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1.
The ultimate bearing capacity of a new strip footing placed on a cohesionless soil medium, in the presence of an existing
strip footing, the load on which is assumed to be known, has been determined. Both the footings are assumed to be perfectly
rigid and rough. The analysis is carried out by using an upper bound finite element limit analysis. For different clear spacing
(S) between the footings, the values of the efficiency factor (ξγ) were determined; where ξγ is defined as the ratio of the failure load for an interfering new footing of a given width (B) to that for a single isolated
footing having the same width. For ϕ < 30°, it is generally noted that the magnitude of ξγ increases continuously with a decrease in S/B. For ϕ > 30°, on the other hand if the applied load on the existing footing
is approximately greater than half the failure load for a single isolated footing having the same width, the peak magnitude
of ξγ was found to occur at around S/B ≈ 0.1 rather than at S/B = 0. The increase in ξγ becomes further significant with an increase in the magnitude of the load on the existing footing. 相似文献
2.
The ultimate bearing capacity of a number of multiple strip footings, identically spaced and equally loaded to failure at the same time, is computed by using the lower bound limit analysis in combination with finite elements. The efficiency factor (ξγ), due to the component of soil unit weight, is computed with respect to changes in the clear spacing (S) between the footings. It is noted that the failure load for a footing in the group becomes always greater than that of a single isolated footing. The values of ξγ for the smooth footings are found to be always lower than the rough footings. The values of ξγ are found to increase continuously with a decrease in the spacing between footings. As compared to the available theoretical and experimental results reported in literature, the present analysis provides generally a little lower values of ξγ. 相似文献
3.
By using an upper bound limit analysis in conjunction with finite elements and linear programming, the ultimate bearing capacity of two interfering rough strip footings, resting on a cohesionless medium, was computed. Along all the interfaces of the chosen triangular elements, velocity discontinuities were employed. The plastic strains were incorporated using an associated flow rule. For different clear spacing (S) between the two footings, the efficiency factor (ξγ) was determined, where ξγ is defined as the ratio of the failure load for a strip footing of given width in the presence of the other footing to that of a single isolated strip footing having the same width. The value of ξγ at S/B = 0 becomes equal to 2.0, and the maximum ξγ occurs at S/B = Scr/B. For S/B?Scr/B, the ultimate failure load for a footing becomes almost half that of an isolated footing having width (2B + S), and the soil mass below and in between the two footings deforms mainly in the downward direction. In contrast, for S/B>Scr/B, ground heave was noticed along both the sides of the footing. As compared to the available theories, the analysis provides generally lower values of ξγ for S/B>Scr/B. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
4.
The ultimate bearing capacity of a group of equally spaced multiple rough strip footings was determined due to the contribution of soil unit weight. The analysis was performed by using an upper bound theorem of limit analysis in combination with finite elements and linear programming. Along the interfaces of all the triangular elements, velocity discontinuities were considered. The value of ξγ was found to increase continuously with a decrease in S/B, where (i) ξγ is the ratio of the failure load of an interfering strip footing of a given width (B) to that of a single isolated strip footing having the same width and (ii) S is the clear spacing between any two adjacent footings. The effect of the variation of spacing on ξγ was found to be very extensive for small values of S/B; ξγ approaches infinity at S/B=0. In all the cases, the velocity discontinuities were found to exist generally in a zone only around the footing edge. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
5.
《Geomechanics and Geoengineering》2013,8(4):274-285
By applying the lower bound finite element limit analysis in conjunction with non-linear optimisation, the bearing capacity factors, Nc, Nq and Nγ, 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 Nc, Nq and Nγ 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 Nγ, the factors Nc and Nq 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. 相似文献
6.
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
7.
In recent times, rapid urbanisation coupled with scarcity of land forces several structures to come up ever closer to each
other, which may sometime cause severe damage to the structures from both strength and serviceability point of view, and therefore,
a need is felt to devise simplified methods to capture the effect of footing interference. In the present study, an attempt
has been made to model the settlement behaviour of two strip footings placed in close spacing on layered soil deposit consisting
of a strong top layer underlying a weak bottom layer. Theory of elasticity is employed to derive the governing differential
equations and subsequently solved by the finite difference method. The perfectly rough strip footings are considered to be
resting on the surface of two-layer soil system, and the soil is assumed to behave as linear elastic material under a range
of static foundation load. The effect of various parameters such as the elastic moduli and thickness of two layers, clear
spacing between the footings and footing load on the settlement behaviour of closely spaced footings has been determined.
