Geo-Congress 2019: Foundations

A new computational method for predicting the nonlinear response of laterally loaded piles is developed. In the formulation, the pile is an elastic Euler-Bernoulli beam and the soil is a three-dimensional continuum characterized by a nonlinear elastic constitutive relationship. The soil displacements in the radial and tangential direction, because of pile movement, are expressed as products of separable functions while the vertical soil displacement is assumed to be zero. The principle of virtual work is applied to obtain the differential equations describing the pile and soil displacements, which are solved numerically using the one-dimensional finite difference method following an iterative scheme. The mathematical accuracy of the formulation is ensured by comparing pile response with those of equivalent three-dimensional finite element analysis.

With the increase of high-rise building construction and the development of underground space, the failures of pile foundations caused by soil excavations are also on the increase. This paper presents the results from field tests which were conducted to investigate the effects of excavation unloading on the performance of CPT cone resistance and laterally loaded piles in Jiangsu deposits of eastern China. The reaction of cone resistance to various excavation types (overall excavation and adjacent excavation) was obtained, and can be used as a direct and reliable evaluation approach to understand the characteristics of the excavation unloading. Based on the cone resistance profiles, the effect of the excavation on the lateral bearing capacity of single piles was analysed using a CPT-based p-y method. In addition, the lateral behavior of the single piles after excavation and its difference from the piles in the free field were presented. The predicted results from CPT profiles were in reasonable agreement with those from the lateral load tests.

Energy piles are an emerging alternative for the reduction of energy consumption to heat and cool buildings. Most of the research to date has focused on thermodynamic properties or axial and radial stress and strain of piles. This paper focuses on the effects of temperature fluctuation on the capacity of driven energy piles in clayey soils. Consolidation of clay surrounding driven piles affects the pile capacity (i.e., set up in clay). The heating and cooling periods of energy piles can create the excess pore-water pressure (EPWP, u_e) or relax the existing one (e.g., due to pile driving or previous thermal loads) in clayey soils (due to the contraction and expansion of water) affecting the pile capacity. In the meantime, the thermal expansion and contraction of the pile also generate or relax the EPWP in the soil, which can be computed using the cavity-expansion theory. This paper studies the resulting changes in the pile capacity due to the daily and seasonal thermal cycles. The results show that thermal cycles in an energy pile can cause a decrease in the pile capacity leading to a delay in reaching the capacity after a complete clay set up.

Cross-median crashes are the most severe type of run-off-road highway crashes. Cross-median crashes represent approximately 2% to 5% of all interstate crashes, yet fatalities and serious injuries occur in as much as 30% of these severe events. Many state departments of transportation (DOTs) install cable median barriers to mitigate the risk of these types of crashes. In research efforts to design a high-tension cable median barrier, a review of several recent crash tests into cable barriers revealed test failures (i.e., vehicle floor pan tearing and penetration into occupant compartment) that were largely caused by a combination of the pile bending strength and cross-sectional geometry with exposed free edges. The bending strength of the pile, embedded in coarse crushed limestone, caused the top of the overridden pile to press up against the undercarriage of the vehicle. The geometry of the pile contributed to sheet metal tearing and penetration into the occupant compartment. Therefore, research efforts were made to design a new, closed-section pile for use in a non-proprietary, high-tension cable barrier system through dynamic component testing and computer simulations using the finite element program, LS-DYNA. A total of 20 bogie (surrogate vehicle) tests were conducted on potential closed-section piles with a 24-in. (610-mm) embedment depth to determine their strong- and weak-axis capacities under impact loading. The pile sections, including hollow structural section (HSS) 3×2×1/8 (76-mm×51-mm×3-mm), mechanical tube (MT) 3×2×11 gauge (76-mm×51-mm×3-mm), and MT 4×2×14 gauge (102-mm×51-mm×2-mm) were evaluated with different patterns of weakening holes. Analysis of test results and simulations indicated that the HSS 3×2×⅛ with two ¾-in. (19-mm) diameter holes at groundline had the most promising potential to meet the desired strong- and weak-axis capacities, while reducing potential concern of floor pan tearing and penetration. Thus, it was recommended for further evaluation through full-scale crash testing.

National Grid embarked on a large-scale substation upgrade of their 40+-year-old Bear Swamp Substation in 2014 involving over 150 new, isolated, drilled shaft (caisson) foundations. A value engineering proposal to re-use the existing foundations was considered, which could significantly reduce planned outages and capital costs. National Grid’s investigation of the existing pier foundations included historic plan review and field measurements, followed by non-invasive confirmation of below-grade pier geometry using low strain impact pile integrity testing. Under proposed design loads, the existing pier foundations were found to not meet the serviceability criteria for the project. Further evaluation of technically feasible options led to the consideration and eventual application of soil strengthening techniques to qualify the existing foundations for reuse. The project was completed at a construction cost savings of over $200,000. Additional soft costs saved by reducing the planned outages otherwise required to facilitate foundation replacement is estimated to double or triple the capital cost savings.

