Bearing capacity of foundation on slope determined by energy dissipation method and model experiments

To determine the ultimate bearing capacity of foundations on sloping ground surface in practice, energy dissipation method was used to formulate the bearing capacity as programming problem, and full-scale model experiments were investigated to analyze the performance of the soil slopes loaded by a strip footing in laboratory. The soil failure is governed by a linear Mohr-Coulomb yield criterion, and soil deformation follows an associated flow rule. Based on the energy dissipation method of plastic mechanics, a multi-wedge translational failure mechanism was employed to obtain the three bearing capacity factors related to cohesion, equivalent surcharge load and the unit gravity for various slope inclination angles. Numerical results were compared with those of the published solutions using finite element method and those of model experiments. The bearing capacity factors were presented in the form of design charts for practical use in engineering. The results show that limit analysis solutions approximate to those of model tests, and that the energy dissipation method is effective to estimate bearing capacity of soil slope.     

Influences of nonassociated flow rules on three-dimensional seismic stability of loaded slopes

The influences of soil dilatancy angle on three-dimensional (3D) seismic stability of locally-loaded slopes in nonassociated flow rule materials were investigated using a new rotational collapse mechanism and quasi-static coefficient concept. Extended Bishop method and Boussinesq theorem were employed to establish the stress distribution along the rupture surfaces that are required to obtain the rate of internal energy dissipation for the nonassociated flow rule materials in rotational collapse mechanisms. Good agreement was observed by comparing the current results with those obtained using the translational or rotational mechanisms and numerical finite difference method. The results indicate that the seismic stability of slopes reduces by decreasing the dilatancy angle for nonassociated flow rule materials. The amount of the mentioned decrease is more significant in the case of mild slopes in frictional soils. A nearly infinite slope under local loading, whether its critical failure surface is 2D or 3D, not only depends on the magnitude of the external load, but also depends on the dilatancy angle of soil and the coefficient of seismic load.     

Seismic failure mechanisms for loaded slopes with associated and nonassociated flow rules

Seismic failure mechanisms were investigated for soil slopes subjected to strip load with upper bound method of limit analysis and finite difference method of numerical simulation, considering the influence of associated and nonassociated flow rules. Quasi-static representation of soil inertia effects using a seismic coefficient concept was adopted for seismic failure analysis. Numerical study was conducted to investigate the influences of dilative angle and earthquake on the seismic failure mechanisms for the loaded slope, and the failure mechanisms for different dilation angles were compared. The results show that dilation angle has influences on the seismic failure surfaces, that seismic maximum displacement vector decreases as the dilation angle increases, and that seismic maximum shear strain rate decreases as the dilation angle increases.     

Seismic ultimate bearing capacity of strip footings on slope

The influence of earthquake forces on ultimate bearing capacity of foundations on sloping ground was studied. A solution to seismic ultimate bearing capacity of strip footings on slope was obtained by utilizing pseudo-static analysis method and taking the effect of intermediate principal stress into consideration. Based on limit equilibrium theory, the formulae for computing static bearing capacity factors, Nq, Nc, Nγ, and dynamic bearing capacity factors, Nqd, Ncd, Nγd, which are associated with surcharge, cohesion and self-weight of soils respectively, were presented. A great number of analysis calculations were carried out to obtain the relationship curves of the static and dynamic bearing capacity factors versus various calculation parameters. The curves can serve as the practical engineering design. The calculation results also show that when the values of horizontal and vertical seismic coefficients are 0.2, the dynamic bearing capacity factors Nqd, Ncd and Nγd, in which the effects of intermediate principal stress are taken into consideration, increase by 4%?42%, 3%?27% and 34%?57%, respectively.     

