Art of Foundation Engineering Practice

The influence of foundations on the design and behavior of supertall buildings is explored by examining two built towers and one proposed project. These buildings are the world's tallest structure, the Burj Dubai; the second tallest tower in North America, the Trump International Hotel and Tower in Chicago; and a proposed 1888 ft tall tower in Las Vegas, the Las Vegas Tower.

The design of slab-on-grade and pier foundation systems requires knowledge of the site conditions including soil type, climatic conditions, and consideration of site anomalies. Case studies of poor performance, well-designed (in theory) slab-on-grade foundations indicate that site anomalies including subsurface perched water, pre-existing vegetation, pre-site development practices (including grading, drainage and surficial anomalies) control the designs. In this study, a heuristic approach is revealed for producing guidelines to avoid substantial site anomalies that cause unexpected and unwanted foundation movement and to provide better performing slab-on-grade and pier foundation systems. The heuristic approach will also be shown to comport with simple laws of thermodynamics including the consequence of the 2^nd Law—the Principle of Increasing Entropy. Relative elevation surveys, unsaturated soil mechanics theory, geotechnical testing, and geo-electrical moisture material imaging resistivity surveys were used to evaluate the performance of the slab-on-grade and pier foundation systems. Exploration of the theoretical design of post-tensioned slab-on-grade foundations is provided including an analysis of the types of factors considered by most designers and a parametric analysis of slab performance under the assumed design conditions. Analysis of the design is performed using well-known industry methods including the Post-tensioning Institute's design methodology as well as finite element method analysis (FEM). The FEM program PLAXIS was used to model the soil-structure interaction mechanism. A new guideline that includes additional design considerations for a slab-on-grade and pier foundation system has been proposed based on theory and the case studies reviewed.

From the Brooklyn Bridge to the towers that define the Manhattan skyline, designing foundations for New York City's urban landscape has always challenged engineers. Sometimes challenges arise due to site constraints, geologic conditions, or the client's desire to maximize the footprint and height of the structures while minimizing costs. This paper discusses two projects, located within several city blocks of each other, where all of the mentioned challenges created a "perfect storm" of sorts for the designers. The Owners, Architects, Structural Engineers, Geotechnical Engineers and Foundation Contractors collaborated to address the combined design and construction needs and achieve a cost effective foundation solution that met the project goals. Mueser Rutledge Consulting Engineers (MRCE) was involved in the two projects.

Pile foundations are commonly used for many types of structures and vertical and/or lateral loading design considerations are very important because the performance of the piles significantly influences the integrity of the structures supported by them. Current design methods of pile foundations often involve an estimation of a constant stiffness as an input, to model the soil-foundation interaction. Nevertheless, pile lateral response is nonlinear. It is therefore desirable to analyze the behavior of the foundation considering this nonlinearity. In the paper an analytical expression to predict the nonlinear behavior of a pile foundation is presented. To validate this closed form solution, computed results were compared with measures derived from loading tests, and it has been shown, that this solution can be used successfully for a provision of the nonlinear response of a soil-pile system.

Weak carbonate rocks are characterized by shear strength and deformation properties that are inferior to those of conventional rocks but superior to those of stiff or dense soils. Although numerous research programs have been carried out on almost all types of piles in various soil profiles, the behavior of drilled shafts in weak carbonate rocks has not been thoroughly investigated. In this paper, an attempt is made to enhance the design practice for drilled shafts in weak carbonate rocks by integrating the results of full-scale static instrumented pile load tests on large-diameter drilled shafts with good quality rock properties derived from reliable geotechnical investigations. The objective of the test program is to investigate the effect of several parameters which are known to influence rock-pile interaction and skin friction mobilization. Observations of the t-z behavior of the tested piles indicate a strong correlation between the normalized skin friction t/t_max and the normalized vertical displacement along the shaft z/z_max. More importantly, results indicated that the maximum mobilized side friction t_max was found to increase with increasing rock modulus and/or decreasing pile diameter thus confirming the possible effect of the constant normal stiffness on load transfer. The predictive performance of six commonly used empirical models which are based on the unconfined compressive strength was investigated. Results indicated that all models except those proposed by Horvath and Kenney (1979) and O'Neill and Reese (1999) tend to significantly overestimate side shear. A simple proposed empirical model that combines the effect of the unconfined compressive strength and the constant normal stiffness showed a better performance when compared to all other models tested in this study.

