黄河三角洲地区砂土路基液化机理探讨及处置

从砂土路基液化机理人手,结合黄河三角洲地区地基土工程地质特征,对该地区路基砂土液化做现场振动试验,找出影响砂土路基液化的影响因素,主要内因有土体的密实度、含水量和土体中是否存在软弱区;主要外因有荷载的大小、作用时间和荷载频率。并针对砂土液化的内外因,结合青银高速公路强夯处理案例展开分析,提出了处理方法。     

CONE模型与地基动力液化的非线性有效应力分析

在分析建筑物地基的地震（或振动）液化时,为了简化分析土壤-地基的动力相互作用,引入Cone模型,在总应力分析的方法基础上,结合了Martin等提出的孔隙水压力发展模型,并且考虑土壤发生液化的动力非线性过程中材料刚度退化的影响,提出了可以直接求解各区域的孔隙水压力的有效应力简化分析法,并进行液化可能性判别。     

复杂环境中大规模桩筏基础的优化设计方法研究

变刚度优化设计对于复杂环境中的大规模桩筏基础始终是一个重要难题。基于有限元分析提出一种两阶段优化设计方法,该方法首先根据传统均匀布桩方案的桩顶应力分布对群桩进行分区,然后依据每个子区域桩顶应力之间的关系确定基桩数量调整系数,最后通过调整桩间距来改变各子区域的基桩数量,从而实现变刚度优化设计。运用该方法对多层土体中承担非均匀上部结构荷载的大规模桩筏基础进行变刚度优化设计,计算结果表明优化设计后筏板的差异沉降、平均整体弯矩和群桩顶部的差异应力均显著降低。该方法计算简单,应用范围广,且不受复杂土层条件、非均匀上部结构荷载以及桩基础规模大小形状的限制。     

荷载作用下土体气压劈裂效果试验研究

采用自行研制的模型试验装置进行了不同喷气压力和上覆荷载下土体的气压劈裂室内模型试验,分析了喷气压力和上覆荷载对土体气压劈裂效果的影响。试验结果表明,向土体中喷入高压气体能在土体中产生裂隙,裂隙可加速超静孔隙水压的消散;喷气结束时裂隙宽度达到最大值,喷气结束后裂隙不完全闭合,残余裂隙宽度为裂隙宽度峰值的1/100。对比不同喷气压力和上覆荷载作用下气压劈裂试验结果发现,气压劈裂影响范围与裂隙宽度均和喷气压力与上覆荷载大小密切相关,其中喷气压力对气压劈裂影响范围与裂隙宽度的影响更为显著;气压劈裂影响范围与喷气压力呈双曲线相关关系,裂隙宽度与喷气压力呈线性正相关关系;气压劈裂影响范围随上覆荷载增加而减小,裂隙宽度与上覆荷载呈线性负相关关系     

波浪作用下饱和砂质海床土体与管线相互作用规律研究

针对波浪引起的饱和砂质海床土体和管线相互作用问题,将Biot动力固结理论与笔者课题组提出的砂土液化变形弹塑性本构模型相耦合,较为合理地再现了简谐波浪作用下较浅饱和砂质海床中管线周围可液化海床土体的超静孔隙水压力瞬态累积变化规律与液化过程。数值计算结果与Sumer等的试验规律一致。结果表明：由于管线的存在,改变了饱和砂质海床液化区域的空间分布。液化首先由管线下部土体开始产生,随着波浪荷载的持续作用,液化区域沿着管线外壁向上演化;同时海床表层土体产生液化并向深层发展,最终管线周围土体都发生液化,这是导致空管上浮的主要原因。当饱和砂质海床中存在管线时,管线附近海床土体液化深度明显变深。超静孔压累积和渗透力变化的耦合作用是导致饱和砂质海床土体产生液化的原因。与将海床土体视为饱和弹性多孔介质相比,可考虑液化全过程的弹塑性动力分析能更为合理地揭示实际波浪作用下饱和砂质海床土体的渗流场和应力场的瞬态时空演变规律。     

