Civil Engineering Works Research Articles

Fatigue Assessment and Behavior of a Shell Steel Element Welded Joint

The paper is proposing an advance research on welded joints of the shell steel elements. The assessment of the fatigue of the existing structures is a current topic in the sustainable development of the civil engineering work. Planning, manufacturing and serviceability of the steel structures under cyclic loads, involves a fatigue designing.Simplified fatigue and fracture mechanics based assessment methods are widely used by the industry to determine the structural integrity significance of evaluate cracks, manufacturing flaws, service-induced cracking or suspected degradation of engineering components under normal and abnormal service loads. In many cases, welded joints are the areas to contain the fabrication defects or cracks initiating and growing during service operation. The welded joints are a major component that is often the cause for structure failure or for being the point at which fatigue or fracture problems initiate and propagate. Various mathematical models for various classes of welded joints are developed by analytically or by simulation software's that can be used in fatigue and fracture assessments.

Experimental and numerical investigation of footing behaviour on multi-layered rubber-reinforced soil

This paper describes the beneficial effects of multiple layers of rubber–sand mixture (RSM). The plate load tests, using circular plate of 300 mm diameter, were performed at an outdoor test pit, dug in natural ground with dimensions of 2000 × 2000 mm in plan and 720 mm in depth to facilitate realistic test conditions. The rubber used in the RSM layers was granulated rubber, produced from waste tires. The optimum thickness of the RSM layer was determined to be approximately 0.4 times the footing diameter. By increasing the number of RSM layers, the bearing capacity of the foundation can be increased and the footing settlement reduced. The influence of the number of RSM layers on bearing capacity and settlement become almost insignificant beyond three layers of RSM, particularly at low settlement ratios. At a ratio of settlement to plate diameter of 4%, the values of bearing pressure for the installation with one, two, three and four layers of RSM were about 1.26, 1.47, 1.52 and 1.54 times greater, respectively, than that for the unreinforced installation. Layers of the RSM reduced the vertical stress transferred through the foundation depth by distributing the load over a wider area. For example, at an applied footing pressure of 560 kPa, the transferred pressure at a depth of 570 mm was about 58, 45 and 35% for one, two and three layers of RSM, respectively, compared to the transferred stress in the unreinforced bed. By numerical analysis, it was found that the presence of soil-rubber layers resulted in expansion of passive zones in the foundation due to the effectiveness of the confinement provided by the rubber inclusions, and this tends to make the bed deflect less. On the basis of this study, the concept of using multiple RSM layers has not only been shown to improve the performance of foundations under heavy loading, but also, the environmental impacts of waste tires are attenuated by re-using their rubber as part of a composite soil material in civil engineering works.

Project Duration Evaluated Using Affine Arithmetic

A civil engineering work can be performed by organizing theavailable resources (manpower, equipment and materials) inmany different ways. Each different configuration results in arealization time and a cost that a building company has to bear.To produce reliable duration forecasts and money savings, itis essential to take into account all the uncertainties involvedin the project operations. Generally, since it is impractical toprocess numerous uncertain variables - also undefined froma statistical point of view -, traditional probabilistic methodsinvolve application difficulties for complex environmentssuch as construction sites. To properly handle this issue, theauthors propose in this paper the application of the AffineArithmetic technique. This method treats the variables as intervalsand returns reliable results, even when the variables aremutually dependent. The numerical example presented in thepaper proves the efficiency of the procedure, even if some analyticalcomplications are included in the analysis (dependencybetween variables, non-linear functions, etc.). Comparisonswith Interval Analysis and traditional procedures are also provided.Adopting Affine Arithmetic, the results are reported interms of intervals, avoiding the definition of unrealistic deterministicvalues that can strongly affect the operation organization.Furthermore, without increasing the problem complexity,the model admits continuous modifications (interval amplitudes,new variable dependencies, etc.) to correct and optimizethe durations.

