Lower-Bound Seismic Bearing Capacity of a Strip Footing Adjacent to an Existing Footing on Sand
Publication: International Journal of Geomechanics
Volume 21, Issue 8
Abstract
The ideal notion of footings placed in isolation is rarely implemented in practice and footings are often placed adjacent to each other, interfering with one another's performance. In this paper, the lower-bound finite-element limit analysis method is used to investigate the pseudostatic bearing capacity of a strip footing placed in close proximity to an already-existing strip footing, over cohesionless soil. The pseudostatic approach is used to model the seismic loading. Analyses conducted for different accelerations, soil friction angles, and service load magnitudes on the existing footing and spacings showed that while the presence of the existing footing can improve the pseudostatic bearing capacity of the new footing, an amplified rate of reduction with seismicity ultimately causes the new footing to withstand smaller accelerations compared with its isolated case. The increase in spacing generally reduced bearing capacity. An exception was observed for a friction angle of 40° for all service loads and pseudostatic accelerations, where a maximum in both bearing capacity and fluidization acceleration was observed around 0.1 of the footing widths.
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Data Availability Statement
All data, models, or code that support the findings of this study are available from the corresponding author upon reasonable request.
Notation
The following symbols are used in this paper:
- B
- width of footing;
- Df
- depth of placement of the new footing to the surface;
- Ed
- number of elements along each vertical interface of embedment;
- Ef
- number of elements under the footing;
- h
- depth of domain;
- kh
- pseudostatic horizontal coefficient;
- kh,lim
- cutoff acceleration;
- kv
- pseudostatic vertical coefficient;
- L
- distance from edge of each footing to boundary of domain;
- m
- service load fraction with respect to Qu,iso;
- NcE
- seismic cohesion bearing capacity factor for new footing in presence of existing footing;
- NcE,iso
- seismic cohesion bearing capacity factor for an isolated footing;
- Nd
- number of nodes along each vertical interface of embedment;
- Nf
- number of nodes under the footing;
- NqE
- seismic surcharge bearing capacity factor for new footing in presence of existing footing;
- NqE,iso
- seismic surcharge bearing capacity factor for an isolated footing;
- Nγ,iso
- static bearing capacity factor of the isolated footing;
- NγE
- seismic unit weight bearing capacity factor for new footing in presence of existing footing;
- NγE,iso
- seismic unit weight bearing capacity factor for an isolated footing;
- NγqE
- seismic bearing capacity factor for new embedded footing on cohesionless soil in presence of existing footing;
- Qu,iso
- ultimate failure load for a single isolated footing;
- QuE
- ultimate pseudostatic failure load for new footing in presence of existing footing;
- QuE,iso
- ultimate pseudostatic limit load of an isolated footing;
- S
- spacing between footings;
- Scr
- spacing at which maximum bearing capacity is achieved;
- γ
- soil unit weight;
- ξcE
- efficiency factor for contribution of cohesion;
- ξqE
- efficiency factor for contribution of surcharge;
- ξγE
- efficiency factor for contribution of unit weight;
- ξγqE
- efficiency factor for an embedded footing on cohesionless soil;
- σn
- normal stress on an arbitrary plane;
- σx
- nodal normal stress along the y axis;
- σy
- nodal normal stress along the x axis;
- τ
- shear stress on an arbitrary plane;
- τxy
- nodal shear stress; and
- φ
- soil internal friction angle.
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Published In
International Journal of Geomechanics
Volume 21 • Issue 8 • August 2021
Copyright
© 2021 American Society of Civil Engineers.
History
Received: Jul 6, 2020
Accepted: Mar 12, 2021
Published online: May 19, 2021
Published in print: Aug 1, 2021
Discussion open until: Oct 19, 2021
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