具有球形空腔饱和土分数导数 黏弹性土的动力特性

将土骨架视为具有分数阶导数本构关系的黏弹性体,基于Biot两相饱和介质模型,建立具有球形空腔饱和分数导数黏弹性土体稳态振动的控制方程。通过引入势函数,得到球对称情形下具有球形空腔饱和分数导数黏弹性土体的位移、应力和孔隙流体压力等解析表达式。考察分数导数模型参数和饱和土参数等对土体振动特性的影响,结果表明,流体压缩性对饱和土体的动力特性有显著影响,而土骨架压缩性和流-固耦合系数的影响相对较小;分数导数阶数对土体动力特性的影响与材料参数比的取值有关。同时,边界不排水条件下饱和土体的动力响应大于排水条件下饱和土体的动力响应。     

砂岩储层射孔压实带孔隙度与渗透率损伤研究

射孔孔眼是储层油气进入生产井筒的通道,聚能射孔过程会在孔眼周围砂岩储层产生不同程度的损伤。基于射孔效能物理试验和数值模拟,提出了一种用于定量评价射孔压实带孔隙度和渗透率损伤程度的方法。应用塑性随动强化材料模型表征高应变率冲击载荷下的砂岩形变特性,通过显式动力分析程序LS-DYNA数值模拟孔眼压实区域的砂岩动力学响应,获得了砂岩骨架应力、塑性应变、体积应变等关键数据,结合射孔压实带孔隙度与渗透率演化模型,量化分析了砂岩射孔压实带损伤程度。以胜利油田粒间孔隙砂岩靶为例,数值结果与靶心流动效能测试、CT扫描数据能够较好地吻合,验证了定量评价方法的有效性。结果表明,聚能射孔对压实区域砂岩的损伤主要表现为塑性挤压和剪胀两种机制。在孔道内壁区域,砂岩骨架主要受剪胀作用,孔隙度增加;但塑性挤压又改变了原始孔隙结构,造成流动通道阻塞,渗透率降低。     

爆破破岩过程中的动态卸载效应探讨

以瞬态载荷作用下弹性介质中球形空腔的动态响应解析解为基础,分析了爆炸载荷动态卸载时对介质中应力分布的影响,探讨了动态卸载效应在爆破破岩过程中的作用,并对爆破工程实践中的一些现象作了合理地解释,指出了深入研究动态卸载效应的必要性。     

基于精确缩尺的颗粒材料流变研究

基于Feng Y T提出的精确缩尺方法,即根据几何相似、静力相似、动力相似3个相似原理建立一套缩尺准则,使得缩尺前后模型的力学响应保持一致。首次将该理论应用于颗粒材料的流变分析当中,采用Burgers黏塑性蠕变模型,引入流变参数,在原缩尺准则上进行理论推导,得到在二维和三维条件下的缩尺准则;其次在理论推导的基础上进行数值仿真验证。研究结果表明：严格按照拟定的缩尺准则选取参数后,缩尺后模型的力学响应能够保证和原尺寸模型完全一致,计算误差在3%以内,同时简要探讨了时间步长、黏性系数、颗粒数目、比尺数对数值试验的影响,为数值试验中相关参数的选取以及如何让数值模型反映材料真实的力学行为提供了有效参考。另外,由于缩尺模型采用与原模型相同的颗粒数目、颗粒形状、颗粒压实状态和比尺数,揭示了等比例缩尺对材料流变行为的影响。     

频域内饱和多孔介质的参数反演分析

基于Biot理论,假定固体颗粒和孔隙内流体均不可压缩,建立了以固体骨架位移表示的的控制方程.考虑单层饱和多孔介质在竖向简谐荷载作用下一维动力响应,通过理论推导获得了骨架位移、应力以及孔隙流体压力等物理量的解析表达式.基于饱和土的简谐动力模型试验数据,与所得到的理论解答相结合,将饱和多孔介质材料参数反演问题归结为非线性多峰函数的最优化问题.全局最优解的求解采用了遗传算法和模拟退火算法,并通过试验和数值算例验证了所得材料参数的正确性.     

