考虑地震影响的地基极限承载力的理论解析解

本文根据塑性力学中的滑移线法,建立了地震力作用下的地基土的滑移线应力方程,并在考虑地基土的自重和不计其自重的情况下,推导出了此时地基土的极限承载力的理论解析解.     

复合地基桩间土承载力折减系数的分析与取值

在多项工程的单桩和复合地基静载荷试验对比资料基础上,经过理论分析计算,针对不同地基土质条件,提出邯郸市区粉喷桩复合地基桩间土承载力折减系数的取值标准,可为复合地基设计提供参考。     

各向异性损伤对地基承载力影响分析

应用耦合损伤的滑移线法,求解平面应变条件下的极限荷载问题,推导出考虑各向异性损伤的平面应变问题应力场的滑移线解,针对平顶钝角楔体极限荷载的滑移线场进行了详细推导,绘出滑移线场图,推导出极限荷载的公式,分析了各向异性损伤对浅基础极限荷载的影响,即损伤对地基承载力系数Nq影响很大;损伤越大,地基承载力系数Nq值越小,且随着D1,D2的增加,Nq越接近最小值。     

地下水位升降对某场地地基土承载力的影响

通过工程实例，分析了对比地下水位升降对地基土的物理力学性质的影响，定量地总结了地下水位上升对地基土承载力的削弱情况。     

压实填土地基承载力深度修正系数研究

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。     

考虑地表沉陷影响的复合地基承载力计算方法

受地下开采的剧烈扰动,采煤沉陷区的复合地基工程会发生非常大的下沉和水平位移,常规的承载力计算方法未考虑地表沉陷影响。在研究地表沉陷影响的复合地基承载特性的基础上,建立了考虑地表沉陷影响的复合地基受力模型,并且提出了考虑地表沉陷影响的复合地基承载力计算方法。通过一个采煤沉陷区桥梁复合地基工程实例的计算分析,发现考虑地表沉陷影响后,复合地基承载力有一定程度的下降。     

强夯法处理地基后承载力的计算

本文结合工程实践介绍了强夯法处理地基后承载力计算的力学模型和计算方法，并附有已搞过的十个工程实例，将计算值与强夯后检测值进行了分析比较，说明本文公式的正确性。     

土钉墙地基承载力问题探讨

土钉墙墙底地基土的承载力验算是土钉墙支护设计的一项重要内容。国内的工程实践中,通常将土钉墙地基承载力与坑底土抗隆起验算合并考虑。针对具体案例,通过Plaxis3D有限元数值模拟,分析研究了土钉墙底部土体发生地基承载力失稳的破坏模式、破坏荷载以及土钉墙墙底应力分布特点等,探讨了依据我国相关规程进行土钉墙坑底隆起或地基承载力计算可能存在的问题。借鉴国外加筋土挡墙地基承载力计算的一般方法,将土钉墙作为荷载倾斜、偏心的刚性基础对待,利用荷载倾斜、偏心条件下传统刚性浅基础的地基承载力的Meyerhof解和Vesic解,对土钉墙地基承载力进行了计算和对比,通过对比发现,Meyerhof解更接近实际,据此,提出了土钉墙地基承载力计算的合理模式。     

特殊条件下地基承载力计算模式分析

本文根据太沙基理论,推导出在地面水平情况下,地基产生整体滑动时的单侧临界长度的计算公式,讨论了单侧临界长度的影响因素;针对位于坡顶上的建筑物、边坡上的建筑物、主裙楼建筑物等特殊情况,根据基底水平延长线到边坡交线的水平距离与单侧临界长度的大小关系,分别建立了地基承载力计算模式,给出了简单、方便、合理的承载力计算方法和计算公式。     

Bearing capacity of foundations on slopes

By applying the lower bound finite element limit analysis in conjunction with non-linear optimisation, the bearing capacity factors, N_c, N_q and N_γ, due to the components of cohesion, surcharge and unit weight, respectively, have been estimated for a horizontal strip footing placed along a sloping ground surface. The variation of N_c, N_q and N_γ with changes in slope angle (β) for different soil friction angle (φ) have been computed for smooth as well as rough strip footings. The analysis reveals that along a sloping ground surface, in addition to N_γ, the factors N_c and N_q also vary considerably with changes in footing roughness. Compared to the smooth footing, the extent of the plastic zone around the footing becomes greater for the rough footing. The results obtained from the analysis are found to compare well with those previously reported in literature.     

Bearing capacity factors of circular foundations for a general c–ϕ soil using lower bound finite elements limit analysis

By using the lower bound limit analysis in conjunction with finite elements and linear programming, the bearing capacity factors due to cohesion, surcharge and unit weight, respectively, have been computed for a circular footing with different values of ?. The recent axisymmetric formulation proposed by the authors under ?=0 condition, which is based on the concept that the magnitude of the hoop stress (σ_θ) remains closer to the least compressive normal stress (σ₃), is extended for a general c–? soil. The computational results are found to compare quite well with the available numerical results from literature. It is expected that the study will be useful for solving various axisymmetric geotechnical stability problems. Copyright © 2010 John Wiley & Sons, Ltd.     