影响加筋土挡墙地震稳定性的参数分析

针对现有挡土墙抗震设计影响因素考虑不足等问题,运用拟静力法和水平条分法分析加筋土挡墙的地震稳定性,并研究土体内摩擦角、水平地震力加速度系数、填土粘聚力、挡土墙倾角和滑动体上部荷载等参数对地震稳定性的影响。结果表明:加筋土挡墙的地震稳定性与水平地震力加速度系数和滑动体上部荷载有显著关系,且变化趋势与之成正比;与土体内摩擦角和填土粘聚力的变化趋势成反比;当条件相同时,倾斜加筋土挡墙的地震稳定性比竖直挡墙的稳定性好。     

Slope stability analysis considering joined influences of nonlinearity and dilation

The soil masses of slopes were assumed to follow a nonlinear failure criterion and a nonassociated flow rule. The stability factors of slopes were calculated using vertical slice method based on limit analysis. The potential sliding mass was divided into a series of vertical slices as well as the traditional slice technique. Equating the external work rate to the internal energy dissipation, the optimum solutions to stability factors were determined by the nonlinear programming algorithm. From the numerical results, it is found that the present solutions agree well with previous results when the nonlinear criterion reduces to the linear criterion, and the nonassociated flow rule reduces to the associated flow rule. The stability factors decrease by 39.7% with nonlinear parameter varying from 1.0 to 3.0. Dilation and nonlinearity have significant effects on the slope stability factors. Foundation item: Project (200550) supported by the Foundation for the Author of National Excellent Doctoral Dissertation of China; Project (200631878557) supported by West Traffic of Science and Technology of China     

Multi-factor sensitivity analysis of shallow unsaturated clay slope stability

An unsaturated clay slope, with various sloping angles and a thickness of 14 m, consists of backfill, slope soil and residual soil. Slide interfaces were determined by geophysical approaches and the original slope was reconstructed. Sub-slope masses were classified based on the varieties of sloping angle. A force recursive principle was proposed to calculate the stability coefficient of the sub-slope masses. The influencing factors such as sloping angle, water content, hydrostatic pressure, seismic force as well as train load were analyzed. The range and correlation of the above-mentioned factors were discussed and coupled wave equations were established to reflect the relationships between unit weight, cohesion, internal frictional angle, and water content, as well as between internal frictional angle and cohesion. The sensitivity analysis of slope stability was carried out and susceptive factors were determined when the factors were taken as independent and dependent variables respectively. The results show that sloping angle, water content and earthquake are the principal susceptive factors influencing slope stability. The impact of hydrostatic pressure on slope stability is similar to the seismic force in quantity. Train load plays a small role in slope stability and its influencing only reaches the roadbed and its neighboring slope segment. If the factors are taken as independent variables, the influencing extent of water content and cohesion on slope stability can be weakened and train load can be magnified.     

马河崩塌体边坡稳定程度敏感性分析

针对雅砻江楞古水电站边坡稳定性问题,以马河崩塌体边坡为例,选取岩体重度、粘聚力、内摩擦角、水位、地震系数为影响因子,以边坡的安全系数为指标,基于均匀设计开展数值试验,对试验结果进行灰关联分析,得出各因素与边坡安全系数之间的关联系数和关联度。研究结果表明,各因素对边坡稳定性的影响大小依次为内摩擦角水位地震系数粘聚力重度。     

浅基础地基极限承载力的有限元分析

为了对浅基础地基极限承载力的主要影响因素进行系统分析，采用关联流动的Mohr-coulomb内切圆屈服准则，通过增量加载的有限元方法，全程模拟了地基由初始的线弹性状态逐渐过渡到塑性流动的极限破坏状态的过程。通过对几种主要因素的对比分析，并结合对照国内外模型试验成果，可知基础刚度和基底粗糙程度对无重土地基的极限承载力影响不大，但刚度和基底粗糙程度对临塑荷载有明显的影响；主要土力学参数对地基破坏机理的影响存在着明显的区别。     

基于传递矩阵法的串联隔震体系稳定性分析

针对串联隔震体系稳定性问题,利用传递矩阵法建立其临界荷载控制方程,并探讨了参数变化对临界荷载的影响.对单个叠层橡胶支座进行力学分析,建立其稳定性分析的场矩阵,进而利用传递矩阵法建立串联隔震体系稳定性分析的场矩阵,推导出临界荷载的控制方程.计算两种不同型号串联隔震体系的临界荷载,重点探讨叠层橡胶支座和地下室悬臂柱参数变化对串联隔震体系稳定性的影响.结果表明,叠层橡胶支座参数对串联隔震体系稳定性影响要比地下室悬臂柱明显,串联隔震体系的临界荷载值可用单个橡胶支座的临界荷载值近似等效.     

