Geotechnical Frontiers 2017: Foundations

Internal erosion occurs when the seepage forces wash out the fines of a non-uniform soil along the pre-existing openings (e.g., cracks and voids), resulting into substantial increase in permeability. Given that the drainage characteristics of soils are significantly influenced by the shapes, packing arrangement and size distribution of their particles, the erosion of fines can alter the drainage characteristics. The assessment for internal erosion potential is normally obtained based on grain size distribution ignoring the effect of compaction and particles’ shapes. In this study, the experimental results of hydraulic gradient controlled erosion tests, conducted over a select range of compacted soils, were used to compare with the internal erosion assessments from some of the existing criteria. Consequently, a new approach that considers the shapes, packing arrangement and size distribution of particles for assessing their internal erosion potential is proposed that showed highest success rate compared to the rest.

Experiments of local scour around pile groups and wide piers are carried out under steady currents. Piers with large diameter and pile groups were arranged properly so that the scour process and maximum scour depth could be compared. Although numerous empirical formulas have been proposed to predict equilibrium scour depth around various bridge piers, there is still no general formula that satisfies all conditions. In addition, the scour characteristics of different types of structures are not clearly understood. This study observed the dynamic scour process and the scour depth of every case was determined. Comparisons of pile groups and wide piers were made to aid in the determination of the influence of several foundation types.

A series of experimental tests were conducted to investigate the effect of pier streamlining on bridge local scour under clear-water conditions. A total of four testing cases were included in this study. Test conditions in all cases were kept the same except that the pier geometry in each case had sequentially increased extents of streamlining. These streamlining features were adopted from a previous numerical study by the authors. This paper compared the time evolution of local scour among cases. Contour maps of the scoured bed were obtained using the structure from motion (SfM) technique. The streamlined piers generally showed advantage over the traditional oblong pier in terms of the scour rate, the maximum scour depth and the total scoured volume at equilibrium. This study suggests that streamlining can be a viable scour countermeasure, but more real-life scenarios including variabilities in soil and flow properties need to be further investigated.

A modified strain wedge model is presented to calculate the effect of scouring on the responses of a laterally loaded pile. The strain wedge (SW) model is capable to derive a p-y curve for the analysis of a vertical beam on a nonlinear foundation. To improve the SW method, a modified strain wedge (MSW) model is developed by assuming a nonlinear lateral deflection of pile to get the nonuniform soil strain in the passive wedge. Treating the soil weight above the scour bottom as a vertical load, an equivalent depth is obtained in the MSW model to consider scour hole dimensions. The applicability of the MSW model in the problem of a pile under scouring is proved by comparing with a model test and also the FEM results. It is found that the deflection ratio at the ground surface maintains 1.8 and 3.0 under large load level for scour depth as S_d =3.2D and 6.4D respectively and the scour induced change on the soil reaction modulus under small load is obvious in the model test and MSW analysis, while negligible in the FEM analysis.

Researches show erodibility of sand is mainly determined by the grain size, or the mass median diameter. The influence of particle shape on sand erodibility has been neglected for simplification. Here using a coupled CFD-DEM method, the influence of sand particle shape on soil erodibility has been analyzed. The model was built prototyping from the erosion function apparatus (EFA) developed by Briaud, where soil sample inside a Shelby tube is extruded into a rectangular flow channel with an extrusion height of 1 mm, and subjected to the erosion of flowing water. Critical shear stress and erosion rate of the soil sample can be obtained through the EFA test. In the simulating cases, spherical particles and non-spherical particles with aspect ratios of 1.10, 1.20 and 1.30 have been tested and compared. The results show grain angularity plays an important role in the formation of erosion resistance. For spherical particles, due to the lack of rolling resistance, no critical velocity has been observed. For non-spherical particles, with the increase of aspect ratio, the critical velocity increases indicating a higher erosion resistance. Erosion rate increases linearly with flow velocity, which is consistent with experimental studies.

Various soil characteristics that affect the erosion of soil also influence in situ bulk electrical resistivity measurements. The objective of this study was to develop two dimensional soil erosion profiles correlating the in situ electrical resistivity of soil with the erodibility measurements from the Kansas State University erosion function apparatus (KSU-EFA). Electrical resistivity surveys were conducted at ten bridge sites. Five samples were collected at each site and tested in the KSU-EFA. Erosion potential profiles were created using the subsurface electrical resistivity distributions. This study showed that the rapid in situ data obtained from an electrical resistivity survey can predict the presence of highly erosive soils. As such, electrical resistivity surveys may be used to identify where further testing is necessary to measure the scour potential or determine which existing bridges should be closed or closely monitored for scour potential during a flood event.

