共查询到19条相似文献，搜索用时 156 毫秒
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在实际工程中,常见天然的或通过人工换填形成的上部砂土、下部黏土的层状地基,目前关于这种双层地基极限承载力和破坏机制研究还不够深入。通过有限差分法建立双层地基数值模型,分析基底粗糙程度、砂土剪胀角和超载对地基破坏模式及极限承载力的影响,并根据有限差分法计算结果对强度加权平均法、应力扩散法和冲剪破坏法等现有实用计算方法的估算正确性进行评价。研究结果表明,基底粗糙程度对极限承载力的影响随着砂土内摩擦角的增大而减小;当剪胀角较小时,剪胀角变化对承载力的影响更为明显;当下层黏土强度较小时,超载的作用更明显。强度加权平均法由于低估破坏面影响深度导致砂土层权重较大,计算结果偏大;应力扩散法忽略了砂土剪切强度,在砂土层较厚时出现低估;冲剪破坏法由于可较为精确地计算砂土破坏面上抗剪强度和被动土压力,是3种实用方法中计算最准确的,当砂土厚度和黏土强度较大时,建议按太沙基经验公式对下卧黏土进行局部剪切破坏修正后确定极限承载力。 相似文献
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利用极限分析上限法求解地基极限承载力问题的关键在于构造合适的破坏模式。当地基下方存在空洞时,地基的破坏模式变得相当复杂。通过分析空洞存在时地基的受力特点及破坏形态,将地基破坏范围划分成为不同的刚性区和过渡区,构造了空洞上方条形基础地基的破坏模式。利用上限法,建立与破坏模式对应的速度场,推导了破坏模式不同区域内的耗散功率和外力功率,得到地基极限承载力的目标函数,并采用数学优化方法进行求解,获得了极限承载力的上限解。通过算例分析,讨论了空洞顶板厚度、空洞大小与地基极限承载力的关系,并与无空洞条件下地基极限承载力进行对比分析。结果表明,随着空洞顶板厚度增加,地基极限承载力增加,破坏模式也由地基与空洞之间扩散到地基两侧;空洞顶板厚度存在临界值,当超过此临界值时,空洞对地基极限承载力的影响可忽略。 相似文献
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临坡地基已成为一种广泛的地基形式。针对临坡条形基础地基破坏模式的非对称性特点,首先引进双侧破坏模式的研究思路,重点考虑临坡地基基础两侧滑块大小和同一滑块几何形状的双重非对称性特征,构建了临坡条形基础地基非对称双侧破坏模式,为临坡地基承载力分析奠定了坚实基础;然后在此基础上,引进极限上限分析和优化理论,建立了临坡条形基础地基承载力分析的模型与方法,该方法不仅可考虑地基破坏模式,还可考虑基础与坡顶距离对临坡地基承载力的影响,而且还可较好地蜕化为平地地基承载力的分析;最后通过工程实例计算,并与现有相关分析方法进行对比分析,表明该方法的可行性与合理性以及普遍适用性。 相似文献
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断层、滑坡、液化等地质灾害引起的场地大变形对埋地管道结构安全产生严重的威胁。开展了中密砂中埋地管道−砂土水平横向相互作用的系列三维数值模拟,根据数值模拟的结果探讨了不同深径比下管−砂土横向相互作用时土体的破坏模式,研究了深径比对砂土极限承载力的影响。基于管周土体的破坏模式建立了简化计算模型,根据极限平衡理论推导了管道水平横向运动时砂土极限承载力计算公式。研究结果表明：极限状态下,浅埋管道周围土体形成延伸到地表的破裂面,轮廓线近似对数螺线;砂土的极限承载力随着深径比增加,最终在临界深径比处达到稳定;随着深径比的增加,土体发生剪切滑动破坏所需的管道位移也逐渐增大;由于横向承载力系数取值依据不同,国内外规范计算所得土体极限承载力差异较大;得到的解析解能够较好地预测中密砂土中浅埋管道水平横向运动时土体的极限承载力。 相似文献
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含下卧软层地基极限分析数值试验及承载力安全性研究 总被引：2，自引：0，他引：2
含下卧软层的地基在工程中比较常见,但目前对其破坏机制和承载力计算还依赖于很多的假设条件和经验。基于极限分析和快速拉格朗日数值模拟方法,对含下卧层地基的加载破坏过程进行应变控制的数值试验。首先用Prandtl的极限承载力解析解验证了数值试验的有效性,然后对一个含下卧层的地基模型按照不同加载尺寸进行加载数值试验,发现模拟结果存在明显的荷载尺寸效应。模拟获得不同荷载条件下的极限承载力以及相应的应力-应变曲线、渐进破坏模式、下卧软层的沉降规律。进一步将下卧层的地基承载力加载安全系数与强度折减系数进行对比,发现折减系数与加载系数随荷载尺寸变化的趋势相同,但前者的数值偏小。 相似文献
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软弱土层上的压实填土地基作为一种非均质地基广泛应用,但目前关于这种地基的破坏模式和承载力机制的研究还不够深入,工程中仍采用现行规范深度修正系数取值为2的方式进行设计。采用有限差分方法建立数值模型,研究了影响压实填土地基承载力深度修正系数的因素,并与现行规范推荐方法的取值进行对比。结果表明：填土越深、基础外超载越大,参与地基剪切破坏运动的土体体积越大,地基极限承载力越高;而随着填土宽度的增大,地基极限承载力先提高,后趋于稳定;砂土内摩擦角的增大也会提高地基极限承载力。总体来说,规范中的推荐值是偏于保守的,会造成承载力的浪费;而在下卧层强度很小、填土深度较大时该推荐值可能高估压实填土地基承载力,存在偏于不安全的可能,在工程设计时应予以考虑。 相似文献
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局部剪切破坏模式下的无重地基承载力 总被引：1，自引：0，他引：1
局部剪切破坏是一种常见的地基破坏模式,该破坏模式下的地基承载力理论计算方法尚不完善,对无重地基局部剪切破坏的极限承载力理论进行了研究。首先从破坏时破裂面延伸位置的角度完善了浅基础3种破坏模式的划分标准。对于局部剪切破坏,土体强度并未完全发挥出来,潜在破坏区处于非极限状态,所以将土体强度逐渐发挥的概念引入地基承载力中,通过适当的假设,建立了局部剪切破坏模式下无重介质地基承载力的理论计算方法,并与已有的经典成果进行比较分析,印证了该方法的合理性。研究成果为解决局部剪切破坏模式下地基承载力的计算提供了理论参考。 相似文献
