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Deep foundations of a high-rise building : An in-situ testing and numerical study
Abstract
The construction of high-rise buildings in urbanized area can be subject to several constraints. When the loads transferred to the foundations become high a shallow foundation becomes insufficient. This is where piles are used to transfer the loads to deeper soil layers or to reduce the settlement. The design of the structure and the foundations starts by a good understanding of the behavior of the ground, the piles and the pile-soil interface subjected to high loads. In the framework of the project “Fondasilex”, this thesis proposes the study of the pile foundations in the tower “Silex2” built in Lyon, France. It is founded on 20 piles, 1.22 m in diameter and 15.5 m deep, which are bored into three layers of fluvial alluviums and anchored in the Miocene molasse. The soil in Lyon is poorly characterized in the literature, which is likely to lead to an oversizing of the foundations and consequently a high increase in construction costs. This thesis presents the geotechnical auscultation and numerical modeling performed within this project which aim to characterize the soil of Lyon and the pile-soil interaction, to predict the long-term behavior of the structure, the foundations and the soil and then to constitute a base of experience to help in the study of other towers planned on the Part-Dieu neighborhood. This work was accompanied by laboratory testing carried out on the alluvial and molasse samples extracted from the site. In the first part, an instrumentation of the foundations and the soil was set up to enable the real-time monitoring of their behavior. It consists of a fiberglass rod extensometer connected to 6 displacement sensors that measure the settlement of the soil at six different depths, concrete pressure cells and strain gages of two types (electrical resistance and vibrating wire) which measure respectively the stress on the head of the piles and the deformation at three positions. At the same time, the pile deformation was also measured using fiber optic sensors using the OFDR technique based on Rayleigh scattering. These measurements were analyzed in the light of the construction progress of the steel structure. In the second part, numerical models were carried out on FLAC3D, based on the finite difference method. A sensitivity analysis performed on an isolated pile model helped to understand the influence of each of the model parameters on the pile’s response. Models with two or more piles were also used to study the group effect that may occur. A perfectly plastic elastic law with a Mohr-Coulomb criterion and the Plastic-Hardening Model were found suitable to represent the behavior of the alluviums and molasse respectively. These laws have been calibrated and validated using the instrumentation and laboratory tests (triaxial, oedometer and shear box tests) carried out, due to the absence of a static pile load test.
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The main purpose of this paper is to present a new method for analysis group efficiency of frictional piles in granular soils. This method is based on consideration of the shear around the perimeter of the group defined by the plan dimensions + the bearing capacity of the block dimension at the points. Thus, the analysis presented here is based on frictional resistance of piles combine to point load in granular or sand soil and some other factors similar to the analysis presented by Sayed and Bakeer. Besides, the stiffness of the pile cap also confirmed that it influence significantly to the distribution of the structural loads to the individual piles and this factor was examined in the presented method. The results from numerical analysis and full-scale field test have obtained a good match together also shown that numerical modeling techniques may come to a suitable agreement with practical experiment results to analyze for group efficiency of piles.
Prestressed high-strength concrete (PHC) pipe pile with the static press-in method has been widely used in recent years. The generation and dissipation of excess pore water pressure at the pile–soil interface during pile jacking have an important influence on the pile’s mechanical characteristics and bearing capacity. In addition, this can cause uncontrolled concrete damage. Monitoring the change in excess pore water pressure at the pile–soil interface during pile jacking is a plan that many researchers hope to implement. In this paper, field tests of two full-footjacked piles were carried out in a viscous soil foundation, the laws of generation and dissipation of excess pore water pressure at the pile–soil interface during pile jacking were monitored in real time, and the laws of variation in excess pore water pressure at the pile–soil interface with the burial depth and time were analyzed. As can be seen from the test results, the excess pore water pressure at the pile–soil interface increased to the peak and then began to decline, but the excess pore water pressure after the decline was still relatively large. Test pile S1 decreased from 201.4 to 86.3 kPa, while test pile S2 decreased from 374.1 to 114.3 kPa after pile jacking. The excess pore water pressure at the pile–soil interface rose first at the initial stage of consolidation and dissipated only after the hydraulic gradient between the pile–soil interface and the soil surrounding the pile disappeared. The dissipation degree of excess pore water pressure reached about 75–85%. The excess pore water pressure at the pile–soil interface increased with the increase in buried depth and finally tended to stabilize.
