Dr. Villalobos-Jara, Felipe

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.

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.

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

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.

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.

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.