Contemporary Issues In Deep Foundations

While seeming simple in principle, thanks to the graphic nature of the output data, the Crosshole Sonic Log method is quite controversial as a quality control method for drilled shaft foundations. In the author's opinion, this is largely due to the inexperience of both the operators, and the analysts. The test is deceptively simple to perform, and the data is relatively easy to understand. Determination of the nature of an anomaly, however, requires an understanding of the test method, the construction method, and an ability to perform a forensic analysis of the documented construction process. Determining the significance of the anomaly requires an understanding of the foundation design, the geotechnical properties of the soil in which it has been constructed, and the physical conditions under which it will support a structure. Not many people embody all these skills, so, usually, several people will be involved in the acceptance or rejection of a deep foundation. It is important that all of the people on this team have faith in the expertise of their fellow players. This paper looks at some of the common errors that have been identified in the last few years, primarily as a result of lack of expertise on the part of one or more people on the test and evaluation team.

Since 2001 the South Carolina Department of Transportation (SCDOT) has regularly used crosshole sonic logging (CSL) to evaluate the integrity of the majority of drilled shafts installed on state bridge projects. The authors have been responsible for approximately half of the logging performed to date. The CSL results are summarized for the purpose of simple statistical analyses in an effort to identify trends. To date more than 400 shafts have been logged on more than 42 projects. The shafts have been installed by 10 different drilling contractors, in a variety of soil conditions using various construction methods. The most pertinent findings of the evaluation are that 1) about 33% of the tested shafts contain an anomaly (or anomalies), 2) nearly 90% of the anomalies are located within the top two diameters or bottom two diameters of the shafts, 3) the vast majority of the anomalies are attributed to concrete placement issues and 4) most anomalies are not considered defects.

Cross-hole Sonic Logging (CSL) has become a common method to evaluate the integrity of drilled shafts. However, the interpretation of test measurements by this method requires some judgment and experience. Many previous proposals rely solely on the arrival time, or wave speed. A proposed method which takes into account both arrival time and signal strength is presented. If defects are detected, then in some cases a tomography analysis may be helpful to further quantify the result. The situations where tomography is useful will be discussed. Recommendations are given for the type and amount of data required for a tomography analysis. This discussion is illustrated with a case history of a test shaft with purpose built defects to demonstrate the advantages of these evaluation methods.

This paper presents velocity tomograms from the Crosshole Sonic Logging (CSL), Crosshole Tomograpahy (CT) and Angled Crosshole Sonic Logging (ACSL) tests on a mock up shaft for comparisons of defect resolution. The CSL method is used to measure the speed of sound between water-filled cast-in-place access tubes. The velocity of the sound wave which travels from source to receiver in a horizontal plane determines the presence of anomalous regions (due to water or air-filled voids or soil intrusions) and therefore the quality of the concrete. For added higher resolution of shaft integrity and defects, the CT velocity imaging method is used. The CT velocity method precisely defines the size, shape, severity, depth, and location of potential defects by determining the spatial velocity distribution of shaft concrete through analysis of numerous sound wave ray paths. The ACSL test is a compromise technique between the CSL and CT test methods. This technique uses arrays of sources and receivers (in this study, 4 sources and 4 receivers) to obtain different angled ray paths. The ACSL method turns every log into a tomogram.

Drilled shafts socketed into bedrock are a common foundation type for support of heavily loaded buildings and bridges in the Mid-Atlantic region of the United States. Along the region, the underlying bedrock of the Wissahickon Formation within the Piedmont Physiographic Province is often present about 10 to 100 feet below the ground surface and overlain mainly by silty residual soils and disintegrated rock. The underlying bedrock mainly consists of gneiss and schist. Two load tests were performed for drilled shafts socketed into bedrock and disintegrated rock in Maryland using the Osterberg load cell and in accordance with ASTM D - 1143 (Quick Test). The objective of the paper is to determine the drilled shaft capacities socketed into rock using field load test data and to compare the results with capacities calculated from empirical correlations. The Reese & O'Neill and Carter & Kulhawy methods were used for estimation of the drilled shaft capacity. The total ultimate capacities from the load tests were about 25% to 50% less than those predicted using the Reese & O'Neill and Carter & Kulhawy empirical methods. However, the total ultimate capacities were close to that of the capacities observed from the load tests, when the skin friction was calculated assuming disintegrated rock layer as Intermediate Geomaterials (IGM).