For friction piles depending on the friction resistance, accurate prediction of unit skin friction around the pile shaft is the dominant resistance to measure the final bearing capacity of a bored-pile. The present study measures the stress–strain transferring in two instrumented bored-piles (BP #1 & BP# 2) embedded within the soil layer in Kuala Lumpur by real-time monitoring global strain extensometer (GSE) sensors. Two bored-piles (i.e., having 1.80 m and 1.0 m diameters, as well as 36 m and 32 m lengths) have been loaded with two times to their design working loads. Extensive data are analyzed to measure the changes in stress–strain in the bored-pile. The effect of loading and unloading stages on the pile’s head and base settlement has been monitored, indicating that Young modulus of elasticity in concrete bored-pile ( Ec ), average strain, and unit skin friction changed along the bored-pile based on the ground site conditions and stress registered. One example of two case studies with great real-time monitoring data has been provided to further design
Distributed fibre optic sensing (DFOS) presents several advantages over traditional point sensors, for measuring strain and temperature in civil and geotechnical infrastructure. DFOS techniques use light transmitted through an optical fibre to enable measurements to be taken all along an embedded or surface-mounted fibre optic cable, which can be up to several kilometres long. This makes DFOS particularly useful for monitoring linear structures and to detect the potential existence of any anomalies which are usually unpredictable. Hence, DFOS has gained in popularity for monitoring reinforced concrete piles, especially during pile testing. The spatially continuous strain data from DFOS provide detailed information about load transfer along the pile but can also be used to calculate vertical displacements and shaft friction through numerical integration and differentiation, which are useful for validating relevant performance-based numerical models. This paper introduces the methodology and illustrates these advantages through an example obtained from an instrumented pile load test in London. While it synthesises a number of lessons learned in the application of DFOS for pile testing, it also supports the case for routine long-term monitoring of working piles.
Instrumented pile tests are vital to establish the performance of a pile and validate the assumptions made during initial design. Conventional instrumentation includes vibrating wire strain gauges and extensometers to measure the change in strain or displacements within a pile. Although these strain and displacement gauges are very accurate, they only provide strain/displacement readings at discrete locations at which they are installed. It is therefore common to interpolate between two consecutive points to obtain values corresponding to the data gaps between points; in practice, these discrete instrumented points could be tens of meters apart, at depths corresponding to different soil layers, and hence simple interpolation between the measurement points remains questionable. The Brillouin optical time-domain reflectometry fiber optic strain sensing system is able to provide distributed strain sensing along the entire length of the cable, enabling the full strain profile to be measured during a maintained pile load test. The strain data can also be integrated to obtain the displacement profile. This paper presents three case studies which investigate the performance of three concrete bored piles in London using both conventional vibrating wire strain gauges and distributed fiber optic strain sensing during maintained pile load tests, which enable comparisons made between the two instrumentation systems. In addition, finite-element analyses show that the ability to measure the full strain profiles for each pile is highly advantageous in understanding the performance of the pile and in detecting any abnormalities in the pile behavior.
This article is focused on the analysis of the use of distributed fibre-optic technology for security monitoring of road tunnel and motorway tunnel structural load. The authors focused on the measurements of deformation utilizing Brillouin Time Domain Reflectometry (BOTDR). The principle is based on the measurement of stimulated Brillouin scattering. The article describes and analyses real measurements within a period of 5 months, which were carried out during the tunnelling and the whole process of building a new tunnel in Žilina, Slovakia. The performed experimental measurements were carried out using a standard optic telecommunication cable with water-absorbing aramid yarns and a jacket with a diameter of 4.2 mm. The contribution of this article lies in the introductory analysis of the implementation and use of the fibre-optic technology for security monitoring of road tunnel and motorway tunnel structural load.