液化土层地震动模拟计算方法及验证

针对目前土层反应分析方法难以模拟液化土层地震动时程的缺欠,在工程力学研究所原有有效应力分析程序基础上提出了一个改进的计算方法并进行了验证。改进方法中,通过每个应力循环模拟土的非线性进程以及液化导致的土刚度衰减过程,并引入了新建立的适于非均等固结随机地震荷载作用下的孔压增长模型。将计算方法与实际地震记录及大型振动台实验结果进行了对比,结果表明：在峰值加速度、液化后波形变化、时频曲线及加速度反应谱等主要特征上,计算结果均与现场实际记录及振动台实验基本一致;在液化引起地震动特征变化上,计算出的液化较非液化土层加速度反应谱的增量与实验结果一致。说明所提出的改进方法可以用于液化土层地震动的模拟。     

饱和层状砂土液化特性的动三轴试验研究

利用GDS动三轴试验系统采用等幅循环应变加载方式对含有不同厚度粉土的饱和层状砂土进行了液化强度试验。分析了均匀砂和含有不同粉粒层厚度的层状砂土在循环荷载作用下的变形和力学特性。试验分析表明：由于含粉粒夹层的层状土特殊的土体结构,其孔隙水压力发展规律与一般的无黏性砂土不同;饱和层状砂土的抗液化强度并不是随着粉粒层厚度的增加而单调增加的,而是存在一个临界点;液化临界剪应变的大小与液化判别标准和循环次数有很大关系。试验结果表明,粉粒夹层对层状砂土的液化特性有很大的影响,且更能模拟自然环境条件下的层状砂土地基液化特性。     

挖填交界区格栅加筋路堤的试验和数值模拟分析

在对半挖半填路堤病害及成因分析的基础上,分析了加筋路堤格栅工作机制。通过现场试验,对采用格栅加筋法处理的路堤挖填交界区域进行了原位观测,观测了路堤填土完成时路面沉降、竖向土压力及格栅变形情况。通过建立有限元分析模型,对路堤填筑完成时格栅的拉力及位移进行了分析,并对不同路面荷载和格栅刚度条件下,格栅的拉力与位移进行了计算。结果表明：路堤挖填交界处铺设格栅后,路面局部差异沉降较小。填方区域格栅底部土压力与填土自重应力相当,格栅存在有效加筋长度,在挖填交界面附近产生较大变形和拉力。上层格栅比下层格栅沉降曲线平缓,下层格栅的拉力在交界区域会陡然增大。路面荷载对格栅拉力和位移有一定影响,随埋深增加影响减小,格栅的竖向位移随着荷载增大略有增大,格栅在挖填交界面附近拉力增大。随格栅刚度增大,其拉力也增大,而位移变化很小。     

大变形固结理论最终沉降量分析

大变形理论的力学机制较为严格,但由于其固有的复杂性和非线性,目前对大小变形理论计算的沉降量差别仍存在争议。基于连续介质力学基本原理,采用土力学符号约定推导了T.L.描述的大变形固结增量有限元方程组及其总应力分析形式。结合算例,分析了材料线性化和材料几何双线性化简化算法的影响,探讨了较合适的荷载增量步长,讨论了大、小变形法计算的最终沉降量差别。结果表明,荷载增量步长对两种线性化法计算结果较为敏感;大变形法计算的沉降量偏大于小变形结果,这可能是由几何非线性问题的“拉压刚度不同”效应引起;初应力矩阵对最终沉降量有较大影响等。     

上海四平大楼加层的工程地质分析

结合上海四平大楼加层工作，根据该建筑物初建时与加层时的两次勘探资料，从工程地质角度，对加层中的砂土液化以及加层引起的建筑物附加变形问题进行了分析探讨。分析结果表明，软土地区建筑物本身荷载的长期作用，对于改善与提高地基土强度以及砂性土层的抗液化性能是非常有益的。     

Assessment of soil liquefaction potential based on numerical method- a case study of an urban railway project

