bluuebunny/crossref_metadata_2025 huggingface dataset:
A discontinuous future for numerical modelling in geomechanics?
Authors: Cundall P. A.
Published: November 2009

Finite-element or finite-difference methods are commonly used in geomechanics to model the response of soil or rock at an engineering site. These methods assume that the material is a continuum (although known discontinuities can be included explicitly). There are two drawbacks with continuum methods. Firstly, an appropriate stress-strain law for the material may not exist, or the law may be excessively complicated with many obscure parameters. Secondly, the natural development of cracks and rupture surfaces is not well-handled by continuum approaches. It is suggested that the future trend for numerical modelling in soil and rock may consist of the replacement of continuum methods by particle methods. Assemblies of discrete particles (bonded together to represent rock, and unbonded to represent soil) capture the complicated behaviour of actual material with simple assumptions and few parameters at the micro level. Complex overall behaviour arises as an emergent property of the assembly. The application of particle methods to large-scale problems is currently difficult or impossible because of high computational demands. It is shown that such applications should be feasible within ten years, and certainly within 20 years. Examples are given of the simulation of granular material and rock by particle methods.
GIS as a tool in geotechnical engineering
Authors: Hellawell E. E. , Lamont-Black J. , Kemp A. C. , Hughes S. J.
Published: November 2009

A geographic information system (GIS) is a relatively new software tool for geotechnical engineers. Its capabilities range from conventional data storage to complex spatial analysis and graphical presentation. This paper demonstrates the potential for a GIS to become a powerful, but routine, office tool. It highlights the importance of the geotechnical engineer in both the development and application of the technology. The impact of a GIS within a geotechnical design office is discussed with reference to a number of case histories. These include an archaeological survey, a landscaping assessment, a contaminated land remediation and a construction planning project. Successful application of the technology required a combination of geotechnical knowledge and the GIS-based skills. This was achieved, in practice, by training the geotechnical engineers to be proficient in using the software as well as understanding the GIS concepts. In terms of technical and financial performance, the multi-tasking functionality of the GIS was found to be well-suited to projects in which large quantities of data were analysed. The GIS enabled automation of repetitive and search procedures and quickly became the tool of choice. The GIS opened up opportunities for viewing and analysing data and enhanced the capabilities of the project engineer.
Briefing: Geotechnical engineering and building research: the early days of soil mechanics at BRS
Authors: Penman A. D. M.
Published: November 2009

An essay on the foremost British government soil mechanics laboratory from earliest times to 1957.
Compressibility of foundation fills
Authors: Charles J. A. , Skinner H. D.
Published: November 2009

The current emphasis on locating building developments on brownfield sites, many of which contain substantial depths of fill, means that the behaviour of fills which support the foundations of buildings is of increasing importance. This paper is concerned with the one-dimensional compression behaviour of these foundation fills. Shallow foundations normally rest on partially saturated ground where the major hazard is associated with settlement due to effects other than structural loading. Consequently consideration is given not only to compression induced by an increase in applied stress, but also to compression consequent on an increase in compressibility associated with an increase in moisture content. A programme of laboratory oedometer tests has been carried out on colliery spoil, an opencast mining mudstone backfill, and a boulder clay fill. The test results have given an improved understanding of fill behaviour in one-dimensional compression and, in particular, the effects of partial saturation on the relationship between applied stress and induced strain. The tests have confirmed that vulnerability to collapse compression on inundation will usually be the most significant hazard for buildings founded on fill. Most types of partially saturated fill are susceptible to collapse compression under a wide range of applied stress when first inundated if they have been placed in a sufficiently loose and/or dry condition. Although creep compression can be a problem in some loose fills, collapse will usually be the more serious hazard. For fills placed dry of Proctor optimum moisture content, collapse potential is principally a function of relative compaction.
Earth pressure on cantilever walls at design retained heights
Authors: Day R. A.
Published: November 2009

There are many methods for the analysis and design of embedded cantilever retaining walls. They involve various different simplifications of the pressure distribution to allow calculation of the limiting equilibrium retained height and the bending moment when the retained heightis less than the limiting equilibrium value, i.e. the serviceability case. Recently, a new method for determining the serviceability earth pressure and bending moment has been proposed. This method makes an assumption defining the point of zero net pressure. This assumption implies that the passive pressure is not fully mobilised immediately below the excavation level. The finite element analyses presented in this paper examine the net pressure distribution on walls in which the retained height is less than the limiting equilibrium value. The study shows that for all practical walls, the earth pressure distributions on the front and back of the wall are at their limit values, Kp and Ka respectively, when the lumped factor of safety Fr ≤2·0. A rectilinear net pressure distribution is proposed that is intuitively logical. It produces good predictions of the complete bending moment diagram for walls in the service configuration and the proposed method gives results that have excellent agreement with centrifuge model tests. The study shows that the method for determining the serviceability bending moment suggested by Padfield and Mair 1 in the CIRIA Report 104 gives excellent predictions of the maximum bending moment in practical cantilever walls. It provides the missing data that have been needed to verify and justify the CIRIA 104 method.
Behaviour of joints containing clay infill under constant normal stiffness, with and without bolting
Authors: Indraratna B. , Aziz N. I. , Dey A.
Published: November 2009

