Pile Response Adjacent to Braced Excavation

The excavation of soil for the construction of basements or cut-and-cover tunnels results in ground movements. One particular concern is that the excavation-induced lateral soil movements may adversely affect any nearby pile foundation. The lateral loads imposed by the soil movements induce bending moments and deflections in the pile, which may lead to structural distress and failure. This paper presents the results of an actual full-scale instrumented study that was carried to examine the behavior of an existing pile due to nearby excavation activities resulting from the construction of a 16 m deep cut-and-cover tunnel. The pile was located 3 m behind a 0.8 m thick diaphragm wall. Excavation to the formation level that was 16 m below the ground surface resulted in a maximum lateral pile movement of 28 mm. A simplified numerical procedure based on the finite-element method was used to analyze the pile response. Generally, the theoretical predictions were in reasonable agreement with the measured results.     

Response of Laterally Loaded Large-Diameter Bored Pile Groups

This paper presents results of full-scale lateral load tests of one single pile and three pile groups in Hong Kong. The test piles, which are embedded in superficial deposits and decomposed rocks, are 1.5 m in diameter and approximately 30 m long. The large-diameter bored pile groups consist of one two-pile group at 6 D (D = pile diameter) spacing and one two-pile and one three-pile group at 3 D spacing. This paper aims to investigate the nonlinear response of laterally loaded large-diameter bored pile groups and to study design parameters for large-diameter bored piles associated with the p-y method using a 3 D finite-element program, FLPIER. Predictions using soil parameters based on published correlations and back-analysis of the single-pile load test are compared. It is found that a simple hyperbolic representation of load-deflection curves provides an objective means to determine ultimate lateral load capacity, which is comparable with the calculated values based on Broms' theory. Lateral deflections of bored pile groups predicted using the values of the constant of horizontal subgrade reaction, suggested by Elson and obtained from back-analysis of the single pile load test, are generally in good agreement with the measurements, especially at low loads.     

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.     

Prediction of Ground Movements due to Pile Driving in Clay

This paper evaluates theoretical predictions of ground movements caused by the installation of driven (or jacked) piles in clay. The predictions are based on an approximate analysis framework referred to as the shallow strain path method that simulates undrained pile penetration from the stress-free ground surface. Large strain conditions close to the pile are solved numerically, and closed-form analytical expressions are obtained from small strain approximations at points further away. These results show that, for closed-ended cylindrical piles of radius R and embedment L, the normalized displacements δL∕R2 are functions of their dimensionless position x∕L. In contrast, for a planar sheet pile or unplugged open-ended pile, the far-field soil displacements at x∕L depend only on the wall thickness w; i.e., δ∕w = f[x∕L]. The proposed analyses show favorable agreement with data from a variety of available sources including field measurements of (1) building movements caused by installation of large pile groups; (2) uplift of a pile caused by driving of an adjacent pile within a group; and (3) spatial distributions of ground movements caused by installation of a single pile (both cylindrical closed-ended and sheet pile wall), including a particularly detailed set of measurements in a large laboratory calibration chamber. The comparisons show that the proposed analysis is capable of reliably predicting the deformations within the soil mass but generally underestimates the vertical heave measured at the ground surface. Further investigation suggests that this discrepancy may be related to the occurrence of radial cracks observed at the ground surface during pile installation and is consistent with tensile horizontal strains computed in the shallow strain path method analyses.     

Vertical Vibration of Full-Scale Pile—Analytical and Experimental Study

This paper presents the results of vertical vibration tests on two full-scale single piles. The diameter of pile and embedded depth were 0.45 and 22 m, respectively. The soil samples were collected from three boreholes located at the site of investigation and it was explored to a depth up to 30.45 m below the ground level. The vertical vibration tests were conducted for different eccentricities to determine the frequency-amplitude response of the pile. Static load tests were also carried out on two single piles. A simple axisymmetric two-dimensional finite-element model was developed to predict the dynamic pile response. Novak’s plane strain model was also used for the prediction of the dynamic response of single pile. It was observed that the finite-element model predicted the natural frequency and peak displacement amplitude of pile reasonably well. However, prediction of dynamic response of the pile was found unsatisfactory by Novak’s plane strain model. Possible reasons for unsatisfactory performance of Novak’s model were investigated and presented.     

