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采用有限元方法模拟了扬子地区印支末期应力场的分布特征.根据模拟结果,对比已知断裂的展布方向,定量分析了扬子地区压应力及主应力方向的分布特征,并探讨了影响扬子地区印支末期构造特征的主要因素.据此得出以下研究结论:通过不断调整模型的边界条件发现,在印支末期,当华北地块为SE向挤压时,模型中压性应力场低值区的分布范围及主应力方向分别与扬子地区已知断裂密度及展布方向具有较好的对应关系. 相似文献
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南沙海槽南缘逆掩推复构造地区的动力学分析 总被引：1，自引：1，他引：1
提出南沙海槽南缘推复构造的运动和形变是一种周期性的弹塑性运动,周期约为14Ma.建立推复楔形体的动力学模型及两个约束条件,求解得推复楔形体的底部中点的推复方向的主应力和逆掩面动摩擦系数的解析式.建立推复楔形体前缘地层被推复剪断的力学模型、密度模型和内摩擦角模型,求得推复前缘地层被推复剪断时的有效主应力、静岩压应力、推复方向的主应力及其合力和推复构造应力的解析式,建立推复底部的有效塑性屈服模型,求得推复底部屈服时中点的有效主应力和推复方向的主应力的解析式.选择两个剖面进行动力学计算,得到推复楔形体前缘的两个应力图、逆掩面的动摩擦系数及推复方向的主应力的合力. 相似文献
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利用大连理工大学的“土工静力-动力液压-三轴扭转多功能剪切仪”,针对相对密实度为70％的福建标准砂,在不排水条件下控制试验过程中的中主应力系数保持不变,进行了不同初始固结应力条件下不同主应力方向的单调剪切试验.以此着重探讨了主应力方向及初始固结应力对饱和密砂单调剪切特性的影响,研究表明,主应力方向和初始固结应力对于密砂的有效应力路径和应力-应变关系均具有十分显著的影响.通过与饱和松砂不排水单调剪切特性的对比分析,探讨了初始相对密实度对砂土剪切特性的影响,研究表明随着主应力方向角增大,密砂的应变硬化效应逐渐减弱,但未出现松砂对应的应变软化现象. 相似文献
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在主应力方向的旋转过程中,主应力方向与塑性主应变增量方向之间存在着非共轴现象。基于屈服角点结构非共轴理论,建立了一种非共轴本构模型,通过有限元软件ABAQUS的二次开发子程序UMAT,将该模型运用到有限元数值计算中。首先,对中密砂单剪试验进行数值模拟,研究了非共轴现象及其对应力-应变关系的影响。然后,针对偏心荷载作用下条形浅基础荷载-变形特性进行数值分析,研究了非共轴现象对荷载-位移关系的影响。研究结果表明:非共轴模型计算得到的荷载增长速度滞后于共轴模型计算结果的增长速度;在地基变形的初期,非共轴现象比较明显,主应力方向的减小速度要滞后于塑性主应变增量方向的减小速度;随着地基沉降的增加,非共轴现象逐渐减弱;非共轴模型与共轴模型计算结果之间的差异在应变硬化情况下更加明显。 相似文献
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海岸带边坡防浪林消浪理论与实验研究 总被引：5，自引：0，他引：5
在海岸边坡上种植防浪林是一种新的护岸形式,应用理论分析和模型实验对其进行了初步研究.建立波浪在斜坡上传播的控制方程及边界条件,应用摄动理论求解非线性解,得到了一阶精确解和二阶近似解.在模型实验中,确定几何比尺为 1∶10,选取桧柏树枝作为防浪林模型,根据量纲分析,确定的主要影响因素是海岸边坡坡度、波高、波周期、水深与防浪林树宽.实验结果表明,防浪林宽度与岸坡坡度对消浪效果影响较大. 相似文献
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提出了一个新的环状非有心势模型. 利用Nikiforov-Uvarov方法求解了其满足的Schrdinger方程,得到了束缚态波函数的精确解及能谱方程. 讨论了角向分量对径向分量的影响及相关参数取特定值时的特殊情况. 相似文献
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土体在剪切变形过程中产生主应力方向的旋转时,主应变率方向与主应力方向之间存在着非共轴现象,然而,传统的弹塑性本构模型并不能考虑该现象的影响。通过在传统本构模型屈服面的切线方向增加一项非共轴塑性应变率,即可实现对非共轴现象的反映。利用有限元软件ABAQUS的材料子程序接口UMAT,通过显式积分算法和自动分步方法实现了非共轴模型在有限元分析中的应用。首先,对砂土的单剪试验进行数值模拟,预测了主应力方向和主应变率方向之间的关系,所得结论与试验结果较为吻合。然后,针对吸力桶与砂质地基间的相互作用问题进行弹塑性有限元计算,分析了土体主应力方向在剪切变形过程中的旋转规律,以及桶体的端部阻力、侧壁摩擦阻力和顶部阻力在变形过程中的变化规律。最后,检验了非共轴现象对地基承载力计算结果的影响。研究结果表明,所开发的非共轴模型对非共轴现象具有良好的预测能力。 相似文献
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海洋中赋存有丰富的页岩油,由于这类储层岩性致密,需要采用体积压裂技术提高产能,而研究体积压裂过程中岩体内多个天然裂缝的扩展规律及其影响因素对于裂缝网络的形成至关重要。在水力压裂主裂缝壁面上及主裂缝两侧脆性岩体的水平切面上,当存在多条同轴天然裂缝时,影响天然裂缝起裂方向及起裂条件的因素较多。因此需要在线弹性断裂力学理论的基础上,运用最大周向拉应变及平面应变理论,建立受远场地应力作用及裂缝面受水压力作用下的理论模型。根据模拟结果,在主裂缝壁面上,随着垂向应力差异系数增加,天然裂缝最小起裂净压力减小,起裂角度增加,因此天然裂缝的扩展与垂向应力的大小有重要关系,垂向压力越小则越利于形成缝网。与有一定倾斜角度的裂缝相比,垂向天然裂缝容易破裂扩展。当天然裂缝的条数增加,天然裂缝的最小起裂净压力降低,有利于形成主裂缝壁面上的裂缝网络,达到体积压裂的效果。在主裂缝两侧岩体的水平切面上,天然裂缝与最小主应力方向的夹角越大,则对应破裂压力越小,且不需要较大的缝内压力（小于最小主应力）即可破裂。存在多条裂缝时,目标裂缝张性破裂的缝内压力均降低。上述模型及应用模拟揭示了脆性岩石在水力压裂过程中,主裂缝壁面岩体... 相似文献
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为了研究天然气水合物降压开采过程的储层应力及其稳定性,运用线性多孔弹性力学和岩石力学知识,考虑水合物储层原始应力、孔隙压力、渗流附加应力及降压开采水合物过程中水合物饱和度的变化,建立了降压开采天然气水合物储层的力学模型,结合墨西哥湾某处水合物藏的基本参数,对降压开采水合物储层应力变化和开采过程的储层稳定性进行研究。结果表明：井底压力是影响水合物储层应力变化的关键因素之一;渗流附加应力在一定程度上减小了储层的应力;水合物分解储层应力发生变化,储层应力在井壁处的波动最大,井壁处是整个储层所受轴向偏应力最大的位置,因此井壁处是优先发生剪切破坏的位置;为了储层的稳定性,降压开采水合物生产压差应小于2.19 MPa。 相似文献
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Yu-Ke Wang Yu-Feng Gao Yue Qiu Xiu-Qing Hu Ying Zhang 《Marine Georesources & Geotechnology》2016,34(5):493-502