To decrease lateral earth pressures on structures, a zone of compressible material or an “inclusion” can be used as a barrier to decrease lateral earth pressures on structures. The compressible material is typically expanded polystyrene or geofoam. Little guidance is available on the development of passive force with an inclusion. To explore this issue, large-scale passive force tests were conducted with and without a geofoam inclusion acting as a barrier between the backfill soil and a simulated bridge abutment. The presence of the geofoam inclusion reduced the passive force by 70% relative to the sand backfill alone. Although the measured force and failure geometry appeared to conform to a log-spiral mechanism when only sand backfill was used, the geofoam inclusion transforms the failure geometry to a Rankine failure mechanism. This suggests that the geofoam acted to reduce the interface friction between the wall and the backfill sand thereby reducing the passive resistance.

Geosynthetic materials have been widely used in reinforcing the weak soil underneath the shallow foundations in the recent years. Many previous static loading studies have shown that the bearing capacity of the soil with a shallow foundation on the surface is greatly increased when the soil is reinforced by a layer of geosynthetic material. The present study visualizes the deformation field and failure mechanism in geosynthetic-reinforced soil underlying shallow foundations using digital image correlation (DIC) technique. A small-scale calibration chamber was built to model a plane-strain condition for a strip footing system. A series of indentation tests were conducted using a rigid model strip footing on unreinforced soil and with soil reinforced with geonet and woven fabric geotextile. The effect of number of reinforcement layers on the deformation field within the bearing soil has been studied. The results highlighted the suitability of DIC technique to visualize the deformation in laboratory-scale experiments and clearly illustrated the effect of reinforcement on progressive failure mechanism of model footing.

This paper presents a case history of design and construction of a geotextile reinforced soil-metal (GRS) 2040 mm diameter structural plate culvert under a 42 m high embankment at a mine in South America. The geotechnical data indicated that the underlying SAPROLITE and laterite soils were very soft with predicted consolidation settlement under the conduit and embankment of up to 3m. Due to the complexity of the problem, two-dimensional non-linear finite element analysis was employed to analyze the soil-structure and soil-geotextile interaction. Results showed that the composite system considerably improved the performance of the culvert under the considered loading conditions. The structure was constructed in 2015 to 2016 and it is reported that the structure is performing satisfactory. The composite GRS-culvert system provided a viable solution for challenging site conditions.

High density polyethylene (HDPE) double-wall corrugated pipe is commonly used for drainage purpose. However, this type of pipe can be damaged by ground subsidence due to its relative low stiffness. In this study, physical model tests are conducted to investigate the effectiveness of geosynthetics to protect buried HDPE pipes subjected to ground subsidence. The tests are carried out in a custom-made test box with a dimension of 2 m in length, 2 m in width, and 1.5 m in height. Two model tests with the inclusion of the geotextile and the geogrid and one test without geosynthics reinforcement are conducted. Test results demonstrate that both types of geosynthetics are effective to reinforce the HDPE pipes in the ground subsidence condition, in terms of reducing vertical displacement and circumferential strain of the pipes. The pipe protected by the geotextile performs better than that reinforced by the geogrid.

The position of the neutral plane is required to be implicitly known for the accurate determination of the magnitude and profile of negative skin friction. In contrary to the conventional analysis of bored piles, this study reports the effect of pile installation procedure on the final position of the neutral plane. Two types of initial conditions are considered, one where the pile driving is simulated (actual) and the other where the pile is considered in place (in situ). Finite element analysis exhibited that the neutral plane is at a greater depth in the ‘actual’ case relative to the ‘in situ’ case. Contours of effective stress near the pile tip implied higher soil stiffness near the pile base in the driven pile (actual) simulation, resulting in a lesser settlement and is postulated as the reason for the lowering of the neutral plane in the latter (in situ) case.

