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Design of Extended Pile Shafts for Liquefaction Effects
Abstract
An equivalent static analysis (ESA) procedure is proposed for the design of extended pile shafts subjected to liquefaction-induced lateral spreading during earthquake loading. The responses of extended pile shafts for a range of soil, structure and ground motion conditions were examined parametrically using nonlinear dynamic finite element analyses (NDA). The results of those parametric analyses were used to develop and calibrate the proposed ESA procedure. The ESA procedure addresses both the nonliquefaction and liquefaction cases, and includes criteria that identify conditions which tend to produce excessive demands or collapse conditions. The ESA procedure, its limitations, and issues important for design are discussed.
The QS is a major key player in a construction project. The involvement of QS in different phases of a project is obligatory in order to meet the project requirement. QS acts as a ‘Financial police’ for a project. The role of a QS is different when working for different organizations such as consultant and main contractor. In order to know the involvement of QS in each project phase when working as a consultant QS and main contractor QS, this study is carried out through data collection by means of a survey done with the QS professionals working currently in the industry. The findings from the survey revealed that the role of the QS working in a consultant and main contractor organization is much different w.r.t to requirement, work and project. The required competencies, skills and experience will also matter when working in the industry as professional QS. Various software tools used by the QS were also found out during this study. Knowledge of the role of a QS in an entire project lifecycle when working for different organizations like consultant and main contractor will help in understanding the things in better way w.r.t to services to be provided, activities, objectives and scope stated for the project which in turn will reflect the professional way of approaching and working in the industry. The study will also be useful to civil engineering graduates who are willing to opt for the quantity surveying profession, industry quantity surveying professionals, educational institutions, service providers and other stakeholders in the construction industry.
The COVID-19 pandemic has affected many commercial activities around the globe, and the construction industry is unquestionably on the wrong end of the curve. Many construction projects are delayed and are already in a huge loss. The stakeholders of construction projects are left clueless, wondering about the new normal. During this uncertain situation, the construction industry is facing a sudden surge in the number of claims being submitted. This research is intended to understand the claims and dispute management aspects of construction, to find the frequent type of claim due to the pandemic and to address the procedure and provisions to claim under FIDIC contracts and Indian Contract Act. From the questionnaire survey, Extension of Time claim turned out to be the most frequent claim, and the procedure adopted for successful claiming of EOT has been explained with a sample project case.
Efficient project delivery is essential in the Indian construction industry. This efficiency can be achieved by reducing errors in construction projects to minimize cost and time. The chances of errors in the designing stage are high, which can lead to construction delays and other claims. BIM (Building Information Modeling) is a technology that can reduce not only human efforts but also the likelihood of errors. BIM is emerging rapidly and transforming the Indian real estate and construction sectors. This study verifies the BIM functionalities that help reduce the design and human errors that occur at various intervals of the project. This study also helps BIM users identify possible errors and their perceived severity, which can occur while working in a construction environment and avoiding these errors by applying BIM functionalities to achieve optimum time and cost. The quantitative technique was difficult to carry out for evaluation. Hence, the qualitative approach for research is carried out based on the perception shared by construction professionals working on the BIM platform. Ineffective design coordination between the design and planning teams, detailing errors, clashing of elements, and lags in most up-to-date information were found to be the most severe errors that affect the project. The analysis explains the seven functionalities that were beneficial in reducing errors. Functionalities with similar natures of reducing errors were clubbed into compound clusters. Although quantity take-off was not very beneficial, it formed a greater number of clusters with other functionalities. Among several functionalities, the natures of the coordination model and work-sharing with a central cloud database were more similar in avoiding chances of errors. More attention is needed on technologies and software that will help reduce such errors. Training on BIM-based software is essential for the Indian construction industry to utilize effective project management systems and reduce claims.