The shear behaviour of bolted and non-bolted joints containing infill material was studied under the constant normal stiffness condition. More than 40 sawtooth-shaped samples having an asperity angle of 18·5° were tested. The shear behaviour of bolted and non-bolted joints containing infill material, up to 7·5 mm in thickness, was studied under various initial normal stress levels between 0·13 and 3·25 MPa, at a constant strain rate of 0·5 mm/min and a constant stiffness of 8·5 kN/mm. Significant reduction in shear strength was observed when the joint contained a layer of clay infill of 1·5 mm. Bolting contributed to increasing the strength and stiffness of the joint composite, except at large normal stress levels and at high infill thickness. The dilation and overall friction angle for bolted and non-bolted joints were also compared along with stress profiles. At high infill thickness, the shear behaviour under both constant normal load (CNL) and constant normal stiffness (CNS) conditions was found to be similar for both bolted and non-bolted joints, while at low infill thickness the CNL strength envelope plotted significantly above the CNS envelope.
The observational method—learning from projects
Authors: Powderham A. J.
Published: November 2009

Simplicity is at the heart of the observational method. Its basis is straightforward and it is an inherently natural approach to address uncertainty. The focus on prediction, monitoring, feedback, and teamwork also creates a strong opportunity for learning. Applications typically involve underground construction and temporary works. The objectives are to save cost or time while maintaining an acceptable level of safety. Application of the method was pioneered by Terzaghi and the principles were formally set down by Peck in his 1969 Rankine lecture. Possible modes of failure must be carefully assessed and controlled, particularly those of a sudden or brittle nature, or those that could lead to progressive collapse. Safety is essential and a high degree of certainty in project performance and schedule is generally required. The observational method overcomes the limitations of conventional design by evaluating feedback from actual conditions. This paper describes how simple measurements were central to resolving complexity and controlling risk. It presents three recent case histories featuring the ‘progressive modification’ approach which removed barriers that may have prevented the opportunity to apply the observational method.
Design of a large soil retaining structure with pressuremeter analysis
Authors: Monnet J. , Allagnat D.
Published: November 2009

The A49 motorway runs along the Isère river near Tèche, between Grenoble and Valence, in France, and a large retaining wall was needed there. This structure is an anchored wall, and its design was made with the help of pressuremeter measurements. The pressuremeter tests were carried out with a lantern probe, which was pushed into the soil by dynamic driving. A new pressuremeter theory was used to determine the internal angle of friction of the gravels. The results allowed the best adjustment of the wall to the geotechnical environment. The A49 motorway has been used since 1991 without trouble.
Improved use of pulverised fuel ash as general fill
Authors: Winter M. G. , Clarke B. G.
Published: November 2009

In the UK, the introduction of a tax on landfill and the tightening of planning consents for disposal provided powerful incentives for the use of industrial by-products such as pulverised fuel ash (PFA) in construction. PFA (known as fly ash in some parts of the world) has a long history of successful use as general fill, including applications in environmentally sensitive locations. However, the current commonly used Specification for Highway Works treats PFA as a manufactured material, and applies an end-product specification for compaction. This form of specification is restrictive as it requires that the maximum dry density and optimum moisture content be determined for each consignment of PFA delivered to site, a process that can take up to two days. In addition, the Specification requires testing to determine effective shear strength parameters under fully saturated conditions for embankment design. No guidance is given on whether peak or post-peak parameters are to be selected for design purposes or, indeed, on appropriate factors of safety. As a result, most engineers test PFA in the fully saturated condition, select post-peak effective shear strength parameters for design, and apply a conservative factor of safety. As the testing protocol represents a worst-case scenario the application of such a conservative approach can be questioned. A method specification is more commonly applied to natural fill materials used as general fill. Historical evidence shows that PFA has been placed using a method specification, and that those fills still function as designed. Thus the introduction of a method-based specification for the use of PFA as general fill would make possible its greater use and thus reduce the UK-wide need for landfill.
Three-dimensional effects in the construction of a long retaining wall
Authors: Gourvenec S. , Powrie W. , De Moor E. K.
Published: November 2009

