Stability analysis of shotcrete supported crown of NATM tunnels with discontinuity layout optimization          下载免费PDF全文

Yiming Zhang  Xiaoying Zhuang  Roman Lackner 《国际地质力学数值与分析法杂志》2018,42(11):1199-1216

For tunnel constructed by New Austrian Tunnelling Method, the crown is the upper part of tunnel section, constructed during excavation process and supported by shotcrete. The stability of the crown has great influence on the safety of tunnel itself and the buildings above, which correlates, among others, with geometrical setup of tunnel and material properties of shotcrete and soil/rock. In this paper, aiming at analyzing the stability of shotcrete supported crown, a recently presented numerical method discontinuity layout optimization is adopted, which introduces a great amount of potential discontinuities cross over one another and provides a wide search space for efficient upper limit analysis. In the analysis, a well‐established hydration model of cementitious material is implemented for accounting the hydration of shotcrete. Then assumptions based on convergence‐confinement method are used for accounting the 3‐dimensional effect in 2‐dimensional analysis, finally providing time‐space–dependent assessments of stability of shotcrete supported crown.  相似文献   

基于概率积分法的采动坡体稳定性预测与分析          下载免费PDF全文

王猛  孙丽丽  薄怀志 《山东国土资源》2018,34(12)

地下采煤会引起地表沉降、变形,甚至引发山体、河堤滑坡等地质灾害。采动坡体的稳定性研究一直是采矿工程中实际关心的问题。该文首先介绍分析了概率积分法移动变形稳态、动态预测模型以及基于极限平衡理论的单滑面采动坡体稳定性预测模型,提出了使用概率积分法结合Knothe时间函数对采动坡体稳定性进行预测分析的方法,并使用C#及XML Schema语言编制了相关的计算程序。最后,结合一个工程实例对采动坡体稳定性和动态变化过程进行了预测与分析,通过实测数据验证了提出方法的可行性,得出了采动引起的坡体下沉是影响坡体稳定性的主要因素,并提出了在坡体拉伸阶段进行注浆加固的方法。  相似文献   

高精度温度计在水温观测中的仪器稳定性分析     

邱永平 《中国地震》2018,34(4):828-836

利用宁波地震台水温10年来的单测项、6年来的同层比测资料,对高精度温度计的仪器短期和长期稳定性进行分析对比。研究发现仪器长期存在漂移现象,漂移量的大小与每套仪器的系统特性有关,但随着观测时间的延续,漂移量逐渐减少,认为该现象对地震前兆观测影响不大;短期稳定性存在不明原因的阶跃和脉冲现象,但次数不多,幅度不大,如果不是并行观测,较难判别。因此,在资料分析时要考虑仪器的这些问题。有时仪器短期非常稳定,数天至20天整点值为同一测值。  相似文献   

Plant root and rhizome strength: Are there differences between and within species and rivers?     

A.M. Gurnell  J.V. Holloway  T. Liffen  A.J. Serlet  G. Zolezzi 《地球表面变化过程与地形》2019,44(1):389-392

The strength and architecture of roots and other below-ground organs of riparian and aquatic plants affect plant resistance to uprooting and contribute to reinforcing river bank, bar and bed materials. Therefore, root properties are an important element in models for estimating river bank stability and such models may focus on the role of plants by using root strength–diameter relationships for the particular plant species that are present. Here we explore the degree to which there appear to be significant differences in strength–diameter relationships between and within species-specific data sets obtained for two riparian tree/shrub (Populus nigra, Salix alba) and two emergent aquatic macrophyte (Sparganium erectum, Phalaris arundinacea) species in different European river environments. While the analysed data sets were not specifically collected to answer these research questions, the results are sufficiently compelling to make the case for the collection of a more comprehensive data set and its rigorous analysis. This would allow recommendations to be made on the degree to which (i) species-specific or more general relationships between root/rhizome strength and diameter are appropriate, (ii) such relationships are applicable within and between rivers in different geographical regions and subject to different local environmental conditions, and (iii) further (minimalist) field observations are needed to calibrate such relationships for investigations of new locales or species. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