Dr. Clyde Baker, the honoree of this GSP (Geotechnical Special Publication) volume, has made many important contributions to the design and construction of world class structures including the Petronas Towers, located in Kuala Lumpur, Malaysia, which were the world's tallest at the time they were constructed. The foundations for these beautiful buildings offered many challenges typical of a karst topography, including uneven foundation support and cavities. This paper explores the immediate and long term impact of cavities and their effect upon design and construction of foundations. Solutions are offered for problems due to cavities.

Silt deposits provide the geotechnical engineer with a challenge by being at the borderline between cohesive clays and cohesionless sands for which separate design methodologies are established. Special care must be taken during the planning and exploration phase of the foundation investigation to obtain samples which have not been disturbed and to follow through with appropriate laboratory testing. Loose silts when combined with high water tables or pore pressures can behave like quicksand; slight disturbances triggered by vibrations and dewatering may result in flowing ground, piping into excavations and drilled shafts, or rapid settlement of embankments. Adequate description of silts requires notation of special properties including apparent cohesion, dilatancy, sensitivity, and the presence of organics or weak cementing agents. The geology of silt deposits should be considered to extend the understanding of the layering, possible age, compaction, diagenesis, and susceptibility of the deposit to liquefaction.

O-cell tests were performed in Singapore on four bored piles in a residual soil and underlying weathered, highly fractured bedrock called the Bukit Timah Granite formation. Two of the piles were 1.2 m diameter, uninstrumented, and 28 m and 38 m long. The other two were strain-gage instrumented, 1.0 m diameter piles, both 37 m long. The latter tests combined the O-cell test with conventional head-down testing. Analysis of the test results indicated that the pile toe stiffness was low. The evaluation of the strain-gage data showed that the pile material modulus was a function of the induced strain. The desired axial working load was 10 MN, and the combined O-cell and head-down tests correlated to a head-down test with a maximum applied load of 38 MN, which, although smaller than the ultimate resistance of the piles, was taken as the capacity of piles constructed similar to the second set of test piles at the site.

The guided wave approach to wave propagation in cylindrical concrete piles and drilled shafts to show the limits of conventional interpretations of surface reflection methods. The solutions to the dispersion equation for both longitudinal and flexural wave propagation and their implications are presented. Theoretical results concerning propagation velocity, attenuation, and displacements are presented. The results show that relatively constant propagation velocities of longitudinal waves in sonic echo and impulse response tests are limited to relatively low frequencies as a function of the diameter of a pile or shaft. On the other hand, flexural waves are dispersive at low frequencies and only become constant at relatively high frequencies. Implications of these results are illustrated for deep foundations and bender element tests. Comparisons are made between the geometric attenuation of longitudinal and flexural stress waves in concrete piles and shafts. Additional limitations of surface reflection tests arise from the stiffness of the soil adjacent to the pile, soil stratigraphy, variability in propagation velocity, and the presence of any intervening structure between the impact and the deep foundation element.

This paper presents a bored cast-in-place concrete piling case history for the port facility of an aluminum smelter project in the Middle East. The port facility is coastal with subsurface conditions consisting of reclamation fill, underlying sand, and deeper weathered rock (intermediate geomaterial). A geotechnical investigation of the port facility mainly included borings, cone penetration tests, and laboratory testing of soil and weathered rock samples. Six pre-production piles were load-tested axially using Osterberg load cells and laterally using a reaction system. Two production piles were also axially load (proof) tested using the conventional top load method with a reaction frame and kentledge. Load test results and capacity analyses are discussed. The results of settlement monitoring of completed structures are also presented. In total, 750 production piles in two diameters, 600 mm and 1,000 mm, were installed. Both the smelter facility and the port facility are constructed and operating satisfactorily.