The load transfer mechanism of micropiles was examined for a bridge during construction in the Foothills Parkway of the Great Smoky Mountains in Tennessee. The bridge is supported on four piers and each rests on a circular pile cap with 20 micropiles socketed into rock with varying depths. The ground is characterized by 4 to 50-ft of sand and gravel overlying metaconglomerate and metasandstone rock. The load transfer of the piers was monitored using strain gages installed along the micropiles cased and bond zones, as well as in the pile cap. In addition, a 3D numerical model was developed using ABAQUS to understand the behavior. Using the collected data from the instrumentation and the numerical simulations, it was found that the weathered rock in the cased zone of the micropiles transfers a significant load (>70% of the total load) despite the small friction at the interface.

In this study, a simplified analytical design and finite element modeling of the piled-raft foundation for a wind turbine are presented. The design loads (vertical, horizontal, and bending moment) were calculated for a 130 m tall hybrid wind turbine and mean wind speed of 201.3 km/h. The number of piles and other dimensions obtained from the simplified analytical design were used to develop a three-dimensional finite element model in ABAQUS considering the interaction between soil and structural components. The piles and soil body were modeled as two bodies in contact with appropriate contact algorithms to accurately model the interaction between them. The comparison of the results obtained from the two methods showed that the vertical settlement and the horizontal displacement obtained from analytical method were 1.76 and 1.26 times higher than ABAQUS results, respectively. While, the differential settlement and rotation obtained from analytical method were 2.18 and 4.50 times lower than ABAQUS results, respectively. Similar results were observed for a range of wind speed and undrained cohesion.

Two large bridges over the Great Miami River in Dayton, Ohio, were constructed. The foundations for these bridges consist of driven piles, and as part of a value engineering change proposal (VECP) the foundation design was optimized for the least cost given the constraints of the site conditions and pile drivability. Over 40 different possible combinations of pile diameter, pile wall thickness, pile capacity, and pile hammer were considered during design, including open ended piles. Cost factors included material costs for steel and concrete including length surcharges over 15.2 m (50 ft), crew and equipment time and costs to unload and drive the piles, and time and material costs for splices. Foundation costs were compared on cost/ton basis. The selected pile design was a 406 mm (16-inch) pipe pile with an ultimate capacity of 2890 kN (650 kips), which exceeded the state DOT’s recommended maximum pile capacity of 1600 kN (360 kips) for this size pile. During construction, two instrumented static load tests and many dynamic load tests (with signal matching analyses) were performed to evaluate the selected foundation design. The results were used to develop a construction pile driving criteria that accounted for pile setup and checked for pile tip relaxation. The results of the static load tests indicated that one pile had an ultimate capacity of at least 2980 kN (670 kips) and the second pile had a capacity in excess of 4900 kN (1100 kips).

Large diameter open-ended pipe piles typically refer to pipe piles with diameter larger than 76 cm (30 inches). These piles, when properly constructed, offers superior load carrying capability to traditional ones. The existing AASHTO specification for pipe piles is based on database collected from pipe piles with diameter typically less than 61 cm (24 inches). Current experience indicate that formation of soil plug due to arching effect is crucial for the bearing capacity of large diameter open-ended pipe piles to be mobilized and sustained. In this paper, the formation of soil plugging has been discussed through numerical simulation with the discrete element method (DEM). Laboratory and geotechnical centrifuge experiments are conducted to analyze the bearing resistance of pipe piles driven in sand with different pile diameter, types of restriction plate, embedment depth, etc. It is shown the formation of soil plugging is highly associated with the arching effect inside soil particles. Two types of restriction plates, i.e., 1-hole restriction plate, and 4-hole restriction plate, are compared and proved to be effective in mobilizing the formation of soil plug after pile driving.

A variety of pile design methods, either soil property-based, or in-situ test-based methods, have been proposed to estimate the ultimate bearing capacity of driven, closed-ended, pipe piles. Yet, due to the limited number of well-documented, high-quality pile load tests, efforts still need to be made to assess the performance of these methods. This paper presents case histories of three carefully-instrumented static load tests, performed in Indiana, U.S., on closed-ended pipe piles driven in multilayered soil. Several property-based and CPT-based pile design methods for both sandy and clayey soils are used to estimate the limit shaft and ultimate base resistances of the test piles. The performance of these design methods is assessed through detailed, layer-by-layer comparison between the estimated resistances and those obtained from pile load test measurements. For the cases considered, the Purdue, ICP, and UWA methods produce the most accurate, reliable, and consistent predictions.

Large open-ended pipe piles have been widely used in offshore and transportation engineering. The design formula for the pipe piles in the current AASHTO specification is based on the load-bearing database of pipe piles with diameters less than 24 inches. Therefore, the load/resistance factors may be inaccurate for the design of large open-ended pipe piles. Centrifuge testing is one of the most commonly used geotechnical test methods to study complex geotechnical problems. In this study, an extensive amount of geotechnical centrifuge experiments was conducted to analyze the load bearing behavior of pipe piles and piles with an innovative restriction plate. A customized loading frame was built to apply static loads. By using the scaling law, centrifuge experiments can scale up the model scale experiment to resemble the field scales. The pile diameters are scaled up by applying the centrifugal accelerations. With the validated experimental setup, the study conducted a program to systematically evaluate the influence of restriction plate on the loading bearing behaviors of large diameter open-end pipe piles. The results showed that by using restriction plates, the ultimate bearing capacity increased significantly compared with the corresponding open-ended pipe piles.