重庆市主体功能区识别的主导因素与空间稳定性约束机理     

汪洋  王力力  祁鹏卫  刘志海 《地理学报》2019,74(1):44-62

主体功能区规划已上升为国家制度和战略,对中国长期空间发展格局优化与再组织将发挥积极的引导和约束作用。从地域性角度出发,探寻主体功能区发生性（形成与演化）和反馈性（识别与规划）时空机理与规律是地理学具有时代意义的重要科学问题。以重庆市为例,通过国土空间开发条件综合评价,识别了主体功能区划分的适宜性空间格局。基于对西南山区发展约束条件的基本认识,提出了地域主体功能空间分异的主导性约束假设,设定地形和区位为原生性主导因素,验证了其与区划指标系统的定量关联性,以此为基础解析了主导因素约束机理并提出了地域主体功能区的空间稳定性机制。研究发现：① 开发与保护适宜性识别结果的格局指向清晰。城市化适宜的区域主要集中于都市区和部分周边区县,区域副中心（万州和黔江）适宜性也相对较高。生态保护适宜的区域集中于渝东北秦巴山区及部分三峡库区区县,同时包括渝东南武陵山区所在区县。② 地形和区位因子在本区域对主体功能区的识别与形成具有主导约束作用。回归分析显示,主体功能区划指标与地形因子相关性水平达到显著的超过70%,区位因子超过40%;两者综合后与区划标志变量（A、B指数）的相线性相关拟合度R²均超过0.8;地理探测器发现,地形和区位因子对区划指标的约束性分别有9个和7个达到0.05显著性水平,对A、B指数的解释度分别约为70%和60%,两者叠加后,约束水平全部达到显著,对A、B指数的解释度在90%左右。③ 空间稳定性机制表现为两个方面,其一是基于主导因素约束的稳定性传递机制,称为客观稳定性;其二是基于指标体系的局域相对性和算法的内部抵消机制,称为主观稳定性。两种机制的协同性验证了区划技术系统的地域适应性和科学性。  相似文献   

Asymptotic scale-dependent stability of surface quasi-geostrophic vortices: semi-analytic results     

G. Badin  F. J. Poulin 《地球物理与天体物理流体动力学》2019,113(5-6):574-593

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Strong variation in weathering of layered rock maintains hillslope‐scale strength under high precipitation          下载免费PDF全文

Jennifer Von Voigtlander  Marin K. Clark  Dimitrios Zekkos  William W. Greenwood  Suzanne P. Anderson  Robert S. Anderson  Jonathan W. Godt 《地球表面变化过程与地形》2018,43(6):1183-1194

The evolution of volcanic landscapes and their landslide potential are both dependent upon the weathering of layered volcanic rock sequences. We characterize critical zone structure using shallow seismic V_p and V_s profiles and vertical exposures of rock across a basaltic climosequence on Kohala peninsula, Hawai’i, and exploit the dramatic gradient in mean annual precipitation (MAP) across the peninsula as a proxy for weathering intensity. Seismic velocity increases rapidly with depth and the velocity–depth gradient is uniform across three sites with 500–600 mm/yr MAP, where the transition to unaltered bedrock occurs at a depth of 4 to 10 m. In contrast, velocity increases with depth less rapidly at wetter sites, but this gradient remains constant across increasing MAP from 1000 to 3000 mm/yr and the transition to unaltered bedrock is near the maximum depth of investigation (15–25 m). In detail, the profiles of seismic velocity and of weathering at wet sites are nowhere monotonic functions of depth. The uniform average velocity gradient and the greater depths of low velocities may be explained by the averaging of velocities over intercalated highly weathered sites with less weathered layers at sites where MAP > 1000 mm/yr. Hence, the main effect of climate is not the progressive deepening of a near‐surface altered layer, but rather the rapid weathering of high permeability zones within rock subjected to precipitation greater than ~1000 mm/yr. Although weathering suggests mechanical weakening, the nearly horizontal orientation of alternating weathered and unweathered horizons with respect to topography also plays a role in the slope stability of these heterogeneous rock masses. We speculate that where steep, rapidly evolving hillslopes exist, the sub‐horizontal orientation of weak/strong horizons allows such sites to remain nearly as strong as their less weathered counterparts at drier sites, as is exemplified by the 50°–60° slopes maintained in the amphitheater canyons on the northwest flank of the island. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