Reliable prediction of settlement behaviour of axially loaded piles is one of the major concerns in geotechnical engineering. Therefore, this paper focuses on the finite element solutions of load-settlement behaviour of a single pile and pile group using PLAXIS numerical package. Three different types of analysis were incorporated: a linear elastic analysis, a complete nonlinear analysis and a combined analysis. The pile case history with settlement measurements made during field pile load test was considered to validate the single pile load-settlement simulation, and the same load test result was extended to simulate the load-settlement behaviour of pile group using RATZ analytical approach. The single pile analysis results suggest that realistic load-settlement predictions can be drawn by considering complete soil as Mohr-Coulomb model at lower working loads, and incorporation of an interface zone thickness of two times pile diameter using Hardening-Soil model is required to simulate the load-settlement behaviour at higher working loads. The group pile analysis results provide a better load-settlement prediction when incorporating an interface zone thickness of pile diameter from the pile shaft using Hardening-Soil model while leaving the remaining soil as Linear-Elastic material.
À Lausanne, comme partout ailleurs avant l’avènement du chemin de fer, les hommes ont puisé dans la roche locale pour construire leurs maisons en dur. Il se trouve que dans cette ville, le sous-sol est essentiellement constitué de Molasse grise, un grès tendre facile à tailler que l’on retrouve sur les parements de la cathédrale Notre-Dame où il vieillit tant bien que mal avec l’édifice depuis le XIIIe siècle.
Ce vieillissement s’accompagnant de formes d’altération spectaculaires, la Molasse grise de Lausanne est qualifiée de « mauvaise » pierre. La présente contribution se propose de discuter le pourquoi, le comment et l’importance de l’altérabilité de cette pierre.
The Defence Science and Technology Group has been conducting full-scale fatigue tests of ex-service F/A-18 Hornet centre fuselages, in support of the Royal Australian Air Force’s structural integrity management programs for its frontline fighter fleet for over 12 years. Historically, conventional electrical resistance foil strain gauges have been used extensively on these tests to monitor and record the structural response to loading; however, there are limitations with these in terms of cost, installation times and physical complexity. Developments in commercially available, distributed fibre optic strain measurement systems presents the opportunity to overcome these limitations, as demonstrated on the most recent centre fuselage test article. Based on Rayleigh scattering, the system (‘ODiSI B’ by Luna Innovations) was trialled which allowed comparisons of strain response, spatial resolution and noise levels with conventional foil gauges. Comparisons were also made of the full-field strain mapping capability of the system with full-field stress mapping by thermoelastic stress analysis. Furthermore, the distributed fibre optics demonstrated their potential to detect crack propagation on a coupon with induced crack growth.
The application of structural health monitoring (SHM) systems to civil engineering structures has been a developing studied and practiced topic, that has allowed for a better understanding of structures' conditions and increasingly lead to a more cost-effective management of those infrastructures. In this field, the use of fiber optic sensors has been studied, discussed and practiced with encouraging results. The possibility of understanding and monitor the distributed behavior of extensive stretches of critical structures it's an enormous advantage that distributed fiber optic sensing provides to SHM systems. In the past decade, several R & D studies have been performed with the goal of improving the knowledge and developing new techniques associated with the application of distributed optical fiber sensors (DOFS) in order to widen the range of applications of these sensors and also to obtain more correct and reliable data. This paper presents, after a brief introduction to the theoretical background of DOFS, the latest developments related with the improvement of these products by presenting a wide range of laboratory experiments as well as an extended review of their diverse applications in civil engineering structures.
