Research Outputs

Now showing 1 - 10 of 12
  • Publication
    2D numerical evaluation of a vertical soil nail wall
    (Australian Geomechanics Journal, 2020) ;
    Peña-Flores, Manuel
    ;
    Villalobos-Cifuentes, Sergio
    The technique of soil nailing has been increasingly used in stabilization works of slopes and excavations. With this, the use of numerical modelling tools in soil nailing projects is becoming increasingly present in Geotechnical companies. This paper includes a case study of a soil nailing wall instrumented in Concepción city, which consists of an excavation of 15 m height in a residual soil of completely decomposed granitic rock. The numerical model was calibrated, comparing the results of the field instrumentation with the numerical estimates provided by the FEM-RS2 software, based on the two-dimensional finite element method and considering an elastic perfectly plastic model. In this way, the strength reduction factor of the geotechnical structure was obtained, which was compared with the overall factor of safety obtained by limit equilibrium analysis. In addition, through the numerical simulation, it was possible to realize an analysis of the loads on the nails, total displacements of the vertical wall, and compare them with the numerical results. The analysis of the results made it possible to confirm the capacity and usefulness of the FEM-RS2 software in the development and elaboration of soil nailing projects.
  • Publication
    Design, construction, and operation of a monitored district heating pipeline system
    (Journal of Pipeline Systems Engineering and Practice, 2019) ;
    Hay, Stefan
    ;
    Weidlich, Ingo
    ;
    Wolf, Ingo
    The need for understanding the performance of district heating pipeline systems has led to the development of a monitoring program. This program includes the design of the connection of an instrumented section of piping within an in-use district heating network. The design complies with the current European district heating recommendations and standards. Monitoring consists of the measurement of earth pressures against the pipes, axial pipe displacements, and temperature of the fluid and soil around the pipes. There are different conditions being tested such as thickness of insulation materials, temperature ranges, and bedding soil type. In particular, there is interest in testing the corner positions. Details of the piping and instrumentation arrangements as well as soil geotechnical characteristics are presented. It was found that when the fluid temperature increased from ambient conditions up to 90°C, pipes were moving all along their length. Moreover, after a fluid temperature drop from 90°C to 20°C over 20 days and subsequent increase to 90°C again, pipe axial displacements did not return to the same values as before
  • Publication
    Study of the anisotropic tensile and compressive strength of a foliated phyllite
    (Emerald Publishing Limited, 2023) ;
    Rodríguez, Paula
    ;
    Vera, Miguel
    Anisotropy is an important characteristic of rocks, especially distinguishable in metamorphic rocks. Transverse isotropy is a particular case of anisotropy where foliation planes are distributed in the rock mass. Anisotropy can also originate from mineral foliation where minerals are oriented in a preferential direction. This inherent anisotropy can affect the rock strength significantly. Here the effect of foliation on the anisotropic strength of a phyllite is experimentally investigated. Phyllite specimens with defined foliation orientations are prepared and a series of laboratory tests carried out. Results for tensile strength and unconfined compressive strength are analysed. Maximum values of tensile strength and unconfined compressive strength are found for β = 0 and 90° and a significant reduction of strength is found for β = 45°. Compressive triaxial tests are conducted under confining pressures up to 20 MPa. The Hoek–Brown failure criterion is found to capture the experimental results in a better form than the Mohr–Coulomb criterion. Anisotropy indexes are adopted to evaluate the anisotropy effect on strength. Confinement is found to reduce the effect of anisotropy on phyllite strength. Cohesion and angle of shearing resistance were also found to be affected by the stress level, and further influenced by β.
  • Publication
    The effect of weathering on the variation of geotechnical properties of a granitic rock from Chile
    (Quarterly Journal of Engineering Geology and Hydrogeology, 2023)
    Flandes, Nicol
    ;
    ;
    The effect of rock weathering on geotechnical parameters can become substantial in geotechnical design. The weathering degree (WD) has usually been divided into five levels from fresh rock to completely weathered rock. In this study, the above five WDs are adopted to analyse the variation of several regularly used geotechnical properties. To that aim, a series of laboratory tests on a Chilean granitic rock in different stages of weathering was carried out. The results of the tests have been analysed by normalizing each geotechnical parameter with respect to the value obtained for slightly weathered samples instead of for fresh rock samples as is usually adopted. In this way, it was found that the unconfined compressive strength reduces steadily and considerably with each WD, as has been previously reported. Conversely, the modulus of deformation and P-wave velocity tend to stabilize the rate of reduction for highly and completely weathered rock samples, which does not agree with the trend and higher rate reductions found by other researchers. This stabilization reduction rate with WD was also found for compaction density, friction angle and Poisson's ratio.
  • Publication
    Study of the elastic shear modulus of Bío Bío sand using bender elements in an oedometer
    (American Society of Mechanical Engineers, 2017) ;
    Ayala, Juan
    ;
    Alvarado, Giovanny
    The objective of the paper is to study the shear stiffness of Bío Bío sand. To this end, a system to measure the travel time of shear waves in Bío Bío sand samples using bender elements was designed and setup in an adapted oedometer device. Measurements were carried out for sand samples with different relative density, pressure/deformation, diameter/height, dry/saturated and varying the frequency, amplitude, and type of the triggered electric signals. The shear wave velocity and elastic shear modulus increased with relative density and effective vertical stress as previously found by other authors. In addition, Hardin type empirical formulas for estimating the elastic shear modulus are used to compare with the experimental results. Estimations proved to be good only in loading for effective vertical stresses around 100 kPa, since underestimation and overestimation of the shear modulus occurred for stresses below and above that value, respectively. Soil shear stiffness during unloading/reloading cycles was underestimated with the expressions used for loading.
