130,492 research outputs found
MODELLING OF PILED RAFT FOUNDATIONS IN SAND
No full textA piled raft is a composite foundation in which the piles are used as
settlement reducers and they share, with the raft, the load from the
superstructure. The applied load is transferred from the raft to the
shallow soil and to the pile heads, and from the piles it is diffused
through the shaft and the base to deeper soil. The pile–raft and pile–pile
interactions represent the distinctive aspect of the piled raft foundations
since they modify the load–bearing behaviour of each foundation
component, compared to an analogous isolated element, thus determining
the overall foundation behaviour.
The main aim of this thesis is to highlight the effects of the raft–soil–pile
interactions on the resistance and stiffness of axially loaded piled raft
foundations in sand.
A series of centrifuge tests on models of rigid circular piled rafts in loose
saturated sand has been performed to this end, employing both non
displacement and displacement piles. The raft settlement and the load
transmitted to the pile heads and bases were monitored during the tests,
which also included unpiled raft and isolated pile tests.
The test results have been analysed in terms of bearing capacity and
stiffness; the former according to a load efficiency method, the latter by
comparing the values obtained from centrifuge tests with those evaluated
through a simplified analytical method.
ii Modelling of Piled Raft Foundations in Sand D. Giretti
In order to clarify the effect of the pressure transmitted by the raft to the
soil on the behaviour of a single capped pile, some of the centrifuge tests
were simulated via finite element numerical analyses, using an elasto–plastic strain hardening constitutive model for the sand. The geometry
and the dimensions of the numerical models corresponded to those of the
physical ones and the simulations were carried out applying an
accelerated gravitational field to the mesh.
The influence of a granular layer, interposed between the raft and the pile
heads, on the load transfer mechanism has also been analysed, through an
additional series of centrifuge tests which was performed on square rigid
raft models on displacement piles in dry dense sand
Density specifications for hydraulic fills [Specifiche per la compattazione di riempimenti idraulici]
No full textA common problem with hydraulic fills arises during construction when acceptance criteria are considered. Contractual disputes are mainly related to degree of compaction and they arise largely because of poor specifications. A good specification is one that can be measured unambiguously in the field using reliable equipment. This paper describes the engineering process which should be followed during design and construction of hydraulic fills, starting from conceptual design all the way through to construction and subsequent use of the fill, focusing on the density requirements, specifications and acceptance criteria for density of the fill. It provides a methodology to specify the density of the fill, which will avoid most of the typical pitfalls related to hydraulic fills. This paper takes the CIRIA publication on Hydraulic Fills (Hydraulic Fill Manual for Dredging and Reclamation Works”, van’t Hoff and van der Kolff, 2012) as its starting point developing further considerations to supplement what is given in that document and in doing so tries to establish what is current best-practice
Teaching Construction in the Virtual University: the WINDS project
No full textThis paper introduces some of the Information Technology solutions adopted in Web based INtelligent Design Support (WINDS) to support education in A/E/C design. The WINDS project WINDS is an EC-funded project in the 5th Framework, Information Society Technologies programme, Flexible University key action. WINDS is divided into two actions: ·The research technology action is going to implement a learning environment integrating an intelligent tutoring system, a computer instruction management system and a set of co-operative supporting tools. ·The development action is going to build a large knowledge base supporting Architecture and Civil Engineering Design Courses and to experiment a comprehensive Virtual School of Architecture and Engineering Design. During the third year of the project, more than 400 students all over Europe will attend the Virtual School. During the next three years the WINDS project will span a total effort of about 150 man-years from 28 partners of 10 European countries. The missions of the WINDS project are: Advanced Methodologies in Design Education. WINDS drives a breakdown with conventional models in design education, i.e. classroom or distance education. WINDS implements a problem oriented knowledge transfer methodology following Roger Schank's Goal Based Scenario (GBS) pedagogical methodology. GBS