skip to main content

Title: Experimental Studies of Rock Socketed Piles with Different Transverse Reinforcement Ratios
Piles socketed into rock are frequently utilized to carry large loads from long-span bridges and high-rise buildings into solid ground. The pile design is derived from internal shear and moment magnitudes following code recommendation and numerical predictions. Little experimental data exist to validate code prescriptions and design assumptions for piles embedded in rock. To help alleviate the lack of large-scale test data, the lateral response behavior of three 18-in. diameter, 16 ft long, reinforced concrete piles was evaluated. The pile specimens were embedded in a layer of loose sand and fixed in “rock-sockets,” simulated through high strength concrete. The construction sequence simulated soil-pile interface stress conditions of drilled shafts. The pile reinforcement varied to satisfy the internal reaction forces per (1) code requirements, (2) analytical SSI predictions, and (3) structural demands only. The pile specimens were tested to complete structural failure and excavated thereafter. Internal instrumentation along with crack patterns suggested a combined shear-flexural failure, but do not support the theoretically predicted amplification and de-amplification of shear and moment forces at the boundary, respectively.  more » « less
Award ID(s):
Author(s) / Creator(s):
; ; ;
El Mohtar, Chadi; Kulesza, Stacey; Baser, Tugce; Venezia, Michael D.
Date Published:
Journal Name:
IFCEE 2021: Installation, Testing, and Analysis of Deep Foundations
GSP 323
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Embedded sensors within infrastructure elements are powerful catalysts for new designs and construction methods, enabling advanced data collection and informed decision making. This paper presents the development, validation, and implementation of a prototype instrumentation tool utilized in large-scale lateral load tests of rock-socketed pile foundations, with the objective to measure shear stresses near the rock-soil boundary. The proposed instrumentation is novel in that it will be the first attempt to determine experimentally the 3D strain field through embedded sensors with immediate application to a broad array of pile foundation engineering problems. Data obtained from the prototype instrumentation is used to clarify whether shear force amplifications in piles crossing soils with strong stiffness contrasts are real, or an artifact of analytical, Winkler-based design methodologies. Three reinforced concrete pile specimens with a diameter of 0.46 m and a length of 4.9 m were subjected to reverse cyclic lateral loading up to complete structural failure. The sensors’ development, design, and construction, as well as their performance in measuring shear stresses will be discussed by comparing experimental data with predictions from conventional software tools. Ultimately, this study aims to improve the design and construction of more practical, resilient, and economical infrastructure. 
    more » « less
  2. 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. 
    more » « less
  3. null (Ed.)
    Most undergraduate civil engineering programs include an introductory course in reinforced concrete design. The course generally includes an introduction to the fundamentals of reinforced concrete behavior, the design of simple beams and one-way slabs to resist shear and flexure, and the design of short columns. Because of the scale of typical civil engineering structures, students commonly do not get to experience large or full-scale structural behavior as a part of an undergraduate reinforced concrete course. Rather, students typically learn fundamental concepts through theoretical discussions, small demonstrations, or pictures and images. Without the interaction with full-scale structural members, students can struggle to develop a clear understanding of the fundamental behavior of these systems such as the differences in behavior of an over or under-reinforced beam. Additionally, students do not build an appreciation for the variations between as-built versus theoretical designs. Large-scale models can illustrate such behavior and enhance student understanding, but most civil engineering programs lack the physical equipment to perform testing at this scale. The authors from St. Louis University (SLU) and Rose-Hulman Institute of Technology (RHIT) have designed and implemented large-scale tests for in-class use that allow students to experience fundamental reinforced concrete behavior. Students design and test several reinforced concrete members using a modular strong-block testing system. This paper provides a detailed overview of the design, fabrication, and implementation of three large-scale experiential learning modules for an undergraduate reinforced concrete design course. The first module focuses on service load and deflections of a reinforced concrete beam. The first and second modules also focus on flexural failure modes and ductility. The third module focuses on shear design and failure modes. Each module uses a large scale reinforced concrete beam (Flexure specimens: 12 in. x 14 in. x 19 ft, Shear specimens: 12 in. x 14 in. x 10 ft.) that was tested on a modular strong-block testing system. The three modules were used throughout the reinforced concrete design course at SLU and RHIT to illustrate behavior concurrent to the presentation of various reinforced concrete design concepts. 
    more » « less
  4. Introduction: With the capture of the first high- resolution, in-situ images of Near-Earth Objects (NEOs) a couple of decades ago [1–4], the ubiquity of regolith and the granular nature of small objects in the Solar System became apparent. Benefiting from an increased access to high computing power, new numerical studies emerged, modeling granular structures forming and evolving as small bodies in the Solar System [5–7]. Now adding laboratory studies on granular material strength for asteroid and other small body applications [8,9], we are steadily progressing in our understanding of how regolith is shaping the interiors and surfaces of these worlds. In addition, our ever-more powerful observation capabilities are uncovering interesting dust-related phenomena in the outer skirts of our Solar System, in the form of activity at large heliocentric distances and rings [10–12]. We find that our recent progress in understanding the behavior of granular material in small body environments also has applications to the more distant worlds of Centaurs and Trans-Neptunian Objects (TNOs). Internal Strength: We currently deduce internal friction of rubble piles from the observation of large numbers of small asteroids and their rotation rates, combined with the associated numerical simulations [13,14]. In the laboratory, we study internal friction of simulant materials using shear strength measurements [8]. Combining observations, modeling, and laboratory work, the picture emerges of rubble pile interiors being composed of coarse grains in the mm to cm range. The irregular shapes of the grains lead to mechanical interlocking, thus generating the internal friction required to match observations of the asteroid population [8,9]. We find that the presence of a fine fraction in the confined interior of a rubble pile actually leads weaker internal strength [9]. Surface Strength: Deducing surface regolith strength for NEOs is usually performed via average slope measurements [15–17] or, most notably, observing the outcome of an impact of known energy [18]. In the laboratory, we measure the angle of repose of simulant material via pouring tests, as well as its bulk cohesion using shear strength measurements [8]. In some cases, this allows us to infer grain size ranges for various regions of the surface and subsurface of pictured NEOs, beyond the resolution of their in-situ images. Surface Activity: The Rosetta mission revealed that a number of activity events on comet 67P/Churyumov–Gerasimenko were linked to active surface geology, most notably avalanches and cliff collapses [19]. In addition, the role of regolith strength in asteroid disruption patterns has been inferred from numerical simulations of rotating rubble piles [20]. By studying strength differences in simulant samples, it becomes apparent that a difference in cohesion between a surface and its subsurface layer can lead to activity events with surface mass shedding, without the presence of volatiles sublimating as a driver [8]. We show that such differences in surface strength can be brought upon by a depletion in fine grains or a change in composition (e.g. depletion in water ice) and could account for regular activity patterns on small bodies, independently of their distance to the Sun. This is of particular interest to the study of Centaur activity and a potential mechanism for feeding ring systems. 
    more » « less
  5. Abstract