Ageing behaviour of polyacrylamide-based excavation fluids

Solutions of synthetic polymers based on the chemistry of partially hydrolysed polyacrylamides (PHPAs) are increasingly being used as a replacement for the more conventional bentonite slurries in the construction of bored piles and diaphragm walls. On a construction site, these fluids may be in use for weeks to months and therefore their ageing behaviour is important. However, rather little has been published on the subject and the literature that is available is contradictory. To develop the understanding of ageing behaviour, a series of tests were undertaken on clean solutions of a commercial PHPA designed for civil engineering works. The tests showed that the PHPA fluids showed a gradual reduction in viscosity over the first days after mixing and that the rate of reduction was slightly dependent on the quality of the mix water. These findings are contrary to the rapid initial reduction in viscosity reported in some studies. An extended ageing test showed that the reduction in viscosity had effectively ceased at about 60 d from mixing with a significant proportion of the initial viscosity retained. These test results will allow foundation contractors to be more confident about the use of PHPA support fluids over extended times.

Spatial variability analysis of subsurface soil in Mashhad city, NE Iran

Reliable characterization of subsurface soil in urban areas is a major concern in geotechnical and geological engineering projects. In this regard, this research deals with development of a 3D geological engineering model on Mashhad City soil using Sequential Gaussian Simulation (SGS) approach. The intense variability of soil in the study area has sometimes caused serious problems in civil engineering projects in the city. Therefore, a better understanding of these deposits is critical for current and future civil engineering work. The main objectives of this study were investigating the spatial variability of soil through variograms and then predicting the values of soil properties at unsampled locations using SGS method. In this study, some geotechnical index parameters including percentage of fine grained material, plasticity index, and liquid limit have been employed as input data. A database including the data of 1750 boreholes was built and the hard data were transformed into normal scores in order for them to be applicable as input data in SGS modeling. Maps related to the average of all realizations along with Coefficient of Variation (CV) were provided for each variable as well. Then the maps were interpreted according to Mashhad City sedimentary environment.

Valorisation de nouveaux matériaux naturels et recyclés dans la construction routière en Algérie

These recent years, the development of the civil engineering and especially the public works sectors in Algeria requires large amount of aggregates. Therefore, the abusive uncontrolled extraction of materials send out distress signals on the over-exploitation and reduction of the usual natural sources of aggregates, particularly alluvial deposits. Indeed, this can certainly maximize the risks of environmental contamination and threaten the aggregates supply continuity of projects, therefore seriously disturbing the development of the public work sector. For those reasons, the exploitation of new aggregates sources and the search for new local materials (natural or recycled materials) are urgently needed and seem to be a promising solution for sustainable development. Indeed, many natural materials such as (schist, marl,…) have been investigated in this area, given their availability and ease of extraction. Also, tons of inert wastes (concrete debris, glass debris,…) are generated from various human activities and abandoned in nature (along the roads) or buried in landfills where they surely represent contamination threats to ground water, while, these materials can be recovered and reused as alternative aggregates in important industrial sectors such as civil engineering and public works. The present experimental study is conducted in this context. It aims at valorizing local natural materials (marl) and recycled materials (glass debris) in road construction. Indeed, marl is among the most available materials in Algeria, it represents over 40% of the soils of Great Kabylia (Tizi-Ouzou). It is close to the surface (accessibility), with thicknesses exceeding 1000 meters (availability). Glass debris are also among the most available types of wastes (found in dumps and landfills). It is widely used in many industrial activities such as packaging, decoration, construction, and therefore it generates a lot of inert waste which take about 5000 years to decompose. For those reasons (large amounts and lengthy decomposition), several studies have been carried out for the glass possible reuse in civil engineering, especially in concrete and roads. To achieve this work, samples are prepared in the form of mixtures of marl with different proportions of glass debris (0, 10, 20, 30 and 40%). They are then submitted after identification to the main mechanical road tests, namely: compaction with modified Proctor tests in order to assess their maximal dry density, penetration with CBR tests (California Bearing Ratio) to evaluate puncture strength immediately under the circulation of vehicles during the construction of pavements or after soaking under water for 4 days (96 h), representing the worst humidity conditions on construction site. The samples are then subjected to direct shear tests using Casagrande shear box to assess their shear strength under traffic, especially during acceleration and braking of heavy vehicles. Finally, they are subjected to fragmentability, degradability, Los Angeles and micro-Deval tests to evaluate the evolution of the grains under different mechanical efforts (traffic, climatic and hydro-geological conditions). The experiments carried out have shown very remarkable results. Unlike the unfavorable behavior showed by the marl or the glass alone; their combination as mixtures presents very interesting mechanical characteristics under the different tests. Particularly, the mixtures with 20% of glass debris have shown the best aptitude to compaction, at low water content, and a high penetration strength in soaked and un-soaked conditions. In addition, it exhibits very interesting mechanical characteristics at shearing, with acceptable fragmentability, degradability, impact and wear behaviors. These results are very valuable and fully satisfy the requirements of standards for materials used in roads under weak and medium traffic. However, to better understand and develop the use of the studied materials in the road construction; further tests are necessary, such as long-term tests under cyclic natural loading (temperature, freeze–thaw,…). This research work may have considerable interests, both on the economical aspect and on the environmental impact in the region, mainly: Conservation of alluvial deposits and exploitation of new sources of aggregates to ensure the projects supply. Preservation of the environment by recovering abandoned glass wastes in nature, consequently, allowing the recovering of important storage spaces and significantly reducing the needs for new landfills. Contribution to the development of the recycling industries and the creation of more employment opportunities for the local population, leading to income generation and poverty reduction in developing countries such as Algeria, which offers a fertile field of recyclable materials (concrete, plastic, glass,…). However, this study must be accompanied by appropriate and selective dumps installation strategies, with a large sensitizing of population in order to allow the easy collection of glass debris and other materials that can be recycled in the civil engineering field and other construction fields.

