Foundation Design Process Research Articles

Influence of Correlation Distance of Soil Parameters on Pile Foundation Failure Probability

Spatial variability of soil parameter distribution is crucial to calculating the pile foundation failure probability. Traditional reliability design methods describe the dispersion degree of soil parameters with their point variance without considering the influence of correlation distance. In this paper, static cone penetration test data of a project site are used, and random field theory is introduced to describe the average spatial characteristics of soil parameters. Then, the method of spatial average is used to calculate the correlation distance of soil parameters in each foundation soil layer. Given the influence of the correlation distance, a variance reduction function is determined to convert point variance to spatial mean-variance and further calculate the failure probability of pile foundation with the Monte Carlo method to study the influence of correlation distance on pile foundation failure probability. Results show that the spatial variability of parameters can be better reflected, and project cost can be reduced by considering the influence of correlation distance during the pile foundation design process. These results lay a foundation for further research on the pile foundation reliability design method.

Backpropagation Neural Network-Based Machine Learning Model for Prediction of Soil Friction Angle

In the design process of foundations, pavements, retaining walls, and other geotechnical matters, estimation of soil strength-related parameters is crucial. In particular, the friction angle is a critical shear strength factor in assessing the stability and deformation of geotechnical structures. Practically, laboratory or field tests have been conducted to determine the friction angle of soil. However, these jobs are often time-consuming and quite expensive. Therefore, the prediction of geo-mechanical properties of soils using machine learning techniques has been widely applied in recent times. In this study, the Bayesian regularization backpropagation algorithm is built to predict the internal friction angle of the soil based on 145 data collected from experiments. The performance of the model is evaluated by three specific statistical criteria, such as the Pearson correlation coefficient (R), root mean square error (RMSE), and mean absolute error (MAE). The results show that the proposed algorithm performed well for the prediction of the friction angle of soil (R = 0.8885, RMSE = 0.0442, and MAE = 0.0328). Therefore, it can be concluded that the backpropagation neural network-based machine learning model is a reasonably accurate and useful prediction tool for engineers in the predesign phase.

A Winkler model for suction caisson foundations in homogeneous and non-homogeneous linear elastic soil

Suction caisson foundations provide options for new foundation systems for offshore structures, particularly for wind turbine applications. During the foundation design process, it is necessary to make reliable predictions of the stiffness of the foundation, since this has an important influence on the dynamic performance of the overall support structure. The dynamic characteristics of the structure, in turn, influence its fatigue life. This paper describes a thermodynamically consistent Winkler model, called OxCaisson, that delivers computationally efficient estimates of foundation stiffness for caissons installed in homogeneous and non-homogeneous linear elastic soil, for general six degrees-of-freedom loading. OxCaisson is capable of delivering stiffness predictions that are comparable to those computed with three-dimensional finite-element analysis, but at a much lower computational cost. Therefore, the proposed model is suited to design applications where both speed and accuracy are essential, such as large-scale fatigue assessments of offshore wind farm structures. The paper demonstrates that the OxCaisson model can also be applied to short, rigid monopile foundations.

Assessment on liquefaction potential of seabed soil in Chang-Bin Offshore wind farm considering parametric uncertainty of standard penetration tests

Liquefaction potential analysis is a required task in the foundation design process of offshore wind turbine in Taiwan. The standard penetration test (SPT) is mostly used in the preliminary soil investigation of the pilot offshore wind farm in Chang-Bin, Taiwan. Due to the different experimental conditions and operating conditions, the N value (SPT-N) of SPT varies greatly. This study applies statistical methods in conjunction with the New Japan Road Association simplified-empirical method (NJRA method) to incorporate the uncertainty of SPT-N values into the offshore liquefaction potential assessment to quantify the risk of seabed liquefaction. The study statistics the field experimental geotechnical parameters SPT-N and determines the probability density function of the SPT-N distribution of each layer of soil in the offshore wind farm. In order to quantify the risk of seabed soil liquefaction potential, the Monte Carlo random sampling method is used, and by the NJRA method to carry out the seabed liquefaction potential in Changhua, Taiwan. After comparing, the results obtained by the current SPT-based soil liquefaction potential assessment by deterministic approach are conservative. In the ground investigation of offshore wind farm development, the method proposed in this paper can access the thickness of liquefiable soil layers under any given probability for optimizing offshore wind turbine foundation design.

Estimation of driven pile capacity in soft soil based on limited geotechnical data: A case study

The lack of qualified geotechnical data for the foundation design process is a present and growing concern among the consultancy practitioners. The clients have been increasingly reluctant to commit to extensive but necessary site investigative program that has no immediate economic benefits or perceived to impede work progress. Consequently, the risk of foundation failure and over-design are a potential reality. Even so, the construction pace is unrelenting. The research attempted to address such a quandary via a project case study with not too dissimilar limitation with respect to the availability of geotechnical data. Selecting the best available data for the type of foundation selected, further analyses were carried out in order to obtain collaborative strength information with the appropriate application of the factor of safety. Next, selection of the governing value from among the derived strength parameter had been based on the currency and accuracy of the testing process. Finally, provisional qualifiers had been attached to the design proposals in case alternate scenarios were encountered during the implementation stage. In the context of the case study, a reasonable driven pile capacity of 15.55 tonnes as determined from the PDA test has been recommended contingent upon the prescribed project scale and ground conditions.

