Oligocene–Miocene thrusting in central Aegean: insights from the Cycladic island of Amorgos     

V. Chatzaras  P. Xypolias  S. Kokkalas  I. Koukouvelas 《Geological Journal》2011,46(6):619-636

In the central Aegean, the Cycladic island of Amorgos consists of two high‐pressure (HP) units, the marble‐rich Amorgos unit, which is correlated to the Mesozoic ‘cover’ sequence of the Menderes Massif, and the Cycladic Blueschist unit. New structural data show that the deformation history of the Amorgos HP‐rocks was principally governed by early Oligocene (or late Eocene)–early Miocene ductile to brittle thrusting (D₁–D₃) followed by middle–late Miocene oblique contractional movements (D₄–D₅). The D₁ phase caused syn‐blueschist‐facies ductile thrusting of the Cycladic Blueschist unit over the Amorgos unit, with ambiguous kinematics. Progressive deformation under continuous NW–SE compression produced a sequence of imbricate NW‐directed thrusts (D_2/3) characterized by a stratification of fault‐related rocks, with mylonitic zones (D₂) giving way downwards to cataclastic zones (D₃). Ductile D₂ thrusting synchronous to greenschist‐facies retrogression, was accompanied by mega‐sheath folding during constrictional and general shear deformation. Brittle D₃ thrusting was associated with NW‐verging F₃ folds trending at a high‐angle to the transport direction. Orthogonal contraction gave way to transpression during which the compression orientation changed from NW–SE (D₄) to NE–SW (D₅). Back‐arc related NW–SE pure extension (D₆) seems to have been established in post‐late Miocene times and related high‐angle normal faulting affected HP‐rocks only after they had already reached the uppermost crustal levels. Oligocene–early Miocene deformation history is interpreted to indicate syn‐compressional exhumation of HP‐rocks possibly in an extrusion wedge. In this case, Amorgos HP‐rocks should have occupied the base of the extrusion wedge. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Effects of frequency and confining pressure on consolidation drainage behavior of soft marine clays     

Yong-Hong Miao  Fan-Bo Zhou  Yan-Chang Sun  Rui-Bing Li  Jian-Fei Lu 《Marine Georesources & Geotechnology》2013,31(6):746-754

Abstract

This article presents an experimental investigation on the dynamic consolidation (DC) drainage behavior of soft marine clays. A sinusoidal harmonic load with different frequencies was applied to simulate the DC method in which the conventional impact load was replaced by the cyclic load. Four geotextile-filter strips were used to form the side drainage channels simulating the wick drain method. A series of loading tests were conducted on soft soil specimens at different confining pressures (i.e., 20, 40, 70, and 100?kPa) and different vibration frequencies (i.e., 0, 0.5, 1, 1.5, 2, and 5?Hz). Test results showed that both confining pressure and frequency have significant influences on the drainage behavior of soft marine clay specimens. The magnitude of drainage volume consistently decreases linearly with increasing confining pressure. Compared to static loading condition, specimens under cyclic loading condition at different frequencies show a better drainage performance. Specimen at applied frequency of 1?Hz exhibits the maximum cumulative drainage volume due to the resonant effect.  相似文献   

TGR-2050型验潮仪在珠江口潮汐测量中的应用分析     

王玉春  方荣华  杨建宇  宁林春  张延飞 《海洋测绘》2013,33(1):63-65

使用压力式TGR-2050型验潮仪,在珠江口等河道入海口测量潮汐时,误差比较大;针对珠江口潮汐的特点,分析和研究了大气压扰动、潮流、海水密度、压力感应零点漂移等因素对潮汐测量带来的误差,有针对性地提出解决方案,并通过实验证明了方案的可行性。  相似文献   

