Negative skin friction on single piles and pile groups

Ph.DDOCTOR OF PHILOSOPH

Coastal Geohazard and Offshore Geotechnics

With rapid developments being made in the exploration of marine resources, coastal geohazard and offshore geotechnics have attracted a great deal of attention from coastal geotechnical engineers, with significant progress being made in recent years. Due to the complicated nature of marine environmnets, there are numerous natural marine geohazard preset throughout the world’s marine areas, e.g., the South China Sea. In addition, damage to offshore infrastructure (e.g., monopiles, bridge piers, etc.) and their supporting installations (pipelines, power transmission cables, etc.) has occurred in the last decades. A better understanding of the fundamental mechanisms and soil behavior of the seabed in marine environments will help engineers in the design and planning processes of coastal geotechnical engineering projects. The purpose of this book is to present the recent advances made in the field of coastal geohazards and offshore geotechnics. The book will provide researchers with information reagrding the recent developments in the field, and possible future developments. The book is composed of eighteen papers, covering three main themes: (1) the mechanisms of fluid–seabed interactions and the instability associated with seabeds when they are under dynamic loading (papers 1–5); (2) evaluation of the stability of marine infrastructure, including pipelines (papers 6–8), piled foundation and bridge piers (papers 9–12), submarine tunnels (paper 13), and other supported foundations (paper 14); and (3) coastal geohazards, including submarine landslides and slope stability (papers 15–16) and other geohazard issues (papers 17–18). The editors hope that this book will functoin as a guide for researchers, scientists, and scholars, as well as practitioners of coastal and offshore engineering

Application Study of Self-balanced Testing Method on Big Diameter Rock-socketed Piles

Through the technological test of self-balanced testing method on big diameter rock-socketed piles of broadcasting centre building of Tai’an, this paper studies and analyzes the links of the balance position selection, the load cell production and installation, displacement sensor selection and installation, loading steps, stability conditions and determination of the bearing capacity in the process of self-balanced testing. And this paper summarizes key technology and engineering experience of self-balanced testing method of big diameter rock-socketed piles and, meanwhile, it also analyzes the difficult technical problems needed to be resolved urgently at present. Conclusion of the study has important significance to the popularization and application of self-balanced testing method and the similar projects

Application of a discrete element model to the analysis of granular soil recovery in an offshore tubular vibrocore

As the human need for ocean resources accelerates, offshore geotechnics continues to grow and become ever more relevant. Seabed soil sampling is crucial in deep-water engineering projects or geological studies where a detailed knowledge of the seabed geology is required. Deep-sea vibrocoring is a relatively new offshore sampling technique. The system consists of a vertical, tubular core barrel with a sharp cutting edge at its lower end vibrated into the seabed by a high-frequency, low-amplitude vibratory motor. In the past, success of a coring operation has been judged primarily by the length of the recovered core. More recently, studies have given focus to the problems associated with achieving soil specimens in which the in-situ sedimentary structure is preserved. In practice, the core recovery ratio - defined as the ratio between the sampled length of core sediment and the length of core barrel penetrated into the soil - is frequently less than unity. Literature suggests that the physical processes governing the dynamic interaction between core barrel and soil are poorly understood. Through review of relevant literature, and the execution of both physical testing and numerical modelling, this study aimed to a) Develop a calibrated 30 discrete element model of a given vibrocore-soil system, and b) Investigate the soil mechanics phenomena influencing the disturbance and recovery of vibrocore soil samples

