共查询到19条相似文献，搜索用时 546 毫秒
1.
层状饱水软土地基三维非轴对称动力响应分析方法 总被引：1，自引：0，他引：1
将饱水软土地基视为两相介质、考虑水的渗流和土骨架9变形的耦合作用，用Fourier展开和Hankel积分变换分析三维非称对称饱和弹性土层波动方程，用刚度矩阵方法，建立了层状饱和软土地基三维非轴对称动力响应的解析分析方法。以数值算例对比分析了单相土介质与两相饱和土介质三维非轴对称稳态动力响应，结果表明：在饱水软土地基动力响应分析中应该考虑土体中孔隙流体的影响。 相似文献
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双控动力固结法加固软粘土地基的应用研究 总被引：1，自引：0，他引：1
饱和软粘土含水率大、渗透性差,强夯处理时,超孔隙水压力不易消散,常规的排水措施效果不佳,而电渗降水已经被证明是一种有效的软粘土排水措施。本文提出了将电渗降水和强夯法相结合的地基处理方法——双控动力固结法,进行了双控动力固结法的处理试验,并与不降水强夯法和井点降水强夯法进行对比分析。结果表明,电渗法可迅速降低地下水位和地基土含水量,有效避免“弹簧土”的产生,提高单点夯最佳夯击能;可有效抑制夯后超孔隙水压力的急剧上升,并促进超孔隙水压力快速消散;在降水速度和土性改良方面,电渗降水优于井点降水。因此,应用双控动力固结法处理软粘土,有着很显著的加固效果。 相似文献
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采用2.5维有限元方法分析孔隙水压力对饱和路基地面振动的影响。根据Biot理论建立饱和多孔介质控制方程,采用双重Fourier变换将控制方程转换为频率 波数域表达式。采用2.5维有限元方法建立饱和路基模型,列车荷载在频率 波数域表示,轨道和路堤采用欧拉梁模拟,采用黏滞阻尼吸波边界减小有限元边界反射。分析列车速度、路基孔隙率和渗透系数对地面振动和孔隙水压力的影响。结果表明：车速较低时,由于饱和路基受孔隙水压力的影响,地面竖向振幅小于弹性地基;车速较高时,孔隙水压力急剧增加,对地面振动影响较大。列车运行速度较高时,饱和地基的孔隙率和渗透系数对孔隙水压力有较大影响。 相似文献
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以天津港北港池码头地区海相沉积软土为研究对象,自行研制了与CT配套的单轴固结装置,取不同深度的土样分别进行单轴固结实验。逐级加载土样固结后,对土样进行CT扫描,结合CT图像分析软土固结过程中特性变化。研究表明:随着压力的增加,CT图像灰度平均值逐渐增大,说明土样被压实,密度增大;固结过程中,不同种类土样的CT图像标准差变化存在差异性,这与孔隙水压力消散引起土样内部结构的变化有关;引入CT图像灰度压缩系数来反映土样的压缩性能,研究结果表明天津港北港池码头软土具有较高的压缩性。 相似文献
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以天津港北港池码头地区海相沉积软土为研究对象,自行研制了与CT配套的单轴固结装置,取不同深度的土样分别进行单轴固结实验.逐级加载土样固结后,对土样进行CT扫描,结合CT图像分析软土固结过程中特性变化.研究表明:随着压力的增加,CT图像灰度平均值逐渐增大,说明土样被压实,密度增大;固结过程中,不同种类土样的CT图像标准差变化存在差异性,这与孔隙水压力消散引起土样内部结构的变化有关;引入CT图像灰度压缩系数来反映土样的压缩性能,研究结果表明天津港北港池码头软土具有较高的压缩性. 相似文献
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新吹填土含泥量大、含水率大、渗透性差、零承载力,常规地基处理工法无法开展,地基处理面临诸多困难。针对该问题,提出了复式负压固结技术,该技术包括3道工序：改性真空预压、电渗降水和强夯动力固结。改性真空预压使地基得到初步固结,具备一定强度,为后序工作做准备;电渗降水可有效降低夯前地下水位和土体含水率,并促进夯后超孔隙水压力的消散;电渗降水和强夯动力固结多遍耦合,共同对吹填土进行地基加固。现场开展了复式负压固结技术工艺试验、土性试验和沉降变形监测。结果表明,应用于吹填泥的地基处理,改性真空预压可快速提高承载力,电渗法可迅速降低地下水位,有效避免强夯时＂弹簧土＂现象的发生,从而提高了最佳夯击能。复式负压固结技术可以有效地应用于新吹填软土地基。 相似文献
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复杂应力条件下松砂振动孔隙水压力与体变特性的试验研究 总被引：5，自引：2，他引：3
利用新研制的土工静力-动力液压三轴-扭转多功能剪切仪,在5种初始主应力方向角与5种中主应力系数相组合的初始固结条件下,对饱和松砂进行了不排水循环扭剪试验。讨论了初始固结条件对不排水条件下饱和松砂孔隙水压力变化规律及对剪胀、剪缩、卸荷体缩等体积变化过程的影响。试验研究表明：（1）分别以稳定残余孔隙水压力和破坏时循环次数归一化后的残余孔隙水压力比和循环次数比之间的关系可以用双曲线模式表达。其参数主要依赖于初始主应力方向,中主应力系数对参数的影响并不显著。归一化后的孔隙水压力比与广义剪应变之间的关系也可以用双曲线模式表达,其中的2个待定参数依赖于初始主应力方向,与中主应力系数无关;（2）在三向非均等固结条件下的不排水循环扭剪试验中,饱和松砂表现出卸荷体缩特性,不同初始主应力方向时,饱和松砂剪缩、剪胀、卸荷体缩呈现出不同的交替变化模式。 相似文献
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地基液化导致沉箱码头破坏及地基加固方法的非线性数值分析 总被引：2，自引：0，他引：2
地震作用引发的地基液化,往往导致沉箱基础的破坏。本文基于Biot两相饱和多孔介质动力耦合理论,采用FE-FD耦合数值分析方法,对液化海床沉箱基础的地震反应进行非线性有效应力分析。在数值分析过程中,建立了以土骨架位移和超静孔隙水压力表达的us-pw动力固结方程和循环弹塑性本构模型,该方法能够很好地模拟地震作用下沉箱码头的动力特性及液化破坏的影响。通过数值模拟计算,分析了采用碎石桩进行置换砂区域的防液化加固方法,并就碎石桩处理区域的选择提出了建议。 相似文献
