Experimental evidences and numerical modelling of debris flow initiated by channel runoff

Debris flow initiation by channel bed mobilization is a common process in high mountainous areas. Initiation is more likely to occur at the outlet of small, steeply sloping basins where concentrated overland flow feeds an ephemeral channel incised in slope deposits. Such geological conditions are typical of the Dolomite region (Italian Alps), which is characterized by widespread debris flow activity triggered by severe summer thunderstorms. Real-time data and field observations for one of these catchments (Acquabona catchment, Belluno, Italian Alps) were used to characterize the hydrological response of the initiation area to rainfalls of varying intensity and duration. The observed behaviour was then reproduced by means of a simple hydrological model, based on the kinematic wave assumption, to simulate the generation of channel runoff. The model is capable of predicting the observed hydrological response for a wide range of rainfall impulses, thus providing a physical basis for the understanding of the debris flow triggering threshold.     

Removal of heavy metal ions from drinking water by alginate-immobilised <Emphasis Type="Italic">Chlorella sorokiniana</Emphasis>

This paper investigates the potential of alginate-immobilised Chlorella sorokiniana for removing Cu²⁺, Ni²⁺ and Cd²⁺ ions from drinking water solutions. The effects of initial metal concentrations, contact times and temperatures on the biosorptions and removal efficiencies of the tested metals were investigated at initial pH values of 5, and pH effects were studied within the range of 3–7. When studying the effects of initial metal concentrations, the highest experimental removal yields achieved for Cu²⁺, Ni²⁺ and Cd²⁺ ions were 97.10, 50.94 and 64.61 %, respectively. The maximum biosorption capacities obtained by the Langmuir isotherm model for the biosorptions of Cu²⁺, Ni²⁺ and Cd²⁺ ions by alginate-immobilised C. sorokiniana were found to be 179.90, 86.49 and 164.50 mg/g biosorbent, respectively. The experimental data followed pseudo-second-order kinetics. At an initial metal concentration of 25 mg/L, immobilised algae could be used in at least 5 successive biosorption–desorption cycles. SEM and EDS analyses revealed that the metals bonded to the biosorbent. Bi- and multi-metal systems of Cu²⁺, Ni²⁺ and Cd²⁺ were investigated at initial metal concentrations of 30, 50 and 100 mg/L. The removal of Cd²⁺ as well as Ni²⁺ in such systems was negatively affected by the presence of Cu²⁺. The removal efficiency for Cu²⁺ in multi-metal systems decreased by 5–7 %, whilst in the cases of Cd²⁺ and Ni²⁺ the efficiencies decreased by up to 30 %. Nevertheless, the results obtained show that alginate-immobilised C. sorokiniana can efficiently remove the metals tested from polluted drinking water sources.     

An integrated approach for analysing earthquake-induced surface effects: A case study from the Northern Apennines, Italy

This paper illustrates research addressing the subject of the earthquake-induced surface effects by means of a multidisciplinary approach: tectonics, neotectonics, seismology, geology, hydrogeology, geomorphology, soil/rock mechanics have been considered. The research is aimed to verify in areas affected by earthquake-triggered landslides a methodology for the identification of potentially unstable areas. The research was organized according to regional and local scale studies. In order to better emphasise the complexity of the relationships between all the parameters affecting the stability conditions of rock slopes in static and dynamic conditions a new integrated approach, Rock Engineering Systems (RES), was applied in the Northern Apennines. In the paper, the different phases of the research are described in detail and an example of the application of RES method in a sample area is reported. A significant aspect of the study can be seen in its attempt to overcome the exclusively qualitative aspects of research into the relationship between earthquakes and induced surface effects, and to advance the idea of beginning a process by which this interaction can be quantified.     

Runoff-generated debris flows: Observation of initiation conditions and erosion–deposition dynamics along the channel at Cancia (eastern Italian Alps)