Rock socketed drilled shafts are frequently used in very soft rocks, with compressive strength less than 2.5 MPa (26 tons/ft²), to support structures. Due to the lack of understanding of the behavior of rock socketed drilled shafts in very soft rocks, the design capacity has to be verified by performing full-scale load test and/or sampling and testing of the rock at the bottom of the borehole using a core-hole sampler, before installing the production drilled shafts. Hence there is a need to better quantify the performance of drilled shafts with and without a core-hole in very soft rocks. In this investigation, field test results are used to first calibrate the end bearing capacity of rock socketed drilled shafts in soft rocks using the finite element method. Effects of rock cohesion and friction angle on the end bearing capacity were investigated and unit end bearing-displacement (q-w) relationships have been developed. Linear and non-linear relationships between ultimate unit end bearing and rock strength have been developed. Effect of the open (not filled with material) core-hole diameter on the ultimate bearing capacity, unit end bearing-displacement relationships and the bearing capacity factor has been quantified. For a 0.1D and 0.4D open core-hole diameter the bearing capacity factor was reduced by 4% and 40% respectively.

Statnamic load testing was performed on three 66 inch (1,676 mm) diameter, post tensioned, spun cast, concrete cylinder piles and one 30 inch (762 mm) square pre-stressed concrete pile as part of a construction phase load test program for the replacement of the US 90 over Rigolets Pass Bridge near Slidell, Louisiana. The test program also included dynamic testing on all piles and static load testing of the 30 inch (762 mm) pre-stressed concrete piling. Statnamic loads approaching 6,000 kips (27 MN) were utilized on the cylinder piles to fully mobilize side shear in these predominantly friction piles. The static load test and Statnamic load test results on the same 30 inch (762 mm) square pile showed excellent agreement in both load and displacement up to the point of the limiting applied static load. The signal match on this pile showed greater displacement at similar loads. The Statnamic tests of the cylinder piles showed ultimate static capacities of 2,966 kips (13.3 MN), 3,077 kips (13.7 MN) and 3,315 kips (14.7 MN). While the CAPWAP analysis of re-strikes on these piles showed ultimate static capacities of 1,245kips (5.5 MN), 2,030 kips (9.0 MN), and 2,116 kips (9.4 MN). These results suggest that the Statnamic test method was able to fully mobilize the pile side shear resistance, while the dynamic test results were subject to the available hammer energy which was not sufficient to fully mobilize the ultimate static capacities.

Cylinder piles have a high axial compressive strength for high bearing capacities, they have a high moment of inertia and therefore can serve well as both a column and a foundation pile under high vertical and lateral loads. Cylinder piles often are used in nearshore applications where smaller foundation piles would require cofferdam construction and other costly measures. Drilled shafts have similar load bearing properties and capabilities, however, they are generally more costly than piles installed by impact driving. While impact driven cylinder piles are a cost effective foundation solution they can pose problems during installation. One problem that has received repeated attention is the potential for pile damage, a second one is an uncertainty, about the. end bearing capacity. During pile installation the end bearing may not be present due to high soil inertia effects, during a static load application it is more likely, though it is not guaranteed, that the soil plug transfers its full end bearing to the inside of the pile. Pile damage developing during the installation can occur at the pile top, along the pile both due to longitudinal and vertical cracking and near the pile bottom. Based on analyses and measurements, this paper examines the likelihood of pile damage developing during pile driving and discusses the end bearing problem.

The North Carolina Department of Transportation (NCDOT) has been testing and designing bridges with concrete cylinder piles since the early 1980s. However, their widespread use in production has been limited. In 1996, a 42.7 m (140 feet) long, 1.68 m (66 inches) diameter concrete cylinder test pile was driven and load tested at Oregon Inlet, North Carolina for the design of a new replacement bridge. Oregon Inlet is a 762 meter (2,500 feet) wide marine channel in a very dynamic scour and sediment transport environment lying just off the North Carolina mainland, separating Bodie and Hatteras Islands. Scour and vessel impact loads governed the new bridge foundation design. The installation of the test pile helped determine the drivability characteristics in this type of environment. Two — 10.2 cm (4 inches) diameter, 33.6 meters (110 foot) long jets were used along side of the pile. The pile was jetted and driven throughout the entire installation process. Due to the pile size and soil conditions, jetting was the primary installation method. An HPSI 3505 single acting hydraulic hammer facilitated the installation. At the end of initial drive, the pile was struck 323 times, and the pile did not move. Following the installation of the cylinder pile, it was axially load tested to 220% of the pile design load and laterally load tested until structural failure from bending.

