Dynamic Soil–Structure Interaction of Bridge Substructure Subject to Vessel Impact

The paper describes the in situ investigation, site stratigraphy, field monitoring, data reduction, and subsequent time-domain analysis of soil–structure interaction from a full scale vessel impact loading of a bridge pier at the St. George Island Causeway. The in situ investigation included standard penetration testing, electric cone, dilatometer, and pressuremeter testing to identify soil stratigraphy, engineering properties (strength and moduli), and axial and lateral static pile resistance (T–z, and P–y). Field instrumentation included soil total stress and pore pressure gauges in front of and behind the pile cap, a fully instrumented pile (strain gauges along length), dynamic load cells to monitor barge impact loads, and accelerometers to monitor pier accelerations, velocities, and displacements. Analyses of the field data reveal significant dynamic forces within the soil–structure system as a result of the duration and magnitude of the loading. Inertia from the piers, cap, and piles provide significant resistance in the early portion of the impact. However, postpeak inertia (i.e., pier deceleration) resulted in maximum deformations of the pier. Soil damping provided most of the resisting force at the peak barge loading, whereas static soil resistance dominated at the peak lateral displacement. Time-domain finite element analysis of an impact event employing viscous soil dashpots, nonlinear P–y and T–z springs with nonlinear beam, and shell elements for the pier, cap, and piles resulted in reasonable load displacement predictions.     

Behavior of Driven Ultrahigh-Performance Concrete H-Piles Subjected to Vertical and Lateral Loadings

In the United States, an estimated $1 billion is spent annually on repair and replacement of deep foundations. In a recent study, the possibility of using ultrahigh-performance concrete (UHPC) for deep foundation applications was explored with the objectives of increasing the service life of deep foundations supporting bridges to 75 years and reducing maintenance costs. This paper focuses on field evaluation of two UHPC piles and references a steel H-pile. An UHPC pile with an H shape was designed to simplify the process of casting the pile and reduce the volume (i.e., cost) of the material needed to cast the pile. Two instrumented UHPC piles were driven in loess on top of a glacial till clay soil and load tested under vertical and lateral loads. This paper provides a complete set of results for the field investigation conducted on UHPC H-shaped piles. The results presented in this paper prove that the designed UHPC piles can be driven using the same equipment used to drive steel H-piles through hard soil layers without a pile cushion. The vertical load capacity of the UHPC pile was over 80% higher than that of the steel H-piles.     

Behavior of Step Tapered Bored Piles in Sand under Static Lateral Loading

The behavior of step tapered bored piles in sand, under static lateral loading, was examined by field tests at one site in Kuwait. A total of 14 bored piles including two instrumented piles were installed for lateral loading. The soil profile consists of medium dense sand with weak cementations and no groundwater was encountered in the boreholes. Laboratory tests were carried out to determine the basic soil characteristics and the strength parameters. Both the ultimate lateral capacity and the deflections at applied loads were examined. The results indicate increased lateral load carrying capacity and decreased deflections at different applied loads for the step tapered piles due to the enlargement or strengthening of the upper section of the piles. The advantages of using this type of pile is emphasized including the cost saving resulting from an economical design.     

Horizontal Bearing Capacity of Piles in a Lateritic Soil

The behavior of pile foundations subjected to horizontal loading is typically evaluated using horizontal load tests. Although load tests are valuable to understand site-specific soil-structure interaction phenomena, validated predictive methods are also useful during the design phase. In this study, the results from horizontal load tests are compared with methods which predict the horizontal bearing capacity of piles using in situ measurements of soil behavior. Specifically, several horizontal load tests were performed in order to evaluate the behavior of two 12-m long Strauss piles and four bored piles with similar length, all installed in a lateritic soil profile. Two prediction methods were evaluated using p-y curves computed from the results of Marchetti’s dilatometer test (DMT) results. The predictive methods using the p-y curves from the DMT showed good agreement with the behavior observed in the pile loading test.     

