Browsing by Author "Ovalle, Carlos"

Now showing 1 - 6 of 6
  • No Thumbnail Available
    Item
    Compressibility and creep of a diatomaceous soil
    (2019) Arenaldi Perisic, Ghio; Ovalle, Carlos; Barrios, Antonio
    Diatomaceous soils are composed by a mix of sand, fines and fossilized diatoms, which are unicellular micro algae composed by a strong silica frustule of 10 to 100 mu m in size, with rough surface and enclosing a void that could give the soil a very low dry density. Due to high water storage capacity within frustules, diatomaceous soils present high Liquid Limit and classifies as high plastic silt (MH). In classical soil mechanics, low density and high plasticity are properties associated to very soft soils, however, previous studies have reported that diatomaceous soils could mobilize high shear strength and present relatively high yield stress.
  • No Thumbnail Available
    Item
    Evaluation of the Effectiveness of a Soil Treatment Using Calcium Carbonate Precipitation from Cultivated and Lyophilized Bacteria in Soil's Compaction Water
    (2021) Valencia-Galindo, Miguel; Saez, Esteban; Ovalle, Carlos; Ruz, Francisco
    Microbial-induced carbonate precipitation (MICP) is a bio-inspired solution where bacteria metabolize urea to precipitate. This carbonate acts as a bio-cement that bonds soil particles. The existing framework has focused mainly on applying MICP through infiltration of liquid bacterial solutions in existing soil deposits. However, this technique is inefficient in soils with high fines content and low hydraulic conductivity, and thus few studies have focused on the use of MICP in fine soils. The main objective of this study was to evaluate the effect of MICP applied to compaction water in soils containing expansive clays and sandy silts. This approach searches for a better distribution of bacteria, nutrients, and calcium sources and is easy to apply if associated with a compaction process. In soils with expansive minerals, the effect of MICP in swelling potential was explored at laboratory and field scales. In sandy silts, the evolution of the stiffness and strength were studied at the laboratory scale. The treatment at the laboratory scale reduced the swelling potential; nevertheless, no significant effect of MICP was found in the field test. In sandy silts, the strength and stiffness increased under unsaturated conditions; however, subsequent saturation dissolved the cementation and the improvement vanished.
  • No Thumbnail Available
    Item
    Geological and geotechnical investigation of the seismic ground response characteristics in some urban and suburban sites in Chile exposed to large seismic threats
    (2022) Maringue, Jose; Mendoza, Laura; Saez, Esteban; Yanez, Gonzalo; Montalva, Gonzalo; Soto, Valeria; Ayala, Felipe; Perez-Estay, Nicolas; Figueroa, Ronny; Sepulveda, Natalia; Galvez, Carlos; Ramirez, Paola; Ovalle, Carlos
    The central area of Chile's Valparaiso Region has been classified as a seismic gap for a major earthquake, which makes it very important to understand the seismic hazard of the zone. Generally, seismic codes consider a qualitative classification of sites to estimate the possible damage in the case of an earthquake scenario. Estimating the values of acceleration could be very important to prevent damages and increase preparedness for these rare events. In this research, a qualitative and quantitative estimation of seismic hazard is performed in the study area (Valparaiso region between Papudo and San Antonio 32 degrees-34 degrees S). This is achieved through an integrated and relatively economical approach which considers the information from Geology, Geophysical experiments (Gravity and seismic methods), and Geotechnical analyses. The results of the geophysical survey and geology information allow dividing the zone into five site types through a new proposal of site classification that depends not only on the V-s30,V- but also on the sites predominant period (T-0), which is an innovation of this work for the Chilean code. The Peak Ground Acceleration (PGA) values in the study zone were estimated using a Ground Motion Predictive Equation developed for the Chilean subduction zone. Additionally, we consider three different seismic scenarios according to the history of events in Central Chile. The results of this quantitative analysis show PGA values up to 0.52 g for the median and 1.2 g for the 84th percentile of the scenarios. Overall, the highest accelerations (PGA) are in zones with low shear wave velocities (< 500 m/s), a long predominant period (> 0.4 s) and where geology establishes the presence of low stiffness soils. The comparison of response spectra from the model against records from 2010 Maule and 1985 Valparaiso earthquakes shows available models tend to overpredict the intensities.