Concrete cylinder piles are large diameter precast piles that are commonly used for water crossings and other marine applications that require foundations with high load resistance that are highly resistant to corrosion. With their high moment of inertia and corresponding high buckling resistance, concrete cylinder piles are well suited for sites where water depth and potential scour result in a long free-length of pile above mudline. This paper provides an overview of concrete cylinder piles, including a discussion of typical pile sizes and properties, fabrication methods, typical applications, advantages and disadvantages, and the unique design and construction issues relevant to this type of pile. The paper also describes common installation problems for this type of pile and typical remedial measures to address these problems. Finally, the paper illustrates pile design and installation issues with case histories from three recent bridge projects.

Two case studies are presented where 1372 mm (54 inch) diameter concrete cylinder piles where used in recent bridge projects in Florida. The primary focus of the paper is on cracking and spalling of the piles during installation and the solutions used to overcome these problems. Field and laboratory test data are also presented which demonstrates some advantages of cylinder piles. The St. George Island Bridge in Apalachicola, Florida utilized segmented spun cast post-tensioned piles. Longitudinal cracking was found in 42 piles believed to be from excessive hoop stress induced by mud and water buildup within the pile during driving, commonly referred to as "water hammer". The Trout River Bridge in Jacksonville, Florida utilized bed cast continuous prestressed piles. Severe spalling of the pile top during installation was encountered due to high localized stresses imparted by the driving hammer system. The cracking experienced on both projects proved to be a result of soil conditions and installation methods. Installation methods were modified to eliminate the cracking. These case studies should provide benefit to the engineering community in solving similar problems should they arise on other projects.

This paper draws upon recent research findings to propose a new CPT q_c based design method for predicting axial capacity of open and closed ended driven piles in siliceous sands. The method incorporates various factors that are acknowledged to have a controlling influence on pile capacity including (i) the effects of soil displacement during installation, (ii) friction fatigue, (iii) sand-pile interface friction angle, (iv) changes in radial stress during loading, and (v) the influence of loading direction.

Piles are often coated with a slip layer such as bitumen to reduce the dragload. The friction between granular soil and coated as well as uncoated pile surfaces were studied using a modified direct shear test apparatus. The lower half of the direct shear box was replaced with a concrete or mild steel block to represent a pile surface. Two types of bituminous coat namely Shalikote and Bitumen of grade 30–40 were evaluated in this study. Shalikote and Bitumen coating reduced the interface friction by more than 70% and 90% respectively. The shearing resistance of pile material-coat-soil is found to be influenced by normal stress, type of coat, and coat thickness. The effect of saturation and the rate of soil settlement on the interface friction are also discussed. Pull out tests were carried out on coated and uncoated model aluminum pile placed in a circular tank filled with granular soil. The results of pull out tests are compared with interface friction tests.

A method of analysis is presented for piled raft foundations where the piles exhibit non linear load-deflection behaviour. The raft is analysed through the use of finite element methods, while the piles are treated as springs having a variable stiffness, so as to model any non-linear behaviour. The soil is treated as an elastic medium that may consist of layers of soil having different stiffnesses. Interaction between the piles in the group is assumed to remain constant even though the stiffness of the piles may change with load level. The method has been incorporated into the computer program GARP (General Analysis of Rafts with Piles). This program is used to analyse a tall building that was constructed on a piled raft foundation, and a comparison is made of the calculated and observed behaviour.

Resistance bias factors for the two static bearing capacity analysis methods of driven steel pipe piles adopted in the Korean Design Standards for Structure Foundations were evaluated as part of study to develop LRFD codes for foundation structures in South Korea. Of the 2,227 static load test data on driven steel pipe piles collected from all around the country, only 43 were found to be useful for this study. These load test piles were sorted into two cases: pile tip in soil case and pile tip in rock case. Pile bearing capacities were measured from the load-displacement curves by six different failure criteria, and Davisson's criterion was found to be most reliable. Statistical analysis of the resistance bias factors was performed, and the results show a significantly high degree of variation in the resistance bias factors.