咬合桩在邻近高填土基坑中的工程应用与实测分析

针对某采用咬合桩围护方案的邻近高填土基坑工程进行分析,当咬合桩作为围护桩时,可采用等效刚度法计算围护桩的桩身变形;作为隔离桩使用时,忽略素混凝土桩的作用,仅考虑钢筋混凝土桩的抗弯能力.现场实测表明,邻近高填土基坑工程在开挖时,咬合桩明显地降低了基坑开挖对紧邻高填土的扰动,满足了高填土自身的稳定,保证基坑工程在高填土作用下的安全.而咬合桩作为一种新型排桩围护结构,也能够起到很好的应力隔离作用,有效地分担了邻近超载的影响,确保了高填土的稳定和基坑工程安全.     

变截面管桩水平承载性状模型试验研究

在室内基坑中对1根等截面管桩和2根变截面管桩进行单桩水平静载荷模型试验,对比研究两类管桩单桩水平承载性能方面的差异。试验结果表明:等截面模型管桩与变径比为0.57与0.71的变截面模型管桩的单桩水平的临界荷载依次为1.2,1.6,1.2 kN;单位体积水平承载力特征值依次为95,147,115 kN/m3。变径比为0.57与0.71的变截面管桩的单位水平承载能力比等截面管桩分别提高了55.1%和21.6%;变截面管桩变径比越小,单位水平承载能力越大;材料的利用率也越高。     

隔板贯通式节点抗震性能试验研究

为了研究方钢管混凝土柱与钢梁连接的隔板贯通式节点的抗震性能,设计了一个低周反复荷载作用下的T字形足尺隔板贯通式梁柱节点试件的拟静力试验。通过研究拟静力试验的滞回曲线来分析研究它的耗能能力。并分析了试件的破坏过程及破坏特征,对节点的延性、能量耗散等抗震性能指标进行了深入的研究,采用ANSYS程序对它进行了有限元分析,探讨了试件的隔板厚度,核心混凝土强度等参数对节点抗震性能的影响。通过研究得出隔板贯通式节点有较高的承载力和较好的延性,较强的耗能能力和抗震性能。     

老化与偏心受压下板式橡胶支座抗震性能拟静力试验研究

板式橡胶支座的老化和偏压甚至脱空对桥梁抗震安全至关重要。将板式橡胶支座进行室内老化试验并测得弹性模量,按老化程度和轴压偏心大小共分16个工况,采用拟静力试验对比分析了热老化、偏压脱空及其耦合下支座的抗震性能指标及变化规律。结果发现：偏心受压下支座滞回曲线较为狭长,滞回曲线面积和等效阻尼比减小,水平等效刚度增大;老化后的支座剪切变形量缩减,在给定的位移幅值下,因滑移量占比加大,滞回曲线更为饱满,对应的等效阻尼比增大;老化和偏心耦合状态下的滞回曲线斜率更为平缓,支座耗能能力明显削弱;位于梁端或长期处于偏压状态的普通板式橡胶支座在地震中存在因单向累计滑移过大而脱落的风险。桥梁维护中应对支座底面采取限位措施,并对偏心受压严重的支座进行及时调整。     

速度滑移对液静压轴承油膜微流动影响敏感度

为了使液体静压轴承油膜性能的研究更加准确,基于计算流体力学(computational fluid dynamics,CFD)和有限差分方法,研究了液体静压轴承间隙油膜微流动的速度滑移现象及其对轴承性能的影响,并定义敏感度物理量对影响程度进行评估.在传统油膜流动假设条件基础上,引入Navier速度滑移边界条件对传统的Reynolds方程进行修正,通过有限元差分方法求解修正后的Reynolds方程,采用梯形积分公式求解轴承承载力等性能参数,对速度滑移影响的轴承性能的敏感度做出定量和定性分析.研究结果表明:油膜压力分布、轴承的承载力、动刚度及油腔流量等轴承性能对速度滑移都有一定的敏感性.最大油腔压力随滑移系数的增加而减小;速度滑移在一定程度上提高了轴承承载能力和油腔流量,但同时降低了轴承动刚度,流量对速度滑移的敏感度最大达到100%.     