  • No Thumbnail Available
    Item
    Mechanical behaviour of undisturbed diatomaceous soil
    (2021) Ovalle, Carlos; Arenaldi-Perisic, Ghio
    The mechanical behaviour of sedimentary marine soils containing diatoms does not follow classical trends usually found in Soil Mechanics, and evidence of geotechnical singularities of undisturbed samples are still scarce. This article presents new insights on the behaviour of natural diatomaceous soil in compression, shearing and cyclic loading, on undisturbed highly plastic diatomaceous silt from Mejillones Bay in northern Chile. Microscopic observations show that the soil contains significant amount of siliceous diatom. Isotropic compression results in high overconsolidation (OCR > 20) and high compressibility after yielding. Similarly, at low confining stress the undrained shear strength does not depend on pressure and is virtually equal to the UCS = 730 kPa. At higher stresses, a transition to frictional behaviour is observed, characterized by high variability in excess pore pressure generation during undrained triaxial shearing tests, presumably due to heterogeneous diatom layering in undisturbed soil samples. Microscopic observations indicate that high compressibility could be attributed to massive diatom breakage and disturbance of the soil microstructure. Compared to conventional data on fine soils, the cyclic behaviour of the diatomaceous soil is more brittle at low strains, with higher normalized shear modulus and lower damping at shear strains lower than 2 x 10(-1)%; however, it presents higher degradation at larger strains.
  • No Thumbnail Available
    Item
    Scale and suction effects on compressibility and time-dependent deformation of mine waste rock material
    (2024) Osses, Rodrigo; Pineda, Jubert; Ovalle, Carlos; Linero, Sandra; Saez, Esteban
    Designing high mine waste rock piles for long-term behavior requires material mechanical characterization over a large range of stresses and variable environmental conditions. However, representative coarse samples cannot be handled by standard testing devices and the common approach is to test small-scaled samples at the laboratory, which might be affected by particle size effects when compared to the field material. Several reported results indicate that coarser samples present higher amount of particle crushing than small-scaled samples, thus lower dilatancy and higher compressibility. However, specific studies of size effects on time-dependent deformation are lacking. The aim of this paper is to identify the effects of particle size and suction on stressdeformation mechanism of partially saturated mine waste rock. Oedometric compression tests on two parallel graded samples are presented: the gravelly fraction (dmax=50 mm) and the sandy fraction (dmax=2.36 mm). Each stress increment triggers << instantaneous >> and delayed strains. The results reveal the combined effects of particle size and humidity on the mechanical behavior. Coarser samples exhibit higher total compressibility and creep deformation, which also increases with the material humidity. The results give empirical support for the development of scaling laws and suggest that total deformation can be decoupled considering a suction dependent index for creep deformation.
  • No Thumbnail Available
    Item
    Testing and modelling total suction effects on compressibility and creep of crushable granular material
    (2021) Osses, Rodrigo; Majdanishabestari, Kasra; Ovalle, Carlos; Pineda, Jubert
    Recent works have shown that delayed events of particle crushing are partially responsible of creep deformation in granular materials, and that Stress Corrosion Cracking promoted by high humidity within particles is the source of this mechanism. A number of experimental studies have focused on creep behaviour of water saturated samples and wetting-deformation after soaking dry material. However, there are few evidences of the effect of varying total suction in time-dependent deformation of partially saturated crushable material, and this mechanism have been rarely considered in constitutive models. The aims of this paper are to present experimental evidence of the effect of total suction on compressibility and creep of sandy sized samples from crushed rock, and to propose a simple one-dimensional elasto-plastic modelling approach based on the enhancement of an existing model. Oedometric compression tests at different total suctions are presented. The results show that compressibility and creep strains increase with both stress and humidity. The model proposed uses a time-dependent hardening law coupling suction with the amount of particle breakage. Based on preliminary calibrations, the model captures the effect of suction and time-dependent behaviour over a large range of total suction. (C) 2021 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society.