Conference Agenda

Soil nailing technique is extensively used for the stabilization of natural slopes and walls due to its unnumbered benefits viz. ease of installation in congested areas, flexibility, and a re-markable performance under seismic conditions. Various literature have highlighted the effec-tive use of soil nailing technique in the stabilization of slopes, cuts, landslides, and excava-tions. Recently, researchers have improved the efficiency of the conventional soil nails by add-ing a set of helices along the length of the nail. The novel soil nail is termed as the helical soil nail. In the present study, the reliability-based analysis of a wall stabilized using the novel hel-ical soil nails, is performed using the pseudo – static framework. The critical mode of failure for a helical soil nailed wall viz. the pullout mode, is considered in the formulation of the limit state function. The probability of failure (Pf) of the wall is approximated using the conventional sampling-based Monte – Carlo Simulation (MCS). The random variables include the internal friction angle of soil (ϕ) and the unit weight (γ). The Pf for a conventional soil nailed wall is compared with that of the helical soil nailed wall, to evaluate the efficacy of the helical soil nailed wall. The results depict a decrease in Pf when helical soil nails are used as a stabiliza-tion measure in place of the conventional soil nails. The influence of the randomness of input parameters is showcased by plotting a graph of Pf against the coefficient of variation (COV) of ϕ. The plot indicates a decrement in the stability of the wall with the increasing randomness which demonstrates the need for reliability analysis of the helical soil nailed walls. The paper also discusses the effect of nail inclination angle on the stability of the helical soil nailed wall. To the best of the authors’ knowledge, the proposed method is original.

<p>Reliability-based design for internal stability limit states for geosynthetic mechanically stabilized earth (MSE) walls provides a more nuanced appreciation of the margin of safety for these systems compared to conventional factor of safety, partial factor, and load and resistance factor design (LRFD) approaches. The paper introduces the basics of probabilistic analysis and design for internal stability limit states for MSE walls using the example of geogrid reinforced soil walls. The general approach uses a closed-form solution for reliability index which is easily implemented in a spreadsheet and thus eliminates the need for Monte Carlo simulation. A novel feature of the formulation is that it includes uncertainty in the choice of nominal values [which is consistent with the notion of level of understanding that appears in the Canadian Highway Bridge Design Code] and the underlying accuracy of the load and resistance models that appear in each limit state equation using bias statistics. The paper demonstrate how bias statistics for tensile load and pullout model accuracy can be gathered from load measurements recorded from instrumented walls and found in laboratory pullout box test databases. The concepts are general and can be applied to any soil-structure interaction problem which can be expressed by a simple linear limit state performance function and for which bias statistics are available. The paper concludes with an example of the calculation of the probabilistic margin of safety against failure of the reinforcement tensile strength limit state for all reinforcement layers in a wall using the AASHTO Simplified Method and the recently adopted AASHTO Stiffness Method in the USA. The calculations were performed for an actual instrumented and monitored production MSE wall constructed in the USA.</p>

Reinforced soil walls (RSW) are a proven alternative to conventional earth retaining struc-tures due to their rapid construction, smaller environmental impact, lower cost, as well as more sustainable social/functional features. Design methods for RSW appear in interna-tional codes and guidelines. However, they often do not provide detailed calculations for global stability assessment. Global stability can significantly affect RSW design for specif-ic geometric cases and/or site-specific boundary conditions. Traditional limit equilibrium (LE) methods have the disadvantage of not considering reinforcements and/or require iter-ations to achieve a safety factor (SF) value. Alternatively, numerical methods can be time consuming for both model generation, particularly for complex geometries, and during calculations. The present study discusses different analytical strategies using limit equilib-rium formulations and a numerical finite element method, and proposes a simplified ana-lytical method for global stability analysis based on a three-part wedge failure mechanism, and simple wall conditions.

<p>Over past few years, geosynthetics has been extensively used for load bearing and slope protection applications. Particularly the confinement and load transfer mechanisms of geocell have been extensively studied. Owing to the three-dimensional geometry providing lateral and vertical confinement, geocell is widely used in confining soils at the slopes and erosion protection work. On the slopes of North Saskatchewan River in Edmonton (Canada) around a light rail traffic tunnel portal, a 200mm thick facial fill for plantation was required on steep slope, already stabilized with soil anchors done by others. The additional thickness of top-soil fill was acceptable to the designer of the soil anchors.</p>

<p>However, additional loads like use of concrete were not an option. The slope varied from 25⁰ to 73⁰ stretching along the slope from 40m to 60m. An attempt was made utilizing novel polymeric alloy (NPA) geocell to retain and confine the facia fill. Conventional design approach with tendons was not possible as there was no anchoring allowed to existing soil anchors or at the top. As there were underground electrical conduits, even anchoring geocell with hooks was limited to specific locations. The entire area was divided into multiple areas with lap zone based on design demands. A hybrid design technique with wire net cover and hooks was developed to hold the geocell pockets in place. Special attention was necessary to prevent progressive failure of fill under the geocell. Current paper discusses the challenges through design and the remediation that was used. The design technique involving a unique combination of wire net and NPA geocell highlights a novel load transfer method. Critical observations during install and within six months after install, didn’t show any soil movement.</p>

The sustainability of protection structures has been attracting attention in recent times, especially after the introduction of the 2030 Agenda for Sustainable Development. However, such an issue has been hardly discussed in the case of flow-like landslides. Here the concept of de-formable protection systems made up of granular soil reinforced by geogrids is explored and compared to more traditional concrete rigid walls. The numerical analyses concern the impact of fast-moving landslides on these two types of protection structures to understand their performance in stopping the propagation of the flow. To this aim, an advanced numerical model-ling capable to consider the non-zero initial velocity of the landslide and the large deformation occurring inside both the landslide and the structure is used. Both the landslide soil and the barrier material are simulated as frictional elasto-plastic non-associative media. The role and the time-space evolution of the pore-water pressure inside the landslide material under different impact scenarios are computed. Furthermore, the amount, type, and features of the needed construction materials are compared towards a sound assessment of the sustainability of both solutions.