Although long retaining walls are usually analysed in the permanent condition by means of a plane strain analysis, three-dimensional effects may be significant in limiting ground movements at certain stages during construction. This is particularly true for embedded diaphragm-type retaining walls propped at formation level. In this paper, a three-dimensional finite element analysis representing a typical construction sequence for such a wall is compared with a corresponding plane strain analysis and field data from the A4/A46 Batheaston–Swainswick bypass. The results are used to assess the significance of three-dimensional effects during construction, and suggest how these can be utilised to minimise ground movements.
Modelling of particle breakage of coarse aggregates incorporating strength and dilatancy
Authors: Indraratna B. , Salim W.
Published: November 2009

The degradation of coarse aggregates under shear stresses and its influence on the shear strength is studied, considering the energy consumption by particle breakage during shearing. An analytical model is developed relating the deviator stress ratio, dilatancy, friction angle and particle breakage under triaxial loading. Large-scale triaxial testing of latite basalt has been conducted, and the extent of particle breakage during shearing has been quantified. The breakage of particles under monotonic triaxial loading has been considered within the scope of this paper, and the modelling of particle breakage of aggregates under cyclic loading will be presented in a follow-up paper. The results show that the breakage of particles continues to increase beyond the peak deviator stress. The energy consumption by particle breakage is non-linearly related to the particle breakage index. The model also evaluates the effect of particle breakage on the friction angle of ballast. This study sheds further light on the basic angle of friction, which is independent of the breakage of particles during shearing.
Influence of preparation techniques on the index properties of clay
Authors: Navaneethan T. , Sivakumar V.
Published: November 2009

Liquid limit (LL) and plastic limit (PL) are frequently used as indicators of the behaviour of fine-grained materials. These parameters are a prerequisite in every geotechnical investigation. Careful and consistent material preparation is a key component in the laboratory procedures adopted to determine the LL and PL. In preparing samples for such tests, various techniques are used in practice, and this paper examines the influence of these techniques on the actual magnitude of LL and PL measured. The index properties of a glaciolacustrine deposit, locally known as Belfast Upper Boulder Clay, which was laid down in glacial Lake Belfast, are examined. The index properties were determined on samples of the material prepared in different ways, including drying the material at two different temperatures (40°C and 110°C), crushing the dried material from coarse granular to fine granular form by adopting varying degrees of crushing effort, and mixing the dry material with both deionised water and tap water. The results indicate that the crushing procedure has a significant influence on particle size distribution and a consequential effect on the LL and PL. Pore water chemistry and the drying procedure also have a measurable influence on the magnitude of LL and PL.
Recently in Géotechnique
Authors: Bond A.
Published: November 2009

The following are a selection of papers published recently in Géotechnique that readers of Geotechnical Engineering may find of particular interest. The selection concentrates on applied rather than pure research topics and covers issues published from April to September 2002.
Civil Engineering Practice
Authors: Beadman David
Published: November 2009

Civil Engineering Practice is the journal of the Boston Society of the Civil Engineers Section of the American Society of Civil Engineers (ASCE) and is published twice yearly, in the Spring and Fall. Subscription rates outside the USA are $40/year for individuals and $45/year for libraries or corporate bodies. ISSN 0886–9685.

Civil Engineering Practice focuses on practice-oriented papers written by practitioners, regulators and academics, and largely reports projects and research associated with the Boston area. There is the occasional paper dealing with an international project, when design or research for the project has been carried out by an organisation based in the Boston area. About 20% of the papers are concerned directly with geotechnics, and many other papers include aspects of geotechnics. The following papers relate to geotechnics from the 2001 Spring and Fall editions of the journal.
Experimental study of vibrations in underground structures
Authors: Thusyanthan N. I. , Madabhushi S. P. G.
Published: November 2009

Vibrations produced on the ground surface by engineering construction processes can damage underground structures. At present there is little knowledge of the level of surface vibrations that could cause such damage. The relevant British Standards, BS 5228 and BS 7385, have little relevance to underground structures. This paper presents experimental investigations on small model tunnels that were instrumented with miniature accelerometers. Impulsive and vibratory loadings were produced on the soil surface by a drop hammer mechanism and an electric eccentricmass motor respectively to simulate dynamic loading from construction activity. It was found that tunnels with different lining materials absorb different amounts of vibration energy. Power spectrum analysis of the acceleration signals showed that the vibrations are transferred into a brass model tunnel at lower frequencies than for a plastic model tunnel. A relationship has been proposed for the ratio of energy transferred and the ratio of impedance mismatch between soil and tunnel lining. Similar experimental studies can be carried out to understand the energy transfer from ground into underground tunnels with various linings (precast concrete lining, shotcrete or steel).
Acoustic emission monitoring of slope instability: development of an active waveguide system
Authors: Dixon N. , Hill R. , Kavanagh J.
Published: November 2009