粘弹性准饱和土中球空腔的动力响应

从工程实际出发,采用粘弹性两相介质模型,考虑土骨架的粘性以及流体与固体之间的耦合作用,利用Laplace变换求解了粘弹性准饱和土中球空腔的动力响应问题,得到了变换域内的解析解。借助数值Laplace反变换,数值分析了粘弹性准饱和土中球空腔动力响应的位移、应力及孔压的变化规律。为分析地下结构动力响应提供了一种有效的方法,模型符合工程实际,有一定的工程应用价值。     

岩石材料冲击压缩特性细观模拟方法研究

岩石材料的细观特性对宏观力学性能有着重要影响。为了分析岩石材料颗粒形态、孔隙和含水等细观特性对宏观冲击响应行为的影响规律,从岩石材料的细观特性入手,结合材料细观结构照片,经制图软件矢量化和轮廓处理,建立了能够反映材料细观分布特性的岩石材料有限元模型。基于AUTODYN有限元计算软件,对岩石材料冲击压缩细观行为进行数值模拟,获取材料颗粒形态、孔隙和含水等细观特性对材料宏观冲击压缩特性的影响规律。确定岩石材料冲击Hugoniot参数,应用于冲击开坑仿真中,并与已有的试验结果进行了对比。结果表明:数值仿真结果与已有试验数据吻合较好;孔隙率和含水率对岩石材料冲击波衰减规律有十分显著的影响;细观模拟确定的Hugoniot参数运用到岩石材料宏观动力学行为数值模拟中,可有效反映岩石材料中颗粒、孔隙和含水等细观特性对冲击开坑行为的影响规律。     

陵水凹陷北坡海底扇孔隙演化和成岩相研究

琼东南盆地陵水凹陷北坡海底扇储层岩性较细,物性较差,并且对其低渗的成因不明、甜点的展布也不清。通过利用岩石薄片、扫描电镜、粒度分析、压汞以及物性等资料来分析其孔隙演化,并从成岩相的研究角度来预测其甜点展布。研究结果认为研究区梅山组二段储层孔隙类型主要为原生粒间孔和铸模孔,处在中成岩阶段A期。从沉积因素和成岩作用两个方面总结出了研究区的孔隙演化模式:沉积环境控制了原始孔隙度的大小,后期机械压实是孔隙减小的主要原因,溶解作用对孔隙增大起到了巨大贡献。研究区主要识别和划分出了中等压实长石溶蚀相、中等压实海绿石胶结相和强压实弱溶蚀相3种成岩相,甜点主要分布在水动力较强的海底扇内扇中等压实长石溶蚀相中。     

降雨诱发边坡破坏数值模拟两个关键问题的解决方法

研究降雨因素对边坡稳定性的影响,最有效的方法是室内外试验和数值模拟方法,最为重要的是设置与实际情况接近的降雨入渗边界与动态流量边界下初始孔隙水压力分布问题。为有效地解决这两方面的问题,首先将现有的降雨数值边界施加方法所得模拟结果与室内试验结果进行了对比分析,指出了传统方法的不足之处,并在此基础上提出了新的降雨数值边界条件,即在土体表面施加一层很薄的"空气单元",表述的是一个动态的边界条件。降雨入渗边界施加在"空气单元"表面,而不直接施加在土体单元表面,应用该方法完成的入渗土柱数值模拟结果更加接近现场和试验测得的降雨入渗率,为有效模拟降雨诱发边坡破坏的边界条件提供准确、真实可行的方法。同时,由于相对渗透系数和负孔隙水压力均为饱和度的函数,通过设置流体的抗拉强度来赋予节点负孔隙水压力模拟基质吸力,在数值模拟中每一个计算步根据节点饱和度自动更新负孔隙水压力和相对渗透系数,可实现FLAC软件中非饱和土的有效渗流分析。此外,为解决非饱和区土体施加负孔隙水压力所带来的问题,提出数值模拟过程中施加动态的流量边界,通过模拟自然界中地下水的补给,很好地解决使用FLAC进行数值模拟时动态流量边界条件下初始孔隙水压力的分布问题。     

