A small-scale field check on the Fisher–Lehmann and Bakker–Le Heux cliff degradation models     

J. N. Hutchinson 《地球表面变化过程与地形》1998,23(10):913-926

The paper considers the development of initially straight, steep rock cliffs, bounded above and below by horizontal surfaces, in which basal debris removal is zero and degradation occurs by the weathering away of fine debris from the cliff face to form a scree at its foot. Of the slope degradation models available, the two earliest and simplest, namely the Fisher–Lehmann and the Bakker–Le Heux models, are regarded as most relevant and are briefly summarized. The main purpose of the paper is to check the predictions of these models, particularly with regard to the shape of the rock surface buried beneath the scree, against field data. Such data are sparse. It is concluded that the best field case currently available, despite its small scale, is that provided by the 1·75 m deep ditch which forms part of the experimental earthwork in the chalk on Overton Down, Wiltshire. The predictions of the two models are checked against field measurements made of the stage of degradation reached on each face of the ditch by July 1968, eight years after its excavation. These stages were influenced to different degrees by the presence of a surface turf layer. For the NE face, where this influence was least, the agreement of the predictions of the Fisher–Lehmann model with the actual rock profile is excellent and that of the Bakker–Le Heux model only marginally less so. For the SW face, as expected, the agreements are somewhat less close. These results may be to some extent fortuitous because of the influence of the turves and because the scree slopes tend to be concave rather than rectilinear, as assumed. Also, the free faces decline with time in a manner intermediate between those assumed in the two models. Larger scale field checks are clearly desirable before firm general conclusions can be drawn. Rates of crest recession for the Overton Down ditch are logarithmic with time after a very rapid initial phase. Extrapolation from the early phase of this logarithmic behaviour leads to a close estimate of the time needed for the slope to develop fully. The associated ultimate crest recession is also closely predicted by equations derived from both models. © 1998 John Wiley & Sons, Ltd.  相似文献   

Effect of geometric and material discontinuities on the reeling of pipelines     

《Applied Ocean Research》2017

The winding and unwinding of a pipeline onto a large diameter reel as practiced in the reeling installation method, induces bending strains of 1–3% followed by straightening, and reverse bending. The operator must ensure that such plastic deformations are sustained free of local buckling or rupture in the line. Such failures are for example precipitated by pipeline discontinuities in wall thickness and yield stress as they act as stress risers, lead to localized deformations severe enough to result in local buckling. The effect of such discontinuities is studied using a large-scale nonlinear finite element model that simulates the reeling/unreeling of a pipeline. Nonlinear kinematic hardening is used to capture the elasto-plastic behavior of the material imposed by the bending/reverse bending history. Discontinuities in wall thickness and yield stress are shown to result in sharp local changes in curvature that extend over 3–4 pipe diameters accompanied by severe local straining and ovalization. The extent of the disturbance is governed by the bending strain imposed by the ratio of pipe to reel diameter. It can be reduced by an increase in the applied tension but at the expense of additional ovalization of the pipeline. It can also be reduced by increasing the pipe wall thickness but with the consequent increase in costs. A parametric study of the effect of such discontinuities demonstrates that for some combinations of process parameters, the disturbance can lead to local buckling either during winding or unwinding. It is concluded that a modeling framework such as the one presented should be used to generate a design protocol for reel-installed pipelines.  相似文献   

Burying receivers for improved time‐lapse seismic repeatability: CO2CRC Otway field experiment          下载免费PDF全文

Valeriya Shulakova  Roman Pevzner  J. Christian Dupuis  Milovan Urosevic  Konstantin Tertyshnikov  David E. Lumley  Boris Gurevich 《Geophysical Prospecting》2015,63(1):55-69

