Foundation Analysis and Design: Innovative Methods

This paper reviews the evolution of settlement analysis for pile groups, and the transition from research to practice over the past 30 to 40 years. The gradual incorporation of important aspects of reality is reviewed and it is shown that recent research has enabled complex practical problems to now be examined in a systematic, albeit approximate, manner. The significance of various parameters is reviewed and suggestions are given regarding appropriate methods of preliminary and detailed analysis, and of methods whereby the key geotechnical parameters may be assessed. The pitfalls of inappropriate application of theoretical research to practice are illustrated by examples.

The liquefaction resistance model developed by Cetin et al. (2004) along with a reference seismic loading model forms a performance function or limit state for liquefaction triggering analysis. Within the framework of the first order reliability method (FORM), the uncertainty of this limit state model is characterized through an extensive series of sensitivity studies using Bayesian mapping functions that were calibrated with a set of quality case histories. With the known model and parameter uncertainties, the probability of liquefaction of a future case can be fairly accurately predicted using the FORM analysis. A procedure is developed to assess the uncertainty associated with the Bayesian mapping function, which was due to use of limited observed data in the development. The effect of this uncertainty on the final assessment of model uncertainty is evaluated, and the variation in the final notional probability obtained from the FORM analysis estimated.

The present paper is to study how to achieve optimization of a piled raft foundation with varied cushion rigidity. The analysis model of piled raft foundation was set up using the fictitious pile method, and Fredholm's integral equations of the second kind were deduced to solve the problems. By simulating the cushion with Winkler springs, the effect of cushion was taken into consideration. The present method is suitable to analyze the foundation under working loads and could be applied to solve problems of different rigidities of piles and cushion. By adjusting the cushion's rigidity, the optimizing goal could be reached. Numerical examples are presented to illustrate the design principles.

The performance of many geotechnical works such as deep foundations is more often governed by displacement requirements. The estimation of pile foundation displacements involves model errors and uncertainty in model parameters. In this study, a sensitivity analysis of settlements of single piles in Hong Kong to model parameters is conducted using a first order, second moment method. The parameters that contribute most to the uncertainty of settlements are found to be the total unit weight, the initial deformation modulus, and the internal friction angle of the soil. Accordingly, these parameters should be carefully characterized in site investigations.

This paper discusses two issues about developing a case-based reasoning system for pile foundation. The new method to calculate similarity degree from fuzzy theory is presented to assess and compare the properties and states of strata along depth of any two piles in two different locations at site. The validation of this method is verified in a case study. Hierarchical representation of cases of static loading bearing capacity tests of piles is put forward and by applying it, the useful information from cases can easily be organized, managed and picked up in the process of evaluating and predicting the vertical bearing capacities of piles.

An ongoing research project supported by the USA National Cooperative Highway Research Program (NCHRP) under the Transportation Research Board (TRB) of the National Academy of Science is aimed at developing the AASHTO LRFD Specifications for Serviceability in the Design of Bridge Foundations. The AASHTO specifications are traditionally observed on all federally aided projects and generally viewed as a national code of US highway practice, hence influencing the construction of all highway bridges throughout the USA. The development of the specifications requires: establishing serviceability criteria, compilation of databases for foundation displacements, determination of analysis methods, finding the uncertainty of the methods, and development of methodology and LRFD parameters for serviceability. The various components are outlined and examples are provided. The need for a multiphase approach in the development of serviceability criteria is presented and its feasibility is demonstrated.

The progress towards harmonized geotechnical design in Europe is traced from the start of work in 1981 on a model limit state code for geotechnical design, through the development of the pre-standard version of Eurocode 7, to the issuing of the official code text, EN 1997-1, in 2004. The reasons for the introduction of three design approaches in Eurocode 7 and the advantages of each are discussed. The example of a spread foundation designed to Eurocode 7 is presented. The work currently being carried out, so that Eurocode 7 can be issued as a harmonized national standard in the different European countries, is described. The findings of an international workshop on the evaluation of Eurocode 7 are presented and an assessment is made of the progress towards harmonised geotechnical design in Europe.

