New Technological and Design Developments in Deep Foundations

Considering the strain incompatibility between end bearing and side friction of drilled shafts, tip capacity is often discounted from total shaft capacity. This is due to the relatively large displacements required to mobilize the tip which often exceed service load displacement criteria. Additionally, concerns regarding shaft tip soil disturbance (i.e. insitu stress relief) and toe cleanliness further discourage designers from using end bearing as available capacity. As a method of mitigating these conditions, pressure-grouting the shaft tip after its construction has been successfully employed throughout the world. With very few exceptions, the benefits of tip-grouting have been disregarded in the United States. Sources of skepticism arise from the uncertainty of the grout formation beneath the tip and the lack of rational design procedures for its use. In cooperation with the Florida Department of Transportation, the University of South Florida is researching the effects of post-grouting on shaft capacity in loose to medium dense sands. This paper presents a review of past and present base-grouting methods used throughout the world and the scope of on-going full-scale load test programs.

A major pile test program was completed at JFK International Airport (JFKIA) to establish the optimum pile types to support structures planned for the JFKIA Redevelopment Program. The test program included drilled shafts and post-grouted drilled shafts to enhance design capacity. Although post-grouting has been used extensively to improve the capacity of tiebacks and minipiles, this method of treatment has had limited usage in the United States for the development of high capacity shafts. It was decided to conduct a comparative evaluation in the test program on non-grouted and post-grouted shafts constructed by different methods and in a variety of shaft sizes, lengths and grouted zones in order to attain planned ultimate capacities ranging from 6250 kN to 8900 kN (700 to 1000 tons). Geophysical logging techniques and low strain dynamic tests were selected to demonstrate the structural integrity of the completed shafts. Static and dynamic bearing capacity tests were performed using different test methods in order to define the permissible design capacity. Test results confirmed the improved bearing capability and apparent cost-effectiveness of the post-grouted shafts. This paper summarizes the test data from this load test program.

This paper presents the results of part of a US12 million program of testing of large-scale deep foundations carried out for the Kowloon-Canton, Railway, Corporation, Hong Kong. The results presented are for five tests carried out to demonstrate both the methodology required and the two to three fold enhancement of the factional capacity of a deep foundation that could be achieved by shaft grouting. The recommendations are based on the results of 30MN load tests on two barrettes, 40m and 50m long, and three piles 30m to 54m long carried out for this project, as well as over 30 other tests carried out elsewhere in Hong Kong. The work draws on the experience of the authors with over 40 load tests up to 40MN on grouted and ungrouted piles in Bangkok as well as published case histories in Europe, the Middle East. South Africa and Australia.

The purpose of the paper is to compare the coring results obtained after base mud cleaning and/or grouting and shaft load test results obtained before and after base mud treatment of the drilled shaft foundation of a building project in Taipei. Three different methods, which used a flat jack, a U-shaped tube and a modified U-shaped tube, were employed in base mud treatment. Procedures and devices for the modified U-shaped tube methods, which were modified in this project, especially those for reverse circulation installed shaft base mud treatment, are introduced. Interpretation of the results based on the coring results obtained after the base treatment was applied using the three different methods is discussed for this case study. In addition, the shaft load test results with and without base grouting are also presented. The comparison shows that the modified U-shaped tube combined with flushing and grouting is an efficient base mud treatment method. In addition, the shaft load test results show that the shaft axial displacement was reduced significantly for the shafts treated using the modified U-shaped tube method.

This paper illustrates how grouting techniques have been used to enhance large diameter caisson performance at different stages in construction. Attention is focused on the basic principles for the repair by grouting of the pile concrete itself — when compromised by cold joints, honeycombing or soil or slurry inclusions. A generalized repair methodology is presented, including the assessment, planning, execution, and verification steps.

