Landslides and instability
Rainfall-induced landslides are devastating phenomena which are responsible for loss of human life and serious damage to infrastructure every year. (From: Centrifuge Model Tests of Rainfall-Induced Landslides)
Rainfall characteristics, i.e. duration, intensity and distribution, play a significant role in the pore water pressure changes and therefore influence the stability of natural and man-made slopes. (From: ditto)
The occurrence of landslides in residual soil slope is attributed to many factors. Rainfall has been considered to be the cause of the majority of landslides Mist of the rainfall0indecuted landslides in residual soils consist of relatively shallow slopes above the groundwater table. (From: Effect of rainfall on matric suctions in a residual soil slope)
Landslides induced by rainfall impose considerable damage to infrastructure and cause major casualties worldwide. Several attempts have been undertaken to investigate the triggering mechanisms of these frequent and often powerful natural hazards. These studies were done using analytical approaches, numerical simulations and also physical modelling techniques. (From: Physical modelling of rainfall induced landslides under controlled climatic conditions)
Landslides are a particularly devastating earthquake-induced phenomenon, posing significant threat to human life and infrastructure (e.g. roads, pipelines, utility lifelines). (From: Seismic performance of loess-mudstone slope by centrifuge tests)
Landslides are one of the most widespread earth processes which involve the failure of sloping earth material. Landslides are considered to be one of the most important problems in geotechnical engineering. This is because landslides are usually among the most costly natural disasters in terms of human fatalities and economic loss. In recent years, natural slope instability has increased especially in tropical monsoon zones, such as Southeast Asian countries. There are several factors that can cause natural slope failures, such as geological activity, hydrological influence and human interference, but seepage and rainfall are the main factors. (From: Laboratory and modelling investigation of root-reinforced system for slope
Landslides may cut off highway infrastructure, utilities, food supplies, and communication networks for an extended period of time. Residences may be destroyed, and inhabitants located at landslide areas may be killed. (From:Centrifuge Model Simulations of Rainfall-Induced Slope Instability)
Instability of various geotechnical structures including soil walls and slopes is a common problem in many parts of the world, causing thousands of deaths and severe infrastructural damage each year. In the literature, many cases of failure have been reported in natural soil slopes, excavated slopes, and road subgrades simply due to rainwater infiltrating in an otherwise stable slope.
Slope failures account for the loss of countless lives around the world, and cause significant economical loss (e.g. Chen et al., 2004; Ochiai et al., 2004; Montrasio et al., 2009). It is widely acknowledged that rainfall acts as a major triggering factor in the failure of soil slopes. Hence, it becomes an issue of great importance to analyse stability levels of slopes under rainfall conditions. Unfortunately, the complicated mechanisms and various influencing factors concerned make rainfall-induced slope failure a difficult problem to tackle. (From: Centrifuge modelling of clay slope with montmorillonite weak layer under rainfall conditions)
1g scale model simulations of natural slopes in the laboratory, which are typically less than 1 m high, may not completely represent field conditions as soil behavior is different within a natural slope because of stress confinement, as opposed to a loose state or a state of low stress confinement in a small model.
Small-scale physical modelling of engineered earth structures has been used in the past to provide insight into corresponding prototype behaviour. However, a limitation of scaled down physical models under normal gravity condition is that the stress levels are much smaller than that of prototype structures.Only full-scale physical models can include all these complexities, but they are expensive and time-consuming and cannot be repeated and replicated with natural hazards like flooding and rainfall. In such situations, geotechnical centrifuge modelling can be used as an effective tool to study the behaviour of engineered earth structures as scaled-down models in a controlled environment. In view of the above, a centrifuge-based physical modelling technique was adopted in the present study for observing the effect of rainfall on geotechnical structures, with special emphasis on soil slopes.
Model tests can serve different purposes; for example, the results from model tests can be used to check the stressstrain theories for the behaviour of the soil as determined from the results in other apparatus. The success of this sort of test would enable those theories to be used for predicting, with confidence, the behaviour of prototype structures. Alternatively, the model test can be used to determine the behaviour of the soil in the mass by observing the movements of the soil under various boundary stresses thereby contributing to the better understanding of the fundamental stress-strain properties of the soil. Again, a model test could be used to predict directly the behaviour, under conditions of similarity, of the full scale prototype structure. Examples of all three types of model test are given by Roscoe (1970). (From: The determination of stress fields from plane strain data)
Centrifuge limitation or benefit
This soil mixture was used with the understanding that particle size smaller than that of the field material should be used in centrifuge modeling. In contrast, it has not been the practice among centrifuge modeling community to scale down the particle size, because a totally different material would result from such scaling. For instance, when sand particle size is scaled down by 100 times, its behavior would resemble that of clay instead of sand.
The inner part of slope was weathered slate rock, which was modeled using concrete cement with a rough surface. Note that this was an idealization, because fracturing of rocks might contribute to rapid local pore pressure rise and slope instability (Johnson and Sitar 1990).
The essential feature of centrifugal testing is to keep the self-weight stresses identical at geometrically similar points in the model and the prototype. Since the same stress patterns are imposed in both cases, the strain patterns must be identical. Hence with the centrifuge it is possible to obtain answers immediately to full-scale problems without having to appeal to, or wait for the development of, any theory. (From: THE INFLUENCE OF STRAINS IN SOIL MECHANICS)
the effectiveness of numerical analysis depends signifcantly on the applicability of the constitutive model of unsaturated soil
The choice of model for landslide susceptibility assessment and mapping is not deterministic. Different methods have different performance towards different study areas and different scales of samples. (From: Review on landslide susceptibility mapping using support vector machines)