Fracture mechanics analysis of multiple cracks in anisotropic media

This paper presents a single‐domain boundary element method (BEM) for linear elastic fracture mechanics analysis in the two‐dimensional anisotropic material. In this formulation, the displacement integral equation is collocated on the un‐cracked boundary only, and the traction integral equation is collocated on one side of the crack surface only. A special crack‐tip element was introduced to capture exactly the crack‐tip behavior. A computer program with the FORTRAN language has been developed to effectively calculate the stress intensity factors of an anisotropic material. This BEM program has been verified having a good accuracy with the previous researches. Furthermore, by analyzing the different anisotropic degree cracks in a finite plate, we found that the stress intensity factors of crack tips had apparent influence by the geometry forms of cracks and media with different anisotropic degrees. Copyright © 2010 John Wiley & Sons, Ltd.     

The exponential decline in saturated hydraulic conductivity with depth: a novel method for exploring its effect on water flow paths and transit time distribution

The strong vertical gradient in soil and subsoil saturated hydraulic conductivity is characteristic feature of the hydrology of catchments. Despite the potential importance of these strong gradients, they have proven difficult to model using robust physically based schemes. This has hampered the testing of hypotheses about the implications of such vertical gradients for subsurface flow paths, residence times and transit time distribution. Here we present a general semi‐analytical solution for the simulation of 2D steady‐state saturated‐unsaturated flow in hillslopes with saturated hydraulic conductivity that declines exponentially with depth. The grid‐free solution satisfies mass balance exactly over the entire saturated and unsaturated zones. The new method provides continuous solutions for head, flow and velocity in both saturated and unsaturated zones without any interpolation process as is common in discrete numerical schemes. This solution efficiently generates flow pathlines and transit time distributions in hillslopes with the assumption of depth‐varying saturated hydraulic conductivity. The model outputs reveal the pronounced effect that changing the strength of the exponential decline in saturated hydraulic conductivity has on the flow pathlines, residence time and transit time distribution. This new steady‐state model may be useful to others for posing hypotheses about how different depth functions for hydraulic conductivity influence catchment hydrological response. Copyright © 2016 John Wiley & Sons, Ltd.     

浅析运营期间电力隧道自动化监测技术

针对城市电力隧道结构、走向多变、电缆设施多、电磁干扰大等因素,常规的监测方法难以顺利完成的现状,对目前先进的3种隧道结构自动化监测系统进行深入的研究比较,光纤传感自动技术解决了电力隧道结构监测点布设困难,数据受电磁干扰大的问题,能实时有效、可靠、高精度地监控电力隧道,及时掌握隧道的应力、应变及振动等主要结构参数,确保隧道结构安全。研究对类似的城市电力隧道自动化监测具有一定的参考意义。     

香港世界地质公园晚侏罗世荔枝庄组岩石组合及其成岩地质过程解析

中国东南大陆晚侏罗世地层普遍缺失,仅零星见于个别地区,香港新界东北的荔枝庄组即为其一。荔枝庄组出露于香港世界地质公园沉积岩园区的荔枝庄地区,自下往上由火山岩—沉积岩—火山岩组合而成,沉积岩中发育大型包卷层理和滑塌构造等典型沉积构造,是香港地区最具代表性的晚侏罗世火山—沉积岩系。通过实测地层剖面研究,确定其成岩过程大体上可划分为早期普林尼式火山爆发、中期破火山口湖相沉积和晚期普林尼式火山爆发三个阶段,以湖相沉积作用为主、火山喷发作用为辅;受晚期火山岩浆活动的影响,沉积岩层普遍发生硅化或炭化。荔枝庄组独特的岩石组合与形成的古地理环境,为探讨中国东南大陆中生代火山活动—沉积作用方式与成岩过程,提供了难得的研究实例。     

贵州铝土矿基底地层特征及其与成矿的关系

目前对于贵州铝土矿含矿岩系基底地层特征及其与成矿关系有一些研究,但缺乏系统性.通过在对省内大量铝土矿床勘查和研究资料的分析,获得一些新的认识.该地区基底地层时空分布上,由南到北、由西到东逐渐变新,黔北主要为硅酸盐岩,但古喀斯特地貌不明显,黔中以碳酸盐岩为主且有显著古喀斯特地貌.基底地层在一定程度上提供了成矿物源,同时也控制了矿体形态.因基底岩性和古喀斯特地貌的不同,使得在铝土物质沉积阶段沉积分选方式有差异,同时导致铝土物质次生富集阶段地下水化学特性及动力系统的差异,使硅排铁作用强弱不同,这些因素都影响矿石类型和品位.     

