次塑性模型及饱和砂土动力弹塑性响应分析

提出了一个新的次塑性模型并用试验作了初步验证,建议用异步交叉迭代显式差分有限元求解固液耦合动力弹塑性问题。利用次塑性模型以及动力固结有限元计算程序,对一简单饱和砂土地基的动力弹塑性响应进行了分析,取得了合理的结果。     

地震载荷下核岛动力响应数值模拟

核电作为清洁型能源具有广阔的发展前景,研究核电站的地震响应具有重要意义。建立了AP1000核岛的有限元模型,进行模态分析获取核岛的振动形态。用无限元模拟远场地基,有限元模拟近场地基,并考虑基础埋置及土与结构相互作用,开展了不同地基条件下的核岛地震响应分析。结果表明：随着地基刚度的增加,核岛节点的响应加速度幅值增大,而加速度反应谱峰值对应的周期减小,核岛节点应力增大,但其相对位移减小;考虑土与结构相互作用之后,软弱地基的响应加速度峰值大幅减小,地基加速度反应谱峰值对应的周期增加,土与结构相互作用对此类地基上核岛的地震输入有较大影响;对于坚硬岩石地基,土与结构相互作用对地震输入的影响可以忽略。     

不同埋深隧道的地震响应振动台试验研究

针对不同埋深下隧道表现出不同震害的特点,对地震响应振动台模型试验进行研究。首先进行了试验方案设计及试验模型的相似比设计,然后对不同地震波类型、地震强度及不同埋深下的隧道依次进行了振动台模型试验。试验结果表明:地震作用下,隧道衬砌应力在隧道埋深较浅时最大,达到一定埋深(约40 m)时,隧道衬砌应力明显减小,之后,隧道衬砌应力随埋深的变化不明显;隧道衬砌应力随埋深的变化规律在不同的地震波类型、不同的地震加速度峰值下相似;不同深度土层的加速度放大系数随着埋深的减小逐渐增大。通过对试验后隧道周边土体观测可知,浅埋隧道周边土体的裂缝多于深埋隧道。试验验证了地震灾害调查结果,为隧道抗震设计提供依据。     

输水隧道地震响应的多物质ALE数值分析

为研究浅埋输水隧道内部流体对隧道地震响应的影响,考虑黏弹性人工边界、土壤的非线性、隧道结构刚度有效率及流-固耦合作用,建立了双线隧道-土体-流体相互耦合作用的力学模型。通过刚度折减试验得到衬砌环环向、径向、轴向刚度,进而引入正交各向异性连续材料作为衬砌材料模型。采用基于任意拉格朗日-欧拉（ALE）描述法的流-固耦合方法,对上海某大直径双线输水隧道在流体作用下的地震响应进行了分析。通过与等效密度法对比,验证耦合模型对于处理输水隧道多物质非线性耦合抗震问题的可行性。计算结果表明,在水平方向地震激励下,无论一致激励或是非一致激励流体对隧道地震变形和内力都有较大影响,但对位移影响较小;对于不同隧道内水量,隧道弯矩均集中于衬砌隧道45°交叉斜线位置;相比于一致激励,非一致激励增强隧道地震位移和变形响应是明显的。     

Numerical evaluation of seismic response of shallow foundation on loose silt and silty sand

This study includes the results of a set of numerical simulations carried out for sands containing plastic/non-plastic fines, and silts with relative densities of approximately 30?40% under different surcharges on the shallow foundation using FLAC 2D. Each model was subjected to three ground motion events, obtained by scaling the amplitude of the El Centro (1940), Kobe (1995) and Kocaeli (1999) Q12earthquakes. Dynamic behaviour of loose deposits underlying shallow foundations is evaluated through fully coupled nonlinear effective stress dynamic analyses. Effects of nonlinear soil structure interaction (SSI) were also considered by using interface elements. This parametric study evaluates the effects of soil type, structure weight, liquefiable soil layer thickness, event parameters (e.g., moment magnitude of earthquake (M _w ), peak ground acceleration PGA, PGV/PGA ratio and the duration of strong motion (D _5?95) and their interactions on the seismic responses. Investigation on the effects of these parameters and their complex interactions can be a valuable tool to gain new insights for improved seismic design and construction.     

