Deep foundations are one of the most common foundation systems used in engineering practice. Prediction of pile response requires a good understanding of the mechanism that governs interaction between the pile and the soil. In order to obtain efficient and economical pile designs, geotechnical engineers utilize experimental studies combined with traditional analytical models. Most formulations used today are based on elastic solutions or Winkler formulations (e.g. p-y curves) that were derived and calibrated with limited amounts of existing test data. Controversies exist with respect to the influence of various parameters, such as head fixity, pile installation techniques, soil profiling, and axial- lateral load. Moreover, the interpretation of the data from pile instrumentation is not straightforward, given the numerical errors that incur in the double differentiation of the bending moment profile. Specifically, this research pursues the following objectives:

1. Selected p-y curves limitations, including the influence of different concrete, reinforcement, and tip restraint, are addressed through combined experimental and numerical studies on model-scale test specimens.

2. Advanced construction materials, such as high-strength polymer concrete and innovative polymeric reinforcement materials, are also examined to assess their suitability for commercial introduction into routine foundation design practice.

3. An innovative strain gauge based instrumentation will help 1D instrumentation (i.e. longitudinal strain measurements).

4. The results obtained from the model-scale lateral loaded tests on concrete piles are evaluated to provide insights into the soil-pile interaction behavior. An optimization technique implemented in a genetic algorithm framework is proposed to facilitate data interpretation and to derive p-y curves even in presence of disturbed data readings and pile nonlinearity. The proposed genetic algorithm targets directly p-y curves and evaluates them through the minimization of a fitness function, represented by the explained variance (EV) between raw p-y values and fitted p-y function. Moreover, this approach allows the generation of p-y curves from an ensemble of different statistical methods.

The ultimate intention of this study is to incrementally eliminate uncertainties associated with pile analysis and provide new understanding for design in practice.

Reliable seismic design of earth retention structures and substructure components necessitates the accurate evaluation of magnitude and distribution of earthquake induced soil pressures. Many experimental, analytical, and numerical studies have been conducted to further our understanding of the complex of the soil-structure interaction (SSI) between an underground component and its surrounding soil, hereby considering the wide range of assumptions inherent to soil and structural properties (e.g., structural stiffness, embedment depth, and nonlinear behavior of the soil material). This thesis research aims to further our understanding of the distribution and magnitude of seismic soil pressures induced on sub-surface structures through a combination of experimental, analytical, and numerical studies.

Large-scale shake table tests performed on underground structures at the E-Defense facility in Miki, Japan serve as experimental platform for this research. A densely instrumented system of large-scale underground structures consisting of two vertical shafts, connected through a cut-and-cover tunnel, and two independent shield tunnels was installed in an 8 m-diameter laminar soil box. The system was subjected to step-sine sweeps and scaled ground motion records of the Kobe (1995) earthquake. The underground structures were embedded in a two-layer soil system. The specimen instrumentation consisted of over 800 sensors, including strain gauges, accelerometers, displacement transducers, bender elements, and pressure sensors. Experimental results, including a dynamic system characterization, site response analyses, pressure time histories, and seismic pressure distribution profiles provided critical benchmark data for the subsequent analytical and numerical sections of this research.

Dynamic soil pressure measurements along the vertical shafts served as reference data to examine the suitability of different analytical methods proposed in literature, such as traditional and recently developed limit-state and elastic approaches for both, cohesionless and cohesive (c-φ) soils, in predicting the seismically induced earth pressures on flexible underground structures. Comparative results suggest that, despite the unique shaft geometry, analytical methods accounting for the structural flexibility were able to closely predict the experimental soil pressures, while methodologies derived for rigid subsurface elements can only serve as rough preliminary estimate and should not be employed in performance-based geotechnical analyses. Moreover, none of the analytical solutions included in this thesis work consider the 3D effects of the system, the nonlinear soil-structure interaction, or elastic-plastic behavior of the soil material. These aspects might not be controlling parameters for the behavior of shallow embedded structures, however, their influence becomes significant for deep non-rigid underground structures and should be taken into account.