西湖凹陷花港组低渗储层微结构及孔隙演化定量评价

东海盆地西湖凹陷发育大量低渗储层,低渗油气具有广阔的勘探前景。通过铸体薄片、扫描电镜、高压压汞、X线衍射、粒度分析及物性等资料,分析了储层微观孔隙结构特征,总结出研究区储层发育有原生孔隙与次生孔隙的六种孔隙类型和五种吼道类型。压实作用、胶结作用和溶解作用是影响研究区储集性能的关键因素,建立沉积之初原始孔隙度和经压实、胶结、溶蚀等成岩作用后次生孔隙度的定量恢复评价方法。经定量计算:压实作用使孔隙度平均降低88.12%,胶结作用导致孔隙损失54.50%,溶蚀作用使孔隙度增加60.99%。定量计算结果与实测结果的之间误差较小,说明该孔隙定量恢复过程可信度较高,对同类储层演化的研究具有借鉴意义。     

Analysis of dynamic spherical cavity expansion in undrained modified Cam Clay soil

In order to capture the influence of the cavity expansion velocity, this paper presents a semianalytical solution for dynamic spherical cavity expansion in modified Cam Clay (MCC) soil. The key problem is solving the six coupled partial differential equations (PDEs) of cavity expansion, in which the dynamic term is considered in the stress equilibrium equation. The similarity transformation technique is used to transform the PDEs into ordinary differential equations (ODEs). Subsequently, the numerical method using the function “ODE45” in MATLAB is selected to solve the ODEs, which allows the stress and excess pore pressure around the expanding spherical cavity wall to be obtained. The proposed semianalytical solution for dynamic spherical cavity expansion was validated by comparting the degenerate solution with the published quasistatic solution for the MCC model. Parametric study was then conducted to capture the influence of the cavity wall velocity on the cavity expansion response. The proposed solution has potential application to geotechnical problems such as dynamic pile driving, the dynamic cone penetration test, and so forth.     

Expansion of cavities in layered elastic system

Theoretical formulations to the problem of expansion of spherical and cylindrical cavities in a layered elastic system are presented. The medium surrounding the cavity is assumed to consist of several layers, and each is idealized as a linear elastic solid. The solutions are expressed in matrix forms and can be obtained using a programmable calculator. The developed solutions are of some importance in geomechanics. The spherical cavity solution can be used to compute the settlement of single axially loaded piles. The predicted settlement using the analysis outlined herein agrees reasonably well with one case of field measurements. The cylindrical cavity solution can be used to manifest the effect of disturbed mass at the cavity wall on the stress–strain and deformation characteristics of the intact mass.     

夯扩桩半模夯扩试验及夯扩机理探讨

设计了夯扩桩半模夯扩试验，采用读数显微镜直接测读上体质点位移，获得了不同密度的均匀砂土中砂粒的位移，由此确定土体的位移场和密度场。借鉴魏西克（Ｖｅｓｉｃ）球形孔穴膨胀理论和梅耶霍夫（Ｍｅｙｅｒｈｏｆ）塑性剪切理论，结合模型试验成果，对夯扩机理作了探讨，并定性地提出了夯扩机理模式。     

Analysis of undrained cavity expansion in elasto‐plastic soils with non‐linear elasticity

A large strain analysis of undrained expansion of a spherical/cylindrical cavity in a soil modelled as non‐linear elastic modified Cam clay material is presented. The stress–strain response of the soil is assumed to obey non‐linear elasticity until yielding. A power‐law characteristic or a hyperbolic stress–strain curve is used to describe the gradual reduction of soil stiffness with shear strain. It is assumed that, after yielding, the elasto‐plastic behaviour of the soil can be described by the modified Cam clay model. Based on a closed‐form stress–strain response in undrained condition, a numerical solution is obtained with the aid of simple numerical integration technique. The results show that the stresses and the pore pressure in the soil around an expanded cavity are significantly affected by the non‐linear elasticity, especially if the soil is overconsolidated. The difference between large strain and small strain solutions in the elastic zone is not significant. The stresses and the pore pressure at the cavity wall can be expressed as an approximate closed‐form solution. Copyright © 2001 John Wiley & Sons, Ltd.     