考虑Gmax附加衰减的场地地震响应离心机试验数值模拟

在常规的场地地震响应有效应力分析法中,通常只考虑Gmax随有效应力和孔隙比的变化,而最新的试验研究表明,Gmax在大应变幅振动下存在附加衰减。收集了不同类型土体在大幅振动下的298组Gmax数据,拟合并给出了对应于两种Gmax附加衰减模式的计算模型,通过编制可考虑Gmax附加衰减影响的一维场地地震响应有效应力分析程序,分别对典型场地和离心机振动台模型场地的地震响应进行分析对比。结果表明：Gmax附加衰减对场地加速度和剪应力响应均有较大影响,将加速场地液化进程和扩大场地最终液化范围;考虑Gmax附加衰减可较好地模拟动力离心模型试验场地动力响应;但在强震情况下,场地迅速液化,Gmax附加衰减对场地动力响应的影响反而减弱。     

俯斜式混凝土重力挡土墙强震反应数值模拟

首先,介绍了基于OpenSees独立开发的一套用于挡土墙-土地震反应相互作用有限元分析计算软件RW_2DPS.据此建立了俯斜式混凝土重力挡土墙-土强震相互作用有限元模型.模型中,引入非线性有限元计算方法,选用多屈服面弹塑性本构模型模拟砂土的动力属性,应用零长度接触单元模拟墙与土体之间的接触特性,且采用一致耗能阻尼边界与速度边界条件.最后,输入随机地震动,进行挡土墙-土强震反应分析,并重点探讨墙背地震土压力和水平地震惯性力沿挡土墙高度分布规律.结果表明,墙背动土压力峰值出现在距挡土墙底约1/3墙高处;挡土墙背加速度具有放大效应,加速度峰值出现在挡土墙顶部;不同地震动作用下,加速度放大系数沿墙高分布规律不同,动土压力沿墙高变化规律基本一致.     

Effect of adjoining structures on seismic response of tunnels

In this paper the seismic behaviour of buried concrete tunnels is studied using the finite element method. The numerical tool employed is the well-known soil–structure interaction computer program FLUSH and thus analyses are carried out in the frequency domain. The seismic environment is supposed to consist of vertically propagating shear and compression waves that reproduce artificial accelerograms of a broad frequency content at selected control points. The effect of near or adjacent massive structures, such as those of nuclear power plants, is evaluated showing their influence on tunnel response. The results calculated for acceleration levels, internal structural loads, response spectra, etc., are analysed and compared either with those obtained from soil free-field response or with others computed using an alternative simplified methodology, providing useful information for preliminary design purposes.     

Numerical modelling of centrifuge dynamic tests of circular tunnels in dry sand

This paper describes the numerical simulation of two dynamic centrifuge tests on reduced scale models of shallow tunnels in dry sand, carried out using both an advanced bounding surface plasticity constitutive soil model and a simple Mohr–Coulomb elastic-perfectly plastic model with embedded nonlinear and hysteretic behaviour. The predictive capabilities of the two constitutive models are assessed by comparing numerical predictions and experimental data in terms of accelerations at several positions in the model, and bending moment and hoop forces in the lining. Computed and recorded accelerations match well, and a quite good agreement is achieved also in terms of dynamic bending moments in the lining, while numerical and experimental values of the hoop force differ significantly with one another. The influence of the contact assumption between the tunnel and the soil is investigated by comparing the experimental data and the numerical results obtained with different interface conditions with the analytical solutions. The overall performance of the two models is very similar indicating that at least for dry sand, where shear-volumetric coupling is less relevant, even a simple model can provide an adequate representation of soil behaviour under dynamic conditions.     