Bearing capacity of shallow foundations in transversely isotropic granular media

The main focus in this work is on the assessment of bearing capacity of a shallow foundation in an inherently anisotropic particulate medium. Both the experimental and numerical investigations are carried out using a crushed limestone with elongated angular‐shaped aggregates. The experimental study involves small‐scale model tests aimed at examining the variation of bearing capacity as a function of the angle of deposition of the material. In addition, the results of a series of triaxial and direct shear tests are presented and later employed to identify the material functions/parameters. The numerical part of this work is associated with the development and implementation of a constitutive framework that describes the mechanical response of transversely isotropic frictional materials. The framework is based on the elastoplasticity and accounts for the effects of strain localization and inherent anisotropy of both the deformation and strength characteristics. The results of numerical simulations are compared withthe experimental data. A parametric study is also carried out aimed at examining the influence of various simplifications in the mathematical framework on its predictive abilities. Copyright © 2009 John Wiley & Sons, Ltd.     

Bearing capacity of strip foundations with structural skirts

A modified bearing capacity equation is proposed for skirted strip foundations on dense sand. A series of tests on foundation models were carried out to study the factors that affect the bearing capacity of foundations with skirts. Several factors including foundation base friction, skirt depth, skirt side roughness, skirt stiffness and soil compressibility were studied and incorporated in the equation. The results obtained from the proposed equation were compared with the results obtained from Terzaghi, Meyerhof, Hansen and Vesic bearing capacity equations for foundations without skirt. Comparison shows that the use of structural skirts can improve the bearing capacity by a factor of 1.5 to 3.9 depending on the geometrical and structural properties of the skirts and foundation, soil characteristics and interface conditions of the soil-skirt-foundation system. This revised version was published online in July 2006 with corrections to the Cover Date.     

土体强度各向异性基坑的抗隆起稳定性分析

天然土体通常为非均质、各向异性土体,目前常用的基坑抗隆起计算方法多是针对均质各向同性土体的。采用非均质非线性各向异性岩石破坏准则,考虑土体原生各向异性,假定Prandtl破坏模式,采用地基承载力模式进行基坑的抗隆起稳定性分析。根据滑移线理论计算承载力,利用有限差分法结合边界条件编制出相关计算程序,并定义基坑抗隆起稳定性系数。研究表明,各向异性比的提高会降低安全系数;内摩擦角和插入比的增大可有效提高基坑的稳定性。     

条形基础极限承载力数值分析

根据塑性力学滑移线理论,推导了条形地基在极限平衡状态下的平衡微分方程,然后利用有限差分法推出地基土在极限状态时的有限差分公式,结合边界条件编制出地基承载力计算程序,该程序求解条形地基极限状态下的滑移线区域及相应的地基极限承载力值时可以考虑基础埋深、地基土重度、土的内摩擦角、基础与地基摩擦等参数。利用程序,得到了土的内摩擦角与地基承载力系数N? 的对应表,并全面讨论了基础埋深、地基土重度、内摩擦角及基础与地基摩擦角等参数对地基承载力和滑移线形状的影响,得到了一些有意义的结论。     

Bearing capacity of foundations on rock mass using the method of characteristics

The method of stress characteristics has been used for computing the ultimate bearing capacity of strip and circular footings placed on rock mass. The modified Hoek‐and‐Brown failure criterion has been used. Both smooth and rough footing‐rock interfaces have been modeled. The bearing capacity has been expressed in terms of nondimensional factors N_σ0 and N_σ, corresponding to rock mass with (1) γ = 0 and (2) γ ≠ 0, respectively. The numerical results have been presented as a function of different input parameters needed to define the Hoek‐and‐Brown criterion. Slip line patterns and the pressure distribution along the footing base have also been examined. The results are found to compare generally well with the reported solutions.     

考虑土体强度增长的黏性土地基承载力分析

近些年国内进行了多处的人工堆山工程,其特点是堆载分层施加、荷载分布面积大、施工期较长且总荷载非常大,常规地基处理不能满足堆山荷载对地基承载力的要求。结合堆山工程逐级施加的堆土荷载之间通常有较长时间间隔的特点,认为地基可在分级堆填间歇时间内发生一定程度固结有效应力提高,导致土体强度增加,因此地基承载力也产生相应的提高,利用固结引起土体强度增长导致的承载力提高是堆山工程成功的关键。应用有效应力法分析了土体固结引起强度增长的机制和计算,提出不排水条件下考虑土体强度增长的地基承载力分析方法,运用该理论对比分析了两个人工堆山工程案例,对堆山工程提出建议可供类似工程参考。