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1.
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
2.
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
3.
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
4.
《Geomechanics and Geoengineering》2013,8(4):271-277
The paper presents the performance of a square footing with a structural skirt resting on sand and subjected to a vertical load through an experimental study. A series of tests were conducted in a model test tank to evaluate the performance in terms of improvement in bearing capacity and reduction in settlement of a square footing with and without a structural skirt. The results of the study reveal that this type of reinforcement increases the bearing capacity, reduces the settlement and modifies the load settlement behaviour of the footing. The various factors influencing the bearing capacity improvements and settlement reduction using a structural skirt are identified. Skirt factors are proposed which can be introduced into the general ultimate bearing capacity equation for a square footing resting on sand. The predictions made through the modified equation are in reasonable agreement with the experimental results. The bearing capacity of square footing is increased in the range of 11.2 to 70%. The improvement in bearing capacity decreases with the increase in base roughness of the footing. Further, an equation for a settlement reduction factor is proposed which can be used to calculate the settlement of the square footing with structural skirt resting on sand. The settlement reduction factor (SRF, defined as the ratio of settlement of footing with structural skirt to the settlement of footing without structural skirt at a given load) was in the range 0.11 to 1.0 depending on applied load and skirt depth ratio with the use of a structural skirt. The results further reveal that for a given depth of the skirt, the settlement reduction factor decreases with the increase in applied load. The improvement in the bearing capacity and reduction in settlement of a square footing with a structural skirt resting on sand are dependent on the geometrical and structural properties of the skirt, footing, sand characteristics and interface conditions of the sand–skirt–footing system. 相似文献
5.
Arash Alimardani Lavasan Ali Talsaz Mahmoud Ghazavi Tom Schanz 《Geotechnical and Geological Engineering》2016,34(6):1791-1805
This paper numerically examines the bearing capacity and failure mechanism of a shallow strip foundation constructed above twin voids. The voids may refer to caves, caverns, underground aqueduct or tunnels due to water seepage, chemical reaction or deliberately excavated in soil deposit. The ability of numerical model to accurately predict the system behavior is evaluated by performing verification analyses on existing researches. Subsequently, a parametric study carried out to reveal the influence of size of footing/voids and their location (i.e. depth, spacing, eccentricity) on the bearing capacity of footing. To clarify the failure mechanism, the distribution of shear strain in the soil for different scenarios is assessed. The parametric study provided a new framework to determine the bearing capacity and the mode of failure for footings on voids. Based on the results, a criterion can be issued to avoid collapse of footing/voids regarding the shape, location and size of voids. The results can also be used to design construction of a footing on existing voids while the acquired failure mechanisms can be appointed to develop analytical solutions for this problem. Results demonstrated that a critical depth for voids and a critical distance between them exist where the influence on the ultimate bearing capacity of footing disappears. 相似文献
6.
The classical solution to the bearing capacity problem predicts the limit load on symmetrically loaded shallow strip footings. A useful hypothesis was suggested by Meyerhof to account for eccentricity of loading, in which the footing width is reduced by twice-the-eccentricity to its ‘effective’ size. This hypothesis sometimes has been criticized as being overconservative. This paper examines Meyerhof’s suggestion and presents the bearing capacity of eccentrically loaded footings calculated using the kinematic approach of limit analysis. It is found that the effective width rule yields a bearing capacity equivalent to that calculated based on the assumption that the footing is smooth. For more realistic footing models and for cohesive soils the effective width rule is a reasonable account of eccentricity in bearing capacity calculations. Only for significant bonding at the soil-footing interface and for large eccentricities does the effective width rule become overly conservative. For cohesionless soils, however, the effective width rule may overestimate the best upper bound. This overestimation increases with an increase in eccentricity. © 相似文献
7.