Results obtained from the shake-table experiments were then used to calibrate a three-dimensional, nonlinear, finite element (FE) model built in ABAQUS. Good agreement was observed between the computed results and experimental data which deemed the reliability of the FE model suitable for the subsequent parametric investigation. By preserving the configuration of the original test system, a selected set of parametric studies was performed, which focused on the (1) the effects of the soil parameters (i.e., cohesion, and friction angle) and (2) the structural flexibility/ stiffness of the subsurface elements.

In the last section of this research, a simplified 3D soil-structure model was developed and influences of the most important parameters on the seismic soil pressures, including the retained soil mechanical parameters, structure and its base flexibilities, amplitude of the ground motion’s acceleration, and geometry of the wall were examined through an extensive set of parametric studies. Results of these parametric studies, including the seismic soil pressure distribution and variations of seismic forces and their corresponding moments against each of the studied parameters were presented as normalized graphs and tables, which could be used in the preliminary analysis and design stage of deep embedded structures.

Large scale cyclic testing was carried out to study the nonlinear behavior of T-shaped, moment resisting frame beams (MRF) with openings. The beams are located in an existing structure in the western U.S., and were designed according to ACI 31-95 and UBC97. Four test specimens were constructed as half-length replicas and scaled by 80% in all cross-sectional dimensions compared to their in-situ counterparts. Cross sections had geometries of 38.4 in. x 24.0 in., and beam lengths varied from 12.4 ft. to 17.5 ft. Three experimental specimens had openings with dimensions of 38.4 in. x 14.4 in.; the control specimen did not have openings. Each beam replica was instrumented with internal and external instrumentation consisting of strain gauges, linear voltage differential transducers (LVDTs), and string potentiometers, and tested to complete structural failure under quasi-static, cyclic load reversals. The cyclic performance of all beams was evaluated in terms of failure progression and plastic hinge development, strength and stiffness degradation, and energy dissipation capacity. In addition, the contribution of shear and flexural deformations to the overall displacement profile was studied. A nonlinear strut and tie model procedure was applied to predict the cyclic envelope and the load versus displacement relationship of the beam specimens. One monotonic and two cyclic strut and tie model arrangements were developed. Additionally, the cyclic truss models were compared using two different steel material models.

The determination of internal shaft reactions is critical to designing and assessing the structural performance of deep foundations. At zones of strong geomaterial stiffness contrast, Winkler-spring-type analyses predict pronounced changes in the shear and moment profiles 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 shaft shear. This “shear spike” results in dense transverse reinforcement designs and poses severe constructability challenges due to reinforcement congestion, increasing the risk of defective concrete on the outside of the cage. This study presents an experimental research program of three large-scale, instrumented drilled shafts with simulated rock. Each shaft had a different transverse reinforcement design intended to bound the amplitude of the predicted amplified shear demand. State-of-the-art instrumentation and monitoring program was implemented to capture the behavior of the test shafts during loading. As part of the instrumentation program, a new sensor was developed that aimed at measuring concrete internal strains in three dimensions. The instrumentation is novel in that it represents the first attempt to determine experimentally the 3D strain field through embedded sensors with immediate application to a broad array of shaft foundation engineering problems. The three large-scale pile specimens were tested to structural failure and subsequently retested after additional soil was placed to raise the fill height above the rock socket. The originally predicted shear failure did not occur; rather, a flexure-triggered failure through the formation of a plastic hinge above the rock-socket was observed. Test results suggested that the shafts experienced a flexure-dominated failure irrespective of the transverse reinforcement detailing. Retesting with 64% more soil compared to the original soil thickness provided an additional 80% capacity compared to Pult of the damaged specimen. Results obtained from the experimental study were used to calibrate a three-dimensional finite element model in PLAXIS 3D to better understand the load-transfer mechanism within the rock socket. Good agreement was observed between the numerically generated results and experimental data. A selected set of parametric studies was performed to investigate the effects of the interface input parameters (i.e., cohesion, and friction angle) and the influence of shaft/rock relative stiffness on the shaft shear response.