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为了对加筋砂土挡墙面板的刚度效果有一个合理、定量的把握,利用非线性硬化-软化弹塑性有限元方法对相关的一系列室内模型试验结果进行了系统全面的数值分析。有限元解析中所采用的砂土本构模型是以修正塑性功为基本状态量的弹塑性硬软化模型,该模型可以较为精确地模拟砂土的应力路径效应。结果表明,利用这种较高精度的有限元方法对加筋砂土挡墙的变形破坏进行解析,不仅能较好地模拟加筋砂土挡墙基础底面的平均压力与沉降之间的关系,同时也能较好地再现由于面板刚度变化对加筋砂土挡墙基础的承载力以及渐进性变形破坏的影响。随着面板刚度的增加,面板对剪切带的抑制作用将随之增加,具体表现在砂土围压σ3增大所带来的砂土强度σ1的提高,进而使得加筋砂土挡墙的峰值承载力也随之增大。 相似文献
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复合加载情况下精确求解非均质地基上条形基础的极限承载力以及评价影响极限承载力的相关因素,具有很强的工程实用与理论参考价值。基于极限平衡原理,在Mohr-Coulomb破坏准则的基础上,将非均质地基上条形基础极限承载力问题等价为一个边界待定的泛函极值问题。利用变分原理得到与平衡方程相等价的积分约束条件以及相应的欧拉方程与横截条件。引入问题边界条件,利用VC++6.0编制了数值计算程序,求得了复合加载情况下非均质地基破坏时的滑裂面函数与破坏包络曲线。从理论上研究了土体内摩擦角、土体黏聚力、土层强度比与地下水位变化等因素对地基破坏包络曲线的影响。研究结果表明,其解答是地基极限承载力真实解的某一最小上限。 相似文献
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Ahmad Safuan A. Rashid Mohammad Gharehzadeh Shirazi Hisham Mohamad Fauzan Sahdi 《Environmental Earth Sciences》2017,76(12):431
Bio-based materials are widely used recently in order to introduce a more sustainable construction material. Kenaf is a type of bio-based material that can be easily obtained in a tropical country, which could be a potential material to be utilised as a geotextile material because it has good tensile strength. The geotextile could be used to improve the bearing capacity of a loose soil. This paper presents a series of small-scale physical modelling tests to investigate the bearing capacity performance of Kenaf fibre geotextile laid on and inside the sand layer. A rigid footing was used to replicate a strip footing during the loading test, and sand was prepared based on 50% of relative density in a rigid testing chamber for ground model preparation. In order to treat the soil, Kenaf fibre geotextile was laid at four difference locations which are on the soil surface and underneath the ground model surface at 50, 75 and 100 mm deep. It was found that the usage of the Kenaf fibre geotextile has improved the bearing capacity of the sandy soil up to 414.9% as compared to untreated soil. It was also found that the depth of the Kenaf fibre geotextile treated into the soil also affects the soil performance. 相似文献
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Reliability analysis of bearing capacity of a strip footing at the crest of a simple slope with cohesive soil was carried out using the random finite element method (RFEM). Analyses showed that the coefficient of variation and the spatial correlation length of soil cohesion can have a large influence on footing bearing capacity, particularly for slopes with large height to footing width ratios. The paper demonstrates cases where a footing satisfies a deterministic design factor of safety of 3 but the probability of design failure is unacceptably high. Isotropic and anisotropic spatial variability of the soil strength was also considered. 相似文献
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Bearing Capacity of Strip Footings Near Slopes 总被引：2，自引：1，他引：1
In the last decades a great attention was given by many authors to the evaluation of the static and seismic bearing capacity