Lateral Resistance of Short Single Piles and Pile Groups Located Near Slopes

Many transmission towers, high-rise buildings, and bridges are constructed near steep slopes and are supported by large-diameter piles. These structures may be subjected to large lateral loads, such as violent winds and earthquakes. Widely used types of foundations for these structures are pier foundations, which have large diameter with high stiffness. The behavior of a pier foundation subjected to lateral loads is similar to that of a short rigid pile, because both elements seem to fail by rotation developing passive resistance on opposite faces above and below the rotation point, unlike the behavior of a long flexible pile. This paper describes the results of several numerical studies performed with a three-dimensional finite-element method (FEM) of model tests and a prototype test of a laterally loaded short pile and pier foundation located near slopes, respectively. Initially, in this paper, the results of model tests of single piles and pile groups subjected to lateral loading, in homogeneous sand with 30° slopes and horizontal ground were analyzed by the three- dimensional (3D) finite-element (FE) analyses. Furthermore, field tests of a prototype pier foundation subjected to lateral loading on a 30° slope was reported. The FE analyses were conducted to simulate these results. The main purpose of this paper is the validation of the 3D elasto–plastic FEM by comparisons with the experimental data.     

Application of Periodic Boundary for Large Pile Group

Full-scale testing of a large pile group is economically not feasible. A concept based on a periodic boundary has been used to study lateral behavior of a large pile group. The approach and findings from anchorage design of a major suspension bridge in California are presented here. Using the repeating nature of soil's displacement field within infinite number of piles arranged in a regular grid pattern, soil-pile interaction phenomenon from the finite area enclosed by one periodic soil boundary effectively represents behavior of the entire pile group. A 3D finite-element analysis was used to create the soil-pile models in which the boundary conditions mimic the repeating nature of the infinite number of piles by slaving the boundary nodes. The soil resistance, as calculated from the finite-element method employing the periodic boundary, is compared with the empirical p-y curve approach for a single isolated pile to determine the group effects. Values of p-multiplier and y-multiplier have been obtained for different pile spacings.     

Behavior of Braced and Anchored Walls in Soils Overlying Rock

This paper presents the results of analyses on the behavior of in situ walls, using the measured data collected from various deep excavation sites with multilayered ground conditions of soils overlying rock in Korea. A variety of in situ wall systems from >60 excavation sites were considered, covering a wide range of wall types, including H-pile, soil cement, cast-in-place pile, and diaphragm. The measured data were thoroughly analyzed to investigate the effects of wall and support types on lateral wall movements as well as apparent earth pressures. A series of 2D finite-element analyses were also performed to provide insights regarding the in situ wall behavior. Based on the results, lateral wall movements and apparent earth pressures are related to primary influencing factors affecting the wall behavior and information is presented in forms to provide tools that can be used for design and analysis.     

Applicability of Conventional p-y Relations to the Analysis of Piles in Laterally Spreading Soil

This paper presents a kinematic analysis of a single pile embedded in a laterally spreading layered soil profile and discusses the relevancy of conventional analysis models to this load case. The research encompasses the creation of three-dimensional (3D) finite-element (FE) models using the OpenSees FE analysis platform. These models consider a single pile embedded in a layered soil continuum. Three reinforced concrete pile designs are considered. The piles are modeled using beam-column elements and fiber-section models. The soil continuum is modeled using brick elements and a Drucker-Prager constitutive model. The soil-pile interface is modeled using beam-solid contact elements. The FE models are used to evaluate the response of the soil-pile system to lateral spreading and two alternative lateral load cases. Through the computation of force density-displacement (p-y) curves representative of the soil response, the FE analysis (FEA) results are used to evaluate the adequacy of conventional p-y curve relationships in modeling lateral spreading. It is determined that traditional p-y curves are unsuitable for use in analyses where large pile deformations occur at depth.     