Pile bents are often used in bridge foundation systems. These sub-structural elements are constructed by installing a row of piles and connecting them with a concrete cap. A common design practice is to use a point of fixity approach which idealizes the soil-pile system as a cantilever of a particular length, forming a single column in an elastic frame. In this paper, current design practices are reviewed, and a new method for calculating point of fixity is developed for engineers who must consider separate single pile lateral analyses and elastic frame analyses. The proposed approach better matches the maximum moments and displacements obtained from non-linear analysis for a pile in the foundation system that is subjected to the lateral loading applied to the bridge. An example that compares a pile bent designed as an equivalent elastic frame with a nonlinear analysis is presented. Comparative results show the elastic frame model with two equivalent lengths (based on transverse and longitudinal loading conditions) satisfactorily matches results from nonlinear analysis, while a frame with a single point of fixity, based on deepest equivalent length, provides a conservative approximation of the nonlinear model.

This paper presents the experience gained by the California Department of Transportation on the use of soil-cement piling techniques for the support of a bridge widening structure in San Francisco, California. Four pre-production soil-cement piles, installed using a soil-cement jetting system, were tested in compression and tension. One of the piles was fully instrumented with strain gauges and tell-tales. The tests revealed that high side resistance measured in dense sands is caused primarily by irregularities in the soil-cement pile surface. Tests also indicate that post-grouting of soil-cement piles represents an effective remedial alternative to mitigate non-compliant piles.

Laboratory testing for foundation design offers advantages over field-testing, especially, where existing installations preclude easy accessibility. Advantages include a homogeneous soil, ability to place instrumentation throughout the soil mass, and capacity to bring the system to failure, as well as control over the failure mechanism. Repeatability is also achievable. Laboratory work, however, has its own challenges. For model-scale work, a main impediment is scaling: strength, dimensions, and boundary conditions hinder accurate modeling of the soil and brings a difficulty in representing scaled foundations. This paper describes the construction-oriented solutions pioneered for meeting the geometric requirements of ⅛^th scaled laboratory testing of composite deep foundations for existing foundation enhancement, including drilled shafts, helical piers, and grouting. Results of the testing program are included as verification of the usefulness of the techniques.

As urban redevelopment becomes more widespread, the problem of what to do with the old foundations from the previous buildings is becoming increasingly important, both financially and environmentally. Reuse of existing foundations generates substantial savings, both financial and environmental, but at what risk? The uncertainty related to the reuse of existing foundations can be minimized by employing state-of-the-art non-destructive testing methods. This paper provides a review of current options with comments about their relative efficacies. Mini-case histories are presented to better clarify where each of the techniques can be effectively used either individually or in tandem.

During urban site redevelopment, many developers are faced with the problem of underground obstructions constraining the installation of foundations for new buildings. Constraints arise from previous deep foundations, subway lines, archaeology and utilities. As cities around the world redevelop in response to changing and growing prosperity, this subsurface congestion will further constrain future development. An alternative is foundation reuse. Reuse of previous foundations has economical, practical, and sustainable advantages. This paper studies the drivers for foundation reuse in a systematic way using Arup's Sustainable Project Appraisal Routine (SPeAR®) diagram and uses this analysis to study the influence of these drivers on London in comparison to different cities within the U.S. Eight drivers are identified and discussed including location, archeology and historical constraints, geological conditions and constraints, sustainability and materials reuse, land value and cash flow projections, construction costs, consistency in building locations, and approvals and development risk.

Axial forces in piers beneath buildings constructed on expansive soil sites will vary with time depending on the wetting pattern and expansive characteristics of the foundation soils. Furthermore, the pier force depends on the deformation characteristics (stiffness) of the foundation. This paper presents a methodology for predicting pier force and foundation stiffness based upon both theoretical considerations and measured deformations. Wetting patterns that are considered include both infiltration from the ground surface and wetting from a deep source. Foundation stiffness is determined by two different methods. One method is based on beam deflection theory and the other utilizes measured heave values. The results of the analyses are applied to observed data measured on a large building. Although measured pier force values are not available, the results demonstrate the range of pier force values that may be expected and demonstrate the application of the methodology.

