From Soil Behavior Fundamentals to Innovations in Geotechnical Engineering: Honoring Roy E. Olson

The fundamental cause of failure of the levee system in New Orleans following Hurricane Katrina was poor decision making. The design hurricane was not updated over time as new information became available. The inevitable settlement of levees founded on compressible soil was not taken into account. Benchmarks used to establish elevations settled over time, but adjustments were not made. Many sections of levee were built of fine sand and silt materials that were not capable of withstanding erosion from overtopping. Unconservative design assumptions contributed to failure of levees that were not overtopped. Warning signs of imminent failure from a full-scale I-Wall test did not trigger reconsideration of design parameters. These observations lead to the conclusion that the failure of the New Orleans flood protection system was the result of a failure of judgment and decision making on the part of engineers and the authorizing/funding agencies. The New Orleans levees provide an example of the importance of the first canon of ASCE's code of ethics: "Engineers shall hold paramount the safety, health, and welfare of the public."

Between 2004 and 2009, five major hurricanes in the Gulf of Mexico loaded numerous offshore platforms and their pile foundations to near or beyond their capacities. The performances of these foundation systems provide a tremendous opportunity to learn about their reliability and to improve design practice. A set of 13 platforms are analyzed in detail based on hindcast data for the hurricane loads. The foundation systems for these platforms represent a range of characteristics with non-redundant and highly redundant systems, systems governed by the lateral capacities and systems governed by the axial capacities of the piles, and systems with piles driven primarily in normally consolidated marine clays and those with piles driven in interbedded sands and clays. An upper-bound plasticity model, calibrated to match a three-dimensional finite element method model, is used to predict the performance of these foundation systems. A probabilistic approach is then used to update information about the systematic bias in predicting the capacities of the foundation systems and hurricane loads. Findings from this work include (a) actual and predicted performances of the 13 foundation systems agree reasonably well, (b) the use of nominal versus expected yield stress for steel affects the predicted performance and reliability, and (c) the robustness and redundancy of a foundation system have a significant effect on its reliability.

This paper compares more than two years of micrometer crack displacement response and structural velocity response of a wood frame house adjacent to an operating aggregate quarry. The same transducers that monitor long term, climatologically induced micro-inch crack response also measure dynamic responses induced by blast-induced ground motions, occupant activities, and wind gusts. The two-story house has been expanded several times, is founded on an irregular basement, framed in wood and clad with wood siding and clapboard. This project is part of a larger research effort of structural health monitoring via autonomous crack monitoring [ACM]. The unusually long monitoring period allowed observation of two maximum, climatologically induced peak crack responses, and as such represents one of the longest periods of continuous observation in the literature. These once a year peak climatological responses are compared with unusually intensive ground motions in excess of that allowed by regulation. Intense ground motions were legally possible because the test house is owned by the quarry and located on the quarry property. These comparisons show that climatic and environmental variations cause greater crack response than ground motions that exceed regulatory limits.

The "φ = 0 Concept" is central to the specification of the undrained shear strength of saturated clays in engineering practice. While the theoretical basis for the concept lies in Mohr's rupture hypothesis, its pragmatic value to geotechnical engineers lies in Terzaghi's effective stress principle. Specifically, the φ = 0 concept circumvents the onerous need for estimating (or measuring) excess pore water pressures in situ during construction, etc., which is required to perform an effective stress analysis. Despite the significance of the φ = 0 concept, a survey of geotechnical engineering textbooks published over the last 60+ years showed that most opt to just state the φ = 0 concept without putting it into proper theoretical or contextual perspective. The authors view this as a missed opportunity to put the various rules of thumb and sets of governing principles for the shear strength of soil into a consistent framework. Accordingly, the objectives of this paper are to review the theoretical basis of the φ = 0 concept in the context of Mohr's rupture hypothesis and Terzaghi's effective stress principle and to discuss some of the pertinent pragmatic issues with implementing the concept. In relation to the latter objective, the procedure for multi-staged rapid drawdown analysis for earthen dams proposed by Duncan et al. and the procedure for determining the strength of liquefied soil proposed by Poulos et al. are reviewed. It is shown that while Duncan et al. fully address all the pragmatic issues in implementing their procedure, Poulos et al. do not.