Rabi Narayan Behera Chittaranjan Patra 《Geotechnical and Geological Engineering》2018,36(5):3029-3080
Extensive laboratory model tests have been carried out on a strip footing resting over dry sand bed subjected to eccentrically inclined load to determine the ultimate bearing capacity (Patra et al. in Int J Geotech Eng 6(3):343–352, 2012a. https://doi.org/10.3328/IJGE.2012.06.03.343-352, Int J Geotech Eng 6(4):507–514, b. https://doi.org/10.3328/IJGE.2012.06.04.507-514). Similarly, lower bound calculations based on finite element method were performed to compute the bearing capacity of a strip footing subjected to an eccentric and inclined load lying over a cohesionless soil with varying embedment depth and relative density (Krabbenhoft et al. in Int J Geomech ASCE, 2014. https://doi.org/10.1061/(ASCE)GM.1943-5622.0000332). The load may be applied in two ways namely, towards the center line and away from the center line of the footing. Based on the results (both experimental and numerical analyses), a neural network model is developed to predict the reduction factor that will be used in computing the ultimate bearing capacity of an eccentrically inclined loaded strip footing. This reduction factor (RF) is the ratio of the ultimate bearing capacity of the footing subjected to an eccentrically inclined load to the ultimate bearing capacity of the footing subjected to a centric vertical load. A thorough sensitivity analysis is carried out to evaluate the parameters affecting the reduction factor. Based on the weights of the developed neural network model, a neural interpretation diagram is developed to find out whether the input parameters have direct or inverse effect on the output. A prediction model equation is framed with the trained weights of the neural network as the model parameters. The predictions from ANN, and those from other approaches, are compared with the results computed from both experimentation and FEM analyses. The ANN model results are found to be more accurate and well matched with other results. 相似文献
8.
Ernesto Ausilio 《Geotechnical and Geological Engineering》2014,32(4):885-899
This paper investigates the performance of geo-reinforced soil structures subjected to loading applied to strip footings positioned close to a slope crest. The kinematic theorem of limit analysis, which is based on the upper bound theory of plasticity, is applied for evaluating the ultimate bearing capacity within the framework of pseudo-static approach to account for earthquake effects. The mechanism considered in this analysis is a logarithmic spiral failure surface, which is assumed to start at the edge of the loaded area far from the slope, consistent with the observed failure mechanisms shown in the experimental tests reported in the literature. A parametric study is then carried out to investigate the influence of various parameters including the geosynthetic configuration, backfill soil friction angle, footing distances from the crest of the slope, slope angles and horizontal seismic coefficients. Attention is paid to the failure mechanism because its maximum depth is the depth at least to which the reinforcements must be placed. Results of the analyses are presented in the form of non-dimensional design charts for practical use. Finally, a simple procedure based on the assessment of earthquake-induced permanent displacements is shown for the design of footing resting on reinforced slopes subjected to earthquake. 相似文献
9.
10.
M. El Sawwaf 《Geotechnical and Geological Engineering》2010,28(4):311-323
The paper presents the results of laboratory model tests and theoretical analysis on the behavior of a strip footing supported
on sheet pile wall-stabilized sandy slope and loaded vertically to failure. The parameters varied in the study include the
height, stiffness and location of the sheet pile wall, the location of the footing relative to the slope crest and the relative
density of sand. Two-dimensional plane strain finite element analyses was used to analyze a prototype strip footing on sandy
slope with same conditions. The results indicate that the inclusion of sheet pile wall has significant effect in improving
the response of the strip footing and the slope itself. The theoretical results confirm the experimental results of the model
footing tests and show reasonable agreement. Based on the numerical and experimental results, critical values of the sheet
pile wall parameters for maximum stabilizing effect are established. 相似文献
11.
Ashis Kumar Bera Ambarish Ghosh Amalendu Ghosh 《Geotechnical and Geological Engineering》2007,25(3):315-325
This paper focuses on the effective utilization of pond ash, as foundation medium. A series of laboratory model tests have
been carried out using square, rectangular and strip footings on pond ash. The effects of dry density, degree of saturation
of pond ash, size and shape of footing on ultimate bearing capacity of shallow foundations are presented in this paper. Local
shear failure of a square footing on pond ash at 37% moisture content (optimum moisture content) is observed up to the values
of dry density 11.20 kN/m3 and general shear failure takes place at the values of dry density 11.48 kN/m3 and 11.70 kN/m3. Effects of degree of saturation on ultimate bearing capacity were studied. Experimental results show that degree of saturation
significantly affects the ultimate bearing capacity of strip footing. The effect of footing length to width ratio (L/B), on increase in ultimate bearing capacity of pond ash, is insignificant for L/B ≥ 10 in case of rectangular footings. The effects of size of footing on ultimate bearing capacity for all shapes of footings
viz., square, rectangular and strip footings are highlighted. 相似文献
12.
