Ignacio Pérez-Rey

An Industrial-Archaeological Approach to the Mineral Loading Docks in Rande Strait, North-Western Spain

During the 20th century, the need for raw material promoted a commercial transportation trade of iron ores from the deposits in north-western Spain, where Vigo city was considered one of the most important ports. The global energy crisis in the 1970s, as well as the strong competition from other exporting countries, dented the prolific activity of companies dedicated to the extraction and trading of iron ore. The main goal of this article is the evaluation of one particular element of the mining and industrial heritage — two old mineral loading docks in Ría de Vigo in the Rande Strait, linking the municipalities of Redondela and Moaña. Their development as a tourist resource would add to the cultural and economic activities already developed in the area.

On the use of machine learning techniques for the mechanical characterization of soft biological tissues

Motivated by the search for new strategies for fitting a material model, a new approach is explored in the present work. The use of numerical and complex algorithms based on machine learning techniques such as support vector machines for regression, bagged decision trees, and artificial neural networks is proposed for solving the parameter identification of constitutive laws for soft biological tissues. First, the mathematical tools were trained with analytical uniaxial data (circumferential and longitudinal directions) as inputs, and their corresponding material parameters of the Gasser, Ogden, and Holzapfel strain energy function as outputs. The train and test errors show great efficiency during the training process in finding correlations between inputs and outputs; besides, the correlation coefficients were very close to 1. Second, the tool was validated with unseen observations of analytical circumferential and longitudinal uniaxial data. The results show an excellent agreement between the prediction of the material parameters of the strain energy function and the analytical curves. Finally, data from real circumferential and longitudinal uniaxial tests on different cardiovascular tissues were fitted; thus, the material model of these tissues was predicted. We found that the method was able to consistently identify model parameters, and we believe that the use of these numerical tools could lead to an improvement in the characterization of soft biological tissues.

A Benchmark Experiment to Assess Factors Affecting Tilt Test Results for Sawcut Rock Surfaces

From the earliest studies on the topic, plane sliding techniques, usually known as tilt tests, have shown contradictory features. On the one hand, they reflect on a small-scale basic principles regarding definition of the friction angle and can reproduce conditions very similar to those of the sliding of blocks on rock slopes; furthermore, tilt angle results agree with friction angles derived from shear and pull tests (Hencher 1977; Muralha 1996). On the other hand, the literature includes several reports of erratic results and it is recognized that even apparently smooth surfaces are actually rough at the microscopic level (Hencher and Richards 2015). Thus, adhesion and textural interlocking may contribute to the variability and the nonreproducibility of tilt test results. A number of authors have carried out simple tilt tests in the past, and several examples illustrate the above-mentioned arguments. Thus, Hencher (2012) observed extreme variability in the results of tilt tests; Nicholson (1994) found that friction angles for sawcut Berea sandstone in direct shear tests varied by 12.5 , despite great attention paid to sample preparation and reproducibility; Coulson (1972) demonstrated that the friction angle of planar surfaces of rock varied with surface finish; Krahn and Morgenstern (1979) reported similar variation for surfaces prepared in different ways and with different surface finishes; and Kveldsvik et al. (2008) found that the basic friction angle for a rock slope, derived from tilt testing of core, varied between 21 and 36.4 . These great differences in measured tilt angles are mainly attributed to different surface finishing and to wear of the rock contacts (Pérez-Rey et al. 2015, 2016), although other reasons, such as testing and ambient conditions, cannot be ruled out. Mehrishall et al. (2016) revealed that the residual friction coefficients of grinded joint surfaces and of rough rock surfaces were almost identical. This manuscript contains interesting findings in rock mechanics practice, derived from large efforts to test the same rocks under different conditions and different laboratories. At the same time, this manuscript presents part of the work which will be used to prepare a Suggested Method on Tilt Testing. It is published in the form of a Technical Note, although its length exceeds what is generally accepted for this type of publication.

Analysis of a complex slope failure in a granodiorite quarry bench

We describe a complex failure mechanism in a 30-m high bench in a granodiorite quarry. This mechanism included a circular failure in completely decomposed granodiorite at the bottom of an unstable area pushing on a block of granodiorite. This first block induced subsidence and failure of a wedge of highly decomposed granodiorite, which pushed a slender block below it, causing it to topple. This toppling block eventually pushed a lower block that slid out of the slope. In this rather complex mechanism, completely weathered rock interacted with rock blocks and ultimately produced a small landslide of around 1500xa0m3 of material. Our study highlights the need to consider the possibility of a complex failure mechanism when analysing rock slope instability. It also highlights the role of toppling in some part of a rock mass prone to instability. When a slender block located in the middle of an initially stable slope experiences a small amount of force, for instance, due to water pressure, that causes it to topple, all the weight is transmitted to the block immediately below the slender block, inducing a greater force that can render the entire area unstable.

Geotechnical characterization of the site and stability of a tailings dam in Ecuador

In this paper we present the design and stability analysis of a tailings dam developed in order to stock up tailings from mineral processing plants located in the left bank of Calera river in the ZarumaPortovelo Mining District, in Ecuador; including a geotechnical study of materials involved. This study first reviews some instability problems that took place in tailings dam in other parts of the world. Then, the geological and geotechnical characterization of various geological materials (soil, rocks and aggregates) that will serve as a foundation or that will be utilized in the dam construction site is presented. Since some of these the materials are ripped and then used to build the dam, they are also characterized according to their granular behavior after set up in the dam construction. Finally, a design fulfilling operational needs is proposed and its stability analyzed in terms of the most probable instability mechanisms (circular failure), and accounting for standard and worst possible hydrogeological and seismic conditions expectable in the area. The ultimate aim of a tailings impoundment is to contain fine-grained tailings. This has to be carried out in a cost-effective manner that provides for longterm stability of the embankment structure and the impounded tailings and the long-term protection of the environment (USEPA,1994). Failure of tailings dams may result in disastrous damages to lives, properties and the surrounding environment. In this way, design, construction and operation of the tailings dams require a high level of care in engineering practice (Ozcan et al., 2013). This article focuses on presenting the background of geotechnical characterization of soils, aggregates and rocks affecting a tailing dams, showing the most relevant variables controlling their stability and presenting an example of a safe particular design in the above named mining zone of Ecuador. 1.2 Problem statement Portovelo is the principal mining region in the south of Ecuador, where, for decades, mining waste management has been a concern. This waste has so far moderately polluted the Puyango river basin. This river flows into Peruvian national territory and finally into the Pacific Ocean, where it flows out in the town of Tumbes. So to mitigate this problem, it was agreed to build a tailings dam, which could help to avoid further polluting and to clean the river basin. Several recent researches provided representative examples to improve material characterization facing toward generate reliable studies of tailing dams design. For example, a study published by Ozcan et al. (2013) analyzes the characterization and stability in a structure like this. It is noted the necessity of performing a complete geotechnical study of the affected materials, the determination of the geotechnical characteristics of the aggregate materials and the assessment of the slope stability. The static and pseudo-dynamic analysis results, based on limit equilibrium methods and numerical approaches, showed that circular failures are the most common critical failure mechanism associated to dam behavior. In this way, the factors of safety tend to diminish as far as the dam is growing in height (Fig. 2). Nevertheless, safety ranges derived by both methods are similar and suitable for dam growing in safety conditions, provided input data are computed in a reasonably accurate way.