4D seismic is widely used to remotely monitor fluid movement in subsurface reservoirs. This technique is especially effective offshore where high survey repeatability can be achieved. It comes as no surprise that the first 4D seismic that successfully monitored the CO₂ sequestration process was recorded offshore in the Sleipner field, North Sea. In the case of land projects, poor repeatability of the land seismic data due to low S/N ratio often obscures the time‐lapse seismic signal. Hence for a successful on shore monitoring program improving seismic repeatability is essential. Stage 2 of the CO2CRC Otway project involves an injection of a small amount (around 15,000 tonnes) of CO₂/CH₄ gas mixture into a saline aquifer at a depth of approximately 1.5 km. Previous studies at this site showed that seismic repeatability is relatively low due to variations in weather conditions, near surface geology and farming activities. In order to improve time‐lapse seismic monitoring capabilities, a permanent receiver array can be utilised to improve signal to noise ratio and hence repeatability. A small‐scale trial of such an array was conducted at the Otway site in June 2012. A set of 25 geophones was installed in 3 m deep boreholes in parallel to the same number of surface geophones. In addition, four geophones were placed into boreholes of 1–12 m depth. In order to assess the gain in the signal‐to‐noise ratio and repeatability, both active and passive seismic surveys were carried out. The surveys were conducted in relatively poor weather conditions, with rain, strong wind and thunderstorms. With such an amplified background noise level, we found that the noise level for buried geophones is on average 20 dB lower compared to the surface geophones. The levels of repeatability for borehole geophones estimated around direct wave, reflected wave and ground roll are twice as high as for the surface geophones. Both borehole and surface geophones produce the best repeatability in the 30–90 Hz frequency range. The influence of burying depth on S/N ratio and repeatability shows that significant improvement in repeatability can be reached at a depth of 3 m. The level of repeatability remains relatively constant between 3 and 12 m depths.  相似文献   

用微振动勘探方法探测隐伏断裂构造   总被引：1，自引：0，他引：1       下载免费PDF全文

范小平  李细兵  赵启光  宋浩  戴波  张帅帅 《地震学报》2015,37(1):134-143

介绍了运用微振动勘探方法探测隐伏断裂构造的方法和思路,并对郯庐断裂带两条分支断裂进行了试验性勘探．通过与人工地震勘探结果对比分析,发现微振动勘探方法对隐伏断裂构造具有较好的空间定位能力,其对岩性差异面形成的断裂定位误差与人工地震勘探结果相当; 又因其具有较大的勘探深度,因而可以有效揭示勘探区域下方地层及断裂的空间分布特征及其接触关系,这对于识别和确定断裂构造的主破裂面具有重要意义. 但微振动勘探方法对地层或断裂构造细节特征的揭示能力较差．因此,在实际地层或断裂勘探中,宜采用人工地震勘探方法与微振动勘探方法相结合的方式确定断裂的深浅构造关系,可以用微振动勘探方法进行普查,在确定断裂初步位置及空间展布特征后,再选用人工地震勘探方法进行断裂精确定位．   相似文献   

轴向荷载作用下管与软土相互作用模型试验     

王建华  杨召焕 《岩土力学》2015,36(Z1):61-65

开展室内模型试验研究了PE涂层足尺管道在软弱黏土中发生纵向位移时静置时间、加载速率以及土层不排水抗剪强度3个因素对轴向摩擦特性的影响。研究表明,管与软黏土纵向相互作用的抗力-位移曲线存在硬化型和软化型两种形式,前者的峰值摩擦阻力一般出现在加载过程的最后阶段,而后者的峰值摩擦阻力则出现在相对位移为（0.005～0.02）D（D为 管直径）范围内;试验测得的峰值摩擦系数取值介于0.12～0.23之间,且该值比美国API规范推荐值偏小;管土纵向峰值摩擦系数与加载速率成正相关关系,且加载速率对抗力-位移曲线类型无显著影响;常见的不排水抗剪强度范围内,土层的不排水抗剪强度值越低,纵向摩擦系数越大。上述结论可为海底埋设管线与软黏土纵向相互作用摩擦系数的确定提供参考依据。  相似文献   

Mechanism on Moho offset induced by aseismic slip of deeply buried faults          下载免费PDF全文

