arXiv subjects

N. A. Labanda

Publications and source records attributed to N. A. Labanda.

5 recordsLinked to original sources

arXiv2020

Stability assessment of a tailings storage facility using a non-local constitutive model accounting for anisotropic strain-softening

Recent failures of upstream-raised tailings storage facilities (TSF) raised con-cerns on the future use of these dams. While being cost-effective, they entail higher risks than conventional dams, as stability largely relies on the strength of tailings, which are loose and normally-consolidated materials that may exhibit strain-softening during un-drained loading. Current design practice involves limit equilibrium analyses adopting a fully-softened shear strength; while being conservative, this practice neglects the work input required to start the softening process that leads to progressive failure. This paper describes the calibration and application of the NGI-ADPSoft constitutive model to evaluate the potential of static liquefaction of an upstream-raised TSF and provides an indirect measure of resilience. The constitutive model incorporates undrained shear strength anisotropy and a mesh-independent anisotropic post-peak strain softening. The calibration is performed using laboratory testing, including anisotropically-consolidated triaxial compression tests and direct simple shear tests. The peak and residual undrained shear strengths are validated by statistical interpretation of the available CPTu data. It is shown that this numerical exercise is useful to verify the robustness of the TSF design.

physics.geo-ph↗

arXiv2020

A Family of Constitutive Models Implemented in PLAXIS to Simulate Cemented Mine Backfill

A family of constitutive models for mine cemented backfill is presented. Four formulas for the density- and pressure-dependency of elastic moduli, five formulas for the density- and pressure-dependency of friction angle and four formulas for the age-dependency of the elastic moduli and effective cohesion are incorporated into an isotropic hypoelasticity with Mohr-Coulomb perfect plasticity framework and implemented in PLAXIS as a user-defined material model. This family includes the standard Mohr-Coulomb, Bolton, Leps, Barton and Hoek- Brown models as trivial cases when both nonlinear elasticity and age-dependency are switched off. In this paper, the formulation of the models is introduced, the basis of the numerical implementation is outlined, and a case history of the application to the cemented backfill of a sublevel stoping mine is presented as an example.

physics.geo-ph↗

arXiv2020

A risk assessment of downdrag induced by reconsolidation of clays after upwards pipe jacking

Salini-Impregilo is building part of the largest sanitary sewer system in the history of Argentina in the suburbs of Buenos Aires City, to serve a population of almost five million people. The project is an outfall TBM tunnel 12 km long, starting from a reception shaft in the river margin, and transporting the sewage 35 meters below the \textit{Rio de la Plata} riverbed to the point of discharge. Within the final kilometer of the tunnel, a set of 36 standing pipes so-called \textit{risers} are constructed by driving steel tubes upwards and passing through dense sands, sandy clays and soft clays. Risers are linked-up with the launching lining segment using flange unions. Driving of risers upwards will generate excess pore pressure and disturbance in fine soils and, once the pipe is placed in its final position, negative skin friction due to reconsolidation and creep. A risk assessment of the downdrag is presented in this paper, based on the estimation of the force and/or displacement in the riser-tunnel union generated by this effect. The issues of whether it is desirable to instalock the riser-tunnel union at an early age after installation of the riser and the time lapse required to reduce negative skin friction effects are discussed. Results are validated by comparing the model results with field measurements in prototype models.

physics.geo-ph↗

arXiv2020

Screening of seismic records to perform time-history dynamic analyses of tailings dams: a power-spectral based approach

Time-history deformation analyses of upstream-raised tailings dams use seismic records as input data. Such records must be representative of the in-situ seismicity in terms of a wide range of intensity measures (IMs) including peak ground acceleration (PGA), Arias intensity (AI), cumulative absolute velocity (CAV), source-to-site distance, duration, among others. No single IM is a sufficient descriptor of a given seismic demand (e.g. crest settlement) because different records, all of them compliant with any IM, can produce a very wide range of results from insignificant damage to global failure. The use of brute force, where hundreds of seismic records compliant with a set of IMs are employed, has proven to be a reasonable workaround of this limitation, at least able to produce a probabilistic density function of demand indicators. This procedure, however, requires a large number of runs, and is therefore expensive and time-consuming. Analyses can be optimized if an a priori simple tool is used to predict which seismic records would yield a given demand, thus obtaining estimations with much fewer runs. In order to perform a more precise selection, a semi-analytical screening procedure is presented in this paper. The procedure makes use of the spectral properties of the seismic record, considering only the intensity of the frequency content which is not filtered by the dam to obtain an a priori estimate of demand, expressed in this case in terms of displacements. The tool is validated using analytical and numerical models that prove insensitivity to the constitutive model used in the analysis, and is applied to a large tailings dam subjected to strong earthquakes.

physics.geo-ph↗

arXiv2020

EPB-TBM tunnel under internal pressure: Assessment of serviceability

The Mantanza-Riachuelo basin recovery is one of the most ambitious environmental projects under construction in Argentina. In this context, the sanitary bureau of the metropolitan area of Buenos Aires (AySA) is building a sewage collection network to transport the waste water of the population in the southern area of the city, composed by almost five million people. The most complex tunnel in this big project is named \textit{Lot 3}, an outfall EPB-TBM tunnel starting at a shaft located at the \textit{Rio de la Plata} margin and running under the river 12 km to a discharge area. The tunnel runs through soft clay belonging to the \textit{post-pampeano} formation and dense sands of the \textit{Puelchese} formation. In operation, it will be pressurized by a pumping station which will produce a piezometer head that, in the first 2000 m, might be eventually higher than the confining pressure around the tunnel. This paper presents the numerical analysis of the structural forces acting on the tunnel rings using a risk-oriented approach that considers the stochastic nature of materials, stratigraphy and tunnel-ground interaction. The compression of the lining is evaluated and compared with field measurements in order to predict the structural forces and the risk of the rings going into tension beyond the structural capacity of the system.

physics.geo-ph↗