Analyses are made of the settlement interaction between two compressible floating piles in a semi- infinite mass, and between two compressible piles resting on a rigid bearing stratum. The results of these analyses are expressed in terms of interaction factors relating the increase in settlement due to the second pile to the settlement of a single pile. It is shown that, as previously found with incompressible floating pile groups, the interaction factors for two piles may be superposed to analyze the settlement and load distribution within any compressible pile group.
The objective of this paper is to evaluate the performance of three constitutive soil models, i.e. Morh-Coulomb model (MC model), Hardening soil model (HS model) and Hardening soil model with small strain stiffness (HSS model), implanted in PLAXIS software, for predicting movements induced by a deep excavation in sands. A case history of deep excavation in thick layers of sand, which is well documented in Kaohsiung city, Taiwan, was adopted as a basic for the numerical analyses in this study. The back analysis method was used to determine input parameters that cannot be directly obtained from tests or reliably empirical equations. In addition, parametric studies were also conducted to evaluate the sensitivity of important input parameters of the MC, HS and HSS models, which were obtained by the back analysis method. Results pointed out that the HSS model yields the best predictions of the wall deflections and ground surface settlements, and the MC model gives the worst results. This study can be helpful to engineers and researches to perform numerical analyses using the constitutive soil models more confidently.
The numerical analysis of pile-soil interaction commonly requires a lot of trial works to determine the interface parameters and the accuracy cannot be ensured normally. Considering this, this paper first conducts a sensitivity analysis to figure out the influence of interface parameters on the bearing behavior of a single pile in sand. Then, a simplified method for the determination of pile-soil interface parameters in layered soil is proposed based on the parameter studies. Finally, a filed loading test is used for the validation of the simplified method, and the calculated results agree well with the monitoring data. In general, the simplified method proposed in this paper works with higher accuracy and consumes less time compared with the traditional trial works, especially on the determinations of interfacial cohesive and interfacial friction angle. © 2015 Higher Education Press and Springer-Verlag Berlin Heidelberg
Results obtained by using the Hrennikoff's method did not agree closely with observed field data in terms of the distribution of loads in the piles. The finite element (FE) method was therefore used to predict the behavior of the lock structure. The FE method simulated major steps of construction including the in situ stress condition, dewatering, excavation, construction of piles and lock, backfilling, filling water in the lock, and development of uplift pressure. Nonlinear behavior of soils and interfaces between the lock and surrounding soils and between the piles and the foundation soils were introduced into the analysis. The distribution of load in piles from the FE analysis showed improved agreement with the field data in comparison with the agreement shown by the Hrennikoff's method. The FE computations verified satisfactorily the measured displacements, and the trend that the piles on the backfill side carried increased contribution of the applied load.
An excellent subsurface investigation is necessary. Good construction techniques are needed, as well as proper inspection. The shear strength of the supporting soil is reduced during construction. Small shafts cannot be constructed successfully. Soil movements during construction are minimized. Exposed soil during construction verifies previous subsurface investigations. The size of the shaft may be adjusted. Drilled shafts can be built rapidly, as compared with other types. Pile caps may be eliminated on many jobs, leading to appreciable economy. Construction noise is tolerable as compared to other types of construction of deep foundations. A good subsurface investigation is important to obtain engineering properties of the soil for design computations and selecting the construction procedure.