Effect of Compressive Load on Uplift Capacity of Model Piles

Thirty six tests on model tubular steel piles embedded in sand were carried out in the laboratory to assess the effects of compressive load on uplift capacity of piles considering various parameters. The model piles were of 25 mm outside diameter and 2 mm wall thickness. The soil–pile friction angles were 21 and 29° in loose and dense conditions of sand. The piles were embedded in sand for embedment length/diameter ratios of 8,16, and 24 inside a model tank. They were subjected to a static compressive load of 0, 25, 50, 75, and 100% of their ultimate capacity in compression and subjected to pull out loading tests. The experimental results indicated that the presence of the compressive load on the pile decreases the net uplift capacity of a pile and the decrease depends on the magnitude of the compressive load. A logical approach, based on the experimental results, has been suggested to predict the net uplift capacity of a pile considering the presence of compressive load.     

Behavior of Slender Piles Subject to Free-Field Lateral Soil Movement

Soil movements associated with slope instability induce shear forces and bending moments in stabilizing piles that vary with the buildup of passive pile resistance. For such free-field lateral soil movements, stress development along the pile element is a function of the relative displacement between the soil and the pile. To investigate the effects of relative soil-pile displacement on pile response, large-scale load tests were performed on relatively slender, drilled, composite pile elements (cementitious grout with centered steel reinforcing bar). The piles were installed through a shear box into stable soil and then loaded by lateral translation of the shear box. The load tests included two pile diameters (nominal 115 and 178?mm) and three cohesive soil types (loess, glacial till, and weathered shale). Instrumentation indicated the relative soil-pile displacements and the pile response to the loads that developed along the piles. Using the experimental results, an analysis approach was evaluated using soil p-y curves derived from laboratory undrained shear strength tests. The test piles and analyses helped characterize behavioral stages of the composite pile elements at loads up to pile section failure and also provided a unique dataset to evaluate the lateral response analysis method for its applicability to slender piles.     

Simplified Approach for the Seismic Response of a Pile Foundation

Pseudostatic approaches for the seismic analysis of pile foundations are attractive for practicing engineers because they are simple when compared to difficult and more complex dynamic analyses. To evaluate the internal response of piles subjected to earthquake loading, a simplified approach based on the “p-y” subgrade reaction method has been developed. The method involves two main steps: first, a site response analysis is carried out to obtain the free-field ground displacements along the pile. Next, a static load analysis is carried out for the pile, subjected to the computed free-field ground displacements and the static loading at the pile head. A pseudostatic push over analysis is adopted to simulate the behavior of piles subjected to both lateral soil movements and static loadings at the pile head. The single pile or the pile group interact with the surrounding soil by means of hyperbolic p-y curves. The solution derived first for the single pile, was extended to the case of a pile group by empirical multipliers, which account for reduced resistance and stiffness due to pile-soil-pile interaction. Numerical results obtained by the proposed simplified approach were compared with experimental and numerical results reported in literature. It has been shown that this procedure can be used successfully for determining the response of a pile foundation to “inertial” loading caused by the lateral forces imposed on the superstructure and “kinematic” loading caused by the ground movements developed during an earthquake.     

Effects of Principal Stress Rotation on Permanent Deformation in Rail Track Foundations

A realistic assessment of the whole life cost of rail track foundations requires analysis of the effects of the repeated loadings applied by trains. This paper reports the effects of principal stress rotation (PSR) during cyclic loading on the permanent deformations measured in a series of hollow cylinder tests. The tests were carried out on a number of reconstituted soils selected in order to simulate foundation materials on an existing heavy haul railway line. Typical loadings and track geometry together with dynamic finite-element analyses were used to define representative stress changes to be applied to these soils, which were then tested with and without principal stress rotation during loading. It is shown that principal stress rotation has a significant and deleterious impact on permanent deformation of some materials. Therefore, it is concluded that cyclic triaxial testing, which cannot impose principal stress rotation, will not necessarily give good estimates of the long-term performance of rail track foundations. As PSR cannot be ignored when evaluating permanent displacements of rail track foundations, the use of more appropriate (realistic) testing methods such as the cyclic hollow cylinder or the cyclic simple shear apparatus is required.     

