Model Uncertainty of Eurocode 7 Approach for Bearing Capacity of Circular Footings on Dense Sand

Abstract This paper reports a theoretical and experimental investigation of the influence of shallow water waves on the bearing capacity of foundations in sea beds. The propagation of pressure waves through a porous sea bed is calculated, assuming plane elastic-plastic soil deformation under undrained loading conditions, and including the effect of dilatancy. The effective stresses thus generated are compared with the soil-stability limits. The consequences for both sand and clay deposits are considered individually. Model experiments in a flume demonstrate how prolonged wave action increases the density of an initially very loose sand, whereas it expands an initially dense sand. Because small changes in void ratio have a significant effect on the bearing capacity of a sediment, the bearing capacity of a loose sand bed increases with prolonged wave action, but that of a dense sand decreases. It was found, however, that under all circumstances the ultimate bearing capacity of a sandy sea bottom is largely sufficient for pile-foundation purposes. In fact, stormy weather tends to stabilize the bearing capacity of a sandy sea bottom. In contrast, calculations for clay deposits show that the excess pore pressure caused by wave action on a normally consolidated clay cannot be dissipated within a practical time limit. Waves are thus unable to compact a clay deposit. The shearing forces generated by shallow waves in an underconsolidated clay may therefore cause soil instability during a severe storm. Our calculations and model experiments seem to indicate that shallow foundations subject to strong wave action will settle gradually within a plastic region of the sea bottom as a result of cyclic wave loading. This paper describes a practical method for calculating a safe depth of burial and bearing capacity for shallow foundations subject to wave action. INTRODUCTION Ocean waves are able to generate significant shearing forces in sea-floor sediments up to total (water + soil) depths of approximately half the length of the waves. Waves could thus affect the end bearing capacity of shallow foundations or the lateral resistance at shallow depths of deep foundation piles. We shall first calculate the pressure fluctuations at the sea bottom due to plane irregular waves using the small-amplitude wave theory. We shall then calculate the stresses and pore pressures generated in the sea bottom by such irregular pressure fluctuations at the bed surface, assuming plane elastic - plastic soil deformation and introducing a pore - pressure parameter for the saturated soil under undrained, biaxial loading condition s. We shall compare those stresses with the soil stability limits and consider soil consolidation due to wave action. Then we shall present the results of model experiments performed in a laboratory flume, showing that prolonged wave action increases the density of an initially very loose sand, whereas it expands an initially dense sand. We shall compare theory and experiment. Finally, we shall discuss a method for calculating a safe depth of burial and bearing capacity for shallow foundations subject to wave action.

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Pressure Settlement Behaviour and Bearing Capacity of Asymmetric Embedded Plus Shaped Footing on Layered Sand

Civil and Environmental Engineering Reports ◽

10.2478/ceer-2021-0039 ◽

2021 ◽

Vol 31 (3) ◽

pp. 152-176

Author(s):

Priyanka Rawat ◽

Rakesh Kumar Dutta

Keyword(s):

Bearing Capacity ◽

Numerical Study ◽

Friction Angle ◽

Thickness Ratio ◽

Embedment Depth ◽

Loose Sand ◽

Dense Sand ◽

Comparison Of The Results ◽

Abaqus Software ◽

Settlement Behaviour

Abstract The aim of the present numerical study was to analyse the pressure settlement behaviour and bearing capacity of asymmetric plus shaped footing resting on loose sand overlying dense sand at varying embedment depth. The numerical investigation was carried out using ABAQUS software. The effect of depth of embedment, friction angle of upper loose and lower dense sand layer and thickness of upper loose sand on the bearing capacity of the asymmetric plus shaped footing was studied in this investigation. Further, the comparison of the results of the bearing capacity was made between the asymmetric and symmetric plus shaped footing. The results reveal that with increase in depth of embedment, the dimensionless bearing capacity of the footings increased. The highest increase in the dimensionless bearing capacity was observed at embedment ratio of 1.5. The increase in the bearing capacity was 12.62 and 11.40 times with respect to the surface footings F1 and F2 corresponding to a thickness ratio of 1.5. The lowest increase in the dimensionless bearing capacity was observed at embedment ratio of 0.1 and the corresponding increase in the bearing capacity was 1.05 and 1.02 times with respect to the surface footing for footings F1 and F2 at a thickness ratio of 1.5.

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Assessment of Seismic Bearing Capacity of a Strip Footing Resting on Reinforced Earth Bed using Pseudo-Static Analysis

Civil and Environmental Engineering Reports ◽

10.2478/ceer-2021-0023 ◽

2021 ◽

Vol 31 (2) ◽

pp. 117-137

Author(s):

Sagar Jaiswal ◽

Vinay Bhushan Chauhan

Keyword(s):