Large earthquakes and tsunamis can damage or lead to the collapse of lifeline bridges, resulting in human and socioeconomic losses as well as prolonged recovery times. Although many simulation models are available for the individual effects of earthquake and tsunami hazards on bridges, there are limited modeling approaches for predicting damage from sequential earthquake and tsunami hazards. A bridge modeling approach, which includes soil-foundation-structure interaction effects, is developed within the finite-element framework OpenSees to quantify sequential earthquake and tsunami-induced damage. Multihazard interaction diagrams that relate earthquake and tsunami intensity measures to bridge system damage show that the residual effects of earthquake loading on the bridge system reduce resistance to subsequent tsunami loading.
Effective-stress nonlinear dynamic analyses (NDA) were performed for piles in the liquefiable sloped ground to assess how inertia and liquefaction-induced lateral spreading combine in long- and short-duration motions. A parametric study was performed using input motions from subduction and crustal earthquakes covering a wide range of durations and amplitudes. The NDA results showed that the pile demands increased due to (a) longer duration shakings, and (b) liquefaction-induced lateral spreading compared to nonliquefied conditions. The NDA results were used to evaluate the accuracy of the equivalent static analysis (ESA) recommended by Caltrans/ODOT for estimating pile demands. Finally, the NDA results were used to develop new ESA methods to combine inertial and lateral spreading loads for estimating elastic and inelastic pile demands.
The seismic behavior of a large diameter extended pile shaft founded on a dense sandy site is investigated in this paper. First, a deterministic analysis is conducted including both nonlinear dynamic analysis (NDA) and pushover analysis to gain insights into the behavior of the pile and make sure an appropriate modeling technique is utilized. Then a probabilistic analysis is performed using the results of NDA for various demands. To this end a set of 40 pulse-like ground motions are picked and subsequently 40 nonlinear dynamic and pushover analyses are performed. The data obtained from NDA are used to generate probabilistic seismic demand model (PSDM) plots and consequently the median line and dispersion for each plot are computed. The NDA and pushover data are also plotted against each other to find out to what extent they are correlated. These operations are done for various engineering demand parameters (EDPs). A sensitivity analysis is done to pick the most appropriate intensity measure (IM) which would cause a minimum dispersion in PSDM plots out of 7 different IMs. Peak ground acceleration (PGA) is found to be the most appropriate IM. Pushover coefficient equations as a function of PGA are proposed which can be applied to the pushover analysis data to yield a better outcome with respect to the NDA. At the end, the pacific earthquake engineering research (PEER) center methodology is utilized to generate the fragility curves using the properties obtained from PSDM plots and considering various states of damage ranging from minor to severe. The extended pile shaft shows more vulnerability with a higher probability with respect to minor damage compared to severe damage.
A dynamic beam on a nonlinear Winkler foundation (or "dynamic p-y") analysis method for analyzing seismic soil-pile-structure interaction was evaluated against the results of a series of dynamic centrifuge model tests. The centrifuge tests included two different single-pile-supported structures subjected to nine different earthquake events with peak accelerations ranging from 0.02 to 0.7g. The soil profile consisted of soft clay overlying dense sand. Site response and dynamic p-y analyses are described. Input parameters were selected based on existing engineering practices. Reasonably good agreement was obtained between calculated and recorded responses for both structural models in all earthquake events. Sensitivity of the results to dynamic p-y model parameters and site response calculations are evaluated. These results provide experimental support for the use of dynamic p-y analysis methods in seismic soil-pile-structure interaction problems.
Methods for predicting the performance of pile foundations in liquefying and laterally spreading ground during earthquakes have developed considerably in recent years. Nonetheless, the mechanisms of soil-pile interaction in liquefied soil are still not well understood and the accuracy of design methods remains to be quantified. Subsequently, a series of dynamic centrifuge model experiments are being performed at UC Davis to study the behavior of single piles and pile groups in a soil profile comprised of a nonliquefied crust spreading laterally over a loose saturated sand layer. This paper will discuss some recent findings on the lateral resistance of liquefied soil, present initial evaluations of simplified pushover design methods against centrifuge test data, and summarize current recommendations for engineering practice.
