change of hydraulic conductivity of cohesive soils due to consolidation treatments with expanding resins

Settlements of ground subjected to foundation load are often due to both natural and/or anthropogenic causes, such as differential consolidation, seepage, periods of drought alternating with heavy rainfalls, growth of tree roots, sewer leaks, vibrations induced by vehicle traffic, excavations, or construction defects. Techniques of soil consolidation and stabilization by means of injection of polyurethane expanding resins have been efficiently used to mitigate or even solve this issue. The efficiency of the resin injection treatment has been well documented also thanks to the develop of a procedure of planning and monitoring which combines traditional geotechnical tests with the application of electrical resistivity tomography, which is strongly sensitive to the presence of water or voids. The combination of these survey methodologies allows to recognize the effect of injection in terms of soil compaction and water migration, a key factor for understanding the phenomenon and planning of resolutive interventions. The present study follows a previous work aimed at evaluating the increase in the geotechnical performance of cohesive soils treated by injection of expanding resins (same soil, resin, at the same site) and integrates it by focusing on the quantification of the effects of consolidation treatments, by means of expanding resins injection, on hydrologic properties of cohesive soils, focusing on saturated hydraulic conductivity measurements. Laboratory permeability test, performed in triaxial cell at different stress conditions and hydraulic gradients, were performed on undisturbed samples collected on "natural (non-treated)" and "treated soils", before and after the injection of resin (MAXIMA ® by GEOSEC ® ) in a full-scale test site characterized by the presence of continuous and homogeneous cohesive soils, (clay and silts). The investigated soil is classified as CH or CL soil, very firm and apparently overconsolidated. The study shows how the treatment is able to modify the characteristics of hydraulic conductivity of the soil. The injected resins partly follow pre-existing weaknesses and partly impregnate homogeneous and continuous masses of soil in a capillary way, giving it, in addition to the already documented greater mechanical strength, a lower hydraulic conductivity. The electrical resistivity investigations allow to appreciate the volumes affected by the treatment to which the variations of the measured properties can be attributed

Piuro Landslide: 3D Hydromechanical Numerical Modelling of the 1618 Event

The Piuro 1618 landslide represents a well-known case history of a large Alpine landslide. It destroyed the ancient village of Piuro (Italian Bregaglia Valley), renowned as an important trading center between the Mediterranean region and Northern Europe. The event had a significant impact among communities of all Alpine regions and was well documented by chronicles and paintings during subsequent decades. However, some aspects, such as the geometry reconstruction of the landslide body, the location of the landslide scarp, and its dynamics, remained undefined in previous studies, and a geomechanical characterization of the failure area is completely missing. Using field and laboratory analysis followed by stress–strain numerical modelling, this work develops a 3D conceptual geomechanical model of the slope considering its complex geological framework. The aim is to back-analyze the 1618 event, defining predisposing and triggering factors of the sliding event, and providing verifications on the geometry and location of the failure scar, as well as on the landslide dynamics. A coupled hydro-mechanical analysis with a 3D numerical approach is presented, assuming a rainfall scenario as a possible triggering factor. Simulated displacement and the development of a deep region of shear strain localization at a depth roughly corresponding to that of the detected Piuro sliding surface, allow us to highlight the mechanical role of geological elements outcropping along the slope and to validate the proposed scenario as a likely triggering factor for the 1618 event

The Last Glaciation in Valchiavenna (Italian Alps): maximum ice elevation data and recessional glacial deposits and landforms

This work presents the first extensive, 1:10,000-scale field survey data concerning glacial deposits and glacigenic landforms in the Valchiavenna territory, which has an area of 578 km². Valchiavenna is an inner Alpine valley in Northern Italy between the Lepontine and Western Rhaetian Alps. A comprehensive 1:25,000 map of deposits and landforms from the last glaciation to the present is provided, describing i) glacial trimline evidence and associated features, such as moraine ridges, erratic boulders, ice-moulded bedrock surfaces and kame terraces; ii) glacial, ice-contact, lacustrine/peat and gravity-reworked till deposits; iii) other supraglacial, marginoglacial and subglacial landforms; and iv) erratics in glacial deposits. Establishing an absolute chronology of glacier dynamics was not the objective of this work. However, a relative chronology was inferred from sedimentological and geomorphological evidence: this allowed the description of the general behaviour of glaciers in the area during and after the Last Glacial Maximum (LGM). The palaeogeography at the LGM and the palaeo-ice-flow pattern were reconstructed on the basis of field data; this data confirmed that the valleys were almost completely filled by glacier ice, covering about 88% of the study area, with only the most elevated ridges and a few nunataks emerging above the ice surface, and allowed the identification of different source areas for the erratics found on opposite sides of the main valley. The observation of stratigraphical and geomorphological relationships between glacial deposits and landforms made it possible to propose a relative chronology of glacial advances and to outline the general glacial dynamics of the area. Both at the LGM and during the deglaciation after the LGM, the valley glacier inserted offshoots in tributary valleys, thus generally blocking the advance of local glaciers. With the gradual melting of the valley glacier during the deglaciation after the LGM, tributary glaciers could deposit tills on areas previously covered by valley glacier ice and at lower altitudes than the older lateral moraines. The main outcome of this work is a rich and homogeneous database of glacial deposits and glacigenic landforms that will be useful for further local and regional studies. It can guide the planning of geochronological dating and represents a fundamental step in the identification of glacial stadials and ice mass modelling. It can also support biogeography studies and the evaluation of the effects of climate change, slope dynamics modelling and hazard prediction