Plunging failures were experienced by some of the cast-in-place drilled piers on a concrete tilt-up office/warehouse project located in northwest Denver, Colorado. The failures occurred upon the application of loads during construction. The piers were installed in clay overburden soils and shallow claystone bedrock. Failures of this type in the Denver area are very rare, but may have occurred on two other occasions that the author is aware of in the past 25 years. The author believes the failures are a result of the formation of a softened zone due to a phenomenon known as "fissure softening". In addition to high slaking and dispersion potential, and the highly fractured nature of the claystone, ground-water levels were high on the site resulting in seepage into the pier holes during drilling. The combination of stress relief and seepage forces exerted on the soil structure are believed to have caused a widening of the fissures surrounding the small blocks of claystone material near the face of the excavation. Alteration of the claystone initiated along the widened fissures and progressed into the small blocks of material until the mass was entirely deteriorated, causing a reduction in shear strength and settlement of the piers. Other geotechnical practitioners in the area have attributed this rare condition to the mixing of water and claystone by the auger drill, resulting in a mechanical "smearing" or redeposition of a thick layer of material on the sides of the pier holes, and in addition, that loose material must have fallen into the bottoms of the holes to explain the loss of end bearing. In any event, although this type of failure is exceedingly rare, geotechnical engineers in Colorado should be aware that it can occur and should consider further research and study of the causes.

A manufacturing facility located in the Front Range area of Colorado was constructed in 1991 and 1992. It was founded on 18 to 42-in. (46 to 107-cm) diameter piers with depths of 23 ft (7.0 m). The bottoms of the piers are approximately 44 ft (13.4 m) below exterior final grade. Movement of the piers and structural floors was initially observed during construction and prior to the occupancy of the building in January 1993. Individual piers had heaved as much as 11 in. (28 cm) within the first six years of being constructed. A geotechnical investigation was performed to predict the maximum pier movement. Analyses based on pier heave prediction methods predicted a maximum final pier heave of about 14 in. (36 cm). This agreed well with values obtained by extrapolation of measured data. The results of the investigation were used by the building owner to assist in making informed decisions regarding the maintenance, usability, and longevity of the building.

Auger cast piles were employed to support major equipment additions under three separate projects during 2005 and 2006 at one electric generation plant in south Alabama. Due to the subsurface profile variations within the plant and differing foundation loading, various lengths of auger cast piles were installed. Axial load tests, lateral load tests and pile integrity testing were used on some of the projects. Several problems during construction required modifications to installation methods, including a change in foundation type mid-project on one of the additions. Predicted and measured capacities for both axial compression and lateral capacity are compared, along with a discussion on the various problems encountered during construction. The paper also stresses how historical information regarding existing facilities plays an important role in the selection and performance of foundation types.

In this study, installation and curing of a 760 mm (30-inch) diameter and 10 m (32 ft) long ACIP pile with a design capacity of 800 kN (92 tons) in very dense sand was investigated. The dense sand layer was about 11 m (35 ft.) thick and was located 7 m (23 ft.) below ground. During the installation, torque on the gear box advancing the auger was recorded and it varied from 2.5 to 50 kN.m (2000 ft-lbs to 36,000 ft-lbs). The auger advancement rate varied from 12 to 83 mm/sec. The grout was characterized using the flow cylinder method and the flow diameter was 20 cm (8 inch). The grout volume ratio and pumping pressures were monitored at every 1 m (3 ft) lift during grouting. The curing of the pile was monitored using axial vibrating wire strain gages at four levels (10 gages) and lateral vibrating wire strain gages at two levels (two gages). The residual strains and temperature profiles in the curing pile was monitored over period of a week to determine the appropriate time for load testing the pile. The peak temperature from the edge of the pile to the center of the pile varied by over 8°C and the peak temperature in the pile was 63 °C in the center of the pile. The maximum temperature measured was over 40 °C higher than the surrounding ground temperature. The average time to reach the peak temperature in the pile was 0.35 days. The average maturity for the grout used in the pile was 1180 °C-hrs. The average residual axial and lateral strains in the pile after 7 days of curing were compressive and increased with depth.

