No abstract

Debris flows occur in mountainous areas characterized by steep slope and occasional severe rainstorms. The massive urbanization in these areas raised the importance of studying and mitigating these phenomena. Concerning the strategy of protection, it is fundamental to evaluate both the effect of the magnitude (that concerns the definition of the hazard), in terms of mobilized volume and travel distance, and the best technical protection structures (that concerns the mitigation measures) to reduce the existing risk to an acceptable residual one. In particular, the mitigation measure design requires the evaluation of the effects of debris flow impact forces against them. In other words, once it is established that mitigation structures are required, the impacting pressure shall be evaluated and it should be verified that it does not exceed barrier resistance. In this paper the author wants to focus on the definition and the evaluation of the impacting load of debris flows on protection structures: a critical review of main existing models and equations treated in scientific literature is here presented. Although most of these equations are based on solid physical basis, they are always affected by an empirical nature due to the presence of coefficients for fitting the numerical results with laboratory and, less frequently, field data. The predicting capability of these equations, namely the capability of fitting experimental/field data, is analysed and evaluated using ten different datasets available in scientific literature. The purpose of this paper is to provide a comprehensive analysis of the existing debris flow impact models, highlighting their strong points and limits. Moreover, this paper could have a practical aspect by helping engineers in the choice of the best technical solution and the safe design of debris flow protection structures. Existing design guidelines for debris flow protection barrier have been analysed. Finally, starting from the analysis of the hydro-static model response to fit field data and introducing some practical assumptions, an empirical formula is proposed for taking into account the dynamic effects of the phenomenon.

Abstract. The aim of this paper is to analyse debris flow impact against rigid and undrained barrier in order to propose a new formulation for the estimation of acting force after the flow impact to safe design protection structures. For this reason, this work concentrates on the flow impact, by performing a series of small scale tests in a specifically created flume. Flow characteristics (flow height and velocity) and applied loads (dynamic and static) on barrier were measured using four ultrasonic devices, four load cells and a contact surface pressure gauge. The results obtained were compared with main existing models and a new equation is proposed. Furthermore, a brief review of the small scale theory was provided to analyse the scale effects that can affect the results.

When studying rockfall phenomena, a single value of the block volume is not sufficient to take into account the natural variability of the geometrical features (orientation, spacing, persistence) of the discontinuity sets. Different approaches for obtaining cumulative distributions of potentially detachable block volumes are compared. A highly fractured rock mass outcropping along the western Lake Garda (Italy), consisting of prevailing limestone and interbedded marls, is studied in detail from geological and geostructural points of view. Then, a representative rock face has been selected and analyzed with traditional and non-contact survey methods to identify the main discontinuity sets and to collect spacing samples. Based on these data, in situ block size distributions for different combinations of sets are built following statistically-based approaches, without the use of a Discrete Fracture Network (DFN) generator. The validation of the obtained distributions is attempted based on the detached block surveyed at the foot of the slope. However, in this particular case study, the detached blocks cover only a minimal volume range compared to both theoretical values and visible rockfall scars. The fallen rock blocks have a marginal role in design block determination, since their volume depends on geological discontinuities (bedding and fractures) and could be affected by other processes after the detachment (e.g., fragmentation). The procedure here described should be standard practice in the study of rockfall events, and it should be uniform in European standards such as Eurocodes. Future developments should involve the scientific community for setting the percentiles of the probability distribution to be considered for block design definition.

Abstract. The Los Humeros geothermal system is steam dominated and currently under exploration with 65 wells (23 producing). Having temperatures above 380 ∘C, the system is characterized as a super hot geothermal system (SHGS). The development of such systems is still challenging due to the high temperatures and aggressive reservoir fluids which lead to corrosion and scaling problems. The geothermal system in Acoculco (Puebla, Mexico; so far only explored via two exploration wells) is characterized by temperatures of approximately 300 ∘C at a depth of about 2 km. In both wells no geothermal fluids were found, even though a well-developed fracture network exists. Therefore, it is planned to develop an enhanced geothermal system (EGS). For better reservoir understanding and prospective modeling, extensive geological, geochemical, geophysical and technical investigations are performed within the scope of the GEMex project. Outcrop analogue studies have been carried out in order to identify the main fracture pattern, geometry and distribution of geological units in the area and to characterize all key units from the basement to the cap rock regarding petro- and thermo-physical rock properties and mineralogy. Ongoing investigations aim to identify geological and structural heterogeneities on different scales to enable a more reliable prediction of reservoir properties. Beside geological investigations, physical properties of the reservoir fluids are determined to improve the understanding of the hydrochemical processes in the reservoir and the fluid-rock interactions, which affect the reservoir rock properties.