桩基负摩阻力时间效应试验研究   总被引：2，自引：0，他引：2  

黄挺  龚维明  戴国亮  郑金海  徐国平 《岩土力学》2013,34(10):2841-2846

由于黏土固结缓慢,桩基负摩阻力存在明显的时间效应,然而目前相关研究仍显不足。设计实施了能实现桩顶加载及较大超载值的单桩及双桩负摩阻力模型试验,桩周土采用砂土和软黏土夹层,测定了模型桩身应力、桩顶位移以及土体分层沉降随固结时间的变化。试验结果显示,沉降、负摩阻力具有明显的时间效应。土表超载作用下土体沉降带动桩沉降,桩与土体的沉降均表现出早期快、后期慢的趋势。试验加载初期,黏土夹层处的负摩阻力略小于砂层,但随土体固结而增长,其基本变化规律与沉降相同。因桩端砂土层沉降稳定迅速,中性点随桩身沉降增长略呈上移趋势。此外,相同荷载作用下桩间距较小的双桩,由于下拉力较小,其沉降较小。试验条件下,3D桩间距的负摩阻力群桩效应系数在0.71～0.77之间,6D桩间距时不存在负摩阻力群桩效应。  相似文献   

饱和黏弹性地基土中管桩纵向振动研究   总被引：1，自引：0，他引：1  

应跃龙  罗海亮  闻敏杰 《岩土力学》2013,34(Z1):103-108

用解析方法在频率域内研究考虑质量耦合效应的饱和黏弹性地基土中管桩的纵向振动特性。基于Biot理论,采用薄层法,推导得到饱和黏弹性地基土的位移、应力等的表达式。将管桩等效为一维弹性杆件处理。根据界面连续性条件,给出饱和黏弹性地基土中管桩的纵向振动一般分析方法和桩顶动力复刚度的表达式。在该基础上,对比分析饱和地基土中实心桩和管桩纵向振动特性。通过算例分析,考察桩周土和桩芯土的力学参数对桩顶刚度因子和等效阻尼的影响。研究表明,饱和黏弹性地基土中实心桩和管桩的纵向振动有明显的差异。  相似文献   

多排抗滑桩治理工程的有限元设计计算与优化   总被引：2，自引：0，他引：2  

唐晓松  郑颖人  邱文平 《地震学刊》2011,(5):548-554

在现行计算方法中,通常采用不平衡推力法等传统方法设计抗滑桩。尽管国内外岩土工程技术人员通过研究使传统算法取得了较大的进展,但仍有许多不完善的地方,特别对于多排抗滑桩治理工程的设计计算,传统方法更难胜任,而采用有限元强度折减法则能解决这些问题。通过文中工程实例的设计计算可以看出,由于有限元强度折减法可以充分考虑桩—土之间的共同作用,可以得到推力与抗力的分布形式;可以分析不同桩长和桩位对治理工程稳定性的影响,并进行治理方案的优化设计;可以得到作用在埋入式抗滑桩上的推力与抗力,因此能较好地进行抗滑桩治理工程的设计计算。  相似文献   

水泥土搅拌桩复合地基的试验和数值模拟分析   总被引：1，自引：0，他引：1  

张伟丽  蔡健  林奕禧  黄良机 《地质科技情报》2009,28(6)

水泥土搅拌桩处理软土地基可以提高地基承载力并减小沉降量。针对珠海地区的淤泥质土,进行了4种垫层厚度的水泥土搅拌桩复合地基现场静载荷试验,并在现场试验的基础上采用FLAC3D对水泥土搅拌桩复合地基进行了数值模拟分析。将数值模拟得到的4种垫层厚度复合地基的沉降曲线与现场试验的沉降曲线进行了比较,两者基本吻合。采用此模型计算了不同桩径和桩距复合地基的承载力和沉降量,研究了桩径、桩距的改变对复合地基承载力和沉降量的影响,并对改变桩径和桩距两种方案进行了比较,为水泥土搅拌桩复合地基的设计提供了参考。  相似文献   

Validation of Practice Oriented Models and Influence of Soil Stiffness on Lateral Pile Response Due to Kinematic Loading     

M. Murat Monkul 《Marine Georesources & Geotechnology》2013,31(3):145-159

Earthquakes usually cause both inertial and kinematic loading of pile foundations. Inertial loading and lateral pile response can be predicted to a certain extent by lateral pile load tests for important engineering projects. However, there is no accepted in situ assessment method for pile behavior due to kinematic loading. Therefore, it is important for geotechnical engineering practice to validate the practice oriented models and examine the influence of soil strength parameters on the performance of kinematically loaded piles due to lateral spreading. For this purpose, a well-documented case of full-scale lateral spreading test conducted at Port of Tokachi in Japan by Ashford et al. (2006 Ashford , S. A. , T. Juirnarongrit , T. Sugano , and M. Hamada . 2006 . Soil-pile response to blast-induced lateral spreading. I: Field test . Journal of Geotechnical and Geoenvironmental Engineering 132 ( 2 ): 152 – 162 . [Google Scholar]) is selected as a primary reference in terms of test data and site conditions. Four p-y analyses are performed using a special purpose software based on finite difference technique. The first two investigate the employment of different p-y curves suggested in the literature. The third one investigates the influence of variations in internal friction angle and undrained shear strength. In the fourth analysis, liquefied shear strength and residual shear strength approaches are utilized for the liquefiable layers and their effects are investigated. In all analyses, mobilized lateral pressures in non-liquefied layers are also scrutinized. The results of the analyses are discussed and compared with the measured values in the field. Finally, conclusions are given based on the analyses and discussions.  相似文献   