A new technology center along the banks of the Delaware River in Camden, New Jersey, required a deep foundation system to support the proposed structures. Concrete-filled pipe piles were selected and over 4,000 were installed. This paper examines the design and installation challenges. The pile capacities varied from 175 to 200 tons. Piles were 16 inch diameter with a 2 inch thick flat plate welded to the tip. Many challenges faced the geotechnical engineer of record for the design, and the contractors who installed the piles including the presence of existing timber piling from the 1800s, remnant construction, highly variable subsurface conditions, pile freezing, and groundwater. This paper outlines the subsurface conditions, pile design alternatives, pile load testing program (static and dynamic), and pile installation challenges that were overcome on this large and complex project.

This paper presents the analyses of load-transfer (t-z) behavior of twelve prestressed concrete (PSC) instrumented test piles that were driven in different locations of Louisiana. The load transfer method is an efficient and practical tool for the analysis of single driven pile to predict the ultimate load. The test piles were instrumented with vibrating wire strain gauges in order to calculate the shear transfer for different soil layers during the static load test. The static load test was performed on all the test piles after 10 to 14 days of end of driving. Empirical load-transfer models were proposed previously by different researchers after analyzing the instrumented test pile results. For this study, load transfer of each soil layer was measured and compared with the previously developed existing model. The stiffness parameter (M) for the hyperbolic equation was calibrated in order to best match the measurements. The good agreement of the proposed curves was then confirmed by applying them to assess the overall load-settlement curve of other pile load test results available in the literature.

In this paper, a feasible finite element technique, using a one-dimensional disk to represent the soil around the pile, is developed with ABAQUS program to explore the impacts of the size of pilot hole on the long-term load carrying capacity of pre-bored piles. The proposed finite element model incorporates cavity expansion theory along with Biot’s coupled consolidation theory to capture the change of stress state of the surrounding soil. The long-term side capacity is examined by applying vertical shear displacement on the soil element adjacent to the pile until the ultimate state is reached. Based on the proposed numerical model, a set of reduction factor curves pertaining to the unit side friction are presented for various combinations of pre-bore size and soil conditions, which are expected to provide guidelines for the design and construction of pre-bored piles.

Dolphin Tower is a 15-story high rise residential building in downtown Sarasota, Florida. It was constructed in early 1970s. Precast 14″×14″ reinforced concrete piles were used as deep foundation. Dolphin Tower experienced punching shear failures in the reinforced concrete slabs of several floors. While the punching shear failures were not related to any foundation deficiencies, as part of the evaluations and design for retrofitting and repairing the structure, it was required by law to assess the structure for compliance with the Florida building code in effect at the time of the repairs. After assessing the loads, it became evident the loads on deep foundations, as per current Florida building code, were larger than the design loads. There were no pile installation or certificate of construction completion records available. A site characterization program consisting of SPT borings and CPT soundings were carried out to characterize the subsurface geological material. Compressive, tensile, and lateral capacity of existing piles were evaluated using up-to-date field data and empirical pile capacity analysis methods. In addition, as part of bringing the building into compliance with the current Florida building code, existing shear walls were enhanced and additional shear walls were proposed. Considering the limitations imposed for installing new deep foundations under an existing building, helical piles were used as the foundation for the new shear walls and where needed for enhancing the existing foundation system.

The cone and piezocone penetration tests (CPT and CPTu) have been widely acknowledged as very useful in situ tests for subsurface investigation and soil characterization. The CPT is fast, robust, and economical test that can provide continuous soundings with depth. Due to similarity between pile and cone, the estimation of pile capacity from CPT data was among the earliest applications of the CPT. Accordingly, different direct pile-CPT methods have been developed based on this analogy between the cone and the pile. Analyses and evaluation were conducted on eighty driven friction piles of different sizes and lengths that were failed during pile load testing. The pile-CPT methods were used to estimate the load carrying capacities of the investigated piles (Q_p). The Davisson method was used to determine the measured load carrying capacities from pile load tests (Q_m). Four criteria were selected for evaluating the different pile-CPT methods: the best fit line for Q_p versus Q_m, the arithmetic mean and standard deviation for the ratio Q_p/Q_m, the cumulative probability for Q_p/Q_m, and the histogram and log normal distribution for Q_p/Q_m. Results of the analyses have been used to evaluate the ability of different pile-CPT methods for estimating the pile capacity.

The bi-directional static load test (“BDSLT”) is widely used to test the geotechnical resistance of deep foundations. Many, if not all, of these tests are performed on instrumented drilled foundations where applied loads, strains, and displacements are measured during the load test. After the test is completed, the measured data are analyzed to determine required parameters for construction of the equivalent top-loading (“ETL”) curve. One of the main parameters used for the data-reduction process is the drilled foundation’s composite-section elastic modulus, E. This parameter directly impacts the foundation’s computed internal forces, ETL curve, and elastic compression. Several published methods have presented graphical and theoretical expressions to aid determination of a foundation’s elastic modulus, whether a composite-section modulus, or the modulus of concrete/grout. This paper presents a review of these methods, and explores the impact of each outcome on the BDSLT results. Two concrete unconfined compressive strengths were considered to analyze the results of a BDSLT on a 72-inch-diameter drilled shaft. The concrete elastic modulus was determined from a method prescribed by the American Concrete Institute (“ACI”), and the composite-section elastic modulus was determined using the tangent modulus (“TM”) method. Parametric studies were performed using load-transfer (t-z) analyses to investigate the effect of different moduli of elasticity on the t-z curves and the constructed ETL. Results of analysis showed that a given displacement of 2 inches and a 12 to 16 percent difference in axial rigidity, resulted in a 550 to 1,200 kips difference in predicted load determined using the ETL curve. Similarly, a given load of 6,000 kips and same percentage change in the axial rigidity, resulted in 0.5 inch to 1.18 inches change in displacement.