Effect of Soil Permeability on Centrifuge Modeling of Pile Response to Lateral Spreading

This paper presents experimental results and analysis of six model centrifuge experiments conducted on the 150?g-ton Rensselaer Polytechnic Institute centrifuge to investigate the effect of soil permeability on the response of end-bearing single piles and pile groups subjected to lateral spreading. The models were tested in a laminar box and simulate a mild infinite slope with a liquefiable sand layer on top of a nonliquefiable layer. Three fine sand models consisting of a single pile, a 3×1 pile group, and a 2×2 pile group were tested, first using water as pore fluid, and then repeated using a viscous pore fluid, hence simulating two sands of different permeability in the field. The results were dramatically different, with the three tests simulating a low permeability soil developing 3–6 times larger pile head displacements and bending moments at the end of shaking. Deformation observations of colored sand strips, as well as measurements of sustained negative excess pore pressures near the foundations in the “viscous fluid” experiments, indicated that an approximately inverted conical zone of nonliquefied soil had formed in these tests at shallow depths around the foundation, which forced the liquefied soil in the free field to apply its lateral pressure against a much larger effective foundation area. Additional p-y and limit equilibrium back-analyses support the hypothesis that the greatly increased foundation bending response observed when the soil is less pervious is due to the formation of such inverted conical volume of nonliquefied sand. This study provides evidence of the importance of soil permeability on pile foundations response during lateral spreading for cases when the liquefied deposit reaches the ground surface, and suggests that bending response may be greater in silty sands than in clean sands in the field. Moreover, the observations in this study may serve as basis for realistic practical engineering methods to evaluate pile foundations subjected to lateral spreading and pressure of liquefied soil.     

Pile Spacing Effects on Lateral Pile Group Behavior: Load Tests

To investigate group interaction effects as a function of pile spacing, full-scale cyclic lateral load tests were performed on pile groups in stiff clay spaced at 3.3, 4.4, and 5.65 pile diameters in the direction of loading with as many as five rows of piles. Group interaction effects decreased considerably as pile spacing increased from 3.3 to 5.65D. Lateral resistance was a function of row location in the group, rather than location within a row. For a given deflection, the leading (first) row piles carried the greatest load, while the second and third row piles carried successively smaller loads. Fourth and fifth row piles carried about the same load as the third row piles. For a given load, the maximum bending moments in the trailing row piles were greater than those in the lead row, but these effects decreased as spacing increased. Cyclic loading reduced the peak load by about 15% after 15 cycles; however, distribution of load within the pile group was essentially the same as at the peak load. Gaps significantly reduced resistance for small deflections.     

Evaluation of Rotational Stiffness of Elastomeric Bearing Pad-Anchor Bolt Connections on Deep Foundation Bents

Experimental tests are performed on a bearing pad-anchor bolt connection to study rotational stiffness and moment transfer capabilities of a typical bridge configuration. The experimental program is divided in two phases. The first phase consisted of shear and compression properties of two types of bearing pads. The second phase consisted of a total of 42 full-scale tests of a bearing pad-anchor bolt connection. The tested bridge-bent configuration includes two AASHTO Type II girders made continuous with a slab and diaphragm, bearing pads, pile caps, and piles. Variables included axial loads applied to the piles and bearing pads, two different sets of bearing pads, and three different pile types. The bridge connection is subjected to lateral cyclic reversed loading in one-cycle displacement increments. Test results show the potential for this type of connection to sustain lateral loads and flexural moments, and to develop the full strength of the pile elements. Shear and compression modulus are also obtained for the bearing pad types used in this study. Rotational stiffness values for the connection are determined as a function of varying axial loads.     

Increasing the Resistance of Piles Subject to Cyclic Lateral Loading

Small-scale tests were carried out on a monopile and fin piles to determine the effect the length of fins had upon the lateral displacement of cyclically loaded piles. A variety of loading conditions were applied to model piles in a dense sand by using a mechanical loading system. Ten thousand cycles were used in each test to represent 20 years of environmental loading on offshore structures. Variables included the magnitude, frequency, and direction of the load; the type of pile tip; and the length of the fins. The reduction in pile head displacement was used as a measure of the efficiency of the fins. The tests show that the fins reduced the lateral displacement by at least 50% after 10,000 cycles.     

Numerical Analysis of Laterally Loaded 3 × 3 to 7 × 3 Pile Groups in Sands

The coupled bridge foundation-superstructure finite-element code FLPIER was employed to predict the lateral response of the single piles and 3 × 3 to 7 × 3 pile groups founded in both loose and medium dense sands. The p-multiplier factors suggested by McVay et al. for laterally loaded pile groups with multiple pile rows were implemented for the predictions. The soil parameters were obtained through a back-analysis procedure based on single pile test results. The latter, as well as the numerical predictions of both the single and group tests, are presented. It was found that the numerical code FLPIER did an excellent job of predicting the response of both the single piles and the 3 × 3 to 7 × 3 pile groups. The latter involved the predictions of lateral load versus lateral deflection of the group, the shears and bending moments developed in the individual piles, and the distributions of the lateral loads in each pile row, which were all in good agreement with the measured results.     

