Mesh-free analysis applied in reinforced soil slopes

One of the most applicable geotechnical structures whose analysis is carried out through iterative procedures is the reinforced soil slope. In this regard, the most successful method for the reinforced slope analysis through numerical methods is the finite element method whose updating mesh may result in some difficulties. In this study, the Natural Element Method (NEM), which is a mesh-free method, in conjunction with conventional limit equilibrium is implemented to find the slip surface in the reinforced slopes. Results demonstrate the convergence and preciseness of the present method in comparison with the other numerical methods and conventional limit equilibrium method.     

An efficient quasi-Newton approximation-based SORM to estimate the reliability of geotechnical problems

The first order reliability method (FORM) is efficient, but it has limited accuracy; the second order reliability method (SORM) provides greater accuracy, but with additional computational effort. In this study, a new method which integrates two quasi-Newton approximation algorithms is proposed to efficiently estimate the second order reliability of geotechnical problems with reasonable accuracy. In particular, the Hasofer–Lind–Rackwitz–Fiessler–Broyden–Fletcher–Goldfarb–Shanno (HLRF–BFGS) algorithm is applied to identify the design point on the limit state function (LSF), and consequently to compute the first order reliability index; whereas the Symmetric Rank-one (SR1) algorithm is nested within the HLRF–BFGS algorithm to compute good approximations, yet with a reduced computational effort, of the Hessian matrix required to compute second order reliabilities. Three typical geotechnical problems are employed to demonstrate the ability of the suggested procedure, and advantages of the proposed approach with respect to conventional alternatives are discussed. Results show that the proposed method is able to achieve the accuracy of conventional SORM, but with a reduced computational cost that is equal to the computational cost of HLRF–BFGS-based FORM.     

渝东南下古生界页岩构造裂缝形成及分布控制因素

天然裂缝对页岩气储集和渗流有重要影响,但目前对页岩构造裂缝研究不够深入。本文通过露头、岩心裂缝观察和分析,探讨了渝东南下古生界页岩构造裂缝类型、形成机理及分布控制因素。基于裂缝特征及力学成因,将剪切裂缝分为高角度剪切裂缝、倾斜滑脱裂缝和水平滑脱裂缝。倾斜滑脱裂缝是在上覆岩层重力和水平构造应力共同作用下沿应力集中的软弱面发生剪切滑动形成,水平滑脱裂缝是在构造挤压应力作用条件下主要沿页理面方向的剪切或层间滑动形成;页理发育程度及岩层曲率是控制水平滑脱裂缝形成的关键因素,岩石矿物组成、构造作用及岩层厚度是控制其它类型构造裂缝形成和分布的主要因素,页岩岩石力学层的划分需要根据裂缝特征、岩性变化特征、岩石力学参数及沉积界面等综合确定,岩层厚度与层间构造裂缝密度呈负相关关系。     

广西隆安下石炭统都结微生物岩微相特征与沉积环境研究

广西隆安县都结乡发育的微生物岩产于下石炭统都安组中—上部地层,分布广、厚度大,是中国南方早石炭世报道较少的碳酸盐岩建造类型,具有较高的研究价值。该微生物岩以颗粒灰岩和粘结岩为主,生物含量丰富,包括微生物、有孔虫、棘皮类、钙球、腕足等。通过岩相分析,可识别出以下8种微相类型:MF1含亮晶胶结物的泥晶包壳生屑灰岩、MF2含腕足似球粒灰岩、MF3无纹层似球粒颗粒灰岩、MF4集合颗粒灰岩、MF5细密纹层状粘结岩、MF6内碎屑鲕粒灰岩、MF7鲕粒灰岩、MF8白云质鲕粒灰岩。伴随海平面升降变化,都结微生物岩沉积环境先后经历了FZ1台地边缘浅滩相、FZ2开阔台地相与FZ3局限台地相这三种沉积相带之间往复变化的沉积相模式。结合前人基础地质资料,该沉积相模式表明该微生物岩发育于低纬度孤立碳酸盐岩台地浅水环境,并经历了初期、主体时期和消亡期3个发育阶段,海平面虽伴有小幅波动,但整体呈下降趋势。微生物岩发育于晚古生代冰期与谢尔普霍夫生物灭绝事件前夕,该时期南盘江盆地微生物岩的富集与后生动物礁的缺失相耦合,海洋生态系统中生物组成发生显著变化。在此基础上,本文从微生物岩的角度初步探讨了冈瓦纳大陆冰川作用对北半球低纬度地区的影响。     

天山北坡中部不同海拔高度雪岭云杉树轮宽度气候响应对比分析

利用天山北坡中部沙湾地区两个坡面随海拔高度采集的雪岭云杉树芯样本,建立了13个树轮宽度年表。分析结果表明,2个坡面年表特征值随海拔高度的变化而不同,不同海拔树轮宽度对气候因子的响应呈现规律性。高低海拔采样点在生长季前对气候因子的响应相同,而在生长季则呈相反的响应。在生长季,高海拔采样点随海拔的升高,树轮宽度对气温的响应降低。不同坡面间受小生境的干扰较大,坡度较小的大鹿角湾高海拔采样点主要受气温的影响,而在坡度较大的石头沟高海拔采点则对降水有更明显的响应。沙湾树轮宽度年表对PDSI指数的响应与大尺度范围的树轮响应一致,即与PDSI呈正相关,低海拔区域响应最显著。主成分分析表明,在同一坡面树轮宽度年表的前3个主分量可以反映因海拔高度变化气候因子对树木年轮生长的影响。2个坡面树轮宽度年表的第一主分量表征持续干旱对整个坡面的影响。     

