Search

In the context of sustainability in the civil engineering industry, chemical ground improvement is becoming increasingly used, as a generally more sustainable alternative to replacing and landfilling unsuitable for construction ground. However, traditional soil stabilisers such as Portland cement or lime are not environmentally impact-free; international research effort is thus focusing on the development of innovative cementing agents. This paper presents results from a feasibility study on the development of suitable alkali-activated slag cements for the stabilisation of two soils. A number of alkali-activators were considered, comprising potassium hydroxide, a range of alkali salts, as well as a material retrieved from waste (Paper Sludge Ash, PSA) which contains free lime. Indicative results of an extensive parametric study in terms of unconfined compressive strength (UCS) are shown, followed by results of ongoing oedometer tests to determine soil compressibility and some preliminary tests on selected soil/binder mixes to observe the durability to wetting-drying cycles. Overall, all alkali-activated cement mixes increased the UCS and stiffness of the soil. Carbonates and Na2SiO3 used on their own gave lower strength increases. The highest strengths were achieved from AAC with KOH and Ca(OH)2 from PSA, which showed similar strength gain. The latter material has shown consistently a lot of promise in terms of strength, stiffness and volumetric stability of the soil as well as treatment durability. Ongoing research focuses on further mix optimisation and a comprehensive mechanical and durability property testing supported by material analysis (mineralogical, chemical and microstructural) to gain a better understanding of the complex mechanisms involved.

Pre­dicted sea level rise due to global warm­ing will ne­ces­si­tate the con­struc­tion of coastal de­fenses to pro­tect the pop­u­la­tions in the vicin­ity of the coasts. Large quan­ti­ties of con­crete will be re­quired with con­sec­u­tive in­creases in green­house emis­sions, hence an in­creas­ing need for al­ter­na­tive to Or­di­nary Port­land Ce­ment (OPC) ce­ments. Fea­si­ble po­ten­tial al­ter­na­tives could be found in al­kali-ac­ti­vated ce­ments , which also in­clude in­dus­trial by-prod­ucts or waste ma­te­ri­als. This pa­per pre­sents a lab­o­ra­tory study of con­crete mixes based on the al­kali-ac­ti­va­tion of an in­dus­trial by-prod­uct, ground gran­u­lated blast fur­nace slag (GG­BFS) and in­cludes an in­dus­trial waste, pa­per slugde ash (PSA) in the al­kali-ac­ti­va­tor mixes. The use of sea­wa­ter as mix­ing and cur­ing wa­ter was also ex­am­ined. The com­pres­sive strength and a num­ber of dura­bil­ity-re­lated prop­er­ties of al­kali-ac­ti­vated mixes in ma­rine en­vi­ron­ment were in­ves­ti­gated and com­pared to OPC sys­tems. The in­cor­po­ra­tion of pa­per sludge ash led to high early strengths, a de­crease in the ef­fec­tive poros­ity of al­kali-ac­ti­vated slag con­cretes and gen­er­ally a re­duced wa­ter ab­sorp­tion, and en­hanced the per­for­mance against chlo­ride ion at­tack in mixes with fresh­wa­ter, as well as the re­sis­tance of the ce­ments in sul­phate at­tack es­pe­cially when mixed with sea­wa­ter. The ad­di­tion of sea­wa­ter in the mixes in­creased the re­sis­tance to sul­phate at­tack and the com­pres­sive strength in al­kali-ac­ti­vated sys­tems, as op­posed to OPC con­cretes in which mix­ing and cur­ing in sea­wa­ter had dele­te­ri­ous ef­fects. The study gives promise for the suit­abil­ity of the tested al­kali-ac­ti­vated con­crete mixes in sea­wa­ter en­vi­ron­ments.

Ground source heat pumps (GSHPs) in urban environments can take advantage of surplus ground heat energy generated by subterranean infrastructures such as underground railways (URs). This paper describes seminal work in this area and a novel 3D numerical investigation into the heat energy recovery from URs with nearby vertical ground heat exchangers (GHEs). The investigation uses the London Underground (LU) as a case study but its results are generic worldwide. The investigation included a number of studies considering different geometrical configurations of the railway tunnels and the nearby GHE array, and the impact of that variation on the GHEs heat extraction rates. The results showed that heat extraction rates of GSHPs installed near UR tunnels can be significantly improved by up to ~ 43%. This will enhance overall GSHP system efficiencies, resulting in substantial savings in both operational costs and carbon emissions. In addition, the outcomes were used to develop a relationship which allows approximating the GHEs heat extraction improvements due to the nearby tunnel(s) heat load(s). This could give guidance to engineers working in fields where thermal interactions between URs and nearby GHEs arise.

