Limit States Design of Deep Foundations

Load and Resistance Factor Design (LRFD) shows promise as a viable alternative to the present working stress design (WSD) approach to foundation design. The key improvements of LRFD over the traditional Working Stress Design (WSD) are the ability to provide a more consistent level of reliability and the possibility of accounting for load and resistance uncertainties separately. In order for foundation design to be consistent with current structural design practice, the use of the same loads, load factors and load combinations would be required. In this study, we review the load factors presented in various LRFD Codes from the US, Canada and Europe. A simple firstorder second moment (FOSM) reliability analysis is presented to determine appropriate ranges for the values of the load factors. These values are compared with those proposed in the Codes. The comparisons between the analysis and the Codes show that the values of load factors given in the Codes generally fall within ranges consistent with the results of the FOSM analysis. For LRFD to gain acceptance in geotechnical engineering, a framework for the objective assessment of resistance factors is needed. Such a framework, based on reliability analysis is proposed in this study. Probability Density Functions (PDFs), representing design variable uncertainties, are required for analysis. A systematic approach to the selection of PDFs is presented. Such a procedure is a critical prerequisite to a rational probabilistic analysis in the development of LRFD methods in geotechnical engineering. Additionally, in order for LRFD to fulfill its promise for designs with more consistent reliability, the methods used to execute a design must be consistent with the methods assumed in the development of the LRFD factors. In this study, a methodology for the estimation of soil parameters for use in design equations is proposed that should allow for more statistical consistency in design inputs than is possible in traditional methods. Resistance factor values are dependent upon the values of load factors used. Thus, a method to adjust the resistance factors to account for code-specified load factors is also presented. Resistance factors for ultimate bearing capacity are computed using reliability analysis for shallow and deep foundations both in sand and in clay, for use with both ASCE-7 (1996) and AASHTO (1998) load factors. The various considered methods obtain their input parameters from the CPT, the SPT, or laboratory testing. Designers may wish to use design methods that are not considered in this study. As such, the designer needs the capability to select resistance factors that reflect the uncertainty of the design method chosen. A methodology is proposed in this study to accomplish this task, in a way that is consistent with the framework

Landslide susceptibility mapping based on triggering factors using a multi-modal approach

Landslide susceptibility mapping has been done using statistical and physically-based assessment techniques with limited focus on mode-specific models to identify failure modes and runout patterns. Because each failure mode has different consequences, it is essential to identify the failure mode associated with each slope inclination category, triggering factor, and geological setting. This paper presents a multimodal regionalscale assessment procedure for rainfall and earthquake-induced landslides, in the country of Lebanon, where landslide inventories are not available. Three failure modes are studied: debris flows, rock-slope failures, and coherent rotational slides. Areas prone to each mode of failure are identified based on geology and topography, then, using mode-specific models, their susceptibility to landslides is assessed. A runout assessment approach is then presented to identify the influence area of each predicted landslide and to obtain comprehensive susceptibility maps. Field assessment validated the proposed model which was in good agreement with actual slope failures across Lebanon. Therefore, the multimodal approach may be used to assess rainfall-induced landslide susceptibility, especially when landslide inventories are unavailable

Assessment of static pile design methods and non-linear analysis of pile driving

Pile foundations are used to transfer loads from the superstructure to deep layers in a soil deposit. Depending on the installation method, piles can either preserve the original soil density and stress state to a certain degree (e.g., bored piles), or induce changes that cannot be easily quantified, leading to greater challenges in obtaining accurate estimates of pile resistance (e.g., driven or jacked piles). Scientific advances in pile analysis have been made in recent decades but their implementation in the estimation of axial capacity has been slow. The modeling of the pile driving process has been traditionally carried out using the one-dimensional wave equation analysis based on empirical factors to control the static and dynamic resistances developed in the soil. Considerable effort has been spent in the past decades to develop models that eliminate the use of these empirical constants. The present research focuses on extending the traditional wave equation analysis to incorporate the nonlinear soil behavior during driving. The analysis incorporates all damping effects induced in the soil and considers the impact of shear modulus degradation on pile drivability. The pile/soil interaction system is described by a mass/spring/dashpot system where the properties of each component are derived from rigorous analytical solutions or finite element analysis. The outcome of this research is an algorithm that can be used to predict pile displacement and driving stresses. Field experiment results are used to validate the numerical simulation. The major contributions of this work are the proper modeling of the physical problem in pile driving by accounting for the non-linear soil behavior and separately modeling all damping effects. The new rheological models show, as expected, that sustained loads remain in the pile after a blow. Pile displacement is accurately predicted when compared to field test results. The resistance curves along the pile shaft and base properly reflect the nonlinear soil behavior. Given the complexity of the pile/soil interaction problem in pile driving and the limitations of the one-dimensional wave equation analysis, the present research should be viewed as an effort towards finding a more general solution based on a continuum analysis

Assessment of Axially-Loaded Pile Dynamic Design Methods and Review of INDOT Axially-Loaded Pile Design Procedure