Analytical approach to ground heat losses for high temperature thermal storage systems

A new approach to estimate the heat loss from thermal energy storage tank foundations is presented. Results are presented through analytical correlations based on numerical solutions for the steady-state heat conduction problem for thermal energy slab-on-grade tanks with uniform insulation. Model results were verified with other well-established benchmark problems with similar boundary conditions and validated with experimental data with excellent agreement. In addition to the TES foundation heat loss, new correlations for the maximum temperature and for the radial evolution of the temperature underneath the insulation layer are also provided, giving important information related to the tank foundation design. The correlated variables are of primordial importance in the tank foundation design because, due to the typical high operating storage temperatures, an inappropriate tank foundation insulation would lead not only to a not desired loss of energy but also to an inadmissible increase of the temperatures underneath the insulation layer, affecting the structural stability of the tank. The proposed correlations provide a quick method for the estimation of total tank foundation heat losses and soil maximum temperature reached underneath the insulation layer, saving time, and cost on the engineering tank foundation design process. Finally, a comprehensive parametric analysis of the variables of interest is made and a set of cases covering a wide range of tank sizes, insulation levels, depths to water table, and storage temperatures are solved.

Refining shear strength characteristic value using experience

Determination of characteristic values for soil properties forms a critical step in the foundation design process. The refinement of such values to account not only for site-specific data but also for existing knowledge and previous experience can result in more efficient design and increased confidence. This paper presents a logical, pragmatic approach for the selection of characteristic values of shear strength for the design of piled foundations within the context of Eurocode 7. The process of refining conceptual models of geotechnical properties in a quantitative, objective manner to include previous knowledge and wider experience is described and demonstrated through case study examples. The result of applying the updating methods is to achieve a revised mean that is a weighted average of the site data and the prior knowledge; the weighting is a function of the variability of each set of data. Such refinement relies upon a quantification of previous knowledge: mean values, trends, variations and distributions of data are required, and in this paper a dataset for undrained shear strength of London Clay is presented and applied to case study examples. Application of the techniques described leads to a better estimate of the ground properties and a reduction in the risk attached to a design solution.

Material testing for sustainable pavement foundation design

The current UK pavement foundation design process is based upon the California bearing ratio, coupled with a ‘method’ specification based on past experience and proven performance. This provides an empirical indicator of adequate performance but limits the use of materials. This in turn restricts the wider use of marginal and recycled/secondary aggregates necessary to achieve sustainability targets. Additionally there is a move towards analytically based pavement design, based upon the fundamental material performance properties of elastic stiffness and shear strength. Analytical design, combined with ‘performance’ specifications, potentially allows any materials that are ‘fit for purpose’. This approach requires field measurements to confirm that the assumed design performance is achieved; performance data for design are required before the materials are used to ensure confidence in their likely behaviour. A large-scale laboratory assessment test has been developed to measure the performance of coarse granular (capping) materials. The test utilises devices proposed to measure/check performance in the field, thus providing directly comparable results. This paper discusses the development of the laboratory performance test, its use and role in the wider context of the design process, and suggests areas where this test can help foster sustainable use of materials.

Foundation design for the Emirates Twin Towers, Dubai

This paper describes the foundation design process adopted for two high-rise buildings in Dubai, the Emirates Twin Towers. The foundation system for each of the towers was a piled raft, founded on deep deposits of calcareous soils and rocks. The paper outlines the geotechnical investigations undertaken, the field and laboratory testing programs, and the design process and describes how potential issues of low skin friction and cyclic degradation of skin friction due to wind loading were addressed. An advanced numerical computer analysis was used for the design process, which was carried out using a limit state approach. This necessitated analysis of a large number of load cases, and the paper describes how the information was processed to produce design information. A comprehensive program of pile load testing was undertaken, and class A predictions of both axial and lateral load–deflection behaviour were in fair agreement with the load test results. Despite this agreement, the overall settlements of the towers observed during construction were significantly less than predicted. The possible reasons for the discrepancy are discussed.Key words: case history, footings and foundations, full-scale tests, piles, rafts, settlement.

Eighteenth Canadian Geotechnical Colloquium: Limit States Design For Foundations. Part I. An overview of the foundation design process

This paper examines the foundation design process in terms of level of safety associated with current state-of-practice, sources of uncertainty and how they are handled, importance of engineering judgement and experience, and the role of codes of practice. Working stress, limit states, reliability-based design approcahes are described and discussed in terms of their historical development, fundamental bases and differences, advantages, and limitations. Limit states are conditions under which a structure no longer performs its intended function. Limit states design considers seperately the two classes of ultimate and serviceability limit states using partial factors of safety. The European factored strength approach and the North American factored overall resistance approach are compared and discussed. The factored resistance approach is a logical extension of working stress design and has the significant advantage that it reflects not only uncertainty in strength, but also in theoretical models, site conditions, construction tolerances, and failure mechanisms. The partial load and resistance factors are interrelated and are a function of characteristic values. A consistent, rational basis for the selection of the geotechnical characteristic value is required. The use of a conservatively assessed mean value is recommended, and an approach for its interpretation is presented. Key words: limit states design, working stress design, characteristic value, partial factors, factored resistance, load and resistance factor design.

A Method for Interpretation of Plate Load Test Results

Abstract The selection of allowable pressure is one of the major problems in the foundation design process. Plate load tests are considered the most reliable sources for the determination of that parameter. This paper addresses the interpretation technique of plate load test results accepted in Eastern Europe/CIS (former USSR). The “four-point” method of the proportionality limit evaluation for a plate load-settlement curve is presented and analyzed. A simple formula describing bearing plate displacements under applied loads has been developed. A new approach for the selection of allowable pressure values is proposed, and a formula for allowable pressure calculations is derived. The values of soil allowable pressure calculated using the proposed formula are compared with proportionality limits found with the traditional “four-point” method.