A rigorous lower bound solution, with the usage of the finite elements limit analysis, has been obtained for finding the ultimate bearing capacity of two interfering strip footings placed on a sandy medium. Smooth as well as rough footing–soil interfaces are considered in the analysis. The failure load for an interfering footing becomes always greater than that for a single isolated footing. The effect of the interference on the failure load (i) for rough footings becomes greater than that for smooth footings, (ii) increases with an increase in ?, and (iii) becomes almost negligible beyond S/B > 3. Compared with various theoretical and experimental results reported in literature, the present analysis generally provides the lowest magnitude of the collapse load. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
13.
Bearing capacity of strip foundation on geogrid-reinforced sand 总被引：1，自引：0，他引：1
E. C. Shin B. M. Das E. S. Lee C. Atalar 《Geotechnical and Geological Engineering》2002,20(2):169-180
Results of small-scale laboratory model tests to determine the ultimate bearing capacity of a strip foundation supported by sand with multiple layers of geogrid reinforcement are presented. Tests were conducted with only one type of geogrid and a sand compacted to one relative density. The embedment ratio of the foundation was varied from zero to 0.6. It is found that, for the given reinforcement-depth ratio, the bearing capacity ratio with respect to ultimate load increases with embedment. The relationship between the bearing capacity ratio at ultimate load and at limited levels of settlement (less than or equal to 5% of foundation width) is also presented. The bearing capacity ratio at limited levels of settlement is smaller than the value at ultimate load. 相似文献
14.
超大型沉井首次接高受力及变形规律初探 总被引：1，自引：0，他引：1
依托马鞍山长江大桥南锚碇沉井的首次接高,对其竖向沉降、隔墙墙底土压力和隔墙底板受力情况进行了监测。结果表明,超大型沉井兼有条形基础的特点和整体工作性能,能够承受较大的竖向变形,与单纯考虑地基承载力相比,更适合于按变形控制接高。沉井接高时普通隔墙下的土压力小于分区隔墙,并且普通隔墙下部土体会先达极限承载力,后续接高产生的荷载转而由分区隔墙（或井壁）来承担。沉井首节混凝土浇筑就已决定了隔墙底板的应力大小和分布情况,后续接高不会再引起大的改变;隔墙底板中间部分受力较小,外围拉应力较大,通过井壁外土体的密实回填可有效降低此部分拉应力。 相似文献
15.
Bearing capacity of two close strip footings on soft clay reinforced with geotextile 总被引：1，自引：1，他引：0
For many years ago, the beneficial effects of using reinforcement to improve the property of soil have been demonstrated. Over the last three decades, the use of polymeric reinforcement such as geotextile has increased in geotechnical engineering. Among the possible applications, earth reinforcement techniques have become useful and economical techniques to solve many problems in geotechnical engineering practice, such as improve the bearing capacity and settlement characteristics of the footing. This research presents the effect of geotextile inclusion on the bearing capacity of two close strip footings located at the surface of soft clay. A broad series of finite element analysis were performed on two footings with width of 1 and 2 m using two-dimensional plane strain model using the computer code Plaxis (ver 8). Only one type of soft clay was used for the analysis, and the soil was represented by two yielding criteria including hardening soil model and Mohr–Coulomb model, while reinforcement was represented by elastic element, and at the interface between the reinforcements and soft clay, interface elements have been used. A wide range of boundary conditions, including unreinforced and reinforced cases, was analyzed by varying parameters such as number of geotextile layers, vertical spacing of layers, depth to topmost layer of geotextile, tensile stiffness of geotextile layers, and distance of between two footings. From numerical results, the bearing capacity ratio and the interference factor of the foundations have been estimated. On the basis of the analysis performed in this research, it can be concluded that there is a best distance between footings and optimum depth for topmost layer to achieve maximum bearing capacity for closely spaced strip footings. The bearing capacity was also found to increase with increasing number of reinforcement layers if the reinforcements were placed within a range of effective depths. In addition, the analysis indicated that increasing reinforcement stiffness beyond a threshold value does not result in a further increase in the bearing capacity. 相似文献
16.
