Probabilistic stability analyses of undrained slopes by 3D random fields and finite element methods

A long slope consisting of spatially random soils is a common geographical feature. This paper examined the necessity of three-dimensional(3 D) analysis when dealing with slope with full randomness in soil properties. Although 3 D random finite element analysis can well reflect the spatial variability of soil properties, it is often time-consuming for probabilistic stability analysis. For this reason, we also examined the least advantageous(or most pessimistic) cross-section of the studied slope. The concept of"most pessimistic" refers to the minimal cross-sectional average of undrained shear strength. The selection of the most pessimistic section is achievable by simulating the undrained shear strength as a 3 D random field. Random finite element analysis results suggest that two-dimensional(2 D) plane strain analysis based the most pessimistic cross-section generally provides a more conservative result than the corresponding full 3 D analysis. The level of conservativeness is around 15% on average. This result may have engineering implications for slope design where computationally tractable 2 D analyses based on the procedure proposed in this study could ensure conservative results.

Theoretical Analysis and Experimental Verification on Flow Field of Piezoelectric Pump with Unsymmetrical Slopes Element

Regular valveless piezoelectric pumps have rectifying elements outside their chambers to produce net flow. These rectifying elements outside the chamber will increase the overall volume of the pump and prevent its minimization. Valveless piezoelectric pump with unsymmetrical slopes elements（USE）, proposed in this paper, differs from other valveless pumps in that it is easy to be minimized by developing the chamber bottom as such a rectifying element. In this research, the working principle of the proposed pump was analyzed first. Numerical models were thereby established and numerical simulation was conducted to the chamber flow field with the method of time-dependent velocity. The effects of the USEs on the flow field in the chamber were shown clearly in simulation. And the particular feature of flow field in the chamber was discovered. It behaves a complex flow field, in which strong turbulent occurs companying a lot of vortexes in different directions and different sizes. This feature is just opposite to what regular piezoelectric pumps expect： a moderate flow field. The turbulent flow could be used to have different liquids stirred and well mixed in the chamber to produce homogeneous solution, emulsion or turbid liquid. Meanwhile, numerical simulation also presents the effect of the angles difference of the two slopes upon the flow field, and upon the flow rate of the pump, which fits to the theoretical analysis. Experiments with the proposed pump were also conducted to verify the numerical results. In these experiments, six USEs with different slope angles were used for efficiency tests, which proved the validity and reliability of the numerical analysis. The data obtained from numerical analysis agree well with that from the experiments. The errors ranged from 4.4% to 14.8% with their weighted average error being 9.7%.

Numerical study on the characteristics of flow field and wave propagation near submerged breakwater on slope

In this study, characteristics of flow field and wave propagation near submerged breakwater on a sloping bed are investigated with numerical model. The governing equations of the vertical two-dimensional model are Reynolds Averaged Navier Stokes equations. The Reynolds stress terms are closed by a nonlinear k - ε turbulence transportation model. The free surface is traced through the PILC-VOF method. The proposed numerical model is verified with experimental results. The numerical result shows that the wave profile may become more asymmetrical when wave propagates over breakwater. When wave crest propagates over breakwater, the anticlockwise vortex may generate. On the contrary, when wave hollow propagates over breakwater, the clockwise vortex may generate. Meanwhile, the influenced zone of vortex created by wave crest is larger than that created by wave hollow. All the maximum values of the turbulent kinetic energy, turbulent dissipation and eddy viscosity occur on the top of breakwater. Both the turbulent dissipation and eddy viscosity increase as the turbulent kinetic energy increases. Wave energy may rapidly decrease near the breakwater because turbulent dissipation increases and energy in lower harmonics is transferred into higher harmonics.

A generalized multi-field coupling approach and its application to stability and deformation control of a high slope