Site specific empirical correlation models to estimate the compression index of inorganic marine clay at Kwangyang new port in Korea are proposed based on 468 consolidation data. Regression analysis is carried out to make correlations in estimating compression index using both single and multiple soil parameters. Soil parameters used include natural water content, void ratio, liquid limit, plasticity index, the passing percentage of 2 μm and specific gravity. Finally, it is found that the compression index predicted by a simple multiple regression equation involving the natural water content, the natural void ratio and liquid limit can reasonably evaluate the real soil compression index.

Sample size is an important factor to be considered in determining mean values of soil parameters. The authors have proposed to determine sample size based both on Type I and II errors in statistical hypothesis testing. In the previous study, however, only independent samples were considered. In the present study, spatially correlated samples are considered in the same framework. It is found that the spatial autocorrelation structure of soil parameters and layer thickness are dominant factors in determining the sample size.

The uncertainties in normalized load-displacement curves for ACIP piles are quantified using a pair of correlated lognormal curve-fitting parameters. To correct for simplifications in the capacity model, it is preferable to use linear regression rather than the standard multiplicative form. The former definition prevents correlation by removing variations that are explainable by the computed capacity.

To ensure safety of bored piles and avoid excessively conservative designs, quality assurance (QA) tests, such as integrity tests, are routinely performed after pile construction. The impact of a specific QA test on the reliability of piles can be translated into monetary values. This paper aims to quantitatively evaluate the cost-benefit of QA tests for bored piles. A cost-benefit model for QA tests is formulated. The role of a QA program is quantified through the changes in the probabilities of pile failure before and after the implementation of the QA program. An example is presented to illustrate the proposed procedure. The results indicate that the updated probability of failure can be significantly smaller than that before the QA tests. The degree of reliability improvement and the cost effectiveness depend on the pile specifics, the availability of prior information, and outcomes from the QA tests.

On the reliability analysis of structural system, the narrow-bound method is often used to compute the system failure probability. But it is difficult to calculate two-dimensional joint failure probability p_fij accurately and conveniently. Based on geometry analysis, a new solution for p_fij is presented in this paper. The solution is pithy and precise; its precision can be adjusted through a parameter Δθ. The system failure probability can be estimated satisfactorily by applying the deduced solution to narrow-bound equation. An example testifies that the new narrow-bound method can narrow the width of bounds of structural system failure probability effectively.

In this study, various limit states for vertical steel pipe piles of an open-type wharf are defined, then partial factors of design formulae are provisionally calculated based on reliability theory. Existing open-type wharves are targeted, and limit states for the ground bearing capacity and bending moment of the piles are examined. Considering the uncertainties of basic variables such as the coefficient of lateral subgrade reaction, the yield stress of the steel pipe piles and the ultimate shaft and tip resistances of piles, the reliability of existing structures that were designed using the current standard is evaluated using the advanced first-order second-moment method, and a set of partial factors is estimated based on the sensitivities of basic variables. Finally, the reliability index in the design section is calculated by the partial factor method, and the validity of the proposed technique is verified.

In Japan, a beam on an elastic medium model is usually used for designing piles loaded perpendicular to the pile axis. Three types of subgrade reaction model, namely Chang's model, S-type model, and C-type model, are usually used. The estimated coefficient of subgrade reaction varies from geotechnical investigation results quite differently for each model. It is therefore important to improve the accuracy of estimating the coefficient of subgrade reaction in reliability design methods. To do this for the most popular Chang's model, a new relationship between SPT-N value and the coefficient of subgrade reaction in Chang's model, k_h, is proposed.

For the design of shallow foundations under combined loading Eurocode 7 provides different partial safety factors for unfavourable and favourable actions and for different ultimate limit states. Several load combinations need to be checked to find the most critical combination of loading and limit state which governs design. Hence, the resulting safety is often not apparent. This paper illustrates the role of actions within the design of shallow foundations and points out the effects on the safety of the system.

Serviceability limit state (SLS) considerations often govern the design of foundations. The objective of this paper is to review the limited literature on reliability-based design for SLS and to suggest useful directions for future work. A review of several new design codes indicates that ultimate and serviceability limit states are not verified in the same way. The former check conforms to reliability principles, but the latter is essentially verified in a deterministic way. To address SLS within the reliability framework, it is necessary to characterize the uncertainties associated with foundation displacements and tolerable displacements. The former is discussed with particular attention to spatial correlation, model uncertainties, and load-displacement nonlinearities. Uncertainties in tolerable displacements are discussed using two case histories.