Primary compression and secondary compression of saturated soils are consistent with the Terzaghi effective stress principle. Both primary compression and secondary compression and associated settlement and increase in undrained shear strength result from the rearrangement of soil particles to more compact packing, assisted by soil particle deformation, soil particle compression, and soil particle damage. The secondary compression behavior of soils is well explained and predicted by the C_α/C_c law of compressibility. The debate on the independence of end-of-primary (EOP) void ratio versus effective vertical stress relation from the duration of primary consolidation continues in spite of the following series of convincing evidence (a) EOP e versus σ'_v relation from laboratory consolidation tests is independent of the duration of primary consolidation, (b) preconsolidation pressure mobilized in the field is equal to EOP preconsolidation pressure determined from laboratory oedometer tests on 20 mm thick undisturbed soil specimens, (c) surface and subsurface settlements measured in the field during primary consolidation of soil subjected to embankment loading are equal to the settlement predicted using the EOP e versus σ'_v relation from laboratory oedometer tests on 20 mm thick undisturbed soil specimens, and (d) data on compressibility with time, (∂e / ∂t)_σ'v, provide an explanation for the independence of EOP e versus σ'_v relation from the duration of primary consolidation. There is no direct observed evidence supporting the "extreme" hypothesis B.

A comprehensive research program was recently completed to evaluate variability and uncertainty in geotechnical design parameters, including those used for consolidation and settlement analyses. Numerous one-dimensional consolidation tests were conducted following incremental load and constant rate of strain loading procedures for specimens obtained from four different sites using "state of the practice" and "state of the art" sampling techniques. The four sites included two "soft clay" sites, one "soft silt" site, and a "stiff silt/clay" site. Laboratory consolidation tests were conducted on specimens from each site to determine compression and recompression indices, preconsolidation stress, and coefficients of consolidation. Results from different sampling and testing methods are compared to draw conclusions regarding the variability and uncertainty associated with consolidation parameters obtained following different sampling and testing protocols. "State of the art" boring, sampling, and testing methods were found to produce lower values of preconsolidation stress, greater values of compression index, and similar values of recompression index and coefficient of consolidation compared with results from "state of the practice" methods for the three soft soil sites. Variability and uncertainty in consolidation parameters determined from state of the art methods were also found to be notably less than the variability and uncertainty established using state of the practice methods for the soft soil sites while the variability and uncertainty in consolidation parameters for the stiff soil site were similar for both state of the art and state of the practice methods.

A simple, easily applicable correlation is proposed for the relationship between the degree of radial consolidation (U_r) and the time factor (T_r) based on the free-strain assumption and drainage to a central drain (inflow radial consolidation). The suggested correlation is successfully applied to the results of a series of tests on soft clayey soils from Louisiana using the incremental radial inflow test equipment developed and utilized by a series of R. E. Olson's former graduate students in the late 1970s and early 1980s. The proposed correlation is practical, yet powerful, and can easily/quickly be applied using spreadsheets. One can also conveniently and consistently determine radial consolidation coefficient (c_r) without the conventional graphical construction.

Soft clays in coastal areas have low shear strength and high compressibility. Consequently, certain construction activities for infrastructure developments in these deposits often pose geotechnical problems due to large time-dependent settlements and lateral movements. Ground improvement techniques are adopted in such terrains to reduce the water content of soft clays by preloading with surcharge fill over vertical drains. Depending on the magnitude of the surcharge load used, substantial immediate settlement with lateral movements can take place during preloading, leading to undrained stability problems in various parts of the clay foundation. Therefore, the use of vacuum-assisted preloading has now become a popular method in ground improvement works where substantial loads need to be carried out to meet a desired rate of settlement and mitigate undrained failure by controlling lateral displacements. To assist the vacuum propagation to significant depths, vertical drains are used in tandem at the Port of Brisbane, Australia, and vacuum-assisted surcharge preloading and conventional surcharge preloading schemes were adopted to reduce the consolidation time and long-term settlement in soft Holocene clays in 2009. It is shown that a combined vacuum surcharge loading system with a standard surcharge fill highlights the obvious benefits of vacuum consolidation in reducing long-term settlement and enhanced stability.