A great amount of earthquakes have caused the collapse of important structures along the history. The design of earthquake-resistant structures depends greatly of the soil-structure interaction. This interaction implies the consideration of relative movements and load transfer mechanism simultaneously. Dealing with liquefiable soils the generation of pore pressure should also be considered.Pile system constitutes a common foundation of structures resting on soil layers of low stiffness and strength in seismic zones. More recently rigid inclusion systems were utilized. The difference is that in the rigid inclusion systems, the rigid elements are separated from the foundation slab by an earth platform that is able to transfer the surface loads and dissipate energy coming from the seismic loading.This manuscript studies the behavior, through numerical models, of inclusions systems (soil-inclusion-platform-structure) and pile systems (soil-pile-structure) considering soft soils under seismic loadings. Finite difference numerical models were developed using Flac3D. Several types of soils were utilized in drained and undrained conditions. For the undrained cases, the analyses were carrying out using dynamic coupled fluid-mechanical simulations with accuracy the behavior of soils. The Rayleigh damping approach was applied to provide additional damping in the elastic part when simple elasto-plastic constitutive models were considered.The objective of the investigation is the identification of the impact of important factors in the response of the analyzed systems. Factor such as the foundation type, the frequency of the input motion, the dynamic characteristics of the structure, the soil profile and the relative density were investigated. Considering the pile and rigid inclusion foundations, the support conditions, the pile group configuration, the pile length, the embedment of the foundation were also examined.Additional and important aspects of numerical model were also explored like the model geometry, dynamic boundary conditions, element size, interface elements, structural element types, dynamic loading.Results in terms of movements and stresses in the soil, superstructure and rigid elements were obtained. They show the great influence of some parameters in the response (accelerations, displacements, efforts, strains, pore pressure) of the evaluated systems. Others highlight the importance of a type of failure in the elements of the system.Keywords: pile; rigid inclusion; numerical modelling; dynamic analysis; soil structure interaction; liquefaction
A completely revised edition of a comprehensive reference on foundation engineering.It is published in colour. It has been published in two separate editions: (a) Hardbound US edition, and (b) softbound SI edition.
This work presents a simplified approach for the nonlinear analysis of the load–displacement response of a single pile and pile groups embedded in multilayered soils. A hyperbolic model is used to capture the relationship between the skin friction and the pile–soil relative displacement developing along the pile–soil interface. The shaft displacement is assumed to be composed of the pile–soil relative displacement developing at the disturbed soil around the pile shaft and the elastic vertical soil displacement developing in the soil mass. The relationship between the shaft displacement and the skin friction is then presented. Moreover, a hyperbolic model is also used to capture the relationship between end resistance and pile end displacement. Considering the interactive effect among piles, hyperbolic models of an individual pile in pile groups are proposed. As to the analysis of the response of a single pile and pile groups, considering the progressive deformation of the pile–soil system, a highly effective iterative computer program is developed using the proposed hyperbolic models. Comparisons of the load–settlement responses demonstrate that the proposed method is generally in good agreement with the field-observed behavior and the calculated results derived from other approaches.
This article presents a general review of contemporary instrumentation concepts and procedures as applied to geotechnical engineering projects in soft clay. The need for instrumentation is discussed, and the types of measurements most frequently required as well as the measurement techniques generally employed are pointed out. A number of hypothetical case studies are presented in order to illustrate the need for observational programmes and to indicate the function of instrumentation in relation to the principal geotechnical problems that are characteristic of the examples cited.(a) /TRRL/
This research is concerned to analyze the behavior of the pile under axial load and to find the ultimate pile capacity regards to present of weak soil layer and cavity using (Plaxis-2D) as a finite element method. The soils and pile is modeled as Mohr-Coulomb and linear elastic non-porous respectively by using axi-symmetric model. 15-node triangle element used to model and interface elements is defined by five pairs of nodes. A total of 37 cases is studied, the first group included piles embedded in dense sand with layer of weak soil ( = 25º and 30º) at different thickness and locations (24 cases), while the second group included 12 cases for existing of cavity with different diameters and locations. The ultimate capacity of the pile for the above cases are compared with pile embedded in dense soil, (1 case). The results obtained from numerical work are compared with those obtained by analytic Berezantsev method and a good agreement has been found. The results indicated that existing of weak soil layer within the surrounding soil around the pile decreases the ultimate pile capacity. This reduction depends on thickness, and depth of the weak layer. The ultimate capacity ratio for the pile decreases as the depth of the weak soil layer increased along the pile shaft. The minimum values was found when the weak soil layer located near pile tip. Also, the ultimate capacity of the pile decreases as the thickness of the weak soil layer increased. The variation between the ultimate capacity ratios with weak soil layer thickness seems to be liner, for all cases for weak soil layer properties. Presented of cavity reduced the ultimate capacity ratio for the pile, the most dangerous situation when the cavity located near the pile base. At this condition the ultimate pile capacity ratio range between (0.8873 – 0.8101).