Human activities, such as blasting excavation, bolting, grouting and impounding of reservoirs, will lead to disturbances to rock masses and variations in their structural features and material properties. These engineering disturbances are important factors that would alter the natural evolutionary processes or change the multi-field interactions in the rock masses from their initial equilibrium states. The concept of generalized multi-field couplings was proposed by placing particular emphasis on the role of engineering disturbances in traditional multi-field couplings in rock masses. A mathematical model was then developed, in which the effects of engineering disturbances on the coupling-processes were described with changes in boundary conditions and evolutions in thermo-hydro-mechanical （THM） properties of the rocks. A parameter, d, which is similar to damage variables but has a broader physical meaning, was conceptually introduced to represent the degree of engineering disturbances and the couplings among the material properties. The effects of blasting excavation, bolting and grouting in rock engineering were illustrated with various field observations or theoretical results, on which the degree of disturbances and the variations in elastic moduli and permeabilities were particularly focused. The influences of excavation and groundwater drainage on the seepage flow and stability of the slopes were demonstrated with numerical simulations. The proposed approach was further employed to investigate the coupled hydro-mechanical responses of a high rock slope to excavation, bolting and impounding of the reservoir in the dam left abutment of Jinping I hydropower station. The impacts of engineering disturbances on the deformation and stability of the slope during construction and operation were demonstrated.

A Study of Soil Nutrients in the Terrace Field Changed from Mountain Slope in Three Gorges Reservoir Region

In order to accurately grasp the soil fertility in Three Gorges Reservoir Region after changing mountain slope into terrace field,we take Wushan County for example,and use the spatio-temporal substitution method to analyze the soil nutrient status and trend about the terrace field changed from mountain slope under different length of implementation.The results show that the soil fertility is generally low in the study area,and according to the soil nutrient grading standards in the second national land survey,the average content of total nitrogen,available potassium,organic matter and available phosphorus reaches Standard III,Standard III,Standard IV and Standard V,respectively,and the spatial heterogeneity of soil nutrients is small.Compared to the sloping land,the terrace field changed from mountain slope has increasing soil nutrients on the whole with the length of farming.The mean of various indicators about soil nutrients in the terrace field changed from mountain slope for 2 years is lower than in the sloping land,and there is the biggest difference in soil fertility,while the mean of various indicators about soil nutrients in the terrace field changed from mountain slope for 14 years shows a linear upward trend,and the difference in soil fertility decreases.

Energy Spectrum of Linear Internal Wave Field in the Vicinity of Continental Slope

The purpose of the research was to investigate two-dimensional modeling of efficiency of mixing, resulting from the reflection of a linear internal wave field (IWF) off a continental slope. Efficiency of deep ocean mixing was associated with the energy balance of the radiating IWF into an interior of the ocean in the vicinity of a sloping bottom topography. Since waves are generated not only at the fundamental frequency but also at all of its harmonics ωn = nω less than buoyancy frequency N and greater than Coriolis frequency f, our analysis includes, in general, an infinite number of discrete internal wave modes n satisfying the dispersion relationship for internal waves. However, since we are interested only in the radiating part of the field, the mode numbers are limited. Due to multiple singularities of order two caused by resonance in the vicinity of critical slope, the energy is visualized in Lδ -norm with δ > 2. Research results include the visualization of the effects of the continental slope and the Earth’s rotation on resulting energy in the vicinity of the slope.

土与强风化岩双元边坡圆弧-平面破坏模式与支护设计方法

为了探究土与强风化岩边坡中强风化岩不破坏的临界坡率及稳定性判断方法,基于济南地层,得出适用于数值模拟的土层参数,并利用强度折减法求出边坡的临界坡率,为施工提供参考。针对强风化岩不破坏的边坡,运用改进的瑞典条分法求出边坡安全系数解析解,并利用滑移线场法求出滑移线,为安全系数解析解的应用提供依据。结果表明,岩层厚度超过边坡高度1/2或坡率大于1:0.5时,强风化岩一定破坏;解析解得出的安全系数偏小,有利于工程安全;针对土与强风化岩边坡,文中结果可确定边坡破坏区域,设计支护方案。

Origin and migration model of natural gas in L gas field, eastern slope of Yinggehai Sag, China

