Determination of ultimate capacity of driven piles in cohesionless soil: A Multivariate Adaptive Regression Spline approach     

Pijush Samui 《国际地质力学数值与分析法杂志》2012,36(11):1434-1439

The determination of ultimate capacity (Q) of driven piles in cohesionless soil is an important task in geotechnical engineering. This article adopts Multivariate Adaptive Regression Spline (MARS) for prediction Q of driven piles in cohesionless soil. MARS uses length (L), angle of shear resistance of the soil around the shaft (?_shaft), angle of shear resistance of the soil at the tip of the pile (?_tip), area (A), and effective vertical stress at the tip of the pile as input variables. Q is the output of MARS. The results of MARS are compared with that of the Generalized Regression Neural Network model. An equation has been also presented based on the developed MARS. The results show the strong potential of MARS to be applied to geotechnical engineering as a regression tool. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

尾矿坝筑坝模袋力学性能试验研究     

李巧燕  王惠栋  马国伟  李之建  周汉民  崔旋 《岩土力学》2016,37(4):957-964

模袋法是解决上游法细粒尾矿堆坝难的一种新方法。为研究模袋法尾矿坝筑坝模袋的基本力学性能,采用与云南省某尾矿坝施工现场一样的土工布和尾砂,通过斜坡滑移、直剪、无侧限压缩试验,对固结不同时间的小尺寸尾矿坝筑坝模袋进行了摩擦和受压性能的试验研究。斜坡滑移试验表明,若含水率相对较低,则模袋间的摩擦系数较大;直剪试验测得固结8 d的模袋间内摩擦角约为28º,黏聚力约为40 kPa;在无侧限压缩条件下,固结1 d和3 d的模袋在受压过程中,其弹性模量都表现为“大-小-大”的变化形式。由于土工布和尾砂的共同作用,模袋的极限抗压强度远大于单纯尾砂堆积体的极限抗压强度。当压应力达到模袋所能承受的极限荷载时,通常会在模袋底部靠近模袋边缘处发生土工布的撕裂破坏,采用主动土压力理论分析了发生破坏的原因。本试验研究可以为模袋法尾矿坝的实践提供理论指导。  相似文献   

循环荷载及静载下土工格室加筋路堤模型试验研究     

高昂  张孟喜  朱华超  姜圣卫 《岩土力学》2016,37(7):1921-1928

为探究土工格室加筋路堤在循环荷载及静载下的各种性能,利用美国GCTS公司的USTX-2000加载装置进行加载,通过改变加筋层数、格室高度,格室焊距对土工格室加筋路堤进行一系列模型试验。对各种工况下加筋路堤极限承载力、长期循环荷载及固定振次循环荷载后极限承载力的变化进行研究。试验表明,土工格室加筋能显著提高地基极限承载力并能显著减小坡顶和坡中临界破坏时的法向累积变形,在加筋间距一定的情况下,加筋层数增加和格室高度增大均可不同程度提高极限承载力并减小临界破坏时坡顶法向累积变形,格室焊距的减小也可在一定程度提高极限承载力,格室焊距对边坡法向变形影响不大;长期循环荷载下固定间距加筋层数对路堤竖向累积沉降量影响不大,而对边坡坡顶法向累积变形有一定影响,格室高度增大和格室焊距减小均可不同程度减小路堤竖向累积沉降量和坡面法向累积变形;越靠近加载点处,路堤土压力值受加筋影响越显著,加筋提高了土体刚度和密实度,使加筋路堤土压力值较无筋路堤明显增大;对于无筋路堤,改变动载幅值和振次均导致振后极限承载力有不同程度的降低,而对于加筋路堤,当动载幅值≥30 kPa或动载振次≥1 000时,振后极限承载力均有不同程度的提高。  相似文献   

吹填场区双层软黏土地基超载比与卸载控制试验研究     

雷华阳  任倩  卢海滨  李宾 《岩土力学》2016,37(11):3072-3078

对于围海造陆工程所开展的超载预压处理方法,地基处理效果通常采用后续变形大小来评价,其大小与超载比和卸载控制时间密切相关。针对天津滨海地区围海造陆工程所形成的典型的上软、下硬的双层软黏土地基,采用改装的固结仪进行了多种超载比和卸载控制时间的试验研究,提出了适宜的超载比和最佳超载作用时间。试验表明：双层软黏土地基超载比大于0.375,超载作用时间超过主固结时间时,超载卸除后地基变形以回弹变形为主,后续的工后沉降将明显减小,减小幅度可高达70%以上;超载卸除后的土体次固结系数明显减小,减小的幅度随超载比的增大、超载作用时间的增加而减小;不同于均质地基和上硬下软的双层地基,上软、下硬双层地基的工后沉降以上部软土层沉降为主,约占总沉降量的73%以上。根据不同超载比和超载作用时间下土体的变形时程曲线,建议适宜天津滨海地区围海造陆工程软黏土地基的超载比控制在0.5以下,超载作用时间控制在1～3倍的主固结时间内。  相似文献   

Third Order Effect of Rotation on Stellar Oscillations of a B Star     

K. Karami 《中国天文和天体物理学报》2008,8(3):285-308

We aim at investigating the effect of rotation up to the third order in the angular velocity of a star on the p and g modes, based on the formalism developed by Soufi et al. Our ultimate goal is the study of oscillations of β Cephei stars which are often rapidly rotating stars. Our results show that the third-order perturbation formalism presented by Soufi et al. should be corrected for some missing terms and some misprints in the equations. As a first step in our study of β Cephei stars, we quantify by numerical calculations the effect of rotation on the oscillation frequencies of a uniformly rotating zero-age main-sequence star with 12 M<,??>. For an equatorial velocity of 100km s-1, it is found that the second-and third-order corrections for (l, m)=(2, 2), for instance, are of the order of 0.01% of the frequency for radial order n=6 and reaches up to 0.5% for n=14.  相似文献   