High-swelling sodium bentonite (Na-bentonite) commonly is used in engineered containment barriers for hydraulic control and containment of liquid-phase contaminants. Such barriers include compacted liners that comprise bentonite-amended natural soils (i.e., sands, silts, and clays); manufactured geosynthetic clay liners (GCLs) that comprise thin (~ 10 mm) sheets of Na-bentonite sandwiched between two porous geotextiles; highly compacted bentonite buffers for high-level nuclear waste disposal; and soil-bentonite (SB) vertical cutoff walls. The primary role of the bentonite in all of these barriers is to serve as a high-swelling, low-hydraulic conductivity, k, material (k < 10^-10 m/s) to minimize seepage of liquids (groundwater, leachates in landfills, pure-phase organic liquids, etc.) and migration of contaminants (e.g., heavy metals, radionuclides, organic compounds, etc.) through the barriers. A primary concern with bentonite-based barriers used for such containment applications is the potential for incompatibility between the bentonite and the liquid being contained, resulting in increase in k and concomitant decrease in the performance of the barrier. With this concern in mind, the purpose of this paper is to provide a review of the factors and potential impacts resulting from such incompatibility (Δk > 0) in several different types of bentonite based-barriers, including traditional GCLs that rely solely upon bentonite as the primary hydraulic-resistant material, compacted soil-bentonites (CSBs), and soil-bentonite backfills (SBBs) used in vertical cutoff walls for control of contaminated groundwater. The results show that the potential for significant incompatibility in bentonite-based barriers (i.e., Δk ranging from one to three or more orders of magnitude) generally increases with decrease in the amount of bentonite in the barrier, increase in the initial void ratio of the barrier, and/or increase in the composition and concentration of dissolved chemical species (solutes) contained in the permeant liquid. Values of k back-calculated from the results of consolidation tests based on Terzaghi's theory typically are unconservatively low and, therefore, should not be relied upon for assessing the performance of bentonite-based barriers.

A stress-path testing program was proposed and performed to investigate shear strength and deformation behaviors due to an open cut excavation in overconsolidated clay. Stress changes due to the staged excavation for different locations of the slope were estimated and applied to undisturbed specimens using a triaxial testing system. Axial load, chamber pressure, and back pressure were actively controlled to implement the various stress paths. Vertical and horizontal deformations were monitored during the stress paths, and then an undrained compression or extension shearing stage followed. Test results for three cases from the testing program, the crest and the toe of the slope, and the base of the excavation are presented. The clay deposit was found to be nonexpansive, based on the deformation behaviors. Effective stresses appeared to govern the vertical and horizontal strains. Failure envelopes for compression and extension were established from the stress path testing. The mobilized undrained shear strength from the stress path approach is substantially lower than one from the conventional method.

This paper compares constrained modulus and related data from a geotechnical engineering investigation of a 40,000 m² site in the Southeastern United States that lies within the Atlantic Coastal Plain. This study includes 47 cone penetration tests (CPTs and SCPTs) and 13 flat-plate dilatometer tests (seismic and nonseismic DMTs) and more than 80 incremental and constant rate of strain consolidation tests. This paper compares the CPT- and DMT-correlated constrained moduli and laboratory test results from co-located borings. The comparative analyses show major differences and key similarities in the correlated values; sources for these differences and similarities are discussed. This paper concludes that in contrast to the DMT, CPT/SCPT soundings and often laboratory consolidation testing underestimate key settlement parameters because of disturbance. Correlations for the investigated soil types are also presented.