Based on the chemical and stable carbon isotopic composition of natural gas and light hydrocarbons, along with regional geological data, the genetic type, origin and migration of natural gases in the L lithologic gas field, the eastern slope of Yinggehai Sag were investigated. The results show that these gases have a considerable variation in chemical composition, with 33.6%–91.5% hydrocarbon, 0.5%-62.2% CO2, and dryness coefficients ranging from 0.94 to 0.99. The alkane gases are characterized by δ13C1 values of -40.71‰--27.40‰,δ13C2 values of –27.27‰– –20.26‰, and the isoparaffin contents accounting for 55%–73% of the total C5–C7 light hydrocarbons. These data indicate that the natural gases belong to the coal-type gas and are mainly derived from the Miocene terrigenous organic-rich source rocks. When the CO2 contents are greater than 10%, the δ13CCO2 values are –9.04‰ to – 0.95‰ and the associated helium has a 3He/4He value of 7.78×10^–8, suggesting that the CO2 here is crustal origin and inorganic and mainly sourced from the thermal decomposition of calcareous mudstone and carbonate in deep strata. The gas migrated in three ways, i.e., migration of gas from the Miocene source rock to the reservoirs nearby;vertical migration of highly mature gas from deeper Meishan and Sanya Formations source rock through concealed faults;and lateral migration along permeable sandbodies. The relatively large pressure difference between the “source” and “reservoir” is the key driving force for the vertical and lateral migration of gas. Short-distance migration and effective “source - reservoir” match control the gas distribution.

双小行星系统表面动力学环境分析

双小行星系统在太阳系中普遍存在,具有独特的探测价值,揭示其表面动力学环境是实现表面巡游探测的关键。相比于单小行星,双星系统成员间的摄动作用对表面动力学环境存在影响,需要加以专门的分析和研究。以近地双小行星系统(66391)Moshup为例,主、次星均采用多面体引力场模型,通过推导质点在主、次星表面附近的动力学方程,计算出主、次星的表面等效重力和表面坡度,以及表面各点处的最小和最大起飞速度,分析分布规律和成因,特别关注次星对高速旋转主星的周期性潮汐力的影响。在此研究结果的基础上,针对主星和次星分析适合探测器着陆和表面巡游的区域。结果表明:由于旋转离心力的影响,主、次星表面的等效重力分布有随纬度减小而降低的趋势,而坡度主要与局部地形相关,主星的北极高纬度区域和次星南北纬80°以上的区域坡度小,且等效重力较大,适合作为探测器的着陆点或开展表面巡游;次星潮汐力对主星表面重力存在周期性影响;主星表面大部分区域的最小起飞速度小于0.3 m/s,次星表面大部分区域的最小起飞速度在0.10~0.25 m/s之间。由于自转影响,主、次星的最小起飞速度方向几乎全部朝东。

基于DNDC模型的红壤旱坡花生地N_(2)O排放模拟研究

为探究DNDC模型在红壤旱坡地N_(2)O排放模拟的适用性,以赣北红壤旱坡花生地为研究对象,设置常规耕作和轻简化免耕2种处理,连续3年(2019—2021年)采用静态箱-气相色谱法开展N_(2)O排放的田间原位观测试验,研究不同耕作处理下N_(2)O排放特征及DNDC模型模拟效果。结果表明:DNDC模型对不同耕作处理下0~10 cm土壤温度(相关系数r为0.86~0.87)和作物产量(r为0.90)的模拟效果较好。该模型能较好地模拟花生季因施肥和降雨引起的N_(2)O排放波动变化,也能较好地模拟常规耕作下土壤N_(2)O排放峰,但会在一定程度上低估轻简化免耕的N_(2)O排放峰和排放总量,且模型对16 mm以下的降雨响应较小。土壤pH值、施肥量对红壤旱坡花生地N_(2)O排放的影响最大,降雨量、土壤有机碳含量和粘粒含量也是影响N_(2)O排放的重要因子。模型模拟2019年不同施肥量下N_(2)O排放总量与花生产量发现,氮肥施用量不能低于76.54 kg/hm^(2),也不宜超过106.78 kg/hm^(2)。研究结果可为红壤坡耕地作物种植优化、农业温室气体减排等提供理论依据。

基于结构面粗糙度随机场表征的抗剪强度变异性

岩体结构面抗剪强度参数具有变异性是客观事实,而受限于室内外直剪试验成本而导致抗剪强度变异性指标获取困难是目前制约岩质边坡可靠度评价发展的主要原因之一。鉴于此,提出了一种利用少量实测结构面粗糙度曲线样本和岩块物理力学参数,结合JRC-JCS(joint roughness coefficient-joint compressive strength)剪切强度模型、随机场理论和非侵入式离散元数值试验,获取结构面抗剪强度参数变异性指标的方法。将此方法应用于某隧道进口段岩质边坡可靠度评价中,研究发现:(1)该岩质边坡主控结构面粗糙度纵坐标方差为0.012 5 cm2,相关距离为0.75 cm,生成的随机粗糙度曲线与实测样本相似;(2)结构面黏聚力和内摩擦角均值分别为0.427 MPa和54.9°,标准差分别为0.229 MPa和4.47°,变异系数分别为53.63%和8.14%;(3)此边坡稳定性系数服从正态分布,失稳概率为2.8%,可靠度为1.52。