A study of impact breakage of single rock specimen using discrete element method

Comminution is a critical stage of mineral processing which aims to reduce the size of ore particles through breakage, consequently increasing the likelihood of the liberation of valuable minerals. However, comminution is highly energy-intensive and an understanding of the key breakage mechanisms has been identified as an important factor in improving the efficiency of the process. Several factors, such as pre-existing cracks, mineralogical composition, ore shape and size are known to affect ore breakage behaviour during breakage. To investigate breakage mechanisms, it is important to be able to determine how individual factor influences the breakage behaviour of rock specimens. However, isolating and investigating individual factors under experimental conditions is challenging and typically impractical. Numerical techniques such as the Bonded Particle Model-Discrete Element Method (BPMDEM) have been developed as a means of investigating in isolation, the effects of different factors on ore breakage behaviour under closely controlled breakage conditions using synthetic rock specimens. This study investigates how individual factors influence rock specimen breakage using BPM-DEM numerical methods. Numerical simulations were conducted using ESyS-particle 2.3.5, an open-source discrete element method (DEM) software package which uses Python-based libraries to generate geometries and simulations and a C++ engine for mathematical computations. Empirical calibration relationships were developed to relate microstructural model parameters to the macroscopic mechanical properties that are typically obtained from standard geotechnical breakage experiments. The robustness of the model was evaluated by considering the sensitivity of fracture measures to the variation of model resolution, size-dependency and macroscopic mechanical properties (Young's modulus and uniaxial compressive strength) of the numerical specimens. A comparative study of single rock specimen breakage using the current BPM-DEM and laboratory SILC experiments carried out by Barbosa et al. (2019) was conducted. The measured fracture force and fracture patterns at different sizes for both cylindrical and spherical synthetic rock specimens were examined. Furthermore, the model was used to study, in isolation, the influence of pre-existing cracks in rock specimens and differing mineralogical compositions upon measurable breakage properties. Numerical rock specimens with pre-existing cracks were constructed using a microcrack approach, while a unique approach with the insertion of "seed points" was developed and demonstrated to construct numerical rock specimens with varying mineralogical compositions. Results from the numerical simulations showed that a high model resolution with a sufficiently large number of DEM-spheres exhibited results with the least deviation and error with respect to fracture measures, and, was therefore considered numerically stable. The dependency of fracture measurements on specimen size showed an expected increase in the measured fracture force as the specimen size increases. The variation of the macroscopic Young's modulus and uniaxial compressive strength against the fracture measures emphasised that the locus of these mechanical properties against the fracture measure can be used to specify a calibration relationship. Results of the comparative study showed that for both cylindrical and spherical rock specimens, the DEM consistently predicted the fragment patterns as well as the increase in the measured fracture force as the specimen size increased. The investigation on the effect of pre-existing cracks revealed that an increasing number of pre-existing cracks in rock specimens necessitated lower fracture force and consequently produced a low amount of new fracture surface area. For the binary phase mineralogical composition in the study, it was found that the fracture force decreased with an increase in the concentration of the softer component due to the increased percentage of weakness in the specimen. It was concluded that, with an appropriate calibration exercise and a realistic specification of material properties from the evaluation study, the DEM as a tool was sufficient to act as a "virtual laboratory" to isolate and study the individual effects of factors that influence ore breakage. The understanding of these results highlighted two important points. Firstly, this study was able to unravel some of the possible causes of the inefficiency in comminution practices, whereby significant amounts of energy can be expended to achieve minimal gains in respect of enhancing liberation due to pre-weakening and mineralogical composition. Secondly, it emphasised some of the causes of the variation observed during ore characterisation on a laboratory breakage device, attributable to pre-weakening and mineralogical composition

Physical and semi-analytical modelling for geosynthetic reinforced piled embankment

Ph.DDOCTOR OF PHILOSOPH

Measured performance of slurry walls

Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2002.Includes bibliographical references (p. 355-361).This thesis evaluates the measured performance of 29 slurry wall supported excavations in Boston, Chicago, Washington DC, and San Francisco - most of which have been constructed since 1980. Each of these case studies includes data on the initial site conditions (soil profile and properties, groundwater conditions and location of adjacent facilities etc.) and designs for support of the excavations. The main goal is to relate construction records to the measured performance of the lateral earth support systems. The principal parameters of interest are the induced ground deformations (and their effects on adjacent structures) and observations of groundwater flows. The actual monitoring data always include inclinometer measurements of lateral deflections within the diaphragm wall and/or adjacent soil. However, other information such as surface settlements, building settlements, heave of the sub-grade or piezometric data were only archived for some of the projects (nearly all in Boston). Even fewer projects contain measurements of structural forces in either the diaphragm wall or bracing system. These data have been grouped according to the soil profile, toe fixity of the wall and type of bracing system (tie-back anchors, prestressed cross-lot and top-down). Most of the projects have succeeded in allowing only small wall deflections, often less than 0.2% to 0.3% of the total excavation depth, and similar magnitudes of the maximum surface settlements. Larger wall movements did occur in several projects but have been linked to either inadequate bracing (poor tieback design or inadequate pre-stressing of rakers), lack of toe embedment or ground softening inside the excavation (installation of drilled caissons or load bearing elements). Unexpectedly large surface settlements in one project (Dana Farer) were clearly linked to ground loss during tieback installation. Several other reported cases of leakage (through panel joints and/or tiebacks) have been repaired by grouting. Given the limited availability of archival data, the thesis has focused on the interpretation of lateral deflections. Wall deformations have been sub-divided into rigid body translation, rigid body rotation and bending modes. Empirical correlations have been proposed for estimating each of these components.b y Dimitrios C. Konstantakos.M.Eng

