169,921 research outputs found
Satellite based radar interferometry to mapping and monitoring swelling/shrinking clay soils
No full textA methodology for the study of swelling/shrinkage through the satellite radar images acquired from 1992 to 2010 by different sensors (ERS, RADARSAT) and processed by means of the SqueeSARTM technique is proposed. The methodology aimed at improving the understanding of the kinematical behavior of swelling/shrinking processes, mapping these soils, monitoring the soil volume change and enabling also non-expert users to handle DInSAR data. The methodology has been applied and validated in an area of the Northern Italy where swelling/shrinking soils are frequent. The map of the ground displacements was compared with the geological model of the subsurface and with the distribution of the damaged buildings. The obtained results are helpful in land use planning to identify and quantify the swelling/ shrinkage of clay soils
Relationship between the residual shear strength and the methylene blue value in weathered clay soils
No full textA new correlation is proposed between the residual shear strength and the methylene blue value (‘value of blue’; VB) for
weathered clay soils on argillaceous bedrock and on alluvial soils in the Oltrepo Pavese area (Northern Italy), which can be
considered as geologically representative of a large part of the Italian Apennines. Shallow landslides occur periodically in these
soils as a result of high-intensity rainfall events. A number of soils were tested. Trench pits were used for sampling and for the soil
profile description (lithology, structure, grade of weathering, thickness). Field surveys were integrated with some standard
geotechnical laboratory tests. The methylene blue dye adsorption (VB) was determined in accordance with the French AFNOR
standards. The residual strength friction angle was measured with direct shear tests; the procedure employed for the measure
involved inserting the soil at the liquid limit in the direct shear ring, applying consolidation in stages and then shearing (Kanji
method). The applicability of some existing correlations between the residual friction angle and index properties were tested.
The correlations are characterized by a large amount of scatter in the data and tend to overestimate the residual friction angle.
The VB test is easy and rapid to perform and appears to be a good indicator of the residual strength friction angle for the tested soils
APPLICABILITA' DI PROVE PENETROMETRICHE STATICHE NELLA RICOSTRUZIONE DEL PROFILO STRATIGRAFICO
No full textSummary
The present paper mainly deals with the stability of debris deposits in the northern Apennines, which is an area of relatively
high seismicity. More specifically, the paper analyses the co-seismic stability of dry infinite slopes by the Limit Equilibrium
Method (LEM) and uses the results of Newmark-type analysis for defining appropriate values of the seismic coefficients
to be used in pseudo-static analysis.
The study areas are the mountainous zones of Garfagnana and Lunigiana (Tuscany – Italy), which consist of hundreds of
square kilometres.
The main purposes of the paper are: to outline a methodological approach, to define criteria for assessing the stability conditions
in the whole study area and to suggest appropriate seismic coefficients for slope instabilities mainly driven by inertial
forces (to be used in LEM analyses)
Appendix A reports information on the strength parameters of debris deposits as obtained from a number of works. Mainly
Appendix A gives a range of possible values. In fact, these values have not been used in the present study, because the objective
of the study is to define general criteria for stability conditions and not to analyse specific case studies.
Appendix B shows plots of the yield -acceleration values that have been obtained from pseudo-static analysis assuming homogeneous
soil profile with c’ and φ’, curvilinear failure surface and different water table. This Appendix has the only purpose
of extending the possible application of the proposed methodology
Site-specific to local-scale shallow landslides triggering zones assessment using TRIGRS
No full textRainfall-induced shallow landslides are common phenomena in many parts of
the world, affecting cultivation and infrastructure and sometimes causing
human losses. Assessing the triggering zones of shallow landslides is
fundamental for land planning at different scales. This work defines a
reliable methodology to extend a slope stability analysis from the
site-specific to local scale by using a well-established physically based
model (TRIGRS-unsaturated). The model is initially applied to a sample slope
and then to the surrounding 13.4 km2 area in Oltrepò Pavese (northern
Italy). To obtain more reliable input data for the model, long-term
hydro-meteorological monitoring has been carried out at the sample slope,
which has been assumed to be representative of the study area. Field
measurements identified the triggering mechanism of shallow failures and
were used to verify the reliability of the model to obtain pore water
pressure trends consistent with those measured during the monitoring
activity. In this way, more reliable trends have been modelled for past
landslide events, such as the April 2009 event that was assumed as a
benchmark. The assessment of shallow landslide triggering zones obtained
using TRIGRS-unsaturated for the benchmark event appears good for both the
monitored slope and the whole study area, with better results when a
pedological instead of geological zoning is considered at the regional
scale. The sensitivity analyses of the influence of the soil input data show
that the mean values of the soil properties give the best results in terms
of the ratio between the true positive and false positive rates. The scheme
followed in this work allows us to obtain better results in the assessment
of shallow landslide triggering areas in terms of the reduction in the
overestimation of unstable zones with respect to other distributed models
applied in the past
Engineering-geological properties of carbonates and shale: their implications for dam construction in Mekelle, Northern Ethiopia
No full textGrowing water demand poses severe problems to the population in the Mekelle Outlier, Northern Ethiopia. Hence, storing of rain water for water supply becomes one of the top agenda in the area. Several earth-fill dams are constructed for irrigation and drinking water supply purposes over the last 15-20 years. However, as collected data indicated more than 60% of these earth-fill dams have excessive leakage due to the problematic engineering geological nature of the carbonates and shale rocks of the study area. Giba dam is one of the currently proposed largest dams to alleviate the water supply problem of the Mekelle city. In the current study, engineeringgeological
mapping, core drilling, geophysical surveys and laboratory works have been conducted for the dam project to evaluate the engineering-geological nature of rocks of the area.