The variation of vertical normal stress at the interface of two different soil layers as well as at the base of the failure
domain also forms an important part of this study. The results are presented in terms of settlement ratio (ξδ), and their variation is obtained with the change in clear spacing between two footings. The present theoretical investigation
indicates that the settlement of closely spaced footings is found to be higher than that of single isolated footing, which
further reduces with increase in the spacing between the footings. 相似文献
8.
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
9.
Current studies of bearing capacity for shallow foundations tend to rely on the hypothesis of an isolated footing. In practice a footing is never isolated; it is mostly in interaction with other footings. This paper focuses on a numerical study using the finite-difference code Fast Lagrangian Analysis of Continua (FLAC), to evaluate the bearing capacity for two interfering strip footings, subjected to centered vertical loads with smooth and rough interfaces. The soil is modeled by an elasto-plastic model with a Mohr–Coulomb yield criterion and associative flow rule. The interference effect is estimated by efficiency factors, defined as the ratio of the bearing capacity for a single footing in the presence of the other footing to that of the single isolated footing. The efficiency factors have been computed individually to estimate the effects of cohesion, surcharge, and soil weight using Terzaghi’s equation, both in a frictional soil with surcharge pressures and in a cohesive-frictional soil with surcharge pressures. The results have been compared with those available in the literature. 相似文献
10.
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
11.
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 Nσ0 and Nσ, 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. 相似文献
12.
《Geomechanics and Geoengineering》2013,8(2):107-111
The stability of eccentrically loaded strip footings on slopes was investigated using the method of finite element analysis based on the theory of elasto-plasticity. The analysis was done for two different soils involving three levels of slope angle, six footing locations, and two levels of load eccentricity plus central vertical loading. The strip footing analysed was a 3-ft (0.9 m) wide reinforced concrete footing embedded to a depth of 3 ft (0.9 m). The analysis focused on footing settlement, plastic yielding of soil, and ultimate bearing capacity. The results of analysis show that the influence of load eccentricity on footing pressure vs. footing centre settlement is negligibly small. However, the progressive soil yielding and ultimate bearing capacity are greatly affected by load eccentricity. Furthermore, the effect of load eccentricity differs considerably with the load location relative to the footing centre and slope crest. The ultimate bearing capacity for the eccentric load located on the slope side is significantly greater than that for the load located on the other side of the footing centre. For a 2(H): 1(V) slope in silty clay, the effect of slope on footing stability decreases with increasing footing location from slope crest as would be expected, and diminishes when the footing is located from the crest at about 5-times the footing width. 相似文献
13.
Failure envelopes and plastic potentials for eccentrically loaded surface footings on undrained soil
M. Fraser Bransby 《国际地质力学数值与分析法杂志》2001,25(4):329-346
The failure envelope in V–M space for surface foundations on undrained material under eccentric loading can be determined using an extended version of the scaling (or effective area) concept of Meyerhof. A similar displacement transformation allows production of the plastic potential. The two‐dimensional finite element analyses of fully attached foundations subject to combined vertical (V) and moment (M) loading have been used to calculate appropriate scaling points for deduction of the failure envelope and plastic potential. Failure envelopes and plastic potentials are presented for footings on uniform and non‐uniform undrained material and it is seen that the equivalent ‘critical state’ or ‘parallel point’ lies slightly beneath the peak moment capacity. For accurate prediction of failure envelopes for footings on non‐uniform strength soil, consideration must be made of the apparent reduction of the soil heterogeneity as the area of footing in contact with the soil decreases. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
14.
由多个分离基础组成的多基础系统是常用的海洋结构基础型式。基于破坏包络面理论,分析了砂土地基多基础系统的失效模式,建立了相应的承载力计算方法,并验证了计算方法的可行性。对比分析了单一基础和多基础系统不同荷载路径下的荷载安全系数,探讨了破坏包络面理论与分项系数法相结合的基础承载力计算方法。失效模式的分析表明,由于水平荷载的增大,四腿平台结构迎浪侧基础首先到达破坏包络线,其失效模式属于滑动失稳,但由于基础间的运动约束,其并不会出现真正的滑移破坏。随着水平荷载进一步地增大,迎浪侧基础承担的水平和竖向荷载不断减小,导致背浪侧基础受到不断增大的荷载。最终,背浪侧基础也到达破坏包络线,多基础系统失效。分析表明,荷载路径对基础的荷载安全系数有决定性的影响,计算基础的荷载安全系数需指明相应的荷载路径。鉴于破坏包络面的大小和形状取决于众多因素,基础设计时需采用特定工况下的破坏包络面进行承载力计算。 相似文献
15.