of footings near slopes. In this paper a model has been developed based on the limit equilibrium method, considering a circular
surface propagates towards the slope until the sloping ground is reached. The bearing capacity is investigated considering
either the distance of the footing from the edge of the slope and/or the effect of the footing embedment. A validation of
the proposed model was made by a comparison with solutions taken from literature regarding the evaluation of the bearing capacity
for a footing adjacent to a slope and for an inclined load. The loading conditions consist in vertical and horizontal stress
on the footing and on the soil below the footing. Both the inertial and kinematic effects of the seismic loading have been
analyzed, and a simple equation has been derived for the evaluation of the seismic bearing capacity. The static and seismic
bearing capacity has been investigated as a function of the soil friction angle, of the seismic coefficient, of the sloping
ground. Finally, the influence of the distance of the footing from the edge of the slope was taken into consideration in the
evaluation of the bearing capacity, and a threshold distance at which the reduction of the bearing capacity due to the sloping
ground vanishes has been defined. 相似文献
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Bearing Capacity of Embedded Strip Footings on Cohesionless Soil Under Vertical and Horizontal Loads
Hadjer Yahia-Cherif Abdelhak Mabrouki Djamel Benmeddour Mekki Mellas 《Geotechnical and Geological Engineering》2017,35(2):547-558
In the last decades a few attention was given to the evaluation of the bearing capacity of embedded footing under inclined loads on a frictional soil. This paper focuses on a numerical study using the finite-difference code Fast Lagrangian Analysis of Continua (FLAC), to evaluate the bearing capacity of embedded strip footing on a frictional soil. The soil is modeled by an elasto-plastic model with a Mohr–Coulomb yield criterion and associative flow rule; the effect of non-associativity of the soil on the bearing capacity is also investigated. The effect of the embedment is estimated though a depth factor, defined as a ratio of the bearing capacity of a strip footing at a depth D to that of a strip footing at the ground surface. The inclination effect is estimated by inclination factors, defined as the ratio of the limit vertical load for a footing under inclined loading to that of the vertically loaded footing. Both swipe and probe analyses were carried out to identify the vertical force–horizontal force (V–H) failure envelope. The results have been compared with those available in the literature. 相似文献