One of the challenging engineering aspects of the new Cowboys Stadium in Arlington, Texas was design of foundations for the retractable roof arches. The two arches, with a clear span of approximately 393 m (1,290 ft), produce a lateral thrust of approximately 86,740 kN (19,500 kips) at each foundation with the lateral thrust line 32 degrees from horizontal. Design criteria included a maximum allowable deflection of approximately 12 mm (0.5 inches) for the foundations. Adding to the complexity was the varying geologic conditions with dense sand being predominant at one end of the arches and sandy shale being predominant at the other. Initial options considered by the design and construction teams included large mat foundations oriented perpendicular to the line of thrust of the arches, horizontal mat foundations with tie-down anchors, both vertical and battered drilled shaft groups, and battered micropile groups with both tension and compression elements. These options were determined to be problematic due to excessive deflection and/or constructability issues. Subsequently, the geotechnical design team proposed a foundation system consisting of slurry-placed diaphragm walls. This option resulted in a foundation system that is completely in compression without tension elements and provided a much stiffer system that could meet the deflection criteria. Preliminary dimensions of the diaphragm wall foundations were established based upon soil strength data obtained from field and laboratory testing. Final dimensions were confirmed based on instrumented load testing of two full-depth sacrificial diaphragm wall panels installed and tested prior to final design.

The geotechnical instrumentation program implemented during construction of the Boston World Trade Center complex included the installation of thirteen multi-point heave gauges within the final subgrade of three high-rise building structures. The structures are supported in the upper portion of a 21 to 33.5 meter (70 to 110-foot) thick deposit of Boston Blue Clay. The deformation of the building subgrade was monitored prior to, during, and subsequent to the construction of each of the three structures, and the results of this monitoring are presented. The results of the multi-point heave gauge readings are discussed herein in conjunction with the phased project development and compared with the subgrade deformations anticipated through the use of empirical formulas for heave and conventional consolidation theory.

Pile load testing has been carried out on two piles installed in a soft normally consolidated clay deposit found in the Oromieh salt water lake in Iran. The load tests were carried out in connection with the design of pile foundations for a new bridge across the lake. One test pile was a new pile installed for the purpose. It was a 66 m long steel pipe pile with diameter 305 mm, and which was load tested 5 months after installation. The other pile was an old pipe pile that had been installed in the lake 15 years earlier. It was 30 m long pile and had a diameter of 356 mm. The paper documents the ground conditions and the pile load test results, and compares the results against design methods and other published evidence of long-term ageing or time effects on the axial pile capacity in clay deposits. Whereas the new pile show a skin friction that is pretty much in line with current design methods (back-calculated α=0.74), the 15 year old pile gave a normalized skin friction that was as much as 2.3 times larger. Most of this more than twofold gain in normalized skin friction, as compared to the new pile, is assumed attributed to time or ageing effects.

An overview is given of the development and practice of foundation engineering for electrical transmission line structures (TLS). The evolution of this specialty field has been very different from its evolution for building and/or bridge structures. The differences involved are substantial and relate to the structure types, loading, threat to life, ground assessment over long corridors, construction issues, and various other factors. Unfortunately, these key issues are not addressed in traditional references such as textbooks or design manuals, and they are not covered in standard university courses in foundation engineering. Accordingly, designers, constructors, and others in the electric utility industry have developed alternative approaches toward foundation engineering for TLS. This paper presents an overview of this specialty field and discusses some pertinent issues regarding the structures, loading, foundations, geotechnical assessment, design philosophy, and construction issues.

In this paper, the behavior and performance of four instrumented drilled shafts and two barrette piles socketed in andesite rock in Taipei are evaluated based on the results of pile load tests. The tests include two compressive and two tensile tests conducted on the drilled shafts and two tensile tests conducted on the barrette piles. The load versus displacement curve at the pile head and t-z curves along the shaft, especially for the part socketed in andesite rock, are main concerns and are presented and discussed in the paper. The value of the load corresponding to the intersection of the load deformation curve and three times the initial tangent slope is used to determine the ultimate capacity of each pile. Comparison of the andesite rock unit frictional resistance of each pile shows the average of the measured values is approximately half of the value suggested by the method of O'Neill and Reese (1999) and is much smaller than the value suggested by the method of Chen (1999).