The effect of median particle size and breadth of particle sizes in clean sands on the SWCC and the van Genuchten parameters α and n is described. For uniform sands, the air entry suction increases (α decreases) and the steepness diminishes slightly (n decreases) for the drying SWCC as the particles become finer. Increasing the breadth of particle sizes also increases the air entry suction (lower α) and reduces the steepness (lower n) of the SWCC. Breadth of the particle size distribution has a larger effect on steepness and n of the SWCC, and median particle size has a larger effect on the air entry suction and α. Similar effects occur for the wetting SWCC, although the impact on the water entry suction is less than the impact on the air entry suction. The systematic effects of median particle size and breadth of particle sizes on the SWCC are captured in a pedotransfer function (PTF) to estimate α and n for clean sand based on d₆₀ and C_u. Comparison with other SWCC data shows that α estimated with the PTF typically is within a factor of 2 of the actual α and n estimated with the PTF is within ± 2 of the actual n. These findings are applicable to α for sands with nonplastic fines provided the fines content is less than 20%, but apply to n only for sands with negligible fines content. A procedure to convert between van Genuchten and Brooks-Corey parameters for sands is also presented.

Driven piles are subjected to high stresses during installation. It is, therefore, important not to exceed acceptable stresses along the pile shaft and at the toe to prevent damage. Dynamic monitoring has been used for decades to evaluate not only the installation stresses, but also to check test piles for signs of structural damage. The Beta Method (β-Method) for evaluation of the location and extent of a potential damage was developed more than 30 years ago and has proven effective as a QC and QA tool. As an aid in the process of pile rejection or acceptance, the β-method also offers a rating scale that translates the automatically determined β-number into a helpful pile integrity assessment tool. The reliability of this algorithm has been proven by numerous extracted piles. However, one limitation of the β-method concerned detection of damage near the pile toe where high toe resistance effects and/or stress wave reflections reduce the effectiveness of the traditional β-method. In the past, therefore, near-toe damage was determined by the testing engineer, not only by visual inspection of the dynamic monitoring data, but also by reviewing the pile toe compressive stresses throughout the monitored driving history and the strength and stiffness of the soil response from the pile toe. This approach has now been automated and subjected to tests on existing data. After a review of the existing methods of pile stress and damage calculations, the paper presents the new method, illustrating its effectiveness by examples from measurements on both concrete and steel piles.

The Illinois Department of Transportation (IDOT) and the University of Illinois collected information on driven piling to improve predictions for pile capacity and to develop resistance factors appropriate for LRFD-based design. Several methods were investigated, including static methods, dynamic formula, WEAP, PDA, and CAPWAP. Pile dynamic testing was conducted on 37 piles from 19 different construction sites throughout Illinois. Measurements of penetration resistance were recorded for end of driving (EOD) and beginning of restrike (BOR) conditions. Estimates for static capacity were based on CAPWAP analyses of pile penetration at beginning of restrike (BOR) conditions. All piles were steel H-piles or closed-ended pile piles and driven with open-ended diesel hammers. Comparisons of measured and predicted capacity were made for several different predictive methods. The agreement between measured and predicted capacity for dynamic formulas, WEAP, and PDA are significantly better than observed in previous studies. The reason agreement improved is due primarily to the limited types of piles and hammers used for driving piles for common IDOT bridges. Improved reliability for predicting capacity can justify higher resistance factors and more efficient pile design.

A bridge was to be constructed across the Lohit River in India. The subsoil consisted of cobbles (80 to 300 mm size) and boulders (>300 mm size) with interspaces loosely packed with gravel (4.75 to 80 mm) and sand (0.075 to 4.75 mm). A soil boring could not be carried out due to the difficulty in making a 150 mm borehole and also as it would not yield any reasonable data. A shaft bore of 1700 mm diameter was made. A test shaft was provided with a steel liner for the full length of the shaft. Four reaction shafts (tension) were cast with liners only for the upper part of the shaft. During the first load test, there was excessive settlement. At the same time, the reaction shafts experienced very little movement. It was inferred that the steel liner prevented friction from developing in this medium. The liner was required to prevent collapse of the soil during boring, but not necessarily to the full depth. A second load test was conducted with a reduced length of liner, and there was a significant increase in the capacity of the shaft. The load test also showed plastic behavior of the medium. However the plastic was minimal in the vicinity of the design loads.

