PROBLEMS OF LANDSLIDES ON SLOPES AND EMBANKMENTS
The Earth’s surface is constantly changing and eroding as a result of weathering of near-surface ground, eluting them out by rivers and atmospheric factors. Another very important factor is human activity, that due to the earthworks and constructing works, interferences natural processes of erosion. Quite often undercuts the mountain slopes, regulates riverbeds and makes transport routes through sloped areas. Humans build also many embankments, dams, barriers, levees and other constructions. When unfavorable weather conditions, too much static load (buildings, embankments) or dynamic (traffic), happen, these objects can be damaged.
The slope with significant landslide movements, below which there is a municipal road.
The idea of stability analysis as a complex determination of the state of equilibrium for geometric systems of all the natural and anthropogenic slopes brings the necessity of consideration many factors. When solving the problems of landslides on embankments and slopes, the most important is proper recognition of groundwater conditions. For such purposes, geotechnical and geophysical investigations are applied. The scope of studies is adapted to the complexity of the problem.
FACTOR OF SAFETY F
The solution of stability studies is to calculate the factor of safety F for certain geometry and geology of the slope using mathematical methods. Boundary condition for the factor of safety F is assumed to be 1 and values above this boundary are regarded to be stable. This parameter is determined for the potentially weakest slip plane of studied slope. Obviously this is not a two-variant classification. There are a number of more complex classifications, which are chosen to particular issues. The calculations are performed using advanced computer programs, that use different methods of calculation of potential slip planes with their factor of safety. By understanding the issue and the suitable choice of calculation method we obtain an approximate assessment of stability for assumed boundary and initial conditions of calculated model.
Schematic calculation of the analytical method is based on the strip method where the slope is divided into parallel vertica stripes. Their width is picked respectively to their geology and the topography of the area. Then, for each of the stripes, it is calculated the distribution of the forces acting on its sides. Stability calculatons are performed based on the interaction of every strip on each other according to various analytical methods such as the Morgenstern-Price, Bishop, Janbu or others. The assumption here, is the supposed location of the slip surfaces and their shapes are defined by particular analytcal methods.
Stripe methods are suitable for simple geological conditions, when slip planes do not have complicated trajectory. The planes are determined individually and separately for each of them.
More advanced method of stability analysis is numeric method. In contrast to stripe methods, during numeric calculations, model is covered with an accurately dense mesh. Force distribution is calculated for each node of the mesh. Such algorithms are executed e.g. in finite difference method FDM or finite element method FEM.
Advantages of numerical methods:
- determining the number of slip planes at the same time,
- greater accuracy of calculation,
- recommended for complex geological conditions,
- possibility to make detailed dynamic, thermal and hydrogeological analyses.
SPATIAL 3D STABILITY ANALYSIS
For a broader understanding of complicated landslides, it is possible to analyze the stability of the spatial arrangement of stresses and strain. Only recently the power of computers has become large enough to be able to calculate so complicated algorithms. 3D analysis allow to detect landslide movements risks on the surface in any direction. 3D method is time-consuming and requires a good knowledge of the studied ground but It allows to more accurate determination of the landslide axis and distribution of shear stresses in the ground.
APPLICATIONS FOR STABILITY CALCULATIONS
- stability assessment of levees, barriers, dams with various levels of water,
- stability of landslides, slopes, hillsides at various atmospheric conditions,
- expert opinions explaining the mechanism of landslide at various load condition,
- stability of road and railway embankments in various dynamic load variants,
- numeric modelling of rock mass behaviour, mining excavations and underground constructions,
- assessment of landslide movements risk,
- stability of slopes and hillsides in mining and post-mining areas,
- safety projects of lanslides.