This paper refers to biocementation of a problematic soil of the UK railway network as a potential stabilisation technique of this soil using indigenous ureolytic bacteria. The soil is peat, a soft foundation soil also subject to oxidation wastage. As the peat is under existing embankments, electrokinetics (EK) is proposed as a promising technique to implement treatments. In the context of unsaturated soils the paper thus focuses on two particular aspects relevant for the implementation of treatments and the stability of this soil, namely: a) the effect of degree of saturation of the peat on the bio-electrokinetic treatment ; b) the soil water retention curve of the soil affecting flow and transport; these are relevant as we focus on understanding and modelling the implementation of treatments through electrokinetics; moreover for the peat it is of importance to understand moisture exchange in the vadose zone and control groundwater table levels (e.g. during electrokinetics) in order to prevent further oxidation. After isolation and screening of indigenous microorgansisms Bacillus licheniformis was selected for further testing. The results in terms of unconfined compressive strength, CaCO3 content, swelling and compression behaviour and water retention proved the feasibility of biocementation using this indigenous microorganism. Ongoing work is assessing the required treated soil characteristics and related required biocementation degree to solve UK rail's peat foundation problems. Upscaling of the techniques towards in situ implementation is also planned in the next stage of the research.

This paper presents research initiated with the aim of assessing the feasibility of biocementing peat fens soil, a problematic soil underlying many of the embankments of the East Anglia railway network (UK). Biocementation of soil is an emerging, novel, ground improvement technique. It has recently attracted the interest of researchers worldwide because it has been proposed as potentially environmentally superior to chemical grouts and other common soil stabilisers – for example, cement or lime (linked to high carbon dioxide emissions). In this study, the authors screened and isolated non-pathogenic indigenous ureolytic microbial candidates with potential for biocementation from samples originating from peat fens in East Anglia, UK. Four strains were selected as the most suitable candidates, based on their growth rate and their viability in a wide range of temperatures, pH and soil moisture contents corresponding to typical seasonal field conditions. After a number of unconfined compressive strength (UCS) tests, one strain (Bacillus licheniformis) was selected as the most promising for this soil treatment and used for further study. Two different methods of implementation of the treatments were considered: namely, pressure flow soil column and electrokinetic injection. The UCS results supported by calcium carbonate measurements proved that biocementation did occur for both implementation methods and for a number of treatment combinations. Ongoing work on optimisation of treatments and implementation methods is being carried out towards the upscaling of the techniques for in situ implementation, which is planned for the next stage of the research.

Organic soils are a continuing challenge to civil engineers, as they are subject to settlements, negatively impacting on civil engineering infrastructure. To improve the in situ properties of these, chemical soil stabilisers (e.g. cement or lime) can be commonly used. Although successful in minimising severe damage, these stabilisers may have environmental side-effects (e.g. cement and lime production is linked to 7%–8% of overall CO2 emissions). Therefore, the development of innovative, superior, cost-effective and overall more sustainable soil improvement techniques is a field of ongoing research effort. In this context, this paper studies the electrokinetic (EK) biocementation of a problematic soft organic soil of the UK railway network using indigenous ureolytic bacteria. The paper focuses on aspects relevant for the effective implementation of treatments, namely the effect of degree of saturation of the soil and different ways of treatment implementation. The results in terms of unconfined compressive strength and CaCO3 content, proved the feasibility of EK biocementation using an indigenous microorganism, either premixed with the soil or injected electrokinetically. Higher strength gains were recorded for degrees of saturation in the region of 85%–95%. Strength gains and increased CaCO3 contents compared to the control samples were also noted when treatment duration was halved to one week although strengths increased further by 13–17% after a two-week treatment. Overall, the study gives promise for the applicability of the EK-biocementation technique under existing infrastructure. Further optimisation of the treatment variables and refinement of the implementation details could enhance the efficiency of the process.