At the time this paper was written the new Comcast Technology Center is entering its final phase of construction in Philadelphia, PA, and will open its doors in the summer of 2018. The structure will be the tallest building in Philadelphia at over 1,100 ft, and one of the top 10 tallest structures in North America. The foundation system for this building is a combination of drilled piers (commonly called caissons) and a mat foundation below the core of the building. This paper outlines the design of the foundation system and provides a summary of the geotechnical investigation, laboratory testing of soil and rock samples, engineering analysis, and observations made by the geotechnical consultant who was involved in the project throughout the investigation and construction process. The importance of keeping the geotechnical engineer of record involved throughout the investigation and construction is examined and discussed.

The Kosciuszko Bridge, the first cable-stayed bridge in New York City, carries a 1.8 km (1.1 mile) segment of the Brooklyn-Queens Expressway (I-278) over Newtown Creek between Morgan Avenue in Brooklyn and the Long Island Expressway interchange in Queens. The project was carried out in 2 distinct phases: Phase I for the design and construction of the east (or Queens) bound structures and Phase II for the design and construction of the west (or Brooklyn) bound structures. In both phases, foundations for the main tower pier consisted of 55 m (180 foot) long high-capacity drilled shafts, with a 2 m (6.5 foot) diameter, 4 m (13 foot) long rock socket. In order to meet the accelerated schedule without impacting the quality of the bridge, bidirectional Osterberg Cell (O-cell) load tests were performed on production shafts. Under such conditions it was necessary to tailor the test performance criteria to production shaft requirements, namely the maximum test load on one hand had to be high enough to demonstrate the required compressive and tensile resistances, on the other hand it had to be limited as not to cause concrete cracking or permanent shaft deformations. This paper focuses on the O-cell test performed for Phase II and includes a discussion on shaft performance inferred from test results, shaft installation process, geotechnical instrumentation, and data acquisition details. Comparison between results of O-cell load test performed in Phase I and Phase II is also provided.

Use of rock-socketed drilled shaft has been popular due to relative advantage in modern highway application. No interaction between drilled shaft and rock is considered in current design guideline due to the complexity and limited data availability. This results in likely conservative design for rock-socketed drilled shaft. The interaction of drilled shaft is significantly influenced by the characteristics of rock. Numerical modeling has been most cost effective to analyze drilled shaft in context of different geometries and parametric study. Numerical modeling was performed to determine behavior of the rock-socket. The numerical results were calibrated in PLAXIS2D from a full-cycle uni-axial O-cell load test. The load test was performed for drilled shaft with rock-socket which was located under a bridge pier. A Hoek-Brown failure criterion, able to consider non-linear strength behavior of rock, was selected for constitutive model of rock. The calibrated model has been selected for parametric study. The factors of parametric study for rock properties include unconfined compressive strength, geological strength index, and disturbance factor. The results of that study will reduce the cost of the drilled shaft construction.

Sinkholes that propagate during construction present a severe safety hazard for on-site personnel and can result in additional, unanticipated project costs. This paper discusses cover-subsidence and cover-collapse sinkholes that occurred on a site in western Citrus County, Florida, between initial geotechnical exploration and completion of drilled shaft construction. The sinkholes occurred in several locations across the project site, which resulted in the deterioration of the working platform and posed an imminent threat to worker safety. This paper also discusses several factors that may have contributed to the propagation of sinkholes. This study includes site investigation, field observation, meteorological, and groundwater data gathered throughout the duration of the project. During this time, more than 110 sinkholes were repaired using more than 1,000 cubic yards of backfill material.

Optimizing foundation design through load testing is not new, but can be critical to mega projects, such as the most expensive private development in U.S. history—Hudson Yards. Encompassing six city blocks, Hudson Yards will become an entirely new neighborhood on the west side of Manhattan. The project includes 12 high-rise towers and several low- to mid-rise towers, some of which are being built on platforms over the Long Island Railroad’s west-side rail yard. With over 600, 3- to 6-foot diameter caissons being drilled as deep as 140 feet to bedrock—many between the 30 active railroad tracks—the foundations are a major cost for the project and a major impact to the schedule. When drilling in an active rail yard that serves as the hub for the busiest commuter rail in the country, every minute counts; so pre-production load tests to justify shorter rock sockets and reduce the drilling times were essential. In NYC, caissons are typically designed with the city’s building code’s presumptive maximum allowable skin friction of 200 psi in rock. Nine caisson load tests with instrumented Osterberg cells were conducted across the rail yards and in several types of bedrock (of variable quality) including in schist and granite. Some of the tests reached average skin friction values as high as 900 to 1,000 psi without failing—almost five times the code allowable value—and justified an increase in the design values. The test data presented here shows the variability in results in relation to rock type and quality, and construction methods. Conclusions and lessons learned from the test program are presented for future projects that may benefit from using load tests to increase design values for rock socketed caissons.