An assessment of the bearing capacity of calcareous and silica sands

A spherical cavity expansion model has been used to study the bearing capacity of foundations on calcareous and silica sands. Two constitutive models have been used to represent each sand: an elastoplastic, collapse-softening model, and a computationally simpler, elastic/perfectly plastic material. The predictions of the limit pressures for spherical cavity expansion are compared with laboratory data on the bearing capacities obtained from model footing tests. It is shown that the numerical predictions of the limit pressures correlate well with the experimental values of bearing capacity, particularly at higher effective overburden pressures.     

High pressure jet-grouting column installation effect in soft soil: Theoretical model and field application

This paper presents a theoretical model for investigating the installation effect of high pressure jet grouting column in soft clay. The model is formulated by assuming the installation process as a series of pressure-controlled spherical cavity expansion in semi-infinite soil, of which the approximate solutions are derived by combining use of two fundamental solutions of spherical cavity expansion in finite spherical symmetry soil and displacement-controlled spherical cavity expansion in semi-infinite soil. The approximate solutions are then validated by comparing the predictions with FEM results as well as published results. The comparison results show that the presented approximate solutions are suitable for the problem of pressure-controlled spherical cavity expansion in semi-infinite soil, particularly in evaluating the limit expansion pressure as well as the expansion pressure-ground surface displacement relation. Subsequently, the proposed approximately solutions are applied to interpret the limit injection pressure and the grouting pressure-ground surface displacement during the installation process of HPJ-GC. Some parametric studies are also conducted. Furthermore, an instrumented field test study of HPJ-GC is conducted in the thick soft soils comprising quaternary alluvial and marine deposits of the Lianyungang-Yancheng Highway located in Jiangsu Province, China. The measured ground heave is compared with the analytical predictions using the proposed theoretical model. Reasonable agreement is achieved.     

准饱和黄土中暗穴水动力扩展响应的研究

为分析强降水过程中暗穴扩展机理,在野外调查资料的基础上,建立了准饱和黄土暗穴的扩展计算模型,概化为弹性准饱和土层中无限长圆柱形孔洞表面受水压力的动力响应问题。通过引入势函数,得到了Lap lace变换域中的应力、位移及孔隙水压力的解析表达式,并利用数值逆变换方法求得时域解,分析了降雨历时及饱和度等因子对暗穴动力响应的影响。结果表明,水动力是引起黄土暗穴扩展的主要因素,水压力作用历时对位移及应力有较大的影响,同时饱和度的细微变化对径向位移有显著影响。     

Elastic‐plastic solutions for expanding cavities embedded in two different cohesive‐frictional materials

An analytical solution of cavity expansion in two different concentric regions of soil is developed and investigated in this paper. The cavity is embedded within a soil with finite radial dimension and surrounded by a second soil, which extends to infinity. Large‐strain quasi‐static expansion of both spherical and cylindrical cavities in elastic‐plastic soils is considered. A non‐associated Mohr–Coulomb yield criterion is used for both soils. Closed‐form solutions are derived, which provide the stress and strain fields during the expansion of the cavity from an initial to a final radius. The analytical solution is validated against finite element simulations, and the effect of varying geometric and material parameters is studied. The influence of the two different soils during cavity expansion is discussed by using pressure–expansion curves and by studying the development of plastic regions within the soils. The analytical method may be applied to various geotechnical problems, which involve aspects of soil layering, such as cone penetration test interpretation, ground‐freezing around shafts, tunnelling, and mining. © 2014 The Authors. International Journal for Numerical and Analytical Methods in Geomechanics published by John Wiley & Sons Ltd.