The deformation behavior and shear strength of soft marine clays subjected to wave or traffic loads are different from that in triaxial loading due to the changes of major principal stress direction β and intermediate principal stress coefficient b. To investigate the anisotropy affected by β and b in natural soft marine clay, a series of drained tests were conducted by hollow cylinder apparatus. The principal stress direction relative to vertical direction were maintained constant under an increasing shear stress, with fixed intermediate principal stress coefficient b. The influence of the b and β on anisotropy of typically Wenzhou intact clay is discussed. It was found that octahedral stress–strain relationships expressed anisotropy with different b and β. The friction angle and deviator stress ratio with different b and β were presented to provide guidance for engineering projects in the coastal zone. 相似文献
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Knowledge of the full present-day stress tensor and pore pressure has significant applications in the exploration and production of conventional and unconventional hydrocarbon reservoirs. The Darling Basin of New South Wales, Australia, is an old sedimentary basin (Late Cambrian/Silurian to Early Carboniferous) in which there was limited information about the present-day stress field prior to this study. In this paper we evaluate the contemporary stress field of the Darling Basin using a dataset from recent exploration wells and perform a geomechanical risk assessment with respect to borehole stability, fracture/fault generation and reactivation. Our interpretations of borehole failures in borehole image logs reveal a prevailing east-west orientation of the maximum horizontal stress throughout the Darling Basin. The estimates of the magnitudes for the vertical, minimum and maximum horizontal stress in the studied wells indicate a transition between thrust and strike-slip faulting stress regime at 600–700 m depths, where the magnitude of vertical stress and minimum horizontal stress are close to each other. However, the presence of borehole breakouts and drilling-induced tensile fractures, that we observe in the image logs at greater depths (900–2100 m) indicate a transition into a strike-slip tectonic stress regime below a depth range of approximately 700–900 m. These findings are in agreement with overcoring stress measurements east and west of the investigated wells. Furthermore, there are several Neogene-to-Recent geological structures in the study area that indicate thrust faulting with an east-west oriented maximum horizontal stress orientation around this old sedimentary basin. The consistency between the orientation of maximum horizontal stress determined from wellbore data and neotectonic structures is significant, and implies that horizontal stress orientations derived from very recent geological features may be valuable inputs to geomechanical models in the absence of wellbore or other data. However, the recent surface geological structures suggest a thrust faulting stress regime that is in slight contrast to the transition between thrust and strike-slip stress regime (SH > Sh ∼ Sv) indicated by petroleum data, and highlights a potential pitfall of using neotectonic structures in geomechanical models. In particular, careful attention and verification should be made when using neotectonic structures for input, calibration or confirmation of geomechanical models, especially in intraplate tectonic settings such as Australia. 相似文献
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Fault patterns at outer trench walls 总被引：1，自引：0，他引：1
D. G. Masson 《Marine Geophysical Researches》1991,13(3):209-225