Estimating and Plotting TLS Midrange Precisions in Field Conditions: Application to Dam Monitoring

Terrestrial laser scanners (TLS) are already widespread among surveyors, with a huge field of applications. The range of scanning distances goes from tenths to a few thousand meters, depending on scanning technology, but precisions of scan measures are not well stated by manufacturers, in particular for medium and large distances. It is necessary to ascertain precisions to optimize the design of “in field” scanning jobs. This is the case of TLS dam monitoring that requires detailed information about precisions for a range of scanning distances and incidence angles, to deal with topographical constraints and ensure the measurement of small dam movements. This article presents a new approach to obtain a complete map-type plot of the precisions of TLS scanning with time-of-flight method at midrange distances. Tests were developed in field-like conditions, similar to dam monitoring and other civil engineering works. Taking advantage of graphic semiological techniques, a map in “distance–angle of incidence” coordinates was designed and evaluated for field-like conditions. A map-type plot was designed combining isolines and sized and colored points, proportional to precision values. Precisions under different field conditions were compared with specifications. For this purpose, processed point clouds were evaluated under two approaches: classical “plane-of-best-fit” and proposed “simulated deformation” that showed improved performance. These results lead to a discussion and recommendations about optimal TLS operation in civil engineering works.

Effectiveness of debris flow mitigation strategies in mountainous regions

Debris flows represent major hazards in most mountainous regions of the world where they repeatedly result in disasters. In order to protect people and infrastructure against future debris flows, many debris flow catchments have been artificially intervened by employing various mitigation measures, including civil engineering works. However, the commonly adapted engineering measures, such as check dams, are not effective for every debris flow catchment, and the failure of such measures even causes more damage, e.g. the Sanyanyu debris flow catchment in Zhouqu, China, killed 1756 people. In order to research the effectiveness of engineering strategies and explore much more effective mitigation works for debris flows in the mountainous regions, we took the Bailong River catchment of Southern Gansu of China as study area, with special emphasis on Sanyanyu debris flow catchment (with civil engineering works) and Goulinping debris flow catchment (without civil engineering works), and comparatively analysed the two catchments. The comparative results show that both catchments have similar material source, geomorphological/environmental and climatic conditions, however, vegetation cover and rock hardness are poorer in Goulinping than in Sanyanyu, the catchment that underwent larger-scale debris flows, suggesting that the mitigation measures had been applied in Sanyanyu catchment were inappropriate. Subsequently, we simulated the effectiveness of controlling debris flow peak discharge with check dams at the lower part of Sanyanyu and Goulinping catchment using the Kanako simulator, and summarised argument based on the hypothesis and facts from positive and negative aspects. We draw the conclusion that it is not reasonable to build check dams in the two catchments and instead, drainage channels should be primarily considered for reducing debris flow hazards in such densely populated areas. Finally, we undertook detailed field investigations and experiments on the native plants in the region, and found that the ecological mitigation measure with planting Robinia Pseudoacacia on the debris flow deposits is an effective method to alleviate debris flow hazards. It is concluded that channel works combined with ecological measures are the preferable approaches to minimize the debris flow damage in debris flow catchments characterised with high mountains, concentrated rainfalls and active neotectonic movement.