In this study, a series of model tests was carried out on a small-scale single pile embedded in gypsum rock with predetermined cavities in order to investigate the effect of different cavity locations on the bearing capacity of the pile. This model was used to calculate a reduction factor for the bearing capacity of piles. Results show that the reduction factor decreased with an increase in the distance from the pile tip to the cavity. The reduction of the pile bearing capacity can be mainly explained by a reduction in the end bearing capacity of the pile. As can be seen from these results, pile capacity is significantly reduced when cavities are located close to the pile tip.

Load and resistance factor design (LRFD) is becoming a design method of choice in practice. However, even with LRFD, the need to reduce the uncertainty in the predicted performance of the geotechnical system is still apparent. The partial factors for a given geotechnical design using a given solution model are often specified in codes. Thus, the main prerequisite of the design using LRFD code is to select appropriate characteristic values of uncertain input parameters. However, the choice of these characteristic values often involves significant subjectivity, and thus the resulting geotechnical design by different designers may be quite different. This paper examines the five methods often suggested for selection of characteristic values for design with LRFD. In addition to cost and reliability, the focus of the evaluation is on the design robustness (i.e., how to make a design with LRFD most robust). For illustration purposes, design of a drilled shaft in sand is adopted and the best method among the five methods examined for selecting the characteristic values of uncertain input parameters is determined.

The Kosciuszko Bridge replacement project involved the construction of two parallel cable-stayed bridges. Both bridge towers are founded on high capacity seven-foot diameter drilled shafts with 6.5-foot diameter rock sockets. The design and construction of the bridge was divided into two phases. Each phase included one cable-stayed bridge structure. High capacity lateral load tests were performed for production drilled shafts in both phases of the project. The full-scale testing allowed the project team to verify single shaft lateral performance and effectiveness of the contractor’s method of construction. The lateral load tests were modeled using the p-y method for analytical results. During load testing the shafts were instrumented in the field to monitor shaft behavior. Instrumentation included direct head movement measurement, and the use of inclinometers for determination of the lateral deformation with depth and estimation of the zone of influence due to the lateral load. The shafts’ design and construction, lateral load test set up, acceptance criteria, and performance for both phases are discussed herein. Comparison between test results and the predicted results from the p-y analysis method are included.

Micropiles were installed at a school site in California to underpin an existing building to mitigate liquefaction hazards. The micropiles were 244 mm (9-5/8 inch) diameter. They were installed through predominately silty and clayey strata with intermittent sand lenses and drilled to a gravel layer approximately 21.3 m (70 ft) below the ground surface. They were grouted under pressure to create an end-bearing zone in the gravel layer. Because of seismic concerns, the regulatory agency (DSA) required that verification tests be conducted under combined lateral and axial loading. Full scale pile load testing under combined axial and lateral loads is sparsely recorded in the literature. A case history is presented including the results of the combined tests on three of the micropiles. The tests were conducted with the piles loaded to 222 kN (50 kips) axial load, then subjected to 40 kN (9 kips) of lateral force (200 percent of superstructure design load for each). Reaction pile movements were also recorded; therefore, conclusions about the relative effects of each force may be drawn.

The objective of this preliminary study is to demonstrate the anticipated geotechnical and structural demand on helical anchors from inclined mooring line loads from aquaculture installations. For onshore applications, helical anchors are typically designed to withstand axial loads; however, lateral demand contributes to the required structural and geotechnical capacity of helical anchors for aquaculture applications. The results of 3D finite element analyses illustrating the capacity of helical anchors in an estuarine environment for aquaculture applications are presented. The behavior of Maine’s Presumpscot marine clay, characterized from high-quality samples, is used to calibrate soil parameters in the 3D finite-element model. Preliminary recommendations regarding suitability of helical anchors to aquaculture are made based on computed results, as well as recommendations for future work.

This case study will highlight the advantages of a pressed-in pipe pile wall installed to protect an exposed bridge foundation. The June 2016 flooding in the southwestern part of Japan heavily scoured the slope in front of one of the Uto Bridge’s abutments. The bridge was traversing a very steep, heavily incised, and unstable gorge, prohibiting the use of conventional construction equipment. The press-in piling method was utilized to haul, pitch, and install 59-inch-diameter pipe piles on the top of already driven piles. The project team promptly and safely completed otherwise a very difficult construction operation with all the piling equipment firmly clamped onto previously driven piles without them sitting on the unstable slope or affecting the vulnerable abutment.

Micropiles have been used in North America since the beginning of 1970s, but it was only after 1990s where technical specifications and design guidelines were established. Micropiles are used in different geological conditions and for different purposes such as foundation support, reinforcement, or slope stabilization. This paper presents a case history of high-capacity micropile design and installation for the Tawatinâ Bridge foundations in Edmonton shale in the Saskatchewan River. A load test program was carried out to confirm the performance of these micropiles where the micropiles are tested to their ultimate geotechnical capacity of up to 5 MN. The design approach, the installation methods, instrumentation, technical challenges, and the results of load tests are provided herein.