Introducing intense rainfall and snowmelt variables to implement a process-related non-stationary shallow landslide susceptibility analysis

The study objective was to derive a susceptibility model for shallow landslides that could include process-related non-stationary variables, to be adaptable to climate changes. We selected the territory of the Mont-Emilius and Mont-Cervin Mountain Communities (northern Italy) as the study area. To define summary variables related to landslide predisposing and triggering processes, we investigated the relationships between landslide occurrences and intense rainfall and snowmelt events (period 1991–2020). For landslide susceptibility mapping, we set up a Generalized Additive Model. We defined a reference model through variable penalization (relief, NDVI, land cover and geology predictors). Similarly, we optimized a model including the climate variables, checking their smooth functions to ensure physical plausibility. Finally, we validated the optimized model through a k-fold cross-validation and performed an evaluation based on contingency tables, area under the receiver operating characteristic curve (AUROC) and variable importance (decrease in explained variance). The climate variables that resulted as being statistically and physically significant are the effective annual number of rainfall events with intensity–duration characteristics above a defined threshold (EATean) and the average number of melting events occurring in a hydrological year (MEn). In the optimized model, EATean and MEn accounted for 5% of the explained deviance. Compared to the reference model, their introduction led to an increase in true positive rate and AUROC of 2.4% and 0.8%, respectively. Also, their inclusion caused a transition of the vulnerability class in 11.0% of the study area. The k-fold validation confirmed the statistical significance and physical plausibility of the meteorological variables in 74% (EATean) and 93% (MEn) of the fitted models. Our results demonstrate the validity of the proposed approach to introduce process-related, non-stationary, physically-plausible climate variables within a shallow landslide susceptibility analysis. Not only do the variables improve the model performance, but they make it adaptable to map the future evolution of landslide susceptibility including climate changes

Deformation of Stromboli Volcano (Italy) During the 2007 Eruption Revealed by Radar Interferometry, Numerical Modelling and Structural Geological Field Data

The activity of Stromboli volcano is characterized by very low energy explosions, occurring every 10-15 minutes, throwing out lava above the crater rim. During 2007, the volcano showed an anomalous activity in which new effusive vents developed (27 February and 9 March) and a major explosion took place on 15 March. This paper presents an integrated study based on a structural geological field survey, interferometric radar monitoring and numerical modelling on the deformations of the upper NW flank of the volcano (Sciara del Fuoco-SdF). The field survey carried out during the 2007 events shows the development of mainly NE-striking fissures and fractures on the northern part of the upper SdF. In January 2007, the ground-based synthetic aperture radar (GB-InSAR), installed on the flank of the SdF, showed a progressive acceleration of movement on the NE crater preceding the eruption of 27 February 2007. By the first half of February, the acceleration also involved the upper portion of the SdF and on 27 February the eruption started with the opening of new vents and deformation rates higher than the measurement capability of the radar device. On 8-9 March 2007, the GB-InSAR highlighted the formation of a bulge on the NW sector of the SdF, preceding the opening of an additional vent. To understand the deformation pattern recorded during the eruption, a numerical simulation was carried out by using the FLAC 3D code. Based on the integration of all the data, the deformations observed in the pre-effusive phase (before 27 February) seem to be related to the intrusion of a SW-NE striking dyke. The bulging recorded before the 9 March vent opening is instead to be associated with the intrusion of a sub-horizontal sill.JRC.G.6-Security technology assessmen

THE CONSOLIDATION AND STABILIZATION OF FOUNDATION SOILS THROUGH THE INJECTION OF EXPANDING POLYURETHANE RESIN UNDER A NON-INVASIVE DIAGNOSTIC CHECK BY 3D-4D-ERT