Bucket foundation has been used extensively in offshore facilities to resist combined lateral and moment loading. The lateral loading capacity and interaction between the soil and foundation is of great interest to geotechnical engineers. In this paper, finite element models of a bucket foundation with two aspect ratios (L/D, where L is the skirt length and D is the foundation diameter) of 0.5, 1.33, were created using the ABAQUS program. Centrifuge model tests were also conducted on the two models. The load-displacement curves of the numerical analysis and test results had good agreement, which verified the reliability of the finite element analysis method for this type of problem. In addition, several 3D numerical models of aspect ratio varied from 0.2 to 2.0 were built to evaluate the effect of the aspect ratio on the lateral loading capacity. The development and distribution of stress and plastic strain were used to study the failure mechanism of bucket foundation for different L/D ratios. The influence of the position of the lateral load applied was analyzed. Sensitivity analysis for the parameters of material properties such as the internal friction angle, the Young’s Modulus, and the friction coefficient between the bucket and soil were performed using non-linear analysis with the Mohr-Coulomb soil model.

In this study the penetration of spudcan foundation for “jack-up rig” type offshore oil platform into a uniform clayey seabed is investigated with three-dimensional finite element modeling (Abaqus 6.14) using Coupled Eulerian Lagrangian method that can handle large deformation problems. One of the goals of this study is to compare the penetration-bearing resistance behavior of spudcan obtained by numerical study with the method suggested in InSafeJIP design guideline. For the spudcan geometry and soil properties used in this study, based on the three dimensional finite element analyses, the required penetration depth for a target bearing capacity of spudcan is less than that required by analytical method in InSafeJIP guideline. The second goal of the study is to explore the effects of some geometrical and soil variables on spudcan bearing resistance-penetration behavior. The variables in this study are spudcan diameter (7.5 to 15 m), the surface roughness of spudcan (roughness coefficient of 0 to 1.0) and undrained shear strength of clay (20 to 80 kPa). Understanding the relations between the factors and penetration behavior may help in future studies on enhanced and economical design of spudcans.

Torpedo anchors are a viable approach for mooring marine hydrokinetic (MHK) energy devices to the seafloor. These anchors will serve to maintain station and to provide the reaction force for the MHK device. The ability of the anchor to perform these duties is a strong function of its penetration depth during installation. This is a large-strain problem not amenable to typical continuum numerical approaches. In the current work, we propose that the discrete element method (DEM) is a more appropriate tool to investigate the shallow penetration of torpedo anchors in sands. The effects of anchor mass, impact velocity, and anchor geometry are considered in the DEM simulations. The relative maximum penetration depths under these factors are quantified and presented in the paper. Comparisons are also made between DEM simulations and the empirical equation developed by Young (1967). Granular material response at the microscale during penetration are used to provide insight into system response.

High strain drop weight dynamic load testing is an effective tool when evaluating the construction quality and axial capacity of offshore drilled deep foundations. This is a result of the complexity and cost of the alternative conventional static load tests. Drop weight systems can be designed for project specific needs, providing sufficient energy to mobilize the required resistance while permitting ease in transporting the device. Test shafts/piles can be instrumented and analyzed using the same dynamic testing techniques used for driven pile foundations. A case study is presented where drop weight dynamic load tests were utilized for offshore drilled shaft foundations. The project includes the design, construction, and quality control for a cement unloading pier at the Tema Port in Ghana, Africa. The foundations are unique, consisting of 0.8m outer diameter steel pipes embedded in 1.0m rock-socketed drilled shafts. Three dynamic load tests to failure and six load verification tests were performed offshore. The load verification tests were carried out due to construction difficulties and/or complex subsurface conditions. The piles’ integrity and mobilized resistances were assessed using the signal matching analysis software CAPWAP. The underlying assumptions in the one-dimensional wave equation formulation on which CAPWAP is based are violated in these complex cases. Finite element analyses were therefore performed using the PLAXIS 2D software in order to examine the validity of the one-dimensional wave equation application under such conditions. This paper briefly describes the project, the associated difficulties, the unique foundations, example load tests and their analyses, as well as some initial processing in examining the validity of the one-dimensional wave equation analyses under the tested conditions.

In this study, a new type of suction pile foundation for floating structures, namely group suction piles, was proposed to improve the shortcomings of conventional single suction piles. Small-scale model tests were performed to estimate the horizontal behavior of single suction piles and group suction piles with different pile spacing (2, 3 and 4 times the pile diameter) under various loading conditions in terms of loading locations and inclinations. The horizontal behavior of group suction piles with different pile spacing was analyzed for various loading locations and load inclinations based on the model tests. For the given group pile configurations (a group pile having 9 component piles with a pile formation of 3 × 3), the horizontal resistance increased with increasing pile spacing. The maximum ultimate horizontal resistances were found at the loading locations of 50% of the embedded depth. Unlikely in the single suction pile case, the significantly maintained residual resistances were found for group suction piles. The residual resistances of group suction piles were at least higher than 40% of the corresponding ultimate horizontal resistances.

