Geosynthetic materials are used in many different applications in the civil and underground engineering. In most cases, the use of geosynthetic material replaces the use of other materials. The authors quantify the environmental performance of commonly applied construction materials (such as concrete, cement, lime or gravel) versus geosynthetics. To this end a set of comparative life cycle assessment studies have been carried out concentrating on various application cases, namely filtration, foundation stabilised road, landfill construction and slope retention. The environmental performance of geosynthetics is compared to the performance of conventional construction materials used for the same application. The specifications of the four construction systems were established by the members of the Association for Geosynthetic Manufacturers (EAGM), which represents the European market for geosynthetic materials, and these specifications represent best current practice.
Sulphate-containing clay soils are know to cause swelling with the application of lime, due to the formation of expansive compounds. Laboratory tests were carried out to examine the potential of fly ash to limit swelling. Artificial soil samples with a 4:1 sand / montmorillonite ratio and 2% added sulphate (in the form of gypsum), were combined with 6% hydrated lime and 3,6, 9 or 12% fly ash or 3,6 or 9% ground granulated blast furnace slag (GGBS). Cylindrical specimens with a 4:1 solids / moisture ratio were compacted under a fixed load and immersed in water at room temperature until their linear expansion levelled off. Most changes occurred within 10-11 days with fly ash and 5-6 days with GGBS. Both treatments gave similarly reduced expansion to that with GGBS, compared to the lime-stabilised artificial soil control. A further field study with relevant UK clay soils was conducted, comparing quicklime with and a range of UK fly ashes. Mellowing periods of 0, 1 and 3 days were considered. Specimens were prepared in accordance with BS EN 13285-53. After one day of fog room storage, the specimens were immersed in a water bath at room temperature and their linear expansion determined after 7 and 14 days. There was an increase in swelling with sulphate level, with Oxford and Kimmeridge clays giving greater expansions than those of London or Lias strata. In addition, swelling of Oxford clay continues after 7 days. Addition of fly ash to the mixes consistently reduced swelling with addition of 12-18% required. Fly ash reduced swelling of lime-stabilised clay soils, with increasing levels and coarser materials producing better results.
The standard (dynamic) penetration test (SPT) is one of the most commonly used in situ tests to determine density and subsequently the in situ strength of granular soils for use in bearing capacity analysis. The test is regularly used in the UK and it it has become common to multiply the SPT N value by a factor of five to provide a very approximate value of undrained shear strength. Research carried out showed that there was little if any relationship between SPT N values ans the undrained shear strength or the coefficient of volume compressibility for fine soils within the geographical area of South Lanarkshire. Consequently the continued use of historical empirical correlations is questioned. The guidance given in Eurocode 7 that the use of SPT should be restricted to a 'qualitative evaluation of the soil profile' as there is 'no general agreement on the use of SPT results in clayey soil' is borne out by the results of the study undertaken by the authors. The implications of Eurocode 7 are debated and the need for further debate of the implications within the industry is emphasised.
Chemical grout injection is a popular method for improving the stability and reducing the permeability of alluvial soils, but it is not always clear if the methodology adopted in a particular application of the practice represents the most efficient or cost-effective option. It is possible to use simple formulae to aid in the selection of injection parameters and to understand their inter-relationship, as well as to optimise injection spacings and times with respect to injection source dimensions and in situ permeability. A better understanding of these parameters can assist when it comes to calculating the real cost of an injection programme and how to modify a scheme in progress to gain the best result. The grout injection schemes considered in this paper are applicable to alluvial soils where a two-stage cement / chemical injection programme is usually used. It is suggested that the theory behind injection work has to bend to the art, as the ground is not an idealised material, and ongoing examination and probable revision to the injection design is the indicator of a job well done.
In July 2007 the European Standard covering the Standard Penetration Test(SPT), BS EN ISO 22476-3 : 2005 was fully implemented into UK practice. It is similar in general terms to the old BS1377 Part 9 : 1990 but requiresthat the energy ratio (Er value) be measured for the hammer when the measured penetration resistance (N value) is going to be used for the quantitative evaluation of foundations or for comparing results. The standard requires that a certificate of calibration of the Er value be available and provides a recommended method for determining the energy ratio and reportingthe results. This study focuses on the measurement of the energy ratio and the results and additional criteria that can be used to determine best practice and quality assurance for the SPT. It is shown that the SPT is farfrom standard. The variability induced by the test equipment, which can be accentuated by poor operation and maintenance, is described. These effects can be assessed by the regular measurement of the energy ratio. Other issues relating to the use of the SPT are discussed.