Vertical differential settlement of buildings is produced by both natural and/or anthropogenic disturbances of the foundation soil, such as, for example, differential consolidation, circulation of water due to rupture of water pipes, seepage, suction, vibrations induced by vehicle traffic, excavations, construction defects and an incorrect design/execution of the work. Techniques of soil consolidation and stabilization by means of expanding resin injections are being advantageously employed to mitigate or even solve this issue. The resin used is a two-component polyurethane compound that, once its chemical reaction is completed, reaches an inert and lightweight solid state so that it is environment-safe and perfectly compatible with the injected soil. The resin is injected directly into the critical volumes by means of small diameter pipes. After the injection, the resin expands rapidly in the soil through an irreversible exothermic chemical reaction, so that it actively counteracts the settlement and its causes. Indeed, the observed effects are threefold: i) filling voids; ii) compacting soil; iii) reducing/removing interstitial water. Among the possible procedures to monitor soil consolidation and stabilization by injections of expanding resins, a procedure is hereafter described which involves the use of electrical resistivity tomography (ERT). The rationale for the use of this non-invasive imaging technique is that electrical resistivity is a physical property sensitive to grain size, porosity and water content of sediments and to voids. Therefore, it can both acquire information about the subsurface structure, also from volumes of difficult access (e.g.,, below the foundations and the floor of the building), which is necessary for the consolidation project, and it can monitor the injection work in progress, in addition to traditional geotechnical testing. Specifically, the process is divided into several steps. A 3D-ERT is acquired first, covering both the volumes affected by the settlement and nearby stable volumes of soil underlying the footprint of the building, to accurately map the different resistivity that characterizes the anomalous volumes. The 3D resistivity model is integrated, wherever necessary, by geotechnical investigations, mainly penetration tests and sample identification, so as to optimally design the injection points, in terms of position, depth and number. During injections, the 3D-ERT and some geotechnical tests are repeated to check progressively the effects obtained by the treatment, so as to allow, if necessary, to modify the injection scheme until reaching the predetermined target, i.e., obtaining the greatest uniformity of chemical and physical characteristics between the stabilized volumes and the nearby stable ones, which are used as a reference. In some sites, where the settlement was stabilized by the above procedure, it was also possible to repeat a 3D-ERT after several years: results confirmed that the situation of the subsurface just after the injections had remained almost unaltered and the effectiveness of the procedure over time was demonstrated. The above approach is described hereafter and is accompanied by the description of the results from a specifically planned test site and from two work sites, selected as examples

THE CONSOLIDATION AND STABILIZATION OF FOUNDATION SOILS THROUGH THE INJECTION OF EXPANDING POLYURETHANE RESIN UNDER A NON-INVASIVE DIAGNOSTIC CHECK BY 3D-4D-ERT

Vertical differential settlement of buildings is produced by both natural and/or anthropogenic disturbances of the foundation soil, such as, for example, differential consolidation, circulation of water due to rupture of water pipes, seepage, suction, vibrations induced by vehicle traffic, excavations, construction defects and an incorrect design/execution of the work. Techniques of soil consolidation and stabilization by means of expanding resin injections are being advantageously employed to mitigate or even solve this issue. The resin used is a two-component polyurethane compound that, once its chemical reaction is completed, reaches an inert and lightweight solid state so that it is environment-safe and perfectly compatible with the injected soil. The resin is injected directly into the critical volumes by means of small diameter pipes. After the injection, the resin expands rapidly in the soil through an irreversible exothermic chemical reaction, so that it actively counteracts the settlement and its causes. Indeed, the observed effects are threefold: i) filling voids; ii) compacting soil; iii) reducing/removing interstitial water. Among the possible procedures to monitor soil consolidation and stabilization by injections of expanding resins, a procedure is hereafter described which involves the use of electrical resistivity tomography (ERT). The rationale for the use of this non-invasive imaging technique is that electrical resistivity is a physical property sensitive to grain size, porosity and water content of sediments and to voids. Therefore, it can both acquire information about the subsurface structure, also from volumes of difficult access (e.g.,, below the foundations and the floor of the building), which is necessary for the consolidation project, and it can monitor the injection work in progress, in addition to traditional geotechnical testing. Specifically, the process is divided into several steps. A 3D-ERT is acquired first, covering both the volumes affected by the settlement and nearby stable volumes of soil underlying the footprint of the building, to accurately map the different resistivity that characterizes the anomalous volumes. The 3D resistivity model is integrated, wherever necessary, by geotechnical investigations, mainly penetration tests and sample identification, so as to optimally design the injection points, in terms of position, depth and number. During injections, the 3D-ERT and some geotechnical tests are repeated to check progressively the effects obtained by the treatment, so as to allow, if necessary, to modify the injection scheme until reaching the predetermined target, i.e., obtaining the greatest uniformity of chemical and physical characteristics between the stabilized volumes and the nearby stable ones, which are used as a reference. In some sites, where the settlement was stabilized by the above procedure, it was also possible to repeat a 3D-ERT after several years: results confirmed that the situation of the subsurface just after the injections had remained almost unaltered and the effectiveness of the procedure over time was demonstrated. The above approach is described hereafter and is accompanied by the description of the results from a specifically planned test site and from two work sites, selected as examples