An experimental study of velocities under pressure for ancient oceanic rocks     

K. V. L. N. S. Sarma 《Marine Georesources & Geotechnology》2013,31(3-4):269-276

Abstract

Seismic velocities of Indus suture rock types from Dras‐Sanko‐Kargil, Kashmir Himalaya, as a function of pressure up to 10 kbar were studied. The high‐pressure measurements on the rocks reflect the depthwise increase in velocity, and in general they help in better understanding and better interpretation of the regional rocks in terms of their geological observations. An attempt has been made at correlation with ocean‐dredged samples, and it was found that the ultramafics, gabbros, and dykes are compatible with oceanic rocks and other ophiolite sequences, whereas metavolcanics are incompatible, suggesting the dismembered nature of Indus ophioli‐tes.  相似文献   

Laboratory Study on the Hydraulic Conductivity and Pore Pressure of Sand-Silt Mixtures     

Mostefa Belkhatir  Ahmed Arab  Noureddine Della  Tom Schanz 《Marine Georesources & Geotechnology》2013,31(2):106-122

The hydraulic conductivity plays a major role on the excess pore pressure generation during monotonic and cyclic loading of granular soils with fines. This paper aims to determine how much the hydraulic conductivity and pore pressure response of the sand-silt mixtures are affected by the percentage of fines and void ratio of the soil. The results of flexible wall permeameter and undrained monotonic triaxial tests performed on samples reconstituted from Chlef River sand with 0, 10, 20, 30, 40, and 50% nonplastic silt at an effective confining stress of 100 kPa and two relative densities (D_r = 20, and 91%) are presented and discussed. It was found that the pore pressure increases linearly with the increase of the fines content and logarithmically with the increase of the intergranular void ratio. The results obtained from this study reveal that the saturated hydraulic conductivity (k) of the sand mixed with 50% low plastic fines can be, on average, four orders of magnitude smaller than that of the clean sand. The results show also that the hydraulic conductivity decreases hyperbolically with the increase of the fines content and the intergranular void ratio.  相似文献   

Cyclic behavior of natural organic clay under variable confining pressure that match traffic loading conditions     

Yuke Wang  Heyang Jia  Hongjian Cai  Xiangyuan Zhang 《Marine Georesources & Geotechnology》2013,31(3):402-407

ABSTRACT

One-way cyclic loading is more typical for traffic loading and cyclic triaxial test has been recognized as a useful method for solving many engineering problems. Under traffic loading, the influence of variable confining pressure on cyclic behavior of natural organic clay subjected to cyclic traffic loading is rarely reported in the literature. In this study, a laboratory investigation on undrained cyclic behavior of natural organic clay is presented and conducted by cyclic triaxial apparatus. Tests are conducted by both constant confining pressure and variable confining pressure, to simulate the loading conditions induced by passing vehicles in actual engineering. Different stress levels are also considered in this study. By comparing between the results of constant confining pressure tests and variable confining pressure tests, it shows that the one-way cyclic behavior of organic clay is influenced significantly by variation of confining pressure, in terms of pore water pressure, permanent axial strain and stress–strain hysteretic loops.  相似文献   

弹性液舱内液体晃荡实验研究   总被引：1，自引：0，他引：1  

蒋梅荣  任冰  温鸿杰  王永学 《海洋工程》2013,31(5):1-10

通过物理模型实验,对水平简谐激励下弹性矩形液舱内液体晃荡问题进行了研究。实验中给出了不同液深和不同激励振幅下弹性液舱内液体最低阶固有频率。采用影像采集与分析系统获得液舱内自由液面的形状和高度,通过压力采集系统得到舱壁上的压力分布。实验中分析了不同液深、不同激励频率下弹性和刚性液舱内自由液面高度和晃荡压力的变化特性。比较了弹性和刚性液舱内不同位置处自由液面高度随外界激励频率的变化规律,以及舱壁上不同位置处的压力峰值随外界激励频率的变化规律。结果表明:非共振情况下,弹性和刚性实验结果及理论值三者的波高和压力较为接近。共振情况下,弹性和刚性波高基本相等,在近舱壁处二者明显大于理论值,而在远离舱壁处二者与理论值存在一定差别;弹性压力较刚性压力略小,但二者与理论值差别较大。  相似文献   