Stress Sharing Behavior and Its Mechanism during Consolidation Process in Composite Ground Improved by Sand Compaction Piles with Low Replacement Area Ratio     

S.-K. You  K. Oda 《Marine Georesources & Geotechnology》2013,31(4):287-304

In order to accurately design a sand compaction pile (SCP) with low replacement area ratio, it is important to understand the mechanical interaction between the sand pile and clay ground and its mechanism during consolidation process in composite ground. In this article, therefore, a series of numerical analyses on composite ground improved by SCP with low replacement area ratio were carried out. The applicability of numerical analyses, in which an elasto-viscoplastic consolidation finite element method was applied, were confirmed by comparing the results obtained from a series of laboratory model tests with the composite ground improved by SCP. Through the results of the numerical analyses, mechanical behavior of the sand pile and clay in composite ground during consolidation is elucidated, together with a stress sharing mechanism between sand pile and clay.  相似文献   

Evaluation of Undrained Shear Strength and Consolidation Characteristics of Disturbed Marine Sedimentary Clay due to SCP Installation     

G.-G. Yea 《Marine Georesources & Geotechnology》2013,31(1):76-90

The behaviors of the marine sedimentary ground improved by sand compaction pile (SCP) method are analyzed. To do this, the results of upheaval characteristics of the sea floor, undrained shear strength, and horizontal consolidation coefficient (consolidation) are investigated. Due to SCP installation on ground, as thickness of a soft clay layer increases, upheaval height increases and upheaval angle decreases. Undrained shear strength of disturbed ground due to SCP construction decreases in early stage after completion of construction, but it shows a trend of recovering as months elapse. As the result of piezocone penetration dissipation tests, consolidation delay phenomenon by the disturbance due to SCP installation clearly is identified and its degree is dependent on the replacement area ratio of SCP and the location of ground.  相似文献   

桩顶荷载对负摩阻力性状影响的现场试验   总被引：7，自引：1，他引：6  

夏力农  雷鸣  聂重军 《岩土力学》2009,30(3):664-668

负摩阻力是桩周土体沉降产生的桩附加沉降和下拽力的综合效应。为了研究不同的桩顶荷载对负摩阻力基桩性状的影响,在同一个试验场地上,对不同桩顶荷载作用下完全相同的3根桩的负摩阻力性状进行了现场测试。测试结果表明,桩顶荷载对于桩的负摩阻力性状有明显影响。随着桩顶荷载的增加,负摩阻力引起的桩附加沉降越大,桩周土体沉降引起的负摩阻力就越小;负摩阻力引起的下拽力也随着桩顶荷载的增加而减小;中性点位置随着桩顶荷载的增加而上升。这对桩基负摩阻力特性的研究是有益的。  相似文献   

刚性桩复合地基地震反应机理分析   总被引：2，自引：0，他引：2  

武思宇  宋二祥 《岩土力学》2009,30(3):785-792

为研究刚性桩复合地基的抗震性能,用刚性桩复合地基振动台试验验证了所采用的等效线性方法及其参数取值,在此基础上针对实际问题进行了三维有限元分析,对地基分层、土体模量、桩径、桩长、垫层厚度和垫层模量等因素对复合地基地震反应的影响进行了分析讨论,对刚性桩复合地基在地震荷载作用下的工作机理进行了较详细的分析。结果表明,等效线性方法能较好地模拟结构-复合地基相互作用的特性;上部结构惯性力和自由场变形对复合地基桩身内力影响都较大;地基明显软硬分层的存在,会使桩身内力显著增大。  相似文献   

桩基础托换开发地下空间不均匀沉降的数值分析     

贾强  张鑫  应惠清 《岩土力学》2009,30(11):3500-3504

桩基础托换法开发既有建筑物地下空间的施工过程可分为桩基托换前、托换后和土方开挖至设计标高3个工况。施工过程会使既有建筑物地基产生二次沉降变形,由此产生的附加内力会影响到上部结构的安全。为了研究一个3层框架结构建筑物增加一层地下室桩基础托换过程的地基沉降规律,建立了3个工况的ANSYS三维有限元模型,并进行数值分析。通过定义路径的方法,可以得到3个工况的沉降曲线和柱脚处地基的沉降差。从沉降分析的结果可以看出：桩基托换前,地基总的沉降趋势是中间部位柱脚大于周边部位柱脚的“盆式沉降”;桩基础托换后,柱脚处的沉降差进一步增大;土方开挖后,由于下层土被“卸载”,中间部位柱脚处的地基明显回弹,使得中间部位柱脚与周边部位柱脚的沉降差出现了减少的趋势。最大的沉降差出现在桩基托换后土方开挖前,此时由沉降差引起的上部结构的附加弯距可以通过ANSYS有限元分析求出。  相似文献