It is often not realized that as the load on a straight drilled shaft increases, that the ultimate side resistance (often called skin friction) is generally fully mobilized when the shaft movement is on the order of 1/4 to 1/2 inch, while the end bearing is not fully mobilized until the movement is in the order of inches. Therefore, as the load on the shaft increases and the movement is small, and is at or near the working load, the load taken by side shear is large and the end bearing is small. As the load is increased to greater than the working load, the side shear becomes fully mobilized and further increases in load are taken by end bearing. The shaft movement versus side shear and the shaft movement versus end bearing can be determined separately by using the Osterberg Load Cell method for load testing a shaft. Load tests on many drilled shafts have shown that at the working load, the load taken by side shear can range from 80% to 95% of the total load. Also, because the load taken in end bearing versus the downward movement of the bottom is determined, the effect of bottom disturbance can readily be seen. Tests have been made on shafts in which the bottom disturbance have caused an initial downward compression of several inches before the disturbed material has compressed sufficiently to fully transmit the load to the lower undisturbed soil. It is shown that when this occurs, the "factor of safety" against large settlement is not as large as is generally assumed. The above does not generally apply to shafts with belled bottoms and to rock sockets.

A large aggregate and concrete supplier has constructed, using the design/build process, a $90 million cement plant in north central Florida, in an area of active karst conditions. The construction includes three large heavily-loaded silo groupings, with an applied base pressure of 476 KPa, and other tall heavy structures with large overturning moments. Both shallow mat and drilled shaft foundations were used. The geotechnical exploration indicated the presence of highly plastic clay overburden soils, with an underlying highly dissolutioned limestone formation. Depth to limestone varied from zero to 12.2 m due to past dissolutioning. Geophysical surveys, standard penetration test borings, pit excavations, dilatometer tests, pressuremeter tests, and 100 mm diameter rock coring were performed at the site to characterize the subsurface profile and limestone quality. Due to the limestone porosity, which included voids, a grouting program was performed in heavily-loaded and settlement-sensitive structure areas to reduce the risk of settlement and sinkholerelated distress. Drilled shaft design parameters were confirmed by Osterberg load test methods. The settlement prediction of shallow mat foundations was complicated by the unknown elastic stiffness of the highly dissolutioned limestone formation, a lack of historical foundation performance data in the area, and adjacent foundation interaction effects. Shallow foundation preparation consisted of plastic clay removal in rock cavities, air jet cleaning, and backfilling with high slump Controlled Low Strength Material (CLSM) to restore limestone competency. On-site excavated limestone was also used as fill/backfill, where appropriate, to further reduce costs. This paper discusses the geotechnical issues and challenges which occurred on this fast-track design/build project, and how they were solved by the contractor/designer/geotechnical consultant team.

Large diameter (D = 2,500 mm) batter steel pipe piles socketed into soft rock were constructed for the off-shore foundations of Kwangan grand bridge in Pusan, Korea. Concrete integrity tests so called cross-hole sonic logging tests were performed for most of off-shore piles. Some of the rock-socketed piles constructed during the initial stage of the project showed minor concrete defects, which were repaired with high pressure cement grouting. One pile had a severe defect near pile tip, which was repaired after three stages of grouting and non-destructive testing to check the repair. But three-dimensional numerical modeling and analysis was performed to check the quality of defect repairing and provide the reinforcement plan if the pile capacity was below the design load. As result of numerical analysis, the pile behaved primarily as a friction pile and most of applied external load was supported by friction resistance above the repaired rock-socket. Estimated bearing capacity (100 MN) of the pile was well larger than design load (24 MN).