Raked Piles—Virtues and Drawbacks

This technical note examines some of the characteristics of behavior of pile groups containing raked piles, via a simplified and hypothetical example. Three cases are examined: (1) a group subjected to vertical and lateral loadings, with no ground movements; (2) a group subjected to vertical and lateral loadings, but with vertical ground movements also acting on the group; and (3) a group subjected to vertical and lateral loadings, but with horizontal ground movements acting on the group. In each case, the effect of pile rake on typical behavioral characteristics (group settlement, lateral deflection and rotation, and pile loads and moments) are examined. It is found that, while the presence of raked piles can provide some advantages when the group is subjected to applied vertical and lateral loadings, especially in relation to a reduction in lateral deflection, some aspects of group behavior may be adversely affected when either vertical or horizontal ground movements act on the group. Thus, caution must be exercised in employing raked piles when such ground movements are expected to occur.     

Interface Characteristics and Laboratory Constructability Tests of Novel Fiber-Reinforced Polymer/Concrete Piles

Conventional pile materials such as steel, concrete, and timber are prone to deterioration for many reasons. Fiber-reinforced polymer (FRP) concrete composites represent an alternative construction material for deep foundations that can eliminate many of the performance disadvantages of traditional piling materials. However, FRP composites present several difficulties related to constructability, and the lack of design tools for their implementation as a foundation element. This paper describes the results of an experimental study on frictional FRP/dense sand interface characteristics and the constructability of FRP–concrete composite piles. An innovative toe driving technique is developed to install the empty FRP shells in the soil and self-consolidating concrete is subsequently cast in them. The experimental program involves interface shear tests on small FRP samples and uplift load tests on large-scale model piles. Two different FRP pile materials with different roughness and a reference steel pile are examined. Static uplift load tests are conducted on different piles installed in soil samples subjected to different confining pressures in the pressure chamber. The results showed that the interface friction for FRP materials compared favorably with conventional steel material. It was shown that toe driving is suitable for installation of FRP piles in dense soils.     

Nonlinear Efficiency of Bored Pile Group under Lateral Loading

A 3×3 bored pile group consisting of nine cast-in-drilled-hole reinforced concrete shafts and a comparable single-shaft were subjected to reversed cyclic, lateral head loading to investigate group interaction effects across a wide range of lateral displacements. The piles had the same diameter of d = 0.61?m and similar soil conditions; however, various equipment constraints led to two differences: (1) a fixed head (zero rotation) boundary condition for the single pile versus minor pile cap rotation in the vertical plane for the group and (2) shaft longitudinal reinforcement ratios of 1.8% for the single pile and 1% for the group piles. To enable comparisons between the test results, a calibrated model of the single pile (1.8% reinforcement) was developed and used to simulate the response of a single shaft with 1% reinforcement. Additional simulations of the pile group were performed to evaluate the effects of cap rotation on group response. By comparing the simulated responses for common conditions, i.e., 1% reinforcing ratio and zero head rotation, group efficiencies were found to range from unity at lateral displacements <0.004×d to 0.8 at small displacements ～ 0.01–0.02×d and up to 0.9 at failure (displacements >0.04×d). Hence, we find that group efficiency depends on the level of nonlinearity in the foundation system. The general group efficiency, although not its displacement-dependence, is captured by p-multipliers in the literature for reinforced concrete, fixed-head piles.     

Numerical Investigation of the Effect of Vertical Load on the Lateral Response of Piles

The laboratory and field test data on the response of piles under the combined action of vertical and lateral loads is rather limited. The current practice for design of piles is to consider the vertical and lateral loads independent of each other. This paper presents some results from three-dimensional finite-element analyses that show the significant influence of vertical loads on a pile’s lateral response. The analyses were performed in both homogeneous clayey soils and homogeneous sandy soils. The results have shown that the influence of vertical loads on the lateral response of piles is to significantly increase the capacity in sandy soils and marginally decrease the capacity in clayey soils. In general, it was found that the effect of vertical loads in sandy soils is significant even for long piles, which are as long as 30 times the pile width, while in the case of clayey soils, the effect is not significant for piles beyond a length of 15 times the width of the pile. The design bending moments in the laterally loaded piles were also found to be dependent on the level of vertical load on the piles.     