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在长456 m、宽5 m、深8~12 m的实验水槽建立了模型与原型比尺为1∶5的模拟波浪—半圆型防波堤结构—软土地基实际工作状态的物理模型实验系统,开展了设计高低水位、不同波高和波浪作用循环次数作用下半圆型防波堤结构稳定性实验研究。通过对实验测试数据分析,得出半圆型防波堤软土地基孔隙水压力的变化规律,孔隙水压力发展趋势分为四种类型。从结构安全不利角度选取增长型曲线进行数据拟合,得到半圆型防波堤下软土地基对数型的最大孔隙水压力发展模型。 相似文献
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Seismic passive resistance with vertical seepage and surcharge 总被引：1，自引：0，他引：1
Jun-Jie Wang Hui-Ping Zhang He-Jun Chai Jun-Gao Zhu 《Soil Dynamics and Earthquake Engineering》2008,28(9):728-737
Present paper focuses on the computation of the seismic passive earth pressure acting on a vertical rigid retaining wall by a soil mass subjected to vertical steady-state seepage and a uniform surcharge load. Based on the basic assumptions of Coulomb's theory and a pseudo-static method of analysis, a general solution for the passive earth pressure containing two coefficients is presented. In the solution, many parameters, such as unit weight of saturated soil, soil effective internal friction angle, soil/wall friction angle, water/soil unit weight ratio, surcharge intensity coefficient, horizontal and vertical seismic acceleration coefficients, Poisson's ratio of soil mass, hydraulic gradient, and coefficients of pore water pressure, are considered. The effects of hydraulic gradient and seismic forces on passive earth pressure coefficient and passive earth pressure distribution are investigated. The results indicate that passive earth pressure increases with increasing hydraulic gradient for downward water flow case, but decreases for upward water flow case, and that the presence of seismic forces induces a reduction in passive earth pressure. 相似文献
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前人曾指出液化后伴随着超孔隙水压重新分配的渗透会引起流体破坏的可能性。为了研究这一现象,利用实验室三轴试验将孔隙水注入土壤检测了土壤的渗透剪切破坏。该实验是在各项异性的固结作用后保持差应力,使用孔隙水控制装置在体积不变的应变控制条件下将孔隙水注入。实验中所用的材料是在1995年神户地震时被液化的常规洁净细砂和风化的花岗岩土壤。本文以实验结果为基础,讨论了由孔隙水注入引起的渗透剪切破坏判据和导致后液化行为的剪切应变发展特征。 相似文献
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Several mechanisms contribute to streambank failure including fluvial toe undercutting, reduced soil shear strength by increased soil pore‐water pressure, and seepage erosion. Recent research has suggested that seepage erosion of noncohesive soil layers undercutting the banks may play an equivalent role in streambank failure to increased soil pore‐water pressure. However, this past research has primarily been limited to laboratory studies of non‐vegetated banks. The objective of this research was to utilize the Bank Stability and Toe Erosion Model (BSTEM) in order to determine the importance of seepage undercutting relative to bank shear strength, bank angle, soil pore‐water pressure, and root reinforcement. The BSTEM simulated two streambanks: Little Topashaw Creek and Goodwin Creek in northern Mississippi. Simulations included three bank angles (70° to 90°), four pore‐water pressure distributions (unsaturated, two partially saturated cases, and fully saturated), six distances of undercutting (0 to 40 cm), and 13 different vegetation conditions (root cohesions from 0·0 to 15·0 kPa). A relative sensitivity analysis suggested that BSTEM was approximately three to four times more sensitive to water table position than root cohesion or depth of seepage undercutting. Seepage undercutting becomes a prominent bank failure mechanism on unsaturated to partially saturated streambanks with root reinforcement, even with undercutting distances as small as 20 cm. Consideration of seepage undercutting is less important under conditions of partially to fully saturated soil pore‐water conditions. The distance at which instability by undercutting became equivalent to instability by increased soil pore‐water pressure decreased as root reinforcement increased, with values typically ranging between 20 and 40 cm at Little Topashaw Creek and between 20 and 55 cm at Goodwin Creek. This research depicts the baseline conditions at which seepage undercutting of vegetated streambanks needs to be considered for bank stability analyses. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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循环荷载作用下饱和砂土的孔压增长规律是土动力学的核心内容之一。基于笔者在给定相对密度、均等固结条件下饱和南京细砂的不排水等幅循环三轴试验结果建立的孔压增量模型,进一步进行了不同相对密度、不同固结比条件下饱和南京细砂的不排水等幅循环三轴试验,将上述均等固结的孔压增量模型拓展为适用于不同相对密度、均等和非均等固结条件的孔压增量模型。采用拓展后的孔压增量模型对试验结果进行分析的结果表明：通过该孔压增量模型预测验证试验的孔压与验证试验测试的孔压具有较好的一致性,说明该孔压增量模型具有普适性。 相似文献
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对某软土重塑样分别进行等向固结和K0固结条件下的三轴试验,研究了不同固结条件、不同围压下软土的强度和应力应变特性,并对试验结果进行了分析和对比。结果表明：低围压下,等向固结三轴压缩试验和K0固结三轴压缩试验土样破坏时的主应力差差别不大,随着围压增大,K0固结条件下试验土体的主应力差要明显大于等向固结条件下的试验土体;与等向固结相比,K0固结条件下的土体粘聚力c值减小,而内摩擦角增大;土体呈现剪缩特性。运用等向固结三轴压缩试验确定的邓肯模型参数模拟K0固结条件下土体的试验曲线,吻合较好,初步验证了邓肯模型参数对K0固结土体的适用性。 相似文献
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Seepage driving effect on deformations of San Fernando dams 总被引：2，自引：0，他引：2
In the process of flow deformation of an earth dam, the seepage force inside the dam plays a role as a driving force. The seepage force acts just like the gravitational force in terms of pushing soils away from their original locations after liquefaction is triggered. This paper draws attention to this seepage driving effect by presenting a set of fully coupled finite element analyses on the well-known San Fernando dams, with the objective of evaluating the impact of this seepage effect. The results indicate that while this effect is always there, its practical significance depends on a number of factors. In the case of the upper San