Numerical analysis of surcharge preloading consolidation of layered soils via distributed sand blankets     

Ruidan Yao  Pengpeng Ni 《Marine Georesources & Geotechnology》2013,31(8):902-914

Abstract

Surcharge preloading consolidation of soft soils often implements a layer of fully arranged aggregate materials. The volume of drained water is abundant at the early stage of consolidation, but it reduces at middle and later stages, during which the fully arranged sand blanket will be a waste. In this investigation, a concept of distributed sand blankets is proposed to save aggregate materials. A series of finite element analyses have been performed on layered soils with distributed sand blankets. A mixed type of drainage boundary is assigned to a representative model, where a half sand blanket is perfectly pervious and a half width of soil among sand blankets is impervious. From parametric study, it has been found that a pave ratio between sand blankets and the total soil width can be selected in a range of 40%–60%, which will save aggregates by approximately 50% but cause an increase of consolidation time by less than 10%. For a fixed pave ratio, more evenly spaced sand strips with smaller width should be employed to optimize the design. The effectiveness of distributed sand blankets is not influenced by the anisotropy of hydraulic conductivity, elastic modulus, Poisson’s ratio, and thickness in multiple soil layers.  相似文献   

埋深基础地基极限承载力的数值求解方法   总被引：5，自引：1，他引：4  

梅岭  梅国雄  宰金珉 《岩土力学》2009,30(6):1810-1814

为确定作用在已知埋深、给定基础形状地基土上的极限承载力,对基底下的土体进行网格划分,先假定一均布荷载作用在此地基土上,运用明德林解的积分公式,结合角点法,编制MATLAB语言程序,求出每个网格节点上附加应力,进而求得每个网格节点上主应力,根据破坏准则,结合程序找出破坏点的坐标,利用MATLAB的图形处理功能,把破坏点的坐标在坐标图中显示出来。继续加大矩形荷载,直至这些破坏点在坐标图中刚好能够形成一个连续的破坏面,此时的矩形荷载即为此地基的极限承载力。此方法不仅可以有效地避免了地基承载力经验公式中一些不合理的假设带来的误差,更符合实际情况,而且可以直观地了解到地基土的三维破坏面。  相似文献   

Hysteretic energy dissipation capacity and the cyclic to monotonic drift ratio for rectangular RC columns in flexure     

Karmen Poljanšek  Iztok Peruš  Peter Fajfar 《地震工程与结构动力学》2009,38(7):907-928

Predictions of energy dissipation capacity and of the deterioration of deformation capacity due to cumulative damage have been made by means of a non‐parametric empirical approach, called the conditional average estimator method, using empirical data on rectangular reinforced concrete columns that failed in flexure. Five input parameters were used: axial load index, index related to confinement, shear span index, concrete compressive strength, and longitudinal reinforcement index. The energy capacity was expressed in three different normalized forms and the deterioration of deformation capacity was defined as the ratio of the cyclic to the monotonic ultimate drift. The longitudinal reinforcement index, the index related to confinement, and the axial load index are the most influential input parameters in the case of energy capacity, whereas the latter two indices exhibit the most significant influence in the case of the drift ratio. Energy capacity decreases with an increasing axial load index, whereas it increases with increasing longitudinal reinforcement and with better confinement. In the case of the shear span index, the trend is more complex. Normal concrete has a higher energy dissipation capacity than high‐strength concrete. Similar trends are observed for the drift ratio, with the exception of the influence of the axial load index, where the trend is opposite. The dispersion of the results is high. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

用弹性模量缩减法分析刚架结构的极限承载力     

杨绿峰  余波  乔永平 《地震学刊》2009,(3):306-312

首先,综合考虑单元的内力和屈服强度,定义了单元承载比、承载比均匀度以及基准承载比等参数的概念和计算表达式;在此基础上,根据相邻迭代步变形能守恒关系,研究建立弹性模量的调整计算公式,建立了一种新型的弹性模量调整策略;进而提出了刚架结构极限承载力分析的弹性模量缩减法,即通过系统地调整高承载比单元的弹性模量来确定结构的极限荷载下限值。该方法对于结构的局部破坏模式及整体破坏模式分析均具有较好的适用性。算例分析表明,本文方法具有较高的计算精度和计算效率。  相似文献   

砂土中边坡附近单桩水平抗力的模型试验研究     

高博雷  张陈蓉  张照旭 《岩土力学》2014,35(11):3191-3198

针对平地p-y曲线对临近边坡桩基的不适用性,开展了砂土中边坡存在对单桩水平抗力影响的室内物理模型试验。依据边坡坡角及边坡到单桩距离的不同,共进行了11次3组试验。采用分段3次多项式对实测桩身应变分布进行拟合,以推算桩身变形和桩侧抗力,有效克服了数据拟合点的奇异。对比无边坡时的试验p-y曲线、美国API规范曲线和双曲线模型,确认了平地p-y曲线的计算表达式。其次获得了边坡条件下的单桩荷载-位移曲线,揭示了边坡坡角和边坡到桩的距离对水平受荷单桩桩身弯矩分布的影响规律。根据试验结果采用折减系数修正浅层桩侧极限抗力,并引入边坡对桩侧初始刚度的削弱表达式,得到边坡条件下水平受荷单桩浅层区域双曲线p-y曲线表达式。最后通过与离心试验结果对比,验证了给出的p-y曲线考虑边坡影响时的合理性。  相似文献