Ultimate Lateral Resistance of Pile Groups in Sand

Experimental investigations on model pile groups of configuration 1 × 1, 2 × 1, 3 × 1, 2 × 2, and 3 × 2 for embedment length-to-diameter ratios L∕d = 12 and 38, spacing from 3 to 6 pile diameter, and pile friction angles δ = 20° and 31°, subjected to lateral loads, were conducted in dry Ennore sand obtained from Chennai, India. The load-displacement response, ultimate resistance, and group efficiency with spacing and number of piles in a group have been qualitatively and quantitatively investigated. Analytical methods have been proposed to predict the ultimate lateral capacity of single pile and pile groups. The proposed methods account for pile friction angle, embedment length-to-diameter ratio, the spacing of piles in a group, pile group configuration, and soil properties. These methods are capable of predicting the lateral capacity of piles and pile groups reasonably well as noted and substantiated by the comparison with the experimental results of the writers and other researchers.     

Effect of Cracking on the Response of Pile Test under Horizontal Loading

Capacity-based design of structures limits the soil-structure interaction mechanism to the determination of the bearing capacity of a pile group. However, in many cases the criterion for the design of piles to resist lateral loads is not the ultimate lateral capacity but the deflection of the piles. Many procedures exist for estimating the response of single piles and pile groups under lateral loading, ranging from application of empirical relationships and simple closed-form solutions to sophisticated nonlinear numerical procedures. With the aim of investigating the effect of cracking, disregarded by most of the above-mentioned methods, a three-dimensional (3D) nonlinear analysis that accounts for cracking is presented. Response prediction correlates well with the experimental data from a full-scale pile load test. Interesting conclusions have also been drawn regarding the discretization of the computational domain and the combination of 3D numerical nonlinear analysis and the structural beam theory.     

Single Piles in Lateral Spreads: Field Bending Moment Evaluation

The results of the six centrifuge models of instrumented single pile foundations presented in a companion paper, are used to calibrate two limit equilibrium (LE) methods to evaluate bending response and factor of safety against bending failure of piles in the field subjected to lateral spreading. These six models simulate single reinforced concrete piles in two- and three-layer soil profiles, mostly end bearing but including also one floating pile, with and without a reinforced concrete pile cap, and one model where the liquefiable sand layer was densified locally around the pile to simulate the effect of pile driving. The measured permanent maximum bending moments in the pile, Mmax, invariably occurred at the boundaries between liquefied and nonliquefied soil layers, and in most cases the moments at such boundaries reached their peak Mmax and then decreased during shaking. These values of Mmax before decrease, which were associated with failure of the soil against the deep foundation, are used to calibrate the two proposed LE engineering methods. For the piles where Mmax was controlled by the pressure of the liquefied soil, the measured prototype Mmax in the centrifuge tests ranged between about 100 and 200 kN?m. It is found that a lateral pressure per unit area of pile or pile cap constant with depth (pl) of 10.3 kPa, predicts Mmax of the single piles tested within 15%. For the cases where Mmax was controlled by passive failure of the shallow nonliquefied layer, the prototype Mmax measured at the upper and lower boundaries of the liquefied soil in the centrifuge tests ranged between 160 and 305 kN?m. The Mmax values of 160–270 kN?m measured at the upper boundary were reached during the shaking, and then observed to decrease towards the end of shaking. At the lower boundary, the measured Mmax of 305 kN?m was reached at the end of shaking. Use of passive pressure against the pile of the shallow nonliquefiable soil layer, obtained from the ultimate plateaus (pult) of p-y curves, in conjunction with basic pile kinematic considerations and parameters addressed herein, explains well the development of moments measured in the centrifuge at both the upper and lower boundaries of the liquefied layer. This good accord validates the simplified LE prediction of Mmax at the upper boundary. The two proposed simplified engineering LE methods are used to evaluate bending response and distress of end-bearing and floating piles in the Niigata Family Court House building during the 1964 Niigata earthquake, with good agreement between predicted and observed performance.