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1. Experimental Studies of Rock Socketed Piles with Different Transverse Reinforcement Ratios

   https://doi.org/10.1061/9780784483404.001  

   Farrag, Rabie; Turner, Benjamin; Cox, Carter; Lemnitzer, Anne (May 2021, IFCEE 2021: Installation, Testing, and Analysis of Deep Foundations)

   El Mohtar, Chadi; Kulesza, Stacey; Baser, Tugce; Venezia, Michael D. (Ed.)

   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. 

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2. Lateral load testing and 3D stress measurements in a pile foundation

   Farrag, Rabie; Slowik, Volker; Lemnitzer, Anne (September 2022, The 11th International Conference on Stress Wave Theory and Design and Testing Methods for Deep Foundations)

   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. 

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3. Ant nest geometry, stability, and excavation–inspiration for tunneling

   https://doi.org/10.1007/s11440-024-02232-z  

   Belachew, Meron; Yamamoto, Karie; Nichols, Elliot; Zhang, Danrong; Frost, J David; Arson, Chloé (March 2024, Acta Geotechnica)

   NA (Ed.)

   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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4. Axial Load Capacity Predictions of Drilled Displacement Piles With SPT- and CPT-based Direct Methods

   https://doi.org/10.37308/DFIJnl.20220512.262  

   Figueroa, Genesis (November 2022, DFI Journal The Journal of the Deep Foundations Institute)

   Drilled Displacement Piles (DDP) provide an ideal foundation solution that combines the benefits of ground improvement with traditional advantages of piling systems. This paper offers insights gathered from 55 construction projects in which nearly 130 DDPs were installed and tested axially. High quality site exploration data (e.g., Cone Penetration Test (CPT) and Standard Penetration Test (SPT)) were evaluated to derive geotechnical analysis parameters. The test sites consisted of mostly mixed soil types with strongly stratified layers of sand, silt, and clay. Pile diameters ranged between 35 and 61 cm (14 to 24 inches). Prior to analyzing the axial performance of DDPs, a variety of failure interpretation methods were assessed to confidently extrapolate failure loads when field testing was terminated prior to pile failure. Results of this study suggested the Van der Veen’s (1953) method to most closely estimate the load that triggers pile plunging behavior specific to DDPs, followed by the Butler & Hoy (1977) and L1-L2 methods (Hirany and Kulhawy, 1989). Hereafter, in-situ axial load test results were compared with a wide range of analytical methods, including those developed specifically for DDPs. Predictive accuracy was assessed in terms of total pile capacity and pile settlement and separated based on pile diameter, stiffness, and soil type. Most examined analytical methods underpredict the in-situ pile capacities for both, CPT and SPT -based analysis. It was also found that the difference between the experimentally determined and predicted capacities is related to the level of improvement in the surrounding soil following pile installation. A general comparison between predictive axial accuracy and the observed level of ground improvement is also discussed for sandy and mixed type of soils. 

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5. A numerical study on the multi-cycle self-burrowing of a dual-anchor probe in shallow coarse-grained soils of varying density

   https://doi.org/10.1007/s11440-023-02088-9  

   Chen, Yuyan; Zhang, Ningning; Fuentes, Raul; Martinez, Alejandro (October 2023, Acta Geotechnica)

   Abstract Development of self-burrowing probes that can penetrate soils without the aid of external reaction force from drill rigs and trucks would facilitate site characterization activities and deployment of sensors underneath existing structures and in locations with limited access (e.g., toe of dams, extraterrestrial bodies). Successful deployment of self-burrowing probes in the field will require several cycles of expansion, penetration, and contraction motions due to the geometric constraints and the increase in soil strength with depth. This study explores the multi-cycle performance of a dual-anchor self-burrowing probe in granular assemblies of varying density using discrete element modeling simulations. The simulated probe consists of an expandable top shaft, expandable bottom shaft, and a conical tip. The expansion of the shafts are force-controlled, the shaft contraction and tip advancement are displacement-controlled, and the horizontal tip oscillation is employed to reduce the penetration resistance. The performance of the self-burrowing probe in terms of self-burrowing distance is greater in the medium dense specimen than in the dense and loose specimens due to the high magnitude of anchorage force in comparison with penetration resistance. For all three soil densities, most of the mechanical work is done by tip oscillation; however, this accounts for a greater percentage of the total work in the denser specimen. Additionally, while tip oscillation aids in enabling self-burrowing to greater depths, it also produces a greater work demand. The results presented here can help evaluate the effects of soil density on probe prototypes and estimate the work requited for self-burrowing. 

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