明显差异。JYA井上覆盖层天然裂缝发育程度较低,以高阻缝为主,高导缝和断层次之,三者的倾角变化范围分别为20.31°~75.83°（平均44.65°）、16.65°~61.17°（平均39.43°）和36.41°。裂缝线密度最高为0.6条/m,其中断层仅为0.025条/m,页岩系统封闭能力较好,压裂投产为高产井。JYB井上覆盖层天然裂缝发育程度较高,且以断层为主,高阻缝和高导缝次之,三者的倾角分别介于13.71°~72.23°（平均37°）、6.9°~78.49°（平均37.9°）和13.53°~61°（平均32°）之间。裂缝线密度高达0.98条/m,其中断层线密度约为0.654条/m,页岩系统封闭能力较差,压裂投产为低产井。裂缝发育类型及其程度决定了不同区块页岩气保存条件与页岩气富集程度。      

Hydro-geochemistry evolution in Ordovician limestone water induced by mountainous coal mining: A case study from North China

This research aimed to investigate the changing mechanism of hydro-geochemistry in Ordovician limestone karst(OL) water induced by mountainous coal mining activities. Thus, the hydrogeochemistry evolution of OL water over 40 years within a typical northern mountainous coal mine named Fengfeng Mine was studied by using Piper diagram, Gibbs scheme, ions correlation and Principal component analysis(PCA) methods. Results showed that, except for HCO_3~-, the ions of Ca~(2+), Mg~(2+), SO_4~(2-),Na~++K~+, Cl~- and total dissolution solids(TDS) values all increased by years as mining continues. Different hydro-geochemical characteristics in different periods can reflect different water-rock interactions.Accordingly, sulfates dissolution gradually took place of carbonates in water-rock interaction. Especially,OL water-rock interactions in different periods were all affected by rock weathering and evaporationconcentration together. At last, evaporationconcentration co-effect dominated the hydrogeochemistry evolution slowly, along with significant cations exchange over years.     

Probabilistic seismic landslide hazard assessment: a case study in Tianshui,Northwest China

Probabilistic analysis in the field of seismic landslide hazard assessment is often based on an estimate of uncertainties of geological, geotechnical,geomorphological and seismological parameters.However, real situations are very complex and thus uncertainties of some parameters such as water content conditions and critical displacement are difficult to describe with accurate mathematical models. In this study, we present a probabilistic methodology based on the probabilistic seismic hazard analysis method and the Newmark's displacement model. The Tianshui seismic zone(105°00′-106°00′ E, 34°20′-34°40′ N) in the northeastern Tibetan Plateau were used as an example. Arias intensity with three standard probabilities of exceedance(63%, 10%, and 2% in 50 years) in accordance with building design provisions were used to compute Newmark displacements by incorporating the effects of topographic amplification.Probable scenarios of water content condition were considered and three water content conditions(dry,wet and saturated) were adopted to simulate the effect of pore-water on slope. The influence of 5 cm and 10 cm critical displacements were investigated in order to analyze the sensitivity of critical displacement to the probabilities of earthquake-induced landslide occurrence. The results show that water content in particular, have a great influence on the distribution of high seismic landslide hazard areas. Generally, the dry coverage analysis represents a lower bound for susceptibility and hazard assessment, and the saturated coverage analysis represents an upper bound to some extent. Moreover, high seismic landslide hazard areas are also influenced by the critical displacements. The slope failure probabilities during future earthquakes with critical displacements of 5 cm can increase by a factor of 1.2 to 2.3 as compared to that of 10 cm. It suggests that more efforts are required in order to obtain reasonable threshold values for slope failure. Considering the probable scenarios of water content condition which is varied with seasons, seismic landslide hazard assessments are carried out for frequent, occasional and rare earthquake occurrences in the Tianshui region, which can provide a valuable reference for landslide hazard management and infrastructure design in mountainous seismic zones.     

Administrative urbanization and city-making in post-reform China: a case study of Ordos City,Inner Mongolia

In post-reform China, local governments, instead of the central state, have become major promoters of urbanization. Differing from the existing literature based on Western theories, this article argues that a localized perspective, ‘administrative urbanization', can provide a contextual explanation for the mechanism of urbanization in the reform era. The case study of Ordos indicates that new town construction, especially in the inland area, has become the main strategy for investment attraction and economic development. The local government has played a dominant role in this construction through a series of administrative measures, including avoidance of central state regulations, land leasing, high standard infrastructure construction, relocation policies and industrial attraction. This article also explores the issue of unsustainability in the new town, and identifies that underdeveloped industrialization, slow population agglomeration and real estate bubbles are primary threats to the sustainability of administrative urbanization.     