Ten years after Hurricane Katrina: monitoring recovery in New Orleans and the surrounding areas using remote sensing

Remote sensing data have been widely used in pre-hazard prevention/preparation, emergency response and post-hazard recovery monitoring. Hurricane Katrina caused serious damage to the environment, society and economy in the southern United States in 2005. On the 10th anniversary of Hurricane Katrina, we monitored the recovery process in New Orleans and the surrounding area based on remote sensing. Results from multi-source remote sensing data indicated that the average vegetation conditions of the affected areas have not fully recovered compared with the pre-disaster conditions, especially in the hurricane’s landfall area. Analysis from moderate resolution Landsat data showed that many civil engineering works have been undertaken in the city of New Orleans to prevent future disasters. Frequent observation using high-resolution images recorded the progress of some of these civil construction projects (e.g. the 17th Street Canal pumping station) in New Orleans. In this case study, we illustrated the capabilities of remote sensing techniques in recovery monitoring following a natural disaster. International/institutional cooperation is suggested to improve Earth observation capability in hazard monitoring. More Chinese Earth observation data are expected to be used in international monitoring.

Fracture Energy-Based Brittleness Index Development and Brittleness Quantification by Pre-peak Strength Parameters in Rock Uniaxial Compression

Brittleness is a fundamental mechanical rock property critical to many civil engineering works, mining development projects and mineral exploration operations. However, rock brittleness is a concept yet to be investigated as there is not any unique criterion available, widely accepted by rock engineering community able to describe rock brittleness quantitatively. In this study, new brittleness indices were developed based on fracture strain energy quantities obtained from the complete stress–strain characteristics of rocks. In doing so, different rocks having unconfined compressive strength values ranging from 7 to 215 MPa were examined in a series of quasi-static uniaxial compression tests after properly implementing lateral-strain control in a closed-loop system to apply axial load to rock specimen. This testing method was essential to capture post-peak regime of the rocks since a combination of class I–II or class II behaviour featured post-peak stress–strain behaviour. Further analysis on the post-peak strain localisation, stress–strain characteristics and the fracture pattern causing class I–II and class II behaviour were undertaken by analysing the development of field of strains in the rocks via three-dimensional digital image correlation. Analysis of the results demonstrated that pre-peak stress–strain brittleness indices proposed solely based on pre-peak stress–strain behaviour do not show any correlation with any of pre-peak rock mechanical parameters. On the other hand, the proposed brittleness indices based on pre-peak and post-peak stress–strain relations were found to competently describe an unambiguous brittleness scale against rock deformation and strength parameters such as the elastic modulus, the crack damage stress and the peak stress relevant to represent failure process.

Bayesian Decision Tool for the Analysis of Occupational Accidents in the Construction of Embankments

AbstractInstability and poor construction practices are responsible for the high accident rate in embankment construction in Spain. Applying a methodology based on data mining and attribute selection and using a 6-year database of accidents, key attributes in accidents associated with the construction of embankments were analyzed. Once the main predictors were identified, Bayesian networks in order to quantify the specific causes of different types of accidents were built. Thus, the main reasons for accidents as a preliminary phase to enhancing safety and embankment stability in mining and civil engineering works can be accurately identified and quantified.