In the Dolomitic region, abundant coarse hillslope sediment is commonly found at the toe of rocky cliffs. Ephemeral channels originate where lower permeability bedrock surfaces concentrate surface runoff. Debris flows initiate along such channels following intense rainfall and determine the progressive erosion and deepening of the channels. Sediment recharge mechanisms include rock fall, dry ravel processes and channel-bank failures. Here we document debris flow activity that took place in an active debris flow basin during the year 2015. The Cancia basin is located on the southwestern slope of Mount Antelao (3264 m a.s.l.) in the dolomitic region of the eastern Italian Alps. The 2.5 km² basin is incised in dolomitic limestone rocks. The data consist of repeated topographic surveys, distributed rainfall measurements, time-lapse (2 s) videos of two events and pore pressure measurements in the channel bed. During July and August 2015, two debris flow events occurred, following similarly intense rainstorms. We compared rainfall data to existing rainfall triggering thresholds and simulated the hydrological response of the headwater catchment with a distributed model in order to estimate the total and peak water discharge. Our data clearly illustrate how debris entrainment along the channel is the main contributor to the overall mobilized volume and that erosion is dominant when the channel slope exceeds 16°. Further downstream, sediment accumulation and depletion occurred alternately for the two successive events, indicating that sediment availability along the channel also influences the flow behaviour along the prevailing-transport reach. The comparison between monitoring data, topographical analysis and hydrological simulation allows the estimation of the average solid concentration of the two events and suggests that debris availability has a significant influence on the debris flow volume. © 2020 John Wiley & Sons, Ltd.     

Parameter identification for a suction‐dependent plasticity model

In this paper, the deterministic parameter identification procedure proposed in a companion paper is applied to suction‐dependent elasto‐plasticity problems. A mathematical model for such type of problems is firstly presented, then it is applied to the parameter identification using laboratory data. The identification procedure is applied in a second example to exploitation of a gas reservoir. The effects of the extraction of underground fluids appear during and after quite long periods of time and strongly condition the decision to profit or not of the natural resources. Identification procedures can be very useful tools for reliable long‐term predictions. Copyright © 2001 John Wiley & Sons, Ltd.     

Coupling versus uncoupling in soil consolidation

Coupling and uncoupling between the equilibrium and mass balance equations in soil consolidation problems in investigated in detail. A procedure for judging the strength of coupling is indicated. In the applications, particular emphasis is given to subsidence problems where the coupled nature of the problem is still sometimes questioned. It is shown that even in the case of a single pumped aquifer most situations are coupled.     

The Direct Shear Strength and Dilatancy of Sand–gravel Mixtures

A total of 87 direct shear tests in a large direct shear-box apparatus have been used to investigate the strength and dilatancy of sand–gravel mixtures. This paper focuses on the differences in behaviour between a silica sand (yellow Leighton Buzzard sand) and sand–gravel mixtures obtained by adding fractions of two kinds of gravel to the sand. The purpose is to find a relation between the grain-size characteristics of the materials and the shearing resistance. Experimental results are analysed in terms of the frictional and dilatant contributions to the strength of mixtures as a function of their relative density, and are compared with dilatancy theories and empirical equations. The addition of gravel to the mixtures, even at low fractions (less than 0.1 by volume), causes an increase in peak friction angle (Φ ′_peak) which results both from higher dilatancy at failure (ψ_max) and higher constant volume friction angle (Φ ′_cv). Use of the minimum voids ratio (e_min) of the materials allows the data for the two families of mixtures to be normalized and interpreted in terms of Φ ′_cv and the ratio (Φ ′_peak − Φ ′_cv)/ψ_max. The relationships between relative density (D_r), ψ_max and Φ ′_peak − Φ ′_cv are only partly explained on a physical basis, so we develop empirical equations to predict the peak shear resistance of sand–gravel mixtures (up to gravel contents of 0.5) on the basis of easily measurable quantities. Such equations constitute a practical tool to overcome the problems arising from the impracticality of testing coarse material in the standard shear-box apparatus.     

Post-earthquake estimates of different ground motion intensity measures for the 2012 Emilia earthquake

Estimates of the earthquake ground motion intensity over a geographical area have multiple uses, that is, emergency management, civil protection and seismic fragility assessment. In particular, with reference to fragility assessment, it is of interest to have estimates of the values of different ground-motion intensity measures in order to correlate them with the observed damage. To this purpose, the present paper uses a procedure recently proposed in the literature to estimate the ground-motion intensity for the 2012 Emilia mainshocks, considering different ground motion intensity measures and directionality effects. Ground motion prediction equations based on different site effect models, and spatial correlation models are calibrated for the Emilia earthquakes. The paper discusses the accuracy of the shakemaps obtained using the different soil effect models considered and presents the obtained shakemaps as supplementary material. The procedure presented in the paper is aimed at providing ground motion intensity values for seismic fragility assessment and is not intended as a tool to estimate shakemaps for rapid emergency assessment.