Logging curves characteristics and response mechanisms of basaltic facies and sub-facies:A case study from eastern sag of Liaohe depression,Northeast China

Based on five types of conventional logging curves including GR, RLLD, CNL, DEN and AC, and 39 core samples from 30 representative boreholes, the logging characteristics and lithofacies and sub-facies of the basaltic rocks were studied. Three basaltic facies and four sub-facies are recognized from the well logs, including volcanic conduit facies(post intrusive sub-facies), explosive facies, and effusive lava flow facies(tabular flow, compound flow and hyaloclastite sub-facies). The post intrusiv...     

低成熟度富有机质页岩微观孔隙结构特征表征——以广东茂名盆地油柑窝组为例

以广东茂名盆地油柑窝组富有机质页岩为例,采用氩离子抛光—场发射扫描电镜(AIP-FESEM)图像处理技术(Image Processing)、MATLAB软件,对微观孔隙进行定量统计,预测页岩微观孔隙发育特征。结果表明:研究区样品大量发育微纳米孔,包括有机质孔、粒间孔、粒内孔及微裂隙。页岩孔隙度低,约为1.56%。孔隙中,粒间孔最发育,孔隙率占比为94.82%,孔径为0.01～2.40μm;其次为有机质孔,孔隙率占比为4.22%,孔径为0.01～10.00μm,其中60%的孔隙孔径在50 nm以下;粒内孔最不发育,孔隙率占比小于1.00%。受沉积环境及储层成岩作用的影响,油柑窝组有机质及有机孔隙演化程度低,有机质成熟度介于0.40%～0.55%,与龙马溪组页岩储层相比,发育最广泛的纳米孔类型为矿物孔隙而非有机质孔,有机质质量分数与热演化程度是塑造优质页岩储层孔隙系统的关键因素。该结果可为低成熟度富有机质页岩储层孔隙结构演化提供依据。     

Excess commuting in transitional urban China: A case study of Guangzhou

During the reform era, Chinese cities witnessed dramatic institutional transformation and spatial restructuring in general and profound change of commuting patterns in particular. Using household surveys collected in Guangzhou, China, in 2001, 2005 and 2010, excess commuting measurements are estimated. Excess commuting shows an overall trend of increasing during 1990–1999, and then declining during 2000–2010. We argue that deepening marketization of the jobs and housing sectors has induced spatial separation of jobs and housing. In other words, institutional transition and urban spatial restructuring are underpinning the changes of commuting patterns in Chinese cities. Excess commuting has strong relationship with individual socio-demographic status, which is by and large due to the increasing flexibilities of jobs and housing location choices enjoyed by urban residents. The findings call for considerations on balancing jobs-housing in making public policies relevant to urban development in general, and land use and transportation in particular.     

KARST ENVIRONMENT AND ECO-POVERTY IN SOUTHWESTERN CHINA： A CASE STUDY OF GUIZHOU PROVINCE

1INTRODUCTIONIn the 1980s and 1990s, there was widespread belief a-mong environmentalists that uncontrolled population growth would be responsible for environment degrada-tion of all types. This neo-Malthusian belief originally surfaced in the publication of ThePopulationBombin the late 1960s. In ensuing years this belief, combined with work on environment carrying capacity and a growing environmental movement, led to the seeming-ly commonsense conclusion that high population growth and …     

Agricultural opportunity costs assessment based on planting suitability: a case study in a mountain county in southwest China

Payment for ecosystem services (PES) has become an increasingly popular means of ecosystem conservation. Opportunity cost is an important factor to increase the investment efficiency of PES projects. However, the distribution of opportunity cost is usually unclear in mountainous regions due to the obvious environment changes. In this study, we developed a framework to assess the distribution of agricultural opportunity costs in mountainous regions and applied this method to Baoxing County, a typical mountainous county in Sichuan Province of southwest China. Planting suitability of 17 crops was assessed based on agricultural statistics and natural conditions data within a GIS environment. Agricultural opportunity cost was quantified with a weighted summation of farmers’ willingness to cultivate and each crop’s opportunity cost. Finally, specific agricultural opportunity cost was obtained according to the spatial areas of the protection programs and land use status. The results showed that agricultural opportunity costs of PES in Baoxing County were estimated to be more than $30 million, with a mean of 400.85 $/ha. Agricultural opportunity costs in mountainous regions displayed some obvious spatial variation and areas with lower agricultural opportunity costs could be selected as priority areas for PES. Our findings revealed that the planting suitability evaluation can make agricultural opportunity costs mapping more reasonable. It will be helpful for the PES programs implementation in mountainous regions.