Ground source heat pumps (GSHPs) can provide an efficient way of heating and cooling buildings due to their high operating efficiencies. The implementation of these systems in urban environments could have further benefits. In such locations the ground source heat is potentially more accessible through alternative sources such as through underground railways (URs). The heat from the ground surrounding an UR tunnel could be exploited to enhance the operation of GSHPs operating in heating mode. To achieve this, the interactions of GSHPs with neighbouring URs must be fully understood but there is little exploration of these in current literature. This paper focuses on the potential benefit of understanding such interactions. It starts with a summary of typical and alternative heat sources for heat pumps and then it highlights the reasons why URs can be regarded as one of the most attractive ones. Then the paper reviews the current approaches used to model GSHPs and URs. Based on that review the paper suggests a method for the combined analysis of GSHPs and URs. The reasons why London is a sensible choice for a case study are also described. Summary of results from a preliminary investigation are also presented.

This paper investigates the effect of suction and lime treatment on the volumetric and shear behaviour of a partially saturated high plasticity clay (London Clay). A series of triaxial tests were performed on statically compacted London Clay and lime-treated London Clay specimens. These were prepared at the same target void ratio and tested under partially saturated conditions. The tests concerned isotropic compression and two different types of shearing tests (a) shearing at constant suction and (b) shearing at constant water content, using the axis translation technique. Based on the results, the effects of suction and lime-induced bonding are evaluated and quantified within an elastoplastic partially saturated soil framework.

This paper assesses comparatively the performance of a number of innovative soil stabilisers for the treatment of a highly swelling-shrinking soil, against that of commercial calcium lime. The production of lime, a most common soil stabiliser, involves high energy consumption, carbon dioxide emissions and the depletion of natural raw materials. Alternatives are actively sought, in particular industrial wastes and by-product materials or lower energy demand cements e.g. reactive magnesia (MgO) cements. In this paper calcium lime, reactive magnesia, industrial wastes and mixes of these with lime are comparatively assessed, based on a number of conventional measures of the propensity of a soil to swell, i.e. plasticity characteristics and swelling characteristics (swelling strains, swelling pressures, swelling indices). Furthermore, as expansive soils are typically in an unsaturated state hence sensitive to both changes in water content and suction, filter paper testing was performed to provide additional evidence of the effect of the treatments on the swelling/shrinking soil. According to the main findings, for the treatment of swelling shrinking soils, binders coming from the paper recycling industry show most promise as alternatives to lime; reactive magnesia cement had a smaller effect than calcium based stabilisers in improving the swelling-shrinking of the soil, yet it also suppressed swelling and shrinkage considerably; it thus shows potential for use as an alternative to common soil stabilisers (Portland cement and calcium lime) to alleviate the environmental impact of the latter.

The paper reviews the common techniques of volume change measurement during unsaturated soil testing, focusing in particular on a newly developed system by the authors. The advantages and accuracy of the system compared to other available volume measurement techniques are discussed. This is followed by the application of the system to the volume change measurement of a lime-treated clay soil during suction-controlled triaxial testing, and a discussion on the behaviour of the soil during shearing.

The paper presents a laboratory investigation, which quantified the beneficial effect of lime on the water retention, compressibility and overall volume changes of a high plasticity clay (London Clay). The study comprised oedometer testing (including suction controlled testing), shrinkage tests, and filter paper testing to determine the soil water retention curves of the drying soils. The latter tests showed that the shallow-mixed lime-treated soils are likely to be partially saturated in situ depending on the environmental conditions; thus, unsaturated soil mechanics concepts are applicable for the description of their behaviour. The oedometer results quantified the marked decrease in the swelling and compressibility of the lime-treated soil compared to the untreated clay and the increase in the vertical effective yield stress (due to suction and cementation bonding). The lime enabled the soil to maintain a more open structure with respect to the untreated soil throughout the compression process, and appears to be the main factor influencing the compressibility of the unsaturated lime-treated soil (rather than suction) for the ranges of suction tested.

© 2016 The Authors. The paper studies the laboratory measurement of the Soil Water Retention Curve (SWRC) of statically compacted London Clay focusing on the effects of different specimen preparation methods and testing techniques to acquire a better understanding of how measurements can be affected by these factors. Testing methods include filter paper, two modified pressure plate systems, and a ceramic pressure membrane extractor. A discussion on the repeatability of the measurements is also made.