In this study, a particle-based continuum numerical approach based on the smoothed particle hydrodynamics (SPH) method coupled with the finite element method (FEM) has been developed to investigate the failure mechanism and ultimate pullout capacity of soil anchors from quasi-static to dynamic conditions. The results of this study suggest that the ultimate pullout resistance depends on the failure mechanism of the mobilized soil. It was found that the failure mechanism and soil deformation depend on the anchor embedment depth and are rate dependent. Anchors embedded at deeper depths are shown to be more influenced by pullout velocities than those embedded at shallower depths. The failure shape depends on the anchor pullout velocity in addition to the soil density and embedment depth.

The influences of construction parameters on the overall axial capacity of hollow-bar micropiles in sandy soils were quantified based on results from full-scale field testing. Eight micropiles were constructed at a site in the Outer Banks of North Carolina in two phases. The field testing program included installation of micropiles to a depth of 25 feet while varying the drilling or drill-bit insertion rate (I_R) and the grout flow rate (Q_R). In addition, the installation methods included micropiles that were continuously drilled and grouted with neat grout water-cement ratio (w/c) of 0.4, and others that were first drilled and grouted continuously with thinner grout (w/c-0.7) and then flushed from bottom to top with thicker grout (w/c-0.4). Eight micropile installations were designated as Fast/Fast (w/c-0.4), Fast/Slow (w/c-0.4), Slow/Fast (w/c-0.4), Slow/Slow (w/c-0.4), Fast/Fast (w/c-0.7/0.4), Fast/Slow (w/c-0.7/0.4), Slow/Fast (w/c-0.7/0.4), and Slow/Slow (w/c-0.7/0.4). The results of pullout field load testing are presented in terms of load-displacement curves and load transfer mechanism. The load-testing results showed an appreciable high ultimate pullout capacity by using slow drilling and slow grout pumping rate (w/c-0.4) as compared to the other three approaches. The result showed that an additional 50% pullout capacity could be achieved by using Slow/Slow construction approach with w/c-0.4 grout, as compared to commonly practiced (Fast/Fast) installation approach.

This paper presents a case history of auger-cast pile installation and load testing for the expansion of a water reclamation facility near Atlanta, Georgia. Three load test piles were initially installed to bedrock, all of which met the refusal criteria of 0.3 meters (one foot) or less of auger penetration per minute; however, only one of the test piles achieved the test load, which is two times the design capacity of 1,100 kN (125 tons). Furthermore, extreme variability in rock depth was encountered between test piles and reaction piles near one corner of the facility. Additional investigations performed to assess the cause of test pile failure included additional borings and rock cores, pile integrity tests, and probe piles to explore the variability in rock depths and auger penetration rates across the site. These investigations revealed extreme variability in rock depth, steep rock slopes, and variable auger penetration rates in the area adjacent to the three failing load tests. Based on the results of a fourth and final load test located within the area of anomalous rock conditions, the pile design capacity for this area was reduced to 575 kN (65 tons), or 52 percent of the original design capacity. Thus, this case history demonstrates that auger-cast piles installed to rock may not always achieve the design capacity even if the standard auger refusal criteria are met. The importance of load testing and effective monitoring during pile installation is highlighted in this paper.

Offshore wind energy has been growing as a promising renewable energy source. Recently, the tripod suction bucket foundation has been considered as an option to support offshore wind turbines. In an offshore environment, the wind turbine foundation should be designed considering cyclic loading, which can lead to permanent deformation of the structure, tilting, and degradation of soil stiffness. However, there are many uncertainties in the prediction of cyclic behavior of the tripod foundation because the tripod is comprised of three individual buckets embedded into the soil in a triangular arrangement. In this study, the behavior of the tripod foundation under cyclic loadings was indirectly investigated by vertical compression and pullout tests of a single bucket because the overturning moment load applied to the tripod foundation presumably acts as vertical compressive and pullout loads on each bucket. A series of centrifuge model tests were performed by applying one-way (i.e., vertical compression and pullout) and two-way cyclic loadings to a single bucket. In addition, the effects of cyclic loading level were investigated. On the basis of the test results, it was confirmed that the cyclic behavior of the single bucket is significantly affected by loading direction and level. This study highlights that it is important to consider the load characteristics when predicting the cyclic behavior of the tripod.

The purpose of this case history is to showcase the viability of high-capacity auger pressure-grouted (APG) piles as an alternative to the traditional deep foundation systems commonly used within the Philadelphia region (e.g. drilled shafts or caissons; driven piles; micro-piles). This case history demonstrates that relatively high capacities can be developed using APG piles when installed in similar geologic settings as the subject site and highlights the circumstances where APG piles may be a favorable alternative. Included is a brief summary of the 500 Walnut Street multi-family residential development, geologic setting, and process of how APG piles were selected and implemented for support of the proposed tower. Explanations are included demonstrating how the designers of the APG piles arrived at the theoretical pile capacities. Finally, this paper summarizes the results of a pile load test program used to confirm the recommended pile capacities, as well as experiences during the installation of production piles.