Reflection seismology. or seismic reflection, is a sophisticated and powerful method of geophysical investigation that has become a cornerstone of the hydrocarbon exploration industry and of earthquake investigation. The technique enables imaging of geological stratigraphy and structure to depths of several kilometres and had been fundamental to the mapping of much of the world's hydrocarbon reserves. The need to investigate to greater depths for geotechnical applications is coupled with increasing subsurface information requirements associated with major infrastructure construction projects such as bridges and dams, nuclear power and waste facilities, geothermal / groundwater exploration, carbon sequestration and natural gas storage. The rapid improvement in computing power, plus more sensitive recording hardware, has meant that some of the approaches used in hydrocarbon work can be scaled for geotechnical applications. However land seismic receivers are sensitive to both ambient ground motion and , airborne acoustic noise and to ambient electrical fields. In general shallow land seismic surveys deploy a single source but multiple receivers. Careful positioning ofsource and receiver locations is critical to shallow investigation work. To image shallow targets, receiver intervals need to be kept small but this has a trade-off in terms of the number of receivers and associated recording channels required per line-km, labour costs and overall productivity.Very shallow surveys (<50m depth) require sources to generate high frequencies in excess of 150Hz to resolve fine detail and, from a processing perspective, to discriminate refracted from shallow reflected energy. Practical considerations when conducting tests, particularly in noise environments are described. modern processing software for shallow applications is largely scaled down from oil and gas applications, but the processing can besimplified to four key elements: signal deconvolution, velocity analysis,CMP stacking and migration. Major construction projects are not limited to seismically benign locations, so a seismic reflection investigation could form part of a seismic risk evaluation.
The widening of the M1 motorway between junctions 25 and 28 has presentedmany challenges to the project team of joint venture contractor MVM (Morgan Est, Vinci and Sir Robert McAlpine) and designer Gifford. The project involves the engineering of 48km of embankment and cutting slopes to accommodate additional traffic lanes on both the north and the southbound carriageways. The working space was constrained by the existing motorway and site clearance limitations set down in the environmental statement. Ground challenges included backfilled open cast coal sites, highly fissured limestone and areas of historic mining. Investigation of the failure of an apparently benign cut slope consisting of stiff gravelly sandy clay overlying middle coal measures indicated that there were two groundwater regimes in the vicinity of the a former open cast mining site. A series of trial excavatioos showed that the remedial works consisted of a geogrid reinforced slope repair. A layer of fine to coarse sand at the base of the remedial works was probably intended as a drainage layer. The slope also showed signs of further distress. As part of the widening works the slope failure was excavated, which revealed a fluvio-glacial channel within the coal measures coincident with the failure. The final design reflected the need to ensureadequate groundwater drainage leading to the specification of a free draining material in the cutting along with removal of the weaker lining to the buried channel.
The placing of the final sections of the second Tyne road tunnel in Newcastle is described. The 1.6 km tunnel, which will eventually carry southbound traffic, has required a variety of tunnelling techniques. The 360 m main crossing uses an immersed tube made up of four elements which have been constructed at the nearby Neptune dry dock. The construction of the elements, each 90 m long and 15 m wide, is outlined. Tubes are built to the same profile as the river bed and each contains 10,000 tonnes of concrete. Details are provided of the transport and positioning of the elements, processes restricted by the state of the tide. Trenches were excavated in 2009 with the material being used for infilling a dock as part of a redevelopment plan. Elements are lowered at night with the aid of divers and connections made using pressure. Details are given of the cross section of the tunnel which is only the third immersed tube to be built in the UK.
Construction of the Canary Wharf Crossrail station in London is described. 310 steel tubular Giken piles have been lowered through water into the dock bed using silent piling technology and a coffer dam has been installedto hold back water from outside the work site and the dock has now been fully drained. A network of 14 dewatering wells was installed in the chalkto remove water from below the clay. Teamwork at the site has made for effective savings against the forecast cost. The next stages of the project will involve the excavation of the dock bed to begin work on the ticket concourse, followed by excavation to the track level to meet the arrival of the tunnel boring machine. The planned completion date for the entire station box is 2015.
Environmental challenges and a unique geology have delayed construction of the planned 19-km fixed link between Roedbyhavn in Denmark and Fehmarn in Germany. The options of a bridge or a tunnel have been considered. In the tunnel option, four running tunnels would be required for both road and rail traffic, and the excavation would cause considerable environmental impact. With a cable stayed bridge, cast in situ concrete or steel piles to depths of 25m would be required. the ground investigation process has found an unusually high level of fat clays which have a liquid limit of over 50, and are some of the most extreme in Europe with a plasticity of around 150. The fat clays that lie around the island of Fehmarn have a flow problem since they have been dislocated by glaciers. A false tunnel of 50,000m3 has been excavated to monitor the behaviour of the clay and steel and concrete pile tests are also in progress. It is planned to complete the link in 2018.
