Publication
Numerical analysis of slope failure in granitic soil slopes : main types of instability and remediation measures
| datacite.subject.fos | Engenharia e Tecnologia::Engenharia Civil | pt_PT |
| dc.contributor.advisor | Cavaleiro, Victor Manuel Pissarra | |
| dc.contributor.advisor | Pinto, Alexandre da Luz | |
| dc.contributor.author | Neves, Manuel João Niza das | |
| dc.date.accessioned | 2016-02-15T16:39:02Z | |
| dc.date.available | 2016-02-15T16:39:02Z | |
| dc.date.issued | 2015 | |
| dc.description.abstract | Slope stability is a worldwide problem which above all affects people’s safety. However, in tropical or temperate regions (such as the Mediterranean), a combination of their topographic, geologic and climate settings contributes to an increased landslide hazard. A full understanding of this topic, and what it entails, requires an accurate knowledge of its triggers and awareness to the different instability mechanisms that may occur. Furthermore, the instability phenomenon may present different particularities for distinct ground conditions, being of major significance in civil engineering, as it forms part of most construction works and mining activities, particularly in large scale geotechnical schemes, such as highways/railways, canals, tunnels, embankment dams and open pit mines. This thesis is primarily focused on the stability assessment of slopes in granitic residual soils resorting to both limit equilibrium (LEM) and finite element (FEM) approaches. In order to do so, it makes use of one LEM based software (SLOPE/W) and one FEM based software (PLAXIS 2D). The LEM approach comprises three different formulations of the method of slices, which despite being based on the static of equilibrium of the soil mass, are constructed on different sets of assumptions which only allows them to partially fulfil the static equilibrium conditions. The FEM method, on the other hand, is based on the stress‐strain relationship and constitutive law of the soils. One of the aims of the study is to establish a comparison between not only different LEM methods but also between LEM and FEM approaches, whilst varying surcharge values and groundwater levels. The LEM methods that have been selected for use are the Bishop’s simplified, Janbu’s simplified and Fellenius’ methods, which have all been well established for many years and are still commonly used in practice for stability analysis. Simplicity and relatively good results are their main advantages. These are then compared with the results of the Hardening Soil Model (available within the PLAXIS 2D software) with and without remedial measures. However, the key objective of this study is to produce a design chart that allows for an expedite assessment of the stability of granitic residual soil slopes, considering different soil properties, geometries, groundwater levels and applied surcharges. The relevant geotechnical soil parameters required for the LEM and FEM simulations have been primarily based on laboratory testing undertaken by other PhD students at UBI and complemented by historical data. The parametric study of the pre-set range of conditions reveals that changes in groundwater levels are more detrimental to the stability of the slope than increases in the applied surcharge at its crest. However, the results from the different LEM methods do not entirely converge, as the Bishop’s and Janbu’s simplified methods appear to be more critical when groundwater level rises in steeper slopes, whereas the Fellenius’ method returns greater reductions in the FoS for slacker slopes. The FEM approach reveals some similarities to the above, with also greater reductions on the least steep configuration. From an overall perspective, reductions in FoS using LEM methods due to rises in groundwater levels appear to be inversely proportional to the cohesion of the intersected materials, i.e., the greater the of the soil, the lesser the consequences of rises in groundwater appear to be. Results also show that, albeit both approaches reveal the FoS to be more sensitive to changes in groundwater levels than to the surcharge applied on the crest, the latter appears to have a more critical effect on the LEM analyses. A direct comparison between FEM and LEM approaches reveals a significant divergence in the obtained FoS for purely granular materials, with all LEM methods overestimating the safety of the slope by up to circa 40%. These differences are more expressive for greater heights and increased applied surcharges. When comparing the outcomes of the Fellenius’ method, the FoS presents a better correlation to the FEM results with both over and underestimates, but generally under circa 5%. No tendency is apparent for changes in either groundwater levels or applied surcharges. In soils with a given effective cohesion, the results of the Bishop’s simplified method are circa 5% to 10% higher than the FEM outcomes. These differences appear to accentuate with the slope’s gradient and height and with rising groundwater levels. However, no noticeable differences are reported for variations in surcharge. The majority of the FoS obtained with the Janbu’s simplified method present the best correlation with the FEM approach (from between all three LEM formulations), with differences predominantly under 5%. The best correlations seem to be obtained for greater surcharge values and in slacker slopes. Nevertheless, the differences in FoS between LEM methods and between FEM and FEM approaches may have little interest if there is a large uncertainty in the input parameters of the soils. Therefore, priority should be given to investigating their shear strength parameters and precise mapping of the slope geometry before undertaking a stability analysis. Furthermore, the stability charts provided within this thesis are only to be perceived as indicative and shall only be used as a preliminary tool to help corroborate site observations. A detailed design will necessarily require further analysis to be undertaken. Similarly, the remedial options discussed and analysed in this thesis are to be interpreted as concept ideas as their gain in terms of FoS will likely vary on a case to case basis. Also, the topography and existing restraints at a site can often lead the Designer to opt between a limited number of feasible choices. Finally, the assessment of the benefits of combining more than one remedial option are excluded from this study. | pt_PT |
| dc.identifier.tid | 101439113 | |
| dc.identifier.uri | http://hdl.handle.net/10400.6/4010 | |
| dc.language.iso | eng | pt_PT |
| dc.subject | Estabilidade de taludes | pt_PT |
| dc.subject | Solos residuais graníticos - Estabilidade de taludes | pt_PT |
| dc.subject | Estabilidade de taludes - Estudo paramétrico | pt_PT |
| dc.subject | Beira Interior (Portugal) - Solos residuais de granítico - Estabilidade de taludes | pt_PT |
| dc.title | Numerical analysis of slope failure in granitic soil slopes : main types of instability and remediation measures | pt_PT |
| dc.type | doctoral thesis | |
| dspace.entity.type | Publication | |
| rcaap.rights | openAccess | pt_PT |
| rcaap.type | doctoralThesis | pt_PT |
| thesis.degree.name | Doutoramento em Engenharia Civil | pt_PT |