Integral abutment bridges (IABs) are being used widely across U.S. due to the elimination of joints and the superior long-term performance of these bridges. However, the performance of IABs is dependent on the soil-structure interactions that are not well understood. This paper describes an effort to understand the complex soil-structure interactions occurring in IABs through a parametric study conducted to extend the results of a field instrumentation study on an IAB in Oklahoma to other IABs with different design variables. Abutment pile type, size and orientation, bridge length, girder depth, soil type, pre-drilled holes around abutment piles, and bridge skew angle were the variables considered in the study. Validated simulation tools GROUP and TeraDysac were used for the numerical simulations. According to the simulation results, in order to accommodate thermal movement in IABs and to reduce bending moments in abutment piles, a smaller H-pile section should be placed in weak axis bending and in pre-drilled holes with low stiffness material, especially at shallow depths. Abutment piles for IABs should be checked for capacities under combined axial force and bending moments. Longer spans with larger girders will increase the axial load on the abutment piles, and therefore long-span IABs should be designed with caution. For IABs with larger skew angles, abutment piles should be oriented in weak axis bending along the transverse direction. Biaxial bending of abutment piles in skewed IABs increases stresses in the concrete superstructure, thus the structural components for IABs with larger skew angles have to be designed carefully to accommodate the thermally-induced deformations.

Crosshole sonic logging tests are commonly used to determine the integrity of drilled shafts. However, selections of signal arrival times can be subjective. Different persons may pick different arrival times from the same record. The lack of consistency can be a source of disputes. This paper proposes use of the integrated continuous wavelet transform (ICWT) method, which applies continuous wavelet transform to interpret direct arrival measurements. The key feature of the method is transferring a nonlinear sinusoidal-like signal to a linear phase angle plot. Peaks in the recorded signal are shown as 0-degree phase. By selecting the time point of 0 degrees with an amplitude above the noise level, the arrival time of the first peak can be uniquely identified. This method removes subjectivity between operators. The ICWT method can also be used for other tests that measure travel time intervals (i.e. pulse echo and seismic CPT tests).

One of the principle shortcomings with lateral analysis of large diameter pile foundations is the reliance on beams on elastic foundation. Within numerical modeling, the fundamental nature of the interactions of steel to concrete, steel to soil, and concrete to soil are often difficult to constrain in non-linearity. Modeling with a simplified cracked modulus for the pile does not capture the path from linearity to non-linearity. The progressive occurrence of concrete cracking with yielding rebar and steel casing, with concrete crushing results in pile non-linearly under bending. Furthermore, the interaction of the structural materials and soil beyond Winkler relationships is desirable so that soil can flow around the foundation and assessment of stress changes in the field to affect adjacent facilities. For large displacement problems the ability of the shaft to rotate, bend, shear, twist, and “oval” under complex lateral loads is important. A numerical methodology that addresses these shortcomings was developed. This paper briefly presents the method along with comparison with conventional methods.

This paper presents the analyses of twelve prestressed concrete (PSC) instrumented test piles that were driven in different locations of Louisiana to develop analytical models to estimate the increase in pile resistance (soil set-up) with time. The twelve test piles were driven mainly in cohesive soils. Detailed soil characterizations including laboratory and in-situ tests were conducted to determine the different soil properties. The test piles were instrumented with vibrating wire strain gauges, piezometers and pressure cells. Several static load tests (SLT) and dynamic load tests (DLT) were conducted on each test pile at different times after end of driving (EOD) to quantify the magnitude and rate of set-up. Measurements of load tests confirmed that pile resistance increases almost linearly with the logarithm of time elapsed after EOD. Case pile wave analysis program (CAPWAP) were performed on the restrikes data and were used along with the load distribution plots from the SLTs to evaluate the increase of shaft resistance of individual soil layers along the piles. The logarithmic set-up parameter “A” for unit shaft resistance was calculated for 70 individual clayey soil layers, and the database set of A was correlated with different soil properties. Nonlinear multivariable regression analyses were performed between A and different soil properties, and three different empirical models are proposed to predict the soil set-up parameter “A” as a function of soil properties.