In this paper, a series of static load tests undertaken to analyze the bearing capacity of bored piles with a straight shaft and another with reamed enlargements are described. The distance between the enlargements greatly affected the bearing capacities around the enlargements, and the effects varied from the sandy soil to the clayey soils. Then Dynamic load tests were employed to evaluate the bearing capacity of the piles. Finally, the effects of the base grouting were discussed.

Lateral soil movements due to deep excavation works for substructure construction may induce excessive bending and lateral deflection on existing pile foundations in the vicinity. As field data on such cases are almost impossible to collect, a series of centrifuge model tests has been performed to investigate the pile responses due to excavation-induced soil movements on piles in sand with various relative densities. The test results are presented in terms of bending moment and pile deflection profiles. Comparison of maximum bending moment and pile head deflection for different tests are reported. The practical implications of the findings are also discussed in this paper.

Pile foundations are used for jacket type offshore structures, which are subjected to large magnitudes of lateral loads due to ocean waves and winds. Use of non-linear p-y curves to represent the static soil resistance is the common approach for analyzing the response of laterally loaded piles. In this paper, a simple and improved method for the construction of hyperbolic p-y curves for a soft clay is proposed for static loading conditions. The initial stiffness of the p-y curve is taken to be increasing with depth which depends entirely on the soil properties. A long, flexible, unrestrained vertical pile in a soft clay is analysed in which an iterative analysis is employed with the secant modulus approach, using the moment area method developed by Sawant et al. The analysis is performed using the p-y curves developed by Matlock Georgiadis et al. and the proposed hyperbolic p-y curves. The results are compared with the field test data reported by Matlock.

The ultimate bearing capacity of single piles is an important design parameter for a single pile. Even though many methods have been proposed, they are based on field tests or mechanical analysis and there has not been an intelligence based approach for predicting the ultimate bearing capacity. This paper proposed, by applying the principles of the Adaptive Neuro-Fuzzy Inference System (ANFIS), an ANFIS based approach for predicting the ultimate bearing capacity of single piles. 42 examples of precast reinforced concrete piles were accumulated from an area in Shanghai, China. 37 examples of them were used to build a new prediction model for the ultimate bearing capacity of single piles. The model was then used to predict the ultimate bearing capacity of the remaining 5 examples. A comparison was conducted between the predicted results and the practical measurements. The comparison results show that the approach has the advantages of high speed of convergence, good capability of fitting, high accuracy of prediction and reproduction of the training process. The results also indicate that ANFIS based approach is an excellent approach for predicting the ultimate bearing capacity of single piles.

In recent years, large diameter long piles have been used widely to support high-rise buildings and long span bridges in China because of their high bearing capacity. However, the load transfer mechanism of long piles is not well understood at present. The design method is not based on the actual mechanism of load bearing and deformation. Therefore, research on load transfer for long piles is important to improve design methods. Through analyzing the results of static load test and axial force testing, the bearing capacity character and load transfer mechanism of long bored piles in soft clay are discussed in the paper. It is concluded the load transfer mechanism of long piles is different from general piles, including the distribution of the axial force and lateral friction resistance. Long piles under design load should be considered floating piles. The test results may offer theoretical reference to improve design methods of long piles.

Response of a pile due to lateral soil movement and axial load has been investigated extensively by the authors. Typical results deduced from single pile tests in sand are presented previously in terms of effect of pile diameter, soil movement profile, sliding depth and magnitude of axial load. In this paper, a brief description of the apparatus was presented. Results from two model tests were reported, which were conducted on two instrumented pile groups embedded in sand subjected to a uniform lateral soil movement at a sliding depth of 0.57L (L = pile embedment length). Analysis revealed the effect of the direction and depth of soil movement, together with the magnitude of axial load, which are illustrated via profiles of bending moment, shear force, soil reaction, and pile deflection along instrumented piles in groups at various stages.