Over a period of 35 years, the author has used pressuremeter test data to predict bearing capacity and settlement of foundations supported on various types of deposits. It was observed that in cohesive soil deposits the bearing capacity predictions using the pressuremeter frequently did not agree with the predictions based upon conventionally obtained soil properties. Some of this difference can be attributed to obtaining in-situ versus laboratory test parameters. Based primarily on interpretation of the pressuremeter test data rather than solely on theory, a correlation has been developed for prediction of the undrained shear strength of cohesive soils. Using this empirically derived shear strength, the prediction of bearing capacity for high rise buildings supported on overconsolidated cohesive soils by the pressuremeter formula and conventional soil procedures were found to be in close agreement. In soft clay soils, the empirically derived shear strength agrees reasonably well with the measured shear strength based upon vane shear tests

Prefabricated vertical drains (PVDs) represent one soil improvement alternative for liquefiable sites. The primary function of PVDs is to expedite the dissipation of excess pore water pressures, ensuring the excess pore pressure ratio (r_u = Δu/σ'_vo) remains below a prescribed maximum value. Full scale dynamic testing using a vibratory hammer excitation source was performed at an active liquefaction remediation site in South Carolina to assess the effectiveness of the PVDs in dissipating excess pore water pressures. Tests were conducted in both the untreated and treated site conditions. For the treated site condition, PVDs were installed in a triangular grid pattern with a center-to-center spacing of approximately 1.5 meters. The field testing program for evaluating the effectiveness of the PVDs consisted of: (1) shear wave velocity measurements via crosshole seismic testing, (2) dynamic loading in the untreated condition, (3) monitoring and recording pore water pressures and accelerations during the installation of the PVDs, and (4) dynamic loading in the drain-treated condition. Instrumentation was installed to capture the response of the test area during staged dynamic excitation in the untreated and treated conditions, and during the installation of the PVDs. This paper presents preliminary results from the in situ staged dynamic testing. The experimental set up is described along with the in situ site characterization. Pore water pressure ratio, acceleration, and shear strain time histories from the untreated and treated conditions are presented.

The North American Drilled Shaft Industry appears to have started on a project in Kansas City in 1890 with the use of hand excavated shafts. The success of this installation was quickly duplicated in many urban centers throughout North America and lead to the creation of an industry which has gone through remarkable growth. Some of the equipment developments were home grown inventions, while others were adaptations from European and Asian technology. Several small companies which sprang up in the early part of the twentieth century have since provided the technology transfer to staff a great many of today's industry leaders. Significant engineering advancements have been made under the tutelage of a few visionary academics and consultants. Original design concepts have been shown to be somewhat simplistic in their understanding of load transfer, and the changes in understanding brought on by research in this area have resulted in technique changes throughout the industry. The paper not only chronicles these technical changes, but also the interrelationship of the companies and academic programs which have spawned the industry.

Geothermal heat exchange (geoexchange) systems have been widely used to reduce energy requirements for cooling and heating of buildings. Details on the design, installation, and post-construction monitoring of conventional borehole-type geoexchange systems in North Dakota are presented in this paper. These case histories, along with others from the technical literature, are reviewed with the goal of providing insight into geotechnical and thermal issues that may be encountered if similar geoexchange systems were incorporated into deep building foundations. Field monitoring observations reflect the need to accurately estimate the thermal demand of the building and the thermal capacity of the ground so that the geothermal heat exchangers are properly sized to avoid sub-freezing foundation temperatures in the winter. Rules-of-thumb that are currently used to size geothermal heat exchange systems in North Dakota are presented. These rules can be used to make preliminary estimates of the quantity of geothermal foundations needed to meet the thermal and geotechnical requirements of a building. The results of a design example emphasize the importance of considering thermo-mechanical effects on foundation performance in the development of LRFD resistance factors for these structural elements.