A robust geotechnical design optimization procedure for piled-raft foundation to support a 130 m tall wind turbine on clayey soil is presented in this study. The initial geotechnical design indicated that the differential settlement of the piled-raft system controls the final design. A parametric study was conducted by varying the wind speed and undrained cohesion to establish a relationship between the design variables (number and length of pile and radius of raft) and random variables (wind speed and undrained cohesion). Finally, a robust design optimization was conducted considering the material cost and the robustness as the objectives. The standard deviation of the response which is the differential settlement of the foundation system was considered as the measure of robustness of the design. The optimization yielded a set of acceptable designs and presented as a Pareto front which can be used to select the best design using the knee point concept.

Although driven steel H-piles are often an economical alternate for bridge foundations, prediction of pile drivability and length in very dense saprolite remains a great challenge pertaining to design and construction practices. A study to evaluate the performance of steel H-piles driven into thick saprolite layers was conducted for several bridge projects in Southeastern Pennsylvania. These saprolite layers of the Wissahickon Schist Formation are completely weathered but retain the fabric and structure of the parent bedrock. A database of numerous test piles from selected projects was established to provide a quantitative understanding of pile geotechnical resistances, pile lengths and a qualitative prediction of the driving conditions. All piles were driven to absolute refusal which is a function of the hammer type, efficiency, and driving procedure. High strain dynamic tests were performed on all piles at the end of initial driving. The results of restrike testing on selected piles were used to evaluate set-up effects on piles in these intermediate geomaterials. Geotechnical resistances from case pile wave analysis program (CAPWAP) were compared against static analysis values to quantify the pile performance. In addition, statistical attributes of the pile database were summarized for pile embedment into saprolite, hammer efficiency, and maximum driving stresses, etc. The paper presents the results of the pile drivability study, identifies the influence of saprolite thickness on pile geotechnical resistances and lengths, and provides recommendations for future projects with similar design challenges.

Estimation of differential settlements for large steel storage tanks is a very important design consideration; however, there is a lack of readily available analysis tools which can be used to accurately and conveniently compute tank differential settlements under various bottom plate dimensions and soil stiffnesses. This paper presents a continuum-based, elastic analysis model for a uniformly loaded, circular tank foundation resting on soil. The analysis captures the three-dimensional nature of the soil-structure interactions and produces settlement profiles of the tank foundation and the surrounding soil. The soil is assumed to behave as a linear-elastic material in a semi-infinite half space, and the foundation is modeled as a circular plate with a finite thickness. The governing differential equations are derived based on energy principles and calculus of variations. Input parameters for the analysis model are the plate diameter, plate thickness and elastic constants of the soil and plate. Model validation includes comparing results from this study with those from the literature and from finite element analyses, and these comparisons show good agreement. Parametric studies are then carried out to investigate the effects of plate diameter, plate thickness, and soil stiffness on differential settlement between the center and the edge of the circular plate. Based on the results from the parametric studies, design charts for use in preliminary design of circular tank foundations are proposed to estimate the differential settlement for given soil properties and plate geometry.

The press-in pile driving method utilizes hydraulic force to push piles into the ground by holding onto previously driven piles. The hydraulic force is provided by a sound-attenuated power pack. It generates very low noise and almost no vibration. It is also suited for physically constrained projects and for projects with limited access. Some urban projects require pile driving in low head room or with very small clearance from existing structures. In other cases, pile driving may have to be conducted without an access road to the piling location. This paper will discuss the solutions for those otherwise very difficult levee embankment upgrade and earth retaining projects with pressed-in sheet pile and pipe pile walls.

Industrial slabs-on-grade are commonly used for warehouse facilities such as storage, retail, and distribution centers. Typical industrial floor slabs are essentially unreinforced concrete usually poured directly onto compacted subgrade. A limited number of studies have shown that the current common practice of design may be overly conservative and yields an excessively high slab thickness, which leads to a high cost of the floor slab. This study aims to experimentally investigate and verify a newly emerged design method that typically results in a smaller slab thickness and significant cost savings. Laboratory-scale slabs-on-grade were built inside a concrete-lined testing box using local soils and aggregates. A total of four 6 ft by 6 ft concrete slabs representing three different concrete mix designs and two slab thicknesses were tested under static loads that simulate storage rack post loads. Based on the limited number of tests, a preliminary finding was that the traditional design method seems to be overly conservative while the newer method may be too liberal.