Crosshole sonic logging (CSL) is a reliable, accurate, and cost-effective quality assurance- (QA-) based tool to investigate the integrity of cast-in-drilled-hole (CIDH) shafts. Through implementation of a nondestructive testing (NDT), CSL program, drilled shaft integrity can be evaluated shortly after concrete placement. Potential shaft anomalies can be detected and defects can be remediated before completion of the structure. The following case history includes CSL data, concrete core logs, compressive-strength test results, and postremediation CSL data. CSL identified the locations of anomalies within two 2.1-meter- (7-foot-) diameter, 20.7-meter- (68-foot-) long shafts that provide the foundation support for a vehicular bridge over the Muddy River in Overton, Nevada. The anomalies were subsequently confirmed as defective areas with concrete coring and laboratory testing. Early detection of the defects provided by CSL testing allowed the contractor to develop methods to mitigate the defects without drilled shaft replacement or major modifications to the bridge superstructure design. The structural engineer was able to evaluate those methods and their effects on the structure, and postremediation CSL testing in combination with construction observation and materials testing were used to assess the results of the remediation work. Detection and remediation of the defective areas before bridge completion avoided a potential structural failure and reduced the potential for future distress to the structure.

Soil and Materials Engineers, Inc. (SME) has utilized micro-piles on a number of projects in the Midwest. These foundation systems consist of drilling small diameter boreholes with a rotary-type drill rig or driving a casing with a small hammer. Mini-pile, micro-pile, or drilled-in pier, are other names for this type of piling system. Installing a structural steel member in the center of the excavated space, and grouting the borehole or casing completes the installation of the pile. The capacity of these piles varies, depending upon subsurface conditions, as well as the structural capacity of the pile. The size and yield strength of the structural steel member will determine the structural capacity. Two projects are presented where high capacity micro-piles were used because conventional driven piles would have been difficult, if not impossible to install.

This paper brings together the results of nearly 20 full-scale load tests on large diameter bored piles and barrettes carried out in Hong Kong over the last 10 years. The paper primarily draws on the results of a US$12million program of 14 full-scale pile tests carried out for the Kowloon-Canton Railway Corporation for the 30km West Rail Project Phase I. The solid geology included eight rock types ranging from igneous and volcanic to metasedimentary in varying degrees of weathering. The piles were tested to confirm that both rock socket and end bearing could be combined and where possible to demonstrate the ultimate capacity of each component. Test loads were applied using combinations of 30MN of kentledge and single 30MN Osterberg Load Cells. The results confirmed that, when compared with the Presumptive Allowable Bearing values given in the Hong Kong Building Regulations of 3 to 7.5MPa, a two to three fold increase could be achieved as well a concomitant increase in socket friction. The results have been used in conjunction with the other tests in Hong Kong as well as published elsewhere to provide design relationships based on unconfined compressive strength and point load test data. Some contractors have used the results in successful design and construct foundation schemes for the project.

For many years prestressed concrete piles have been the most popular pile type in the San Francisco Bay Area because of their relative economy and good performance. However, prestressed concrete piles displace considerable volume of soil and can cause significant heave, lateral deformations, and subsequent settlements when driven through thick deposits of soft soils. The ground deformations caused by pile driving can have significant impacts on adjacent structures and must be controlled within relatively small values. Predrilling is often used to minimize the soil deformations caused by pile driving. However, in certain areas along San Francisco's waterfront, where very thick deposits of soft soils are present, predrilling through the full depth of the soft soils is both impractical and uneconomical. Steel H-piles offer an economic alternative under conditions where capacities in the range of 1.8 MN to 2.7 MN can be safely mobilized. The paper describes two case histories involving high capacity H-piles driven into Franciscan Rock. Extensive indicator driving programs, dynamic tests with the Pile Driving Analyzer (PDA) and static load tests were used to verify the design loads. The results of the tests together with the results of production pile driving are reviewed and evaluated in terms of: (1) driving criteria, (2) penetrations in rock, (3) safe design loads, and (4) potential for pile damage. Statistical summaries of the results of production pile driving are presented to provide guidance for future projects for estimating pile lengths, formulating practical driving criteria, and for anticipating potential problems during driving.