Profiles across subduction-related trenches commonly show normal faulting of the outer trench wall. Such faulting is generally parallel or sub-parallel to the trench and is ascribed to tension in the upper part of the oceanic plate as it is bent into the subduction zone. A number of authors have noted that outer trench wall faulting may involve re-activation of the oceanic spreading fabric of the subducting plate, even when the trend of this fabric is noticeably oblique to the extensional stress direction. However, one previous review of outer trench wall fault patterns questioned the occurrence of a consistent link between fault orientation and such controlling factors. This latter study predated the widespread availability of swath bathymetry and longrange sidescan sonar data over trenches. Based only on profile data, it was unable to analyse fault patterns with the accuracy now possible. This paper therefore re-examines the relationship between outer trench wall faulting and the structure of the subduction zone and subducting plate using GLORIA and Seabeam swath mapping data from several locations around the Pacific and Indian Oceans. The principal conclusions is that the trend of outer trench wall faults is almost always controlled by either the subducting slab strike or by the inherited oceanic spreading fabric in the subducting plate. The latter control operates when the spreading fabric is oblique to the subducting slab strike by less than 25–30°; in all other cases the faults are parallel to slab strike (and parallel or sub-parallel to the trench). Where the angle between spreading fabric and slab strike is close to 30°, two fault trends may coexist; evidence from the Aleutian Trench indicates a gradual change from spreading fabric to slab strike control of fault trend as the angle between the two increases from 25 to 30°. The only observed exception to the above rule of fault control comes from the western Aleutian Trench, where outer trench wall faults are oblique to the slab strike, almost perpendicular to the spreading fabric, and parallel to the convergence direction. Re-orientation of the extensional stress direction due to right-lateral shear at this highly oblique plate boundary is the best explanation of this apparently anomalous observation. 相似文献
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The reliability and/or stability of the lifeline structures against failure under seismic loads are of critical concern, and must be studied carefully. Therefore, the main objective of this paper is to demonstrate the commonly encountered backfill effects on the dynamic response of rectangular tanks. However, only the exterior wall of the tank which interacts with both the backfill and fluid is tackled, as each part of the structure shows considerable differences in terms of both the load bearing mechanisms and the geometrical and positional differences. Finite element analyses are employed, taking into consideration the fluid-wall-backfill interaction. The analyses are conducted to observe whether or not both backfill and wall behavior can be affected by variation of the internal friction angle. For that purpose, some comparisons are made on vertical displacements of the backfill, roof displacements, stress responses, etc., by means of internal friction angle variations of the backfill from 25° to 40°. Consequently, it is observed that the variations on maximum vertical displacements are affected considerably. In contrast, the maximum stress responses are affected partially. However, the inertial effects of the backfill show that pseudo-static approximations may be insufficient to understand the dynamic behavior of the backfill-wall-fluid system. 相似文献
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M. R. P. Tingay R. R. Hillis C. K. Morley R. E. Swarbrick E. C. Okpere 《Marine and Petroleum Geology》2003,20(10):1201-1212