Sedimentary facies analysis and depositional model of gravity-flow deposits of the Yanchang Formation,southwestern Ordos Basin,NW China

During the deposition of the Chang-7 (Ch-7) and Chang-6 (Ch-6) units in the Upper Triassic, gravity flows were developed widely in a deep lake in the southwestern Ordos Basin, China. Based on cores, outcrops, well-logs and well-testing data, this paper documents the sedimentary characteristics of the gravity-flow deposits and constructs a depositional model. Gravity-flow deposits in the study area comprise seven lithofacies types, which are categorised into four groups: slides and slumps, debris-flow-dominated lithofacies, turbidity-current-dominated lithofacies, and deep-water mudstone-dominated lithofacies. The seven lithofacies form two sedimentary entities: sub-lacustrine fan and the slump olistolith, made up of three and two lithofacies associations, respectively. Lithofacies association 1 is a channel–levee complex with fining-/thinning-upward sequences whose main part is characterised by sandy debris flow-dominated, thick-bedded massive sandstones. Lithofacies association 2 represents distributary channelised lobes of sub-lacustrine fans, which can be further subdivided into distributary channel, channel lateral margin and inter-channel. Lithofacies association 3 is marked by non-channelised lobes of sub-lacustrine fans, including sheet-like turbidites and deep-lake mudstones. Lithofacies association 4 is represented by proximal lobes of slump olistolith, consisting of slides and slumps. Lithofacies association 5 is marked by distal lobes of slump olistolith, comprising tongue-shaped debris flow lobes and turbidite lobes. It is characterised by sandy debris flow, muddy debris flow-dominated sandstone and sandstone with classic Bouma sequences. Several factors caused the generation of gravity flows in the Ordos Basin, including sediment supply, terrain slope and external triggers, such as volcanisms, earthquakes and seasonal floods. The sediment supply of sub-lacustrine fan was most likely from seasonal floods with a high net-to-gross and incised channels. Triggered by volcanisms and earthquakes, the slump olistolith is deposited by the slumping and secondary transport of unconsolidated sediments in the delta front or prodelta with a low net-to-gross and no incised channels.     

Magma associations in Ediacaran granitoids of the Cachoeirinha‒Salgueiro and Alto Pajeú terranes,northeastern Brazil: Forty years of studies

Granitic magmatism in the Cachoeirinha‒Salgueiro and Alto Pajeú terranes in the Transversal Zone Domain of the Borborema Province, northeastern Brazil, occurred in three main time intervals: 650–620 Ma, 590–560 Ma and 545–520 Ma. The oldest one is characterized by intrusions of magmatic-epidote (mEp) bearing calc-alkalic (some with trondhjemitic affinities) and high-K calc-alkalic plutons, synkinematic to the main regional foliation, under contractional tectonic regime, and exhibits T_DM < 2.0 Ga and ƐNd (0.6 Ga) from −1 to −4, and δ¹⁸O (zircon) values from 7.1 to 10‰_VSMOW. O- and Nd-isotope data for the 650‒620 Ma group of plutons is compatible with partial fusion of subducted oceanic basaltic crust (mEp-bearing calc-alkalic tonalites/granodiorites, equivalent to adakites). Voluminous intrusions in the 590–560 Ma interval are represented by abundant mEp-free high-K calc-alkalic, peralkalic, ultrapotassic, mEp-bearing high-K calc-alkalic, and less abundant shoshonitic magmas. Nd-model ages for this group of plutons vary from 1.5 to 2.5 Ga and ƐNd (0.6 Ga) ranges from −8 to −20; δ¹⁸O (zircon) varies from 6.4 to 7.9‰_VSMOW. Values of δ¹⁸O (zircon) for the 590‒560 Ma old group of plutons coupled with Nd isotope data are compatible with remelting of crustal (negative ƐNd, 1.6 to 2.0 Ga old) source rocks. O- and Nd-isotope data for this group of plutons are compatible with underplating of basaltic magma in the base of the lower crust for the high-K calc-alkalic granitoids, coeval to transcurrent movements along sigmoidal shear zones. Intrusion of one shoshonitic (Serrote do Arapuá), one calc-alkalic (Riacho do Icó) plutons besides the peralkalic Manaíra-Princeza Isabel dike set have witnessed this transition from contractional to transcurrent movements along shear zones, around 610‒600 Ma.     