In a set of companion papers presented at GeoCongress 2006, the authors described a Data Acquisition System that is included on the installation platforms for drilled displacement piles and, in general terms, defined how the acquired pile installation data can be used both for quality assurance / control and as an element of the pile design process. The system described was subsequently used by Berkel and Co. Contractors Inc (Berkel) as part of a design-build project in Orlando FL in March and April of 2006. The acquired installation data was used in the following manner. First, the pile installation data acquired during the preliminary foundation design and performance testing phase was used for final design of the foundation system for the project. Secondly, the data acquired during production pile installation was used, in real-time, for quality assurance / control during the project's entire pile installation phase. In addition, daily review of the acquired pile installation data revealed subsurface anomalies in one portion of the site that were subsequently attributed to other subsurface construction activities that occurred immediately prior to pile installation. The authors demonstrate how these anomalies were detected, how appropriate capacities were assigned to the piles in question and how appropriate remediation measures were planned and executed. Unless otherwise noted, the use of the term "pile" or "displacement pile" in this paper refers to the Berkel Displacement Pile (as described in NeSmith, 2002). Likewise, design methodologies and construction recommendations described herein also refer specifically to this foundation system.

Micropiles are small diameter replacement piles that are capable of developing high axial capacities. Their installation equipment can penetrate hard rock with greater efficiency than tools used for other more conventional foundation types. It is due, in part, to their high capacity and their ability to penetrate hard unsuitable rock, that micropiles have emerged as an effective, and often preferred, foundation for heavier structures located in karst terrain composed of hard limestones and dolostones. However, the implementation of micropiles in karst terrain involves the combination of two complex systems. Typical karst conditions can include very soft soils, chert boulders, sloping rock surface, and cavitose bedrock. Meanwhile, the micropile installation process involves subsurface grouting and a variety of possible drilling techniques. The first case history illustrates how certain micropile drilling techniques can significantly degrade the clay above the rock surface and reduce the lateral resistance around the upper micropile. The second case history describes how unconventional micropile design details coupled with associated accommodations during installation can lead to quality problems. The third case history illustrates a success in anticipating the karst conditions and selecting the appropriate drilling technique to fulfill the intent of the design. Understanding that success depends on anticipating potential modes of failure, the case histories are offered to help others anticipate, and thereby avoid, future micropile failures.

A three-story building was founded on 19.1 cm (7½ in) diameter micropiles socketed 4.3 m (14 ft) into the underlying bedrock to meet the strict settlement requirements for a light rail system. A static load testing program consisting of three test piles located across the site was conducted to verify design assumptions concerning micropile axial loading and settlement. In addition, extensive installation monitoring was conducted during micropile installation. The results of the micropile load testing program showed that micropile installation could have a significant influence on pile top load-displacement relationships and pile capacity. Therefore, an extensive production pile monitoring program was conducted to verify proper micropile installation.

The cutter and pinnacle features of karst present foundation challenges as encountered by the interchange and frontage road improvement project along Interstate 70 (I-70), Frederick County, Maryland. The project area traverses a karst area with an aggressive sinkhole occurrence rate of approximately eight new sinkholes per year, with 147 known sinkholes documented by 2003. Two pump stations lift and remove storm water from geosynthetic lined storm water ponds. The deep foundation system for these pump stations required penetrating 34 m (110 ft) or more of soil and epikarst to bear in competent material. Micropiles are well suited for the anticipated subsurface conditions since installation techniques enable a production pile to also serve as a verification hole of the bond length. Proper application of pile termination criteria ensure an acceptable foundation element and will aid in minimizing grout loss. A total of 61 micropiles were installed for the two pump stations. The 180 mm (7 in) O.D. micropiles were bonded into limestone rock to provide an axial resistance ranging from 355 to 445 kN (80 to 100 kips). Pile depths varied from 8 to 49 m (25 to 161.5 ft), indicating the highly variable subsurface rock contours. Three load tests were performed, with one micropile exhibiting a plunging-type failure when it was bonded in and subsequently sheared a pinnacle.

As the concrete in drilled shafts cures, extremely high internal temperatures can be generated (even when relatively small in diameter) giving rise to mass concrete conditions. When the concrete temperature exceeds safe limits, the concrete may not cure correctly and can ultimately degrade via delayed ettringite formation. Minimizing the peak temperature (and the associated defects) can be undertaken by casting the shafts without concrete in the core thereby removing a large amount of the energy producing material in a region that is least likely to benefit the structural capacity and that is less able to dissipate the associated core temperatures due to the presence of the more peripheral concrete. This paper presents the field temperature results of shafts cast under normal conditions and the surprisingly alarming findings. A numerical model was subsequently calibrated and used to show the tremendous potential for voiding shafts. Finally, construction issues that are likely to be encountered are summarized with possible solutions.