Installation of driven piles generate ground vibrations as the pile shears and displaces soil during its penetration. Typically, the magnitudes of ground vibrations from driven pile installations are greater as the pile penetrates stiff/dense soils than in soft/loose soils. For thirteen piles driven at six project sites in the Charleston, South Carolina area, ground vibration and dynamic pile measurements taken during pile installation were compared to available insitu soil testing parameters. The results showed the following: (1) peak ground vibrations generally occurred during pile installation through the dense sands located above the Cooper Marl formation, (2) the peak vibrations were typically observed along the longitudinal and/or vertical axes, and (3) the average peak vector sum vibrations within the Cooper Marl were 68% of the average peak vector sum magnitude within the dense sands.

The geothermal use of concrete geostructures (piles, walls and slabs) is an environmentally friendly way of cooling and heating buildings. With such geothermal structures, it is possible to transfer energy from the ground to fluid-filled pipes cast in concrete and then to building environments. A comprehensive research work was run at the EPFL (Switzerland) to improve the knowledge in the field of geothermal structures and to quantify the thermal influence on the bearing capacity of heat exchanger piles. In this paper, some features of the behavior of a pile subjected to thermo-mechanical loads are presented. Numerical finite element results are supported by in-situ measured values.

When jacked piles are installed, horizontal and vertical movements develop in the soil surrounding the piles. These movements will tend to develop the displacement in adjacent buildings and roads that have already been built. This paper presents a synthesis of the field measurements obtained in a series of pile installations. The field test was preformed at the HaiYan city in China. The test project included lateral ground deformation, vertical surface displacement, soil excess pore pressure and displacement of adjacent buildings and roads induced by jacked piles. For the project, some measures such as prebored hole and groove were taken in order to decrease the compacting effects on buildings and roads in the vicinity. The results show that the prebored holes and groove to relax stress were effective measures against the compacting effects of pile installation.

Rock socketed drilled shafts are used as foundations for bridges and other transportation structures because of their load carrying capabilities. However, only limited information is available in the literature on the effects of roughness on the unit side resistance of rock socketed drilled shafts. The objective of this study was to investigate the effect of drilling tools on the socket roughness in soft clay shale in Texas. Field study showed that the drilling tools, auger and core barrel, produced different roughness in the boreholes.

Data from ten Auger Cast-in-Place (ACIP) test piles located at six sites in the southeastern United States were used to compare prediction methods against observed capacities. The Chin Hyperbolic method was used to analyze load test data and develop values for ultimate skin friction support. These values were then compared against the skin friction values developed from various design methodologies. Comparison of predicted values of ultimate pile skin friction capacity to load test data showed that recent design methodologies developed specifically for ACIP piles provide an accurate method of predicting skin friction support.

The squeezed branch pile used in hundreds of high-rise buildings is a new type of pile with high bearing capacity and low settlement. The mechanism of bearing, compaction efficiency and loading transfer behavior of the squeezed branch pile are analyzed systematically based on the results of static loading test for exploring the connotations of the high bearing capacity and low settlement of the squeezed branch pile. It is shown by test results that behavior of bearing disks has obvious time effect and is different from other types of piles by means of calculation. Squeezed branch pile with specific property of frictional end-bearing pile bears load mainly by bearing disks, and the ultimate load of the pile is 150 ~ 200 percent of straight pile. The load shared by disks is about 60 ~ 70 percent of the ultimate load.

Conventional piled foundation is usually designed to provide adequate load carrying capacity for buildigs and to limit the overall settlement and to control differential settlement within tolerable limits. Conventionally, piles are often installed into competent stratum or to ‘set'. However, this solution generally only addresses the short-term problem associated with soft clay as pile capacity will be significantly reduced due to negative skin friction. This often reduces the cost-effectiveness of such ‘conventional solution'. In this paper, the design methodology of a ‘floating' piled raft foundation system for medium rise buildings (5-story) on very soft clay is discussed. The main design objective is to control differential settlement at the onset rather than only limiting the overall settlement. The piled raft foundation of the said medium rise building is designed using skin-friction piles of varying length. The design also considers the interaction between the piled raft and soil in order to produce an optimum design which satisfies both serviceability and ultimate limit states. The design methodology and monitoring results of the successfully implemented piled raft foundation for medium rise building are also presented in the paper.