Paying special attention to geotechnical hazards such as liquefaction in huge civil projects like urban railways especially in susceptible regions to liquefaction is of great importance. A number of approaches to evaluate the potential for initiation of liquefaction, such as Seed and Idriss simplified method have been developed over the years. Although simplified methods are available in calculating the liquefaction potential of a soil deposit and shear stresses induced at any point in the ground due to earthquake loading, these methods cannot be applied to all earthquakes with the same accuracy, also they lack the potential to predict the pore pressure developed in the soil. Therefore, it is necessary to carry out a ground response analysis to obtain pore pressures and shear stresses in the soil due to earthquake loading. Using soil historical, geological and compositional criteria, a zone of the corridor of Tabriz urban railway line 2 susceptible to liquefaction was recognized. Then, using numerical analysis and cyclic stress method using QUAKE/W finite element code, soil liquefaction potential in susceptible zone was evaluated based on design earthquake.     

大采高综放面区段煤柱合理留设研究

侧向支承压力分布、资源回收率以及煤柱和巷道的稳定性是大采高综放面区段煤柱宽度留设要兼顾的因素,为了确定大采高综放面区段煤柱宽度,以某矿8103面为工程背景,首先,采用理论计算和现场应力监测等方法确定大采高综放工作面倾向支承压力分布规律,得出应力降低区宽度约为8 m,原岩应力区为巷帮侧28 m外。其次,采用工程类比方法确定大采高综放工作面巷帮外侧煤体严重破裂区宽度约为4 m。最后,采用FLAC3D数值软件分析了下区段工作面回采时窄煤柱（6、8 m）和宽煤柱（28、30 m）的应力场、位移场及塑性区特征,获得不同煤柱宽度时巷道和煤柱力学特征。研究表明：当煤柱宽度6 m和8 m时,在采动支承压力下煤柱几乎无承载能力,且巷道变形量较大;当煤柱宽度28 m和30 m时,在采动支承压力下煤柱中央仍有一定的弹性核,煤柱保持稳定且巷道变形量较小。综合考虑资源回收、巷道稳定性、次生灾害控制等因素,确定大采高综放工作面区段煤柱宽度为28 m。     

Liquefaction Hazard Assessment of Earth Quake Prone Area: a Study Based on Shear Wave Velocity by Multichannel Analysis of Surface Waves (MASW)

The shear wave velocity (V_S) profile based on the dispersive characteristics of fundamental mode of Rayleigh type surface waves indicate underground stiffness change with depth as well as near surface stiffness. The most important utility of shear wave velocity (V_S) is to estimate the liquefaction hazard potential of an area particularly in seismically active region. Rayleigh type surface waves were utilized to estimate the velocity (V_S) of shallow subsurface covering a depth range of 30–50 m employing multichannel analysis of surface waves. The liquefaction hazard map predicts an approximate percentage of an area that will have surface manifestation of liquefaction during an earth quake. The surface wave data acquired in an earth quake prone region of Jabalpur (Seismic zone III), India, yields a velocity (V_S) range of 200–750 m/s corresponding to the subsurface depth of 30–35 m. The results were analyzed for possible liquefaction hazard in the study area and presented here besides the N values.     

液化土层上建筑物倾斜计算要点初步分析

地震中饱和砂土地基液化会引起结构物倾斜并导致其功能丧失,但目前缺乏相应的数值模拟方法。通过振动台简单模型试验,寻找输入波-基底竖向动应力-基底孔压-结构震陷之间的关系,提出发展液化土层上建筑物倾斜数值模拟方法所需要考虑的要点和应满足的条件。结果表明：（1）分析方法中孔压增长模型应适于不规则波计算,能准确地计算出孔压增长过程,准确地计算出峰值一样但不同波形下孔压增长的差别;（2）孔压增长模型应能反映土的各向异性特性对孔压增长的影响,能合理地计算出拉、压不同应力作用下孔压增长的差异;（3）孔压增长模型应能反映非均等固结条件对孔压增长过程的影响,能合理地计算出结构底部不同固结比土体中孔压增长过程;（4）分析方法中土体变形的计算应能跟踪液化过程中的变形发展,且具备大变形计算能力。     