Resistance factors for the geotechnical design of driven piles within the framework of the Load Resistance Factor Design (LRFD) plays a significant role in the safety and economy of the pile structure. Determination of the Resistance Factors for driven pile design using the reliability-based-calibration factors by fitting to Allowable Stress Design (ASD) as specified in the AASHTO LFRD for Highway and Bridge Substructure Specifications needs to be investigated and verified by probability-based resistance factors for different prediction models. The data used in this study was obtained from pile static load tests. The database covers a wide spectrum of variation in soil formations, stress history, geographic locations, pile types, and pile geometry. Statistically based resistance factors are determined for 11 commonly used design methods for driven piles. Comparisons with AASHTO LFRD specifications are delineated. The presented work provides recommended resistance factors for driven piles that are judged to deliver the best combination of reliability and economy.

The FHWA Deep Foundation Load Test Database is a centralized source of information for those involved in the design, construction and maintenance of our nation's highway infrastructure as well as other geotechnical design activities. A wealth of geotechnical and foundation load test data exists in literature, State DOT files, and various laboratories. When compiled and organized this can serve as the basis of a high quality geotechnical information repository. This system will benefit Federal and State Agencies, Universities, Consultants and Contractors, Administrators and Managers, Design Engineers and Planners, and Research and Development professionals.

The design of drilled shaft foundations can be based on ultimate load concepts, combined with suitable values of factor of safety, for cases where deflections of the foundations are of secondary interest. One example where deflection is not the controlling condition is for drilled shaft sound barrier walls foundations. This paper describes a simple and practical ultimate load design method for drilled shaft foundations. Field load tests were performed on 20 model drilled shaft foundations, 203 mm (8 inches) or 229 mm (9 inches) nominal diameter, at five sites in Virginia, where the foundation soils were partially saturated silts and clays. The results of these tests were used to examine the accuracy and reliability of the ultimate load theories developed by Broms (1964) and Brinch-Hansen (1961). It was found that Broms's theory provides an adequate method of analysis for drilled shafts in cohesionless soils, and Brinch-Hansen's theory provides a suitable method for soils with both cohesion and friction.

Lateral load tests were performed on 20 drilled shafts, 200 mm and 230 mm in diameter, at five sites in Virginia, where the foundation soils consisted of partially saturated silts and clays with both cohesion and friction. Laboratory strength tests were performed on undisturbed samples of the soils, and the deflections measured in the field tests were compared with deflections computed using LPILE Plus 3.0 The measured deflections were compared with deflections calculated using the p-y formulation developed by Evans and Duncan, modified to include Brinch-Hansen's three-dimensional factors. The p-y formulation described here uses Brinch-Hansen's theory to calculate ultimate values of p, and is applicable to soils with cohesion (c) and friction (φ). Comparisons were also made with the "silt" p-y formulation in LPILE Plus 3.0, which is also applicable to soils with c and (φ). It was found that the LPILE Plus 3.0 formulation underestimated the contribution of cohesion, and therefore resulted in ultimate load capacities that were considerably smaller than those measured. The LPILE Plus 3.0 default "silt" p-y formulation also resulted in larger deflections than those measured, for loads exceeding about 50% of the ultimate. In order to generate p-y curves with the Evans and Duncan formulation, it was necessary to determine appropriate values of the stress-strain coefficient "A" by matching the computed deflections with the measured deflections. It was found that the best match, at 50% of the ultimate capacity, was achieved with values of the product of A times ∊₅₀ (A∊₅₀) that varied from 0.011 to 0.023, with an average of 0.014. In cases where tests are not available to calculate this factor, using a value of A∊₅₀ = 0.014 appears to be a reasonable approximation, based on the results of this study. An Excel spreadsheet was developed to compute p-y curves based on the Evans and Duncan formulation for c-φ soils. The spreadsheet can be used to generate curves at any desired depth, in a format suitable for use with LPILE Plus 3.0.

