Publications

Dynamic penetrometer is a worldwide practice in geotechnical exploration and the French Panda®(1) lightweight variable energy is the most developed device nowadays. Widely used in France and other countries, The Panda penetrometer is relatively unknown for characterizing surface soils domain and the possibilities it offers. In this Article, the authors offer a brief review of the principle of measurement, its uses, advantages and disadvantages calibration, and interpretation, as well as the different relationships with other in-situ test (CPT, SPT…) and some geotechnical parameters. A summary of the works that can be found and that are based on this technology is also presented. The overall aim is to provide the reader with a basic historical document for a better understanding of the operation and analysis of the results obtained with this device, enabling it to be integrated, as a complement, into in situ investigation campaigns.

Dynamic penetration tests DPT have been routinely employed in the geotechnical characterization of thesubsoil in different types of engineering projects. The evaluation of the results of these tests has been performed consideringa limited number of parameters obtained in the field, so the definition of new parameters allows a more accurate evaluationof soil characteristics. The purpose of this paper is to present a methodology for the evaluation of the dynamic modulus(Ekd) based on the analysis of the dynamic force and velocity signals recorded in each hammer impact. Variable energyDPT tests were performed on Fontainebleau NE34 sand specimens in a K0 calibration chamber. For each hammer impacton the penetrometer, a decoupling and wave reconstruction method was applied to obtain the force and velocity signals atthe cone-soil interface, which are analyzed in the frequency spectrum to obtain the Ekd modulus. The results show that it ispossible to evaluate the dynamic modulus at different vertical loading conditions and independent of the impact energy levelof the hammer on the penetrometer.

Dynamic penetration tests (DPT) are largely applied for soil in situ characterization. Cone resistance assessment from DPT isusually based on driving formulas derived from Newtonian approach. These are nevertheless often considered inaccurate and unable to fullydescribe dynamic penetration phenomenon. Wave equation approach provides a more rigorous analysis but remains less common for practicalreasons (requiring instrumentation and a more complex analysis). Historically, driving formulas derived from Newtonian approach are oftenpreferred for its simplicity. Thus, these formulas still play a major role in DPT interpretation and their use is recommended by currentstandards. It is important to evaluate different methods derived from wave equation and also to verify if a simple approach, such as Dutchformula (DF), combined with good practice (e.g., energy measurement, skin friction control) can produce satisfactory results. For that,laboratory and field tests were performed employing instrumented dynamic penetrometers (a lightweight and a super-heavy dynamic penetrometer).The main contribution of this paper is demonstrating the importance of method applied when determining resistance from DPTand providing comparison between common methods when testing different type of soils. Results showed that on average DF results werecomparable to those from cone penetration test (CPT) resistance (diverging by no more than 15%). Wave equation methods results werecomparable (
30%) to CPT cone resistance in most cases when testing shallower nonplastic layers. CASE method underestimated by morethan 50% the resistance for shallower layers. DF including energy measurements produce lower results than all methods examined and up to50% inferior to CPT. This work shows that, for shallow soils, DF method does not produce less accurate for assessment of soil resistance thatwave equation-based methods. Other key aspect brought to light is that wave equation-based methods considerably overestimated resistancein deeper plastic saturated layers which suggests that skin friction correction application should also be considered in such conditions forthese methods. When only unsaturated zones are considered, these methods tend to underestimate resistance: Simplified method and tip forceintegration method produced results 18% and 24% inferior to CPT whereas DF with energy measurement and other wave equation methodssignificantly underestimated resistance (on more than 40%).

The degradation of the substructure plays a crucial role in the geometric deterioration of railway track. The condition of the substructure is evaluated by means of geotechnical diagnostics that consider various parameters, among which the geotechnical layer model stands out (Basye et al., 2020). The accuracy in the determination of this model is essential, since it significantly influences decision making and ensures the efficiency of the measures taken. In this study, data fusion is proposed to reduce the uncertainty and increase the reliability of the geotechnical layer model of the substructure. This technique combines different types of data and monitoring results, integrating geotechnical indicators (Pandoscope®) and volumetric geophysical measurements (Ground penetration radar - GPR). The results show that data fusion increases the accuracy of the geotechnical model, improving decision making in railway maintenance.

Railway tracks, like all civil works, experience degradation after being put into service, thus losing their initial design conditions. This degradation manifests itself mainly through misalignment and specific deterioration mechanisms of each component, which reduces safety and comfort during the passage of trains. In order to maintain their operational capabilities or prolong their service life, continuous monitoring, diagnosis and maintenance processes are carried out. These actions aim to restore the physical, mechanical and geometrical properties necessary for track operation. In practice, rail managers often employ hegemonic techniques such as geometric measurements to detect defects and routine maintenance to realign, known as tamping. Although these practices have proven to be effective, in some cases they do not technically and economically competently solve the root problem. For this reason, diagnosis should be multidisciplinary and incorporate various disciplines associated with the track components. This paper aims to highlight the importance and impact of geotechnical diagnosis in the management of railway networks. To achieve this, the Article has the following structure: (a) Railway track components: the main elements of the track are described and the role of geotechnical components in the stability of the infrastructure is highlighted, (b) Track degradation: The main deterioration of the track, such as loss of geometry, and its relation to the wear of the geotechnical elements are addressed, (c) Monitoring and monitoring: the most commonly used geotechnical inspection methods and their effectiveness in the analysis of granular material are presented, (d) Geotechnical diagnosis: Current maintenance management is analyzed and guidelines for a comprehensive diagnosis are suggested, highlighting cases where poor assessment has generated problems, (e) Maintenance techniques: Preservation methods are reviewed, stressing the importance of accurate diagnosis for their effectiveness, and (f) Future perspectives: Trends such as the use of artificial intelligence and advanced data management in the railway sector are explored.