考虑消落带岩体劣化影响的典型危岩岸坡稳定性研究

三峡库区周期性水位升降引起的消落带岩体劣化对典型危岩岸坡稳定性具有重大影响。基于野外调研及地勘资料,采用通用离散单元法程序(universal distinct element code,简称UDEC)研究了消落带劣化区形态对近水平层状高陡危岩岸坡的稳定性影响。研究表明:目前三峡库区巫山段的近水平层状危岩岸坡消落带岩体劣化严重,在不同消落带劣化区存在紧密层状、松散碎裂状、溶蚀凹腔状、含挤压碎裂带等典型消落带劣化区形态;含有第1种消落带劣化区形态的危岩岸坡稳定性较好,危岩体位移较小,失稳模式为滑移破坏;含有第2种消落带劣化区形态的危岩岸坡危岩体先向坡内偏移,其后随着消落带岩体支撑强度弱化向坡外倾倒破坏;含有第3种消落带劣化区形态的危岩岸坡危岩体向坡外位移较大,失稳模式为倾倒破坏;含有第4种消落带劣化区形态的危岩岸坡稳定性主要受挤压破碎带的力学性质控制,易产生沿破碎带切割面的旋转滑移破坏;通过对以上4种劣化区形态的危岩岸坡增加防治加固措施,危岩体的变形位移得到了不同程度的有效控制。

隧道路面横坡对流淌火燃烧蔓延规律影响的实验研究

为探究地面横坡对隧道流淌火燃烧蔓延规律和温度场分布特征的影响,搭建缩尺寸隧道模型开展研究。研究结果表明:当泄漏速率较小时,有横坡的隧道流淌火的燃烧扩散可分为4个阶段,分别为燃烧横向扩散阶段、回缩阶段、燃烧稳定阶段以及熄灭阶段;当泄漏速率较小时,流淌火仅存在横向扩散阶段,而当泄漏速率较大时,在燃料横向扩散阶段之后会形成贴壁纵向扩散,进而形成隧道内的“T型火”。通过理论分析建立相应的流淌火横向扩散距离以及纵向扩散距离的理论预测模型。此外,当泄漏速率较小时,隧道顶棚高温区域在隧道中心。当形成“T型火”时,火焰贴壁一侧的温度明显高于隧道中心线温度。研究结果可为隧道流淌火火灾的探测设计提供理论支撑。

滑坡自然电场物理模拟研究

为了厘清自然电位法监测中岩土种类、含水率、坡度角在滑坡产生前的响应规律,研究了各因素作用下模拟滑坡时自然电位曲线的变化特征,通过厘清单因素、多因素综合影响的前提下滑坡产生前后自然电位如何变化,总结出实验条件下滑坡的自然电位响应规律。结果表明,采用自然电位法预测滑坡时与其自然电位数值无关,只与自然电位变化率有关;不同岩土类型和坡度角在发生滑坡之前自然电位信号值会升高,升高速率越大发生滑坡的严重程度越高;不同含水率实验在滑坡产生之前自然电位信号值会降低,且滑动前自然电位信号降低速率越快发生滑坡的严重程度越高。

坡地下沉式窑洞建筑设计构想

窑洞建筑作为我国传统建筑,历史悠久,有绿色环保、造价低廉的优点,能够满足一些欠发达地区的建筑使用需求。文章以山地村落为研究对象,在坡地规划下沉式窑洞,利用自然条件补齐资金短板,这种新型窑洞的搭建旨在探寻偏远地区受限于经济因素的建筑形式,以及在传统建筑逐渐淡出人们视野的趋势下寻求其新的发展模式。

基于离散元的岩质高边坡开挖支护数值模拟

为分析岩质路堑高边坡的开挖支护对边坡变形破坏及边坡稳定性的影响,利用离散元数值模拟与原位监测相结合的方法,对开挖适时支护与开挖未支护两种工况进行比较,评价了锚杆支护的效果。结果表明:边坡开挖引起的竖向位移主要集中于开挖面中部;在相同开挖条件下,经适时支护后,边坡开挖面临空向水平位移最大值减小2.50 cm,安全系数提高8.62%,处于基本稳定状态;数值模拟结果与原位监测数据基本吻合,说明离散单元法对于分析岩质边坡稳定性问题的适用性。