The behavior of a 1.5-m (5-ft) diameter reinforced concrete caisson socketed in a clayshale and subjected to lateral loading was investigated. The study involved field testing and computer analysis. In the field testing, caisson deflections and strains of reinforcing steel as well as concrete were monitored. From these strain and deflection data, the p-y curves at top, mid-height, and bottom of the clayshale stratum were obtained. The computer analysis was performed using Ensoft. COM624 software to generate the predicted caisson deflection profiles and p-y curves. The results of computer analysis were compared with the results derived from the field test data. It was concluded that Reese's method of analysis for caissons in weak rock can render reasonable results for the clayshale investigated in this study. However, its application to very weak and moderately weak rock requires some special considerations. For material classified as very weak rock, strength reduction caused by load-induced fracturing has very little impact on the accurate determination of p-y curves. For rock strata displaying a wide range of rock quality, a modified relationship between RQD vs. strength reduction factor is proposed. For very weak and moderately weak rock, the correlations based on the RMR system render more reliable input values of elastic modulus than RQD correlations. Bending stiffness profiles obtained from computer analysis using pre-construction material properties are adequate only for predicting deflection when the shaft bending moments are equal to or greater than the ultimate values.

Prototype lateral load tests were performed on two sets of 4–400mm cast-in-situ concrete piles at two different locations to verify the validity of theoretical approaches for predicting pile head movements and the empirical relations between soil elastic moduli (E_s) and N values from SPT. To this end, the load-displacement curves obtained from the lateral load tests are compared with Chang, Randolph, and p-y curve methods. For the linear methods, such as Chang and Randolph, empirical constants of E_s/N are varied from 7 to28 as suggested in various references. As a result of comparisons, it is known that the linear methods can predict the pile head movements within the usual range fairly well, if appropriate empirical values of E_s/N are adopted. The p-y curve method predicts the pile head movements consistently in a conservative way. In average, the predicted loads by the p-y method for given pile head displacements are about 70% of the minimum values of the test results for the same displacements. For the prediction of ultimate lateral resistances of piles, it is found that Broms' method could give too small values compared to the actual ultimate resistances depending upon the types of soils where the piles are embedded.

It is generally believed that the current FHWA guideline for designing drilled shafts is overly conservative when applied to stiff soils. Practitioners who are designing drilled shafts in soils with relative densities of 50% to above 95% have to look elsewhere for design guidance. Various researchers have proposed solutions that are peculiar to stiff soils. Another solution is to perform load tests on pilot drilled shafts prior to installing production shafts. To date, the New Mexico State Highway and Transportation Department had performed full-scale load tests on more than a dozen drilled shafts. Most of them were installed in stiff soils. This paper presents and interim comprehensive drilled shaft design equation that is applicable to soils of all relative densities including those near or at 100%. The solution extends the design approach described in the FHWA drilled shaft design manual to include dense cohesionless soils. The development of this equation was based in part on results of the most recent full-scale fully instrumented test in which Osterberg cells were used. A nonlinear large-deformation capable finite element program, GEOT2D, was used to match the test data and afterwards generated the information needed to develop the design equations. This interim design equation is shown to be comparable with predictions using the FHWA equations if the soil relative density is assumed to be about 35%.

A large body of experimental data has been collected on pile-soil setup and axial load-deformation behavior in highly plastic clays near the Mississippi River delta. The data provide unique insight into the behavior of foundation piles subjected to static and cyclic axial loading in both tension and compression. Static tests with a 30-inch-diameter pile driven to a penetration of 234 ft below the mudline are compared with instrumented pile segment probes 1.72 and 3.0 inches in diameter. Excellent agreement is shown between the pile and the probes. Correlations include (a) the effects of diameter and wall thickness on the rate of consolidation and setup, (b) the effects of time and the degree of consolidation on the static axial capacity, and (c) the effects of depth and loading history on the nonlinear shear transfer versus displacement. In this paper, correlations are developed relating the ultimate static shear transfer to commonly measured soil properties, including directly relating the shear transfer to the undrained shear strength. It is shown that complex effective stress methods are not necessary for normally consolidated and underconsolidated highly plastic clay soils.

The favorable effect of long-term set-up of driven piles in non-cohesive soils is very seldom utilized to any significant extent in piling projects, mainly because there is no simple geotechnical method that can be used to evaluate the set-up potential at a specific site. This paper describes a novel method where torque tests on driven rods are used to predict the set-up of piles. A series of torque tests was performed on instrumented rods at different times after installation. The test results correlated very well with the set-up of full-scale concrete piles, driven at the same site. The method proved to be a most valuable tool for estimating set-up as it is very cost and time-efficient, and also extremely easy to perform.