Field monitoring in the UK has shown that during dry summers, shrinkage of high plasticity clay embankments occurs, causing railway track deformation requiring speed restrictions. Charing Embankment in Kent, UK, is believed to have been built in 1874and is 590m long with a maximum height of 8.5m. The embankment was constructed by end-tipping, without compaction, the locally excavated Gault clay. A clod and matrix structure exists where clods of original clay are surrounded by a matrix of softened, more permeablematerial. The matrix increases the permeability of the fill and is often partially saturated, providing a suitable medium for plant and tree growth. Instrumentation was installed and monitored at two cross-sections for 2007 which was not an extremely wet or an extremely dry year. Positive and negative pore water pressures were found in the top 1-1.5m of the soil. A finite element model of Charing embankment was created using VADOSE/W to consider the impact of an extremely dry summer and of an extremely wet winter. Site investigation and laboratory testing of the embankment fill found the in situ soil permeability to be one order of magnitude greater than the laboratory measured permeability. The near surface of the embankment hada five times greater permeability than the embankment core. Daily climatedata were applied to the model for 2007 using data recorded by the Charing weather station. Dry summer weather was simulated using data for 1995 and a wet winter using data from 2000-2001. A root water uptake model was utilised to model water removal at depth due to plant transpiration. This differs from large-scale hydrological models which consider water removal atthe soil surface. Modelling results fitted the observed pattern of continuous seasonal drying at Charing due to the presence of mature trees. The dry summer weather produced large soil suctions within the plant root zone,progressing into the embankment. Consideration of an extremely wet wintershows that hydrostatic pore water pressures can occur in grass covered areas, while in tree covered areas, residual soil suctions may remain at depth. These changes need to be considered when dealing with the maintenance of railway embankments.
A rundown area of Orford Park in Warrington is undergoing a facelift including the construction of a sports village. The site is a former landfill site and special measures were required to construct the access road. Capping the site with clay was considered unsuitable as it was only 5m from a block of flats and this would result in noise, vibration and dust. Using ageosynthetic solution was therefore considered the most neighbour-friendly solution. Aecom originally suggested using a geosynthetic membrane to prevent any gases escaping, and a sandwich of geogrids and fill levels to stabilise the existing ground but manufacturer Naue suggested integrating Secudrain, a geosynthetic material with inbuilt drainage. Secudrain is a composite material consisting of a drainage core made of polypropylene monfilaments that are firmly attached to a non-woven geotextile. It can be rolled out easily and acts as an efficient drainage mechanism, especially in road construction. It also contains contamination, so another membrane is not required for this purpose. However a layer of Secutex is placed below the Secudrain composite to act as a cushion for the geomembrane. To completethe road, three further layers of 150mm of locally sourced recycled type 1 stone are laid on top, with Secugrid geotextile grid laid between the layers to resist tensile force loading without deforming.
In February 2008, construction finally began on the missing link that will connect the M74 to the M8 to relieve traffic on the heavily congested M8 and regenerate areas in the south and east of Glasgow. The construction site is peppered with weak ground, old coal mines and toxic contamination. Chromium ore processing residue was historically used to infill clay pits but it is highly toxic and can pose a risk to public health. As the contamination extends down to 15m depths, the strategy was to cap it rather than remove it. Paper pulp and slag contaminants were also found and treated on site. the new stretch of motorway is set in the predominantly urban central Glasgow area, which means that 13 structures - the largest of which is the 12-span 740m long Port Eglington bridge - are being built to traverse the many existing roads and railway lines across the route. Piled foundations were necessary for these structures as permeability is low in the clayey Clyde alluvium and the load of the structure had to be taken onto sandstone and mudstone bedrock below. Each pile travelled 1.5 m into the bedrock. The more economical continuous flight auger (CFA) piling technique was used for 10% of the piles, notably for 33ft deep piles adjacent to the railway line at Rutherglen station. Band drains were installed to consolidate settlement.. At the nearby chromium works, 750mm CFA piles were installed with extended metal casing to a depth of 33m to prevent contamination of the bentonite. The intense piling works too two years to complete and the motorway link should be completed in August 2011.