Design with Uncertainty: The Role of Future Options for Infrastructure Integration

AbstractDecision making for effective infrastructure integration is challenging because the performance of long‐lasting facilities is often difficult to foresee or well beyond the designer's control. We propose a new approach for integrating the construction/retrofitting of two or more types of facilities. Infrastructure integration has many perceived benefits, but practitioners also express serious doubts, particularly when it comes to civil engineering works. To substantiate this approach, we test all of the major options for integrating a ground source heat pump system with the construction/retrofitting of an archetypal office building. We use actual data from the United Kingdom, which represent a middle‐of‐the‐road setting among major developed countries. The model highlights the sensitivity of the range of cost‐effective solutions to the embedding of future options. The findings point to a clear need for appropriate standards for managing infrastructure integration. We expect this kind of model to find increasing applications among infrastructure complexes, particularly as cities become denser and more multifunctional.

AN ANALYSIS OF THE PERFORMANCE OF DECONSTRUCTED TIRES FOR USE AS PADS IN RAILROAD TRACKS

The use of end-of-life (EOL) tires is now widespread in civil engineering work. In most cases, the tires are shredded and recycled as crumb rubber. However, this research focuses on an alternate method in which EOL tires were deconstructed to manufacture rail pads. In other words, their outer layer was removed, which made it possible to benefit from the mechanical properties of the tires without having to grind them up. The performance of the recycled tire rubber was analyzed by means of static and dynamic stiffness tests as well as by fatigue tests. The results reflected the long-term performance of the material. Also analyzed was the deterioration of its properties after various thermal and anti-ageing treatments. The results obtained were compared with those of commercial crumb rubber rail pads. The excellent performance of the rail pads made from deconstructed EOL tires shows the high potential of this material for use in railroad tracks.

Evaluation of Density-Measurement Methods for Construction Slurries

Abstract The density of slurries is an important quality-control parameter for many types of geotechnical works, such as slurry trenching, grouting, and bored piling. Although the working range of this parameter has been refined over the years in many standard specifications, surprisingly almost nothing has been done to improve the accuracy of the density-measurement technique. For density testing, almost all of the current standards specify the use of the conventional mud balance, although it has a measurement range far greater than what is actually needed for civil engineering works. To provide a scientific basis for the possible adoption of other measurement tools, this paper compares the performance of four different tools, namely, mud balance, digital density meter, aerometer, and pycnometer. From the results, it was found that the performance of the pycnometer depends on its measurement volume, and that the one with a nominal volume of 2 liters gives the best overall performance (measurement error ≤0.001 g/cm3). The accuracy of the mud balance and the aerometer has been found to be dependent on how they are read (i.e., to the original scale division or with care to a half a division) and also on the specimen. The digital density meter, although having good overall performance, cannot be used to measure fluids containing coarse soil particles because of the small diameter of the internal vibrating U-tube. The findings of this study will find applications in geotechnical works involving the use of slurries or grouts.

Occurrence and geographical distribution of metals and metalloids in sediments of the Nerbioi-Ibaizabal estuary (Bilbao, Basque Country)