encourages the learning of both skills and cases, and fosters creative problem solving. Multidisciplinary Design Education. Design requires creative synthesis and open-end problem definition at the intersection of several disciplines. WINDS experiments a valuable integration of multidisciplinary design knowledge and expertise to produce a high level standard of education. Innovative Representation, Delivery and Access to Construction Education. WINDS delivers individual education customisation by allowing the learner access through the Internet to a wide range of on-line courses and structured learning objects by means of personally tailored learning strategies. WINDS promotes the 3W paradigm: learn What you need, Where you want, When you require. Construction Practice. Construction industry is a repository of ""best practices"" and knowledge that the WINDS will profit. WINDS system benefits the ISO10303 and IFC standards to acquire knowledge of the construction process directly in digital format. On the other hand, WINDS reengineers the knowledge in up-to-date courses, educational services, which the industries can use to provide just-in-time rather than in-advance learning. WINDS IT Solutions The missions of the WINDS project state many challenging requirements both in knowledge and system architecture. Many of the solutions adopted in these fields are innovative; others are evolution of existing technologies. This paper focuses on the integration of this set of state-of-the-art technologies in an advanced and functionally sound Computer Aided Instruction system for A/E/C Design. In particular the paper deals with the following aspects: Standard Learning Technology Architecture The WINDS system relies on the in progress IEEE 1484.1 Learning Technology Standard Architecture. According to this standard the system consists of two data stores, the Knowledge Library and the Record Database, and four process: System Coach, Delivery, Evaluation and the Learner. WINDS implements the Knowledge Library into a three-tier architecture: 1.Learning Objects: ·Learning Units are collections of text and multimedia data. ·Models are represented in either IFC or STEP formats. ·Cases are sets of Learning Units and Models. Cases are noteworthy stories, which describes solutions, integrate technical detail, contain relevant design failures etc. 2.Indexes refer to the process in which the identification of relevant topics in design cases and learning units takes place. Indexing process creates structures of Learning Objects for course management, profile planning procedures and reasoning processes. 3.Courses are taxonomies of either Learning Units or a design task and Course Units. Knowledge Representation WINDS demonstrates that it is possible and valuable to integrate a widespread design expertise so that it can be effectively used to produce a high level standard of education. To this aim WINDS gathers area knowledge, design skills and expertise under the umbrellas of common knowledge representation structures and unambiguous semantics. Cases are one of the most valuable means for the representation of design expertise. A Case is a set of Learning Units and Product Models. Cases are noteworthy stories, which describe solutions, integrate technical details, contain relevant design failures, etc. Knowledge Integration Indexes are a medium among different kind of knowledge: they implement networks for navigation and access to disparate documents: HTML, video, images, CAD and product models (STEP or IFC). Concept indexes link learning topics to learning objects and group them into competencies. Index relationships are the base of the WINDS reasoning processes, and provide the foundation for system coaching functions, which proactively suggest strategies, solutions, examples and avoids students' design deadlock. Knowledge Distribution To support the data stores and the process among the partners in 10 countries efficiently, WINDS implements an object oriented client/server as COM objects. Behind the DCOM components there is the Dynamic Kernel, which dynamically embodies and maintains data stores and process. Components of the Knowledge Library can reside on several servers across the Internet. This provides for distributed transactions, e.g. a change in one Learning Object affects the Knowledge Library spread across several servers in different countries. Learning objects implemented as COM objects can wrap ownership data. Clear and univocal definition of ownerships rights enables Universities, in collaboration with telecommunication and publisher companies, to act as "education brokers". Brokerage in education and training is an innovative paradigm to provide just-in-time and personally customised value added learning knowledg
Sul comportamento di una fondazione mista in presenza di uno strato granulare interposto tra platea e pali.