It is axiomatic that those who have the greatest interest in reliable and high quality field data should have a major role in specifying the requirements and obtaining the data. Despite this, many contracts assign the responsibility for selecting geotechnical instruments and for field instrumentation services to people with fragmented roles and limited interest in the overall process. Two general categories for procurement of geotechnical instruments, and for the associated field instrumentation services are considered in this article: the lowest-price method and the professional service method. Pros and cons of both are discussed, and recommendations made for the use of the latter. The various tasks that relate to geotechnical instrumentation and monitoring are defined, and references are cited that give the views of others in the profession. The authors hope that this article will be useful when trying to convince decision-makers to adopt professional service methods.
Les inclusions rigides sont un concept récent développé dans le prolongement des fondations mixtes, avec un matelas de transfert de charges entre les colonnes et la structure. Des méthodes de calculs et des concepts de sécurité existent pour ces systèmes combinés, notamment en France où le module pressiométrique mesuré et les recommandations ASIRI (IREX 2012) pour les inclusions rigides sont utilisés. Le dimensionnement classique des pieux basé sur une simple vérification de la portance des colonnes isolées ne peut pas être appliqué à ces systèmes combinés. Les tassements peuvent être plus importants du fait de la part significative de charge reprise par le sol. Le présent travail est une contribution au développement des méthodes de calcul et de dimensionnement en déplacement (préconisé par l'Eurocode 7, EN 1997-1 2004) pour les systèmes combinés sous charge verticale, en particulier au niveau international où des mesures in situ de module de sol ne sont généralement pas disponibles. Les éventuelles particularités de ces systèmes, notamment la sensibilité de colonnes non renforcées de petit diamètre, devaient également être examinées. La méthode de transfert de charge (“load transfer method”, LTM) est identifiée comme un outil d'ingénieur particulièrement adapté au calcul des systèmes combinés présentant une géométrie relativement simple. L'interaction sol-colonne en frottement et en pointe est définie par des courbes de transfert de charge (ou courbes “t-z” et “q-z”). Les méthodes en milieu continu comme la méthode des éléments finis sont à réserver en général aux cas complexes. Le comportement non-linéaire des semelles est examiné sur la base de mesures obtenues dans la littérature. Cette étude aboutit à la proposition d'une courbe charge-tassement hyperbolique pour les semelles. Cette courbe de mobilisation est définie de sorte qu'il y ait concordance avec la méthode linéaire habituelle pour un tiers de la charge ultime de la semelle. Le comportement de pieux isolés est étudié avec de nombreux essais de chargement instrumentés et non-instrumentés pour différents types de pieux et de sol. Une alternative aux courbes de transfert de charge selon Frank et Zhao (1982), basées sur le module pressiométrique, est recherchée. Des courbes de transfert de charge de type racine cubique et hyperbolique sont proposées pour tous types de pieux et de sol. La raideur des courbes proposées dépend d'une bonne estimation des valeurs ultimes de frottement et de résistance de pointe. Au contraire, la raideur initiale des courbes de Frank et Zhao est entièrement définie par le module pressiométrique, ce qui permet d'éviter des erreurs en termes de raideur. Les courbes de mobilisation proposées pour les fondations superficielles et pour les pieux sont combinées et étendues au cas des systèmes combinés. Cette méthode est implémentée comme option LTM dans le programme KID (Keller company 2015). Les prévisions avec le modèle proposé sont en très bonne adéquation avec les mesures effectuées sur 3 sites documentés dans la littérature. Une étude paramétrique montre une transition continue entre la fondation mixte et les inclusions rigides et une possibilité d'optimisation avec une diminution significative des efforts dans les colonnes et dans la fondation superficielle si un matelas est utilisé. En complément, une comparaison avec des calculs en éléments finis en 3D dans un cas théorique de semelle sur colonnes confirme que la méthode de transfert de charge développée est très performante pour des géométries simples. Une analyse de sensibilité est effectuée avec des modèles éléments finis axisymmétriques et 3D avec Plaxis (2013, 2014). Les imperfections géométriques ont principalement une incidence sur l'intégrité structurelle des colonnes non-armées de faible diamètre. Cependant, ces effets sont atténués dans les systèmes combinés en comparaison avec la colonne isolée du fait des possibilités de redistribution des charges dans le système
