Inge Hoff

A Study on the Influence of Water and Fines on the Deformation Properties and Frost Heave of Unbound Aggregates

A study on the influence of water and fines on the deformation properties and frost heave of unbound aggregates

Determination of space behind pre-cast concrete elements in tunnels using GPR

Many tunnels in Nordic countries are lined with prefabricated concrete elements to protect against frost and leakages. This protective lining is fixed to the rock face in a few points, but when installed renders the rock surface inaccessible, owing to the lack of predesigned inspection hatches. Safety inspections have hitherto consisted of random drilling into the concrete lining. However, such random inspection is both unreliable and expensive. Therefore Ground Penetrating Radar has been introduced in the vault walls to map the contours of the gap more systematically. Such scanning technology provides satisfactory data, given optimal location of apertures. The scanning technique is therefore extended to the vault roof to pinpoint potential rockfalls.

Detection of Rockfall on a Tunnel Concrete Lining with Ground-Penetrating Radar (GPR)

Experiments were conducted using Ground-Penetrating Radar (GPR). The performance of six GPR systems was assessed in terms of: (1) remotely mapping cavities behind concrete linings, (2) detecting rockfall from the tunnel roof onto an inner lining comprising, for example, precast concrete segments. Studies conducted in Norway and the United States demonstrate that the GPR technique is a simple and reliable method that can assist stability inspection in existing Norwegian tunnels. The ground-coupled GPR systems represent a step forward in the remote detection of rockfall on tunnel concrete linings, and are particularly suited to self-standing inner linings. The analysis of the data is relatively straightforward and reasonably accurate.

Finite element modelling for prediction of permanent strains in fine-grained subgrade soils

Roads are designed with good reliability to fulfil the long-term performance during the design period. In order to achieve an effective design, the long-term performance of pavements should be optimized during the design phase. One of the strategies is to develop models which are capable of predicting the long-term performance. This paper focuses on one of the most critical distress modes in flexible pavements, namely, rutting. The plastic strain of subgrade soils is modelled to quantify the amount of rut contributed from the subgrade. The deformation from the first loading cycle is incorporated in the elastoplastic theoretical framework based on the Drucker–Prager yield criterion. The proximity of deviator stress to the static failure limit of subgrade soils is considered to predict the amount of incremental plastic strains at each loading cycle. The model is implemented in the User Material Subroutine in the finite element program ABAQUS™. The prediction of plastic strains using the proposed model provides a good agreement with laboratory test with deviator stress level up to 50% of the static strength of the soil. The mobilisation of subgrade soils in pavements is normally low due to reduced stress magnitude at the subgrade level, which makes the proposed model in this study more appealing to understand the development of plastic strains in subgrade soils.

Modeling Surface Temperatures for Snow-Covered Roads: A Case Study for a Heated Pavement in Bærum, Norway

Heated pavements are used as an alternative to removing snow and ice mechanically and chemically. Usually a heated pavement system is automatically switched on when snowfall starts or when there is a risk of ice formation. Ideally, these systems run based on accurate predictions of surface conditions a couple of hours ahead of time, for which both weather forecasts and reliable surface temperature predictions are needed. The effective thermal conductivity of the snow layer is often described as a function of its density. However the thermal conductivity of a snow layer can vary considerably, not only for snow samples with a different density, but also for snow samples with the same density, but with a variation in the liquid water content. In this paper a physical temperature and surface condition model is described for snow-covered roads. The model is validated for an entire winter season on a heated pavement in Norway. Two different models to describe the thermal conductivity through the snow layer were compared. Results show that the thermal conductivity of the snow layer can be best described as a function of the density for snow with a low liquid water content. For snow with a high water content, the thermal conductivity can be best described as a function of the volume fractions and thermal conductivity of ice, water, and air, in which air and ice are modeled as a series system and water and air/ice in parallel.