No full textSettlement prediction of shallow foundations for quality controls of sandy hydraulic fills
No full textThis paper describes a procedure for settlement prediction of shallow foundations on carbonate sands, but it is fully applicable and valid for siliceous sands. For practical purposes, the design of shallow foundations resting on medium dense and dense granular soils is typically governed by limiting settlement to tolerable values. Predicting foundation settlement is therefore important, but in standard practice it is necessarily based on indirect (and therefore often conservative) determinations of soil compressibility (or modulus), due to the intrinsic difficulties in obtaining direct measurements.While numerical analyses incorporating non-linear soil behaviour may be a preferred method for computing expected total and differential settlement of shallow foundations of given geometry and stiffness on sand under static loading, the method described in this paper consists of a simplified and expeditious method based on equivalent linear elasticity. The method uses: i) the elastic soil stiffness profile at small strain, E0(z) obtained from the shear wave velocity as the primary measurement of deformability and ii) the reduction in modulus as a function of strain magnitude, E(ε) to account for stiffness non-linearity. The beneficial effect on the soil initial stiffness of the applied footing load is also considered. The method was developed as an on-site tool for checking the compaction of hydraulic fills made of carbonate sand to form artificial islands, but its application can be extended to other natural and anthropogenic coarse-grained materials
Mechanical properties of a carbonate sand from a dredged hydraulic fill
No full text This paper focuses on the properties of a crushable, uncemented, carbonate sand, retrieved from an artificial island to be used for petroleum production offshore of the United Arab Emirates. The sand was dredged from an offshore borrow area, placed hydraulically within engineered bunds to create the island and densified by vibroflotation. The results of a comprehensive laboratory testing programme are summarised in this paper, providing a set of mechanical properties for carbonate sand. The laboratory programme included static, cyclic and dynamic tests, the results of which are interpreted in a critical state soil mechanics framework, including stress dilatancy. The results of this testing programme contribute to on-going research on the behaviour of carbonate sands under static and cyclic loading conditions. The results are also compared with selected data for other carbonate and siliceous sands, and highlight the behaviour of crushable, carbonate sands used as hydraulic fills. </jats:p
Liquefaction assessment based on centrifuge CPTs
No full textThe paper presents a semi-empirical method for the liquefaction assessment based on CPTs. The cone resistance qc and the cyclic resistance CRR of a un-aged, un-cemented soil depend on the same properties: type of soil, fabric, stress level and density. The latter two quantities can be synthesized through the state parameter ψ, which in this paper is used to link qc, measured via centrifuge CPTs, to CRR, derived from cyclic undrained triaxial tests. A relationship between the normalized cone resistance and ψ was calibrated from the results of 27 centrifuge CPTs on dry Ticino Sand (TS4) models. The results of 16 cyclic undrained triaxial tests on TS4 were interpreted to define a correlation between ψ and CRR at a given number of cycles N. The centrifuge and triaxial test results were combined to deduce a direct relationship between the normalized cone resistance and the CRR, which can be used for liquefaction assessment from field CPTs.
Introductio
Mechanical properties of a carbonate sand from a dredged hydraulic fill
No full textThis paper focuses on the properties of a crushable, uncemented, carbonate sand, retrieved from an artificial island to be used for petroleum production offshore of the United Arab Emirates. The sand was dredged from an offshore borrow area, placed hydraulically within engineered bunds to create the island and densified by vibroflotation. The results of a comprehensive laboratory testing programme are summarised in this paper, providing a set of mechanical properties for carbonate sand. The laboratory programme included static, cyclic and dynamic tests, the results of which are interpreted in a critical state soil mechanics framework, including stress dilatancy. The results of this testing programme contribute to on-going research on the behaviour of carbonate sands under static and cyclic loading conditions. The results are also compared with selected data for other carbonate and siliceous sands, and highlight the behaviour of crushable, carbonate sands used as hydraulic fills
Physical Modeling of Raft on Settlement Reducing Piles
No full textThe paper presents the results of extensive centrifuge tests modeling rigid circular piled rafts laying on a bed of loose very fine silica sand. The tests were aimed at investigating the behavior of rafts on settlement reducing piles. The testing program included: an unpiled raft, rafts on 1, 3, 7 and 13 piles. In each test, some model piles were instrumented with load cells to determine the distribution of load along the shaft. Beneath the rafts, two types of model piles, close-ended and free headed were installed: quasi displacement (QD) and quasi-non displacement (QND) piles. The obtained results permitted figuring out the role of piles in terms of their effectiveness as settlement reducers and to quantify the load sharing mechanism between piles and the raft-soil contact. The tests were aimed at investigating the load transfer mechanisms adopted in the design approach, and in particular at validating a numerical code which can be used in engineering practice. The paper describes the details of experiments undertaken, the adopted procedures and some of the results; where not specified, all the experimental data given in this paper referred to model scale. The adopted numerical code is briefly described and its validation, via test results on quasi-non displacement piles, is also reported
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