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建筑物或构筑物基础临近边坡置放的情况在实际工程中十分普遍,但目前对于临近边坡基础的地基承载力及破坏模式尚缺乏深入研究。采用不连续布局优化（DLO）极限分析法建立数值模型,分析边坡几何尺寸、土体参数和基础位置对临坡条形基础的极限承载力和边坡破坏模式的影响,并对国内外现行规范推荐的计算方法进行评价。结果表明：极限承载力随边坡高度和边坡倾斜角的增大而减小,当坡高超过临界高度后,极限承载力将不受其影响;极限承载力随土体黏聚力和内摩擦角的增大而提高,滑动面随黏聚力的增大而变浅,随内摩擦角的增大而变深;极限承载力随基础与坡肩相对距离的增大而提高,当基础置放位置超过某临界距离后极限承载力不受边坡影响。在土体强度高、坡角较大时,《建筑地基基础设计规范》规定的临坡基础最小置放距离偏于危险,设计时仍需考虑边坡对承载力的减损作用;在土体强度较低、坡角较小时,规范规定值偏于保守。美国AASHTO规范对边坡地基极限承载力的取值在砂土边坡时较为可靠,但其仅适用于坡面破坏模式的情况;饱和黏土边坡的承载力曲线有悖于理论解,对临界距离的规定同样存在低估。 相似文献
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Jin-chun Zhan Xiao-song Guo Yun-feng Fei Zheng-yang Chang 《Geotechnical and Geological Engineering》2013,31(2):713-718
Classical bearing capacity expressions can not afford variant engineering requests, since they were deducted under hypotheses of strip footing on homogeneous soil. An often met case was taken into account that circular footing on two-layered ground, which has firm crust and weak subgrade. Weighted method and layered method were used in capacity deduction, respectively. The former counts layered soils as single layer of weighted structure and material parameters. But it is restricted to conditions with close strength to each layer. The latter is preferred in engineering calculation, which regards the whole bearing capacity as subgrade’s capacity under the influence of the upper layer. Thus the issue is transformed to K. Terzaghi model plus stress reduction and dispersion effects. At last, the expressions gained from both methods and finite element analysis (FEA) were used in an example calculation, respectively. It approves layered calculating method and suggests the corresponding security coefficient based on elastoplastic FEA results. 相似文献
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Hamed Gholami Ehsan Seyedi Hosseininia 《Geotechnical and Geological Engineering》2017,35(5):2137-2146
Ring footings can be more effective and economical than circular footings. In spite of similarities between circular and ring footings, their behaviors are different in some respects such as bearing pressure distribution under the footing and settlement. But no exclusive theoretical prediction of ultimate bearing capacity has been reported for ring footings. In the present study, stress characteristics method is employed for coding the bearing capacity of ring footing with horizontal ground surface. In the calculations, friction at the contact between the soil and foundation is considered. In this research, the soil obeys the Mohr–Coulomb yield criterion and that is cohesive–frictional-weighted with applied surcharge pressure. The bearing capacity factors Nγ, Nq and Nc for ring footings were calculated by a written code based on the method of characteristics. Bearing capacity was determined for different conditions of soil and different ratio of radii in comparison with the principle of superposition results. The findings show that the principle of superposition is effective for determining the bearing capacity of a ring footing. 相似文献
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