Fernando dam, which experienced a significant, but restricted, downstream movement during the 1971 earthquake, the seepage driving effect was indeed significant. On the contrary, for the lower dam, which failed and slid into the upstream reservoir during the same earthquake, this seepage effect was relatively less pronounced. The detailed results of the analyses reveal the likely mechanisms of failure and deformation of the two dams and the likely cause behind the difference between their responses during the earthquake. 相似文献
18.
Tomomi Terajima Ei‐ichiro Miyahira Hiroyuki Miyajima Hirotaka Ochiai Katsumi Hattori 《水文研究》2014,28(23):5711-5724
Knowledge of the mechanisms of rain‐induced shallow landslides can improve the prediction of their occurrence and mitigate subsequent sediment disasters. Here, we examine an artificial slope's subsurface hydrology and propose a new slope stability analysis that includes seepage force and the down‐slope transfer of excess shear forces. We measured pore water pressure and volumetric water content immediately prior to a shallow landslide on an artificial sandy slope of 32°: The direction of the subsurface flow shifted from downward to parallel to the slope in the deepest part of the landslide mass, and this shift coincided with the start of soil displacement. A slope stability analysis that was restricted to individual segments of the landslide mass could not explain the initiation of the landslide; however, inclusion of the transfer of excess shear forces from up‐slope to down‐slope segments improved drastically the predictability. The improved stability analysis revealed that an unstable zone expanded down‐slope with an increase in soil water content, showing that the down‐slope soil initially supported the unstable up‐slope soil; destabilization of this down‐slope soil was the eventual trigger of total slope collapse. Initially, the effect of apparent soil cohesion was the most important factor promoting slope stability, but seepage force became the most important factor promoting slope instability closer to the landslide occurrence. These findings indicate that seepage forces, controlled by changes in direction and magnitude of saturated and unsaturated subsurface flows, may be the main cause of shallow landslides in sandy slopes. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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固结试验是研究软土动力特性的重要环节,固结时间是影响软土动力特征参数的重要因素。围绕岩土工程及科研工作中对动三轴试验中固结时间影响规律的认识较为模糊的问题,拟对天津滨海软土开展动三轴平行试验,分别采用8h、12h、24h、48h进行固结,针对软土的最大动剪切模量Gmax、最大阻尼比λmax及动剪切模量比Gd/Gmax和阻尼比λ随动剪切应变γd的变化规律,分析固结时间对软土动力特性参数的影响。试验结果表明:Gmax、λmax、Gd/Gmax-γd曲线、λ-γd曲线受固结时间的影响较为显著。Gd/Gmax-γd曲线随着固结时间的增加而减小。阻尼比试验结果表明动剪切应变存在明显的分界点,分界点以下,中长期固结时间所得阻尼比较大,而分界点以上,短期固结时间所得阻尼比较大。 相似文献