基于组合权重与灰色关联度分析法的地铁深基坑开挖稳定性评价     

郎秋玲  王伟  高成梁 《吉林大学学报(地球科学版)》2020,50(6):1823-1832

伴随着城市的快速发展，地铁深基坑工程越来越多。在开挖过程中如何对其稳定性进行评价，是当前需要重点关注的问题。以成都地铁十七号线凤溪站深基坑支护开挖工程为依托，利用层次分析确定的主观权重与利用熵值法确定的客观权重计算获得组合权重，并与灰色关联度分析法相结合，通过现场数据采集并进行综合评判，客观评价地铁深基坑开挖的稳定性。结果表明，各监测项目对基坑稳定性的重要程度从大到小依次为桩顶水平位移（0.29）、地表沉降（0.24）、建筑物沉降（0.19）、桩顶沉降（0.18）、内支撑轴力（0.10），基坑稳定性综合评判结果等级为"非常好"。所建立的评价模型可为类似地铁深基坑开挖稳定性评价提供新的方法。  相似文献   

The effect of long-term aerial exposure on intertidal mudflat erodibility     

Hieu M. Nguyen  Karin R. Bryan  Conrad A. Pilditch 《地球表面变化过程与地形》2020,45(14):3623-3638

Intertidal zones by definition are exposed to air at low tide, and the exposure duration can be weeks (e.g. during neap tides) depending on water level and bed elevation. Here we investigated the effect of varying exposure duration (6 h to 10 days) on intertidal mudflat erosion (measured using the EROMES device), where the effects of water content and biofilm biomass (using chlorophyll-a content as a proxy, Chl-a μg g⁻¹) were taken into account. Sediments were collected between spring and summer (in October 2018, January 2019 and February 2019) from an intertidal site in the Firth of Thames, New Zealand. Longer exposure duration resulted in more stable sediments [higher erosion threshold (Ƭ_cr, N m⁻²) and lower erosion rate (ER, g m⁻² s⁻¹)]. After 10 days, exposure increased Ƭ_cr by 1.7 to 4.4 times and decreased ER by 11.6 to 21.5 times compared with 6 h of exposure. Chl-a and water content changed with exposure duration and were significantly correlated with changes in Ƭ_cr and ER. The stability of sediments after two re-submersion periods following exposure was also examined and showed that the stabilizing effect of exposure persisted even though water content had increased to non-exposure levels. Re-submersion was associated with an increase in Chl-a content, which likely counteracted the destabilizing influence of increased water content. A site-specific model, which included the interplay between evaporation and biofilm biomass, was developed to predict water content as a function of exposure duration. The modelled water content (W_Mod.) explained 98% of the observed variation in water content (W_Obs.). These results highlight how the exposure period can cause subtle changes to erosion regimes of sediments. An understanding of these effects (e.g. in sediment transport modelling) is critical to predicting the resilience of intertidal zones into the future, when sea-level rise is believed to exacerbate erosion in low-lying areas. © 2020 John Wiley & Sons, Ltd.  相似文献   

Geochemical evolution of groundwater in hard-rock aquifers of South India using statistical and modelling techniques     

Annadasankar Roy  Hemant Mohokar  Diksha Pant  Uday Kumar Sinha  G. N. Mendhekar 《水文科学杂志》2020,65(6):951-968

ABSTRACT

Multivariate statistical analysis and inverse geochemical modelling techniques were employed to deduce the mechanism of groundwater evolution in the hard-rock terrain of Telangana, South India. Q-mode hierarchical cluster analysis (HCA) and principal component analysis (PCA) were used to extract the hydrogeochemical characteristics and classify the groundwater samples into three principal groups. Use of thermodynamic stability diagrams and inverse geochemical modelling in PHREEQC identified the chemical reactions controlling hydrogeochemistry of each of the groups obtained from statistical analysis. The model output showed that a few phases are governing the water chemistry in this area and the geochemical reactions responsible for evolution of groundwater chemistry along the flow path are (i) dissolution of evaporite minerals (dolomite, halite); (ii) dissolution of primary silicate minerals (albite, anorthite, K-feldspar, biotite); (iii) precipitation of secondary silicate minerals (kaolinite, quartz, gibbsite, Ca-montmorillonite) along with anhydrite and calcite; and (iv) reverse ion exchange processes.  相似文献