列车动载作用下交叠隧道动力响应数值模拟

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。     

近距离地铁施工的有限元数值模拟

在地铁施工中受地形条件限制有时会遇到两条单线隧道近距离施工情况,有的间距超出了规范的要求。以深圳市轨道交通二期1号线续建工程为例,应用ABAQUS程序对实际情况进行了数值模拟分析,揭示了在开挖右线工程的时对左线既有隧道产生的影响,包括地表沉降、应力分布和衬砌变形及对地面建筑的影响,得出一些有益的结论,为今后近距离地铁施工提供可靠的依据。     

Numerical simulation of bolt‐supported tunnels by means of a multiphase model conceived as an improved homogenization procedure

This paper examines the possibility of applying a homogenization procedure to analyze the convergence of a tunnel reinforced by bolts, regarded as periodically distributed linear inclusions. Owing to the fact that a classical homogenization method fails to account for the interactions prevailing between the bolts and the surrounding ground and thus tends to significantly overestimate the reinforcement effect in terms of convergence reduction, a so‐called multiphase model is presented and developed, aimed at improving the classical homogenization method. Indeed, according to this model, the bolt‐reinforced ground is represented at the macroscopic scale as the superposition of two mutually interacting continuous phases, describing the ground and the reinforcement network, respectively. It is shown that such a multiphase approach can be interpreted as an extension of the homogenization procedure, thus making it possible to capture the ground–reinforcement interaction in a proper way, provided the constitutive parameters of the model and notably those relating to the interaction law can be identified from the reinforced ground characteristics. The numerical implementation of this model in a finite element method‐based computer code is then carried out, and a first illustrative application is finally presented. Copyright © 2008 John Wiley & Sons, Ltd.     

Numerical simulation of round robin numerical test on tunnels using a simplified kinematic hardening model

The paper summarizes the numerical simulation of the round robin numerical test on tunnels performed in Aristotle University of Thessaloniki. The main issues of the numerical simulation are presented along with representative comparisons of the computed response with the recorded data. For the simulation, the finite element method is implemented, using ABAQUS. The analyses are performed on prototype-scale models under plane strain conditions. While the tunnel behavior is assumed to be elastic, the soil nonlinear behavior during shaking is modeled using a simplified kinematic hardening model combined with a von Mises failure criterion and an associated plastic flow rule. The model parameters are adequately calibrated using available laboratory test results for the specific fraction of sand. The soil–tunnel interface is also accounted and simulated adequately. The effect of the interface friction on the tunnel response is investigated for one test case, as this parameter seems to affect significantly the tunnel lining axial forces. Finally, the internal forces of the tunnel lining are also evaluated with available closed-form solutions, usually used in the preliminary stages of design and compared with the experimental data and the numerical predictions. The numerical analyses can generally reproduce reasonably well the recorded response. Any differences between the experimental data and the numerical results are mainly attributed to the simplification of the used model and to differences between the assumed and the actual mechanical properties of the soil and the tunnel during the test.     

软土矩形地铁隧道地震反应特性分析

为研究在不同类型的软土地层条件下地铁隧道的地震反应特性,本文选用El-Centro波作为隧道基岩处水平输入的地震波,利用大型有限元软件ANSYS分析上海矩形地铁隧道在三种典型场地中的地震反应特性,获得了矩形隧道在三种场地中的地震反应规律,结果表明:处于软土地层中的矩形地铁隧道,应力的抗震薄弱位置在衬砌形状突变处,水平位移的抗震薄弱位置在隧道顶部,水平加速度的抗震薄弱位置在隧道底部,设计时应加强薄弱部位的抗震设防,这为矩形地铁隧道抗震设计提供了参考依据。     