This paper introduces the concept of using active waveguides as part of an acoustic emission monitoring system for assessing the stability of soil slopes. In soil, acoustic emissions are generated by inter-particle friction, and hence the detection of acoustic emission is an indication of straining. The components of a field monitoring system are introduced, and the factors controlling design and performance of waveguides are discussed. It is proposed that active waveguides (i.e. those that generate acoustic emission when deformed by the host soil) can be used as an efficient method of obtaining signals from depth within a deforming soil body. The results of laboratory tests conducted to validate the active waveguide model are presented. The role played by the soil surrounding the steel tube waveguide is highlighted. Results from two full-scale field trials that involved monitoring unstable slopes provide evidence for the relationship between detected acoustic emission and slope deformation rate. It is shown that active waveguides in conjunction with relevant signal processing methods can be used to provide an early indication of slope instability.
Lime slurry stabilisation of an expansive soil
Authors: Rao S. M. , Thyagaraj T.
Published: November 2009

Lime slurry and lime pile techniques are viable choices for in-situ stabilisation of expansive soil deposits. This paper reports the results of a laboratory study on in-situ chemical stabilisation of an expansive soil that permeated lime slurry through an artificially desiccated expansive soil specimen. The soil was desiccated in the laboratory to induce shrinkage cracks in the compacted expansive soil. The shrinkage cracks greatly assisted migration of lime slurry in the expansive soil mass. The efficiency of lime slurry in chemically stabilising the desiccated expansive soil was investigated by comparing the physico-chemical properties and engineering properties of the treated soil with those of the natural soil specimen at two radial distances. Experimental results indicated that migration of lime slurry through the desiccated soil promoted strong lime modification and pozzolanic reactions in the soil mass. The strong soil–lime reactions rendered the soil less plastic, reduced the swell magnitude, and increased the unconfined compressive strength of the lime-slurry-treated specimens. Laboratory results indicate that slurry application to soil deposits with shrinkage is effective, and that it may therefore be preferable to chemically stabilise soil deposits during the dry season.
Use of settlement reducing piles to support a raft structure
Authors: Love J. P.
Published: November 2009

This paper introduces the concept of settlement reducing piles (SRPs), describing how they may be usefully employed to improve raft performance in certain ground conditions. A simple method of soil–structure interaction analysis for the incorporation of SRPs is proposed, and a successful case history is presented.
Local settlements and sinkholes due to EPB tunnelling
Authors: Shirlaw J. N. , Ong J. C. W. , Rosser H. B. , Tan C. G. , Osborne N. H. , Heslop P. E.
Published: November 2009

Most of the tunnelling for the North East Line in Singapore was carried out using earth pressure balance (EPB) shields. Settlements were generally well controlled; however, there were occasional large settlements, exceeding the design estimates, sinkholes or losses of ground. Most of the larger surface settlements, sinkholes and losses of ground can be related to the use of insufficient face pressure. Other documented experience of settlements over EPB shields is also reviewed and the same pattern of occasional, but large, settlements or sinkholes is found repeatedly. The factors associated with such settlements are also common in many of the cases reviewed.
Sampling disturbance effects in soft laminated clays
Authors: Long M.
Published: November 2009

Sample disturbance effects in the laminated facies at the Bothkennar soft clay research site are examined by comparing the results of laboratory tests on specimens obtained from three fixed piston tube samplers. A significant feature of the results is that the sampling process associated with the conventional piston tube used in the UK and Ireland appears to increase the post-yield stiffness and the CAUC triaxial undrained strength, reduce the preconsolidation stress and the pore pressure coefficient at failure, and induce a strong tendency for dilatant behaviour post-peak when compared with tests on specimens from a sampler with a modified (sharper) cutting edge angle. It is reasoned that these findings are caused by material destructuration during the sampling process with the conventional tubes. Increased densification of these specimens caused both by sampling and during anisotropic consolidation may also contribute to these effects. The results are supported by reference to recent analytical work and data for three other soils. It is recommended that the use of these conventional thin-walled tubes with a crude cutting edge is abandoned and that some with improved cutting edge geometry replace them.
Approaches to the design of cantilever retaining walls
Authors: Trenter N. A.
Published: November 2009