Pseudostatic Approach for Seismic Analysis of Single Piles

This paper evaluates a simple approximate methodology for estimating the maximum internal forces of piles subjected to lateral seismic excitation. The method involves two main steps: computation of the free-field soil movements caused by the earthquake and the analysis of the response of the pile to the maximum free-field soil movements (considered as static movements) plus a static loading at the pile head, which depends on the computed spectral acceleration of the structure being supported. The applicability of this approach has been verified by an independent benchmark analysis developed by the writers. It is demonstrated that the proposed method yields reasonable estimates of the pile maximum moment and shear. The methodology is then used to obtain the response of the Ohba-Ohashi bridge in Japan to one of the earthquakes that occurred in the 1980s. Good agreement is found between the computed and measured pile moments.     

Performance of Sheet Pile Wall in Peat

To study the performance of sheet pile wall in peat during roadway construction, a long-term instrumentation program was conducted over a period of two years, measuring total lateral earth pressures, sheet pile deflections, soil movements, and water table level variances during construction. The analysis of field data indicated: (1) The earth pressure distribution in peat matched well with the classic Rankine earth pressure; (2) the expected long-term postconstruction sheet pile movement due to the creep behavior of peat was not observed; (3) fully passive earth pressure in peat was mobilized once the maximum measured sheet pile deflection exceeded 0.8% of sheet pile length; and (4) arching effect due to the protruding cross section of sheet pile caused pressure differences of 3–10?kPa between the inside web and outside web of the sheeting. Then, all the construction stages were continuously modeled by finite-element method and the calculated results were compared with the field measurements. The comparisons showed that the calculated results were consistent with the field data and provided reasonable explanations and helpful insights to understand soil–structure interaction mechanism. Finally, some conclusions and suggestions for sheet pile design and construction in peat were reached.     

Slope Stabilizing Piles and Pile-Groups: Parametric Study and Design Insights

This paper uses a hybrid method for analysis and design of slope stabilizing piles that was developed in a preceding paper by the writers. The aim of this paper is to derive insights about the factors influencing the response of piles and pile-groups. Axis-to-axis pile spacing (S), thickness of stable soil mass (Hu), depth (Le) of pile embedment, pile diameter (D), and pile group configuration are the parameters addressed in the study. It is shown that S = 4D is the most cost-effective pile spacing, because it is the largest spacing that can still generate soil arching between the piles. Soil inhomogeneity (in terms of shear stiffness) was found to be unimportant, because the response is primarily affected by the strength of the unstable soil layer. For relatively small pile embedments, pile response is dominated by rigid-body rotation without substantial flexural distortion: the short pile mode of failure. In these cases, the structural capacity of the pile cannot be exploited, and the design will not be economical. The critical embedment depth to achieve fixity conditions at the base of the pile is found to range from 0.7Hu to 1.5Hu, depending on the relative strength of the unstable ground compared to that of the stable ground (i.e., the soil below the sliding plane). An example of dimensionless design charts is presented for piles embedded in rock. Results are presented for two characteristic slenderness ratios and several pile spacings. Single piles are concluded to be generally inadequate for stabilizing deep landslides, although capped pile-groups invoking framing action may offer an efficient solution.     

Pile Responses Caused by Tunneling

In this paper, a two-stage approach is used to analyze the lateral and axial responses of piles caused by tunneling. First, free-field soil movements are estimated based on an analytical method, and, second, these estimated soil movements are imposed on the pile in simplified boundary element analyses to compute the pile responses. Through a parametric study, it is shown that the influence of tunneling on pile response depends on a number of factors, including tunnel geometry, ground loss ratio, soil strength, pile diameter, and ratio of pile length to tunnel cover depth. Simple design charts are presented for estimating maximum pile responses and may be used in practice to assess the behavior of existing piles adjacent to tunneling operations. A published case history has been studied in which the measured lateral pile deflections are compared with those computed using the present method and fair agreement is found.     