Drilled shaft foundations on major bridge projects often require the use of underwater placement of large volumes of concrete through densely placed rebar, with the cage often made even more congested with the placement of additional tubes for post-construction integrity testing. Such conditions represent the most difficult circumstances for constructors in terms of concrete placement to achieve a shaft which is free of defects or anomalies in the integrity testing. The concept of "high performance" for drilled shaft concrete is that the mixture should address the most critical performance requirements related to workability. This paper describes the important considerations in concrete mixture design for drilled shaft construction including the use of admixtures and mixture components associated with self-consolidating concrete (SCC). Some case histories of difficulties associated with concrete are also described.

Post stressing of drilled shaft tips using pressure grouting techniques can significantly increase the ultimate capacity of the shafts. Conventional drilled shafts generally require substantial tip movement to develop full end bearing. Recent studies have found that the end bearing component can be significantly increased utilizing pressure grouting after the placed concrete has had sufficient time to set up. The post construction stressing of the tip of the shaft mobilizes the deformation of the supporting soils needed to develop increased end bearing. This paper presents a discussion of the geotechnical design considerations of this innovative construction technique. The paper also presents a summary of recent research that utilized full-scale load tests to evaluate post stressed drilled shaft design and construction. The studies were performed along the Gulf coast from Florida to Texas. In addition, the results of several full load tests performed in the Houston area will be presented.

The Sutong Bridge across the lower Yangtze River in China will have, when completed, the longest span (1,088 m) and the highest towers (306 m) of any cable stayed bridge in the world. The foundations for this record-setting span are drilled shafts under each of the main pylons. The North Pylon is supported on 131 drilled shafts, 2.5 m diameter and 114 m long. The South Pylon is supported on 131 drilled shafts 2.5 m in diameter and 117 m long. The tips of all drilled shafts were post-grouted after an extensive test program confirmed significant increase in capacity with post-grouting. This paper presents a description of the post-grouting test program, the results obtained, and the construction methods used for post grouting of the production drilled shafts.

In construction of drilled shafts under water, placing concrete in the shafts is technically demanding and involves complex construction logistics. Past construction experience has demonstrated that high quality concrete can be placed in drilled shafts under water with a proper concrete mix and proper placement techniques. However, a significant number of failures have occurred which have resulted in excessive cost overruns and delays. These problems may have occurred because proper underwater concrete construction techniques have not been widely disseminated within the industry. This is a technical area where competent design and sound construction planning can achieve a significant reduction in both risk and cost. This paper will discuss some key technical issues in the concrete mix design, concrete production and placement for the drilled shaft construction. The paper also describes two lesson-learned case histories from drilled shaft construction projects.

This paper presents details of instrumented pile tests performed to examine the effects of plugging on the capacity of open-ended piles installed in soft clayey silt. Four pile installations are described, including tests on three closed-ended and one open-ended pile. The closed-ended piles ranged in size from 73mm steel circular piles to 250mm square concrete piles. The open-ended pile was a 168mm diameter steel tube, with double wall construction to allow the separation of internal and external shear stress. The soil core development during the installation of the open-ended pile is presented. The pile was found to be partly coring during installation, with a final Plug Length Ratio of 86% (PLR = Soil Plug Length/Pile Penetration) suggesting a relatively low level of soil disturbance during installation. Installation radial total stresses developed on the open and closed-ended piles are compared to examine the effects of partial plugging on shaft resistance. Due to the twin walled construction adopted, the components of base resistance of the open-ended pile, namely the plug and annular resistances were measured directly. The bearing stress beneath the pile annulus was similar to the CPT q_c resistance throughout installation. The plug capacity was relatively low throughout installation, being only 5–10% of the q_c value.