Cantilever (stem and pad) retaining walls are among the simplest earth-retaining structures to construct, and accordingly may offer significant economic benefits. Their design involves use of bearing capacity and sliding stability theory, and application of the factors of safety laid down in the code to which the designer is working. Two typical L-shaped cantilever walls founded on and retaining dry cohesionless soil are considered, designed in accordance with the procedures given in CP2:1951 and BS 8002:1994. It is shown that the width of the foundation base depends upon which philosophy of factor of safety, and hence which code, is adopted. It is also shown that BS 8002:1994 produces larger (more conservative) foundation bases than the CP2:1951 it replaces, although the difference is significant only for more steeply sloping backfills and deeper foundations.
Optimal design of highway cuttings in residual soils
Authors: Shein A. , Snaith M. S. , Holt C. C.
Published: November 2009

It is argued that rainfall-induced slope failure is the dominant form of instability for highway cuttings in residual soils, and that the optimal slope design should be based on the total cost of the highway cutting over its design life. The maintenance cost in each year of operation can be evaluated by applying the estimated failure rate and the discount factor for that year to the volume of earthwork for repair. A preliminary methodology to predict the failure rate, or probability distribution, of a highway cutting throughout its life has been developed and is presented herein. The proposed design methodology is aimed primarily at the design of highway cuttings in residual soils, which do not contain pronounced structural features such as relict jointing or bedding, and adverse hydrogeological factors. A relatively simple but practical engineering model for the rainfall-induced instability of slopes in residual soils is proposed, based on the concepts of unsaturated soil mechanics. Using this model, failure probability for a highway cutting is estimated, which in turn gives the failure distribution with the age of the slope. The design approach is demonstrated by means of a numerical example. It can be used to choose between options for highway cut design in terms of whole-life cost rather than mainly on the basis of capital cost.
Briefing: Analysis of piled stabilisation of landslides
Authors: Chmoulian Alexander Y.
Published: November 2009

In this briefing the author presents some corrections arising from his experience of use of the pile analysis method outlined in Viggiani's paper ‘Ultimate lateral load on piles used to stabilise landslides’.
Long-term pile testing in London Clay: a case study
Authors: Unwin H. , Jessep R. A.
Published: November 2009

This paper describes how a series of large-diameter auger-bored test piles were constructed for the Terminal Five development at London's Heathrow Airport. The piles were tested over a period of one year, prior to the start of the permanent works, to investigate how the shaft resistance within the London Clay varies with time. The test procedure is described, and some of the results are presented and briefly discussed. A further two piles were constructed to investigate the base resistance in the London Clay at depths of up to 47 m. Osterberg Cells were used to generate the testing force, and the construction and testing of these piles is also discussed in the paper.
Non-linear finite element analysis of piled-raft foundations
Authors: Maharaj D. K. , Gandhi S. R.
Published: November 2009

This paper presents the results of three-dimensional non-linear finite element analysis of raft and piled raft foundations that have been loaded until failure. The raft, pile and soil have been discretised as eight-noded brick elements. The soil has been modelled as a Drucker–Prager elasto-plastic medium. The analyses have been done for a raft, a piled raft, a group of piles and an individual pile. The load–settlement behaviour of all these foundations is presented. The effect of raft thickness and soil modulus on the load–settlement behaviour of rafts and piled rafts is also presented. The axial load distribution for piles in a piled raft foundation is shown, the development of contact stress with increase in loading intensity is presented for rafts, and curves of contact stress against settlement are shown for rafts and piled rafts. The addition of even a small number of piles has been found to increase the load-carrying capacity of a raft foundation. The axial load distribution shows that the piles in a piled raft foundation reach their ultimate capacity earlier than the raft does. The contact stress is found to be minimum at the centre of the raft and maximum at the corner. When the raft reaches its ultimate load-carrying capacity, uniform contact stress is found below the raft except for a very small zone at the corner of the raft. This uniform contact stress is found to be the maximum value that can develop below a raft and a piled raft. The finite element results compare well with the reported literature.
Full-scale load tests on instrumented micropiles
Authors: Russo G.
Published: November 2009

In September 2001, following an exceptional rainfall event with an estimated return time of about 500 years, a number of ancient buildings located in a restricted area in the historical centre of Napoli underwent significant settlement and heavy structural damage. Structural collapse on saturation of the pyroclastic soils and loss of bearing capacity by submersion are believed to be the origin of the observed phenomena. After the settlements came to a standstill, a subsoil investigation was carried out and a remedial solution was designed, based on a massive underpinning of the damaged buildings by micropiles. The size of the project and the well-known dependence of the behaviour of micropiles on technological details suggested that some preliminary load tests on piles should be undertaken. The results of two load tests on instrumented piles installed with different procedures are reported and discussed. A new technique to install embedded vibrating wire gauges was tested, and was revealed to be successful. The experimental findings are in good agreement with the Bustamante and Doix method. Also, the simplified approach proposed by Randolph and Wroth to evaluate the stiffness of the soil layer was checked, providing good results. The experimental finding about the mobilisation of some negative skin friction along the pile shaft, probably due to the large grouted volumes, is confirmed by several finite element analyses.
Comparison of ballast index tests for railway trackbeds
Authors: McDowell G. R. , Lim W. L. , Collop A. C. , Armitage R. , Thom N. H.
Published: November 2009

