Seismic response of shallow circular tunnels in two-layered ground     

《Soil Dynamics and Earthquake Engineering》2015

The effect of ground stratification on the seismic response of circular tunnels is investigated, as most practice-oriented studies consider homogeneous ground. A finite element plain-strain model of a circular tunnel cross-section embedded in a two-layered ground is used to highlight the influence of stratification on the tunnel׳s seismic response. The layers interface was placed at the crown, centre and invert level.It is proved that ground stratification has an important role in the lining seismic forces. When the tunnel is fully embedded in one of the layers, the seismic lining forces may vary significantly in comparison with the single-layer case. If the tunnel intercepts both layers, maximum lining forces aggravation occurs when the lower layer is very stiff.  相似文献   

Comparative mineralogy and geochemistry of hydrothermal iron‐rich crusts from the Pitcairn,Teahitia‐mehetia,and Macdonald hot spot areas of the S. W. pacific     

P. Stoffers  G. P. Glasby  D. Stuben  R. M. Renner  T. G. Pierre  J. Webb 《Marine Georesources & Geotechnology》2013,31(1):45-86

Abstract

Hydrothermal iron‐rich crusts have been recovered from a number of hot spot volcanos including Crough Seamount, Pitcairn Volcanos 2 and 1, Cyana Seamount, Teahitia, Moua Pihaa, and Macdonald Seamount in the S. W. Pacific. Mineralogically, the crusts consists of ferrihydrite with traces of the weathering products of volcanic ash (feldspar, nontronite, pyroxene, and serpentinite). The iron oxyhydroxide phase has a mean particle size of 3–4 nm indicating rapid deposition. Electron microprobe studies have revealed the presence of filamentous iron‐silica deposits within the crusts reflecting the possible bacterial oxidation of iron from the hydrothermal fluids. The crusts display wide variability in composition both between individual sampling stations and between seamounts. Endmember analysis shows that the compositional data can be resolved into three endmembers: a Fe‐rich endmember, a light and heavy rare earth element endmember, and a Ba (barite)‐rich endmember. The Fe‐rich endmember appears to contain very low concentrations of most trace elements. For bulk samples, the composition of the iron‐rich crusts reflects dilution of the iron oxyhydroxide phase by volcanic ash and, to a lesser extent, a hydrogenous component. This is illustrated by the wide variability in SiO₂ (11.1–71.3%) and Mn (0.01–1.21%) contents of the crusts. For iron‐rich crusts containing greater than 40% Fe, the Pitcairn crusts display lower contents of Pb, Ba, Mo, U, Th, As, and rare earth elements (REE) and lower cerium anomalies than those from Teahitia. REE profiles of crusts from each of the hot spot volcanoes are characterized by small negative cerium anomalies but pronounced positive europium anomalies. The low average La/Fe ratios of the crusts from the various seamounts (47–572 X 10^‐6) and positive Eu anomalies of the crusts suggest rapid deposition of the iron oxyhydroxide near the hydrothermal vent. The high Fe/Mn ratio of vent fluids at hot spot volcanoes (8.5–5.6) may account for the formation of these iron‐rich crusts. The present data indicate that there may be differences in the nature of the iron‐rich crusts based on the depth of occurrence. This influences the temperature of the venting hydrothermal fluids and the possibility of occurrence of submarine phreatomagmatic eruptions.  相似文献   

An elastoplastic evaluation of the stress state around cylindrical openings based on a closed multiaxial yield surface   总被引：1，自引：0，他引：1  

Li Li  Michel Aubertin 《国际地质力学数值与分析法杂志》2009,33(2):193-213

There are many applications encountered in geo‐engineering where there is a need to evaluate the stress state around circular openings. This paper presents a new analytical solution for evaluating the stresses around a cylindrical excavation in an elastoplastic medium defined by the closed MSDP_u yield surface. The proposed formulation takes into account the 3D stress geometry with a plasticity criterion that intersects the mean stress axis on the positive (compressive) and negative (tensile) sides. The results shown here illustrate how the stress distribution and yielding zone size are affected by various influence factors. Validation of the proposed formulation is made by comparing calculated results with existing analytical solutions and a numerical simulation. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

盾构隧道与周围土体在列车振动荷载作用下的动力响应特性     

杨文波  陈子全  徐朝阳  晏启祥  何川  韦凯 《岩土力学》2018,39(2):537-545

为研究列车振动荷载作用下盾构隧道结构及周围土体的动力响应特性,采用模型试验方法,通过布置在盾构隧道底部的激振器施加扫频激振荷载和列车振动荷载,采用频率响应函数FRF与最大加速度分析了盾构隧道衬砌结构与周围土体不同位置处的动力响应及其衰减规律。研究结果表明：FRF是隧道衬砌结构和周围土体自身的动力响应特性的体现,与激振力的大小、扫频方向及扫频时间无关;在隧道管片衬砌结构的底部和顶部均体现出高频响应大于低频响应的特性,隧道顶部加速度响应沿隧道纵向衰减幅度明显小于隧道底部;隧道周围土体的动力响应沿深度有明显变化,但均表现出沿隧道轴向衰减的规律。隧道结构上部第1层测点土体的动力响应在全频域内随频率的增加逐渐增大。但在第2层和地表的第3层测点,土体的动力响应在30～90 Hz区段线性增长,在90～300 Hz区段出现波动变化,并无明显增大趋势;与扫频激振荷载引起的动力响应规律一致,由列车运行振动荷载引起的隧道管片衬砌结构和周围土体的振动沿隧道轴向逐渐衰减,隧道底部的加速度响应大于顶部,随着列车车速的增大,在隧道内部引起的加速度响应将显著增大。同时,在列车振动荷载作用下发现地表存在加速度放大效应,地表第3层测点的加速度响应均大于隧道结构上部第1层测点。  相似文献   

