Performance parameters and target values for construction of UK road foundations

There is impetus in the UK to move away from empirical design of road foundations and method specification towards analytical design assured by end product testing during construction. Current research at Loughborough University, sponsored by the Highways Agency, is aimed at introducing such a performance based specification. This paper introduces the philosophy behind the research and explains the primary objectives. Selective results are presented from a full-scale field trial construction of a road foundation on a soft subgrade, which was characterised by a variety of field devices and subsequently trafficked. This paper focuses on insitu stiffness modulus (ER), measured by several devices for comparison. The setting of suitable target values for field ER is seen as a key factor and the influence of inherent variability in material response a concern. The discrepancy between devices and the problem of long-term stability are discussed and highlighted as a key focus for the remainder of the work

Threshold stress and asymptotic stiffness of UK clays in the repeated load triaxial test.

Recent research at Loughborough University has produced a draft performance specification for pavement foundations. To assess the performance parameters of stiffness and resistance to permanent deformation of the subgrade, an extensive series of repeated load triaxial tests has been performed on a range of fine grained subgrades. Assessment of the data has shown that the deviator stress at which the cumulative permanent deformation starts to increase significantly (i.e. the threshold stress) is equal to half that at failure (and occurs at approximately 1% permanent strain). The resilient stiffness of the materials tends to low asymptotic values at higher deviator stress. Comparison between the elastic and plastic behaviour has shown that the deviator stress at ‘threshold’ is coincident with the stiffness asymptote. This paper presents a suggested simplified mechanistic design approach for pavement foundations based on these findings

Stiffness behaviour of trial road foundations.

This paper reports the results of two full-scale field trials to determine the stiffness and density of granular materials receiving different levels of compaction energy and support. The research showed that there were greater improvements in density with initial input of compaction energy, and yet little change in density, but significant increases in stiffness, with the final applications of compaction energy. Density is thus an inappropriate indicator of performance (i.e. resilient elastic stiffness

Workplace parking levies: the answer to funding large scale local transport improvements in the UK?

Despite positive experiences in Australia of utilising area wide workplace parking place charges to pay for public transport improvement, only one UK local authority, to date, Nottingham City Council has chosen to implement a Work Place Parking Levy scheme (WPL). This scheme intends to allocate the revenue raised to fund (amongst other things) two new tram lines. Acceptance by the public and the business community are seen as key barriers to implementing a WPL. The two major criticisms of the Nottingham scheme prior to its implementation were that a WPL would discourage business investment and thus damage the economy while its intended impact on traffic congestion would be minimal. Therefore a detailed assessment of the Nottingham WPL scheme’s performance is essential in order to facilitate transferability of this approach to other UK and European Cities and thus bring WPL into the mainstream for funding transport improvements. This paper outlines the barriers to implementation of the Nottingham WPL scheme, and the rationale behind the chosen use of revenue and how the scheme’s performance will be evaluated as a transport demand management measure, as well as some initial performance monitoring data following the first year of operation. The results to date are discussed with a view to identifying any early indications as to whether traffic congestion and business investment has been impacted by the scheme’s introduction

Stakeholder views of materials selection for road pavements

The growing prominence of Carbon calculators in the road construction sector has lead to a greater general awareness of the sustainability issues associated with road pavement materials and their selection. This paper presents results from a series of semi-structured interviews conducted with key stakeholders from the highways industry, which were used to gain an understanding of industry perceptions on the use of sustainability assessment in the selection of highway materials for road construction. The stakeholders consulted ranged from government bodies and trade associations to contractors and academics. Analysis of the interviews has shown that there is a clear focus on Carbon/Climate change. The frequency with which various topics were mentioned has been used in the analysis to produce a basic hierarchy of sustainability drivers for the highways industry. A comparison is also made against the existing civil engineering environmental quality assessment and award scheme (Ceequal) categories to identify gaps and areas of consensus to further enhance Ceequal. The paper concludes that several factors should be taken forward within any on-going development of LCA (Life Cycle Assessment) frameworks or Carbon assessment methodologies for road construction projects including, Carbon (footprinting)/Climate change, Maintenance phase considerations and broader Environmental Issues

Subgrade equilibrium water content and resilient modulus for UK clays

The main functional requirement of the subgrade is to resist excessive deformations during construction and in service. Deformation is controlled by ensuring adequate foundation resilient modulus. UK pavement design currently relies upon the determination of long-term CBR values for subgrades, which results in conservative pavement foundation design. To allow more realistic design an analytical approach is required, including measured values of resilient modulus at anticipated short- and long-term equilibrium subgrade water contents. Resilient modulus is determined from repeated load triaxial tests with on-sample strain measurement. Results from these tests on samples adjusted to model the subgrade behaviour at various design conditions are presented. These results are discussed, highlighting problems both with measuring small strains on undisturbed soils and in predicting and modelling accurately long-term soil behaviour. RÉSUMÉ: Le critère principal d’une sous-couche est de résister à des déformations excessives en construction puis en service. La conception des chaussées au Royaume-Uni est actuellement basée sur la détermination de l'indice portant Californien (CBR) à longterme des sous-couches. Pour une conception plus réaliste, il est nécessaire d'adopter une approche prenant en compte des valeurs de module de résilience mesurées à des degrés d'humidité de sous-couches à l'équilibre simulés à court et long-terme. Le module de résilience est déterminé à partir d'essais répétés en charge triaxiale avec mesure des contraintes sur l'échantillon. Dans cet article les résultats de ces tests sur des échantillons simulant le comportement de la sous-couche sous diverses conditions de conception sont présentés. Ces résultats sont discutés, en soulignant les problèmes résultant de la mesure de faibles contraintes sur des sols non-perturbés, et dus à la prédiction et à la modélisation du comportement des sols à long-terme

