Study on Seepage Characteristics of Composite Bucket Foundation Under Eccentric Load

Under the effect of eccentric loads,when the suction pressure of the composite bucket foundation is leveled,the seepage failure is very easy to occur.The seepage failure occurrence causes the foundation to settle unevenly and impairs the bearing performance.This study uses ABAQUS finite element software to establish a composite bucket foundation model for finite element analysis.The model simulates the seepage of the foundation penetrating process under eccentric load to reveal the induced seepage characteristics of the bucket foundation.The most vulnerable position of seepage failure under the eccentric loading is elucidated.Critical suction formulas for different offset eccentric moment strategies are derived and compared with existing literature formulas.Then the derived formula is supplemented and corrected according to the pressure difference between adjacent cabins.Conclusions can be drawn:(1)Under eccentric loads,the critical suction decreases about 7%−10%.(2)The pressure difference between adjacent cabins impacts significantly on the seepage field,and the critical suction,at most,can be reduced by 17.56%.(3)the offset strategies have little effect on the seepage field.Efficient and appropriate strategies can be selected to meet the requirement of leveling in engineering project.

Influence of location of large-scale asperity on shear strength of concrete-rock interface under eccentric load

The location and geometry of large-scale asperity present at the foundation of concrete gravity dams and buttress dams affect the shear resistance of the concrete-rock interface.However,the parameters describing the frictional resistance of the interface usually do not account for these asperities.This could result in an underestimate of the peak shear stre ngth,which leads to significantly conservative design for new dams or unnecessary stability enhancing measures for existing ones.The aim of this work was to investigate the effect of the location of first-order asperity on the peak shear strength of a concrete-rock interface under eccentric load and the model discrepancy associated with the commonly used rigid body methods for calculating the factor of safety(FS)against sliding.For this,a series of direct and eccentric shear tests under constant normal load(CNL)was carried out on concrete-rock samples.The peak shear strengths measured in the tests were compared in terms of asperity location and with the predicted values from analytical rigid body methods.The results showed that the large-scale asperity under eccentric load significantly affected the peak shear strength.Furthermore,unlike the conventional assumption of sliding or shear failure of an asperity in direct shear,under the effect of eccentric shear load,a tensile failure in the rock or in the concrete could occur,resulting in a lower shear strength compared with that of direct shear tests.These results could have important implications for assessment of the FS against sliding failure in the concrete-rock interface.

Penetration Resistance of Composite Bucket Foundation with Eccentric Load for Offshore Wind Turbines

The penetration of the composite bucket foundation(CBF)is crucial in its construction process.In actual projects,the foundation is inevitably subjected to eccentric load caused by towers and turbines,as well as wind,wave,and flow,during the one-step installation.Moreover,the eccentric load is bound to affect the penetration method and penetration resistance of the foundation.To examine the above-mentioned issues,the penetration resistance of CBF with eccentric load was calculated and analyzed based on model tests,and the seepage field of the CBF under eccentric load was analyzed using ABAQUS.The influence of different magnitudes of eccentric load and various offset strategies on penetration resistance was analyzed,and the theoretical and measured values were compared.The result indicated that the negative pressure of the offset room was found to be smaller than that of other rooms when the CBF penetrated the soil under eccentric load.The penetration resistance of CBF under eccentric load was larger than that without eccentricity,and the larger the eccentric load is,the greater the penetration resistance.The influence of different eccentric load offset strategies on penetration resistance was found to be negligible.The calculated penetration resistance under eccentric load was in good agreement with the measured value.

DEM analysis of passive arching in a shallow trapdoor under eccentric loading

This study analyzed the passive arching effect under eccentric loading by developing a series of trapdoor discrete numerical models.The numerical models were validated by comparison with laboratory test results.The deformation pattern,soil arching ratio,force chain distribution,and coordination number under various surcharge magnitudes and deviation distances were analyzed.The numerical results showed that the deformation diagram of soil particles can be divided into three zones:principal displacement zone,transition zone,and static zone.With an increase in the surcharge magnitude,the range of the principal displacement zone decreased,but the range of the transition region increased.The curve of the soil arching ratio on the trapdoor can be divided into three phases,which can be well characterized by the tangent modulus.The passive arching effect is degraded by a surcharge.The ulti-mate soil arching ratio could be approximated as a W-shaped distribution along the+x-direction.With an increase in the trapdoor displacement,the force chain on the trapdoor gradually expanded outward to form an inverted funnel shape.The most powerful force on the trapdoor was mainly distributed on its edge.The average coordination number decreased gradually as the trapdoor moved upward.