Piles driven in the Puget Sound Lowlands frequently exhibit a high magnitude of soil setup or gain in capacity over time. In fact, the energy associated with production pile driving hammers is often insufficient to fully mobilize pile toe bearing resistance during dynamic restrike testing. Due to the potential for significant increases in capacity, practitioners often must consider the uncertain trade-off between the potential for setup and time to restrike. This study presents the results of 76 pile case histories from the Puget Sound Lowlands that were dynamically monitored during end of drive (EOD) and begin of restrike (BOR). The setup time (i.e., time between EOD and BOR) ranged from 5.5 to 312.5 hours. Signal matching using CAse Pile Wave Analysis Program (CAPWAP) indicated that the majority of the piles experienced significant increases in shaft resistance. To assess setup, piles were grouped into three categories: closed-end steel pipe piles, open-end steel pipe piles, and solid concrete piles. The accuracy and uncertainty of the well-known Skov and Denver setup prediction model was evaluated using the mean bias, defined as the ratio of measured and predicted shaft resistance, and the coefficient of variation (COV), defined as the ratio of the standard deviation of the point biases to the mean bias. The Skov and Denver model exhibited considerable uncertainty (COV = 45 to 59 percent) when evaluated using the local database. Recalibration efforts made using a hyperbolic function and least squares regression resulted in a reduction of the COV to 29 to 32%. Based on considerable scatter in the setup ratio (i.e., ratio of BOR to EOD shaft resistance), it was determined that the behavior of setup over time could not be adequately captured by considering total shaft resistance. Therefore, setup due to the overall increase in shaft resistance between EOD and BOR was characterized in an initial effort to provide guidance for incorporating setup into pile design. Closed-end concrete piles exhibited the largest average setup ratio (3.92), followed by closed-end steel piles (2.37), and open-ended steel piles (2.26).

This paper presents a case history where 91.4-centimeter (36-inch) diameter open-end pipe piles were installed using both impact and vibratory installation techniques. Thirteen dynamically tested piles were installed along a new sheet pile containment wall located in the Southern Branch of the Elizabeth River, bounded by Chesapeake and Portsmouth, Virginia. The soil conditions encountered generally consisted of interbedded layers of silt, sand, and clay forming the Alluvium and the Norfolk Formations. The piles were advanced into the underlying Yorktown Formation bearing stratum consisting of clayey to silty sand with varying amounts of marine shell fragments. At two test pile locations, impact-driven test piles were extracted and relocated by vibratory hammer and subjected to restrike driving with dynamic analysis to assess bearing capacity. Seven to 14 day restrikes were performed on the 13 hammer-driven test piles. Restrikes at one or more months were performed on one impact-driven pile, and both vibratory installed test piles. Signal matching analyses of restrike-driving events indicate an approximate 50% reduction in overall bearing capacity of the vibrated piles compared with the driven piles. Additionally, long-term restrike driving of vibrated piles did not continue to gain capacity akin to driven piles.