There is a Lacustrine deposits area in the West of Shanghai and its profile and properties are different from those in the Center of Shanghai. In this paper, the behavior of the pile foundation in the Lacustrine deposits area is studied by the field experimental analysis on a case history of a six-story building. The test results show that the influence of shallow hard soil layers on the behavior of piles is obvious. The actual bearing capacity of pile is about 1.7 times that calculated using Shanghai codes. The observed settlement of a pile foundation is less than predicted value. The interaction between the piles and subsoil is analyzed based on the measured contact pressure under footing. The analysis shows that the bearing capacity of shallow subsoil has been neglected. The actual method for the design of piles in the Lacustrine deposits area should be improved.

In this study, a new kind of doubled steel tubular pile for inner excavation method was proposed. 2 pieces of bored steel tubular pile specimens and 8 pieces of doubled steel tubular pile specimens were made and compression test was carried out. The main parameters of experiment are the end shape of steel tube, extension length of outer steel tube (OSTE length), and steel tube with or without rib. According to the experimental results, the effect of parameters on the bearing capacity and plugging effect of doubled steel tubular piles was clearly analyzed. In addition, the optimum range of OSTE length was suggested. As a result, doubled steel tubular piles have higher bearing capacity and better plugging effect than bored steel tubular piles.

Drilled shafts socketed into rock have been widely used as a foundation for bridges to resist both vertical and lateral loads. Although numerous research efforts on rock socket drilled shafts under vertical loads have been carried out, similar research efforts on rock socketed shafts under lateral loads have been lacking. Few existing published analysis methods are still in their early stage of development due to meager lateral load tests data for verification. Additionally, most existing lateral load tests were performed on drilled shafts socketed in rock with a relatively thick layer of overlying soils, which may limit the extent of interaction between the rock and the shaft. The main objective of this paper is to present a lateral load test result on two fully instrumented drilled shafts 2.44 m in diameter socketed in shale. The effect of the overlying soil was isolated by using a larger diameter casing during the load test. An existing analysis method is evaluated using the presented load test and additional two load tests compiled from literature. It is found that the existing method tends to under predict the deflections by 53% to 97% for the three actual load tests studied.

A natural gas-fueled turbine power plant is being built on the south bank of the Yangtze River, near Nanjing City, China. The project site is located on existing farmland that includes fishing ponds. Subsurface investigations indicated that significant deep soft clay deposits exist in the plant area. To address this situation, prestressed high strength concrete (PHC) piles are being used to support important structures, such as the turbine pedestal. Because of the contingent schedule, the pile lateral capacity was initially developed using the software program LPILE. The pile group for the turbine pedestal was then designed following appropriate procedures in Chinese design codes. Later, however, the pile load test results indicated that the lateral capacity had been greatly overestimated. This paper discusses the reason for this overestimation and presents a methodology to increase lateral capacity. The differences in lateral capacity design between Chinese codes and U.S. practice are also compared and discussed.

A coupled pile-soil-structure interaction (SPSI) analysis method is presented to study the liquefaction effects on lateral pile behavior of the highway bridges. Pile-soil interaction is simulated by the dynamic nonlinear p-y method including the effect of liquefaction. The liquefaction effects to the pile-soil interaction are taken into account by introducing a degradation multiplier to the p-y curve. The degradation multiplier is related to the excess pore water pressure buildup at the pile-soil interface. The SPSI analysis method is implemented into a Missouri highway bridge site near the New Madrid Seismic Zone (NMSZ) rift complex for future earthquake scenarios of M_w 7.0. Synthetic motions at rock base were developed to the bridge foundation level for SPSI analyses. Results from analysis indicate that the degradation of p-y curve due to the excess pore water pressure significantly increases displacement of superstructure and moment of pile foundation.

The squeezing effect of prefabricated piles in soft clay usually causes heave in surficial soil around piles and lateral squeezing in deep soil. The theory of cylinder cavity expansion which is used to analyze the squeezing effect of prefabricated pile presently consider the process of pile-sinking as axis symmetric condition, cannot explain soil heave. This paper tries and analyzes the heave mechanism in surficial soil using the theory of sphere cavities expansion. And based on it, this paper advances a simple formula to estimate the range and magnitude of soil heave.