Pollution in estuaries is an issue of high concern for scientists, local stakeholders and authorities. Sediments have been frequently used as sentinels of chemical pollution, including metals and metalloids. The estuary of the Nerbioi-Ibaizabal River was subjected to an important input of metals since the late XIXth century until about 1975. Afterwards, a significant decrease in chemical pollution has occurred due to a progressive closure of the most polluting activities and the pre-treatment of waste waters. However, a large scale civil engineering work, including a large movement of highly polluted sediments, has recently started in order to reduce the effects of floods and improve the urban image of the city. A precise description of the magnitude and geographical distribution of chemical pollution in the estuary nowadays would make feasible a future quantification of the effects derived from the above-mentioned work. With this aim, we collected sediments at about 50 sites in the inter-tidal part of the estuary in January 2009, 2010, 2011 and 2014, and the concentration of fourteen elements (Al, As, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Sn, V and Zn) in the acidic extract of the samples was simultaneously measured by ICP/MS. Afterwards, geoaccumulation indexes were calculated in order to estimate the metal fraction of anthropogenic origin. The Normalized and Weighed Average Concentrations (NWAC's) were also calculated to identify areas of higher concern. Finally, the mean Effect-Range-Median quotients (mERMq's) allowed us to estimate the toxicity associated to the sediments. The results show that: i) the geographical distribution of metals is rather heterogeneous within the estuary and changes from sampling campaign to sampling campaign, ii) hotspots of metal pollution are concentrated in a few points (the surroundings of the Gobela and Galindo tributary rivers and the closed dock of Deusto in 2009, 2010 and 2011, and the Abra Bay, the dock of Portu and the point where the effluent of the biggest waste water treatment plant of the area is released into the river in 2014), and iii) most of the sediments collected in those hotspots of pollution are highly toxic, mainly due to the presence of Pb, Cd, Zn, Cu and As of anthropogenic origin.

An investigation into the Accuracy of Distance Measurements to an object with the Pulse (Non-Prism) Total Station

In order to achieve the results that meet the specifications of a given project, like engineering surveys (e. g., Surveying of Buildings) , the knowledge of the reliability and accuracy of the surveying equipment is inevitable. The reflectorless total stations are used nowadays for several applications in civil engineering work due to their highly accurate , easy and fast measurements in an automated measuring process. The present paper investigates the accuracy and limits for prismless instrument Total Station especially in relation to observations with large (horizontal and/or vertical) angle of incidence to the reflecting surface , its colours and types, and beam divergence of the measuring signal. This study has been carried out with various surveying field tests by prism and prismless modes, using the pulse (non-prism) TOPCON GPT-2006 Total Station to evaluate the limitations and accuracy of this instrument in surveying the buildings (distance measurements).
 The current study has confirmed that while observations at right angles to an object ( building) are generally well within manufacturer specifications (σ=±10 mm), observations to surfaces of a building from a position that is not at right angles to the surface of the building ( signal beam) can introduce errors.
 Also , this study suggests that the angle of incidence of the measuring signal to the building points ( external and internal corners and wall surface points) has a large influence on the accuracy of that measurement. It is recommended to use horizontal angle of incidence for measuring the detail survey points between (-36 to + 36) degrees from the normal. Also, in case of measurements to a vertical surface, the maximum measured vertical angles of incidence was about forty degrees when using prismatic observations and fifty degrees for reflector less measurements. Some surveying techniques and recommendations are suggested to overcome these problems. Moreover, a good understanding of the non-prism instrument is required to get the required accuracy of the project. When using other total station equipment, the results of the current study can be used as a general guide only. The results of the current practical field experiments, computations and analysis of these tests using various calculations and least squares theory and computer programs (Excel and AutoCAD 2010) are also presented in digital and/or graphical forms.

Organisational culture and quality management system implementation in Indonesian construction companies

Purpose– The review of literature found that there is a significant correlation between a construction company’s organisational culture and the company quality performance. The purpose of this paper is to assess the organisational culture profiles of Indonesian construction companies, and to examine the influence of the companies’ organisational culture profiles on their quality management systems (based on QMS-ISO 9001:2008) implementation. Prior to conducting the examination, there are examinations of the relationships among the quality management system (QMS) variables.Design/methodology/approach– The methodology employed a survey questionnaire of construction industry practitioners who have experience in building and civil engineering works. The Organizational Culture Assessment Instrument was selected due to its suitability in assessing organisation’s underlying culture.Findings– Within the examination among the QMS variables, it was found that problematic issues associated with the implementation of QMS-ISO 9001:2008 in Indonesian construction companies can affect the implementation of the QMS and contribute to the lower level of companies’ business performance. It was also found that there is no significant relationship between the QMS implementation and the companies’ business performance. By using the Competing Values Framework diagram, it was found that most of the construction companies’ organisational culture is characterised by a Clan type which is reflected in how employees are managed, how the organisation is held together, and how the organisation’s success is defined; the leadership style is Hierarchy-focused, while the organisation’s strategy is Market type. It was also found that different culture profiles have different influences on the QMS implementation.Originality/value– A strong mixed Hierarchy and Market culture needs to be developed within the construction companies in Indonesia, as the driver to support proper and successful implementation of their QMS in order to enhance business performance in a quality performance-oriented Indonesian construction industry.