Fluked (aka finned) torpedo anchors are increasingly being used for tethering of offshore structures. In this study, the effect of the torpedo fluke length on penetration and pullout capacity was explored. Three model torpedoes of equal mass having different fluke shapes were installed in a synthetic transparent soil surrogate used to model soft clay. Images acquired during embedment and extraction provided data for digital image correlation (DIC), from which time-resolved data for anchor movement and soil displacements were obtained. Pullout loads were also measured. The affected zones around the anchors during penetration and pullout were found to be approximately four times the shaft diameter, and were larger where flukes were present. Increasing the fluke dimensions decreased penetration but increased peak pullout loads. Results suggest that the area of the leading and trailing edges of the flukes is responsible for both decreased penetration and elevated pullout capacity for fluked torpedoes.

This case history discusses geotechnical design challenges of constructing an approximately 146 m (480 ft) tall high-rise building in the heart of Boston, abutting an existing structure (parking garage and office building) that will remain in service during construction. Interactions between Haley & Aldrich, the geotechnical engineer, and McNamara | Salvia, the structural engineer, were paramount in the foundation and structural design. Due to the loading conditions and various physical site constraints, foundations consist of high-capacity drilled-in micropiles, drilled shafts, and load-bearing elements. Geo-structural parameters such as foundation vertical and lateral stiffnesses were critical in modeling the structure behavior and were relied upon to resolve loading down through foundation elements, which was complicated by the constrained site configuration and dimensions. The iterative nature of this project’s building design highlights the importance of interaction between the geotechnical and structural disciplines and the technical expertise required to evaluate complex soil-structure interaction.

A large mat foundation was constructed in Tysons Corner, Virginia, to support a bank building resting on residual silts of the Appalachian Piedmont geologic province. The subsurface conditions were evaluated in the vicinity using borings and DMT-SPT relationships, primarily for calculating settlements to assess the viability of the foundation system. A survey system was established prior to construction and deformations were monitored over a one-year period. Measured settlements were on the order of 38 to 76 mm (1.5 to 3.0 in) and comparable to those calculated using a simple elastic continuum solution that accounts for foundation size, finite layer thickness, soil modulus variation with depth (Gibson vs. homogeneous), foundation rigidity, and embedment effects.

This paper compares traditional foundation design to direct cone penetration testing (CPT) design using CPT data (i.e., measured cone tip resistance, sleeve friction, and/or measured porewater pressure). Shallow foundations have traditionally been designed in a two-part process to approximate the required size and shape of a foundation: determining the bearing capacity and expected settlement (commonly referred to as displacement) of the soil. The Minnesota Department of Transportation (MnDOT) has created an easy to follow CPT design manual, establishing a process for shallow foundation design directly using CPT data. A systematic procedure is available to transition from the CPT data to bearing capacity accounting for settlement. This paper will focus on applying the design guide to an existing project in Minnesota. The paper will describe a case history from a bridge replacement on TH 24 over the Mississippi River in Clearwater, Minnesota. This project used traditional methods for shallow foundation design and is reexamined using the new MnDOT CPT guide. This study demonstrates efficiency of using direct CPT design in geotechnical practice.

The natural fibers are cheap compared to synthetic fibers. On the other hand synthetic fibers are costly, though they last for long term but may pose environmental problems. However, the drawback of natural fibers is that it undergoes biodegradation. Even though coir fiber is durable for 8 to 10 years, treatment can be imparted to increase their durability by reducing water absorption of coir fibers. Sodium hydroxide based treatment used to treat the surface of the coir mat reduced the water absorption of coir mat by 35% compared to untreated coir mat. Model footing test were conducted using treated coir mat as reinforcement in sand to evaluate bearing capacity and settlement. Based on the above experimental investigation, it was found that the alkali treated coir mat showed significant improvement in bearing capacity in the range of increase varying from 8% to 10% in comparison to untreated coir mat reinforced sand.

Circular plates have been widely used as foundations of large-diameter storage tanks. Investigation of the flexural behavior of a uniformly-loaded circular plate on elastic soil is of significant interest in the tank design process. This paper presents a continuum-based, semi-analytical, elastic analysis model for a uniformly-loaded circular plate resting on a multilayered soil deposit. The governing differential equations are derived based on variational principles and solved semi-analytically. Results from the proposed analysis model are compared with those from PLAXIS and show reasonable accuracy. Parametric studies for a circular plate resting on two- and three-layered soil deposits using the semi-analytical model provide important insights about the effects of soil layering on the differential settlement of circular tank foundation.

The present study pertains to the analyses of two closely spaced strip footings embedded at shallow depths and supported on fibre-reinforced cohesionless soil medium using finite element method software ABAQUS. For the analyses, the two footings are considered to be symmetrical and foundation soil reinforced only in vicinity of the footings. Further, a case of footings embedded in unreinforced cohesionless soil medium is taken up for comparison. Mohr-Coulomb plasticity model with non-associated flow rule is used to model the foundation soil medium inputting the equivalent soil properties of the fibre-reinforced soil in reinforced zone. Discretizing the domain with four node continuum plane strain elements (CPE4R), the mesh, domain sizes, and reinforcement zone are optimized. The effect of interference on bearing capacity and settlement aspects measured at permissible conditions have been studied by varying clear spacing between the footings, percentage of fibre reinforcement, and depth of footing embedment. The results are presented in terms of non-dimensional interaction factors defined as the ratio of bearing capacity/settlement of interfering footings resting on reinforced medium to the same measured for that of an isolated footing resting on unreinforced medium. It has been observed that the interference affects predominantly on the behaviour of an isolated footing embedded both in reinforced and unreinforced soil medium. Interaction factor for bearing capacity is found to be greater than one whereas the same for settlement is observed to be less than one, for interfering footing embedded in fibre-reinforced soil. However the same are contrary for interfering footing embedded in unreinforced soil. In the zone of major interference, with increase in percentage of fibre-reinforcement, the bearing pressure is found to enhance and settlement lowers considerably compared to unreinforced case.