Non-linear analysis of pile groups under general loading conditions

A computer program (called PGROUPN) has been developed for the non-linear analysis of pile groups subjected to any combination of vertical loads, horizontal loads and moments. The code is based on a complete boundary element approach and may be regarded as a generic descendant of the program PGROUP (Banerjee & Driscoll, 1976) which has been extended in order to make the analysis numerically efficient for practical problems and to include the effects of soil nonlinearity by means of a stepwise linear incremental procedure. One of the main advantages of a non-linear analysis system over a linear elastic approach is that it has the desirable effect of demonstrating a reduction of the corner loads in larger groups in both the vertical and horizontal senses. This observation is of basic importance in practice because it offers the prospect of tangible improvements in design procedures and potential saving of materials. The non-linear analysis put forward in this thesis may be applied to large pile groups embedded in cohesive soil, specifically fully saturated clay under undrained conditions. The soil is modelled as an elastic-perfectly plastic material, which is assumed to behave linearly elastic at small strain levels, but fails when the stresses at the pile-soil interface reach certain limiting values. The analysis only requires the definition of three soil parameters whose physical meanings are clear, ie the (initial tangent) Young’s modulus Es, the Poisson’s ratio vs and the undrained shear strength Cu. This represents a significant advantage over more common load-transfer approaches which are based on either empirical parameters or the results of full-scale pile load tests. The validity and accuracy of the proposed PGROUPN solution have been verified by comparison with alternative numerical analysis for single piles and pile groups subjected to axial and lateral loads. Benchmark solutions in the linear and non-linear range are presented, and the critical question of estimation of soil parameters is addressed. Finally, two published case histories are described which demonstrate the applicability of the method to practical problems

Response of piled buildings to the construction of deep excavations

Trends in the construction of deep excavations include deeper excavations situated closer to buildings. This research provides insight into mechanisms of soil-structure interaction for piled buildings adjacent to deep excavations to be used in the design and monitoring of deep excavations in urban areas. Most methods to assess building response have originally been developed for tunnelling projects or buildings with shallow foundations. Monitoring data of the construction of three deep excavations for the North South metro Line in Amsterdam, The Netherlands have been used to validate these methods specifically for piled buildings. In all three of the Amsterdam deep excavations studied, the largest impact on the ground surface and buildings is attributed to preliminary activities instead of the commonly expected excavation stage. The in situ preliminary activities caused 55-75% of the surface settlement and 55-65% of the building settlements. Surface settlements measured behind the wall were much larger than the wall deflections and reached over a distance of 2-3 times the excavated depth away from the wall. The shape of the surface settlements found resembles the hogging shape as defined by Peck (1969). For the excavation stage only, the shape of the displacement fits the profile proposed by Hsieh and Ou (1998). Most prediction methods overestimate the soil displacement at depth. An analytical method has been established and tested for the behaviour of piled buildings near excavations. This method includes the reduction of pile capacity due to lower stress levels, settlement due to soil deformations below the base of the pile and development of negative (or positive) skin friction due to relative movements of the soil and the pile shaft. The response of piles in the case of soil displacements depends on the working load of the pile, the percentages of end bearing and shaft friction of the pile, the size and shape of the soil settlements with depth and the distribution of the maximum shaft friction with depth. A method is derived to determine the level for each pile at which the pile and soil settlement are equal. Buildings in Amsterdam built before 1900 and without basement are most sensitive to soil displacements. For all other buildings, the pile settlement depends mainly on the working load. The actual damage experienced in buildings depends also on the relative stiffness of the building compared to the soil. Cross sections in Amsterdam have been evaluated and it is concluded that the Goh and Mair (2011) method provides a realistic, although rather large range of possible modification factors for the deflection of buildings next to excavations, deforming in hogging shape. For the incidents that happened at Vijzelgracht some well known damage indicators have been evaluated.This works was supported by Deltares and COB The Netherlands

On the significance of stratigraphy in the prediction of the engineering behaviour of soils and rocks in Southern Africa

The object of this thesis is to demonstrate that a knowledge of the stratigraphic unit occupying a site provides a basis for making broad generalisations regarding likely terrain and foundation conditions which may be used to advantage in designing a relevant site investigation programme. Stated simply: very different exploration programmes would be designed for a house on Oranqe Grove quartzite and a dam on Transvaal dolomite. If climate as well as stratigraphy, is taken into account we may recognise a Regional Stratigraphic unit and achieve a higher level of generalisation which will lead to more accurate predictions being made regarding the likely engineering properties of the local rocks and soils. Subdivision of the regional stratigraphic unit into land patterns, and of land patterns into their constitutent land facets, represent yet further advances from lower to higher levels of generalisation. Apart from specific case histories, however, it is the regional stratigraphic unit that is adopted as the main level of discussion throughout most of the thesis. The importance of the correct identification of the origin of each horizon of the soil profile during site investigation work is emphasised as this, too, may lead to meaningful predictions regarding the engineering behaviour of the soil. The significance of the pebble marker as an aid to the correct identification of soil origin is also emphasised. The introductory chapter concludes with a number of very broad generalisations about the typical forms of the soil profile in Southern Africa and the environmental factors responsible for their development.Thesis (DSc)--University of Pretoria, 1977.GeologyDScUnrestricte