New model for predicting Instantaneous Cutting Rate of axial-type roadheaders

Roadheaders are mechanical excavators which have been extensively used in tunneling, mining and civil engineering works. Performance prediction of the roadheader is major factor in determining the economy of an underground excavation project. In this study, a new model for predicting the Instantaneous Cutting Rate (ICR) has been developed. The performance of EBZ260W axialtype roadheader has been evaluated in the laboratory artificial rock cutting tests and in the tunneling field tests. Using the model, the processes of the artificial rock cutting in the laboratory tests have also been simulated. The predicted average ICRs in the laboratory tests, and in the simulations, together with the measured average ICRs in the laboratory tests and in the field tests are presented in this paper. The comparison of the predicted and measured ICRs shows that the relative error is within 5%. There are also reasonable agreements and strong correlations between the model and tests results. The new ICR prediction model is also supported by the empirical prediction formulas developed by other researchers. Hence, the model can be used to reliably predict the ICR for axial-type roadheaders.

Simulation of the Basin Effects in the Po Plain During the Emilia-Romagna Seismic Sequence (2012) Using Empirical Green’s Functions

The two main earthquakes that occurred in 2012 (May 20 and 29) in the Reggio-Emiliano region (Northern Italy) were relatively small (Mw 6.1 and Mw 5.9) but they generated unexpected damages in a large area around the epicenter. On some stations, the observed seismic levels exceeded design levels recommended by the EC8 seismic code for buildings and civil engineering works. The ground motions generated by the two mainshocks have specific characteristics: the waveforms are mainly controlled by surface waves generated by the deep sedimentary Po plain, by local site effects and also, on some stations, by non-linear behaviors. In this particular context, we test the ability of an empirical Green’s function (EGF) simulation approach to reproduce the recorded seismograms in a large frequency band without any knowledge of the underground medium. We focus on the possibility to reproduce the strong surface waves generated by the basin at distances between 25 and 90 km. We choose to work on the second mainshock of the sequence (Mw 5.9), which occurred on May 29, 2012, because it is better recorded by the seismological networks than the May 20th first mainshock. We use a k-2 kinematic source model to generate a set of 100 slip distributions on the fault plane and choose the recordings of a close-by Mw 3.9 event as EGF. We then generate a set of broad-band seismograms (from 0.2 to 35 Hz) and compare them to the mainshock signals at 15 stations (Seismograms, Fourier spectra, PGA, PGV, duration, Stockwell Transforms) at epicentral distances from 5 to 160 km. We find that the main specific features of the signals are very well reproduced for all the stations within and beyond the basin. Nevertheless, at nearby stations, the PGA values are over-evaluated, which could be explained by the fact that non- linear effects are not taken into account in the simulation process. A better fit was found for a position of the nucleation point to the bottom west of the fault, that suggest a directivity effect of the rupture process of the May 29th event towards the North–East.

Mechanical Fatigue of a Stabilized/Treated Soil Tested with Uniaxial and Biaxial Flexural Tests

During Civil Engineering works, it is a common practice to upgrade mechanical performances of in situ soils by adding few percent of hydraulic binders such as lime and/or cement. But the specificity of stress state in railways structures (biaxial tension) and the lack of knowledge about the fatigue mechanical performances of treated/stabilized natural soils under this stress state have led to the non-use of treated soils in HSR layers. To enable the use of treated soils in railways infrastructures a specific test was developed to induce biaxial tension. This biaxial test, dedicated to railways structures and a uniaxial test from pavement design are applied to a treated soil. Results are compared; it appears that the treated soil has better performances under biaxial tension.