Monotonic, static beam on nonlinear Winkler foundation (BNWF) methods are used to analyze a suite of dynamic centrifuge model tests involving pile group foundations embedded in a mildly sloping soil profile that develops liquefaction-induced lateral spreading during earthquake shaking. A single set of recommended design guidelines was used for a baseline set of analyses. When lateral spreading demands were modeled by imposing free-field soil displacements to the free ends of the soil springs (BNWF-SD), bending moments were predicted within -8% to +69 (16th to 84th percentile values) and pile cap displacements were predicted within -6 to +38%, with the accuracy being similar for small, medium, and large motions. When lateral spreading demands were modeled by imposing limit pressures directly to the pile nodes (BNWF_LP), bending moments and cap displacements were greatly overpredicted for small and medium motions where the lateral spreading displacements were not large enough to mobilize limit pressures, and pile cap displacements were greatly underpredicted for large motions. The effects of various parameter relations and alternative design guidelines on the accuracy of the BNWF analyses were evaluated. Sources of bias and dispersion in the BNWF predictions and the issues of greatest importance to foundation performance are discussed. The results of these comparisons indicate that certain guidelines and assumptions that are common in engineering design can produce significantly conservative or unconservative BNWF predictions, whereas the guidelines recommended herein can produce reasonably accurate predictions.
Eight dynamic model tests were performed on a 9 m radius centrifuge to study the behavior of single piles and pile groups in liquefiable and laterally spreading ground. Pile diameters ranged from 0.36 to 1.45 m for single piles, and from 0.73 to 1.17 m for pile groups. The soil profile consisted of a gently sloping nonliquefied crust over liquefiable loose sand over dense sand. Each model was tested with a series of realistic earthquake motions with peak base accelerations ranging from 0.13 g to 1.00 g. Representative data that characterize the important aspects of soil-pile interaction in liquefiable ground are presented. Dynamic soil-pile and soil-pile cap forces are backcalculated. Directions of lateral loading from the different soil layers are shown to depend on the mode of pile deflection relative to the soil, which depends on the deformed shape of the soil profile, the pile foundation stiffness, and the magnitude of loads imposed by the nonliquefied crust. Procedures for estimating the total horizontal loads on embedded piles and pile caps (i.e., passive loads plus friction along the base and sides) are evaluated. Due to liquefaction of the sand layer beneath the crust, the relative displacement between the pile cap and free-field crust required to mobilize the peak horizontal loads is much larger than expected based on static pile cap load tests in nonliquefied soils. Journal of Geotechnical and Geoenvironmental Engineering
The performance of pile foundations during an earthquake significantly influences the integrity of structures supported by them. Therefore, in the overall seismic design process of the structures, modeling of the soil-pile-superstructure interaction is an essential part. Although finite element based coupled analysis of the soil-pile-superstructure interaction models have the potential to provide accurate results, they are computationally expensive and often complex to utilize. In practice, many geotechnical engineers tend to use simple methods for obtaining the internal response of piles subjected to earthquake loading. Therefore this paper presents a simple pseudostatic approach where a single pile is considered, including the contribution of the superstructure to the pile and the interaction between the pile and the soil. The method involves two main steps. First a nonlinear free-field site response analysis is carried out to obtain the maximum ground displacements along the pile and the degraded soil modulus over the depth of the soil deposit. Next a static load analysis is carried out for the pile, subjected to the maximum free-field ground displacements and the static loading at the pile head based on the maximum ground surface acceleration. The method has been verified using an independent dynamic pile analysis program developed by the writers for the seismic analysis of piles in liquefying soil. It is demonstrated that the new method gives good estimates of pile bending moment, shear force, and displacement, despite its relative simplicity. The method is then used to compute the response of pile foundations during the Kobe 1995 earthquake and some centrifuge tests found in the literature where extensive soil liquefaction has been observed. Very good agreement is observed between computed and recorded pile bending moments.