It is important to have consistent ballast testing methods that provide results reflecting the performance of different ballast materials in the railway trackbed. Extensive laboratory tests have been conducted to investigate the correlation between simple ballast index tests and box tests simulating ballast field loading conditions in a simplified and controlled manner. Ballast is tamped using a vibratory poker, which causes particles to rearrange as the level of the sleeper is raised. The index tests used include single particle crushing tests, oedometer tests, and attrition tests in a revolving drum (WAV, MDA and LAA tests), in addition to water absorption and particle shape characteristics and petrographic analysis. The attrition tests performed in a revolving drum (WAV, LAA and MDA) have been found to give the best correlations with the performance of ballast in the box tests. It is considered that this may be due to the rearrangement of particles in the box test caused by the simulated tamping.
Assessing the contribution of vegetation to slope stability
Authors: Greenwood J. R. , Norris J. E. , Wint J.
Published: November 2009

Many embankments and cuttings associated with the transportation infrastructure in the UK are only marginally stable. Engineering techniques such as soil nailing, geosynthetic reinforcement, improved drainage and ground improvement by stabilisation are available to improve stability, but the cost can be high. A lower-cost solution may be to utilise vegetation, either self-seeded or planted. The benefits and drawbacks associated with vegetation have been the subject of some debate. The problems caused by vegetation in relation to building foundations are well documented, and confirm that vegetation can have very significant influences on geotechnical parameters. Appropriate properly maintained vegetation can have the same significant influence to help provide additional stability to soil slopes. This paper considers the potential engineering influences of vegetation and how it can be characterised on site within a geotechnical framework for stability assessments. The direct reinforcement available from the roots of trees and shrubs is identified as providing one of the most significant contributions to slope stability. Case studies in the UK, Greece and Italy demonstrate how results from in-situ root pull-out tests may be used to estimate the potential reinforcement forces available from the roots. A scheme is presented to designate zones of influence within the soil according to the size and nature of the vegetation.
Jet grouting applications in soft rocks: the Athens Metro case
Authors: Mihalis I. K. , Tsiambaos G. , Anagnostopoulos A.
Published: November 2009

The Athens Metro is an underground project, which is constructed mainly in soft rock conditions (the Athenian schist formation), and has provided extensive experience for all stages of soft rock tunnelling: the geotechnical investigation, the design and the construction. The present work gives an overview of the geological and geotechnical aspects, which are related to the design of the Athens Metro, and places emphasis on the application of jet grouting techniques for the needs of the project. Features and limitations of the applied jet grouting techniques are examined with the aid of executed full-scale trial tests in two sites of the project, where anticipated extreme surface subsidence and severe over-break incidents needed to be adequately confronted. The results from these tests are appropriately evaluated, and conclusions that can be applied to similar geological and geotechnical conditions are derived. Finally, the efficiency of the applied jet grouting techniques, relative to the acceleration of TBM tunnelling operations and to the minimisation of surface settlements, is addressed, with reference to the detailed work progress records and to the settlement measurements obtained by a comprehensive monitoring programme.
Numerical modelling of groundwater pumping processes
Authors: Mavroulidou M. , Gunn M. J. , Woods R. I.
Published: November 2009

Engineers need versatile tools in order to design successful dewatering schemes to counteract the effects of changing groundwater levels in cities. In the present paper, a finite-element program is used to perform pumping analyses, involving moving phreatic surfaces and possible desaturation of materials. First, a problem of local dewatering from a line of wells is analysed, involving desaturation of the soil. The results from an analytical solution as well as those of the numerical model are compared with field data. It is shown that the numerical results, accounting for soil desaturation, are closer to field measurements. Second, the ability of the finite-element program to model falling and subsequently rising groundwater levels in cities due to variable water abstraction (as in the case of London) is assessed. The techniques show promise and are sufficiently flexible to be applied to other geologies and boundary conditions.
Predicting ground displacements caused by pipe-splitting
Authors: Chapman D. N. , Rogers C. D. F. , Ng P. C. F.
Published: November 2009