This paper presents the method proposed to calculate the bearing capacity of a square footing under oblique and eccentric oblique loading condition (satisfying both shear failure and settlement criteria) resting on fiber reinforced sand layer underlain by sand with geosynthetic/fabric sheet at the interface. Large direct shear tests were carried out to investigate the shear strength parameters of sand and randomly distributed fiber reinforced sand (RDFS) and soil-plastic fabric sheet bond. The ultimate bearing capacity of RDFS was determined using direct shear results. Non-dimensional charts proposed by Kumar (Behaviour of eccentrically–obliquely loaded footing on reinforced earth slab. Ph.D. thesis, University of Roorkee, Roorkee, India, 2002) were used to consider the contribution of plastic fabric sheet in increasing the bearing capacity. Also, for calculating the settlement, horizontal deformation and tilt at a given pressure the regression analysis of plate load test data have been carried out. The predicted values of ultimate bearing capacity, settlement, horizontal deformation and tilt are compared with the experimental values which are in good agreement with each other. There appeared to be an increase in the residual shear strength and angle of internal friction of RDFS. 相似文献
17.
By using small scale model tests, the interference effect on the vertical load-deformation behavior of a number of equally
spaced strip footings, placed on the surface of dry sand, was investigated. At any stage, all the footings were assumed to
(i) carry exactly equal magnitude of load, and (ii) settle to the same extent. No tilt of the footing was permitted. The effect
of clear spacing (s) among footings on the results was explored. A new experimental setup was proposed in which only one footing
needs to be employed rather than a number of footings. The bearing capacity increases continuously with decrease in spacing
among the footings. The interference effect becomes further prominent with increase in soil friction angle. In contrast to
an increase in the bearing capacity, with decrease in spacing of footings, an increase in the footing settlement associated
with the ultimate state of shear failure was observed. The present experimental observations were similar to those predicted
by the available theory, based on the method of characteristics. As compared to the theory, the present experimental data,
however, indicates much greater effect of interference especially for larger spacing among footings. 相似文献
18.
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
19.
The ultimate bearing capacity of two closely spaced strip footings, placed on a cohesionless medium and loaded simultaneously
to failure at the same magnitude of failure load, was determined by using an upper bound limit analysis. A logarithmic spiral
radial shear zone, comprising of a number of triangular rigid blocks, was assumed to exist around each footing edge. The equations
of the logarithmic spiral arcs were based on angles φL and φR rather than soil friction angle φ; the values of φL and φR were gradually varied in between 0 and φ. The ultimate bearing capacity was found to become maximum corresponding to a certain
critical spacing between the footings. For spacing greater than the critical, the bearing capacity was found to decrease continuously
with increase in the spacing. The extent of the spacing corresponding to which the ultimate bearing capacity becomes either
maximum or equal to that of a single isolated footing increases with increase in φ. The results compare reasonably well with
the available theoretical and experimental data. 相似文献
20.
S. Benmebarek S. Benmoussa L. Belounar N. Benmebarek 《Geotechnical and Geological Engineering》2012,30(4):907-923
Natural soils are often deposited in layers. The estimation of the bearing capacity of the soil, using conventional bearing capacity theory based on the properties of the top layer, introduces significant inaccuracies if the thickness of the top layer is comparable to the width of the rigid footing placed on the soil surface. Saturated normally consolidated and lightly overconsolidated clays indicate that under undrained condition the cohesion of soil mass increases almost linearly with depth. A few theoretical studies have been proposed in the literature to incorporate the variation of cohesion with depth in the computation of the ultimate bearing capacity of strip and circular footings. In this paper, after reviewing previous works, numerical computations using the FLAC code (Fast Lagrangian Analyses of Continua) are reported to evaluate the two layered clays effect on the bearing capacity beneath rigid strip footing subject to axial static load. The results of the bearing capacity relating to the relative thickness of the top layer, the strength ratio of the soil two-layered clays and the rates of the increase of soil cohesion with depth are presented in Tables and graphs. The obtained results are compared with previous published results available in the literature. 相似文献