Zhen Fu  Hai-ming Zhang  Shu-wen Dong 《地震科学（英文版）》2014,27(3):247-256

Recent high-resolution deep seismic reflection profile across the Kunlun fault in northeastern Tibet shows clearly that the Moho is cut off by a complex thrust fault system. Moho offset is a general phenomenon, but little is known about the dynamic mechanism. In this study, contact models with Maxwell materials are used to simulate the mechanical process of Moho offset induced by the aseismic slip of deeply buried faults. Based on the seismic reflection data, we project a single fault model and a complex fault system model with two faults intersecting. The deformations of the Moho, the aseismic slips, and contact stresses on faults in different models are discussed in detail. Results show that the Moho offset might be produced by aseismic slip of deeply buried faults, and the magnitude is influenced by the friction coefficient of faults and the viscosity of the lower crust. The maximum slip occurs near the Moho on the single fault or at the crossing point of two intersecting faults system. Stress concentrates mainly on the Moho, the deep end of faults, or the crossing point. This study will throw light on understanding the mechanism of Moho offset and aseismic slip of deeply buried faults. The results of complex fault system with two faults intersecting are also useful to understand the shallow intersecting faults that may cause earthquakes.  相似文献   

隧道穿越引起地下管线竖向位移的能量变分分析方法   总被引：1，自引：0，他引：1  

刘晓强  梁发云  张浩  褚峰 《岩土力学》2014,35(Z2):217-222

隧道穿越引起的地层位移可能造成地下管线变形过大或断裂等事故,引起工程界的高度关注。基于假定的地下管线竖向位移分布模式,通过能量方法建立变分控制方程,提出了求解隧道穿越地下管线竖向位移的能量变分解法,运用叠加原理将单线隧道解答延拓至双线隧道中。与离心机试验和工程实例的对比,验证了方法的正确性。通过参数计算,分析了管材弹性模量、管线埋深、地层损失率等相关因素对地下管线竖向位移的影响规律,研究结论具有工程参考价值。  相似文献   

辽河坳陷滩海区海月潜山裂缝型储层预测研究     

崔玉哲 《现代地质》2014,28(4):867-874

裂缝型储层是潜山油气藏的重要储集层,裂缝形成的控制因素复杂,识别难度大;然而裂缝形成机制和地震反射特征是有规律可循的。因此,对裂缝发育控制因素和分布规律进行了分析探讨,并采用蚂蚁追踪裂缝识别、吸收衰减属性分析和多属性聚合分析等技术对潜山储层进行预测,细化处理流程,多种预测相互印证,减少单一预测方法存在的多解性和局限性,提高了潜山储层预测的可靠性。利用该方法在辽河坳陷滩海区海月潜山裂缝型储层进行实际应用,并取得了较好的效果,为潜山勘探提供了重要依据。  相似文献   

跨越断层埋地管线地震反应研究述评   总被引：2，自引：2，他引：0  

胡明袆  林均岐  李祚华  申选召 《地震工程与工程振动》2005,25(1):159-163,175

本文论述了跨越断层埋地管线地震反应研究工作概况,包括理论研究和实验研究的进展,并介绍了不同情况下采用的研究方法和建立的相应的研究模型,通过对数据结果进行整理分析,得出跨越断层埋地管线地震反应规律。同时,本文还对埋地管线研究中的一些重要参数对研究结果的影响作了详尽的阐述,提出了需进一步研究的问题和今后可能的研究发展方向。  相似文献   

渤海残留盆地油气地球物理研究综述   总被引：3，自引：2，他引：1       下载免费PDF全文

吉治平 《地球物理学进展》2005,20(4):1039-1046

本文阐述了海相残留盆地的概念,对近年来渤海海相残留盆地油藏的烃源岩、储集体、构造带及圈闭类型分布特征的研究进展进行总结,并对国内外海相盆地潜山油藏勘探历程进行概述,重点对海相残留盆地及潜山油藏综合地球物理研究现状及进展进行综述,并对未来发展趋势进行展望.  相似文献