Qualitative and quantitative rock masses properties such as permeability, strength and deformation are analyzed using Packer test, Rock Quality Designation (RQD), and Rock Mass Rating (RMR) systems. Analyzed results displayed that: (i) the RQD values are highly variable for all the rock masses. For example, 60% of limestone (Lst), 50% marly limestone (MLst) and 72% shale (Sh) are categorized as poor /very poor RQD values. RMR values also imply that Lst, MLst and gypsum are classified class-III while Sh is classified in class-IV (ii) considering the
rock mass shear strength parameters (C, φ), the Lst, MLst, and gypsum have a moderate strength while Sh as low strength. More than 92% the Lst and 84% of the MLst falls in the 5-50 and >50 Lugeon Value classes. Thus, area covered by both the Lst and MLst needs treatment (e.g.
grouting). Similarly, 50% and 20% of the packer test values of shale falls in the <1 and 1-5 Lugeon value classes respectively. The studied rock properties implies that the limestone layer is not suitable for the construction of the earth-fill dams in terms of water tightness while that of
the calcareous shale and/or mud rock is good site for reservoir area as it is water tight
Evaluating liquefaction potential of soils using CPT: a case study in the central Po River Plain, Italy
No full textANIONIC POLYACRYLAMIDE AS AN ADDITIVE TO PREVENT SOIL PRONENESS TOWARDS LAND DEGRADATION LEADING TO SLOPE INSTABILITIES
No full textClimate change and the intensification of extreme weather events constantly pose new threats to all human activities, damaging roads and communication networks, as well as economical activities and threatening human lives. Recently new materials are being considered as potentially useful tools in the prevention of land degradation leading to slope instabilities; among them polymers such as anionic polyacrylamide (PAM) are gaining more and more interest. PAM is known and employed as an additive in agriculture, in the prevention of irrigation -connected erosion, to maximize irrigation and fertilization efficiency and to enhance agricultural yield. Samples were reconstructed in laboratory using kaolin clay and silty sand, respectively, without mixing them to observe the effects of application of anionic polyacrylamide (PAM) on their physical, volumetric, mechanical, and hydrological properties. Fixed values were dry density (1.2 g/ cm 3 for kaolin clay and 1.4 g/cm 3 for silty sand), initial water content (20% and 25% respectively) and polymer application rates (moving from the original 0%, 0.003%, 0.03%, 0.3%, 1% by weight for both "parent materials" to 0.01%, 0.03% and 0.05% for kaolin clay and 0.1%, 0.3% and 0.5% for silty sand, based on the results of previous analysis). Additional samples consisting of kaolin clay and quartz powder and polyacrylamide (with a concentration of 5% and 50%) were reconstituted specifically for ESEM analysis. The polymer, a granular anionic polyacrylamide provided by Micronizzazione Innovativa Srl, has been manually applied and mixed with the samples, reconstituted in pvc cylinders with a diameter of 9.5 cm and 5 cm high (although some were reconstituted in different cases for specific tests). Samples were then submitted to Atterberg limits with different curing times, hyprop and filter paper tests, WP4C, shear tests, and the record of volumetric characteristics. Results showed that the increase of PAM percentage in samples generally coincided with a widening of samples plasticity range, as well as with the increase of liquid limit and plasticity index; PAM influence was also a matter of time, being more relevant few days after the treatment and then slowly decreasing. Rise in PAM percentage coincided with an increase in samples porosity, and with a higher water retention, although it was impossible to identify a polymer characteristic structure with SEM analysis. These results can shed light on the potential application of polymers such as anionic polyacrylamide as a useful additive for the improvement of soil characteristics that impact on soil stability, in a frame of sustainable solutions for reduction of landslides hazard and risk
Comparison between different approaches of modeling shallow landslide susceptibility: a case history in the area of Oltrepo Pavese, Northern Italy
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