Since the technology has moved strongly into a number of different areas a textbook of this sort could be used by a wide variety of academic departments including physics, electrical engineering, mechanical engineering, civil engineering, aerospace engineering and bioengineering. To make the second edition as widely appealing as possible a series of significant upgrades were made. 1. The book is structured to support a variety of academic programs and it can also be used as a general reference by practicing engineers and scientists. 2. The introductory chapter has been revised to outline the new content of the second edition and provide a overview of the current status of fiber optic sensor technology. 3. A new, extensive chapter has been added covering fiber optic grating sensor technology and its application to aerospace, civil structures, oil and gas and power generating applications. 4. A second new chapter has been added on the emerging field of biomedical fiber optic sensors. This is one of the most rapidly growing fields of use for fiber optic sensors and with rising health costs and medical advances promises to be an important area for many years to come.
Conventional instrumentation method of incorporating high temperature-resistant strain gauges into the heatcured production process of spun piles is extremely unpopular due to high cost of these gauges and the uncertainty over their ability to survive the pile production and driving processes. Due to these difficulties, the engineering community has been using an approximate instrumentation method for the past few decades, by installing an instrumented steel pipe into the hollow core of spun piles followed by cement grout infilling. The shortcoming of this method is the infilling of cement grout substantially alters the structural properties of the piles, thus rendering their load-response behaviour significantly different from that of the actual working piles. This paper describe the use of Global Strain Extensometer technology, a state-of-the-art deformation monitoring system for monitoring loads and displacements at various levels along the pile shaft and toe of instrumented spun concrete piles. Recent case histories are presented to demonstrate the advantages of this novel instrumentation technology. Results show high quality, reliable and consistent data, clearly far exceeding the capability of both conventional and approximate methods.
In the past, the design of a pile in a given soil against undue settlement has entailed lengthy numerical analysis for a variety of pile geometries. Similarly the back analysis of load tests on piles has usually been accomplished by repeated analysis with differing soil stiffness profiles in order to arrive at the profile which gives best agreement with the measured results. The recent development of an approximate close form solution for the problem of a vertically loaded pile has enabled these two processes to be considerably simplified. The present paper takes the solution as developed and extends it to the case of piles bearing on a stiffer stratum of soil. The solution may then be used both for the design of single piles and also for the back analysis of pile tests.
A simple method to account for the effects of nonlinearities in the analysis of pile foundations is presented. A short outline of current methods of analysis is first given; a simple approach is then proposed to account for the influence of the nonlinear response of a single pile on the distribution of a given load. The results obtained following this approach are presented and discussed, and some final considerations are given.
The Brillouin optical time domain reflectometer (BOTDR) is a newly developed measurement and monitoring technique, which utilizes Brillouin spectroscopy and optical time domain reflectometer to measure strain generated in optical fibers and distributed in the longitudinal direction. Hence, the BOTDR has the characteristics of distributed measurement, long distance, high precision and durability. In this paper, the basic principle and features of the BOTDR are briefly introduced; and taking Nanjing Gulou Tunnel as a case, the technical and monitoring schemes of BOTDR are presented; the installation of sensing optic fiber and the temperature compensation method are introduced; the influence of environmental factors such as temperature and vibration on the measurement results is discussed. Finally, the monitoring results of the tunnel are analyzed and the health diagnosis is given. The monitoring achievements demonstrate that the BOTDR is a feasible and powerful technique for the strain measurement and health diagnosis of the tunnel engineering.