Bearing Capacity ◽

Dynamic Loading ◽

Ultimate Load ◽

Strip Footing ◽

Shallow Foundation ◽

Coarse Grained ◽

Geosynthetic Reinforcement ◽

Load Bearing Capacity ◽

Load Bearing ◽

Dense Sand

Abstract The use of geosynthetic reinforcement to enhance the ultimate load-bearing capacity and reduce the anticipated settlement of the shallow foundation has gained sufficient attention in the geotechnical field. The improved performance of the shallow foundation is achieved by providing one or more layers of geosynthetics below the foundation. The full wraparound technique proved to be efficient for the confinement of soil mass and reduction in settlement of foundation however lacks the literature to ascertain the performances of such footing under dynamic loading. In view of the above, the present study examines the effect of geosynthetic layers having a finite length with full wraparound ends as a reinforcement layer, placed horizontally at a suitable depth below the foundation using the finite element modeling (FEM) and evaluates the ultimate load-bearing capacity of a strip footing resting on loose and dense coarse-grained earth beds under seismic loading and further compared to those of footing resting on unreinforced earth bed. Moreover, the effect of horizontal seismic acceleration coefficient (kh) on the ultimate load-bearing capacity has been investigated by varying kh from 0.1 to 0.6 at an interval of 0.1, for both reinforced and unreinforced earth bed having loose and dense soil strata. Furthermore, this study demonstrates that by adopting the new practice of using the geosynthetic reinforcement with the full wraparound ends in foundations, it is possible to support relatively heavier structures under static as well as dynamic loading without allowing large footing settlements. From the outcomes of the present study, it is noted that the ultimate load-bearing capacity of footing resting on loose and dense sand bed found to be improved by 60% and 18% for soils having friction angle of 25° and 40°, respectively compared to respective unreinforced earth beds under static condition.

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Bearing Capacity Estimation of Shallow Foundations on Dense Sand Underlain by Loose Sand Strata Using Finite Elements Limit Analysis

Lecture Notes in Civil Engineering - Construction in Geotechnical Engineering ◽

10.1007/978-981-15-6090-3_14 ◽

2020 ◽

pp. 203-214

Author(s):

Pragyan Paramita Das ◽

Vishwas N. Khatri

Keyword(s):

Finite Elements ◽

Bearing Capacity ◽

Limit Analysis ◽

Shallow Foundations ◽

Loose Sand ◽

Capacity Estimation ◽

Dense Sand

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Bearing capacity of rectangular footing on layered sand under inclined loading

Journal of Achievements of Materials and Manufacturing Engineering ◽

10.5604/01.3001.0015.5064 ◽

2021 ◽

Vol 108 (2) ◽

pp. 49-62

Author(s):

V. Panwar ◽

R.K. Dutta

Keyword(s):

Bearing Capacity ◽

Numerical Study ◽

Thickness Ratio ◽

Failure Pattern ◽

Width Ratio ◽

Loose Sand ◽

Sand Layer ◽

Inclined Load ◽

Dense Sand ◽

Inclined Loading

Purpose: The study presents the numerical study to investigate the bearing capacity of the rectangular footing on layered sand (dense over loose) using ABAQUS software. Design/methodology/approach: Finite element analysis was used in this study to investigate the bearing capacity of the rectangular footing on layered sand and subjected to inclined load. The layered sand was having an upper layer of dense sand of varied thickness (0.25 W to 2.0 W) and lower layer was considered as loose sand of infinite thickness. The various parameters varied were friction angle of the upper dense (41° to 46°) and lower loose (31° to 36°) layer of sand and load inclination (0° to 45°), where W is the width of the rectangular footing. Findings: As the thickness ratio increased from 0.00 to 2.00, the bearing capacity increased with each load inclination. The highest and lowest bearing capacity was observed at a thickness ratio of 2.00 and 0.00 respectively. The bearing capacity decreased as the load inclination increased from 0° to 45°. The displacement contour shifted toward the centre of the footing and back toward the application of the load as the thickness ratio increased from 0.25 to 1.25 and 1.50 to 2.00, respectively. When the load inclination was increased from 0° to 30°, the bearing capacity was reduced by 54.12 % to 86.96%, and when the load inclination was 45°, the bearing capacity was reduced by 80.95 % to 95.39 %. The results of dimensionless bearing capacity compare favorably with literature with an average deviation of 13.84 %. As the load inclination was changed from 0° to 45°, the displacement contours and failure pattern shifted in the direction of load application, and the depth of influence of the displacement contours and failure pattern below the footing decreased, with the highest and lowest influence observed along the depth corresponding to 0° and 45°, respectively. The vertical settlement underneath the footing decreased as the load inclination increased, and at 45°, the vertical settlement was at its lowest. As the load inclination increased from 0° to 45°, the minimum and maximum extent of influence in the depth of the upper dense sand layer decreased, with the least and highest extent of influence in the range of 0.50 to 0.50 and 1.75 to 2.00 times the width of the rectangular footing, respectively, corresponding to a load inclination of 45° and 0° Research limitations/implications: The results presented in this paper were based on the numerical study conducted on rectangular footing having length to width ratio of 1.5 and subjected to inclined load. However, further validation of the results presented in this paper, is recommended using experimental study conducted on similar size of rectangular footing. engineers designing rectangular footings subjected to inclined load and resting on layered (dense over loose) sand. Originality/value: No numerical study of the bearing capacity of the rectangular footing under inclined loading, especially on layered soil (dense sand over loose sand) as well as the effect of the thickness ratio and depth of the upper sand layer on displacement contours and failure pattern, has been published. Hence, an attempt was made in this article to investigate the same.

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