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.     

Wave Propagation in a Pipe Pile for Low-Strain Integrity Testing

This paper presents an analytical solution methodology for a tubular structure subjected to a transient point loading in low-strain integrity testing. The three-dimensional effects on the pile head and the applicability of plane-section assumption are the main problems in low-strain integrity testing on a large-diameter tubular structure, such as a pipe pile. The propagation of stress waves in a tubular structure cannot be expressed by one-dimensional wave theory on the basis of plane-section assumption. This paper establishes the computational model of a large-diameter tubular structure with a variable wave impedance section, where the soil resistance is simulated by the Winkler model, and the exciting force is simulated with semisinusoidal impulse. The defects are classified into the change in the wall thickness and Young’s modulus. Combining the boundary and initial conditions, a frequency-domain analytical solution of a three-dimensional wave equation is deduced from the Fourier transform method and the separation of variables methods. On the basis of the frequency-domain analytic solution, the time-domain response is obtained from the inverse Fourier transform method. The three-dimensional finite-element models are used to verify the validity of analytical solutions for both an intact and a defective pipe pile. The analytical solutions obtained from frequency domain are compared with the finite-element method (FEM) results on both pipe piles in this paper, including the velocity time history, peak value, incident time arrival, and reflected wave crests. A case study is shown and the characteristics of velocity response time history on the top of an intact and a defective pile are investigated. The comparisons show that the analytical solution derived in this paper is reliable for application in the integrity testing on a tubular structure.     

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.     

Response of an Earth Dam to Spatially Varying Earthquake Ground Motion

The stochastic response of the Santa Felicia earth dam, in southern California, to spatially varying earthquake ground motion (SVEGM) is analyzed. An SVEGM model that accounts for both incoherence and propagation of seismic waves is used, the results are compared with those for various simplified excitations, and the sensitivity of the responses to coherency models proposed by different researchers is investigated. A 3D inhomogeneous finite-element model is used to represent the dam. Finite element-based random vibration analysis is performed and the statistical moments of Cartesian displacement, stress, and strain responses are computed. Statistical moments of the maximum shear stress are computed using Monte Carlo simulation that utilizes results from the random vibration analysis. The results indicate that the stress response of stiff material near the base of the dam can be significantly increased due to SVEGM, and that the increase is sensitive to the low-frequency variation of ground motion coherency.     

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.     

Low Strain Integrity Testing of Piles: Three-Dimensional Effects

Results of low strain integrity testing of piles are normally interpreted using one-dimensional (1D) stress wave theory. While 1D stress wave theory is acceptable for pile-driving analysis, it may not adequately simulate the response of piles in sonic integrity tests where the hammer is small in relation to the size of the pile. Extensive parametric studies were performed using 1D and 3D (axisymmetric) wave equation models to study this problem. The main 3D effect in intact piles lies in the initial velocity response that becomes negative after the first positive peak. This response resembles that of a pile with an anomaly near the pile head. If this is not recognized, it will lead to a wrong assessment of the pile condition with attendant cost implications. This potential source of error can be removed by maintaining a distance between hammer and receiver that is greater than 50% of the pile radius.     

Sensitivity Statistics of 3D Structures under Parametric Uncertainty

Determination of sensitivity gradient is a major prerequisite for structural optimization, reliability assessment, and parameter identification. As the conventional deterministic sensitivity analysis cannot provide complete information, stochastic analysis is needed to tackle the uncertainties in structural parameters. This study focuses on the utility of the stochastic finite-element method for random response sensitivity analysis. The stochastic modeling of a random parameter is based on a commonly used 2D local averaging method generalized for a 3D case. The Choleski decomposition technique is then employed for digital simulation. The Neumann expansion based finite-element simulation method is extended for stochastic sensitivity analysis. This technique leads to a considerable saving of computational time. Example problems are used to compare the accuracy of this method to the direct Monte Carlo simulation and perturbation method in terms of varying stochasticity and efficiency in CPU time.