As the number of uncertain parameters affecting pile foundation capacity is large, there is a need for a more systematic and comprehensive approach to address these uncertainties. Intelligent hybrid system involving Artificial Neural Network approach and Fuzzy Logic techniques is proposed herein as one alternative that is capable of capturing the uncertainties associated with the controlling design parameters.

A new foundation system employing in situ grouting of helical screw piles has recently been developed. As the anchor is installed into the soil, a column of grout is "pulled down" around the anchor shaft providing an in-situ grouted shaft. This foundation system has been successfully employed at several sites with very soft soils overlying a more competent stratum. The grouted column significantly increases the anchor shaft's resistance to buckling and provides additional corrosion protection. The grouted shaft also increases the stiffness of the column and bearing capacity of the foundation. The paper discusses design considerations, installation procedures and results of full scale field load tests. Several case histories with field performance data are also described.

A theoretical model is developed to support the well known empirical relationship between capacity and torque for helical foundations and anchors. The model is based on energy exerted during installation and that required to displace the helical foundation or anchor once in place. Through the equivalence of energy, the model relates bearing and pullout capacity directly to installation torque. Downward force during installation, helical blade geometry, multiple helices, blade pitch per revolution, and hub radius are taken into account. The model is applied to determine the capacity and installation torque for several helical foundations and anchors of different geometric configurations. Theoretical predictions are shown to correlate with previously published field and laboratory measurements.

Over the past 20 years the square shaft solid steel helical screw pile has come into expanded use as a permanent deep foundation element in new construction of heavily loaded structures, i.e., column loads in excess of 445 kN (100,000 lbs). This increased use, along with recognition by every national building code in the United States of at least one manufacturer's helical screw pile, emphasizes the importance of helical screw pile technology as it pertains to new construction. This paper presents an introduction to design methodology for heavily loaded helical screw piles in new construction common to all manufacturers of helical screw piles, covers pile load capacity, installation torque versus capacity, discusses the helical screw pile as a pure axially loaded element where special consideration is given to pile placement for lateral load transfer such as seismic and wind forces, discusses pile grouping and pile cap design, concrete to pile shaft load transfer hardware, settlement, long-term creep, corrosion, slenderness buckling of the pile shaft, water migration along the shaft in expansive clays, discusses the refusal condition, covers the economics of helical screw pile technology, especially in difficult soils, tight access and environmentally sensitive areas, or where schedule improvement is required, and lists the manufacturers of helical screw piles and how they can be contacted. The paper concludes with a case history of a project where helical screw piles were designed and installed for new construction under a heavily loaded structure. The helical screw pile is a viable and accepted deep foundation for construction of new heavy structures that should be considered anytime a deep foundation is contemplated.

Routine inspection of the existing Rock Run Dam, an Ambursen type dam located in Coatesville, PA, revealed major stress cracks and water stains on the inside face of the 6 m by 4.6 m (20 ft x 15 ft) east end bay. To prevent a catastrophic failure, stabilization of the bay was deemed necessary while the dam remains in service. The dam is approximately 85 years old and there were no foundation information available from the original construction drawings. Due to uncertainties regarding the construction buttress foundations and cutoff wall and the generally poor quality concrete in the dam, the repair selected for the east bay was an interior concrete support system which remains completely isolated from the existing structure. This eliminated uncertainties related to imposing additional stresses on the existing dam structure. Test borings taken inside the chamber showed 4.3 m (14.1 ft) of silty sand, followed by 4.1 m (13.4 ft) of decomposed rock overlying gneiss bedrock. The support system was designed to limit differential movement relative to the existing structure. A micro pile system was selected and was designed to have minimal impact on the existing structure. Concrete filled nominal 200 mm (8-inch) diameter steel pipes were used as micro piles which were designed to develop their full resistance from the rock sockets. The piling system included both vertical and battered piles to accommodate variable hydrostatic loading. The piles were installed and load tested under limited headroom (less than 3.4 m).