    We present an approach for the inclusion of nonspherical constituents in high-resolutionN-body discrete element method (DEM) simulations. We use aggregates composed of bonded spheres to model nonspherical components. Though the method may be applied more generally, we detail our implementation in the existingN-body codepkdgrav. It has long been acknowledged that nonspherical grains confer additional shear strength and resistance to flow when compared with spheres. As a result, we expect that rubble-pile asteroids will also exhibit these properties and may behave differently than comparable rubble piles composed of idealized spheres. Since spherical particles avoid some significant technical challenges, most DEM gravity codes have used only spherical particles or have been confined to relatively low resolutions. We also discuss the work that has gone into improving performance with nonspherical grains, building onpkdgrav's existing leading-edge computational efficiency among DEM gravity codes. This allows for the addition of nonspherical shapes while maintaining the efficiencies afforded bypkdgrav's tree implementation and parallelization. As a test, we simulated the gravitational collapse of 25,000 nonspherical bodies in parallel. In this case, the efficiency improvements allowed for an increase in speed by nearly a factor of 3 when compared with the naive implementation. Without these enhancements, large runs with nonspherical components would remain prohibitively expensive. Finally, we present the results of several small-scale tests: spin-up due to the YORP effect, tidal encounters, and the Brazil nut effect. In all cases, we find that the inclusion of nonspherical constituents has a measurable impact on simulation outcomes.

    more » « less