An analytical formulation is derived to fit the observed relationships and utilized to govern the behavior of a one- dimensional element which serves as the interface between two dimensional soil and retaining wall elements in finite element analyses. Analyses are presented of a retaining wall- backfill system with varying modes of wall behavior and degrees of wall roughness. Earth pressure distributions before the ultimate conditions are reached are shown to be nonlinear. Ultimate conditions and general behavior of the system are shown to be in agreement with classical theory. Simulation of the exact construction sequence of a retaining wall- backfill system.
Ultimate loads of shallow foundations were analyzed. Rational compressibility criteria for soils subjected to foundation loads was formulated. It was shown that the greatest shortcoming of available theories lied in the unreserved assumption of soil incompressibility. The conventional, static analysis of bearing capacity can be used for footings subjected to moderately rapid loadings.
Data are presented herein on the increase in supporting capacity of a pipele with the passage of time, the distribution of applied loads along the pile, and the pore-water pressu res developed in the soil adjacent to the pile when given into soft, saturated clay. Soil test data are interpreted to determine the effect of pile driving on the clay and the resis tanc e of the clay to movement the pile. A procedure is prese nted for using the results of vane shear tests determine the relationship between load and settlement for a pile driven to clay.
The performance degradation of secondary lining is the main disease that affects the operation of tunnel, monitoring the secondary lining is an important means to ensure the tunnel operate healthily. The changes of secondary lining are studied to apply embedded FBG strain sensor. According to the layout schemes of FBG and temperature compensation technology, the strain variation of the tunnel cross-section is analyzed. The results show that the data curve trend reflects changes in the tunnel secondary lining, the effective support is provided for disease forecasting further. ©, 2014, Editorial Board of Optical Technique. All right reserved.
A simplified approach for nonlinear analysis of the load-displacement response of a single pile and a pile group is presented using the load-transfer approach. A hyperbolic model is used to capture the relationship between unit skin friction and pile-soil relative displacement developed at the pile-soil interface and the load-displacement relationship developed at the pile end. As to the nonlinear analysis of the single pile response, a highly effective iterative computer program is developed using the proposed hyperbolic model. Furthermore, determinations of the parameters related to the hyperbolic model of an individual pile in a pile group are obtained considering interactions between piles. Based on the determinations of the parameters presented in the hyperbolic model of an individual pile in a pile group and the proposed iterative computer program developed for the analysis of the single pile response, the conventional load-transfer approach can then be extended to the analysis of the load-settlement response of an arbitrary pile in a pile group. Comparisons of the load-settlement response demonstrate that the proposed method is generally in good agreement with the field-observed behavior and the calculated results derived from other approaches.
A parametric study was carried out to investigate the collapse of a buttress retaining wall that occurred at Malveira, Portugal. Typical values of interface properties for retaining wall problems are discussed, as well as the influence of friction, cohesion, normal and shear stiffness at the interface between the wall and soil. Results show that for this interface, the greater the friction angle is, the more the retaining wall inclines, and so does the cohesion along the interface. However, the influence of cohesion on the deformation of soil behind the wall is greater and more sensitive than that of the friction angle. The normal and shear stiffness also have significant effects upon the analysis results. A definite cause of instability happens when shear stiffness is low to maintain continuity of displacements between the wall and the retained soil. Reasonable values of stiffness are dependent on the properties of both the soil and the retaining wall. Main findings of this study are related to the advantages of using interface elements for accurately simulate the real behavior of buttress retaining walls, which indicate that the main cause of the observed collapse was due to a difference in depth with respect to the design documents, and no field measures were taken to improve the safety factor against overturning.