Augercast piles are commonly used in south Florida to support heavily loaded structures including high-rise condominium towers, hotels, and arenas. South Florida's geologically young sedimentary rock is ideally suited to this pile type since the rock can be readily augered yet sustain high applied load at low displacement. In the early 1980's, individual augercast pile capacities on the order of 625 kN (70 tons) were used for 355-mm-dia (14-in-dia) piles. With recent equipment and construction material advances, 615-mm-dia (24-in-dia) piles for future projects are being evaluated to potentially sustain design loads of 4000 kN (450 tons). Selected cases from past and current projects are presented to illustrate the use of the augercast pile in south Florida, with particular emphasis on experience gained by the author's firm on projects in the coastal areas of Miami-Dade and Broward Counties. A database developed from over sixty full-scale field compression and six lateral load tests is presented and compared to the results of theoretical analysis and correlations available in the literature.

A comparative study was performed at the Auburn University's Spring Villa NGES test site aimed at quantifying the effects of grouping and amelioration on the axial capacity of augered displacement piles. Amelioration is defined as the addition of sand or stone during drilling to "improve" the pile-soil interface. The test site lies in the Piedmont geologic formation and is comprised of residual soils best classified as silty-clay to clayey-silt. The tested piles were specialized, full displacement continuous flight auger piles. The scope of testing involved quick load compression tests on five different pile configurations: isolated single pile, isolated single pile ameliorated with sand; isolated single pile ameliorated with #89 crushed stone; single pile centered in symmetric 5 pile group; single pile centered in symmetric 5 pile group ameliorated with sand. Previous studies of this test site indicate low variability across the site with respect to stratigraphy and soil strength. Differences in these side by side load tests can be attributed primarily to pile configuration. The tests quantified substantial increases in axial capacity with both grouping and amelioration. The nature of the full displacement piles is such that the group effect substantially increases lateral soil stresses over the depth of the pile, resulting in higher side friction with the installation of adjacent piles. Amelioration with either the sand or the crushed stone also resulted in an increase in capacity, though quantitatively not as much as with the group effect. While both grouping and amelioration provided marked increases in capacity, their combined effects were not as substantial.

Augercast piles were designed and installed for electric power generating facilities at three sites in Louisiana, Mississippi and Texas. The soils at the three sites were predominantly very stiff to hard clays, and extensive field and laboratory test data were available. The geotechnical design of these piles was based on the use of ultimate pile shaft/soil adhesion, c_a, in accordance with the commonly available analytical procedures where c_a=α⋅s_u. Although the piles were statically load tested to compressive loads that exceeded 4,000 kN in some cases to confirm design assumptions, the ultimate compressive load was not reached for two piles. The static load test results were extrapolated, where necessary, to provide an estimate of ultimate compressive load. Values of c_awere then backcalculated and values of α obtained. Comparisons were made between the backcalculated values of α and those recommended for the analytical procedures. The backcalculated α-values from load tests showed considerable variation, but the median values were close to the α-values used in the analyses. Also, a trend of decreasing α-values with increasing undrained shear strength was observed.

This paper reports on a study of 43 compression load tests (five fully instrumented) and ten pullout tests of auger cast-in-place (ACIP) piles in sand. Eight design methods reported in the literature were used to predict the measured pile capacities. Ultimate load capacities of the ACEP load tests were determined using two different definitions of ultimate capacity and compared with predictions. Load transfer behavior was determined from a study of the fully instrumented pile tests and compared to predicted values. Recommendations are made regarding the design approach most appropriate for these foundations and the best procedure for estimating ultimate capacity from pile load tests.