Grains exiting an underwater silo exhibit an unexpected surge in discharge rate as they empty. This contrasts with the constant flow rate of dry granular hoppers and the decreasing flow rate of pure liquids. Here we find that this surge depends on hopper diameter and happens also in air. The surge can be turned off by fixing the rate of fluid flow through the granular packing. With no flow control, dye injected on top of the packing gets drawn into the grains. We conclude that the surge is caused by a self-generated pumping of fluid through the packing. The effect is modelled via a driving pressure set by the exit speed of the grains. This highlights a surprising and unrecognized role that interstitial fluid plays in setting the discharge rate, and perhaps in controlling clog formation, for granular hoppers whether in air or under water.
General guidance on geotechnical sampling has been part of BS 5930, both in its 1981 and 1999 editions. Within this standard, the UK geotechnical community has been able to find information on sampling methods and sample types. BS EN ISO 22475-1, which was first published in 2006, is titled: 'Geotechnical investigation and testing - sampling methods and groundwater measurements.' Together with other standards, it is a normative reference cited in BS EN 1997-2, that is Eurocode 7 Part 2 (EC7-2), published in 2007. Unlike the existing BS 5930, which is a code of practice, 22475-1 has the full status of a British Standard. Implementation of 22475-1 into UK practice should be in progress and could be completed during 2009. While much of 22475-1 describes the various methods for the sampling of the ground,it also reiterates the quality classes defined in EC7-2 that relate to each sampling type. It is this issue of quality that is likely to be problematic for the UK geotechnical industry. This paper compares the general philosophy of BS 5930 with 22475-1 and makes comment on how geotechnical sampling in the UK may be affected in the near future. Some recommendations are also made as to possible solutions to help address the potential problems that the new standard has thrown up.
The undulating stretch between junctions 25 and 28 on the M1 has always been a bottleneck and has long been earmarked for improvement by the Highways Agency. The aim is to widen both the northbound and the southbound carriageways between the junctions from three lanes to four lanes. A few metres from the toe of the existing cutting have been taken, steepening the batter to create the required extra space. This procedure can leave the new face dangerously unstable, so following geo-technical investigations it was decided to install 5000 soil nails to stabilise the slope. In some places the underlying rock was strong enough to stand alone and the nails were not required there after all. The procedure of inserting the nails is described in detail, and a description of how the widening was delivered appears in an inset. The project box explains details of the scheme including contractors and costs.
The presentation provided background to the construction sequence and described the key observations made prior to the collapse of the temporary support system for a 33 metre deep excavation in soft clay for a cut and cover section of the tunnel for the new Circle Line in Singapore, an accident which occurred in April 2004. The post collapse investigations into the ground conditions, the jet grout and the strut-waler connections were described. An explanation was offered for the triggering of the collapse, including the concept of forced sway failure of the strut-waler connection induced by relative vertical displacement between the diaphragm wall panels and kingposts. The Circle Line Stage 1 project is summarised followed by an overview of ground conditions, temporary works, diaphragm walls, kingposts, jet grout piles, excavation and propping, the strutting system, instrumentation, the mechanism of the collapse and a report of the discussion held by professionals involved in the administration and in the construction of the project.
Premises of this theory date back as far as Coulomb's work about pressure behind retaining walls in 1773. Yield Design Theory has been worked out by Salencon (1983, 1990 and 2002). It comes as a rigorous comprehensive framework for assessing the stability of any structure when the failure criterion of its constituent material is known. It provides lower and upper bounds of the ultimate loads than can be sustained by the system respectively, by an interior approach, based on statically admissible stress fields, and by an exterior approach, based on kinematically admissible virtual velocity fields. The author looks at the implementation of the Yield Design Theory in Tairen4 software. The benefits of Yield Design calculations are assessed including a look at the stability of soil nailed walls; estimation of active and passive earth pressures; overall stability of double sheet pile walls and cofferdam; and an analysis of soil nailed walls with block mechanisms. The wide range of applications to earth retaining structures illustrated demonstrates the extended capacity. Many other applications are also being discovered when this updated tool is used for checking stability of other geotechnical works.
The results presented from centrifuge tests for differential displacement at the embankment surface show clear maxima at the pile cap locations, the differential settlement increasing with g-level. Centrifuge test results modelling a working platform below pile cap elevation show a rapid increase in uniform settlement of the embankment surface at higher g-levels. The centrifuge test data are then plotted as a 'ground reaction curve' (GRC) to represent the presence of a thick working platform which causes significant settlement on an embankment. The curve shows a characteristically 'brittle' response where a point of maximum arching is reached at a relative settlement of about 5 per cent but then stress on the subsoil increases again with subsequent settlement. It is suggested that a GRC curve could be used in the design process as part of an interaction diagram. The effects of the additional load capacity of a geogrid could then also be factored in. Equations are presented to demonstrate this. Other factors which would need to be considered are noted such as 3-dimensional behaviour.