The field performance of various pile foundations that experienced soil liquefaction and lateral spreading in the 1995 Hyogoken-Nambu earthquake are summarized. It is found that (1) damage tends to occur in non-ductile piles and at the interface between liquefied and nonliquefied layers; (2) the piles of a building near the waterfront show different failure modes in the direction perpendicular to the waterfront, while those away from the waterfront show similar deformation patterns. Cyclic and permanent ground displacements during and after earthquakes are estimated from field and aerial photographic surveys as well as analyses of strong motion records, and a simplified method for evaluating those displacements is presented. Pseudo-static analyses using p-y curves are conducted for well-documented case histories of pile foundations on which ground displacements estimated from the proposed method are imposed together with inertial forces from superstructures. The computed results agree reasonably well with the field performance of various pile foundations subjected to different ground movements. These findings confirm that the kinematic forces from cyclic and permanent ground displacements together with their spatial variation could have significant effects on pile damage. The proposed model could be effectively used to estimate deformation and stresses in piles subjected to ground movements.
The seismic design of extended pile shafts for the combined effects of dynamic shaking and liquefaction-induced lateral spreading is investigated using nonlinear dynamic finite element analyses (NDA). Results of NDA parameter studies are used to illustrate how inertia and lateral spreading loads combine during shaking. The NDA results are used to evaluate equivalent static analysis (ESA) methods. Implications for design practice are discussed.
Nonlinear static and dynamic analyses were used to evaluate the inelastic seismic response of bridge and viaduct structures supported on extended cast-in-drilled-hole (CIDH) pile shafts. The nonlinear dynamic analyses used a beam-on-nonlinear-Winkler foundation (BNWF) framework to model the soil-pile interaction, nonlinear fiber beam-column elements to model the reinforced concrete sections, and one-dimensional site response analyses for the free-field soil profile response. The study included consideration of ground motion characteristics, site response, lateral soil resistance, structural parameters, geometric nonlinearity (P-Delta effects), and performance measures. Results described herein focus on how the ground motion characteristics and variations in structural configurations affect the performance measures important for evaluating the inelastic seismic response of these structures. Presented results focus on a representative dense soil profile and thus are not widely applicable to dramatically different soil sites.
In saturated clean medium-to-dense cohesionless soils, liquefaction-induced shear deformation is observed to accumulate in a cycle-by-cycle pattern cyclic mobility. Much of the shear strain accumulation,occurs rapidly during the transition from contraction to dilation near the phase transformation,surface,at a nearly constant low shear stress and effective confining pressure. Such a stress state is difficult to employ as a basis for predicting the associated magnitude of accumulated permanent shear strain. In this study, a more convenient,approach,is adopted,in which,the domain,of large shear strain is directly defined by strain space parameters. The observed cyclic shear deformation is accounted for by enlargement and/or translation of this domain in deviatoric strain space. In this paper, the model,formulation,details involved,are presented,and,discussed. A calibration phase,is also described,based,on data from,laboratory sample,tests and dynamic,centrifuge experiments,for Nevada sand at a relative density of about 40%. DOI: 10.1061/ASCE1090-02412003129:121119 CE Database subject headings: Liquefaction; Constitutive models; Cyclic plasticity; Soil dynamics; Centrifuge models.
An analytical model, based on the commonly used equivalent cantilever concept, is developed for assessing the local ductility demand of a yielding pile-shaft when subjected to lateral loading. For elastic response of the pile-shaft, an equivalent depth-to-fixity is assumed, which can be derived by equating the lateral stiffness of the cantilever to that of the elastic soil-pile system. In adapting the equivalent cantilever model to yielding pile-shafts, however, the depth-to-maximum-moment is assumed to occur at a depth above the depth-to-fixity. The lateral strength, which depends on the depth-to-maximum-moment, is determined using the flexural strength of the pile and the ultimate pressure distribution of the soil. By assuming a concentrated plastic hinge rotation at the depth-of-maximum-moment, a kinematic model relating the local curvature ductility demand to global displacement ductility demand is developed. The kinematic relation is shown to depend on the aboveground height, depth-to-maximum-moment, depth-to-fixity, and equivalent plastic hinge length. The model is illustrated using a pile-shaft embedded in cohesive and cohesionless soils.