Static loading tests using single-level O-cells were carried out in mid-2008 on two bored piles constructed at the Binh Loi Bridge, crossing the Saigon River at Ho Chi Minh City, Vietnam. The soils consist of surficial layers of soft clay and silt to 11 and 15 m depth on compact silty sand to about 55 m depth followed by dense to very dense silty sand. Two bored piles, 2.0 m and 1.5 m in diameter, were installed to 73.5 m and 73.0 m depth, respectively, and constructed using reverse circulation technique and bucket drill with casing advanced ahead of the hole. Drilling slurry was composed of polymer slurry for the 2.0-m diameter pile and bentonite slurry for the 1.5-m diameter pile. For both piles, the O-cell assembly was attached to a reinforcing cage lowered into the stabilized hole to 11.4 and 11.6 m, respectively, above the pile toe, five and two days after completing drilling and cleaning, respectively. Each reinforcing cage was instrumented with two pairs of diametrically opposed vibrating wire strain gauges at three levels below and five levels above the O-cell level. The static loading tests were performed 49 and 28 days, respectively, after the piles had been concreted. The strain-gauge records, when based on the nominal pile diameters, indicated Young's modulus values of about 25 GPa for the nominal cross-sections of the piles. Analysis of the records showed that residual load had developed during the wait time. The unit shaft resistance above the O-cell for the 2.0 m diameter, polymer-slurry constructed pile was moderately larger than that for the 1.5-m diameter, bentonite-slurry constructed pile. Detailed analysis showed the shaft resistance to be post-peak softening. The pile toe stress-movement responses were essentially linear and almost identical for the two piles.

The effects of settlement on the development of bending moments in battered piles were studied for a flood protection structure using a nonlinear three-dimensional finite element model. The model was of one configuration for a flood protection structure consisting of an earth embankment and a pile-supported T-wall. The constitutive models used for the soil were the Mohr-Coulomb and the bounding surface plasticity models. Both models were used for drained and undrained analyses. The drained analyses represented the long-term consolidation analysis of the embankments, and the undrained analyses represented the short-term loading conditions present during a storm surge loading event. The time rate of consolidation and dissipation of pore water pressures in the embankment and supporting subsoil were not modeled in these analyses. The study found that different levels of bending moments were developed in the three rows of batter piles due to the settlement of the embankments and the maximum moments were developed in the flood side row of piles. The undrained analyses of storm surge loading event revealed that bending moments in the flood side row of piles increased, the moments in the protected side rows of piles decreased, and the sign of the moment in the piles was reversed.

Two types of vibration damage caused by driving piles have been reported in the literature: direct structural damage and damage due to settlement. Direct damage results from vibratory excitation of structures at amplitude exceeding the structural tolerance. Damage from settlement is a consequence from vibratory densification of loose soils resulting in total or differential settlement of structures. Problems of settlement due to pile driving have been experienced recently by the Michigan Department of Transportation (MDOT) during operations associated with replacement of deteriorating bridges. The work described here represents an attempt to understand the mechanisms of energy transfer from steel H-piles driven with diesel hammers to the surrounding soil and the energy attenuation through the soil by measuring ground motion in the near vicinity of the pile. The main feature of this study consisted of installing motion transducers very close, within 0.5 ft, to piles and measuring the resulting ground motion during pile driving. Selection, fabrication, and installation of the transducers and preliminary measured pile driving vibrations are presented.

During the installation of offshore wind farm foundations and deep water foundations, the underwater piling noise of hydraulic impact hammers induces considerable hydro sound that is radiated from the piles into the surrounding water. These very high underwater noise emissions can reach dangerous levels and are potentially harmful to marine life in a large area. Both knowledge about the complex mechanisms and dynamic interactions of the hammer and pile system and knowledge about the acoustic behavior of the piles, the shallow water, and the ground are necessary to understand the generation and radiation of underwater piling noise and to develop effective noise mitigation systems. The new mitigation method of hydro sound dampers (HSD) uses curtains of robust air-filled elastic bladders showing high resonant effects, similar to air bubbles, and special dissipative PE-foam elements to reduce impact noise. These HSD elements are fixed to pile surrounding fishing nets. HSD-systems are independent of compressed air and not influenced by currents. The theoretical background, numerical simulations, laboratory tests, and offshore tests with noise mitigations between 17 dB to 35 dB (SEL) are described.