The general aim of the present research is to identify areas of improvement and propose changes in the current methodologies followed by INDOT for design of axially loaded piles, with special focus on the dynamic analysis of pile driving. Interviews with INDOT geotechnical engineers and private geotechnical consultants frequently involved in INDOT’s deep foundation projects provided information on the methods and software currently employed. It was found that geotechnical engineers rely on static unit soil resistance equations that were developed over twenty years ago and that have a relatively large degree of empiricism. Updated and improved static design equations recently proposed in the literature have not yet been implemented in practice. Pile design relies predominantly on SPT data; cone penetration testing is performed only occasionally. Dynamic analysis of pile driving in standard practice is performed using Smith-type soil reaction models. A comprehensive review of existing soil reaction models for 1-dimensional dynamic pile analysis is presented. This review allowed an assessment of the validity of existing models and identification of their limitations. New shaft and base reaction models are developed that overcome shortcomings of existing models and that are consistent with the physics and mechanics of pile driving. The proposed shaft reaction model consists of a soil disk representing the near field soil surrounding the pile shaft, a plastic slider-viscous dashpot system representing the thin shear band forming at the soil-pile interface located at the inner boundary of the soil disk, and far field- consistent boundaries placed at the outer boundary of the soil disk. The soil in the disk is assumed to follow a hyperbolic stress-strain law. The base reaction model consists of a nonlinear spring and a radiation dashpot connected in parallel. The nonlinear spring is formulated in a way that reproduces realistically the base load-settlement response under static conditions. The initial spring stiffness and the radiation dashpot take into account the effect of the high base embedment. Both shaft and base reaction models capture effectively soil nonlinearity, hysteretic damping, viscous damping, and radiation damping. The input parameters of the models consist of standard geotechnical parameters, thus reducing the level of empiricism in calculations to a minimum. Data collected during the driving of full-scale piles in the field and model piles in the laboratory are used for validating the proposed models

Machinic Utopias, Automated Futures: Scenarios of Potential Automated Futures in Westland

‘Machinic Utopias, Automated Futures’ speculates on the role of designers as active agents addressing the potential implications of automated technologies on urban space in the specific context of the horticultural production center in the Westland. Successive expansions of greenhouses and their typological and technological transformations have resulted in an unprecedented productive cluster that conditions both the spatial character and structure of Westland and its social dynamics. Shortages of high-skilled labor, international competition, and pressures to reduce production costs have prompted growers to invest in automated technologies and machinery. While mostly concealed inside greenhouses and overlooked by municipal visions, this project portrays how these technologies have spatial implications on the surrounding social and built environment, and on the future of work, that need to be addressed by designers in order to conduce the Westland to sustainable modes of urbanization. The project shifts from the socio-economic debate on automation to highlight the spatial implications of this phenomenon. In this regard, it documents emergent technologies and production processes in the horticulture productive cluster and depicts successive accretions in greenhouse sizes that are analogous to radical technological shifts and changes in production patterns. With the help of scenarios, the project formulated possible futures for Westland. An overall strategy consisted of shifting productive premises from one part of the cluster to another. Productive premises were merged with existing urban components to create mixed-use sustainable urban typologies afforded by automated technologies. The project culminated in a design for two pilot projects - Maasdijk and Honderland- and assumed automation as a platform that forced new spatial conditions. It engaged with the emergent phenomenon of automation to stir development in Westland and conduce the area to sustainable modes of urbanization

Landslide susceptibility mapping based on triggering factors using a multi-modal approach

Landslide susceptibility mapping has been done using statistical and physically-based assessment techniques with limited focus on mode-specific models to identify failure modes and runout patterns. Because each failure mode has different consequences, it is essential to identify the failure mode associated with each slope inclination category, triggering factor, and geological setting. This paper presents a multimodal regionalscale assessment procedure for rainfall and earthquake-induced landslides, in the country of Lebanon, where landslide inventories are not available. Three failure modes are studied: debris flows, rock-slope failures, and coherent rotational slides. Areas prone to each mode of failure are identified based on geology and topography, then, using mode-specific models, their susceptibility to landslides is assessed. A runout assessment approach is then presented to identify the influence area of each predicted landslide and to obtain comprehensive susceptibility maps. Field assessment validated the proposed model which was in good agreement with actual slope failures across Lebanon. Therefore, the multimodal approach may be used to assess rainfall-induced landslide susceptibility, especially when landslide inventories are unavailable

Understanding land take in small and medium-sized cities through scenarios of shrinkage and growth using autoregressive models

Rapid transitions induced by migration flows and socio-economic developments brought about massive changes in urbanization processes and resulted in increasingly uncertain futures. The implications and complexities of the ensuing urbanization patterns are difficult to predict and project into the future. While most studies are focused on large cities and major urban centers, urbanization processes in small and medium-sized cities have garnered little scholarly and political attention. To understand future urbanization patterns, we used the TOPOI method, a novel approach for classifying territorial settlements, and spatial autoregressive models to examine contrasting futures of population growth and shrinkage in one small and one medium-sized city in Lower Saxony, Germany. Results revealed that despite planning frameworks, high population density and functional mix, respectively, were insufficient mechanisms to reduce land take. Contrary to current assumptions on the functional mix of small and medium-sized towns, our findings showed that more than half of the settlements across the study area accommodated three or more functions. Since the share of residential buildings and functional mix strongly influenced land take, further research is needed to understand their implications on sustainable urban planning. Shrinking towns in Lower Saxony continue to present multidimensional challenges and emphasize the need for transforming local planning cultures and institutional frameworks to sustainably manage and repurpose these potentially vacant areas