Natural and anthropogenic agents in the present geomorphological dynamics of the Torrent Corlo mountain catchment (Northern Apennines, Italy)

The morphological changes affecting a small mountain catchment in the territory of Modena (Italy) have been taken into account. In particular, based on detailed field surveys and analysis of remote sensing imagery, an assessment was made on the natural and anthropogenic agents which have modelled this basin in the past 80 years. For several decades, the Torrent Corlo catchment was subject to intense exploitation of clay raw materials in order to supply a flourishing ceramic tile industry. As a result, a strong, negative impact has affected the landscape and, in some areas, the geomorphological evolution due to man’s activities greatly surpasses the changes ascribable to natural processes, such as landslides or stream channel processes. Since 2008, all quarrying activities have ceased and the local public administration has started a project of reclamation of the abandoned clay pits, although it will not be possible to restore completely the original, natural features of this catchment. A comparison is made with the sub-catchment Rio delle Vigne valley, which has been spared from anthropogenic changes and has been affected only by natural gravity-induced processes, which have produced some twelve landslides. The final products of this research are the implementation of the first geomorphological map of the T. Corlo mountain catchment and an updated version of the hydrological hazard map, in which active and dormant landslides are much more numerous than those mapped in any other previous geological map (s.l.). These documents can be utilized for any intervention by public boards aiming at recuperating and improving this intensely exploited area

Evaluation of structural modification of a hard deep clayey rock due to wetting/drying cycles

International audienceNew wetting / drying tests including cycles effects were performed on the same argillaceous deep rocks coming from Callovo-Oxfordien deposit from eastern France. Bulk volume and water content were measured in order to estimate the importance of physical changes. Then mercury injection tests were performed on dry and wet samples in order to quantify the influence of hydraulic history on fracture. Results showed that shrinkage and swelling originated micro-cracks which led to important volume variations, and thus strongly altered structures and organizations of the rock. Mercury injection tests performed on wet samples equilibrated with different hygrométrie saline solutions allow describing unsaturated pores and complete classical water retention curves to explain changes in microstructure and related mechanical and physical properties

Digital volume correlation applied to X-ray micro-tomography images in uniaxial creep tests on anisotropic clayey rock

Creep tests are commonly performed to characterize time-dependent deformation of geological materials. Classical measuring methods are not suitable for long term tests and not able to provide full three-dimensional strain fields. In this study, Digital Volume Correlation (DVC) is applied to X-ray micro-tomography (XRMT) images from creep tests on a hard clayey rock. In situ uniaxial compression creep tests are performed under different levels of stress and with different loading orientations with respect to the structural anisotropy of rock. Based on the XRMT images taken during the creep tests, DVC is applied to compute the full three dimensional strain fields and global averages strains of tested samples. The effects of bedding planes and hard inclusions on the non-uniform distribution of strains are analyzed

The peculiarities of clayey rock swelling in electrolyte solutions

Osmotic pressure in swelling clay rock depends on the type and concentration of the pore solution. At zero concentration of the pore solution osmotic pressure is generated by ions-compensators negative electric charge of clay particles. Last is the cause of heterovalent substitution of iron ions in the octahedral sites and silicon ions in tetrahedral sites. If the osmotic pressure is balanced by the external pressure on the osmotic system, the latter starts to swell. The presence of electrolytes in the water changes the magnitude of the osmotic pressure in the clayey rock. The dependence of the concentration of the osmotic pressure of the solution is rather complex, therefore at different solution concentrations swelling of clayey rocks proceeds differently