The prediction of pile-bearing capacity to include installation effects is a very complex problem, especially for jack-in piles. This paper describes a series of full scale pile load tests that shed light on the effects of jack-in force on the ultimate bearing capacity of jack-in piles. Three spun piles were installed in similar soil conditions under different jack-in forces. The extensive in-situ investigations, including standard penetration test (SPT), pressuremeter test (PMT), and piezocone penetration test (CPTU), were conducted in the experimental site to get better understanding of the soil condition around the test piles. The results of the tests show that the different jack-in forces did not affect the shaft friction significantly and that the difference in behaviors between test piles is caused by the difference in the toe stiffness response. The data show that the larger the jack-in force, the larger the stiffening effect, which is due mainly to the increase in volumetric compression of the bulb of soil below the toe of the piles.

The limit shaft resistance of displacement piles decreases with the number of axial loading cycles applied during pile installation (e.g., jacking, driving) or due to the nature of superstructure loading. This study examines the mechanisms governing the phenomenon of friction fatigue along piles jacked in sandy soils. Finite element analysis (FEA) of a thin disk of soil surrounding the pile shaft is performed. The pile installation process is modeled as a sequential combination of cylindrical cavity expansion and vertical shearing along the pile-soil interface. The soil disk is subjected to several vertical shearing cycles to simulate the successive application and removal of jacking loads. An advanced soil constitutive model based on two-surface plasticity and critical state theory is used in the FE simulations. FEAs examine the development and evolution of the normal stress acting on the pile shaft, which multiplied by an appropriate friction coefficient yields the value of mobilized shaft resistance. Results show that, in the absence of loading cycles, the normal stress attains values considerably larger than the in situ vertical stress. However, with subsequent application of loading cycles, the normal stress decreases at rates that increase with decreasing relative density and in situ vertical stress.

An analysis framework is presented for piles with rectangular cross section. Existing analysis and design methods are mostly applicable for piles with circular cross section. For piles with cross section other than a circle, an equivalent circle is often assumed and the methods for circular piles are applied. The newly developed framework explicitly takes into account the rectangular cross section and produces the response of piles under axial and lateral loads. A rational soil displacement field surrounding the rectangular cross section of the pile is assumed, and the total potential energy of the loaded pile-soil system is considered. The potential energy is minimized using calculus of variations to obtain the differential equations governing the pile and soil displacements. Closed-form solutions are obtained for pile settlement and axial force in the case of axially loaded piles. For laterally loaded piles, closed-form solutions are obtained for lateral deflection, slope of the deflected curve, pile bending moment, and shear force. The input parameters needed for the analysis are the pile geometry, applied load, and the elastic constants of the soil and pile. The new analysis framework produces results in seconds and has the accuracy of equivalent three-dimensional finite element analysis.

Advancements in high-speed computing and developments in material modeling techniques are increasingly allowing for large-scale three-dimensional (3d) linear and nonlinear geotechnical finite-element (FE) simulations. The open-source computational platform OpenSees provides such 3d simulation capabilities for static/seismic ground-foundation analyses. With the aid of the graphical user interface OpenSeesPL (http://cyclic.ucsd.edu/openseespl), 3d computations for pile and pile group studies are greatly facilitated. Using this FE framework, an effort is made to capture key features associated with axial and lateral loading on piles and pile groups. For that purpose, the behavior of a laterally loaded 3×3 pile group at different pile-spacing scenarios is presented first and contrasted with that of the corresponding single pile scenario. Response under linear and nonlinear soil behavior representations is discussed. Lateral pile-group performance and efficiency considerations are investigated. Thereafter, the behavior of a large (8×4) pile group foundation supporting a high-clearance (for marine navigation) bridge deck is addressed. For seismic response evaluation, push-over combined axial/lateral loads along with a substantial moment are imposed. All studies are presented within a scope that highlights current modeling capabilities and directions for further research.