Liquefaction analysis and soil improvement in Beydag dam

Beydag dam is under construction on Kucukmenderes River for irrigation purposes. Due to the scarcity of core material and liquefaction of alluvium at the dam site, the original design was changed to Roller Compacted Concete (RCC) from rockfill dam with claycore. Although the new design was safer, it nearly doubled the cost of the dam, so the owner, State Hydraulic Works of Turkey, (DSI) set out to find more economical but equally safe alternative. Since jet-grouting is a cheap ground improvement tool in Turkey, such an alternative was developed for the ground improvement against liquefaction together with concrete face rockfill dam sitting on top of improved ground. This paper presents a detailed discussion of how the new alternative was developed and evaluated: it discusses the determination of jet grouting pattern, the placement of jet grouted blocks, and the assesment of liquefaction. On one hand the soil cement strength of jetgrout columns, internal friction angle of alluvium and rockfill were important in determining the dimensions of the blocks, on the other hand the location of the blocks were highly affected by the areas where liquefaction occurred. One of the most important parameter that has a considerable influence in delineating the boundary betweeen liquefaction and non-liquefaction was the value of stress reduction coefficient (r _d), being primarily sensitive to the weight of overburden, which is calculated by the height from the face of dam to the depth where the calculation was made. This approach is justified by two-dimensional ground response analysis. Most importantly, this paper shows that there exists an alternative solution for building dams on the liquefaction prone sites without removing alluvium by using a well known jet grouting technique for improving ground at only selected places.     

深基坑竖向支承系统的侧向刚度研究

在逆作法深基坑围护结构体系支撑刚度计算中,通常认为结构自重及施工荷载均由竖向支承体系承担,而忽略了其横向承载能力,造成了工程上的浪费。本文对竖向支承体系所具有的侧向刚度进行研究,提供一种基于数值分析结果的侧向刚度的计算方法,可用于快速计算工程中各类立柱结构形式的侧向刚度。文章通过工程实例对不同形式下的钢管柱和格构柱结构体系的侧向刚度进行数值计算,给出相应的侧向刚度拟合计算式。分析表明拟合算式所得侧向刚度略大于数值计算所得,误差在2.50%~9.26%之间,根据拟合算式计算排架结构的侧向刚度能够满足围护结构分析的要求。本文提出的侧向刚度计算方法可靠,能够用于类似工程,可供深基坑工程设计、施工人员参考。     

基于自组织神经网络的砂土液化评价

在分析自组织特征映射(SOFM)神经网络基本学习算法的基础上,从提高算法收敛速度和性能出发,提出了一种改进算法:根据实际应用并结合专家经验确定初始连接权值;采用高斯函数作为拓扑邻域函数;将算法分为粗调整和细调整两个阶段,分别采用不同的学习率和邻域函数,然后采用改进后的SOFM算法对砂土液化进行评价。实例研究表明,应用SOFM神经网络评价砂土液化高效可行,为砂土液化评价提供了新方法。     

Criterion for flow liquefaction instability

This study describes a general liquefaction flow instability criterion for elastoplastic soils based on the concept of loss of uniqueness. We apply the criterion to the general case of axisymmetric loading and invoke the concepts of effective stresses and loss of controllability to arrive at a general criterion for the onset of liquefaction flow. The criterion is used in conjunction with an elastoplastic model for sands to generate numerical simulations. The numerical results are compared with experimental evidence to give the following insights into predicting liquefaction. (1) The onset of liquefaction flow is a state of instability occurring under both monotonic and cyclic tests, and coincides with loss of controllability. (2) The criterion proposed herein clearly and naturally differentiates between liquefaction flow (instability) and cyclic mobility. (3) Flow liquefaction not only depends on the potential of the material to generate positive excess pore pressures, but more importantly, it also depends on the current state of the material, which is rarely predicted by phenomenology.