Simulation of Train-Turnout Coupled Dynamics Using a Multibody Simulation Software

With the advancements of computing power, multibody simulation (MBS) tool is used to study not only train dynamics but also more realistic phenomena such as train-track coupled dynamics. However, train-turnout coupled dynamics within MBS is still hard to be found. In this paper, a train-turnout coupled model methodology using a MBS tool GENSYS is presented. Dynamic track properties of a railway track are identified through numerical receptance test on a simple straight track model. After that, the identified dynamic track properties are adopted in a switch and crossing (turnout) to simulate train-turnout coupled dynamic interaction including parameters such as rail bending stiffness and sleeper mass variation along the turnout. The train-turnout coupled dynamic interaction is compared to the dynamic interaction simulated from a widely accepted moving mass train-turnout model. It is observed that the vertical and lateral normal forces for the new train-turnout coupled model and the conventional moving mass train-turnout model are in good agreement. In addition, the new train-turnout coupled model can provide additional track dynamics results. It is concluded that the train-turnout coupled model can provide a more realistic train-turnout dynamic interaction compared to the moving mass train-turnout model.

Mechanical Assessment of Crushed Rocks Derived from Tunnelling Operations

The Norwegian Public Roads Administration is currently running the “Ferry-free coastal route E39” project, which reduces the travel time along the Norwegian coast from Trondheim to Kristiansand. The plan includes the creation of several long tunnels, which will generate a surplus of blasted rocks; these could be used in the road unbound layers close to the place of production. The research presented here has three goals. The first aim is to map the geology encountered along the E39 road alignment. The second aim is to check whether the rocks fulfil the existing code requirements for road unbound layers, defined in terms of Los Angeles and micro-Deval limit values. The third aim is to investigate the crushing and the variation in grain size of the unbound materials during both construction phase and service life phase. The construction stage is achieved by a full scale testing to assess rock soundness after rolling, the service life stage is simulated by the repetition of a specific load in the triaxial cell apparatus. The current tunnelling operations located south of Bergen are producing blasted rocks, they adequately represent the geology spread along the entire E39 alignment. Three types of crushed rocks are selected and tested. The major part of the rocks excavated are suitable for direct use in pavement unbound layers. The most significant modification in grain size distribution curve takes place during the compaction phase for all the materials.

Laboratory Testing Methods for Evaluating the Moisture Damage on the Aggregate-Asphalt System

The durability of the bitumen-aggregate system is a critical factor affecting the performance of asphalt pavements. It is achieved by a careful selection of the materials based on the analysis of their compatibility and their water sensitivity. Currently, a variety of analytical test methods are used to evaluate the power of the binder to adhere to various aggregates and their susceptibility to moisture. Many of these methods are time consuming and/or require sophisticated and expensive instrumentation. The most common procedure, the indirect tensile strength (ITS) test, has been questioned by many researchers and simpler testing procedures, such as the rolling bottle test, are considered to be an indicative measure. Several studies have introduced a new test procedure, the binder bond strength (BBS) test. The test, based on the pull-off strength of the bond between asphalt and aggregate measured before after water conditioning, has shown good repeatability, reliability and the ability to determine the effects of different aggregate type, conditioning time and moisture on the aggregate-asphalt system. This paper explores the potential of the BBS test by correlating the results of test methods presently used to evaluate the strength of the bond of the asphalt-aggregate system measured with the BBS test. Four different aggregate types and a traditional bitumen were tested according to the respective European standard, including type, length and temperature of conditioning. However, the different aspects of the mixture considered in each test method determine a poor agreement of the results. Comparable levels of moisture resistance are observable only in the long term.

Facilitating the adoption of sustainable technologies in the asphalt sector

A need exists to bridge the gap between innovation in the bituminous materials sector and adoption of the new technologies by national road administrations (NRAs). The Evaluation and Decision process for Greener Asphalt Roads (EDGAR) enables NRAs to do this by providing an assessment methodology which makes sustainability information on new technologies readily accessible to the decision-making process, and therefore facilitates quick adoption of the technologies that offer the greatest sustainability benefits for the highways sector and society as a whole. EDGAR commenced with a wide-ranging review of the range of ‘green’ technologies in the bituminous materials sector and the sustainability benefits that they offer. Two methodologies to assist NRAs were then devised. The first acknowledged that the ability to recycle asphalt is its foremost environmental attribute, and devised a quick, qualitative method for the assessment of recyclability. The second devised a methodology for a more detailed assessment of the sustainability of any bituminous technology, considering all three facets of sustainability: environmental, social and economic, with particular attention given to how the information might be used in the decision process by NRAs, and the common challenges they might encounter when assessing a ‘novel’ technology.