<p>A common system for specification and certification of geosynthetics, NorGeoSpec, has been in operation in the Nordic countries since 2002. Experiences have revealed a lack of relevant requirements related to installation and function of geosynthetics in a cold climate. A Nordic development project ROUGH (RecOmmendations for the Use of GeosyntHetics in Nordic conditions) has been established to identify special requirements for geosynthetics to ensure technically and economically optimal solutions in country-specific climates and soils. Traffic Authorities in Finland, Sweden and Norway, research institutes, universities and a group of producers participated in the project. The project is especially focusing on local cold climates, local soil conditions in Nordic countries and local construction methods and typical aggregate materials. The project includes a survey of experiences, literature studies, laboratory investigations and a full-scale test site established near Kemi in Northern Finland. The test site was established along an ongoing construction project to upgrade the Highway 4 (E8/E75). [UV1] The Traffic authority in Finland, FTIA, provided the test site and the contractor, GRK Infra Oy, carried out the construction work during installation and extraction on the site. Altogether 13 products were installed covering the functions reinforcement/stabilization, filter and drainage. The products were installed as a part of a road structure and a drainage ditch in temperatures down to -15 °C. The installation and compaction were carried out according to pre-determined procedures, while the procedures for the extraction of the products had to be specially adapted to be able to remove the fill material on top of the geosynthetics, without creating added potential damages due to excavation. The tests provided valuable information on potential damage during installation of geosynthetics. It is completed by laboratory testing and this brings a good basis for the preparation of guidelines for the installation of geosynthetics in a cold climate</p>

Design criteria for geosynthetic-reinforced earth walls are usually based on simplified limit equilibrium approaches, taking into account ultimate conditions both with respect to soil strength and reinforcements’ resistance (tensile and pull-out). Convenient values of partial safety factors are then introduced to get a safe structural dimensioning. The stability of in-ternal failure mechanisms is however based on the mobilization of soil-geosynthetic inter-face shear stresses and the reinforcement action should rather be computed as a function of the current internal displacements within the wall. In the paper a simplified displace-ment-based hybrid approach is introduced, combining traditional limit equilibrium anal-yses of internal failure mechanisms together with displacement controlled non-linear pull-out analyses of the reinforcements. A consistent relationship between the safety factor and the performance of the wall (i.e. façade displacement) can then be derived, providing the designers of an objective tool to optimize the design choices and to run consistent struc-tural safety checks.

<p>Rockfalls are high-velocity landslide events that have massive destructive potential and hence pose a widespread natural threat in the Himalayan regions of India. An effective solution for arresting and deviating the falling rocks is the construction of Rockfall Protection Embankments (RPE) at the toe of the hills. Such elevated structures are not only cost-efficient but also have the highest impact resistance capacities. However, the design of such RPEs is not yet standardised. Thus, a comprehensive review of reported experimental studies on RPEs is conducted to understand the various parameters influencing its impact response. The review details the dimensions and materials used in the RPEs and studies the respective impact responses in terms of impacting velocity and kinetic energy of the rock block, height and width of the RPE at the zone of impact, and penetration width induced by the impacting blocks. The efficacy of these RPEs is then assessed using the kinetic energy criterion.</p>

<p>From the detailed review, a direct correlation is observed between the kinetic energy factor (Kinetic energy of impacting block / 250*Cross-sectional area of RPE) and the penetration width experienced by the RPEs. Once the veracity of the kinetic energy criterion is established, it is used to design a protection embankment for a probable rockfall event on the Manali-Leh highway in the Himalayan region of Northern India. The rockfall parameters considered in the design, like, maximum probable bounce heights and kinetic energies of falling rocks, are considered from a reported study on rockfall analysis conducted for the Manali-Leh highway. The dimensions of the protection embankment are then determined using the kinetic energy criterion and empirical approaches recommended by the Highway Research Board of Indian Roads Congress (2014). Thus, this paper provides technical guidance for the design of rockfall protection embankments. </p>

<p>Due to rapid and extreme climate changes, in mountain and hilly regions infrastructures and people are more often treathened by rockfalls events. Falling boulders can have extremely high speeds, and these events involve a complex pattern of movement (e.g. detachment, fall, rolling, sliding, bouncing, etc) of one or more rock fragments. Rockfall Protection Embankments (RPE) reinforced with geosynthetics proved to be a safe measure for protecting people, structures and infrastructures from rockfall events, designed to absorb even very high impact energy (up to 30,000 kJ). RPEs can be constructed in various shapes and sizes, with different reinforcements (geogrids, geotextiles, geostrips, steel wire meshes, etc.) and facing materials (wrap-around, gabions, tires, etc.). The vast majority of existing RPE structures have been designed with basic approaches, considering dynamics only to a minor extent. The Authors have then developed a new analytical design method which consider the effect of all the variables playing a role in the resistance to penetration on the uphill face and the resistance to extrusion on the downhill face, in order to finally compute approximate yet consistent values of the penetration depth and of the extrusion length; hence the designer can quickly try different solutions and finally select the best combination of design variables which afford to respect all design limits and Factors of Safety. To the Authors’ knowledge, at present this is the only design method for RPEs which allows to take into account all the parameters contributing to the penetration and extrusion resistance, including the type and properties of geosynthetics, the layout and spacing of reinforcement in longitudinal and transversal direction of embankment, the type of facing, the properties of the fill and the geometry of the embankment. A back analysis of full scale tests is used to validate the presented design method.</p>