Numerical simulation of a stratigraphic model

A multi-lithology diffusive stratigraphic model is considered, which simulates at large scales in space and time the infill of sedimentary basins governed by the interaction between tectonics displacements, eustatic variations, sediment supply, and sediment transport laws. The model accounts for the mass conservation of each sediment lithology resulting in a mixed parabolic, hyperbolic system of partial differential equations (PDEs) for the lithology concentrations and the sediment thickness. It also takes into account a limit on the rock alteration velocity modeled as a unilaterality constraint. To obtain a robust, fast, and accurate simulation, fully and semi-implicit finite volume discre tization schemes are derived for which the existence of stable solutions is proved. Then, the set of nonlinear equations is solved using a Newton algorithm adapted to the unilaterality constraint, and preconditioning strategies are defined for the solution of the linear system at each Newton iteration. They are based on an algebraic approximate decoupling of the sediment thickness and the concentration variables as well as on a proper preconditioning of each variable. These algorithms are studied and compared in terms of robustness, scalability, and efficiency on two real basin test cases.     

凤爪沟边坡稳定性评价

主要研究了一个边坡在施加冷却塔荷载前后的稳定性问题。采用有限元法和摩尔-库仑屈服准则计算和分析了冷却塔荷载对边坡稳定性的影响,得到较理想的结果。结果表明,边坡的整体稳定性问题,主要是变形稳定性问题;玄武岩柱状节理的存在对边坡稳定性产生了不利的影响;冷却塔的修建对边坡稳定性是有影响的;边坡的变形破坏随时间的增长而增加;边坡的破坏形式以倾倒破坏为主。     

江苏松散沉积层地区地下水资源评价模型发展趋势

江苏松散沉积层厚度大、结构复杂、容易发生固结压缩,地下水可采资源量评价具有较大的不确定性,容易造成重复或缺失,地下水的过量开采又容易引发地面沉降地质灾害。针对以上问题,提出了地下水资源评价的地下水渗流三维数学模型及其地下水渗流与地面沉降耦合模型。地下水渗流三维数学模型可以将整个松散沉积层作为一个统一的水文地质体进行计算,对不同水力性质的含水层同时进行刻画描述,克服了以往二维或准三维模型将各含水层之间的粘性土层概化为越流层给评价结果带来的重复或缺失。地下水渗流与地面沉降耦合模型可以结合地面沉降环境控制,评价出地下水的可采资源量,尤其是以比奥固结理论为基础,考虑了土体的非线性特征及土的渗透性随应力状态的动态变化的全耦合模型,使评价结果更趋科学、合理。     

Bounding surface model for soil resistance to cyclic lateral pile displacements with arbitrary direction

The development of a two-surface elastic–plastic bounding surface P–Y model for cyclic lateral pile motions is described. The kinematic-hardening model is applicable to the analysis of pile foundations subjected to loading with arbitrary azimuths relative to the pile axis. The model realistically captures the hysteretic energy damping associated with dynamic loading of subsea foundations through physically correct plastic mechanisms and provides results consistent with those observed in physical tests including cyclic loading. Its performance is demonstrated in element states of stress and in pile foundation analyses. The development based on the incremental theory of plasticity results in more robust solutions than may be obtained using alternative elastic, variable moduli and deformation plasticity formulations.     

Metamorphic reactions in dry and aluminous granulites: a Perple_X <Emphasis Type="Italic">P–T</Emphasis> pseudosection analysis of the influence of effective reaction volume

In high-Mg, Al metapelites, monophase sapphirine corona occur around spinel–corundum aggregates in monomineralic cordierite layers, and bi-phase orthopyroxene–sillimanite aggregates replace locally warped sapphirine in polygonized cordierite aggregates. P–T phase topologies computed (Perple_X software) using compositions of cordierite-rich layers that host the reaction textures did not match the assemblages for the discontinuous reactions spinel + corundum + cordierite → sapphirine and sapphirine + cordierite → orthopyroxene + sillimanite. Instead, the reaction assemblages were reproduced using P–T pseudosection analysis for micro-domain reaction volumes estimated from compositions of product phases in the volume proportion they occur. The results are consistent with known phase relations deduced using Schreinmakers P–T grids. Apparently, the compositions of cordierite-rich layers that hosted the reaction textures were inadequate chemical proxies for determining P–T–X relations of phase-boundary controlled reactions influenced by compositions of the nearest-neighbor minerals in the proportion they react (effective composition), and not in the proportion they existed in the layer/bulk rock. In other words, P–T–X phase topologies and reconstructed P–T paths in dry and aluminous rocks may be best understood by thermodynamic modeling of reactions using effective reaction volume compositions rather than the bulk composition of the rock or the mineralogical layer that host the reaction textures.     

Numerical modelling of soil nails in loose fill slope under surcharge loading

A plane–strain numerical model has been developed to mimic a nailed loose fill slope under surcharge loading. The model has been used to back-analyse a field test that was conducted to examine the behaviour of soil nails in loose fill slopes under surcharge loading. Incremental elasto-plastic analyses coupled with pore water diffusion have been performed to study the internal deformation, water content redistribution in the soil, and the performance of the soil nails during and after the application of surcharge loading. The model parameters describing the mechanical and hydraulic properties of the nailed slope were obtained from field or laboratory tests. Different modelling techniques and boundary conditions for mimicking soil–nail interaction in loose fill material have been examined. Comparisons between numerical predictions and field measurements demonstrate that a new interfacial model, denoted as the embedded bond–slip interface model, is more suitable for mimicking the interfacial behaviour. Despite the simplicity of the numerical model, the predicted responses are in close agreement with the field test results, in particular the mobilisation and distribution of nail forces in response to surcharge loading. Both the numerical and the field test results suggest that soil nails are capable of increasing the overall stability of a loose fill slope for the loading conditions considered in this study. The increase in confining stress along the soil nails near the surcharge area is central to the overall stabilising mechanism. On the contrary, the nail forces mobilised near the nail heads are much smaller, indicating that the beneficial effect of having a structural grillage system at the slope face is limited for the range of surcharge pressures considered in this study.     

GPS-measured land subsidence in Ojiya City, Niigata Prefecture, Japan

Land subsidence caused by compression of clay layers in Ojiya City, Japan was measured by global positioning system (GPS) between 1 April 1996 and 31 December 1998.

Three baselines were selected in and around the city, and height difference on a WGS-84 ellipsoid was measured by GPS on each baseline. The ground at the GPS station in the city subsides and rebounds 7 cm every winter and spring, respectively. Measurement accuracy was 9.5 mm standard deviation. Ground water level was observed at a well near the GPS station. Regression analysis between total strain, calculated as ratio of the height difference displacement to the total thickness of the clay layers, and the layers' effective stress change with ground water level change gave good correlation. The slope of regression line 7.0×10⁻¹¹ m²/N was obtained as an average apparent coefficient of volume compressibility of the layers.     

灌注桩后注浆单桩竖向极限承载力研究

近年来,后注浆技术得到了广泛的应用。钻孔灌注桩可大大降低建筑物的沉降,并使建筑物的沉降更加均匀,文章介绍后注浆工艺的承载力提高机理及在天津地区的几个工程实例,分析了注浆前后单桩竖向极限承载力对比情况及影响单桩竖向极限承载力的几个因素。