川西南公路顺层边坡桩锚组合结构加固分析——以乐西高速ZK9+352~ZK9+526边坡为例

四川盆地周边地形地质条件复杂,公路建设中顺层边坡的工程病害频现。通过工程地质分析和数值计算,基于滑面损伤本构模型,研究顺层边坡支护前后滑面应力、位移和边坡稳定性系数等特征量的变化规律,验证桩锚组合结构加固顺层边坡的适用性;通过施工全周期现场监测,获取边坡深部位移、抗滑桩桩身弯矩和锚索应力的时效特征。结果表明:开挖扰动下顺层边坡具渐进性失稳破坏特征;自坡脚沿滑面向后缘,位移呈指数型平滑递减,剪应力先增大后降低,滑面损伤变量自剪应力峰值位置开始同频衰减;采用桩锚组合结构加固顺层边坡后,滑面位移最大值降低88.62%,最大损伤变量降低84.75%,稳定系数提高25.20%;坡体深部位移、抗滑桩桩身弯矩、锚索应力等监测验证了桩锚组合结构加固的有效作用。

Effects of gully terrain on stress field distribution and ground pressure behavior in shallow seam mining

This study proposes a novel approach to study stress field distribution and overlying ground pressure behavior in shallow seam mining in gully terrain.This approach combines numerical simulations and field tests based on the conditions of gully terrain in the Chuancao Gedan Mine.The effects of gully terrain on the in situ stress field of coal beds can be identified by the ratio of self-weight stress to vertical stress(η) at the location corresponding to the maximum vertical stress.Based on the function η =j(h),the effect of gully terrain on the stress field of overlying strata of the entire field can be characterized as a significantly affected area,moderately affected area,or non-affected area.Working face 6106 in the Chuancao Gedan Mine had a coal bed Jepth <80 m and was located in what was identified as a significantly affected area.Hence,mining may cause sliding of the gully slope and increased loading(including significant dynamic loading) on the roof strata.Field tests suggest that significant dynamic pressures were observed at the body and foot of the gully slope,and that dynamic loadings were observed upslope of the working face expansion,provided that the expanding direction of the working face is parallel to the gully.

GeoStudio软件Slope-W模块在堆浸场边坡稳定性分析中的应用

堆浸场边坡稳定性对于矿山堆浸场的经济性和安全环保性方面具有重要意义。基于极限平衡条分法原理开发的Geo Studio软件,其中的Slope-W模块作为一种岩土结构稳定性分析通用软件,能通过建立有限元模型,施加荷载和边界条件,有效模拟土条受力以及土条间作用力,建立力平衡和力矩平衡方程,求解堆浸场最危险滑弧以及最小安全系数,从而全面掌握堆浸场边坡抗滑稳定性。本文通过该软件在工程实例中的应用,为今后堆浸场的稳定性安全设计和评价提供了一定的参考依据。

Weathering Characteristics of Sloping Fields in the Three Gorges Reservoir Area, China

For the purpose of understanding the weathering characteristics of surface layers in purple mudstone sloping fields of the Three Gorges Reservoir area of China, oxide content of major elements, composition of clay minerals, magnetic susceptibility, and difference in weathering characteristics of surface layers under different slope gradients were determined. The results showed that the oxide content of Si, Al, and Fe ranged from 60% to 75% and the weathering coefficient with depth showed no trend along the slope gradient. Also, for gentle (10° and 15°) and intermediate (25° and 40°) slopes the clay relative diffraction peak for kaolinite at the surface between 0-10 cm and 10-20 cm declined with an increase in slope gradient, while the relative diffraction peak for kaolinite in weathered layers on steep slopes (50° and 60°) disappeared altogether. Magnetic susceptibility decreased with increasing depth and, for a given depth layer, decreased with an increase in slope gradient. Analysis of the oxide content, weathering coefficients, clay minerals, and magnetic susceptibility showed that in the Three Gorges Reservoir area, the pedogenesis of the weathering layer in purple mudstone sloping fields was weak with weaker soil formation going from gentle slope to steep slope.