The vertical or lithostatic stress is an important factor in tectonic and geomechanical studies and is commonly used in the prediction of pore pressures and fracture gradients. However, the vertical stress is not always calculated in situ and the approximation of 1.0 psi/ft (22.63 MPa/km) is often used for the vertical stress gradient. Vertical stress has been determined in 24 fields in the Baram Basin, Brunei, using density log and checkshot velocity survey data. The Baram Basin shows a variation in vertical stress gradient between 18.3 and 24.3 MPa/km at 1500 m depth below the surface. This variation has a significant effect on in situ stress related issues in field development such as wellbore stability and fracture stimulation. The variation is caused by a bulk rock density change of 2.48–2.07 g/cm3 from the hinterland of the delta to its front. Differential uplift and erosion of the delta hinterland and undercompaction associated with overpressure are the interpreted causes of the density and hence vertical stress variation. 相似文献
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The mixed layer depths over the Arabian Sea were computed for the three successive years 2004-2006 using ARGO floats data. The large availability of ARGO floats for the above period resulted in better estimation of mixed layer depth (MLD) over the Arabian Sea. The results were compared with World Ocean Atlas 1994 MLD Climatology. Marked variability in MLD on a monthly time scale is observed and it was in accordance with the wind stress and/or net heat gain variability, which are the principal factors influencing mixed layer over Arabian Sea. With the availability of large number of ARGO profile data, an attempt is made to study the monthly variability of Mixed Layer. 相似文献
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Waterfront retaining walls supporting dry backfill are subjected to hydrostatic pressure on upstream face and earth pressure on the downstream face. Under seismic conditions, if such a wall retains a submerged backfill, additional hydrodynamic pressures are generated. This paper pertains to a study in which the effect of earthquakes along with the hydrodynamic pressure including inertial forces on such a retaining wall is observed. The hydrodynamic pressure is calculated using Westergaard's approach, while the earth pressure is calculated using Mononobe-Okabe's pseudo-static analysis. It is observed that when the horizontal seismic acceleration coefficient is increased from 0 to 0.2, there is a 57% decrease in the factor of safety of the retaining wall in sliding mode. For investigating the effect of different parameters, a parametric study is also done. It is observed that if φ is increased from 30° to 35°, there is an increase in the factor of safety in the sliding mode by 20.4%. Similar observations were made for other parameters as well. Comparison of results obtained from the present approach with [Ebeling, R.M., Morrison Jr, E.E., 1992. The seismic design of waterfront retaining structures. US Army Technical Report ITL-92-11. Washington DC] reveal that the factor of safety for static condition (kh=0), calculated by both the approaches, is 1.60 while for an earthquake with kh=0.2, they differ by 22.5% due to the consideration of wall inertia in the present study. 相似文献
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地下气库的围岩稳定性关系到地下气库的安全与使用。影响地下洞室稳定的因素很多,解析法虽然可以得到精确解,但是只能针对圆形洞室。而数值计算方法可以计算各种情况下围岩的应力、变形、塑性分布等情况。利用有限元分析软件分析了洞室形状对围岩稳定性的影响,确定了合理的洞形;讨论了围岩应力应变随深度的变化规律,以及不同的支护类型对围岩变形的影响,确定了经济合理的支护类型。最终为该地质条件下的洞室围岩稳定设计提供了依据。 相似文献