Numerical analysis of rapid drawdown: applications in real cases

In this study, rapid drawdown scenarios were analyzed by means of numerical examples as well as modeling of real cases with in situ measurements. The aim of the study was to evaluate different approaches available for calculating pore water pressure distributions during and after a drawdown. To do that, a single slope subjected to a drawdown was first analyzed under different calculation alternatives, and numerical results were discussed. Simple methods, such as undrained analysis and pure flow analysis, implicitly assuming a rigid soil skeleton, lead to significant errors in pore water pressure distributions when compared with coupled flow-deformation analysis. A similar analysis was performed for the upstream slope of the Glen Shira Dam, Scotland, and numerical results were compared with field measurements during a controlled drawdown. Field records indicate that classical undrained calculations are conservative but unrealistic. Then, a recent case of a major landslide triggered by a rapid drawdown in a reservoir was interpreted. A key aspect of the case was the correct characterization of permeability of a representative soil profile. This was achieved by combining laboratory test results and a back analysis of pore water pressure time records during a period of reservoir water level fluctuations. The results highlight the difficulty of predicting whether the pore water pressure is overestimated or underestimated when using simplified approaches, and it is concluded that predicting the pore water pressure distribution in a slope after a rapid drawdown requires a coupled flow-deformation analysis in saturated and unsaturated porous media.Peer ReviewedPostprint (published version

Comparing 1D-3C et 1D-1C nonlinear dynamic responses of deep and shallow japanese sites, considering various assumptions

International audienceIn this paper, we present the results obtained with the CyberQuake computation code for two Japanese sites selected from the KiK-net and PARI accelerometric networks, which were proposed within the PRENOLIN international benchmark. The deep Kushiro (KiK-net KSRH10) and the shallow Sendai (PARI) sites were chosen as they are very close to a 1D geometry (horizontal layers). During the PRENOLIN benchmark, various 1D-1C computing assumptions with vertical incident waves were considered. Here, we present further works comparing results of 1D-1C / 1D-3C nonlinear transient dynamic computations, considering effective-stress / total-stress approaches, as well as vertical / oblique incident input motions, in order to review the usual main assumptions in 1D nonlinear site effects analyses, depending on site conditions. For the selected shallow site, the 1D-1C analysis with vertical incidence seems to be a better option. No clear trend is found in this case with respect to preferring the effective-stress or the total-stress model. The effective-stress analysis provides however better results in terms of predicted time-history ground motions at the site. For the deep site, the new computations performed in this study confirm that 1D-3C effective-stress analysis do improve the predictions. However, the discrepancy between the predictions and the recordings is still remaining since PRENOLIN, and cannot be explained by the new assumptions tested in this study. For both sites, no significant effect is observed, when considering oblique incidence for propagating waves. Computations with vertical incidence lead sometimes to better results

Impact of a 70°C temperature on an ordinary Portland cement paste/claystone interface: An in situ experiment

International audienceRadioactive wastes in future underground disposal sites will induce a temperature increase at the interface between the cementitious materials and the host rock. To understand the evolution of Portland cement in this environment, an in situ specific device was developed in the Underground Research Laboratory in Tournemire (France). OPC cement paste was put into contact with clayey rock under water-saturated conditions at 70°C. The initial temperature increase led to ettringite dissolution and siliceous katoite precipitation, without monosulfoaluminate formation. After one year of interaction, partial decalcification and diffuse carbonation (calcite precipitation) was observed over 800 μm in the cement paste. At the interface, a layer constituted of phillipsite (zeolite), tobermorite (well-crystallised C-S-H), and C-(A)-S-H had formed. Globally, porosity decreased at both sides of the interface. Geochemical modelling supports the experimental results, especially the coexistence of tobermorite and phillipsite at 70°C, minerals never observed before in concrete/clay interface experiments

Damage on a Main Gas Pipeline Due to Landslide of Soils Derived From Volcanic Ashes in Colombia

In December 2011 a great proportion slope failed affecting the main gas pipeline (20” diameter) that supplies Colombia’s southwest area. The landslide involved materials formed by soils derived from volcanic ashes and residual soils, typical in Colombia’s central zone, which acquired great energy flowing in an avalanche through the natural watercourse. The avalanche generated soil erosion over the torrent banks, generating the watercourse deepening and the deterioration of adjacent slopes over which the pipeline runs. There were identified as landslides triggering aspects the atypical raining period due to “La Niña” climatic phenomenon and the soils removal at the slope base due to a minor stream. The article contains an analysis based on the characterization of this particular soil and the main landslide and avalanche incidence on the adjacent slopes stability. Additionally, it presents the results of the numerical soil-pipe interaction analysis with finite elements models that was completed to define and design the stabilization works