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The determination of internal pile reactions is critical to designing and assessing the structural performance of deep foundations. Internal shear and moment profiles strongly depend on lateral pile-soil interaction, which in turn depends on pile and soil stiffnesses as well as the stiffness contrast between soft and stiff strata, such as occurs at a soil/rock interface. At zones of strong geomaterial stiffness contrast, Winkler-spring-type analyses predict abrupt changes in the internal pile reactions for laterally-loaded foundation elements. In particular, the sudden deamplification of internal moments when transitioning from a soft to stiff layer is accompanied by amplification of pile shear. This “shear spike” can result in bulky transverse reinforcement designs for drilled shaft rock sockets that pose constructability challenges due to reinforcement congestion, increasing the risk of defective concrete on the outside of the cage. This paper presents an experimental research program of three large-scale, instrumented drilled shafts with simulated rock sockets constructed from concrete. Each shaft had a different transverse reinforcement design intended to bound the amplitude of the predicted amplified shear demand, with a particular emphasis on performance of shafts with shear resistance less than the predicted demand and below the code minimum. Test results suggested that the shafts experienced a flexure-dominated failure irrespective of the transverse reinforcement detailing.
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Ant nest geometry, stability, and excavation–inspiration for tunneling
Underground construction and tunnel excavation are known to redistribute stresses and cause ground displacement. Analytical solutions for stress distribution typically break down at shallow depths or in soil masses that exhibit high spatial variability, making numerical simulations necessary. Seeking to find new geometries and excavation strategies for underground construction, we propose to look to nature for inspiration. We extract 3-D digital twins of Florida Harvester ant (Pogonomyrmex Badius) structures from a nest cast in situ and simulate the stress and displacement fields around that nest with the Finite Element Method (FEM). Stress invariants around the main shaft are compared to those around idealized geometric representations of that shaft, i.e. helixes with a fixed pitch angle and a uniform elliptical cross-section. Helical structures made of circular cross-sections and horizontally oriented elliptical cross-sections interact in a way that reduces the risk of tension failure and distributes the shear stress more evenly. One can show that in addition to the extra stability that they offer and the lower risk of tensile or shear failure that they exhibit, helical shafts have the advantage of requiring less power to excavate than straight sub-vertical shafts.
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- PAR ID:
- 10563232
- Editor(s):
- NA
- Publisher / Repository:
- Springer Nature
- Date Published:
- Journal Name:
- Acta Geotechnica
- Volume:
- 19
- Issue:
- 3
- ISSN:
- 1861-1125
- Page Range / eLocation ID:
- 1295 to 1313
- Subject(s) / Keyword(s):
- ant nest, 3D scanning, Finite Element Method, tunneling
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1007/s11440-024-02232-z