It is only a matter of time until space exploration enters a new phase that will include additional manned and unmanned landings and explorations on the Moon, Mars, and perhaps on asteroids. Detailed knowledge of the soils and rocks will be needed for the design of foundations for structures, for excavation and underground space utilization, for design of surface vehicles and construction of transportation systems, for evaluation of their suitability as construction materials and development of construction methods. In-situ resource utilization can be expected to play a major role in these activities owing to the high cost and difficulty in transporting needed materials from Earth. The extreme environments in which the work is to be carried out will complicate virtually every activity to be undertaken. Current knowledge about the rocks and soils on the Moon and Mars is summarized, with particular emphases on their compositions, geotechnical properties and in-situ states. Some implications for geotechnical engineering and foundation design are stated. Were it not for the unique and harsh environmental conditions, in addition to the great distance from Earth and its impacts on material transport and communications, engineering and construction on, in, and with the silty fine sandy soils of the Moon and Mars would be straightforward.

Driving displacements resulting in ground and pile heave are common when piles are driven into saturated, fine grained soils. In the case of preformed piles such as precast concrete or steel pipe piles, it is a relatively simple matter to redrive all piles that have been observed to heave. However, driven cast in situ concrete piles may suffer distortion or fracture of the freshly-cast concrete shafts or separation of shaft and base as ground displacements occur during pile driving. This paper presents heave measurements and loading test data for cast in place concrete piles installed in dense sands, alluvial deposits consisting of alternating sands and clays, residual soils and weak rocks.

The response of deep foundations under vertical loading is classically evaluated using a combination of limit plasticity and static equilibrium solutions for bearing capacity and elastic continuum solutions for displacements. Here, in-situ geotechnical test data are first processed to provide determinations of soil engineering parameters (γ_t, OCR, σ_p' K_o, s_u, φ', E, v) that are then input into the theoretical equations. Alternatively, the foundations can be assessed via direct methods, whereby the results of in-situ tests are scaled to produce response curves. A review of direct methods and several indirect CPT interpretations is presented using a case study from the response of a large deep drilled shaft at the newly constructed Golden Ears Bridge over the Fraser River in Vancouver, British Columbia, which was subjected to a staged Osterberg load testing sequence. Interpreted geotechnical parameters are obtained from a 100-m deep seismic piezocone sounding that provided four separate readings with depth (q_t, f_s, u₂, and V_s).

An seven-story reinforced concrete building on an unevenly thick clayey sand layer became inclined due to differential consolidation settlement triggered from a nearby deep excavation site, and was leveled by fracture grouting with quick-setting grout through the end of grout pipes. Although sand is the primary component and clay is the secondary component of clayey sand, the permeability and strength of this foundation soil are controlled by clay. This suggests that fracture grouting is a proper grouting method. A grout mixture of Portland cement and sodium silicate with gel time of 10 to 15 seconds was injected into foundation soil. The elevations of building's basement were closely monitored to evaluate the heaved volume of mat foundation immediately after grouting, and the settled volume of mat foundation during pore pressure dissipation. The elevation of nearby ground surface and lateral movements of subsoil were also monitored. All these results indicate that the grouting process can be separated into two stages. During the first stage, the building elevation remains unchanged and the anisotropic foundation soil is densified laterally by repeatedly fracturing with grouts. When foundation soil becomes near isotropic, the building starts to lift and this is the second stage. The factors to control grouting efficiency consist of soil type, soil stress history, and building weight. A final grouting efficiency of 27% and a linear relationship between grout take and elevated percentage are obtained after this building was successfully and permanently leveled.

This paper describes a laboratory study conducted on the effects of compaction grouting of model shaft tips embedded in a dry cohesionless soil prepared to different target relative densities. These tests were conducted within a circular steel test chamber 2.4 m in diameter and 2.7 m high. The soil used in this series of tests was a dry sub-angular fine sand (SP) having a D₅₀ of 0.24 mm and a C_u of 1.64. The soil was prepared to relative densities of 50%, 70%, and an initial test on a variable but high relative density specimen. The chamber was filled with the sand in one foot lifts, and densified by vibration in the case of tests on soils at 50% and 70% relative densities, and by hand tamping for soil in the initial variable high density test. The model shaft was placed within the chamber as filling of the tank progressed. Densities were measured using a combination of nuclear density gage measurements and dynamic cone penetrometer (DCP) readings. Nuclear density gage readings were made at 300 mm height intervals as filling progressed while DCP recordings, when possible, were made subsequent to the completion of tank filling operations and application of overburden pressure. At both 50% and 70% relative densities two shafts were load tested, with one being tip post-grouted while the other was not. Additionally a lone ungrouted shaft was load tested within soil of the Initial (variable high density) Test. Grouting of the shaft tip involved pumping a low mobility compaction grout, into the said tip using a system of hoses and pipes as currently used in the industry. Tip pressures induced during the grouting stage together with volume of grout pumped and strains induced within the shaft and test chamber were continuously monitored and recorded in real-time. Based on analyzed load test results, a significant improvement in tip capacities is noted for the grouted shafts over the ungrouted shafts. This tip capacity increase was thereafter analyzed with a view to developing relationships between the grout volume pumped, tip pressures induced during grouting and the load — displacement response of the grouted model shafts. The behaviors of the tip and skin friction capacities during load testing were also studied.