Pipe splitting is used for the on-line replacement of pipelines made from ductile materials, for example ductile iron and steel. It is a relatively new technique, and so there is limited knowledge about the associated ground displacements, in contrast to the pipe-bursting operations used for pipelines constructed of brittle materials, such as clay, concrete or cast iron. Understanding, and hence predicting, the ground displacements generated by pipe splitting is of vital importance when considering safe distances to other services and controlling possible damage to the road surface. This paper describes the results from some analytical studies that have been conducted in an attempt to develop such a method of prediction, and follows on from a series of full-scale laboratory experiments and an instrumented field trial. The observed ground displacements obtained from this work showed that an elliptical expansion of the soil locally to the existing pipe best represented the general behaviour of the ground for the most common types of pipe splitter currently used in practice. Consequently the analytical work has concentrated on assessing this assumption. The results from these analyses suggest that the elliptical assumption for the localised displacement is generally valid as a first estimate. However, pipe-splitting operations cause more complicated ground displacements than pipe-bursting operations as the displacements are less symmetrical in nature, and are controlled to some extent by the way the pipe-splitting device is used in practice.
Design procedures for installation of suction caissons in sand
Authors: Houlsby G. T. , Byrne B. W.
Published: November 2009

Suction-installed caisson foundations are being used or considered for a wide variety of offshore applications ranging from anchors for floating facilities to shallow foundations for offshore wind turbines. In the design of the caissons the installation procedure must be considered as well as the in-place performance. The scope of this paper is to consider the calculations appropriate for the installation of caissons in sands. Calculation methods are presented for determining the resistance to penetration of open-ended cylindrical caisson foundations both with and without the application of suction inside the caisson. Comparisons are made with case records. A companion paper addresses the calculation procedure for installation in clays as well as in other soils.
Lateral behaviour of composite tapered piles in dense sand
Authors: Sakr M. , El Naggar M. H. , Nehdi M.
Published: November 2009

When used in harsh environments and offshore applications, conventional pile materials (such as steel, timber and concrete) are prone to costly durability problems, such as corrosion in reinforced/prestressed concrete and steel shell piles. Fibreglass-reinforced polymer (FRP) composites provide a corrosion-resistant construction material. FRP–concrete composite piles have been used successfully over the last decade in several projects for fendering applications. This paper investigates the behaviour under lateral loading of FRP composite tapered and cylindrical piles filled with self-consolidating concrete (SCC) and driven in dense sand enclosed in a pressure chamber. Seventeen pile installations were conducted using toe driving and conventional head driving. The piles were subsequently subjected to static lateral load tests. The results show that the pile taper increased its lateral capacity and enhanced its overall performance. A taper coefficient, Ktl, was introduced to account for the taper effect on the lateral response of piles. The experimental results were compared with two commonly used approaches for the analysis of the lateral response of piles: the p–y curves approach and the strain wedge model (SWM). The taper coefficient can be easily incorporated in both methods to account for the effect of pile taper. The comparison between the measured and computed responses showed that both the p–y curve approach and the SWM, modified using Ktl, can be used for the prediction of the lateral response of tapered piles.
Effect of trenchless technologies on existing iron pipelines
Authors: Hunter A.
Published: November 2009

Impact moles and directional drilling units form tunnels of up to approximately 300 mm in diameter at a depth of 1–2 m. They are typically used for the installation of electricity cables or small-diameter pipelines. This type of tunnelling differs from conventional tunnelling owing to the lack of soil excavation. The tunnel is formed by dynamically expelling soil outwards in a predominantly radial direction. This creates a stress and displacement field that has the potential to damage existing services and buildings. To reduce the risk of damage to existing structures installation guidelines detailing acceptable proximity distances need to be provided. This paper details a methodology that has been used to calculate acceptable proximity distances to existing grey iron pipelines that have a transverse geometric configuration to the new pipeline. The study utilises finite difference techniques in conjunction with analytical cavity expansion solutions to determine the stress–strain field induced by tunnelling operations in idealised cohesive and frictional soils. Results from the finite difference study have been used in conjunction with a knowledge of acceptable pipeline strain and joint rotation levels to form acceptable proximity guidelines for this type of tunnelling operation.
A review of modern particle sizing methods
Authors: Abbireddy C. O. R. , Clayton C. R. I.
Published: November 2009

The methods routinely used for the determination of particle-size distribution of soils were introduced about a century ago and have changed little in the intervening period. In other areas, such as chemical and process engineering and sedimentology, there has been considerable development of automated apparatus. This paper presents a critical review of the available methods of determining particle-size distribution. The authors then assess the potential for the replacement of current methods with new technology by applying these methods to a range of synthetic and natural soils, and draw conclusions.
Limit-equilibrium assessment of drystone retaining structures
Authors: Mundell C. , McCombie P. , Bailey C. , Heath A. , Walker P.
Published: November 2009