A wide variety of ocean energy converters (OEC) are being considered worldwide, including tidal, wave, and current ocean energy. Regardless of the type of ocean energy device a major technical and cost challenge for these systems is their foundation systems. The specific focus of this paper is for ocean stream energy converters supported on monopile foundations. One of the key design considerations for these OEC devices is related to the long-term performance of the foundation system, which can be subjected to more than 10⁷ cycles of low-magnitude lateral loading during its design life. This very high number of lateral load cycles can result in a gradual long-term accumulation of pile head deformations and rotations. In some cases these pile head deformations can exceed the OEC serviceability limits. Analyses of laterally loaded piles, based on conventional p-y methodologies, typically cannot predict these accumulations of deformations and rotations. This manuscript presents results of 3D dynamic finite element analyses for this soil-structure interaction (SSI) problem. Results from these analyses reveal that this gradual accumulation of pile head deformation could be an important design consideration for certain monopile conditions. These numerical results correspond well with published experimental data. Finite element analysis (FEA) parametric studies, which investigate the influence of different pile installation variables, are presented to shed light on possible design options that mitigate or minimize the accumulation of pile head deformations.

Stone column reinforced foundation has gained popularity as an effective ground improvement technique available in practice. The design of large group of columns is normally done assuming infinite columns grid under a wide loaded area (i.e., unit cell concept). However, the design for small column groups is often approached empirically due to the lack of research on this issue. This study is aimed at investigating the behavior of small column groups by establishing the relationship between the number of columns and the settlement improvement factors. Two-dimensional (2D) concentric ring approach is adopted. This 2D approach is validated by comparison with a three-dimensional model before being used subsequently for detailed analyses. From the results, the optimum length for the columns group is determined where further lengthening of the column provides no further improvement for the system. Simple design method is suggested for rigid spread footings supported by small column groups, and the comparison is made to the settlement performance obtained from the unit cell concept.

This paper presents a field investigation of pullout resistance of steel anchors in rock. The field testing involves pullout tests of six steel anchors installed in biotite gneiss rock by gravity grouting and pressure grouting methods. The field pullout tests suggest a progressive failure mechanism, which was manifested through the progressive elongation of the bond zone. The pressure-grouted anchors yielded higher pullout resistance than did the gravity-grouted anchors. The increase in rock-grout bond strength from pressure grouting is likely due to a combination of several factors, including the resultant higher grout strength, higher rock-grout contact stresses, and grout injected under pressure into the fractures/fissures that existed in the bedrock.

This paper documents the thermo-mechanical characterization of an energy foundation constructed as part of a new single-story building at the U.S. Air Force Academy. During a 39-hour heating test, the foundation increased in temperature by 21.7 °C, while the sandstone subsurface only increased in temperature by less than 1 °C at a distance of 1.22 m from the center of the foundation. The distributions in thermal axial stress and displacement in the foundation were calculated from the measured thermal axial strain values, and a maximum compressive thermal axial stress of 5.2 MPa was observed near the middle of the foundation and a maximum upward displacement of 1.55 mm was observed at the head. The thermal axial stresses and displacements measured were well within acceptable limits for structural elements.

Settlements are usually the primary concern in designing shallow foundations on freely draining granular soil. Settlement predictions are traditionally based on empirical correlations with in-situ penetration tests due to difficulties in obtaining undisturbed samples. In the proposed framework, field measurements of shear wave velocity (V_s) are used to characterize the in-situ condition in terms of small-strain shear modulus (G_max) profiles. Disturbed field samples are recovered to determine gradation characteristics. Normalized shear modulus-shear strain relationships (G/G_max-log γ) that have been developed from dynamic resonant column testing of reconstituted sands and gravels are used to model stress state, strain amplitude, and material dependencies. The G/G_max-log γ relationships are modified to extend to strains of several percent. A subroutine has been implemented in the finite element program PLAXIS to combine the field G_max profiles, modified G/G_max-log γ relationships, and gradation characteristics to estimate stress-strain response under loading. The usefulness of the approach is demonstrated by comparing predicted and measured load-settlement curves from field tests with 0.46and 0.91 m diameter footings. Nonlinearity and settlement values are predicted well at loads in the working stress range.