Load eccentricity effects on behavior of circular footings reinforced with geogrid sheets

In this paper, an experimental study for an eccentrically loaded circular footing, resting on a geogridreinforced sand bed, is performed. To achieve this aim, the steel model footing of 120 mm in diameterand sand in relative density of 60% are used. Also, the effects of depth of first and second geogrid layersand number of reinforcement layers （1e4） on the settlement-load response and tilt of footing undervarious load eccentricities （0 cm, 0.75 cm, 1.5 cm, 2.25 cm and 3 cm） are investigated. Test results indicatethat ultimate bearing capacity increases in comparison with unreinforced condition. It is observed thatwhen the reinforcements are placed in the optimum embedment depth （u/D ？0.42 and h/D ？0.42）, thebearing capacity ratio （BCR） increases with increasing load eccentricity to the core boundary of footing,and that with further increase of load eccentricity, the BCR decreases. Besides, the tilt of footing increaseslinearly with increasing settlement. Finally, by reinforcing the sand bed, the tilt of footing decreases at 2layers of reinforcement and then increases by increasing the number of reinforcement layers.

Reliability Analysis of Symmetrical Columns with Eccentric Loading from Lindley Distribution

This paper shows the reliability of the symmetrical columns with eccentric loading about one and two axes due to the maximum intensity stress and minimum intensity stress.In this paper,a new lifetime distribution is introduced which is obtained by compounding exponential and gamma distributions(named as Lindley distribution).Hazard rates,mean time to failure and estimation of single parameter Lindley distribution by maximum likelihood estimator have been discussed.It is observed that when the load and the area of the cross section increase,failure of the column also increases at two intensity stresses.It is observed from the results that reliability decreases when scale parameter increases.

Behavior of eccentrically loaded concrete-filled GFRP tubular short columns

The glass fiber reinforced polymer (GFRP) tube is an effective material that can increase the bearing capacity and ductility of concrete.To study the mechanical behavior of this composite structure,twenty-one concrete-filled GFRP tubular short columns were tested under an eccentric load.The principle influencing factors,such as the eccentricity ratio,concrete strength and ratio of longitudinal reinforcement were also studied.In addition,the course of deformation,failure mode,and failure mechanism were analyzed by observing the phenomena and summarizing the data.The test results indicated that the strength and deformation characteristics of core concrete increase as a result of the addition of the GFRP tube.However,the gain in strength due to the addition of the GFRP tube decreases as the ratio of e /d increases.An increase in the longitudinal steel ratio can improve the bearing capacity of the composite short column effectively.Furthermore,the study showed that the constraint effect of the GFRP tube on high-strength concrete is not as effective as that on common concrete.The reason is that the lateral deformation of the high-strength concrete is less than that of the common concrete when the concrete column was tested under the same axial compression ratio.

Experimental research on self-stressing and self-compacting concrete filled steel tube columns subjected to eccentric load

A total of fifteen self-stressing and selfcompacting concrete(SSC)filled steel tube columns and three common self-compacting concrete filled steel tube(CFST)columns are tested under eccentric compression load to analyze the the effect of initial self-stress on the compression behavior of CFSTs.The results show that the elastic working range of the columns is lengthened because of initial self-stress and it slightly decreases with the increase of load eccentricity ratio and slenderness ratio.Because of the initial self-stress,the concrete core is always under compression in three directions,so the compactness is enhanced and the ultimate bearing capacity obviously increases;but the initial self-stress hardly affects the failure mode of the columns.

Behavior of ring footing resting on reinforced sand subjected to eccentric-inclined loading

Ring footings are suitable for the structures like tall transmission towers, chimneys, silos and oil storages.These types of structures are susceptible to horizontal loads(wind load) in addition to their dead weight.In the literature, very little or no effort has been made to study the effect of ring footing resting on reinforced sand when subjected to eccentric, inclined and/or eccentric-inclined loadings. This paper aims to study the behavior of ring footing resting on loose sand and/or compacted randomly distributed fiberreinforced sand(RDFS) when subjected to eccentric(0 B, 0.05 B and 0.1 B, where B is the outer diameter of ring footing), inclined(0°,5°,10°, 15°,-5°,-10° and-15°)and eccentric-inclined loadings by using a finite element(FE) software PLAXIS 3 D. The behavior of ring footing is studied by using a dimensionless factor called reduction factor(RF). The numerical model used in the PLAXIS 3 D has been validated by conducting model plate load tests. Moreover, an empirical expression using regression analysis has been presented which will be helpful in plotting a load-settlement curve for the ring footing.

Experimental investigation on seismic behavior of single piles in sandy soil

This paper describes a quasi-static test program featuring lateral cyclic loading on single piles in sandy soil. The tests were conducted on 18 aluminum model piles with different cross sections and lateral load eccentricity ratios, e/d, （e is the lateral load eccentricity and d is the diameter of pile） of 0, 4 and 8, embedded in sand with a relative density of 30% and 70%. The experimental results include lateral load-displacement hysteresis loops, skeleton curves and energy dissipation curves. Lateral capacity, ductility and energy dissipation capacity of single piles under seismic load were evaluated in detail. The lateral capacities and the energy dissipation capacity of piles in dense sand were much higher than in loose sand. When embedded in loose sand, the maximum lateral load and the maximum lateral displacement of piles increased as e/d increased. On the contrary, when embedded in dense sand, the maximum lateral load of piles decreased as e/d increased. Piles with a higher load eccentricity ratio experienced higher energy dissipation capacity than piles with e/d of 0 in both dense and loose sand. At a given level of displacement, piles with circular cross sections provided the best energy dissipation capacity in both loose and dense sand.