Negative skin friction (NSF) along pile caused by soil consolidation is greatly concerned by engineers. The NSF is time-dependent, due to the development of soil deformation and shear strength. However, most past researches emphasized on the behavior of NSF when the soil consolidation is completed. In the paper, a modified hyperbolic interface model is developed to account for the development of shear strength during soil consolidation and the loading-unloading situations. One dimensional consolidation theory is invoked to estimate soil deformation and shear strength. The evolution of load transfer along piles with time is solved by differential quadrature method. The influences of pile load magnitude and the time of pile loading (at different soil consolidation stages) are studied. The loading and unloading situations at the pile-soil interface are found during soil consolidation, which accounted for the movement of the neutral point with time.

Piles in China originated some 6000 ~ 7000 years ago. Through presenting the important archaeological discovery of the Hemudu Remains Site, the paper explains how the Bar Railing Style Architecture took place and how tree trunks functioned as piles originally. Application and development of piles in China since remote ancient times up to nowadays are described with examples of all ages. Finally, a table is given showing the main types of piles at present in common use in China, and the reasons why a number of different types are being used for some 50 million piles per year are explained.

In the article, theoretical basis of the stochastic medium theory is introduced. Formula and procedure for of predicting ground displacement and deformation induced by large diameter pile are proposed by using the theory of stochastic medium. Comparison between field test results and calculation indicated that the proposed calculation method and procedure are satisfactory for prediction. The method provided in the article can be used to estimate the extent of influence on the ambient environment caused by construction of large diameter piles.

Foundations are an important part of a construction project. Foundation construction is highly variable due to the fact that a construction process faces difficult problems such as, poor soil conditions, congested traffic and unpredictable weather. Designers are often unable to obtain reliable information in order to improve the accuracy of project time estimation that often leads to more delays and disputes. Field construction data related to this research were collected from twenty-five Texas highway projects within a two-year period to develop three models that could predict production rates of drilled shafts and prestressed concrete piles more accurately.

This paper studies the stress of a pile based on the Unified Strength Theory (UST). The stress of the soil around the pile in the compaction process of pile is discussed. The elastic solution and elastic limit load during the hole formation for a driven pile are obtained. The relationship between the uniform pressure on the hole wall and the plastic radius is also obtained, safe distance between piles can be determined according to the plastic radius. This solution considered the intermediate stress effect and the strength difference effect in tension and compression. Mohr-Coulomb solution is a special example of this solution obtained in this paper. The obtained results have practical value for comprehensively study the function of the pile and evaluate the safety of foundation.

Due to the sensitivity of high-speed rails to settlements, the most challenging task that geotechnical engineers generally have to face is to control settlements. Pile supported piers have been widely used for elevated monorails to provide required load resistance and to control the settlements. In this paper, authors discussed several settlement analysis methods for pile foundations that are generally used for design practice. These methods include: Equivalent Raft Foundation Method, Mindlin Stress Integration Method and 3-D Finite Element Method. A study was also presented to compare the applicability of these methods with the observed settlements. In addition, the methodologies to predict the time related settlement were also discussed. Results of the study suggested that the hyperbolic method provides better settlement prediction than the exponential method.

Based on the exponential curve fitting method, a new method—geometric progression method for calculating the final settlement of soft clay ground is introduced in this paper. By using the settlement observation curve of a trial embankment of express railway on soft clay ground, two methods were compared and analyzed through the computation of the final settlement. The results showed that the final settlement of soil ground by the exponential curve fitting method calculating is quite often to generate errors. If chosen different time interval Δt and value of time (t), there will be varied final settlements. The new method could avoid such kind of error made by the exponential curve fitting method.

The data of foundation settlement are commonly unequal time-intervals. The former Grey Model, GM(1,1), is a unequal time-interval model based on gray theory. Some deficiencies have been detected in practical applications. The aim of the paper is focused on the application of the gray model to establish model groups. Using optimization method for every weight in each model of the groups, the weighted optimizing forecasting-model of unequal time-interval model groups have been build up. Better results are gained compared with the previous model.

A Bayesian inference approach (BIA) is developed to estimate the parameters of the settlement prediction model that is an exponential function. The parameters' prior distributions are non-informative prior. To obtain the parameters' posterior distributions, the Markov chain Monte Carlo (MCMC) simulation is adopted. Compared with the traditional least-square method (LSM), BIA obtains not only the mean values of the model parameters, but also their distributions. The case shows that when the prior distributions are non-informative, the parameters' means obtained from BIA are close to those from LSM.