The major constituent in the augered cast-in-place (ACIP) pile is the grout, and hence, understanding the grout behavior is essential. A laboratory study was undertaken to evaluate the working and mechanical properties and chemical resistance of grout mixtures of which one batch was collected from a field project. Grout behaviors of interest were fluidity, setting time, mechanical properties and chemical resistance. Chemical resistance of the grout mixes was studied by immersing the specimens in sulfuric acid (pH = 4), hydrochloric acid (pH = 4) sodium sulfate (0.5%), and sodium chloride (0.5%) solutions for a period of two years. Use of additional fluidifier and fly ash in the grout and their effects on the flow properties and compressive strength of the grout was quantified and compared to the field samples. Variation of compressive strength, modulus and pulse velocity with curing time for the field samples has been quantified. Grout cube strength was higher than the cylinder strength. The ratio of cylinder strength to cube strength varied from 0.89 to 0.93 with an average of 0.91. Increasing the fly ash content 25 to 35% did not affect the fluidity or compressive strength of the standard grout. During the two years of immersion test on grouts weight change and the amount of calcium leached from the specimens has been quantified. The weight change observed varied from –3 to +3% and the maximum calcium leached was 0.5%. Of the solutions studied, 0.5% sodium sulfate solution had the greatest damage on the grout. The data suggest that ACIP piles may be more susceptible to sulfate attack than concrete piles.

Where soil conditions are favorable, augercast piles have significant economic advantages, but they also have some uncertainty due to the construction methods. To confirm bearing capacity and structural integrity, static testing can be performed on a small sample of piles. However, the load test piles are not necessarily constructed in a manner representative of production piling. Additional assessment methods must be used on more piles to increase confidence in augercast piling foundations. Non-Destructive Evaluation (NDE) methods like Pulse Echo are frequently specified for a large percentage of the production piles. However, such NDE methods require testing the pile after the grout or concrete has hardened. If problems are found, then the repair or replacement can be relatively expensive. The confidence in the quality of augercast piles can be improved by automatically monitoring the grout volume pumped as a function of depth. If a low grout volume is measured for any depth increment, the pile can be repaired immediately while the grout is still fluid. Such installation monitoring equipment can be of great help to the installation crews and may reduce the need for subsequent NDE tests. While Pulse Echo tests and monitoring during installation can assess the pile structural integrity, the bearing capacity cannot be assessed by these methods. Bearing capacity accurate; errors as much as 20% have been observed. Further, the counting of strokes is usually done manually per 1.5 m (5 ft) interval. This large interval does not always give sufficient precision. The visual definition of the 1.5 m (5 ft) interval has been observed to be not very precise, with 0.3 m (1 ft) errors being common. Alternative methods of more accurate volume determination are desirable.

In recent years the Augered Cast-In-Place (ACIP) Pile industry has seen a substantial increase in the quality control options available to Contractors, Engineers, and Owners. Quality control methods range from the simple, manual techniques that have been used for years to relatively complicated computerized installation monitoring equipment and sonic integrity testing methods. Our ability to monitor and test ACIP piles has grown to such a degree that the industry is struggling to determine how much quality control is enough. This paper reviews the many options available and describes the pros and cons of each. The various sonic integrity testing methods, in particular, have been difficult to apply reliably due to misapplications of methods and misinterpretation of the results. ACIP piles have unique properties that require the various sonic testing methods available be considered very carefully in determining the method most appropriate for a particular project. Some sonic testing methods, as well as automated monitoring equipment, potentially can be applied effectively to increase the level of quality control for ACIP piles. The experience gained on real projects using these new methods, in conjunction with the old procedures, provides valuable information for future applications.

Cyclic lateral loading tests were performed for the Texas Department of Transportation on a series of augered, cast-in-place (ACIP) piles in overconsolidated clay at the National Geotechnical Experimentation Site — University of Houston. Pile diameters and penetrations were varied. A p-y model, modified from the Welch-Reese model developed in similar soils for drilled shafts, was found to give excellent predictions of pile performance, and a simplified hand solution that does not require the use of a computer was provided predictions of behavior up to the load that produced tensile cracking in the test piles.