Thirty-one nearly full-size reinforced concrete columns, of circular, square, or rectangular wall cross section, and containing various arrangements of reinforcement, were loaded concentrically with axial compressive strain rates of up to 0.0167/s. The circular sections contained longitudinal and spiral reinforcement, the square sections contained longitudinal reinforcement and square and octagonal transverse hoops, and the rectangular wall sections contained longitudinal reinforcement and rectangular hoops with or without supplementary cross ties. The longitudinal stress-strain behavior of the confined concrete was measured and compared with that predicted by a previously derived stress-strain model with allows for the effects of various configurations of transverse confining reinforcement, cyclic loading, and strain rate. The measured longitudinal concrete compressive strain when the transverse steel first fractured was also compared with that predicted by equating the strain energy capacity of the transverse reinforcement to the strain energy stored in the concrete as a result of the confinement.
The requirements of performance-based earthquake engineering place increasing importance on the optimal characterization of earthquake ground motions. With respect to liquefaction hazard evaluation, ground motions have historically been characterized by a combination of peak acceleration and earthquake magnitude, and more recently by Arias intensity. This paper introduces a new ground motion intensity measure, CAV(5), and shows that excess pore pressure generation in potentially liquefiable soils is considerably more closely related to CAV(5) than to other intensity measures, including peak acceleration and Arias intensity. CAV(5) is shown to be an efficient, sufficient, and predictable intensity measure for rock motions used as input to liquefaction hazard evaluations. An attenuation relationship for CAV(5) is presented and used in an example that illustrates the benefits of scaling bedrock motions to a particular value of CAV(5), rather than to the historical intensity measures, for performance-based evaluation of liquefaction hazards.
This paper contains ground-motion prediction equations (GMPEs) for average horizontal-component ground motions as a function of earthquake magnitude, distance from source to site, local average shear-wave velocity, and fault type. Our equations are for peak ground acceleration (PGA), peak ground velocity (PGV), and 5%-damped pseudo-absolute-acceleration spectra (PSA) at periods between 0.01 s and 10 s. They were derived by empirical regression of an extensive strong-motion database compiled by the "PEER NGA" (Pacific Earthquake Engineering Research Center's Next Generation Attenuation) project. For periods less than 1s , the analysis used 1,574 records from 58 mainshocks in the distance range from 0 km to 400 km (the number of available data decreased as period increased). The primary predictor variables are moment magnitude M, closest horizontal distance to the surface projection of the fault plane RJB, and the time-averaged shear-wave velocity from the surface to 30 m VS30. The equations are applicable for M =5-8 , RJB 200 km, and VS30= 180- 1300 m / s. DOI: 10.1193/1.2830434
Effects of inertial and kinematic forces on pile stresses are studied based on large shaking table tests on pile-structure models with a foundation embedded in dry and liquefiable sand deposits. The test results show that, if the natural period of the superstructure, Tb, is less than that of the ground, Tg, the ground displacement tends to be in phase with the inertial force from the superstructure, increasing the shear force transmitted to the pile. In contrast, if Tb is greater than Tg, the ground displacement tends to be out of phase with the inertial force, restraining the pile stress from increasing. With the effects of earth pressures on the embedded foundation and pile incorporated in, pseudo-static analysis is conducted to estimate maximum moment distribution in pile. It is assumed that the maximum moment is equal to the sum of the two stresses caused by the inertial and kinematic effects if Tb Tg. The estimated pile stresses are in good agreement with the observed ones regardless of the occurrence of soil liquefaction.
Seismic Design Criteria
- Caltrans
Caltrans (2006). "Seismic Design Criteria." California Department of Transportation.
Soil Liquefaction and Lateral Spreading Analysis Guidelines, Memo to Designers MTD 20-15
- Caltrans
Caltrans (2008). "Soil Liquefaction and Lateral Spreading Analysis Guidelines,
Memo to Designers MTD 20-15. California Department of Transportation.
Special Issue on Geotechnical Aspects of the
Japanese Geotechnical Society (1996). "Special Issue on Geotechnical Aspects of the
January 17, 1995, Hyogoken-Nambu Earthquake." Soils and Foundations.