  • Publication
    Discussion: Analysis of a full-scale slope failure test on a sludge embankment
    (Emerald Publishing Limited, 2020) ;
    Verreydt, Kristof
    ;
    Van Gemert, Dionys
    ;
    Rauwoens, Pieter
    ;
    Houtmeyers, Jules
    ;
    Claes, Tom
  • Publication
    Study of the anisotropic elastic response of a foliated phyllite
    (ICE Publishing, 2022) ;
    Rodríguez, Paula
    ;
    Vera, Miguel
    Anisotropy is a crucial characteristic of metamorphic rocks whereby minerals oriented in a preferential direction can originate mineral foliation. Inherent anisotropy can affect the rock behaviour significantly. Transverse isotropy is a particular case of anisotropy where foliation planes are distributed in the rock mass. Therefore, in this study the anisotropy effect on the elastic properties of a foliated phyllite is considered. To this end, a series of laboratory tests was programmed. Triaxial tests were carried out under confining pressures up to 20 MPa. Elastic parameters such as elasticity modulus, E, and Poisson's ratio, ν, are assessed from triaxial test results as well as from ultrasonic tests, where compression and shear wave velocities are determined. Empirical relationships for elastic parameters are suggested as a function of foliation angle, β, and confinement. In addition, anisotropy indexes are adopted to evaluate results, comparing when possible with those of previous works. It was found that E increases with confinement; however, the effect of anisotropy on E reduces with confinement. It was also found that ν is affected by β but not by confinement.
  • Publication
    Effect of nail spacing on the global stability of soil nailed walls using limit equilibrium and finite element methods
    (Elsevier, 2021)
    Villalobos, Sergio A.
    ;
    The limit equilibrium method LEM is widely used for static and pseudo-static soil nailing designs. Soil nailed wall stability is usually evaluated based on a global factor of safety FSG under a predefined failure mechanism. When appropriate failure surfaces are adopted, FSG should reduce with the soil nailed wall inclination β for different nail geometries (length L, inclination α and diameter D), soil–nail strength rs, soil cohesion c’ and angle of friction ϕ’. However, nail spacing S can change this trend since FSG increases with β under certain combinations of β and S. In this study the nail spacing effect has been evaluated using LEM assuming a bilinear failure surface with two rigid blocks and the Morgenstern-Price method where the failure surface is neither linear nor circular. However, it was found that FSG increases with β for S < 2.00 m, which can lead to potentially unsafe designs. Alternatively, the finite element method FEM was chosen including the strength reduction factor SRF methodology which is equivalent to FSG under failure conditions. It was found that results from FEM represent a significant improvement respect to those from LEM because curves in a FSG-β-S plot follow a logical trend as with the other parameters (L, α, D, rs, c’ and ϕ’). Finally, it is recommended to choose FEM instead of LEM in soil nailing designs. In case of using LEM, results should be carefully assessed, in particular for steep walls and close nail spacing.
  • Publication
    Geotechnical properties of a natural zeolite
    (ICE, 2018)
    Georgiannou, Vasiliki N.
    ;
    Lefas, Demetrios
    ;
    Konstadinou, Maria
    ;
    Perraki, Maria
    ;
    The work presented by Georgiannou et al. (2017) on geotechnical properties of a natural zeolite is an important contribution because there are not many published works on this subject. The authors mention some of the several studies with natural zeolites in other research areas, mainly in environmental applications such as waste-water treatments, soil–bentonite mixtures and in the improvement of cement and concrete properties. They also mention the existence of numerous engineering and industrial applications of natural zeolites in farming, fisheries, textiles and construction materials. This discussion will complement and comment on some of the results obtained by the authors and suggest that extra information would be useful in order to make a more comprehensive analysis.
  • Publication
    Observations from a parametric study of the seismic design of soil nailing
    (ICE, 2018) ;
    Villalobos, Sergio
    ;
    Oróstegui, Paulo
    A parametric study of the seismic design of soil-nailed walls is performed. Values of a set of geometrical and mechanical parameters for the nail and soil of a slope have been varied to assess their effects on the global factor of safety FSG. Equations of limit equilibrium of forces based on the Coulomb criterion for a two-block-failure mechanism are adopted. Pseudo-static force analyses with a horizontal seismic coefficient of 0·15 are carried out, which is normally used in engineering practice for temporary soil-nailing projects. It was found that FSG clearly increases with soil cohesion and friction as well as nail length, diameter and inclination, although nail inclinations higher than 15° can become detrimental. It was found that there is a combination of nail spacing and wall inclination for which the trend of FSG changes from decreasing to increasing. This situation is caused by a software mathematical optimisation routine, which does not take into account whether it is possible for the failure surface shape to occur or not. Additionally, perforation diameters larger than 100 mm are necessary for FSG ≥ 1·1 and soil–nail shear stress rs values of more than 200 kPa are not significantly beneficial.