Seismic and Petrophysical Relationships from UK Continental Shelf Rocks at Elevated Pressures     

Solomon Assefa  Clive Mc Cann  Jeremy Sothcott 《Marine Georesources & Geotechnology》2013,31(2):119-140

Abstract

There are few published seismic (P- and S-waves) properties for seafloor bedrocks. At low pressures (1 to 10 MPa), velocities and attenuations are determined mainly by open microcracks. At higher pressures, the microcracks close, and the velocities and attenuations depend primarily on the matrix porosity. We have investigated both the relationships between the acoustic, petrophysical, and geological properties of the rocks at 40 MPa pressure and the effect of microcracks on the acoustic properties at 10 MPa pressure. In this paper we discuss the former; the latter will be discussed separately.

P- and S-wave velocity and attenuation measurements were carried out on a suite of seabed sedimentary and igneous rocks at effective pressures from 10 to 40 MPa at ultrasonic frequencies. The porosities and permeabilities of the rocks ranged from 0% to 32% and 0 to 110 mDarcy, respectively. Characterization of the rocks revealed that most of the sandstones have a substantial clay content (kaolinite, illite, and chlorite) and fractures. Most of the igneous rocks are chloritized.

The seismic properties of the rocks are markedly lower than those of similar continental rocks because of the microporosity formed by the alteration of feldspars, micas, and mafic minerals to clays (e.g., chloritization of pyroxenes) and the corresponding reduction of the elastic moduli. The results of this study suggest that the values of velocities and quality factors used for ocean acoustic propagation models are lower than normally assumed.  相似文献   

循环荷载下加固土体孔压的模糊正交试验分析     

闫春岭  唐益群  王元东  李仁杰 《吉林大学学报(地球科学版)》2011,41(3):805-811

针对地铁循环荷载下加固软粘土的孔隙水压力发展规律,对上海地铁4号线宝山-海伦引导段隧道周围的加固软黏土进行室内GDS循环三轴试验。结合重复正交设计法安排试验,借助模糊数学的理论与方法处理试验数据,充分考虑了振动频率（0.5、1.5、2.5 Hz）、动应力幅值（20、30、40 kPa）、固结比（1、1.4、2）以及超固结比（1、1.5、2）对土体孔隙水压力的影响。研究结果表明:振动频率、动应力幅值、固结比及超固结比对加固软黏土孔隙水压力的影响率分别为0.722、15.821、0.944及6.628;这说明影响加固软粘土孔隙水压力变化的主要因素是动应力幅值及超固结比,而固结比和振动频率的影响不显著。  相似文献   

深埋顶管顶力理论计算与实测分析   总被引：1，自引：0，他引：1  

杨仙  张可能  黎永索  彭环云  黄常波 《岩土力学》2013,34(3):757-761

针对管幕预筑法中深埋顶管顶力进行理论和实测分析。顶管顶力与垂直土压力密切相关。参照隧道开挖中垂直土压力的计算方法,常用的垂直土压力计算理论有：普氏理论和太沙基理论。在详细分析了这两种垂直土压力计算理论的适用性和缺陷之后,结合普氏理论和太沙基理论,提出了改进的垂直土压力计算理论公式,并编写MATLAB程序计算改进理论公式的数值解。改进理论既考虑了土拱效应,又考虑了拱下土体的挟持力,更符合实际土体变形情况。将普氏理论、太沙基理论和改进的理论应用于沈阳地铁新乐遗址站管幕预筑法顶管工程中,计算不同深度的两根大埋深管道顶力,并把计算与实测结果进行比较,发现普氏理论和太沙基理论计算结果都远大于实测值,改进理论计算结果稍大于实测值,更适合于深埋顶管顶力估算。  相似文献