1,721,013 research outputs found
Changes in natural clay microstructure due to laboratory weathering
No full textPart of the research to characterize the soils involved in shallow landslides is described in the paper. The studied landslides were the slide-flows occurred in September 2000 in the Jonian side of Calabria (Italy). In particular, the results of micro-structural investigations performed on natural clay specimens taken from samples near detachment zones are shown. The comparison of the results between the investigation on intact and artificially weathered specimens showed the wide micro-structural changes due to weathering cycle
The design of geotextile filters for granular soils
No full textThe use of geotextile filters is very common in geotechnical and in environmental engineering. In these structures the flow conditions (steady and unsteady flow, parallel or normal flow to filter, high or low hydraulic gradients) and the boundary conditions (vertical effective stresses, continuity of contact between the filter and the base soil) can be very different. In all applications the functions of filter are to prevent the movement of fine particles of base soil and to avoid the development of excessive pore water pressure on interface between base soil and filter. The main filter functions are retaining the base soil: pore size distribution and filtration opening size must be lower than fixed limits (retention criterion); being more permeable than base soil: pore size distribution and filtration opening size must be higher than fixed limits (permeability criterion). The available design criteria are often the result of theoretical and experimental analyses carried out in laboratory under experimental conditions different respect to the field conditions. Moreover, the design criteria do not consider the different flow conditions and the boundary conditions. In this paper, on the base of the current knowledge and trends in geotextile filter design and research a new procedure for the design of geotextile filter is show
Landslide susceptibility assessment by TRIGRS in a frequently affected shallow instability area
Full text linkLandslide susceptibility assessment over large areas is considered a preliminary step for the planning or design of the
most appropriate risk mitigation measures. The use of physically based models is considered a useful tool for landslide susceptibility
assessment. Sometimes, using the available geotechnical input data, physically based models can be used to assess landslide
susceptibility to obtain a susceptibility map which allows the expert to identify areas where detailed in situ investigations and
laboratory tests should be carried out. In this context, the paper proposes a methodology based on the use of TRIGRS to assess
landslide susceptibility in an area of about 1 km2 frequently affected by shallow phenomena in weathered gneiss. Owing to the fact
that these materials are extremely complex to characterize from a mechanical and hydraulic point of view, the methodology starts
with the collection and analysis of the geotechnical data available for weathered gneiss outcropping in the study area. These data are
combined with the data provided by scientific literature on soils similar, for genesis and stress history, to those of the studied area.
Through the application of TRIGRS, the data are combined in order to obtain the values of parameters that better analyze shallow
landslide source areas. Subsequently, using the abovementioned values, several susceptibility maps are obtained.
Finally, the most representative shallow landslide susceptibility map for the area is chosen by means of the error index (EI), the
true positive fraction (TPF), and the forecasting index (FI). The success of the best map is confirmed by the high value of the area
under the receiver operator characteristic curve (AUC) that demonstrates a good level of forecasting ability
Assessment of internal stability of granular soils by means of theoretical and laboratory methods
No full textThe assessment of the internal stability of a base soil is a fundamental aspect in the design of the filtering transitions. It can be evaluated by means of semi-empirical, theoretical and experimental methods; the assessment of internal stability of a soil using the available semi-empirical criteria can provide different results. In the paper, in order to verify and validate two methods recently proposed by the authors (Moraci et al. 2012a, b; Moraci et al. 2015), the internal stability of granular soils using different methods is evaluated. The internal stability of test soils has been firstly obtained by Kezdi, Sherard and Kenney and Lau criteria (semi-empirical methods), then it has been assessed theoretically by the method “SimulFiltr” and finally it has been verified by long term filtration tests performed in a rigid wall permeameter. The obtained results allowed us to better define the zones that constitute the new graphical method “Butterfly Wings Chart”, recently proposed by the authors
Factors affecting geotextile filter long term behaviour and their relevance in design
No full textGeotextile and granular filters are widely used in civil (e.g. earth dams, embankments, drainage trenches, etc.) and environmental (e.g. landfills, permeable reactive barriers, etc.) engineering works. Geotextile filters are considered to be an effective alternative to conventional granular filters whose function is to prevent the movement of fine particles from the base soil allowing the liquid to flow as freely as possible. The design of a geotextile filter requires the knowledge of the base soil–filter interaction that is a very complex process due to the large number of factors involved.
In this paper, the complex cases of geotextile filter design in contact with internally unstable cohesionless soils and in critical/severe applications are analysed based on recent research also developed by the authors. Moreover, the influence of the main factors affecting geotextile/filter
long-term behaviour which are generally neglected in current design criteria, such as vertical effective stress, partial clogging, flow conditions, type of contact at the interface and type of permeant, are examined. Furthermore, various performance tests to evaluate the long-term soil–geotextile filter behaviour and the reliability and limits of different design criteria for cohesionless
soils are discussed
A new theoretical method to evaluate the internal stability of granular soils
No full textThe geotextile filter design is particularly complex when granular base soils are internally unstable. In these conditions,
the design criteria available in literature are not always reliable. This paper deals with a new theoretical method developed
to evaluate the internal stability of granular soils. To simulate, theoretically, the filtration process inside these soils,
a set of spherical particles and different soil relative densities have been considered. The soil has been represented by means
of a sequence of parallel layers, containing constrictions and particles, placed upon each other at a distance, in the direction
of hydraulic flow, which is a function of the soil relative density. The movement of the fine particles through the different
soil layers has been simulated by means of a mechanism that compares each particle contained in the i layer with the constrictions
contained in the next i + 1 layer. The results of the numerical simulations were used to evaluate the internal stability
of the analyzed granular soil and the corresponding critical diameter of suffusion, Dc. Finally, the reliability of the
proposed theoretical method was evaluated by means of the results of experimental long-term filtration tests performed using
a rigid-wall permeameter on different unstable granular soils
The use of a physically based model for susceptibility assessment of debris flow source areas
No full textA new theoretical method to evaluate the upper limit of the retention ratio for the design of geotextile filters in contact with broadly granular soils
No full textThe geotextile filters design is based on the retention and the permeability criteria. In particular, the
retention criterion, that a filter must satisfy in comparison to the base soil, is commonly expressed as
OF D85, where OF is the geotextile characteristic opening size and D85 is the soil particle diameter
corresponding to the 85% of the passing soil mass grain size distribution. As consequence, the filter
should retain only the larger particles of the base soil. This criterion works if the larger particles retain
the smaller particles and this condition is verified when these particles form the solid skeleton
(constituted by interconnected particles that transfer the stresses).
When the granular soil has a broadly grain size distribution, with uniformity coefficient greater than 3,
the larger particles generally do not belong to the solid skeleton but they are “immersed” in the smaller
particles matrix that constitutes the solid skeleton (Giroud, 2010). So, for broadly granular soils, if the
retention criterion previously defined is satisfied, this condition does not guarantee that the whole base
soil is retained. In fact, the base soil could be subjected to an internal erosion phenomenon if the geotextile
filter characteristic opening size is too large and the larger particles retained by the filter are not
able to retain the smaller particles of the base soil and a hydraulic flow of dragging exists.
The paper focuses on the development of a new theoretical method that, starting from the base soil
mass grain size distribution and from its relative density, determines the upper limit value of the geotextile
filter characteristic opening size, OF, to be used in the retention criterion in order to avoid the
internal erosion of broadly granular base soi
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