This paper sets out the principles of using computer programs for pile group response to design a pile foundation system via a limit state design approach. The approach involves three sets of analyses: (1) An overall stability analysis; (2) A serviceability analysis; (3) An analysis to obtain the structural actions for structural design of the raft and the piles. The approach is illustrated via its application to a high-rise building in the Middle East.

Design of foundations in earthquake prone areas needs special considerations. Shallow foundations may experience a reduction in bearing capacity and increase in settlement and tilt due to seismic loading. The reduction in bearing capacity depends on the nature and type of soil and ground acceleration parameters. In the case of piles, the soil-pile behavior under earthquake loading is generally nonlinear. The nonlinearity must be accounted for by defining soil- pile stiffness in terms of strain dependent soil modulus. A comparison of observed and predicted pile behavior under dynamic loads has attracted the attention of several investigators. The lateral dynamic pile response of single piles predicted by analytical models often yields higher natural frequencies and lower resonant amplitudes compared to those determined from field tests in horizontal vibrations only. This has been found to be due to overestimated shear modulus and radiation damping of the soil. The authors made an investigation to determine a simple method to improve the theoretical predictions of piles embedded in fine soils. Based upon this investigation shear strain dependent reduction factors are proposed for determining the shear modulus and damping for pile response calculations.

Signal matching is the preferred analysis method for Dynamic Load Test (DLT) evaluations. It is applicable to DLT records of driven piles, auger-cast piles, drilled shafts, and even on dynamic penetrometers. Although signal matching is considered standard best-practice, required by many code specifications and therefore routinely used on thousands of deep foundation projects worldwide, and of significant importance to the deep foundation industry, many features of the CAPWAP® signal matching model and procedure are not well known. CAPWAP's signal matching is possible because of the availability of redundant measurements of load and movement, and it is necessary to determine the unknown boundary conditions. The goal of CAPWAP is the determination of dynamic and static soil resistance parameters of the generally accepted Smith-type pile-soil interface model. However, the classic Smith model cannot explain some of the phenomena that occur during the impact event. For reliable signal matching results, therefore, several modifications of the original Smith model were made. While some modifications fundamentally do not affect the signal match, other more substantial changes are of considerable importance to the reliable determination of the all-important static load bearing capacity result. Before discussing the CAPWAP procedure and its automatic analysis tools, this paper describes the more unusual CAPWAP pile and soil model parameters and their effects on the final results. Measurement and analysis results from actual projects demonstrate the various features of the program and aspects of the models. The paper includes a summary of recommended limits for model parameters, match qualities, and calculation procedures and a few suggestions for additional research.

To predict structure settlement, a designer must know the thicknesses of active (deformation) zones that develop under structure foundations. Numerous methods have been offered to calculate active zone dimensions, generally based on the assumptions that active zone thicknesses are functions of the applied load values, physical and mechanical properties of supporting soils, and footing depths, as well as footings geometry and dimensions. This paper presents a method for estimating active zone dimensions, based on the knowledge of soil structural pressure values, σ_sz (structural pressure value, σ_sz, is the maximum stress value for which only recoverable deformations may be observed). The applicability of the obtained equations were verified, using only the results of tested square footings supported by similar quasi-elastic cohesive soils in which physical and mechanical properties did not vary significantly. It was assumed that the stresses applied to footings decreased linearly with depth, and that no friction existed between soils and footings. The paper presents empirical relationships between footing settlements, active (deformation) zone thicknesses, and footing dimensions.