This paper presents a study on the bearing capacity of eccentrically-loaded rough ring footings resting over cohesionless soil. To this aim, a series of 3D numerical simulations were performed using the finite difference method. In order to consider the effect of load eccentricity, reduction factor method is applied. In this method, the ratio of an eccentrically-loaded bearing capacity to the bearing capacity of the same footing under vertical load is defined. Comparison between the results of the numerical simulations with those of analytical solutions and experimental data indicates good agreement. A mathematical expression is also introduced for eccentrically-loaded ring footings. 相似文献
16.
Field and Laboratory Tests Investigating Settlements of Foundations on Weathered Keuper Marl 总被引：1，自引：1，他引：0
Ernst-Dieter Hornig 《Geotechnical and Geological Engineering》2010,28(3):233-240
Measured settlements of buildings on the weathered Keuper Marl appeared to be much smaller than calculated settlements, which
were based on stiffness modulus from standard oedometer tests. Therefore, both special triaxial K
0-tests and oedometer tests were carried out for an accurate determination of stiffness moduli. Modulus obtained in the triaxial
K
0-tests were at least two to three times the values obtained in the oedometer tests. To verify observations from the laboratory
tests, the loads and the settlements of two single footings on weathered Keuper mudstone have been measured during construction
of a building over 1 year. Also, a large scale footing load test with measurements of deformations were conducted on the weathered
Keuper mudstone. The measured settlements of the two single footings and the tested foundation were compared with the settlements
based on conventional calculations with moduli from oedometer tests and triaxial K
0-tests. Up to a foundation pressure of σv = 500 kN/m2 the calculated settlement based on E
S-modulus obtained from triaxial K
0-tests was found to correspond well to the measured deformation. For foundation pressure beyond 500 kN/m2, the foundation
response was highly non-linear and it could not be described any more with the linear-elastic model. Therefore the footing
load test was also simulated by FEM analyses. 相似文献
17.
Yakov M. Reznik 《Engineering Geology》1998,50(3-4):319-327
Footing settlements depend not only on physical and mechanical properties of base soils, but also on applied load intensities and their distributions with depth, as well as on footing rigidity, shape and dimensions. An analytical expression relating rigid bearing plate and/or footing settlements to thicknesses of deformation (active) zones, which form below footing bottoms, has been previously offered by the author. The results of tests performed with 0.5, 1.0 and 4.0 m2-area square footings, constructed on undisturbed clayey soils and containing data describing active zone development, were collected from literature and analyzed. This paper presents graphical relationships between square footing settlements, active zone thicknesses and footing dimensions, which are verified by published test results performed with experimental square footings, having areas different than the ones selected for statistical analyses. 相似文献
18.
非均质地基承载力及破坏模式的FLAC数值分析 总被引：3，自引：0，他引：3
利用基于Lagrangian显式差分的FLAC算法，通过数值计算，对黏结力随深度线性增长的非均质地基上条形基础和圆形基础的极限承载力及地基破坏模式进行了对比计算与系统分析。研究表明：（1）随着地基黏结力沿深度非均匀变化系数的增大，地基的破坏范围逐渐集中在地基表层和基础两侧：（2）即使地基的非均质程度较小，当将非均质地基近似地按均质地基考虑时，由此所估算的承载力可能过于保守；（3）地基承载力系数随黏结力沿深度非均匀变化系数的增大而非线性地增大。与数值解相比，skempton与Peck等近似公式均可能高估了非均质地基承载力。 相似文献
19.
Jyant Kumar 《国际地质力学数值与分析法杂志》2009,33(2):275-284
By using the method of characteristics, the effect of footing–soil interface friction angle (δ) on the bearing capacity factor Nγ was computed for a strip footing. The analysis was performed by employing a curved trapped wedge under the footing base; this wedge joins the footing base at a distance Bt from the footing edge. For a given footing width (B), the value of Bt increases continuously with a decrease in δ. For δ=0, no trapped wedge exists below the footing base, that is, Bt/B=0.5. On the contrary, with δ=?, the point of emergence of the trapped wedge approaches toward the footing edge with an increase in ?. The magnitude of Nγ increases substantially with an increase in δ/?. The maximum depth of the plastic zone becomes higher for greater values of δ/?. The results from the present analysis were found to compare well with those reported in the literature. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
20.
The stress characteristics method (SCM) has been used to compute the bearing capacity of smooth and rough ring foundations. Two different failure mechanisms for a smooth footing, and four different mechanisms for a rough footing have been considered. For a rough base, a curvilinear non-plastic wedge has been employed below the footing. The analysis incorporates the stress singularities at the inner as well as outer edges of the ring footing. Bearing capacity factors, Nc, Nq and Nγ are presented as a function of soil internal friction angle (ϕ) and the ratio (ri/ro) of inner to outer radii of the footing. 相似文献