Expansive soils cover extensive areas worldwide and are found to cause serious damage to a wide range of structures. The geotechnical engineers require a protocol to investigate and deal with such conditions. Introduction of a systematic approach can help and provide a step by step guide to assess and evaluate structures founded on expansive soils. This can cover the current and expected future soil structure interaction. This proposed protocol covers the must do procedures to evaluate risks and points of concern. A building in Al-Ghatt town in Saudi Arabia, subjected to serious damage and distress due to expansive clay shales was investigated. Structural and geotechnical conditions of the building were assessed. The state of cracks and displacements were reviewed in view of historical and current environmental conditions. Boreholes and tests pits were conducted as part of the investigation program. Discussions of possible solutions for foundations on expansive soils based on the geotechnical practice in Saudi Arabia are presented.

Slab-on-grade is one type of shallow foundation with unreinforced plain concrete directly poured onto compacted subgrade. Slab-on-grade foundations are commonly used as industrial floor slabs for warehouse facilities such as storage, retail, and distribution centers. As one type of geosynthetics, geogrids have been used in earthen structures such as earth retaining walls, slopes, pavements, and embankments primarily to provide reinforcement to the unbound geomaterials of the structures. This study is aimed to investigate the potential benefits of embedding geogrids in concrete slabs-on-grade. In addition to four-point bending tests on unreinforced and reinforced concrete beams, large slabs-on-grade were built on top of local soils and aggregate inside a testing box and tested under monotonic static loads. Results of the four-point bending tests show that the geogrids carried additional load after the crack initiated and delayed the collapse failure of the concrete beams. Results from tests on fully-supported slab-on-grade show that the inclusion of geogrids allows for developing secondary crack after the first crack and results in a greater collapse load of the slab.

The ratio of settlement estimates obtained using strain-dependent and high-strain elastic modulus values is examined. This settlement ratio (SR) cannot be less than the ratio of the high strain to low strain elastic moduli (E_H/E_L) of the soil. SRs are plotted against the ratio of E_L to applied foundation load for various soils. For soil profiles with a single E_L value within the influence zone of the foundation, the size of the foundation has no impact on these plots. Different plots are obtained under the center and corner of a flexible foundation. Different values of strain assumed for the high strain elastic modulus are examined and discussed.

A strong input energy, e.g., earthquake, may cause a partial separation of foundation from the underneath geomaterials. The concept of rocking behavior of shallow foundations has become popular in performance-based design (PBD) earthquake geotechnical specifications as an energy-dissipation mechanism. The two main performance indicators of the soil-structure systems during rocking are: (1) the moment capacity of the assembled soil-structure system that gradually mobilized under cyclic loading, and, (2) the dissipation of energy governed by the rotational moment hysteresis loops. The aim of this study is to evaluate the rocking responses of slender high-rise structures using global sensitivity analysis (GSA) methods. For this purpose, a finite element (FE) analysis database was generated using a wide range of geomaterials with different stiffness properties. To avoid the implementation of time-consuming FE analyses, random forest (RF) metamodels were developed using the synthetic database for the rocking responses. This paper discusses two different GSA methods including elementary effects (EE) and Sobol’s method to assess the impact of input parameters on the rocking responses. The results show that both methods are efficient in evaluating the impact of input parameters on the responses. EE requires a smaller number of generated samples and less computational effort. However, Sobol’s method is more efficient in measuring the joint effects despite the higher computational cost.

A class “A” prediction of conical test-induced settlements in Central Florida soils is conducted using one conventional Mohr-Coulomb and two advanced hardening soil and hypoplasticity constitutive models. A conical load test is performed by constructing a cone-shaped mound of soil on the ground surface, placed over a center plate to measure settlement arising from the self-weight of the conical soil arrangement. Constitutive soil parameters for the numerical models presented in this paper are determined from previous case histories with similar expected soil behavior based on field test records. A conical load test is modeled using the finite element numerical software PLAXIS 2D to predict the evolution of the settlement during the construction of a conical load test. Results obtained from the numerical model showed that predicted settlements for the Central Florida soil conditions ranged from 24 to 36 mm. Given the soil conditions, excess pore water pressures generated from the construction of the conical load were negligible.

An analytical method is developed to analyze the coupling problem for classical circular plate on elastic continuum foundation by considering the horizontal and vertical displacements of the plate-foundation axisymmetric system. By implementing the modified Vlasov’s foundation model together with separation of variables’ technique, the radial (horizontal) and vertical displacements are expressed as product of the displacement functions at the ground surface and decay functions along the depth of the continuum. The governing differential equations, and their associated boundary conditions of the system are extracted by applying the variational principle to the total strain energy functional of the system. An iterative procedure is developed to, numerically, solve the coupled system of differential equations. The study is illustrated by a practical example.