This paper describes the design and construction of rock-socketed caissons in hard gneiss for a mid-rise building in Yonkers, New York. The design considered lateral and uplift loading conditions, in additional to vertical loads. Because the presumptive design parameters for rock sockets in the building code were so low, the work included two Osterberg load-cell tests and two lateral load tests on production caissons to justify the use of higher values. The lateral load resistance was verified by a load test. Construction considerations included problems of ordering casings due to wide variability in the depth of rock. To address this situation, the authors made probe holes at every caisson location. The paper also discusses: use of temporary and permanent casings, video-camera inspection techniques and equitable payment methods for drilling through obstructions.

Pile foundations have been used in construction for thousands of years but only in the last few decades has there been significant progress in the technology of pile installation. This progress on construction has not been matched by progress in the analysis and design of these foundation elements, which has lagged considerably. This is in large part due to considerable difficulties in analyzing both pile installation and the response of piles to various types of loadings rigorously. Given these difficulties, the profession has in general relied heavily on empiricism and relatively crude design approaches. This may well change due to pressures from different directions, particularly the progress in code design (the push towards load and resistance factor design in geotechnical engineering requires a much better grip on all the factors that need to be considered in calculating pile resistances and on the uncertainties in quantities and analyses, requiring sounder analytical frameworks) and economics (materials costs have been rising from multi-decade lows a few years back, a trend that would make it more economically interesting to have optimal designs). In this paper, we will examine the design process for axially-loaded non-displacement piles with a focus on assessing the strength of the recently developed analyses. We will show that, for these types of piles, design can be placed on a strong theoretical basis and discuss the implications for the future.

A case history of a mat foundation enhanced with settlement-control piles to support a high-rise building in Downtown Orlando is presented. Column loads were substantially variable with a maximum load in excess of 13 MN. The original geotechnical studies recommended auger-cast-in-place piles to support the tower as well as the parking due to difficult soil conditions and highly variable loads. A value engineering study was performed by the authors. After few iterations of structural and geotechnical analysis, a mat foundation was recommended; however, the structural analysis resulted in high contact pressures at highly loaded columns and edges of the tower portion. The authors recommended adding settlement-control piles at specific locations to increase the mat stiffness, relieve the concentration of contact pressures, and reduce potential differential settlement. A pile load test was performed to verify stiffness of the settlement-control piles. Results of the structural analysis utilizing settlement-control piles showed lower and more uniform contact pressures. The results of the monitoring program confirmed the benefits of adding settlement-control piles to the mat. The system resulted in saving more than $1.0 million over conventional deep foundations and about 120 construction days.

Drilled shaft capacity computations are routinely performed by geotechnical professionals using the Alpha and Beta methods outlined in the Federal Highway Administration (FHWA) Publication FHWA-IF-99-025. For cohesionless intermediate geomaterials, the analysis relies heavily upon the Standard Penetration Test sampler blowcounts obtained from exploratory borings. In the presence of alluvial gravel, cobble and boulder deposits, such evaluation cannot be reliably performed. This paper presents information obtained from Osterberg Cell load testing of 2.5 meter (98-inch) diameter shafts advanced using the casing oscillator method at the Cypress Avenue Bridge over the Sacramento River in Redding, California. The relationships between side shear transfer, end bearing, and settlement in cobble and boulder rich deposits with various matrix materials and degrees of weathering are demonstrated. The effects of particle dilation in the development of shaft side resistance and zones of higher stress concentration are also discussed. The results of instrumented pile load testing are compared with the results of drilled shaft capacity estimates made using the FHWA methods in an effort to better correlate field performance with analytical methods.

Onshore pile capacity is often determined by means of a static load test, but this is too expensive for offshore piles because of the environment and high loads required. McClelland, et al. (1969) presented criteria for clay and sand that was incorporated in the API Recommended Practice for "Planning, Designing and Constructing Fixed Offshore Platforms" the same year. The evolution of methods used to compute the unit skin friction and unit end bearing for deep foundations in the offshore environment is presented. Recent developments, including using cone penetrometer test (CPT)-based methods for predicting axial pile capacity in sands and revised metocean design criteria, and remedial measures, are discussed.