This paper presents the results of a pile installation and testing program for instrumented 30-in long, 3.5 in diameter steel pipe piles with wall thicknesses 0.120 in, 0.216 in, and 0.290 in, installed by jacking into Oklahoma Sand specimens created by pluviation in a CPT calibration chamber at the University of Texas. Continuous measurements of pile penetration, plug height and pile resistance were obtained as the piles were pushed into the sand specimens with the calibration chamber pressurized at 10 psi. The instrumentation involved a load cell, a position transducer, and an LVDT. For comparison purposes, an additional test was performed on a 3.5 in diameter closed end pile. This paper presents a description of the model pile installation facility, the instrumented piles, the model sand, the testing program, and, the test results obtained. The results of the testing program indicate that piles with thicker walls require less penetration to develop plugging. Pile capacities were also predicted using the conventional procedures and found to under-predict measured values. The differences are attributed to development of higher side friction caused by plugging.

Load-deflection relations of piles subjected to lateral loading are routinely required for design. The use of large diameter open pipe piles became common since its application as foundations for offshore structures, and more recently for bridge retrofitting and new construction designed for withstanding earthquake loading. The accuracy and reliability of the analysis methods remains usually unknown as it requires the systematic examination of the measured performance of many piles. As part of a research aimed at developing the serviceability limit states for the AASHTO specifications, an evaluation of the methods predicting the response of piles to lateral loads was required. This paper presents a database of laterally loaded open and closed pipe piles which were examined by various analysis methods. The performance of the methods when applied to open pipe piles and all pipe piles is reported along with practical conclusions for their use.

Open ended pipe (OEP) piles are frequently used as a deep foundation solution in the Atlantic Coastal Plain (ACP) physiographic province. Typically, these piles act as low displacement piles during installation as the pile advances through the soil. However, if the soil plug becomes stationary within the pile, the pile acts as a full displacement pile. Plugging of an OEP pile can have significant effects on pile design and installation. Typically, measurements of pile plugging are conducted after pile installation is completed by measuring the depth to the soil plug and the embedment depth of the pile. The following paper presents the results of eight case histories of open ended pipe piles with pile plugging measurements in the Atlantic Coastal Plain. For each case history, the individual pile plug length ratio (PLR) and incremental fill ratio (IFR) was determined and the plug behavior during static and/or dynamic load testing (if available) was examined. Examination of the case history data showed that the piles experienced little plugging during installation, although pile plugging did increase with depth. In addition, the increase in measured tip capacity with time from pile installation suggests that OEP piles driven in ACP soils act as plugged with time.

This paper presents the results of a pile installation monitoring and performance assessment program for pile foundations supporting 14 piers and 2 abutments of the 1700-ft long bridge crossing over a river in Baltimore, Maryland. Dynamic measurements were conducted during installation and restrike of 16 test piles, one at each support location. The foundation piles were 30-inch diameter, 0.75 inch thick pipe piles at the piers and 24-inch diameter, 0.5 inch thick at the abutments. The piles at the piers were approximately 100 ft long and were designed to carry 260 kips service load with a factor of safety of 2.25. The piles were driven open ended into a variable site stratigraphy containing recent deposits of organic clayey silts near the mud line followed by loose to medium dense sand, with some silt, and then by soil deposits from the Cretaceous period consisting primarily of dense to very dense, poorly- to well graded sands and gravels and cobbles, with occasional seams of very hard to very stiff, low to moderate plasticity silts and clays. This paper presents the approach taken to evaluate the driven index piles and to develop criteria for driving production piles, and provides the Engineer with some data on pile driveability in Cretaceous soils in the Baltimore area, soil set-up effect, and an estimate of pile capacity.

Monopile foundations are frequently used for offshore wind energy converters. These piles are highly laterally loaded structures with large horizontal forces and bending moments. Due to the harsh environmental conditions in the southern North Sea diameters of 4 to 8 m are required to maintain serviceability. In common practice smaller laterally loaded pipe piles are designed using the well-known p-y-method, in which the pile-soil stiffness is considered by nonlinear p-y-curves derived from field tests. An alternative design method is the strain wedge method in which the pile response is derived from the stress-strain relationship of the soil assuming a certain failure zone ahead of the pile. In the present paper, the design of a large diameter monopile foundation for typical loading conditions is presented. The pile response in cohesionless soil determined by the p-y method and the strain wedge method is compared with a finite element (FE) analysis with respect to scale effects when extrapolated from commonly used pipe pile diameters to large size monopiles.