P波作用下跨断层隧道轴线地震响应分析     

赵密  欧阳文龙  黄景琦  杜修力  赵旭 《岩土力学》2019,40(9):3645-3655

基于近场波动有限元方法并结合黏弹性人工边界条件,针对3D断层场地,通过求解等效二维场地地震响应,从而获得3D场地地震动输入的自由场响应,并将自由场响应转化为3D模型边界面上的等效节点力,从而建立含断层3D场地P波入射的倾斜输入方法。自由场算例验证所提方法具有较好精度,进而基于建立的输入方法,开展了跨断层隧道地震响应的数值模拟研究。数值模拟结果表明:在P波作用下,隧道跨断层部位处于拉、压、剪切的复杂受力状态,且断层处的隧道衬砌地震响应明显大于其他部位的地震响应;围岩的力学性质与断层的力学性质相差越大,断层处衬砌的地震响应放大越明显;断层处衬砌地震响应随断层深度的增加而增加。另外,跨断层隧道的地震响应受P波入射角度的影响较大,随P波入射角度的增加,断层处隧道衬砌的轴力、弯矩先增加后减小,而剪力具有逐渐减小的规律。  相似文献   

钻孔灌注桩基础对紧邻地铁隧道产生竖向附加应力和变形的计算分析   总被引：8，自引：1，他引：8  

楼晓明  金志靖 《岩土力学》1996,17(3):48-53

采用群桩基础共同作用的分析方法，对某高层建筑钻孔灌注桩基础跨越地铁隧道线可能带来的影响进行了计算分析，计算中考虑了孔底沉渣的影响。计算结果表明，超长桩基础下卧层中的竖向附加应力与土的自重应力相比很小，引起桩基沉降的主要因素是桩身的压缩变形和孔底沉渣的变形，桩基础在隧道轴线方向上引起的最大相对变形曲率发生在基础边缘附近。  相似文献   

列车动载作用下交叠隧道动力响应数值模拟   总被引：24，自引：3，他引：24  

陈卫军  张璞 《岩土力学》2002,23(6):770-774

采用上海地铁某区间隧道现场实测振动加速度数据，对南浦大桥近距离交叠隧道在列车振动荷载作用下的动力响应进行了有限元数值模拟。模拟结果表明：上下重叠隧道在动载作用下相互影响显著；随着隧道间净距的增加，相互影响逐渐减弱；对隧道结构而言，土压静载是结构设计的控制荷载，列车振动引起的附加内力增幅较小。  相似文献   

2D dynamic response of unlined and lined tunnels in poroelastic soil to harmonic body waves     

S. E. Kattis  D. E. Beskos  A. H. D. Cheng 《地震工程与结构动力学》2003,32(1):97-110

The problem of harmonic wave diffraction by tunnels in an infinite poroelastic saturated soil obeying Biot's theory is studied numerically under conditions of plane strain and the effect of poroelasticity on the response is assessed through some parametric studies. The method is based on the theory of Mei and Foda, which considers the total field to be approximated by the superposition of an elastodynamic problem with modified elastic constants and mass density for the whole domain and a diffusion problem for the pore fluid pressure confined to a boundary layer at the free boundaries. Both problems are solved numerically by the boundary element method in the frequency domain. Results dealing with the response of a circular tunnel with and without an elastic concrete liner in an infinite poroelastic medium to incident harmonic P and SV plane waves are provided and compared against analytical ones as well as to those corresponding to linear elastic soil behaviour. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Practical Estimate of Deformations and Stress Relief Factors for Deep Tunnels Supported by Shotcrete   总被引：1，自引：1，他引：1  

A. Graziani  D. Boldini  R. Ribacchi 《Rock Mechanics and Rock Engineering》2005,38(5):345-372

Summary. Even though ground-support interaction in the vicinity of the tunnel face is a typical 3D problem, tunnel support design is usually based on simplified plane strain models, which are strongly dependent on the assumed degree of ground stress relief at the time of lining installation. The paper focuses on tunnels supported by shotcrete close to the face, where the interaction between the loading process and progressive hardening of the green shotcrete makes the problem time-dependent. A constitutive law characterized by the time-dependent stiffness and strength of the shotcrete is employed herein. The results of an extensive parametric study based on 3D axisymmetric models are presented in the form of non-dimensional design charts, which can provide guidance to a preliminary evaluation of convergences and support loadings. Moreover a strategy is proposed to enhance the capability of simplified design methods (2D models, Convergence-Confinement Method). This consists in a “guided estimate” of stress relief factors, which again is based on the results of 3D time-dependent analyses. Finally, by way of example, the proposed method is applied to two well-documented case-histories.  相似文献   

人工神经网络在岩石变形温度估算中的应用     

李三忠  朱晓军 《岩石矿物学杂志》1995,(3)

Ｃｈｒｉｓｔｉｅ（１９６２）、Ｓｍｉｔｈ（１９７２）和张翊钧（１９８５）都提出了钠质斜长石的△１３１－（或σ）、Ａｎ与温度Ｔ的关系图，后来又提出了钠质斜长石变形温度的计算公式。但由于图解的不便之处及目前应用的公式中推断分界点的不确定性和σ、Ａｎ与Ｔ之间存在一种非线性关系的特点，本文基于具有高度非线性映射能力的人工神经网络，提出了求解岩石变形温度的新方法。文中先介绍了变形温度计的研究概况，然后阐述了ＡＮＮ（ＡｒｔｉｆｉｃｉａｌＮｅｕｒａｌＮｅｔｗｏｒ）模型，最后应用该模型估算岩石变形时的温度，经对比得出，利用人工神经网络在岩石变形温度估算中具有良好的应用效果。  相似文献