高坝明流泄洪洞掺气减蚀三维数值模拟分析

高坝明流泄洪洞的掺气减蚀问题倍受关注。以溪洛渡水电站3#泄洪洞为研究对象,结合大比尺单体模型试验成果,应用分段计算方法对泄洪洞掺气减蚀问题进行了三维紊流数值模拟分析。结果表明:泄洪洞各道掺气坎布置合理且有稳定掺气空腔,掺气坎体型基本合理,明流段洞顶余幅足够。泄洪洞反弧段及末端一段区域水力特性复杂,应重点关注此部位的设计及施工问题。对于高流速、大梯度泄洪洞水力学问题,采用分段计算能提高计算速度。     

Numerical simulation of the seismic response of the Zipingpu concrete face rockfill dam during the Wenchuan earthquake based on a generalized plasticity model

The strong ground motion of the 2008 Wenchuan earthquake in China caused considerable damage to the Zipingpu concrete face rockfill dam (CFRD). The maximum crest settlement was approximately 1.0 m, and compressive failure and joint dislocations were observed in the face slabs. This damage has made it necessary to understand the damage pattern and safety of high CFRDs subjected to strong earthquake shaking, and the response of the Zipingpu CFRD during the Wenchuan earthquake can be used as a benchmark for this purpose. In this study, a 3D dynamic procedure was employed to simulate the dynamic responses of the Zipingpu CFRD. The rockfill materials were described using a generalized plasticity model, while the interfaces between the face slabs and cushions were modeled using zero-thickness interface elements that follow a perfect elasto-plastic stress–strain model in the tangential direction using Coulomb’s friction law. Dam deformation, face-slab stress, and face joint dislocations were simulated, and the results were compared with the field measurements. Using the generalized plastic model, the residual deformation of the dam during the earthquake could be directly obtained without being complemented by separate, semi-empirical procedures. The rockfill materials shrank to the center of the valley due to the strong shaking, causing crushing damage in the zone of the slabs. The dislocation of construction joints was also duplicated by the numerical procedure. The results of this study indicate that a 3D finite element procedure based on a generalized plasticity model can be used to evaluate the dynamic responses of CFRDs during strong earthquakes.     

Numerical simulation of a tunnel surrounded by sand under earthquake using a hypoplastic model

A numerical model of a centrifuge experiment on tunnel located in sand is being presented. The experiment was carried out under seismic loading using a dynamic actuator. The responses of the tunnel and of the sand were measured. The numerical model is based on a hypoplastic constitutive model with intergranular strains implemented in the FE-code TOCHNOG. The calculated accelerations in the sand match the measured results, while the surface settlement and the bending moments in the tunnel lining are only qualitatively reproduced by the numerical model.     

Validation of an elastoplastic model for chalk

A new elastoplastic model for porous rocks (chalk) has been developed [1]. It is based on the concept of two plastic deformation mechanisms[2]. In this paper, we present the validation of this model for both homogenous tests and a typical boundary condition problem, hollow cylinder test. Comparisons between experimental results and predictions by the model are presented for each test. Influences of parameter perturbations on numerical simulation are also studied.     

非均匀煤岩渗流-应力弹塑性耦合数学模型及数值模拟

利用Weibull分布模拟煤岩弹性模量和强度的非均匀性,结合煤岩弹塑性变形理论和瓦斯渗流理论,建立了非均匀煤岩渗流-应力弹塑性耦合数学模型,给出了该数学模型的有限元离散方程,开发了相应的数值计算程序Coupling Analysis。利用建立的模型模拟了辽宁某瓦斯抽放试井瓦斯抽放过程,结果表明,在瓦斯抽放过程中,有效应力变化诱发煤岩局部进入塑性状态,塑性区透气系数增加了约4.9倍,而弹性受压区的透气系数最大减小至22 %,计算实例的瓦斯压、煤岩有效应力和煤岩变形都呈现非对称性,但服从理论规律,表明采用Weibull分布能很好地模拟煤岩力学参数的非均匀性。