Constructing DDPs involves a drilling process which combines the application of an axial force with the generation of a simultaneous torque to create a borehole in which the soil is first loosened (drilled) and then displaced towards the outside of the borehole using a drilling rod with integrated displacement body. This installation method has the potential to induce soil densification around the borehole vicinity, the magnitude of which depends on the soil type, pile installation procedure, and pile geometry/spacing. This thesis offers insights gathered from 55 construction projects in which more than 100 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. 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. The use of SPT based predictions is recommended against.

An evaluation of pre- and post-installation soil properties surrounding newly installed DDPs have been carried out by interrogating a subset of data from 10 construction sites where Cone Penetration Tests (CPT) were performed before (CPTPRE) and after (CPTPOST) pile construction. CPT key measurements, i.e., tip resistance (q_t) and sleeve friction (f_s), were corrected for overburden stress to obtain the normalized cone resistance (Q_t) and normalized friction ratio (F_r) and compared with pre-installation in-situ data to quantify the soil improvement ratio. Comparisons of pre and post installation measurements suggests the change in CPT-based soil resistances to be mostly associated with soil behavior type (Ic) and soil fines content (FC). Cohesive soils suggested substantially lower improvement potential than cohesionless soils. The spatial improvement was assessed by comparing pre-and post-installation soil measurements within 2-3 times of the pile diameter surrounding the DDP. Results show that there is no significant improvement is yielded at distances larger than 2D. Analytical comparisons between axial pile load capacities estimated with CPTPRE and CPTPOST data does not differ considerably when using CPTPOST parameters for cohesive soils but showed a notable improvement (1.3-1.6 times) for mixed and cohesionless soils. However, when compared to in-situ failure loads observed from axial load tests, the use of post-installation CPT-based soil parameters for design was deemed too ambiguous.

Pile foundations are extensively used in the construction of various types of superstructures, including tall buildings, bridges, freeways and offshore structures. Hereby, rock-socketing offers an attractive solution for achieving maximal tip resistance and improving the load transfer capabilities of the foundation element. In soil profiles with very soft surface soils, rock-socketing often provides the only reliable source of axial and lateral resistance. This thesis investigates the nonlinear performance behavior of piles embedded in soil stratigraphies consisting of soft surface soil underlain by rock via experimental and numerical studies. Model scale test results of a (0.254m) 10in diameter pile, socketed in simulated rock, and subjected to quasi-static, reverse-cyclic lateral loading, provided reference performance data for a series of future experimental studies on large scale rock-socketed piles. Via numerical studies using the FEM tool Abaqus, this thesis complements the experimental research program, by first validating a previously conducted experiment published in literature and using the modeling experience gained from this preliminary exercise by seeking to replicate the test observation numerically. Results obtained from the model simulation provided pile response profiles that agreed reasonably well with experimental observations. Structural failure was observed through plastic hinging about two pile diameters below soil surface and captured well by the numerical model. The numerically obtained load deflection behavior over-predicts the experimental pile stiffness and indicated larger pile capacities compared to experimental observations. A discussion of the experimental results, numerical model development, modeling assumptions, modeling results including important pile demand parameters such as shear and moment demands, as well as recommendations for the upcoming large-scale tests are provided.

Abutment walls are integral components of bridge superstructures and play an important role in resisting lateral forces due to static and dynamic loading. Empirical methods for calculating lateral passive earth pressures are desirable computational tools in the design of bridge abutment systems. This thesis examines the development of lateral pressures behind a simple, vertical bridge abutment by analyzing the development of engineering strains in the fill material upon lateral loading. Laboratory testing, such as triaxial shear strength testing was conducted and/or evaluated on fill soils implemented in three unique load tests published in literature. The stress-strain curves from these tests were analyzed with respect to normal stresses and shear strains, and used to develop a mobilized shear strength profile for each representative soil type. Using log-spiral passive wedge failure modeling as proposed by Terzaghi combined with recent lateral displacement models found in literature, peak passive resistance was predicted within 17% of the experimental results with all case studies, with the load-deflection curve shape in general agreement with the measured curve for both strong and brittle wall failures.