A semi-analytical solution is presented in this paper for analysis of axially loaded pile groups embedded in multilayered elastic soil profiles. The proposed method links the soil displacement around a pile group to the axial displacement of the piles in the group through displacement decay functions assigned to the piles. The product of the axial displacement of each pile and its associated decay function is then summed up for all piles in the group. Principle of virtual work and calculus of variations are used to derive the governing differential equations that describe the response of the soil and piles. The governing differential equations that predict the response of the piles are solved analytically using the method of eigenvalues and eigenvectors, whereas the differential equations that describe the soil decay functions are solved numerically using the finite-difference method. The method produces displacement fields that are very close to those produced by the finite element method but with less computational effort.

This paper presents the results of axial load tests performed on instrumented model piles with different surface roughnesses. The model piles were pre-installed in a large-scale, half-circular chamber with a viewing window in its flat-side wall. Uniform silica sand samples in dense and medium dense states were prepared using dry pluviation. Digital image correlation technique (DIC) was used to study the effects of pile surface roughness and soil density on the response of the soil during loading of the model piles. Test results show that the extent of the zone next to the pile that is affected by loading of the pile increases as the pile surface roughness and soil density increase. The development of a shear band next to the pile shaft was also studied by carefully analyzing images taken with a digital microscope during loading of the model piles. Furthermore, the shaft resistances of the loaded piles were measured during the loading tests to investigate the effect of soil density and surface roughness on the response of the model piles.

A blind prediction of the load-settlement response of an axially loaded drilled shaft in Santa Catarina, Brazil, was carried out in June of 2015. The original results were developed using “best-estimate” soil properties within a t-z analysis framework developed by Norris (1986) and modified by Ashour et al. (1998). However, this approach relies heavily on the estimation of the axial strain at 50% of maximum deviatoric stress, termed ε₅₀. Thus, a thorough literature review was carried out on published ε₅₀ values and empirical relationships. The original estimates of ε₅₀ were also varied in this study to explore how sensitive the prediction results are in this regard. It was found the average root mean squared error between the predicted and measured results were significantly affected by changes in ε₅₀ and that the t-z style predictions were substantially influenced by the estimates of ε₅₀, highlighting the need for proper and careful estimation of this important parameter.

Multi-level O-cell tests were carried out on two strain-gauge instrumented bored piles at the Can Tho Bridge crossing the Hau (Bassac) River in the Vietnamese Mekong Delta. The soil profile consists of about 70 m thick soft, deltaic silty clay deposited on dense to compact sand. The test piles, 2.0 and 2.5 m in diameter, were installed into 87 and 98 m depth, respectively, by a combination of casing the upper length and using bentonite slurry to stabilize below the casing. The lower and upper O cell assemblies in the two test piles were located 2.5 m through 3.0 m and 12 m through 15 m above the respective pile toe level, respectively. The tests were performed in four Stages and the maximum loads applied by the lower and upper O-cells were about 21 and 26 MN, respectively. The measurements indicated that the pile toe stiffness of Pile TP1 was very low. The fit of the q-z Ratio Function shows ratio exponents of 0.2 and 0.1 for Pile TP1 and TP2, respectively. The stress-movement curves at the strain gage level GL1 show no tendency toward an ultimate resistance. The evaluation of the strain-gauge data showed that the pile axial stiffness was a function of the induced strain, ranging from a stiffness of 103 through 85 GN. The average unit resistance of both pile shafts placed in dense sand layer is about 460 kPa.

The design of driven piles in glacial tills and outwash soils is frequently conservative in regards to pile length and foundation cost and ineffective in accurately characterizing the soil-pile interaction. Technology such as high-strain dynamic testing can be utilized to more efficiently and sustainably design and construct deep foundation systems. High-strain dynamic testing was utilized in a design-build project in the Minneapolis/St. Paul metropolitan area to characterize the properties of the soil-pile interaction and more economically construct the substructure foundations. At each substructure, initial drive and restrike tests were performed on 12 ¾-inch outside-diameter, steel, closed-ended pipe piles driven into glacial soils. The unit side resistances and unit end bearing resistances were determined from wave matching analyses using CAPWAP on restrike and/or initial drive data. The differences in the predicted and measured unit side resistance and unit end bearing resistance in glacial till and outwash soils for driven pile are discussed. For the seven structures currently completed, the actual driven pile lengths varied from 24.9 percent greater to 50.7 percent less than the expected lengths and the driven pile lengths were shortened on average by approximately 3.9 percent corresponding to an overall cost savings of approximately $98,000.