Insitu assessment of stiffness modulus for highway foundations during construction

Several portable field devices that measure stiffness modulus are reviewed in detail in this paper including the German Dynamic Plate Test (also known as the Lightweight Drop Tester), the TRL foundation tester (UK), the Prima (Denmark) and the Humboldt Soil Stiffness Gauge (USA, also known as the GeoGauge). Laboratory and field data are presented which explain the many important influences on the measured data and demonstrate comparative performance with respect to the Falling Weight Deflectometer. These field data show significant scatter and site specific correlation. A strategy for compliance testing during construction, as part of a performancebased specification approach for the UK, is suggested. Conclusions are made regarding the devices’ relative merits and limitations, and considerations for their introduction into contractual use for routine assessment during construction

Drainage behavior of sports pitches–A case study review

The drainage behavior of sports pitches has traditionally been designed from experience with hydraulic performance rarely measured in detail. Within the wider industry and regulatory bodies there is a perception that storm water and increased drainage rates from sports pitches contribute to local flood risk. Empirical observations have suggested that in reality pitch drainage systems may discharge water at low volumes and rates and there is often limited surface run-off. Furthermore it appears that lack of technical guidance on the discharge of water from sport pitch drainage systems may have led to misunderstanding their drainage behavior and possible benefits they could bring to water management as opposed to perceived dis-benefits. This paper summarizes selected results of a case study which included field measurements of weather and discharge behavior on a range of natural turf sports pitches in England. The findings from this study indicate that natural turf sports pitches can provide resistance to flow and hence advantageous attenuation of rainfall and storm water. Additionally sports pitches can store large volumes of water within the pervious materials used in their design. The study has confirmed that sport pitches demonstrate the key functions that are reflected in the design requirements of Sustainable Urban Drainage Systems (SuDs) such as pervious pavements providing source control of surface rain water

The performance of pavement foundations during construction

There is an impetus in the UK to move away from empirical pavement foundation design and the current method specification, towards an analytical design approach. For an analytical design approach to be adopted, the required performance properties of stiffness and resistance to permanent deformation of the foundation materials (sub grade and capping) need to be measured, both in the laboratory for design and in the field in order to ensure compliance. This thesis studies the influence of the sub grade on the constructability and performance of a series of full-scale pavement foundations. This has been achieved by measuring the performance parameters of several sub grade materials in the laboratory, using repeated load triaxial testing. These data have been compared to comparable data collected in situ using dynamic stiffness measuring devices during the construction of trial pavement foundations. The performance of the trial foundations has been measured during the placement and compaction of the different foundation materials, and again after their subsequent trafficking. The testing demonstrates the stress dependency of the foundation materials. The laboratory testing shows that the sub grade permanent deformation under cyclic loading (used to simulate construction operations) becomes unstable at a deviator stress of half the deviator stress at failure (0.5qmax)· The stiffness at this applied stress and above is shown to be approaching a consistent value. This indicates that large changes in the stiffness of inversely stress dependent fine grained soils occur below the deviator stress at which the permanent deformation becomes unstable. Significant variability of data has been found in the performance parameters measured (both in the laboratory and in the field) for samples of subgrade collected from small areas of the same site. However comparable patterns of stress dependency have been observed between measured laboratory and field performance using the different apparatus. The resistance to permanent deformation is shown to be a more critical design load case for construction than the need for adequate stiffness of support required to compact the foundation layers. The performance of a composite road foundation is shown to be material and site specific, and this will have important implications for design and site compliance testing

A case study on evaluating and selecting soil /pipeline interaction analysis software for the oil and gas industry

The evaluation and selection of appropriate software solutions to meet an organisation’s inherent business requirements can be a problematic process that if done incorrectly can have a significant, costly and adverse effect on the business and its processes. The aim of this paper is to showcase a process and evaluation criteria in order to identify the right engineering software for the identified business requirement such as functionality and usability. A case study approach coupled with an action-based research methodology was undertaken to aid an organisation within the Oil and Gas Industry, by using an innovative solution suitable for conducting stress analysis for Soil-Pipeline Interaction Analysis (SPIA). Through development and use of the below presented software selection and evaluation process to capture and measure key requirements, it was possible to determine a viable approach to selection of a suitable software for the organisation’s requirements. This paper investigates software evaluation criteria for evaluating software packages and methodologies for selecting software packages. The study will also provide an explanation of the adopted methodology. The key findings of the study are: (1) there is currently no universal selection criteria within the gas and oil engineering industry, (2) how the presented methodology could be used to capture business requirements to evaluate software for SPIA consultants (3) findings must be validated based on the evaluation technique and evaluation criteria for selecting software packages for the engineering industry. The findings of the study are offered to support consultants in the Oil and Gas industry to improve software selection methodologies for SPIA