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.

The present paper deals with the numerical modelling of trench drainage in variably saturated porous media. In particular, the effect of the unsaturated storage coefficient form on the rate of transient seepage into the trench is investigated. Several numerical analyses are performed for two different soil types. The numerical results derived using a pressure head-dependent storage coefficient, are compared to those derived using constant storage coefficients. It is shown that simplifying assumptions using constant storage coefficients may predict too fast drainage rates.

This paper gives a brief account of ongoing research on the mechanical behaviour of lime-treated clays. First indicative results of a series of suction-controlled triaxial tests using the axis translation technique are presented based on which the effect of cementation is assessed. The results showed the overall beneficial effect of the lime on the compressibility behaviour of the soil as well as the dramatic increase in strength gained for ranges of strain relevant to engineering applications. A constitutive model for the behaviour of lime-treated soils is then introduced to account for the combined effects of suction and cementation.

The paper discusses various models which have been proposed to simulate the hysteresis of the water retention curve. Three of these models were implemented into a finite element computer program for flow in variably saturated porous media and were applied to the solution of transient flow through a soil column subject to drying-wetting cycles. The performance of these models was assessed through comparisons with previously published experimental results. A linear hysteresis model was shown to reproduce satisfactorily the experimental results, although it was simple to implement and required minimal experimental data to be formulated. Overall, the results indicate that the fact of including hysteresis in the numerical model improved the predictions with respect to the case when single-valued functions were used.

The knowledge of the soil water retention curve (SWRC) is of particular importance for unsaturated soils. However common techniques to determine SWRC may be much more time-consuming than other soil property testing techniques and may lack flexibility in controlling the stress state of the soil in the field, which is of most relevance for geotechnical engineering applications. The paper presents a transient testing technique for the continuous measurement of SWRC in a triaxial cell during which testing rates are adjusted based on numerical modeling results simulating the testing. This enables the optimization of the experimental process and hence a more efficient determination of the SWRC. The technique is then successfully applied to determine the SWRC of statically compacted silica flour specimens, tested under different confining stresses.

The paper demonstrates a novel non-contacting volume change measurement system for triaxial soil testing. The system uses an ultra high accuracy laser displacement sensor that measures water volume changes resulting from the volume change of the specimen during testing. The paper presents the design, working principles, system calibrations, and the validation of the system through comparative measurements of volume changes of soil specimens during triaxial shearing, against results of conventional volume measurement techniques.

Photogrammetry is the science of acquiring and interpreting three-dimensional data of physical objects by measuring and analyzing their images on photographic plates. The development of this technology since the mid-seventies has increased its credibility for application to industrial and shipbuilding use. Analytical photogrammetry is now routinely employed in shipbuilding for tasks as diverse as predicting the fit-up of structural steel assemblies prior to their joining, verifying the circularity of submarine hulls, and checking the alignment of catapult trough components on aircraft carriers. The authors address the practical applications of photogrammetric technology, and identify the reliability, versatility, and productivity of photogrammetric surveying when applied to shipbuilding.

This paper investigates the drying and wetting soil water retention curves (SWRCs) of statically compacted lime-stabilised London Clay specimens. A series of tests were performed using the contact filter paper method, pressure plate apparatus and a suction-controlled triaxial system incorporating the axis translation technique. These investigated the water retention of the soil under different boundary and stress-state conditions and simultaneously determined the volume change in the soil during drying and wetting. Factors relevant to the lime treatment of soils, such as curing period and method (air vs. water curing), were also considered. Finally, the hysteresis of the SWRC of the chemically treated soil (for which there appears to be a lack of information in the international literature) was investigated. The results showed that the treatment with lime increased the volumetric stability but reduced the water retention ability due to a more open structure enabled by the flocculation and chemical bonding effects. Curing period and method effect appears to be small. Hysteresis was noted to some degree in all instances.

Les microformes en halogenure d'argent sont actuellement disponibles sur un support en acetate de cellulose ou en polyester. L'auteur compare, dans cet article, les avantages et les inconvenients de ces deux types de support pour les prises de vues et les services de copies