Dealing with the consequences of lowered groundwater levels and consequent untreated timber pile deterioration in Boston’s Back Bay is not uncommon. Urban sprawl in this area in the late 1800s and early 1900s was made possible through land reclamation, filling in the remnants of the old bay. Untreated timber piles were often used as the foundation of choice in these conditions. Unfortunately, urban construction also resulted in decreased groundwater levels as a result of underground construction, leaking utilities, and leaking basements. The Mother Church (TMC), located on The First Church of Christ, Scientist (TFCCS) campus, is a historic landmark in downtown Boston supported on hundreds of untreated timber piles, and has long been implementing a system of movement and groundwater monitoring to identify any areas at risk of timber pile deterioration. In particular, the surveys indicated that the bell tower of The Original Mother Church (TOMC) was at a high risk of having deteriorated timber piles, and test pit investigations confirmed this. To mitigate future settlements, and extend the service life of the structure, we designed and implemented a foundation underpinning and repair scheme consisting of two phases: underpinning of the main tower with steel needle beams and pre-loaded micropiles, and cut-and-post underpinning in the remaining areas of the TOMC. The design and construction of the foundation underpinning had to accommodate for highly congested and restricted access areas, maintain the integrity of the unreinforced masonry tower structure during the load transfer process, incorporate micropiles needled through the forest of timber piles below the tower, and provide for a system with minimal future settlement and a service life in the order of 500 years. The project was completed successfully and on schedule, with minimal adjustments to the contract plan. Follow up movement monitoring surveys shows no additional movement of the TOMC bell tower has occurred.

Augered cast-in-place (ACIP) piles were installed for an elevated roadway in the City of Atlanta, as part of the infrastructure improvements for a new stadium project. The design-build project team opted to support the continuous span bridge on groups of 610 mm diameter ACIP piles, principally to avoid noise and vibration issues in the downtown environment. The ground conditions comprised a sequence of fill, Piedmont residual soil and partially weathered rock (PWR), overlying precambrian metamorphic rocks. Results of two instrumented static load tests on non-production piles demonstrate the axial loads are transferred principally in shaft resistance. Mobilized unit side resistance values of 73 kN/m² in the Piedmont residual soil and 199 kN/m² in the PWR were derived from strain gauge arrays. For production piling, confirmation of the embedment lengths and grout volumes were key quality control parameters, verified during construction with automated monitoring equipment (AME).

Differential settlements experienced by a number of historic monuments have been remediated using the soil-extraction method. Italy’s leaning Tower of Pisa and the Mexico City’s Metropolitan Cathedral are two well-known structures where the soil-extraction method was applied to address issues associated with differential settlements. This paper describes a case study for a seven-story building in Mexico City, where differential settlements generated vertical inclinations ranging from 241-mm (9.5-in) to 310-mm (12.0-in) to the north, and 70-mm (2.75-in) to 98-mm (3.9-in) to the east. For the remediation of these inclinations, the soil-extraction method was applied through rectangular cavities excavated underneath the foundation element. The general bearing capacity theory was used to determine the location and dimensions of these cavities. After finalizing the soil-extraction process, an average settlement and upward movement of 87-mm (3.5-in) and 24-mm (1.1-in) were recorded, respectively. After the completion of the soil-extraction process, all deformations were brought within tolerable limits specified by the local building code.

A procedure is developed to minimize cost and CO₂ emissions for the design of reinforced concrete strip footings subjected to dynamic loading, satisfying geotechnical limit states and using a big bang-big crunch (BB-BC) algorithm. The objectives of this research are to develop low-cost and low-CO₂ emission designs of strip footings when subjected to dynamic loading. Cost is based on materials and labor required for the construction of strip footings. The CO₂ emissions are associated with the extraction and transportation of raw materials; processing, manufacturing, and fabrication of products; and the emissions of equipment involved in the construction process. The cost and CO₂ objective functions are subjected to dynamic soil bearing and dynamic displacement limits. A design example is presented to compare low-cost and low-CO₂ emission designs. Results are presented that demonstrate the effects of different magnitudes of applied dynamic loads for strip footings founded in different types of soils.