In the context of railways, it is essential to have a reliable ground model to ensure their safety and smooth operation. To achieve this, geophysical monitoring, and geotechnical techniques, are often used. However, effectively combining geophysical and geotechnical data remains a challenge. In this study, a methodology based on data fusion of Ground Penetrating Radar (GPR) and Pandoscope data and based on belief functions is proposed in order to define the ground model of the railway substructure. The fusion of these data using Smets, Dempster-Shafer and PCR6 normalization rules allows to improve the character-ization of horizontal interfaces and to achieve an accurate assessment of the sub-surface conditions on railway tracks.

Although ballast layer can be characterized by different parameters, the literature notes the absence of global performance indicators of ballast in ser-vice. This Article presents a methodology that proposed to obtain local perfor-mance indicators (based on the functions performed by the ballast layer) and global performance indicators (based on the combination of the above). The pro-posed methodology consists of three phases: (i) the first is the performance of a functional analysis (FA) for the identification of the key functions of the ballast layer, (ii) application of the failure mode and effects analysis (FMEA) for the creation of the failure trees of the functions identified in the previous phase and (iii) application of data aggregation to combine the parameters and indicators in the form of a model to obtain the performance indicators. The results of perfor-mance indicators can be useful for the planning of corrective actions and in case of failures or defects to identify their causes. The methodology allows adapting the conditions and/or needs of each railway manager by modifying the failure modes and modifying the scales proposed for data aggregation.

Coastal beach and dune ecosystems are critically important for shoreline protection and significant resources have been allocated to their conservation. Dune vegetation is known to modify site response to wind, waves, and storms, but little focus has been given to understanding how belowground sediment structures enhance dune stability. A first step in addressing this knowledge gap is to determine optimal methods to measure subsurface sediment properties in onshore sandy environments. Our team performed a comparison of geotechnical and geophysical methods on a restored beach and dune system on Florida’s Atlantic coast. Methods included two types of dynamic cone penetrometer (DCP) systems, a multi-channel analysis of surface wave (MASW) system, a ground penetrating radar (GPR), soil vibracores, and grain size analyses. Two transects were investigated, a 50-meter cross-shore transect and an intersecting 20-meter along-shore transect. The transects were selected to study the gradient of sediment properties from the swash zone to the high dune. Key findings from this study were that the PANDA DCP provided a higher resolution of measurements compared to the standard DCP, which is extremely advantageous in the shallower, less consolidated soils. MASW shear wave velocity results showed similar trends to the DCP cone tip resistance and allowed for measurement of stiffer soils where the DCP reached refusal. In addition, the results from the DCP, GPR and vibracores compared well. Thus, the use of the DCP and GPR systems as minimally intrusive testing options in fragile dune systems was verified.

El equipo de Penetrómetro dinámico ligero a energía variable (PANDA) se ha destinado principalmente alcontrol de calidad de compactación, dejando de lado su uso para la clasificación o identificación del tipo de material, talcomo se ha hecho con resultados del ensaye de CPTu. Con un sondeo de PANDA se aprovecha la versatilidad de ser unequipo compacto y con posibilidad de acceder a zonas donde es complicado ingresar con equipos convencionales para laejecución de SPT y CPTu, con la finalidad de caracterizar los materiales en áreas específicas, de difícil acceso o donde nose requiere llegar a una profundidad mayor a los 5 m. En el presente artículo se propone el desarrollo de una correlaciónpara identificar el tipo de material a partir de la resistencia dinámica de punta (qd) de sondeos de PANDA, llevados a caboen un depósito con descarga de jales fluidos (slurry), partiendo de una calibración con resultados de pruebas de laboratorioen muestras de jales gruesos y jales finos (lamas) extraídas en el mismo punto de ejecución de los sondeos de PANDA,con el propósito de contar con una expresión con mayor aplicabilidad en los jales, que permita una rápida caracterizaciónen zonas superficiales o de difícil acceso dentro del depósito.

The progressive degradation of railway ballast over time increases the degree of ballast fouling and poses significant drainabilityconcerns leading to frequent maintenance activities. To avoid such issues, an effective and continuous characterization ofthe physical properties of the ballast layer is deemed necessary. This paper introduces the combined use of a bender element(BE) piezoelectric field sensor and a PANDA dynamic cone penetrometer for periodic evaluations of ballast condition overthe traffic use. To simulate various levels of ballast degradation, box tests were conducted using a dolomitic ballast materialcompacted in a laboratory-sized testbed with fouling indices ranging from zero to 39%. BE sensor pairs were embedded inthe ballast layer to calculate the small strain modulus behavior of the ballast assessed through shear wave velocity measurementsunder different confinement conditions. Strength profiles of the ballast at different fouling levels were also measuredusing the PANDA penetrometer. Experimental findings from both test methods indicate the existence of a dense state ofballast linked to a certain fouling index that maximized stiffness and strength characteristics of the tested ballast in dry condition.Accordingly, the potential use of BE field sensors embedded within in-service ballasted track coupled with periodicpenetration testing can be a viable approach to evaluate ballast layer degradation. Various void packing conditions associatedwith ballast fouling levels can be linked to important ballast layer modulus and strength behavior. Further, such smart sensingof ballasted track behavior can provide long-term performance monitoring solutions for ballast cleaning and maintenancescheduling.