A limit-equilibrium analysis program has been developed as part of an investigation into the stability of drystone retaining structures. Initial verification of the program's function was in relation to field trials conducted in 1834 by Lieutenant-General Burgoyne, which have been the main reference to date for checking numerical modelling of drystone retaining walls. Parametric studies and investigations of bulging mechanisms are reported and analysed. Program predictions have been compared with the initial results from new small-scale and full-scale drystone retaining wall tests.
Predicting uplift resistance of deep piles with enlarged bases
Authors: Xu H.-F. , Yue Z. Q. , Qian Q.-H.
Published: November 2009

A theoretical method is presented for predicting the uplift resistance of deep piles with enlarged bases. The piles are deeply embedded in soil, so that an axisymmetric logarithmic-spiral (or ‘peach-shaped') slip surface in the soil around the pile is buried underground throughout the uplifting process. The uplift resistance is considered to be equal to the sum of the pile shaft and base uplift resistance as well as the pile weight. The pile shaft and base uplift resistance were derived from the unit skin frictional resistance model and the peach-shaped slip surface model in the soil around the base. The equations associated with the proposed theoretical method are analytically formulated using the classical limit equilibrium method and the axisymmetric pile uplift model. Three base uplift resistance capacity factors, Nc, Nq and Nγ, were obtained, corresponding to the effects of cohesion, surcharge and self-weight respectively. Charts of these three factors are presented at the serviceability failure limit (defined as pile upward displacement equal to 10% of the pile shaft diameter). The proposed theoretical method is then validated with results from full-scale field tests. It is shown that the proposed theoretical method can effectively estimate the uplift resistance capacity at the serviceability failure limit for deep piles with enlarged bases in various soils.
Rate effects during pipeline upheaval buckling in sand
Authors: Bransby M. F. , Ireland J.
Published: November 2009

Knowledge of the uplift capacity of buried pipelines is critical in selecting appropriate burial depths to ensure their stability against upheaval buckling. Much work has focused on their capacity under either fully drained or fully undrained conditions. However, partial drainage conditions may be provoked for low-permeability silty sand seabeds, and this has not been studied in detail. This paper reports a series of physical model tests investigating the effects of pipeline displacement rate on both the uplift capacity of pipelines and the displacements required to mobilise peak load. It is shown that these drainage rate effects can be significant, and the drainage conditions will depend on the dimensionless velocity vD/cv, as suggested by previous researchers studying penetration and foundation problems. A change in normalised pipeline velocity will trigger different degrees of drainage and provoke different deformation mechanisms in the soil, and these will affect the load–displacement response of the pipelines. Designers should consider carefully how rate affects the upheaval buckling resistance of pipelines, especially in silty sands.
Observations of minipile performance under cyclic loading conditions
Authors: Cavey J. K. , Lambert D. V. , Miller S. M. , Krhounek R. C.
Published: November 2009

Pressure-grouted minipiles were installed and tested to evaluate load-carrying capacity under reversed-direction, cyclic loading conditions. The minipiles, expected to support catenary structures along Amtrak's Northeast Shoreline East Corridor, were installed through loose to medium dense sand and silt. Tests were conducted such that loads were applied in varying increments and decrements of the calculated design capacity of 50 kip. Load tests, performed in accordance with the ASTM D1143 Quick Loading Method, showed considerable reduction in capacity after only two cycles of loading at as low as 60% of the ultimate capacity. This observation indicated that, similarly to previous tests on drilled shafts, minipiles installed in cohesionless soils have a critical level of repeat loading that is well below the ultimate pile capacity under static conditions.

Des minipiles cimentées sous pression ont é té installées et testées afin d'évaluer leur capacité porteuse dans des conditions de charge cyclique, à direction inversée. Ces minipiles, qui doivent soutenir des structures de caténaires le long de la ligne Northeast Shoreline East Corridor de Amtrak ont é té installées dans des sables et limons de densité moyenne à meuble. Les essais ont été conduits de facçon a` ce que les charges soient appliquées en divers incréments et décréments de la capacité nominale calculée de 50 kip. Les essais de charge, effectués en conformité avec la méthode de chargement rapide ASTM D1143, ont montré une nette réduction de la capacité après seulement deux cycles de chargement à un bas niveau—60% de la capacité ultime. Cette observation indique que, de meê;me qu'avec les essais précédents sur des puits forés, les minipiles installeés dans des sols non cohésifs ont un niveau critique de chargement répétitif qui se situe bien en dessous de la capacité ultime de la pile en conditions statiques.