As part of a current research project on dynamic soil-pile interaction, the parallelized boundary element method (BEM) code BEASSI was modified to enable analysis of three-dimensional dynamic behavior of pile groups surrounded by multiple multi-layered soil zones, with rigorous account of radiation and material damping. Dynamic soil-pile interaction was then analyzed in the frequency domain for a single pile and a 2×2 pile group, each surrounded by an inner disturbed-zone and an outer half-space zone. The layered inner zone enables effects of inhomogeneity, pile installation, and strain-dependent modulus and damping to be approximated, while the outer layered half-space zone can account for the far-field wave propagation in a vertically heter-ogeneous soil medium. The performance of the modified code is validated by comparison to static and dynamic benchmark solutions from the literature. A general formulation for analyzing the dynamic response of pile groups using impedance functions from the BEM analysis is also presented, with the above-ground pile segments modeled as beam-columns and the pile cap treated as a rigid body. For the present case of the 2×2 pile group, a 24×24 global stiffness matrix is formulated to capture the influence of each pile’s six displacement degrees-of-freedom on the other piles due to pile-soil-pile interaction. The form and symmetries of the global stiffness matrix are verified by imposing displacements at the soil surface elevation for each pile cross-section separately, enabling future analyses to be performed more efficiently by specifying displacements at only one of the piles. Results of this study will lay the foundation for developing calibrated computational continuum models by analyzing upcoming full-scale vibration tests of pile groups.

Concrete pier foundations for transmission structures are widely used with high-voltage transmission lines. Current design practice focuses on strength design ensuring the foundation and top structures are safe. However, the performance design criteria for deflection and rotation on top of this kind of pier foundation are not well defined in any major code or guide resulting in utility firms and engineering companies adopting their own differing criteria. This article discusses the development of appropriate performance criteria for foundation design relating to transmission poles. Common pitfalls faced by geotechnical and structural engineers during the design and analysis and ways to avoid them are also discussed. Current common practices and procedures for transmission structure foundation design are discussed together with the importance of adopting appropriate performance criteria to ensure the safety, economic feasibility, and aesthetics of the foundation. Finally, three case studies—tangent pole, light angle pole, and dead end pole—are conducted using the software applications PLS CAISSION, MFAD, and LPILE. The results are compared in terms of shear distribution, moment distribution, and deflection along the length of the pile foundation to establish the ways and extent performance criteria can affect the design.

Short span bridges in the U.S. that are located near rivers and streams typically use sheet piles to defend the abutment against erosion and scour. In such bridges, the abutment axial load demands are usually carried by driven piles installed behind the scour protection sheet piles. An alternative bridge abutment design approach, successfully used for decades in Europe and in some projects in the U.S., involves installing sheet piles for the double function of scour protection and axial load bearing. This design paradigm shift has the potential to significantly reduce construction cost. However, widespread implementation and acceptance of this design approach requires full-scale axial load tests on instrumented sheet piles. This paper presents an axial load test program carried out at a test site in North Carolina that shows that the axial stiffness and load capacity of the sheet pile was comparable to the response recorded in the comparison H-pile when normalized for differences in the tip and surface areas.

A series of instrumented pile load tests was performed on augered cast in-place piles in an area northeast of Austin, Texas. The site soils primarily comprised of clays. The load test program included testing various pile diameters and lengths. Ten compression and tension load tests were performed. Five of the test piles were instrumented with internal strain gages at multiple levels. Load test results provided valuable insight on distribution of loads along the pile shaft and at the toe. This paper summarizes the site subsurface conditions, results of the pile load tests, observed load distribution in instrumented piles, and compares back-calculated skin friction and toe resistance factors from the load tests with those commonly used in pile design.

The Minnesota Department of Transportation has instrumented several driven pile bridge foundations with the intent of gaining an improved understanding of complex pile-soil interaction given various construction layouts, structural and earth fill loading sequences, and geotechnical site conditions. Axial pile loading behavior was examined throughout construction and into bridge service as part of a bridge performance monitoring program. Three similar case studies of instrumented pile pairs at bridge abutments are examined: a comparison of the behavior of a pile within an existing roadway footprint and a pile installed in a widened side-hill fill on a bridge reconstruction project; a comparison of interaction between leading and trailing row piles in a 3-row pile group; and a comparison of pile loads seen on a pile in an integral abutment and a structurally unloaded pile positioned outside the pile cap. These sites have allowed unique observations and interesting conclusions relative to pile-soil interaction.