化学锚栓加固植筋混凝土构件抗震性能试验

为了研究化学锚栓能否用于地震地区和受拉区混凝土构件,对化学锚栓加固植筋混凝土构件的锚固性能进行了试验。通过拟静力试验,研究了锚固构件的破坏形态、锚栓在反复荷载作用下的锚固效果和抗震性能。试验结果表明：化学锚栓的动载锚固效果良好,可以用于地震地区和受拉区混凝土构件的锚固;化学锚栓提高了构件的承载力和延性,尤其在反复荷载试验后期,在限制构件承载力下降和位移增大方面起到了重要作用;锚栓施工技术是影响构件抗震性能的重要因素。     

超载预压法的超载比及卸载控制研究

超载预压法处理地基的效果可以从超载卸除后地基在建筑物荷载作用下后续变形的大小得到反映，而后续变形的大小与超载比和超载作用的时间有直接的关系。对超载预压法中常用的卸载控制理论进行了简要的分析，并通过室内模拟试验，对超载预压法的超载比及超载作用时间进行了研究，得出了软粘土的卸载控制曲线，并建议超载比应控制在0．4～0．5范围内．     

条形荷载下加筋边坡稳定影响因素敏感性分析

结合12 m高土工格栅加筋边坡算例,通过有限元程序Midas/GTS 4.0,对条形荷载作用下边坡加筋与未加筋时的安全系数、最大水平位移与竖向沉降进行了对比分析.根据正交分析方法对10种影响因素,即粘聚力、内摩擦角、填土重度、坡比、坡顶荷载、荷载距离坡顶处间距、荷载宽度、土工格栅长度、格栅弹性模量、格栅铺设层数对加筋土边坡稳定影响因素的敏感性进行分析,给出了各个因素的敏感性顺序.计算结果表明:土体内摩擦角、粘聚力与荷载宽度对边坡稳定性影响最为显著.     

设芯柱的蒸压加气混凝土砌体承重墙抗震性能试验

通过3片设芯柱的蒸压加气混凝土砌体承重墙足尺试件的低周反复荷载试验,研究了这种组合墙体的破坏过程与特征,以及滞回特性、承载力、变形、刚度退化、耗能等方面的性能,并比较了开洞对墙体性能的影响.试验表明,在蒸压加气混凝土砌体墙中设置芯柱后,对墙体形成有效的约束,使墙体具有很好的极限变形能力,实现裂而不倒,是将蒸压加气混凝土砌块砌体墙用作承重墙体的一种有效抗震构造措施.研究还表明,这种组合墙体变形性能的改善程度与芯柱的设置情况有关;而墙体的抗剪承载力受开洞影响较大,随洞口水平截面积的增大而明显降低.研究结果为蒸压加气混凝土砌块砌体承重墙结构体系的应用提供了试验依据.     

钢板剪力墙振动台试验的等效模型

为解决钢框架钢板剪力墙结构振动台试验缩尺模型中的剪力墙钢板厚度过薄的问题,依据结构初始抗侧刚度或承载能力等效的原则,提出中心支撑和I形钢板剪力墙两种等效模型,采用数值分析的方法,通过有限元软件ABAQUS建立精细化模型,对原型结构的钢板剪力墙和等效模型的刚度与承载力等抗震性能进行了对比分析。研究结果表明：两种等效替代模型均具有良好的耗能能力,能够在抗侧刚度或承载能力方面满足原型结构的等效设计要求,解决了模型结构中剪力墙钢板厚度小的难题;中心支撑等效方案仅可实现剪力墙的刚度或承载力单目标等效,而I形钢板剪力墙可以通过控制开洞口的尺寸,实现其刚度和承载力同时等效,为钢板剪力墙振动台试验模型的等效替代提供了参考。