Observer presence may alter the behaviour of reef fishes associated with coral colonies

Although underwater visual census (UVC) is the most frequently used technique for quantifying reef fish assemblages, remote video analysis has been gaining attention as a potential alternative. In the South Atlantic Ocean, Millepora spp. (class Hydrozoa) are the only branching coral species; however, little is known about the ecological role that they play for reef fish communities. We compared these two observation methods (remote video and UVC) to estimate reef fish abundance and species richness associated with colonies of the fire‐coral Millepora alcicornis at Tamandaré Reefs, Northeast Brazil. Additionally, the two different techniques were used to compare species behaviour in association with fire‐corals in order to examine the biases associated with each technique and provide useful information for behavioural ecologists studying fish–coral associations. There were no differences in reef fish abundance or species richness sampled by remote video or UVC. However, a significant difference in the behaviour of associated fish was recorded between the two methods. In the presence of a diver carrying out a UVC, fish were observed spending more time sheltered amongst the coral branches compared with passively swimming on coral colonies with the remote video technique. Specifically, on the remote video recordings agonistic interactions between fish and passive swimming accounted for 33.3% and 22.2% of the census time, respectively. By comparison, when observed by a diver fish spent 34.8% of their time sheltering amongst the coral branches. We demonstrate that both techniques are similarly effective for recording fish abundance and species richness associated with fire‐corals. However, differences were observed in the ability of each method to detect the behaviour of coral‐associated fishes. Our findings show that behavioural ecologists studying complex fish–coral associations need to ensure that their aims are clearly defined and that they choose the most appropriate technique for their study in order to minimize methodological biases.     

半潜平台浮子式系泊系统参数优化研究

通过在系泊缆中设置浮子可以改善系泊系统性能,降低平台运动响应。建立浮子式系泊系统的数值计算模型,验证浮子式系泊系统数值计算方法,详细分析浮子设计参数(设置位置和净浮力大小)变化对系泊缆张力特性与平台运动的影响规律,并根据得到的规律选择了优化的浮子系泊系统方案。最后对优化方案进行评估,表明优化方案可以显著降低系泊中的平台水平运动,尤其是低频运动,同时系泊缆张力变化不大,仍满足安全要求。研究结果可为今后浮子式系泊系统设计提供参考。     

天水盆地新近纪伸展构造——来自沉积与构造变形方面的证据

天水盆地位于青藏高原东北缘高海拔挤压隆升区与鄂尔多斯低海拔伸展区的过渡部位,新构造活动强烈。然而,新构造活动对天水盆地的影响尚不清楚。通过对盆地的沉积环境、构造沉降、构造变形等方面的研究,结果显示:1盆地由风成堆积、洪积扇、河湖相与湖泊相沉积组成,代表沉积中心的河湖相与湖泊相沿控盆断裂(西秦岭北缘断裂、西和断裂与礼县-罗家堡断裂)分布;2盆地经历了16~14Ma、9.2~7.4Ma和3.6~2.6Ma三次加速沉降期;3控盆断裂在同沉积期为正断层。沉积中心沿断裂分布、快速沉降事件及生长正断层表明,天水盆地至少在中新世晚期受控于走滑伸展构造,记录了青藏高原向北东方向的构造挤出作用。