下扬子PTB界线深水相区粘土岩的火山成因研究及其对LPME的指示意义

全球,尤其是特提斯域二叠—三叠纪之交(PTB)剖面中普遍发育火山成因的粘土岩,对理解晚二叠世末生物大灭绝(LPME)的触发机制及相关基础地质问题具有重要意义。本文报道了在华南下扬子区新发现两条深水PTB剖面(皖南牛山和蔡村)的粘土岩工作,包括岩石学、矿物学和全岩地球化学等,填补了区域研究空白。研究结果发现,粘土岩主要由伊利石等粘土矿物,以及石英、岩浆锆石、长石等斑晶矿物组成。在地球化学上具有高K_2O、低Na_2O、相对富集大离子亲石元素(LILE)、相对亏损高场强元素(HFSE)等特征。据此,认为这些粘土岩为火山成因的钾质斑脱岩,其原岩可能为中酸性流纹英安岩,具有弧岩浆作用的源区背景。对比华南其他地区已发现的PTB界线粘土岩,发现它们成因类似,可能来源于古特提斯洋周缘陆陆碰撞,抑或是泛大洋俯冲潘吉亚大陆东缘(包括华南板块)所导致的长英质火山岩浆喷发,且具有多期多源性特点。PTB时期全球活跃的火山岩浆活动(包括镁铁质火山作用和华南地区火山灰所指征的长英质火山作用)可能是导致LPME的主要原因。     

云蒙湖流域不同坡度的土壤侵蚀特征

针对定量分析土壤侵蚀在各坡度等级上的空间分布研究较少的现状,该文选用通用的土壤流失预报方程,对云蒙湖流域1986—2010年间的土壤水力侵蚀状况进行了定量的估算,以探讨不同坡度上的土壤侵蚀特征,并进一步分析了土壤侵蚀变化与人类活动的关系。分析得出:土壤侵蚀强度发生在人类活动比较频繁的区域上(8~25°坡度)更为严重;2010年比1986年强度以上所占比例在15°坡度等级上相对更低,在15°坡度等级上有所增加;云蒙湖流域主要土壤侵蚀量发生在25°坡度上;2010年比1986年耕地面积减少、林地和居民用地面积增加是土壤侵蚀降低的主要因素。     

边坡单元的SAR数据特征

针对传统D-InSAR技术以栅格单元为研究对象而无法充分反映地形条件的问题,该文提出了以边坡单位为研究对象的D-InSAR数据特征分析。通过基于边坡单元的区域地形因子与后向散射系数和相干系数关系的分析方法,建立了研究区域SAR数据的可信区域滤波方法,提取出了研究区域SAR数据分析结果的可信区域。该方法提高了SAR数据的有效性,为滑坡早期监测提供了可靠的数据基础。通过对金沙江乌东德区域的SAR数据实例分析,验证了该方法的实用性。     

The Coarse-Grained Lacustrine Slope Apron Deposits in the Moliqing Area, Yitong Basin, Northeast China

Overlapping gravity accumulation bodies were formed on the northwestern steep slope of the Shuangyang Formation in the Moliqing fault depression of northeast China. This study analyzed in detail the spatial distribution of the lithofacies and lithofacies associations of these accumulation bodies based on more than 600 m of core sections, and summarized 12 major types of lithofacies and three types of lithofacies associations: (1) the proximal zone consists of gravelly debris flows dominated by alluvial channel conglomerates; (2) the middle zone is dominated by various gravity flow deposits and traction flow deposits; and (3) the distal zone is dominated by mudstones with intercalations of sandy debris and turbidites. Combining with the grain size cumulative probability curves analysis, we determined the transformation of debris flows to sandy debris flows and to turbidity currents in the slope zone of the basin margin, and further proposed a lacustrine slope apron model that is characterized by (1) an inconstant multiple source (line source), (2) an alternation of gravity flow deposits and traction flow deposits dominated by periodical changes in a source flood flow system, and (3) the transformation of sandy debris flow deposits into distal turbidity current deposits. This sedimentary model may be applicable to other fault depressions for predicting reservoir distribution.     

不同地形条件地面同步光谱定标场对比研究

利用美国ASD公司的FieldSpec Pro FR地面波谱仪,选择5°视场角探头和135cm探头距测试地物高度,开展0°、5°、10°、15°、20°等五种不同地形坡度明、暗地物自然定标场地面波谱测试。通过对比研究不同地形坡度具代表性、能真实反映被测试目标平均自然性的各波谱测试点波谱曲线特征,得出0°、5°地形坡度获取的波谱曲线连续、平滑,信噪比高,没有混入大气水气吸收、仪器噪声等因素导致的剧烈波动、跳跃现象或尖锐锯齿状噪声,波谱特征明显,吸收峰最小值位置清晰可辨,各波谱测试点波谱曲线变化幅度小,整体反射率值变化小,Fe~(2+)、Fe~(3+)、Al-OH、Mg-OH、CO_3~(2-)等分子基团与离子波谱的诊断性波谱特征位置清晰可辨。因此0°和5°坡度地形条件获取的地面同步自然场光谱定标波谱曲线,可以满足航空高光谱遥感数据的大气校正、光谱重建和空、地回归分析等所需的地面波谱数据要求。