The analytical and experimental undrained displacement behavior of spread footings in clay is investigated in this study. Three spread footings ranging in size from 0.76 to 2.74 m were loaded and displaced up to 130 mm into medium stiff to stiff Beaumont clay. Load-displacement curves were determined, and soil displacements below the edge of the largest instrumented footing were measured. The footing displacements were modeled using linear elastic stress distributions and a nonlinear constitutive model calibrated with common in-situ and laboratory tests results. The effect of soil nonlinearity and footing rigidity on soil displacement behavior was also investigated. Results show that the linear elastic stress distributions used in a nonlinear constitutive setting resulted in very good prediction of undrained displacements at the footing center. Displacements at the edge of the footing were less well predicted. Regardless of the assumption of footing rigidity, when nonlinear, in-situ stress-dependent behavior is modeled, realistic concentrations of displacement towards the footing boundaries are observed.

This paper evaluates the performance of eight cone penetration test (CPT) methods in predicting the ultimate load carrying capacity of square, precast, prestressed concrete (PPC) piles driven into Louisiana soils. The CPT methods were evaluated based on their ability to predict the measured ultimate pile capacity. Four criteria were selected to evaluate the ratio of the predicted to measured pile capacities. Based on this evaluation, the de Ruiter and Beringen and LCPC/LCP methods showed the best performance in predicting the load carrying capacity of PPC piles driven into Louisiana soils. The CPT methods that showed the best performance, Ruiter and Beringen and LCPC/LCP, were implemented into a Visual Basic computer program to facilitate their use. The Schmertmann method was also implemented in the program, as it is one of widely used CPT methods.

A method for estimating the nominal base resistance of drilled shafts in fractured rock based on uniaxial compressive strength and the Geological Strength Index (GSI) is presented and evaluated against a limited number of field load tests. The method is based on a bearing capacity model which is formulated in terms of the Hoek-Brown strength parameters, which are evaluated empirically through correlation to GSI and rock type. The method accounts for the effect of overburden stress, which is shown to increase in significance as the intact rock strength decreases. Comparison to a limited number of field load test results indicates this method provides a useful tool for estimating base resistance in rock mass that is appropriately characterized by GSI.

At the Savannah River Site (SRS), a Department of Energy (DOE) installation in west-central South Carolina, a unique geologic stratum exists at depth that has the potential to cause surface settlement resulting from a seismic event. In the past the particular stratum in question has been remediated via pressure grouting, however, the benefits of remediation have always been debatable. Recently the SRS has attempted to frame the risk issue in terms of an event tree or decision tree analysis. This paper describes that analysis, including the input data required.

This paper presents proposed modifications to the existing methods that were originally developed to derive in-situ p-y curves from pressuremeter tests in soils to apply for pressuremeter tests in rock and/or intermediate geomaterials. The derived in-situ p-y curves can be used for the design of laterally loaded drilled shafts in rock and/or intermediate geomaterials. The proposed methodology was validated against two full-scale field lateral load tests conducted by the authors and five conducted by others from literature with rock pressuremeter or dilatometer tests performed at the test sites. The pressuremeter or dilatometer tests were performed in prebored holes cored using double tube core barrels. The modified methods for p-y curves of rock and intermediate geomaterials derived from pressuremeter interpretation would improve current design practice of laterally loaded drilled shafts socket in rock or intermediate geomaterials.

Uncertain geotechnical truth affects our ability to produce cost effective high rise foundation design. Virtually no amount of subsurface exploration and laboratory testing can ever provide the complete geotechnical truth. However, structural engineers and geotechnical engineers working as a team balance the available knowledge, including site geology and performance prediction history using in-situ empirically developed geotechnical parameters, with the level of acceptable risk and cost. A brief history of the author's Chicago experience and development with the Menard pressuremeter for in-situ testing is presented. Advice to follow for best results is outlined together with case histories to illustrate the following: (1) Maximizing allowable bearing pressure; (2) Use of mixed foundation systems; (3) Use of highly stressed piles for settlement reduction; (4) Reuse of existing foundations; (5) Construction surprises requiring remediation

This talk will be a mixture of my views, philosophies and reminiscences mixed with what I hope are some relevant case histories.